How to Choose Ceramic Pressure Sensor?

How to Choose Ceramic Pressure Sensor?

When discuss the topic of “how to choose ceramic pressure sensor” for your application, the choice between a monolithic design and a flush diaphragm configuration can have a significant impact on the sensor’s performance, durability, and suitability for your specific needs.

Both types of ceramic pressure sensors offer unique advantages, and understanding the key differences can help you make an informed decision that aligns with your requirements.

In this post, we will explore the critical factors to consider when choosing between monolithic ceramic pressure sensor and flush diaphragm ceramic pressure sensor, providing you with a framework to make the most appropriate selection for your application.

Construction structure & sensing element

Monolithic

In a monolithic ceramic pressure sensor, the sensing elements are directly fabricated onto the ceramic diaphragm.

The key aspects are:

  • The sensor has a single, monolithic ceramic structure.
  • The sensing element is a thin, ceramic diaphragm, typically made of alumina (Al2O3) or zirconia (ZrO2).
  • The ceramic diaphragm typically ranges from 50 to 500 micrometers (μm) in thickness.
  • Piezo resistors or strain gauges are directly deposited onto the surface of the ceramic diaphragm using thick-film or thin-film techniques.
  • The sensing elements are integrated onto the diaphragm but are not part of the diaphragm itself.

This construction provides a robust and integrated design, where the sensing elements are directly coupled to the deformation of the ceramic diaphragm when pressure is applied.

ESS501 Monolithic Type

how to choose ceramic pressure sensor-monolithic type

Flush Diaphragm

In a flush diaphragm ceramic pressure sensor, the sensing elements are integrated directly into the ceramic diaphragm itself, creating a seamless interface with the sensor’s housing or surface.

The key aspects are:

  • The sensing element is a thin, ceramic diaphragm, typically made of alumina (Al2O3) or zirconia (ZrO2).
  • The sensor has a ceramic diaphragm, typically ranging from 50 to 500 micrometers (μm) in thickness, that is flush with the sensor’s housing or surface.
  • The pressure-sensing elements, such as piezo resistors or capacitive sensors, are embedded within the ceramic diaphragm itself.
  • This integrated design creates a smooth, uninterrupted surface, where the sensing elements are part of the diaphragm.

The flush diaphragm design is advantageous in applications where clogging or buildup of media needs to be avoided, as the seamless interface facilitates easy cleaning and maintenance of the sensor.

ESS502 Flush Diaphragm Type

how to choose ceramic pressure sensor-flush diaphragm type

Pressure and range requirements

Another important consideration is the pressure and temperature range requirements.

Both monolithic and flush diaphragm ceramic pressure sensors can cover a wide range of pressure measurements, typically from as low as 0-7 psi (0-50 kPa) up to as high as 0-10,000 psi (0-69 MPa). However, flush diaphragm sensors tend to have a slightly higher pressure range capability compared to monolithic sensors, due to their robust and integrated construction.

Monolithic

  1. Pressure Range:
    • Monolithic ceramic pressure sensors are available for a wide range of pressure measurements, typically from as low as 0-7psi (0-6.9 kPa) up to 0-5,000 psi (0-34.5 MPa).
    • The specific pressure range for a monolithic sensor is largely determined by the thickness and design of the ceramic diaphragm.
  2. Diaphragm Thickness:
    • The ceramic diaphragm in a monolithic sensor typically ranges from 50 to 500 micrometers (μm) in thickness.
    • Thinner diaphragms, around 50-100 μm, are used for lower pressure ranges, while thicker diaphragms, around 300-500 μm, are used for higher pressure ranges.
    • The diaphragm thickness is a critical factor in determining the sensor’s pressure range and sensitivity.
  3. Sensitivity:
    • Thinner diaphragms in monolithic sensors generally exhibit higher sensitivity, as they can undergo greater deformation under the applied pressure.
    • This increased sensitivity allows monolithic sensors to accurately measure lower pressure ranges, down to 0-7psi (0-50 kPa).

Flush Diaphragm

  1. Pressure Range:
    • Flush diaphragm ceramic pressure sensors can cover an even wider pressure range, typically from 0-7 psi (0-50 kPa) up to 0-10,000 psi (0-69 MPa).
    • The flush diaphragm design, combined with the inherent strength of the ceramic material, enables these sensors to withstand higher pressure levels.
  2. Diaphragm Thickness:
    • The ceramic diaphragm in a flush diaphragm sensor also typically ranges from 50 to 500 micrometers (μm) in thickness.
    • However, the flush diaphragm design allows for slightly thinner diaphragms, as the sensor’s housing and construction provide additional support and protection.
  3. Sensitivity:
    • Similar to monolithic sensors, thinner diaphragms in flush diaphragm sensors tend to exhibit higher sensitivity, enabling accurate measurements at lower pressure ranges.
    • The flush configuration and integrated design of the sensing elements within the diaphragm also contribute to the sensor’s sensitivity.

When it comes to temperature, both sensor types can operate over a wide range, often from -40°C to 125°C or higher, depending on the specific design and materials used.

Accuracy Performance of ESS502 Flush Diaphragm Ceramic Cell @ 25℃

That said, the flush diaphragm configuration may offer slightly better temperature resistance and stability, as the integrated design provides enhanced thermal management properties.

Accuracy Performance of ESS502 Flush Diaphragm Ceramic Cell @ 135℃

Technical Characteristics
Parameter
Description
Sensor typeMonolithic, Flush diaphragm, Absolute (A), Gauge (R) or Sealed gauge (S)
TechnologyCeramic Piezoresistive
Diaphragm materialCeramic Al2O3 96% (standard), 99.6% or sapphire (on request)
Weight≤ 8g (ceramic cell only)
Response time≤ 1ms
Supply voltage2...36Vdc
Offset‐ 0.1 ± 0.1 mv/v(Other nominal values available on request)
Current cons.≤ 3mA @ 10V
Operating-40...+85℃ (-40 °F...+185 °F)
Storage temperature-40...+125℃ (-40 °F...+257 °F)
Impedance11 ± 30%kΩ

Pressure type

When measuring sealed gauge or absolute pressure, it is generally better to choose a flush diaphragm ceramic pressure sensor over a monolithic type.

Monolithic

  • For sealed gauge or absolute pressure measurements, monolithic ceramic sensors would require a sealed and evacuated reference chamber within the sensor housing.
  • Maintaining a high-quality vacuum reference can be more complex and potentially prone to degradation over time, which can affect the accuracy and long-term stability of the absolute pressure measurements.

Flush Diaphragm

  • Flush diaphragm ceramic sensors can integrate the absolute or sealed pressure sensing elements directly into the ceramic diaphragm.
  • This integrated design allows for a more robust and reliable absolute pressure measurement, as the sensing elements are an integral part of the diaphragm, minimizing the potential for leaks or instability in the reference vacuum.
  • The flush configuration also provides a more compact and streamlined sensor design, which can be advantageous in applications with limited space.

In both sealed gauge and absolute pressure measurements, the integrated design and flush configuration of the flush diaphragm ceramic pressure sensors can offer several advantages over the monolithic type:

  1. Improved Stability and Reliability: The integrated sensing elements and robust diaphragm design of flush diaphragm sensors can provide better long-term stability and reliability for sealed or absolute pressure measurements.
  2. Compact and Space-Saving: The flush diaphragm design allows for a more compact and space-efficient sensor, which can be beneficial in applications with limited available space.
  3. Enhanced Media Compatibility: The flush diaphragm configuration can also offer better resistance to media-induced issues, such as clogging or buildup, making it more suitable for applications involving harsh or contaminated process fluids.

Media compatibility

Media compatibility is another crucial factor to consider.

It is fact that both types are ceramic based solutions and share the most same characteristic when handle most material however, flush diaphragm ceramic pressure sensors are generally more resistant to clogging, buildup, and corrosion due to their seamless, flush interface with the process media. This makes them particularly well-suited for applications involving harsh or abrasive fluids.

Monolithic sensors, while still suitable for many industrial applications, may be more susceptible to media-induced issues, as the sensing elements are fabricated onto the diaphragm surface rather than being integrated into it.

Dimension and cost requirements

In addition to the application requirements and media compatibility, the size and form factor of the sensor can also play a role in the selection process.

Flush diaphragm ceramic pressure sensors can often offer a more compact and space-saving design compared to monolithic sensors. This is because the flush interface allows for a smaller overall sensor footprint, as the sensing elements are integrated directly into the diaphragm (instead of onto).

Drawing of ESS502 Flush diaphragm ceramic pressure sensor cell

Click to Download Datasheet: ESS502 Flush Diaphragm Ceramic Sensor Cell

Monolithic sensors, on the other hand, may have a slightly larger form factor due to the separate construction of the diaphragm and sensing elements.

Drawing of ESS501 Monolithic ceramic pressure sensor cell

Click to Download Datasheet: ESS501 Monolithic Ceramic Sensor Cell

Finally, cost and availability should also be considered. Monolithic ceramic pressure sensors are generally more widely available and may have a lower cost, especially for lower-end applications. Flush diaphragm sensors, due to their specialized manufacturing process and design complexity, can be more expensive.

However, the enhanced performance and suitability for certain applications may justify the higher cost for specific use cases.

Application and Cost

Application Considerations

Monolithic ceramic pressure sensors are well-suited for general industrial applications where a robust, integrated design is preferred. These sensors feature a single, unified ceramic structure with the sensing elements directly fabricated onto the diaphragm, providing excellent mechanical stability and resistance to harsh environments.

Monolithic sensors are commonly used in applications such as pneumatic systems, hydraulic equipment, and general process control.

how to choose ceramic pressure sensor-ESS501 monolithic ceramic cell

On the other hand, flush diaphragm ceramic pressure sensors are better suited for applications where the sensor needs to interface with a process fluid or media, such as in the food processing, pharmaceutical, or chemical industries.

The flush diaphragm design creates a seamless, uninterrupted surface that facilitates easy cleaning and prevents clogging or buildup of the media, making it the preferred choice for these types of applications. Flush diaphragm sensors are commonly used in applications involving corrosive liquids, slurries, or other aggressive media where a clean and easily maintainable sensor interface is required.

Cost Considerations:

Monolithic ceramic pressure sensors are generally more widely available and may have a lower cost compared to flush diaphragm sensors, especially for lower-end applications. The simpler and more integrated construction of monolithic sensors can contribute to their relatively lower manufacturing costs, making them a more cost-effective option for applications where the higher degree of integration and robustness is sufficient, without the need for the specialized flush diaphragm design.

Conversely, flush diaphragm ceramic pressure sensors may be more expensive due to the specialized manufacturing process and design complexity required to achieve the seamless, flush interface. The additional steps and materials involved in the production of flush diaphragm sensors can result in a higher overall cost compared to monolithic sensors.

