Combined Pressure and Temperature Sensor for Hot Harsh Environments
Sensors
Combined Pressure and Temperature Sensor for Hot Harsh Environments (LEW-TOPS-156)
Enables Real-time Pressure Measurements, Corrected for Temperature Effects
Overview
Accurate and reliable pressure data is fundamental for monitoring engine health for the safe and efficient operation of high performance engines. Innovators at NASA's Glenn Research Center have developed a single pressure and temperature sensor system that provides in-situ data in harsh operating environments like combustion. Although current SiC pressure sensors can operate at 800°C inside combustion chambers, the output response is sensitive to temperature changes and requires temperature compensation schemes that rely on a second separate temperature sensor to get a true measure of pressure. The new NASA pressure/temperature (P/T) sensor chip enables real-time translation of pressure and uses only a single tap for two engine measurements. This important sensor system and packaging can provide more accurate data for combustion simulations and to monitor engine health to improve performance and extend the service lifetime of commercial and military aircraft, automotive engines, and power plants.
The Technology
A team of NASA Glenn researchers has developed a portfolio of SiC-enabled electronics and sensors. SiC's ability to function in harsh environments—high-temperature, high-power, high radiation—enables much better performance in many combustion applications. Building on their successful and miniaturized SiC pressure sensor package, the team added a resistance temperature detector (RTD) to the same chip. Having both sensors on a single SiC substrate facilitates the simultaneous measurement of pressure and temperature. The integrated P/T sensors are fabricated with a prescribed sequence of photo lithography and reactive ion etching fabrication steps to create patterns and structures and deposit RTD elements and other layers. Designed to monitor jet engine health, this P/T sensor can be placed directly on the engine, close to the combustion source, for highly accurate, real-time data analysis. As shown in the figures below, the sensor has been tested and characterized for long-term high-temperature stability and response. The data