However, the enhanced performance and suitability for specific applications, such as those involving harsh media or strict hygiene requirements, may justify the higher cost for certain use cases.

Take example

Let’s consider a practical example.

how to choose ceramic pressure sensor-regular industry use

Imagine you are working on a food processing application that requires monitoring the pressure of a corrosive cleaning solution. In this case, a flush diaphragm ceramic pressure sensor would be the more appropriate choice. The seamless, flush interface of the sensor’s ceramic diaphragm would prevent any buildup or clogging of the cleaning solution, ensuring reliable and consistent pressure measurements.

Additionally, the enhanced media compatibility of the flush diaphragm design would provide superior resistance to the corrosive nature of the solution, extending the sensor’s lifespan and reducing the need for frequent maintenance or replacement.

On the other hand, if you are working on a general industrial application, such as monitoring the air pressure in a pneumatic system, a monolithic ceramic pressure sensor may be the more suitable option.

The robust, integrated construction of the monolithic sensor would provide the necessary durability and resistance to withstand the harsh industrial environment, while the lower cost and wider availability of these sensors could be advantageous for your application.

Take away

For your quick reference and help guide the selection, here are some take away we concluded when choosing between a monolithic ceramic pressure sensor and a flush diaphragm ceramic pressure sensor.

Application requirements:

  • Monolithic sensors may be more suitable for general industrial applications where a robust, integrated design is preferred.
  • Flush diaphragm sensors are better suited for applications where the sensor needs to interface with a process fluid or media, such as in food processing, pharmaceutical, or chemical industries, where a flush and easily cleanable surface is essential.

Pressure range:

  • Both monolithic and flush diaphragm sensors can cover a wide range of pressure measurements, typically from 0-7 psi (0-50 kPa) up to 0-10,000 psi (0-69 MPa).
  • However, flush diaphragm sensors tend to have a slightly higher pressure range capability compared to monolithic sensors, due to their robust construction.

Temperature range:

  • Both sensor types can operate over a wide temperature range, typically from -40°C to 125°C or higher, depending on the specific design and materials used.
  • However, the flush diaphragm design may offer slightly better temperature resistance and stability due to the integrated construction.
  •  

Media compatibility:

  • Flush diaphragm sensors are generally more resistant to clogging, buildup, and corrosion due to the seamless, flush interface with the process media.
  • Monolithic sensors may be more susceptible to media-induced issues, but can still be suitable for many industrial applications.

Size and form factor:

  • Flush diaphragm sensors can offer a more compact and space-saving design, as the flush interface allows for a smaller overall sensor footprint.
  • Monolithic sensors may have a slightly larger form factor due to the separate construction of the diaphragm and sensing elements.

Cost and availability:

  • Monolithic ceramic pressure sensors are generally more widely available and may have a lower cost compared to flush diaphragm sensors, especially for lower-end applications.
  • Flush diaphragm sensors may be more expensive due to the specialized manufacturing process and design complexity.

Infographic of Monolithic VS Flush Diaphragm

Wrap up

In summary, when choosing between a monolithic ceramic pressure sensor and a flush diaphragm ceramic pressure sensor, consider the specific application requirements, pressure and temperature ranges, media compatibility, size constraints, and cost factors to determine the most suitable option. Consult with experienced engineers or manufacturers to ensure the selected sensor meets the necessary performance and reliability requirements for your application.

Datasheet Download

Ceramic Piezo Resistive Pressure Sensor

Ceramic Piezo Resistive Pressure Sensor

Introduction

Ceramic piezo resistive pressure sensor is one of the most popular models that adopt the sensing technology of ceramic piezo resistive, which have excellent piezo-resistive sensing features like high stability, good accuracy and temperature features, what is more, ceramic piezo resistive pressure sensor also have remarkable ability to work under corrosive situation where silicon piezo-resistive sensing is not very suitable.

The demand for more robust, stable, and versatile pressure sensors led to the development of ceramic piezo resistive pressure sensors. These sensors employ a ceramic diaphragm combined with a Wheatstone bridge, screen-printed with conducting layers. Ceramic piezo resistive pressure sensors offer several advantages, such as:

  • – High accuracy levels
  • – Long-term stability
  • – Wide pressure range
  • – Resistance to corrosion and abrasion
  • – Versatility in various applications

As a result of their unique benefits, ceramic piezo resistive pressure sensors have become an attractive choice for both engineers and manufacturers.

The Design and Composition

Ceramic piezo resistive pressure sensors bring together the unique characteristics of ceramic materials and advanced thick film technology, creating a highly reliable and stable pressure sensing solution. Here, we will explore the design and composition of these sensors, focusing on the materials used, the importance of the ceramic substrate, and the screen-printed resistive circuitry and electrodes.

Materials used in the Construction

Ceramic piezo resistive pressure sensors employ a combination of materials that work together to ensure durability, precision, and stability in various environments. The primary materials used are:

Ceramic substrate: Alumina (Al2O3) or zirconia (ZrO2) are the most common ceramic materials for the substrate. They provide excellent mechanical and thermal characteristics, contributing to the sensor’s resistance to pressure, temperature, and corrosion.

Thick film materials: A combination of conductive and resistive paste materials, usually comprising metal alloys or metal oxide mixtures, are used to create the sensing elements and their conducting paths.

Protective coating: An additional layer of glass or polymer material may be applied to shield the sensing elements from mechanical damage and corrosive effects.

How ceramic sensor build

The Role of Ceramic Substrate

Stability and Strength: The Foundation for Resilience
When it comes to pressure sensing, stability and strength are paramount. Ceramic materials, with their excellent mechanical properties, provide the robust and durable foundation that ceramic thick-film pressure sensors require. 

Chemical Resistance: Thriving in Harsh Conditions
In many industrial and process control applications, the pressure sensors are exposed to a wide range of corrosive gases, liquids, and chemicals. Ceramic substrates shine in this regard, offering exceptional resistance to these harsh elements.

Thermal Stability: Maintaining Precision Across Extremes
Temperature fluctuations can wreak havoc on pressure sensing systems, but ceramic substrates are engineered to withstand these challenges. With their low thermal expansion coefficients, ceramic materials can accommodate wide temperature ranges with minimal impact on the sensor’s performance. 

Compatibility: Forging a Reliable Bond
The integration of thick-film pressure sensing elements onto the substrate is a critical step in the sensor’s fabrication. Ceramic materials exhibit excellent compatibility with the thick-film materials, facilitating a stable and reliable bond between the two. This compatibility helps to ensure the sensing elements remain firmly in place, maintaining the sensor’s integrity and performance over its lifetime.

Screen-printed Resistive Circuitry and Electrodes

The Wheatstone Bridge: The Heart of Pressure Sensing
At the core of a ceramic thick-film pressure sensor is the resistive circuitry, typically designed as a Wheatstone bridge. This ingenious configuration consists of four resistive elements that are strategically deposited onto the ceramic substrate using the screen-printing process.

As pressure is applied to the sensor’s diaphragm, these resistive elements change their resistance in a predictable and measurable way, enabling the accurate detection and monitoring of the applied pressure.

Wheatstone bridge and 4 piezo-resistors

Reliable Conductive Pathways: Ensuring Robust Electrical Connectivity
In addition to the Wheatstone bridge, the screen-printing process also allows for the creation of consistent and reliable conducting paths on the ceramic substrate. These conductive traces play a crucial role in transmitting the electrical signals from the sensing elements to the external connectors or circuitry, ensuring the seamless flow of data and enabling precise pressure measurements.

Stable and Robust Electrodes: The Backbone of Electrical Integration
Complementing the resistive circuitry and conductive paths, the screen-printing process is also used to deposit metal electrodes onto the ceramic substrate. These electrodes, typically made from materials such as silver, gold, or platinum, provide stable and reliable electrical connections between the sensing components and the external interface.

Precision and Repeatability: The Hallmarks of Screen-Printing
The beauty of the screen-printing process lies in its ability to create these critical sensor elements with remarkable precision and repeatability. By carefully controlling the deposition of the conductive and resistive materials, engineers can ensure consistent and reliable patterns, ensuring the sensor’s performance remains stable and predictable over its lifetime.

Ceramic piezo resistive screenprint

Unlocking the Full Potential of Ceramic Thick-Film Pressure Sensors
The screen-printing process is a testament to the engineering prowess that goes into the fabrication of ceramic thick-film pressure sensors. By leveraging this advanced manufacturing technique, engineers can unlock the true potential of these remarkable devices, delivering unparalleled precision, reliability, and performance in a wide range of industrial, automotive, and process control applications.

Scheme-of-piezoresistive-sensor-Information-materials

Applications of Ceramic piezo resistive Pressure Sensors

Ceramic piezo resistive pressure sensors have firmly established themselves as essential components in the pursuit of enhanced efficiency, safety, and performance across a wide range of critical applications.

Check below table for details of application that used ceramic piezo resistive pressure sensor

IndustryApplicationPressure RangeTemperature Range
AutomotiveEngine Control Systems0 to 250 kPa-40°C to 125°C
AutomotiveTransmission Systems0 to 60 bar-40°C to 150°C
AutomotiveTire Pressure Monitoring0 to 450 kPa-40°C to 125°C
Aerospace/AviationAltitude Sensing0 to 1100 hPa-40°C to 85°C
Aerospace/AviationEngine Monitoring0 to 350 bar-55°C to 150°C
Aerospace/AviationHydraulic Systems0 to 1000 bar-40°C to 120°C
MedicalBlood Pressure Monitors0 to 300 mmHg0°C to 55°C
MedicalRespiratory Devices0 to 100 cmH2O0°C to 50°C
MedicalInfusion Pumps0 to 50 psi0°C to 50°C

Not suitable cases

While ceramic thick-film pressure sensors excel in static or slowly varying pressure applications, they may not be the optimal choice for dynamic pressure measurement scenarios that require an exceptionally fast response time. In applications where the pressure changes rapidly, such as in high-speed automotive or aerospace systems, sensors with a quicker reaction time and higher bandwidth may be more suitable.

Although ceramic thick-film pressure sensors are known for their thermal stability, there are certain applications that operate in temperature ranges beyond the typical limits of these sensors (-40℃-125℃). In environments with extreme temperatures, either extremely high or cryogenic, specialized pressure sensing solutions designed for such conditions may be necessary to ensure reliable and accurate pressure monitoring.

In some applications, the materials used in the construction of ceramic thick-film pressure sensors may not be compatible with the specific chemicals, solvents, or media present in the operating environment.

In such cases, engineers may need to explore pressure sensing technologies that utilize alternative materials better suited to the given application’s requirements.

ESS5 series ceramic pressure sensor

ModelESS501ESS502ESS503
Ceramic piezo resistive Pressure Sensors-ESS501Ceramic piezo resistive Pressure Sensors-ESS502Ceramic piezo resistive Pressure Sensors-ESS503
DatasheetDownloadDownloadDownload
SensingCeramic piezoresistiveCeramic piezoresistiveCeramic piezoresistive
TypeMonolithicFlush diaphragmMonolithic
Min range0-0.5bar0-5bar0-5bar
Max range0-480bar0-600bar0-400bar
Diameter18*3.5mm18*3.5mm18*3.5mm
Diameter21*6.5mm21*6.5mm21*6.5mm
Accuracy0.5%0.5%0.5%
Power supply2-30V2-30V2-30V
Outputmvmvmv
Working temp.-40-135℃-40-135℃-40-135℃
Temp. compensation0-50℃0-50℃0-50℃

Comparison among different piezo-resistive sensing

Silicon Piezo-resistiveCeramic Piezo-resistiveThin-film Piezo-resistive
Silicon Piezo-resistive EST330S 300-300Ceramic Piezo-resistive-EST3120 300-300Thin-film Piezo-resistive-EST380 300-300
Click to product pageEST330SEST3120EST380
DatasheetDownloadDownloadDownload
PrinciplePiezo-resistive effectPiezo-resistive effectPiezo-resistive effect
Fabrication methodDiffused Silicon (single)Thick-film PrintThin-film spluttering
Sensing elementMade of silicon, where piezo-resistors are diffused into the silicon substrate.Made of a ceramic material, typically a mixture of oxides, onto which a thick-film piezo-resistive layer is deposited.fabricated using a sputtering deposition process, where a thin layer of piezo-resistive material is deposited onto a substrate, often silicon or ceramic.
MOCSS316Ceramic Al2O3, dry typeSilicon nitride (Si3N4), ceramic
Min pressure to measure0-7kpa0-0.05bar0-4bar
Max pressure to measure0-1000bar0-480bar0-2200bar
Filled fluidSilicon OilNoneNone
Highlight features• High sensitivity
• High stability
• Good linearity
• Temperature compensation
• High temperature resistance
• Good chemical resistance
• Cost-effective for high volume production
• High sensitivity
• Good stability over time
• Suitable for high-pressure applications
Suitable industry• Biomedical instruments
• Precision industrial controls
• Aerospace and defense
• Automotive (e.g., engine management systems)
• HVAC systems
• Industrial process control
• Aerospace
• Oil and gas industry
• High-precision industrial applications

Silicon piezo resistive

Silicon piezo resistive

What is silicon piezo resistive sensing

The underlying principle of silicon piezo-resistive pressure sensing is the piezo-resistive effect, where the electrical resistance of certain materials, in this case, silicon, changes when subjected to mechanical stress or pressure. By leveraging this phenomenon, silicon piezo-resistive pressure sensors can accurately detect and measure pressure variations.

Structure of strain gauge

The key components of a silicon piezo-resistive pressure sensor are:

Silicon Substrate:

  • The sensing element is fabricated on a silicon substrate, which serves as the foundation for the sensor.
  • Silicon is chosen due to its excellent mechanical properties, enabling it to withstand the applied pressure without deformation.

Piezo-Resistors:

  • Piezo-resistors are carefully diffused into the silicon substrate, precisely positioned to detect the pressure-induced changes.
  • These piezo-resistors are typically made of doped silicon, which exhibits a strong piezo-resistive effect.
  • The resistance of the piezo-resistors varies linearly with the applied pressure, allowing for accurate pressure measurement.

cross section view of peizoresistive-semiconductor (silicon)

Wheatstone Bridge Configuration:

  • The piezo-resistors are arranged in a Wheatstone bridge circuit, which is a fundamental electrical configuration used to measure small changes in resistance.
  • This configuration enables the sensor to detect the pressure-induced resistance changes and convert them into an electrical output signal, typically a voltage or current.

electrical schematics of Silicon piezo resistive-Wheatstone Bridge

How silicon piezo resistive working

As mentioned above, the working principle of silicon piezo-resistive pressure sensors is based on the piezo-resistive effect, which is the fundamental phenomenon that enables these sensors to detect and measure pressure changes.

Pressure Application

  • When an external pressure is applied to the sensor, the silicon substrate experiences mechanical deformation, which in turn causes the piezo-resistors to undergo a change in their electrical resistance.
  • The magnitude of the resistance change is directly proportional to the applied pressure, following a linear relationship.

Piezoresistive sensing-Proportional change between pressure and mv signal

Wheatstone Bridge Configuration:

  • The piezo-resistors are connected in a Wheatstone bridge circuit, which is a well-established electrical arrangement used to measure small changes in resistance.
  • In the Wheatstone bridge, the piezo-resistors are connected in such a way that two of them experience an increase in resistance, while the other two experience a decrease in resistance, when pressure is applied.
  • This differential resistance change creates an electrical imbalance in the Wheatstone bridge, which can be measured as a voltage or current output.

Wheatstone bridge and 4 piezo-resistors

Signal Conditioning and Amplification:

  • The small voltage or current output from the Wheatstone bridge is then processed by signal conditioning circuitry, which typically includes amplifiers, filters, and analog-to-digital converters (ADCs).
  • The signal conditioning stage amplifies the sensor output, filters out any unwanted noise, and converts the analog signal into a digital format for further processing and analysis.

ADC-analog to digital

Silicon piezo resistive Example: diffused silicon pressure sensor

The diffused silicon pressure sensor is a device that fabricated under the principle of Silicon piezo resistive sensing, in case of diffused silicon pressure sensor, the externally applied pressure is transferred to a sensitive chip through a stainless steel diaphragm and internally sealed silicon oil (the sensitive chip does not directly contact the tested medium).

This causes the diaphragm to produce a micro-displacement proportional to the medium pressure, causing a change in the sensor’s resistance value. This change is detected by an electronic circuit and converted into a standard measurement signal corresponding to this pressure.

With its high sensitivity output, good dynamic response, high measurement accuracy, good stability, and easy miniaturization, it is sensitive to temperature. However, it is the preferred choice for mid-range sensors that can measure pressures greater than 7kPa, but less than 1000bar normally.

How diffused silicon pressure sensor fabricated?

The fabrication of diffused silicon pressure sensors involves a series of well-established semiconductor manufacturing processes, which leverages the semiconductor manufacturing techniques, enables the production of high-quality, reliable, and cost-effective silicon piezo-resistive pressure sensors.

Let’s delve into step by step as following,

  1. Silicon Wafer Preparation
  2. Thermal Oxidation
  3. Photolithography
  4. Dopant Diffusion
  5. Interconnect Formation
  6. Packaging and Passivation

Infographic of How diffused silicon pressure sensor fabricated-2

The precision and control achieved during above fabrication steps are crucial in delivering the exceptional performance characteristics that make these sensors so widely used in various industries.

Pros and cons

Firstly, let’s delve into the key strengths that have made silicon piezo-resistive pressure sensors a go-to solution for so many applications.

Pros 1: Unparalleled Sensitivity and Precision

One of the standout features of these sensors is their exceptional sensitivity, with typical values ranging from 0.1 to 10 mV/V/kPa. This remarkable responsiveness allows them to detect and measure even the slightest pressure changes, making them invaluable in applications that demand the utmost precision, such as industrial process control, medical equipment, and high-performance automotive systems.

Pros 2: Remarkable Accuracy and Linearity

Accuracy is another area where silicon piezo-resistive pressure sensors truly shine. With errors typically less than 0.1% of the full-scale output, these sensors deliver unparalleled precision, ensuring reliable and consistent pressure measurements. Moreover, the highly linear pressure-to-output relationship simplifies the calibration and signal processing requirements, further enhancing the overall performance.

Pressure Sensor Accuracy-and-precision

Pros 3: Lightning-Fast Response Times

In today’s fast-paced world, speed is of the essence. Silicon piezo-resistive pressure sensors rise to the challenge, boasting response times in the microsecond range. This lightning-fast performance enables real-time pressure monitoring and control, making them indispensable in applications that require rapid, high-precision pressure management.

Pros 4: Exceptional Temperature Stability and Durability

Engineered to withstand the rigors of demanding environments, silicon piezo-resistive pressure sensors are designed to maintain their performance across a wide temperature range, typically from -40°C to 125°C or beyond. Coupled with their inherent reliability and resistance to factors like vibration, shock, and corrosion, these sensors ensure consistent and dependable pressure measurement, even in the most challenging conditions.

While the advantages of silicon piezo-resistive pressure sensors are truly impressive, it’s important to acknowledge the potential drawbacks that engineers must consider when selecting the appropriate technology for their applications.

Cons 1: Sensitivity to Mechanical Stress and Strain

As these sensors rely on the piezo-resistive effect, they are inherently sensitive to mechanical stress and strain, which can impact their output. Careful design and packaging are required to minimize the influence of external mechanical forces on the sensor performance.

Cons 2: Temperature Dependence and Compensation

While modern silicon piezo-resistive pressure sensors have improved temperature stability, there is still some residual temperature dependence in their output. This necessitates the implementation of temperature compensation circuitry or algorithms to maintain accurate pressure measurements across a wide temperature range.

cons 3: Susceptibility to Moisture and Environmental Factors

Silicon-based sensors can be vulnerable to moisture and other environmental factors, which can potentially degrade their performance or even lead to sensor failure. Robust packaging and sealing techniques are essential to protect the sensor from these environmental influences.

Cons 4: Manufacturing Complexity and Cost

The fabrication of silicon piezo-resistive pressure sensors involves a multi-step semiconductor manufacturing process, which can be more complex and costly compared to some alternative pressure sensing technologies. This complexity can impact the overall cost and scalability of sensor production.

Cases that silicon piezo resistive is not suitable

Case 1: Dynamic, vibration or shock

One of the primary drawbacks of silicon piezo-resistive pressure sensors is their inherent sensitivity to mechanical stress and strain. This sensitivity, which is a core aspect of their operating principle, can become a double-edged sword in certain applications. For instance, in environments with high levels of dynamic, vibration or shock, the sensor output may be susceptible to interference from these external mechanical forces, leading to inaccuracies and potential failures.

In such cases, alternative pressure sensing technologies (piezo-electrical sensing) that are less sensitive to mechanical disturbances may be more appropriate.

Case 2: Rapid temperature fluctuations

While modern silicon piezo-resistive pressure sensors have made significant strides in improving temperature stability, there is still some residual temperature dependence in their output. In applications where the operating temperature range is particularly wide or where rapid temperature fluctuations are common, the need for sophisticated temperature compensation circuitry or algorithms can add complexity and cost to the overall system design.

For these scenarios, pressure sensors with inherently better temperature stability or self-compensation capabilities may be a more suitable choice.

Case 3: Some corrosive projects

Silicon-based pressure sensors, like many electronic devices, can be susceptible to the detrimental effects of environmental factors such as moisture, corrosive substances, and extreme atmospheric conditions. In applications where the sensor is exposed to harsh environments (for example ocean water) or where it must operate in the presence of these environmental stressors, the need for robust packaging and sealing becomes paramount.

Failure to adequately protect the sensor can lead to performance degradation, premature failure, and unreliable pressure measurements. In such cases, the use of specialized enclosures or the selection of pressure sensors designed for rugged environments may be necessary.

For example, in some corrosive seawater monitor system, it is better to use titanium alloy housing, ceramic capacitive sensing type level/ pressure transmitter, check details of: EST341 ceramic capacitive sensing transmitter

Case 4: Affordable budget cap

The fabrication of silicon piezo-resistive pressure sensors involves a multi-step semiconductor manufacturing process, which can be more complex and costly compared to some alternative pressure sensing technologies. In applications where cost is a critical factor or where the production volumes are relatively low, the higher manufacturing complexity of silicon sensors may make them less economically viable. In such scenarios, engineers may need to explore more cost-effective pressure sensing solutions (like ceramic piezo-resistive sensing instead) that still meet the necessary performance requirements.

Case 5: Other cases that more than the limitation

Let’s take an example of ESS319, one of the most popular models of silicon piezo resistive pressure sensor made by Eastsensor, the minimal measurable pressure is 7kpa, and max is 1000bar, any pressure if range less than 7kpa, or bigger than 1000bar (check EST380 for 2200bar), then silicon piezo resistive solution will be no the best one.

The most workable operation temperature for silicon piezo resistive is -40℃ to 85℃, any working temperature lower or higher than that, it is better to look for other solution, check the details in our blog: how to handle in extreme and harsh environments

The widely accepted accuracy for silicon piezo resistive sensing is 0.1% -0.5%/FS, if the project need higher accuracy, for example, 0.075 or 0.05%/FS, you may need to refer to EST4300M industry pressure solution.

Comparison among different piezo-resistive sensing

Silicon Piezo-resistiveCeramic Piezo-resistiveThin-film Piezo-resistive
Silicon Piezo-resistive EST330S 300-300Ceramic Piezo-resistive-EST3120 300-300Thin-film Piezo-resistive-EST380 300-300
Click to product pageEST330SEST3120EST380
DatasheetDownloadDownloadDownload
PrinciplePiezo-resistive effectPiezo-resistive effectPiezo-resistive effect
Fabrication methodDiffused Silicon (single)Thick-film PrintThin-film spluttering
Sensing elementMade of silicon, where piezo-resistors are diffused into the silicon substrate.Made of a ceramic material, typically a mixture of oxides, onto which a thick-film piezo-resistive layer is deposited.fabricated using a sputtering deposition process, where a thin layer of piezo-resistive material is deposited onto a substrate, often silicon or ceramic.
MOCSS316Ceramic Al2O3, dry typeSilicon nitride (Si3N4), ceramic
Min pressure to measure0-7kpa0-0.05bar0-4bar
Max pressure to measure0-1000bar0-480bar0-2200bar
Filled fluidSilicon OilNoneNone
Highlight features• High sensitivity
• High stability
• Good linearity
• Temperature compensation
• High temperature resistance
• Good chemical resistance
• Cost-effective for high volume production
• High sensitivity
• Good stability over time
• Suitable for high-pressure applications
Suitable industry• Biomedical instruments
• Precision industrial controls
• Aerospace and defense
• Automotive (e.g., engine management systems)
• HVAC systems
• Industrial process control
• Aerospace
• Oil and gas industry
• High-precision industrial applications

Piezoresistive sensing

Piezoresistive sensing

Piezoresistive Sensing

Piezoresistive sensing is kind of technique that used to measure force, pressure, or mechanical stress by exploiting the piezoresistive effect, which is the change in electrical resistance of a material when it is subjected to mechanical deformation or strain.

The piezoresistive effect is the change in electrical resistivity of a material when it is subjected to mechanical stress or strain. This effect is observed in certain materials, such as semiconductors (e.g., silicon, germanium) and some metals and semiconductor ceramics. The change in resistivity is proportional to the applied stress or strain, allowing the measurement of force, pressure, or mechanical deformation by monitoring the change in electrical resistance.

The principle behind piezoresistive sensing is based on the fact that when a material is subjected to mechanical stress or strain, its atomic structure and electronic band structure are altered, leading to a change in its electrical resistivity. This change in resistivity is typically linear and proportional to the applied stress or strain within a certain range.

Piezoresistive sensing-Proportional change between pressure and mv signal

Piezoresistive sensor

In a piezoresistive sensor, a piezoresistive material is integrated into a sensing element, often in the form of a thin film or a bulk material with a specific geometry. When a force or pressure is applied to the sensing element, it deforms, causing a change in the resistance of the piezoresistive material. This change in resistance can be measured and converted into an electrical signal output that is proportional to the applied force or pressure.

Piezoresistive sensors are widely used in various applications, including:

  1. Pressure sensors: Used to measure pressure in various fields, such as automotive, industrial, and medical applications.
  2. Force sensors: Used to measure forces in load cells, strain gauges, and tactile sensors.
  3. Accelerometers: Used to measure acceleration and vibration in applications like inertial navigation, shock detection, and motion sensing.
  4. Tactile sensors: Used in robotics and haptic interfaces to detect touch, pressure distribution, and surface texture.

In now days, the piezoresistive effect is often combined with other sensing principles, such as capacitive or piezoelectric sensing, to create more advanced and versatile sensor systems.

Click to check: 5 Pressure Sensor Working Principles You Need to Know

How Piezoresistive Pressure Sensors Work

Piezoresistive pressure sensors are a type of sensor that work through the piezoresistive effect, which is the change in resistance of a material when mechanical strain is applied. This effect is usually obtained with semiconductor materials such as silicon or germanium.

The basic structure of a piezoresistive pressure sensor includes a diaphragm and a resistor, or piezoresistor. When pressure is applied to the diaphragm, it deforms or flexes, causing a strain that changes the resistance of the piezoresistor.

Wheatstone bridge and 4 piezo-resistors

Steps breakdown

Here’s a step-by-step breakdown of how piezoresistive pressure sensors work:

  1. The sensor is exposed to a pressure input (such as air or liquid pressure). The pressure is typically applied to a thin silicon or metal diaphragm where the piezoresistors are located.
  2. The applied pressure causes the diaphragm to deform or flex. The amount of deformation is proportional to the amount of applied pressure.
  3. The deformation of the diaphragm causes a change in the strain experienced by the piezoresistors.
  4. This strain changes the electrical resistance of the piezoresistors. Typically, the change in resistance is proportional to the applied pressure, allowing for a measurement of the pressure.
  5. The change in resistance is then measured by an electrical circuit. This is typically done through a Wheatstone bridge configuration, an electrical circuit setup used to measure the resistance.
  6. The change in resistance is then converted into an electrical signal (voltage or current) that can be read, processed, and interpreted by a readout or control device.

Infographic of how piezoresistive sensing working

An example

Imagine you have a small, thin square of silicon, which is a semiconductor material. This square is called a piezoresistive sensing element. It’s designed to change its electrical resistance when it’s deformed or squeezed.

Now, let’s say we want to measure the pressure of a gas or liquid. We take this piezoresistive sensing element and carefully mount it on a thin, flexible metal diaphragm. This diaphragm acts like a drumhead – it can bulge or deflect when pressure is applied to it.

When there’s no pressure, the diaphragm and the piezoresistive sensing element are flat and unstressed. In this state, the sensing element has a specific resistance value, let’s say 1000 ohms.

But when we apply pressure to the diaphragm, it starts to bulge or deflect. This deformation causes the piezoresistive sensing element to be squeezed or stretched, changing its resistance value. The higher the pressure, the more the resistance changes.

For example, in a typical piezoresistive pressure sensor designed for automotive applications, the sensing element might have a resistance change of about 0.2 ohms for every 1 psi (pound per square inch) of pressure applied. So, if the pressure is 100 psi, the resistance would change from 1000 ohms to around 1020 ohms.

We can measure this resistance change using a simple electrical circuit and convert it into a 4-20mA current or 0-5v voltage or I2C digital signal that represents the pressure value.

Now, let’s talk about some specific technical specifications:

  • Sensing Element Material: Silicon is commonly used for its excellent piezoresistive properties and compatibility with integrated circuit fabrication processes.
  • Diaphragm Material: Stainless steel, silicon, or other materials with good mechanical properties and compatibility with the sensing element.
  • Pressure Range: Piezoresistive sensors can be designed for various pressure ranges, from millibar (mbar) levels for low-pressure applications to thousands of psi for high-pressure applications.
  • Sensitivity: Typically expressed as the resistance change per unit of pressure, e.g., 0.2 ohms/psi.
  • Linearity: Most piezoresistive sensors have good linearity (linear resistance change with pressure) over a wide range, often better than 0.5% of full-scale output.
  • Temperature Compensation: Integrated circuits or software algorithms are used to compensate for temperature effects on the sensing element and electronics.
MaterialPiezoresistive CoefficientTemperature StabilityChemical ResistanceSize CompatibilityCost
SiliconHigh (up to 200x)Low to MediumMediumExcellentModerate to High
Metal FoilLowHighHighGoodLow to Moderate
CeramicMediumHighHighGoodModerate
Polymer (e.g., PVDF)Medium to LowMediumVariableExcellentLow to Moderate

The most common types of piezoresistive sensing

Silicon Piezo-Resistive (Diffused) | The Epitome of Sensitivity and Speed

Silicon piezo-resistive pressure sensors harness the power of the piezo-resistive effect, where the electrical resistance of certain materials changes in response to mechanical stress or pressure. These sensors feature a silicon-based sensing element, with piezo-resistors carefully diffused into the substrate. By arranging these piezo-resistors in a Wheatstone bridge configuration, these sensors can precisely detect and measure the pressure-induced resistance changes. What sets silicon piezo-resistive sensors apart is their exceptional sensitivity, remarkable accuracy, and lightning-fast response times, often reaching the microsecond range. These capabilities make them indispensable in a wide array of applications, from industrial process control and medical equipment to automotive systems.

Ceramic Piezo-Resistive (Thick-Film) Pressure Sensors: Rugged and Versatile

Ceramic piezo-resistive pressure sensors offer a unique approach to pressure measurement. Instead of relying on silicon, these sensors utilize a ceramic-based sensing element, typically a mixture of oxides, with a thick-film piezo-resistive layer deposited on top. This design allows for the creation of pressure sensors with an impressive range, from low pressures in the millibar range to high pressures in the hundreds of bars.

Ceramic piezo-resistive sensors are renowned for their exceptional robustness, exceptional temperature stability, and remarkable resistance to harsh environmental conditions. These attributes make them invaluable in industrial automation, process control, and automotive applications where durability and reliability are paramount.

Thin-Film Piezo-Resistive (Sputtering) Pressure Sensors: Miniaturized Precision

Thin film piezo resistive innovative devices leverage the sputtering deposition process to create a highly sensitive and compact sensing element, often just a few microns thick.

This thin-film approach allows for the fabrication of miniaturized pressure sensors with remarkable sensitivity and fast response times, making them ideal for integration into micro-electromechanical systems (MEMS) and other compact, high-performance applications.

From medical diagnostics and industrial process control to consumer electronics, thin-film piezo-resistive pressure sensors are redefining the possibilities of pressure measurement.

Comparison among different piezo-resistive sensing

Silicon Piezo-resistiveCeramic Piezo-resistiveThin-film Piezo-resistive
Silicon Piezo-resistive EST330S 300-300Ceramic Piezo-resistive-EST3120 300-300Thin-film Piezo-resistive-EST380 300-300
Click to product pageEST330SEST3120EST380
DatasheetDownloadDownloadDownload
PrinciplePiezo-resistive effectPiezo-resistive effectPiezo-resistive effect
Fabrication methodDiffused Silicon (single)Thick-film PrintThin-film spluttering
Sensing elementMade of silicon, where piezo-resistors are diffused into the silicon substrate.Made of a ceramic material, typically a mixture of oxides, onto which a thick-film piezo-resistive layer is deposited.fabricated using a sputtering deposition process, where a thin layer of piezo-resistive material is deposited onto a substrate, often silicon or ceramic.
MOCSS316Ceramic Al2O3, dry typeSilicon nitride (Si3N4), ceramic
Min pressure to measure0-7kpa0-0.05bar0-4bar
Max pressure to measure0-1000bar0-480bar0-2200bar
Filled fluidSilicon OilNoneNone
Highlight features• High sensitivity
• High stability
• Good linearity
• Temperature compensation
• High temperature resistance
• Good chemical resistance
• Cost-effective for high volume production
• High sensitivity
• Good stability over time
• Suitable for high-pressure applications
Suitable industry• Biomedical instruments
• Precision industrial controls
• Aerospace and defense
• Automotive (e.g., engine management systems)
• HVAC systems
• Industrial process control
• Aerospace
• Oil and gas industry
• High-precision industrial applications

Thin Film Pressure Sensor

Thin Film Pressure Sensor

What is Thin Film Pressure Sensor?

A thin-film pressure sensor is a type of pressure sensing device that utilizes a thin-film sensing element deposited on a substrate material. The sensing element is typically a thin layer of material, such as polysilicon, silicon nitride, or metal alloys, with a thickness ranging from a few nanometers to a few micrometers.

The basic structure of a thin-film pressure sensor consists of the following components:

Substrate: The substrate material serves as the base for the sensor’s construction. Common substrates used include silicon, glass, or ceramic materials.

Thin-film sensing element: This is the core component responsible for pressure sensing. The sensing element is deposited on the substrate using techniques like sputtering, chemical vapor deposition (CVD), or other thin-film deposition methods.

Diaphragm: A thin, flexible diaphragm is created on the substrate, often through micromachining or etching processes. The thin-film sensing element is strategically placed on or near the diaphragm.

Thin film sensor cell cross section view

The diaphragm structure is often bonded to a backing material or a second substrate to create a sealed cavity or reference pressure chamber.

The sensing principle

The operating principle of a thin-film pressure sensor is based on the piezoresistive effect, where the electrical resistance of the thin-film sensing element changes in response to the mechanical strain or deformation caused by applied pressure.

When pressure is applied to the diaphragm, it deflects, causing the thin-film sensing element to experience strain, which in turn changes its electrical resistance.

Thin film piezo-resistive

This change in resistance is detected and converted into an electrical signal using appropriate signal conditioning circuitry, allowing the measurement of pressure.

The thin-film sensing element is often configured in a Wheatstone bridge or other resistive circuit arrangement to enhance sensitivity and provide temperature compensation.

Thin film sensor cell bridge

The thin-film sensing element is often configured in a Wheatstone bridge arrangement, with two active resistors (sensing pressure) and two reference resistors (not subjected to pressure). This configuration allows for temperature compensation, increased sensitivity, and common-mode noise rejection.

The change in resistance of the active resistors due to the applied pressure creates an imbalance in the Wheatstone bridge, resulting in a measurable voltage difference across the bridge’s output terminals.

The output voltage from the Wheatstone bridge is typically small and requires amplification and signal conditioning. This is achieved using instrumentation amplifiers, analog-to-digital converters (ADCs), or dedicated signal conditioning circuits.

ADC-analog to digital

The conditioned output signal is then processed, often by a microcontroller or digital signal processor, to calculate the corresponding pressure value. This calculation is based on the calibration data and the known relationship between the output signal and the applied pressure.

Pressure Sensor Output signal-2

Thin-film pressure sensors can be designed and optimized for different pressure ranges, sensitivities, and environmental conditions by adjusting factors such as the diaphragm size, thickness, and material properties, as well as the dimensions and configurations of the thin-film sensing element.

Additionally, these sensors can be integrated with microelectronic circuits and signal conditioning components on the same substrate, enabling the development of compact, highly integrated pressure sensing solutions for various applications, including automotive, industrial, medical, and consumer electronics.

Highlight feature

High accuracy and precision: ±0.1%-±0.25%

One of the most significant advantages of thin-film pressure sensors is their ability to achieve high accuracy and precision in pressure measurements.

High-quality thin-film sensors can typically achieve an accuracy of ±0.25% to ±0.5% of the full-scale output (FSO) or better like±0.1%.

For example, a common automotive manifold absolute pressure (MAP) sensor with a 0-5 bar range and ±0.25% FSO accuracy would have an error of ±12.5 mbar across the entire pressure range.

Wide pressure range: 0.001bar(1mbar)~2000bar

Thin-film pressure sensors can be designed to measure pressures ranging from a few millibars (mbar) to hundreds of bars, making them suitable for a wide range of applications.

For instance, some thin-film sensors can measure low pressures as low as 1 mbar, materials like sputtered or implanted polysilicon are commonly used due to their high sensitivity and good performance;

Thin film sputtered-eastsensor

For high pressures, up to 2000 bar or even higher in specialized applications, materials like silicon carbide (SiC) or specific metal alloys (e.g., platinum, nickel-chromium) may be preferred due to their high strength and stability under extreme conditions.

The sensing element design and layout can be optimized for different pressure ranges, with larger sensing resistors for low pressures and smaller resistors for high pressures.

However, after assembly process, when such sensor has been produced pressure transmitter or transducer, in order to keep full balance and ensure long term stability, the minimal measurable range will increase to 4bar about.

On the other hand, the technics of packaging and sealing also take important effect to achieve wide pressure range.

Hermetic packaging techniques, such as welding or brazing, are essential to ensure a leak-tight enclosure and prevent moisture ingress or contaminants from affecting the sensor’s performance.

For high pressures, specialized pressure ports and fittings made of high-strength materials like stainless steel or Inconel may be required to withstand the extreme pressures without leakage or deformation.

It’s important to note that achieving such a wide pressure range often results in larger sensor sizes, higher manufacturing costs, and increased complexity. Additionally, rigorous testing and qualification processes, including pressure cycling tests, burst pressure tests, and long-term stability evaluations, are essential to ensure the reliability and performance of these specialized thin-film pressure sensors.

Temperature compensation: -20℃~120℃;  -20℃~150℃/200℃

The main techniques to design a thin film pressure sensor that endures high temperatures is: Choose tough materials. Design it to handle thermal expansion. Pack it up in a material that can take the heat. Use wiring that won’t melt. Add circuits that adjust the readings when it gets hot. And don’t forget to use a temperature-resistant adhesive.

It’s important to note that designing thin-film pressure sensors for high-temperature operation often involves trade-offs in terms of sensor size, cost, and complexity. Extensive testing and qualification processes, including temperature cycling tests and long-term stability evaluations, are crucial to ensure the reliability and performance of these specialized sensors.

High burst pressure performance: 3X-10X

By carefully selecting materials, optimizing diaphragm designs, implementing robust packaging techniques, and incorporating overload protection mechanisms, it is possible to develop thin-film pressure sensors with high burst pressure capabilities, ranging from 3X to even 10X the maximum rated pressure, while maintaining the desired accuracy and performance characteristics.

How to design High Temperature thin film pressure sensor

Designing thin-film pressure sensors to withstand high working temperatures up to 150°C (302°F) requires a careful selection of materials, specialized fabrication techniques, and effective temperature compensation strategies.

Substrate Material Selection

It’s true that most silicon substrates have a temperature limit of around 125°C, beyond which their properties can degrade. For some high-temperature applications up to 150°C or higher, suitable substrate materials include aluminum nitride (AlN) and silicon carbide (SiC).

Film-system-used-for-the-thin-film-sensors

AlN has a high thermal conductivity (180-200 W/m·K) and a compatible coefficient of thermal expansion (CTE) with silicon, making it a good choice for temperatures up to 300°C.

SiC has an even higher thermal conductivity (270-370 W/m·K) and can withstand temperatures up to 600°C, making it suitable for extreme high-temperature environments.

Diaphragm Material Selection

The diaphragm material should have a compatible CTE with the substrate to minimize thermally induced stress and deformation. For temperatures up to 150°C, materials like silicon nitride (Si3N4), polysilicon, or silicon carbide (SiC) can be used for the diaphragm.

Si3N4 has good mechanical properties and can withstand temperatures up to 850°C. Polysilicon exhibits good piezoresistive properties and can operate up to 300°C.

SiC has excellent mechanical strength and can withstand temperatures up to 600°C.

Thin-Film Sensing Element

Thin Film Pressure Sensor Diaphragm

It is important that the thin-film sensing element should maintain its piezoresistive properties and stability at high temperatures.

In practice, sputtered or implanted polysilicon is a common choice for temperatures up to 300°C.

Silicon carbide (SiC) thin films can be used for temperatures up to 600°C due to their exceptional stability and piezoresistive properties.

Metal alloy thin films, such as platinum (Pt) or nickel-chromium (NiCr), can also be used for high-temperature applications, but they may require additional temperature compensation techniques.

Temperature Compensation

Implementing effective temperature compensation is crucial to maintain accuracy over a wide temperature range.

Basically, the Wheatstone bridge configuration, with two active and two reference resistors, can provide basic temperature compensation by canceling out resistance changes due to temperature.

Advanced compensation techniques involve integrating on-chip temperature sensors, such as resistive temperature detectors (RTDs) or diodes, and implementing compensation algorithms in the signal conditioning circuitry or digital signal processing.

Good compensation algorithms can account for non-linear temperature effects and variations in material properties, ensuring accurate pressure measurements across the entire temperature range.

Packaging and Sealing

Pressure Sensor Package & Sealing Structure v1.0-eastsensor

Hermetic packaging techniques, such as welding or brazing, are essential to prevent moisture ingress and ensure a leak-tight enclosure.

Materials used for packaging should have compatible CTEs with the sensor components to minimize stress and deformation at high temperatures. Glass-to-metal sealing or ceramic packaging may be employed for high-temperature applications.

Signal Conditioning and Interfacing

High-temperature signal conditioning circuits and interfacing components are required to ensure proper operation and accuracy at elevated temperatures.

Specialized high-temperature operational amplifiers, analog-to-digital converters (ADCs), and microcontrollers can be used to process and digitize the sensor output signals.

ADC-analog to digital-2

Digital signal processing techniques can further enhance accuracy, stability, and temperature compensation capabilities.

How to design High Accuracy thin film pressure sensor

To achieve high accuracy like 0.1% or 0.25% , the designers always need to focus on several key aspects of the sensor design and manufacturing process.

First, the diaphragm, which is the primary component responsible for translating the applied pressure into mechanical deflection, needs to be designed with utmost precision. The diaphragm thickness and geometry play a crucial role in determining the sensor’s sensitivity and linearity.

Typically, materials like silicon, silicon nitride, or single-crystal silicon carbide are used for high-accuracy diaphragms. The thickness can range from a few micrometers to tens of micrometers, depending on the pressure range and desired sensitivity.

Additionally, specialized diaphragm geometries, such as corrugated or bossed designs, can improve linearity and reduce stress concentrations, which can affect accuracy.

Next, the thin-film sensing element, which converts the diaphragm’s deflection into an electrical signal, must exhibit excellent piezoresistive properties, stability, and minimal hysteresis (the tendency to exhibit different output values for the same input, depending on the direction of change).

Sputtered or implanted polysilicon is a common choice due to its high sensitivity and good linearity. Silicon carbide thin films can also be used, especially in high-temperature applications, as they offer exceptional stability and linearity.

Effective temperature compensation is crucial for maintaining high accuracy over a wide temperature range. This involves integrating on-chip temperature sensors, such as resistive temperature detectors or diodes, and implementing advanced compensation algorithms in the signal conditioning circuitry or digital signal processing.

These algorithms can account for non-linear temperature effects, variations in material properties, and offset and span errors, ensuring accurate pressure measurements across the entire temperature range.

High-resolution analog-to-digital converters (ADCs) with low noise and high linearity are essential for achieving high accuracy.

Specialized instrumentation amplifiers with low offset and drift can be used to amplify the sensor’s output signals with minimal error.

Digital signal processing techniques, such as linearization algorithms, filtering, and advanced calibration methods, can further enhance accuracy and compensate for non-linearities and errors.

Rigorous calibration and trimming processes are necessary to achieve high accuracy specifications. Laser trimming techniques can be used to precisely adjust the resistor values in the sensing element or bridge circuit, minimizing offset and span errors.

Automated calibration systems and mathematical models can be employed to characterize and compensate for non-linearities, hysteresis, and other error sources.

Finally, hermetic packaging techniques, such as welding or brazing, are essential to prevent moisture ingress and ensure long-term stability. Packaging materials and designs should minimize stress concentrations and thermal gradients that can introduce errors or non-linearities.

Environmental protection measures, such as shielding and filtering, may also be necessary to minimize electromagnetic interference (EMI) and other external factors that can affect accuracy.

By carefully considering and optimizing these various aspects of the sensor design, manufacturing, and calibration processes, it is possible to achieve thin-film pressure sensors with high accuracy levels, such as 0.1% or 0.25% of the full-scale output.

Click to check more details about Pressure Sensor Accuracy

Pressure Sensor Precision and Accuracy

Other Piezo-Resistive Pressure Sensors

On top of above discussed Thin-film pressure sensor which using piezo-resistive principle, with four resistors are placed on a diaphragm in a Wheatstone bridge pattern to track the diaphragm’s deformation under pressure.

There are also other types of piezoresistive pressure sensor, like the following:

Ceramic Thick-Film Pressure Sensor

Thick-film sensors use the same setup as thin-film sensors by grouping four resistors into a Wheatstone bridge. But instead of attaching them to the base, thick-film sensors print the resistors onto a base such as ceramic using special technology, and then they heat it to a high temperature. They also detect change in resistance due to the diaphragm’s deformation, caused by stretching and compressing the material.

Diffused Silicone Piezo-resistive Pressure Sensor

Unlike the first two types, diffused silicone, actually act as kind of semi-conductor to uses a silicon measuring diaphragm with special diffused structures. They take advantage of the piezoresistive effect, which involves changing electrical resistance in the silicon due to stretching and compressing, thereby affecting electron mobility under mechanical stress.

EST380 Thin-Film Pressure Sensor

Thin-Film | Silicon Carbide | Sputtered | Hermetic Packaging

0-4bar-2200bar | -40℃~150℃ | 0.1%.FS/0.25%/FS

Monocrystalline Silicon Pressure Transmitters

Monocrystalline Silicon Pressure Transmitters

The application of high-stability pressure and differential pressure transmitters is becoming increasingly important in the field of automation. Developing high-stability pressure transmitters is a significant challenge that manufacturers face.

However, it has been demonstrated through practice that significant improvements in the overall performance, accuracy, and reliability of high-stability pressure and differential pressure transmitters can be achieved through breakthroughs in various technological aspects.

These aspects include the selection of ultra-stable monocrystalline silicon principle chips, stress-free packaging of ultra-stable monocrystalline silicon wafers, elimination of hysteresis errors, reduction and compensation of static pressure errors, expansion of the range ratio of the instruments, special treatment of the wetted surface, and ultra-high-temperature measurement techniques.

Current High Stability Pressure and Differential Pressure Transmitters

The mainstream high-stability pressure and differential pressure transmitters in the current market are primarily of three types and principles.

1.1 Metal Capacitive Pressure Principles

One type is the metal capacitive pressure and differential pressure transmitters developed and produced by some manufacturers, with representative models such as the 1151, 3051, and 3351 series.

Their working principle is as follows:

  • The external pressure difference is transmitted to the internal metal capacitor plates.
  • When the plates are displaced, a change in capacitance occurs.
  • This change in capacitance is collected, amplified, and processed with software compensation by electronic circuits, resulting in a linear output of the pressure signal.

Capacitive Pressure Sensors -small

Since the technology of the 1151 series capacitive sensors was introduced to China in the 1980s, it has been widely replicated and promoted domestically.

By 2016, there were nearly 100 local manufacturers, with more typical domestic manufacturers located in Shanghai, Xi’an, Beijing, Chongqing, and other companies under the Nuclear Industry Department.

After years of research and exploration, most of above instrument manufacturers began to miniaturize the 1151 transmitters at the beginning of the 21st century. The volume was significantly reduced, and the transition from analog to digital circuits was gradually made, eventually achieving an improvement in accuracy grade from 0.5 to 0.1.

However, these improvements did not fundamentally change the sensor structure; therefore, despite the advancements, there were still considerable limitations.

The accuracy, long-term stability, EMI performance, static pressure performance, and temperature performance still had a significant gap compared to their original counterpart’s products. This ultimately led to the situation where many pressure transmitters remained far behind those from EU and USA.

However, the 3051C/S series transmitters have made significant improvements based on the 1151 series, achieving substantial enhancements such as structural isolation, suspension, and improved circuit reliability. These transmitters have reached an accuracy level of 0.05%, a significant leap in performance.

However, the technical difficulties and barriers presented by the 3051C/S pressure transmitters have not been effectively overcome by Chinese domestic enterprises, leading almost all Chinese manufacturers to abandon further exploration and research into capacitive transmitters.

In other words, currently, most China domestic manufacturers in the field of metal capacitive pressure transmitters can only maintain an accuracy level of 0.1-0.2%.

If 0.1-0.2% accuracy class can be accepted and workable for your application, please click to check one of leading example produced by Eastsensor: ESS343 (the metal capacitive sensing element and sensor core)

Metal Capacitive Pressure Sensor

1.2 Monocrystalline Silicon Pressure Principles

The second type is the monocrystalline silicon pressure transmitters and differential pressure transmitters developed and produced by Japanese manufacturers, with representative models being the Yokogawa EJA and EJX series.

Their working principle is as follows:

  • The external pressure difference is transmitted to the internal monocrystalline silicon resonant beam.
  • Under the action of pressure, the resonant beam generates a pair of differential frequency signals that vary with the pressure.
  • These differential frequency signals are then collected, amplified, and processed with software compensation by electronic circuits, resulting in a linear output of the pressure signal.

The Yokogawa EJA series monocrystalline silicon resonant transmitters have certain advantages in manufacturing cost control compared to capacitive sensors.

The main advantages are reflected in the temperature and static pressure compensation stages, that is, the original differential signal output of the dual resonant circuit, which is not affected by temperature and static pressure, making the temperature compensation and static pressure compensation processes of the transmitter relatively simple.

These transmitters ultimately reach an accuracy level of 0.065%, slightly inferior to the Rosemount 3051C/S series.

However, since the bulk production technology of monocrystalline silicon resonant beam chips is monopolized by the company Yokogawa, the technical difficulties and barriers brought by these chips cannot be effectively overcome by Chinese domestic enterprises either.

Therefore, almost all Chinese manufacturers have also abandoned further exploration and research into monocrystalline silicon resonant transmitters.

1.3 Monocrystalline Silicon Resistive Pressure

The third type is represented by German and Swiss monocrystalline silicon resistive pressure and differential pressure transmitters.

Their working principle involves

  • An external pressure difference being transmitted to a monocrystalline silicon full-dynamic piezoresistive Wheatstone bridge inside the device.
  • The Wheatstone bridge generates a voltage signal that varies with pressure.
  • This voltage signal is collected, amplified, and processed with software compensation through electronic circuits to produce a linear pressure signal output.

These monocrystalline silicon resistive sensors are characterized by high output sensitivity, large signal output, and minimal hysteresis. Additionally, their circuit design tends to be simple and reliable.

Therefore, many Chinese domestic transmitter manufacturers prefer this approach for the development and manufacturing of high-end transmitters.

However, compared to metal capacitive sensors and monocrystalline silicon resonant sensors mentioned earlier, the application of monocrystalline silicon resistive chips has specific technical requirements.

These are mainly reflected in the stress-free packaging technology of silicon chips and the unidirectional overload protection technology of silicon thin films. These two application technologies were firmly held by Western countries before the year 2000.

After 2010, Chinese enterprises, through technical cooperation, introduction, and further research and development with some Swiss companies, have fully grasped multiple related technologies.

This has enabled the large-scale domestic manufacturing of high-stability silicon pressure and differential pressure transmitters.

EST4300M Monocrystalline Silicon Pressure Transmitters which designed and manufactured by Eastsensor, is one of them.

The accuracy level of the EST4300M series of high-stability monocrystalline silicon transmitters has reached 0.075%, which is better than 0.1%-0.2% of EST4300, and narrowing the gap with renowned transmitter brands from industrialized countries.

1.4 Working Principle of Monocrystalline Silicon Pressure Transmitters

As shown in below figure, the sensitive element of the EST4300M monocrystalline silicon sensor is created by diffusing P-type impurities onto an N-type silicon wafer, forming a very thin conductive P-type layer.

When leads are soldered on, it becomes a “monocrystalline silicon strain gauge.” Its electrical performance is that of a full-dynamic piezoresistive effect Wheatstone bridge.

Structure-diagram-of-Monocrystalline Silicon Pressure Transmitters

This piezoresistive Wheatstone bridge is combined with elastic elements (the N-type silicon substrate). The medium pressure is transmitted to the positive cavity side of the silicon diaphragm through sealed silicon oil, creating a pressure difference with the medium acting on the negative cavity side.

The combined effect causes one side of the diaphragm to compress and the other to stretch. The pressure difference unbalances the bridge, producing a signal corresponding to the pressure change. After electronic circuit processing, the Wheatstone bridge’s output signal generates a linear 4-20mA standard signal output in relation to pressure changes.

  • For gauge pressure sensors, the negative cavity side is usually open to the atmosphere, using atmospheric pressure as the reference pressure.
  • For absolute pressure sensors, the negative cavity side is typically a vacuum chamber, using a vacuum as the reference pressure.
  • For differential pressure sensors, the negative cavity side’s pressure medium is usually the same as the positive side, such as silicon oil, fluorinated oil, vegetable oil, etc.

As described in above figure, under the effect of the pressure difference between the positive and negative chambers, the measuring silicon diaphragm (also known as the elastic element) bends and deforms.

When the pressure difference P is below the required stress proportionality limit σp of the measuring silicon diaphragm, the bending can be fully reversed.

However, when the pressure difference P exceeds σp, the material reaches its yield stage and even the hardening stage. At this point, if the pressure difference is removed, the measuring silicon diaphragm cannot return to its original position, resulting in irreversible measurement deviations.

If the pressure difference P reaches or exceeds the maximum stress σb that the measuring silicon diaphragm can withstand, it ruptures, causing direct damage to the sensor.

Therefore, by preventing or weakening the direct transmission of the external overload pressure difference P to the measuring silicon diaphragm, one can effectively protect the measurement accuracy and lifespan of the sensor. This leads to the issue of designing overload protection for the monocrystalline silicon chip.

EST4300M- One of the most Reliable Monocrystalline Silicon Pressure Transmitters

EST4300M is type of Monocrystalline Silicon Smart Pressure Transmitter, which designed and manufactured by Eastsensor, it features 4-20mA+Hart to deliver accurate (0.075%/FS) outputs for data collection and control devices.

The precision and stability of EST4300M Monocrystalline Silicon Pressure Transmitter stand as their most distinguishing features, it boasts incredibly high accuracy, typically reaching levels up to 0.075% or 0.1% of Span.

This simply means that the margin of error in the detection and transmission of pressure levels is minuscule. Consequently, tasks that require minute attention to detail and accuracy can be conducted with confidence, knowing these transmitters provide one of the highest performance levels in pressure sensing.

EST4300M has recognized for their stability over extended periods, it has a remarkably low drift rate of less than 0.25% per annum. This characteristic means that EST4300M offer consistent, reliable information about pressure levels that remains accurate over the long term.

This kind of stability also ensures that processes relying on pressure measurement continue operating optimally, without the need for regular sensor recalibrations or replacements.

Smart HART Pressure Transmitter-EST4300M Monocrystalline

On top of precision and stability, you can also find below details about other features of EST4300M.

2.1 Pressure Overload Protection Design and Implementation

To overcome the deficiency of the poor overload resistance of monocrystalline silicon chips, the EST4300M is equipped with a differential pressure sensor that has unidirectional pressure overload protection.

As shown in below figure, this unidirectional pressure overload protection differential pressure sensor is not only capable of measuring the pressure difference within the rated pressure range in the field conditions but also can effectively protect itself in the event of a unidirectional pressure overload.

Schematic Diagram of a Differential Pressure Sensor with Overload Protection

This avoids damage caused by unidirectional pressure overload of the silicon differential pressure sensor.

Such overload protection is typically achieved through design features that limit the deformation of the silicon diaphragm.

For example, mechanical stops may be incorporated into the sensor design, which come into play when a certain deformation threshold is exceeded, thereby preventing further deformation and potential damage to the silicon diaphragm.

Additionally, the material properties and thickness of the diaphragm can be selected to provide the necessary resistance to overload while still allowing the necessary sensitivity for accurate measurement within the normal operating range.

The protection mechanism can be passive, where the design inherently protects the sensor, or active, where electronic or mechanical components react to the overload condition to prevent damage.

In some cases, a combination of both passive and active protection features is used to ensure the sensor’s longevity and reliability.

The description provided outlines a safety mechanism for protecting the monocrystalline silicon chip within a differential pressure sensor from pressure overloads that exceed its allowable working range.

The operational principle of this overload protection can be summarized as follows:

  • When a differential pressure that is higher than the allowable working range of the differential pressure measuring silicon diaphragm occurs, a central isolation diaphragm within the sensor moves toward the low-pressure side.
  • This movement causes the external isolation diaphragm on the high-pressure side to align with the inner wall of the chamber.
  • Consequently, the silicon oil on the high-pressure side is forced entirely into the chamber and cannot transmit any higher pressure to the monocrystalline silicon chip.
  • By preventing further pressure transmission, the occurrence of excessively high pressure on the monocrystalline silicon chip is avoided, effectively protecting it from overload.

This mechanism is an example of a passive protection system. In essence, the sensor’s structure is designed in such a way that it naturally adapts to excessive pressure conditions and prevents them from affecting the sensitive measuring component, i.e., the monocrystalline silicon chip.

By using a movable isolation diaphragm and a strategically placed external isolation diaphragm, the system ensures that the pressure is not transmitted beyond a certain threshold, which would otherwise compromise the integrity and accuracy of the pressure sensor.

This design is crucial for applications where pressure sensors are subject to fluctuating or unexpected pressure spikes. It ensures that the sensor can continue to operate within its specified parameters and provides reliability and longevity to the system it is monitoring or controlling.

Diagram of Overload for Positive-Negative Cavity

The overload protection design of the EST4300M effectively safeguards the long-term stability of the monocrystalline silicon chip, particularly in scenarios where water hammer phenomena are present.

This is because the rapid pressure surges associated with water hammer can easily damage sensitive components without such protection.

2.2 Superior Rangeability

The EST4300M benefits from the large output signal of the monocrystalline silicon chip. With a 5V constant voltage source excitation, the typical range output reaches 100mV. This makes it relatively easy for the backend electronics and software to implement signal compensation and amplification.

Compared to metal capacitive pressure and differential pressure transmitters, monocrystalline silicon-based pressure and differential pressure transmitters exhibit superior rangeability.

The common pressure transmitters have an adjustable range ratio of up to 100:1, and the micropressure transmitters have an adjustable range ratio of 10:1.

Even after the range is compressed, they still maintain high base accuracy, significantly expanding the adjustable range of the monocrystalline silicon pressure transmitter, which is convenient and meaningful for users.

As shown in Table 1, the accuracy assessment results of three sampled EST4300M differential pressure transmitters after range compression of 10:1 and 100:1 are as follows.

With a full scale of 0-250kPa, after 10 times compression, the range changes to 0-25kPa, and after 100 times compression, the range changes to 0-2.5kPa.

The experimental results show that when the range is compressed by 10 times, the basic errors are 0.019%, 0.012%, and 0.025%, respectively, which can still maintain the accuracy of class 0.05. After compressing the range by 100 times, the basic errors are 0.147%, 0.219%, and 0.197%, respectively, which are still better than the accuracy of class 0.25.

These results demonstrate the EST4300M’s ability to maintain high accuracy even when its measurement range is significantly reduced.

This rangeability is advantageous in applications where a wide variety of pressures need to be measured with the same device or when fine-tuning is necessary to achieve the best possible measurement resolution within a smaller subset of the sensor’s full scale.

This flexibility in the range also implies that fewer models of the transmitter need to be stocked, as one model can cover a wide range of pressures, reducing inventory costs and simplifying process design and maintenance.

AccuracyEST4300M-S1EST4300M-S2EST4300M-S3
10:1100:110:1100:110:1100:1
%%%%%%
1Total Error0.0910.1470.0120.2190.0250.197
2Non-Linearity0.0040.1010.0030.0690.0000.116
3Hysteresis0.0060.1590.0090.2340.0090.106
4Repeatability0.0060.0600.0050.0740.0090.069

Based on your description, Table 2 would present the accuracy assessment results for three EST4300M pressure transmitters after their measurement range has been compressed by factors of 10:1 and 100:1.

Here is a narrative interpretation of what such a table might show, based on the results you mentioned:

The full scale range of the transmitters is 0-40MPa. When the range is compressed by a factor of 10, it changes to 0-4MPa, and when compressed by a factor of 100, it changes to 0-400kPa. The experimental results indicate the following:

  • After a 10:1 range compression, the basic errors for the three samples are 0.041%, 0.047%, and 0.034%, respectively. These values demonstrate that the transmitters can still achieve the accuracy of Grade 0.05.
  • After a 100:1 range compression, the basic errors for the three samples are 0.15%, 0.063%, and 0.153%, respectively. Despite the significant reduction in range, these errors are still better than the accuracy of Grade 0.25.

The results from Table 2 would suggest that the EST4300M pressure transmitters exhibit excellent rangeability while maintaining high accuracy, even when the measurement range is greatly compressed.

This level of performance makes these transmitters suitable for a variety of demanding applications where precision is critical, even at significantly reduced measurement ranges.

The EST4300M’s ability to maintain accuracy across such a wide range of conditions underscores its flexibility and the robustness of its design, which can be particularly advantageous for users with diverse and variable pressure measurement needs.

AccuracyEST4300M-S3EST4300M-S4EST4300M-S5
10:1100:110:1100:110:1100:1
%%%%%%
1Total Error0.0410.1500.0470.0630.0340.153
2Non-Linearity0.0340.0460.0390.0060.0320.082
3Hysteresis0.0060.0940.0090.0690.0120.094
4Repeatability0.0030.0510.0050.0290.0060.054

2.3 Superior Pressure Hysteresis Performance

Pressure hysteresis, also known as the return error characteristic or simply hysteresis, is an important performance metric for pressure and differential pressure transmitters. The magnitude of hysteresis directly affects the measurement accuracy and long-term drift performance of the transmitter.

A typical error curve comparison between monocrystalline silicon sensors and metal capacitive sensors might look something like this, as show in below figure:

Curve of Sensor Error-EST4300M

From such a diagram, we would observe that the monocrystalline silicon sensor exhibits a very small hysteresis. The ascending (pressure increasing) and descending (pressure decreasing) curves almost overlap, indicating that the hysteresis is negligible and does not significantly affect the sensor’s output accuracy.

This minimized hysteresis suggests that the sensor’s readings are highly repeatable and reliable, regardless of whether the pressure is increasing or decreasing.

In contrast, the metal capacitive sensor’s error curve would show a larger hysteresis, with the ascending and descending curves forming an open loop. This gap indicates that the sensor’s readings may differ when the pressure is increasing versus when it is decreasing, which could lead to inaccuracies in the transmitter’s output.

The superior hysteresis performance of the EST4300M suggests that it would be particularly suitable for applications where high precision and repeatability are required over a wide range of operating conditions.

The reduced hysteresis would also contribute to the stability of the sensor’s output over time, indicating a design optimized for reliable, long-term use.

2.4 Unique Static Pressure Characteristics

Differential pressure transmitters are commonly used to measure tank levels or pipeline flow rates. If the effect of static pressure is not corrected or compensated for, it can introduce significant errors into the measurement. This effect is particularly pronounced when the level range is small or the relative flow rate is low.

For instance, a capacitive differential pressure transmitter, when used with a flow restriction device to form a differential pressure flow meter, may have a full-scale static pressure error of ≤±2% FS under a working static pressure of 32MPa.

While the zero-point error can be eliminated through zero adjustment, the full-span output error is unavoidable. This static pressure error directly affects flow measurement accuracy and can have a significant impact.

In such applications, the performance of a differential pressure transmitter under static pressure is crucial. If this static pressure error is compensated for, or if the transmitter inherently has minimal static pressure error, the accuracy of the measurements can be greatly improved.

The EST4300M differential pressure transmitter utilizes a unique encapsulation process for its monocrystalline silicon chip. After encapsulation, the inner and outer chambers of the chip reach pressure equilibrium. An illustrative diagram (below figure ) would show the encapsulation of the monocrystalline silicon wafer.

Monocrystalline Silicon wafer packaging schematic

When working static pressure is applied to the positive and negative chambers of the measuring silicon wafer, the pressure is balanced through the silicon oil in the outer positive chamber and the silicon oil in the inner negative chamber, loading the pressure onto the measuring wafer. This process achieves a counterbalance, resulting in minimal bending deformation of the measuring silicon wafer due to the working static pressure.

This approach significantly enhances the static pressure impact performance of the differential pressure transmitter.

By effectively balancing the pressure within the device, the EST4300M is capable of providing accurate measurements even under high static pressure conditions, minimizing errors that could arise from pressure-induced deformation of the sensor element.

This feature makes the EST4300M particularly suitable for high-precision applications in challenging environments where static pressure can have a detrimental effect on measurement accuracy.

Monocrystalline Silicon Pressure Cell structure schematic

In the application of micro differential pressure transmitters, due to the extremely small magnitude of the differential pressure signal, the sensitivity to the impact of static pressure is very high, and the unique encapsulation design and technology described above cannot completely eliminate or weaken the impact of static pressure.

To address this issue, the EST4300M micro differential pressure transmitter has integrated an absolute pressure sensor within its sensor, which can measure the working static pressure, as shown in the structural schematic of the EST4300M micro differential pressure sensor (refer to above figure).

This absolute pressure sensor can provide real-time feedback of the measured working static pressure signal to the internal microprocessor. The microprocessor uses this static pressure coordinate to automatically correct the micro differential pressure output signal, thus achieving static pressure compensation.

With the unique encapsulation process and the addition of an absolute pressure sensor, the static pressure performance of the EST4300M differential pressure transmitter has been greatly enhanced, thereby ensuring the measurement accuracy and high stability of the pressure transmitter.

2.5 Unique Diaphragm Processing Technology

Compared to the isolation diaphragm welding methods used by American Rosemount’s metal capacitive sensors, Japan’s Yokogawa’s single-crystal silicon sensors, and Europe’s ABB’s silicon differential pressure sensors, the EST4300M differential pressure sensor adopts a more advanced hygienic diaphragm welding method without isolation rings.

This hygienic diaphragm welding technique results in smooth welds with no gaps or dead angles. It allows for direct welding of various diaphragm materials, such as 316L stainless steel, Hastelloy C, tantalum, and Monel.

Click to check more details about Pressure Senor Material

The absence of gaps also permits direct gold plating and PTFE coating on the liquid contact surface. This design and special processing technology significantly extend and expand the range of fluid contact for the differential pressure transmitter and greatly enhance the service life of the transmitter in corrosive environments.

2.6 Unique High-Temperature Remote Transmission Design and Implementation

It is well known that in the application of pressure and differential pressure transmitters, high-temperature remote transmission diaphragm seals pose significant safety risks when the medium temperature exceeds 350°C.

Issues such as silicone oil vaporization, data distortion, or reduced lifespan are likely to occur, which requires the process medium to have a certain working static pressure to form a back pressure ensuring the normal operation of the diaphragm seal. This requirement has limited the application range of remote liquid level measurements by pressure and differential pressure transmitters.

However, the high-temperature remote transmission pressure transmitter designed for temperatures up to 600°C utilizes advanced measurement technology for high-temperature media, with the measurable temperature of the medium reaching up to 600°C.

Filled-Fluid Chamber of Super High Temperature
Filled-Fluid Chamber of Super High Temperature

As shown in Figure 8, the schematic diagram illustrates the structure of this ultra-high temperature remote transmission.

This structure is divided into two chambers:

  • One for ultra-high temperature filling fluid
  • The other for regular high-temperature filling fluid.

A diaphragm, welded between the two chambers, isolates them, and a heat dissipation rod is placed inside the ultra-high temperature chamber. The ultra-high temperature filling fluid, which comes into direct contact with the medium, can withstand temperatures up to 600°C.

However, due to its high viscosity, it is not suitable for filling into capillaries for pressure transmission. Therefore, the pressure is further transmitted through the isolation diaphragm to the chamber with the regular high-temperature filling fluid, ensuring limited pressure transfer and rapid response.

After heat dissipation, the temperature of the heat transferred to the regular high-temperature chamber is significantly reduced, guaranteeing the normal operation of that chamber.

This method expands the application range of high-temperature remote transmitters and improves the reliability and lifespan of ultra-high temperature remote transmitters.

2.7 Performance Indicators and Reliability

Through the technical introduction and analysis of the EST4300M series, we’ve briefly describes the realization process of the EST4300M monocrystalline silicon high-stability pressure and differential pressure transmitter project.

We enhance the overall performance, accuracy, and reliability of high-stability pressure and differential pressure transmitters from multiple aspects: selecting monocrystalline silicon principle chips, stress-free packaging of monocrystalline wafers, eliminating return error, reducing static pressure influence, expanding range ratios, special processing of wetted surfaces, and extending ultra-high temperature measurement capabilities.

Through the introduction and assimilation of various technologies, combined with innovative designs, the EST4300M series of high-stability pressure and differential pressure transmitters has reached the market leadership levels. Its main technical advantages are:

  • Accuracy level reaches 0.05, and it has obtained a manufacturing license for measuring instruments, achieving domestic advanced levels.
  • The micro-differential pressure transmitter adopts a unique dual overload protection diaphragm technology, achieving a high measurement accuracy of ±0.075%, with a maximum working static pressure of 16MPa and a minimum measurable differential pressure range from -50Pa to 50Pa, far exceeding domestic and international technological levels.
  • The highest working static pressure for the differential pressure transmitter can reach 40MPa, with a unidirectional overload pressure of up to 40MPa.
  • An absolute pressure sensor can be optionally encapsulated inside the differential pressure sensor for the measurement and display of on-site static pressure, as well as for static pressure compensation, resulting in excellent static pressure performance for the monocrystalline silicon pressure transmitter, with the typical specification static pressure error being an optimal ≤±0.05%/10MPa.
  • The integration of the internal absolute pressure sensor also ensures the successful development of the EST4300M multiparameter transmitter, which can be widely used in the field of gas flow measurement and fills the domestic gap in high-end multiparameter transmitters.
  • An internal high-sensitivity temperature sensor in the pressure and differential pressure sensors ensures excellent temperature performance, with an optimal ≤±0.04%/10K.
  • Low-pressure range gauge/absolute pressure transmitters of 6kPa and 40kPa can use unique non-pressure-loss overload protection diaphragm technology, with a unidirectional overpressure of up to 7MPa, significantly expanding the application scope of low-pressure sensors in special fields.
  • The typical long-term zero-point drift is ≤±0.1%/3 years, and it has passed 120,000 cycles of 90% full-scale extreme pressure fatigue testing, achieving a maintenance-free capacity of 10 years.
  • It realizes an extremely wide measurement range of 0-100Pa to 60MPa, with the highest 100:1 adjustable range ratio output.
  • The remote transmitter uses ultra-high temperature technology, suitable for over 400°C ultra-high temperature measurement situations, breaking through the bottleneck of remote product application and measurement.

Warp up:

Monocrystalline Silicon Pressure Transmitters are vast in their application and highly efficient, with a range of features that make them stand out in the field of pressure measurement.

  1. Precision: They possess incredibly high accuracy, reaching levels up to 0.075% of Span. This equates to maximum accuracy in the detection and transmission of pressure levels, making them ideal for tasks that require meticulous measurements.
  2. Stability: These transmitters are renowned for long-term stability, with a drift of less than 0.25% per annum. Hence, despite the passage of time, they continue to provide accurate and reliable performance.
  3. Wide Pressure Range: With the capability to measure pressure from very low to extremely high levels, typically in the range of 0-0.6 kPa to 0-6 MPa, they can be used in a vast range of industrial applications.
  4. Temperature Endurance: Monocrystalline Silicon Pressure Transmitters excel in various environmental conditions, proven to function efficiently in a temperature range of -40 to 85°C.
  5. Corrosion Resilience: Their monocrystalline silicon sensor resists corrosion, ensuring a long life span and reliable performance even in harsh, corrosive environments.
  6. Exceptional Output Resolution: They offer a resolution of output signal typically below 0.01% Span, allowing the accurate detection of even the smallest pressure changes.
  7. Diverse Output Signals: These pressure transmitters provide different output signals including digital (HART, PROFIBUS PA, Foundation Fieldbus) and analog (4-20mA), making them easily compatible with a range of existing systems.
  8. Overpressure Protection: they stand out for their high overload resistance of up to 400% of Upper Range Limit, providing safety and preventing the transmitters from damage in cases of pressure surges.

With these features, Monocrystalline Silicon Pressure Transmitters, including ET4300M, can be deployed across numerous industries from petrochemical, food and beverage to bio-medical and HVAC, providing top-notch performance and invaluable data.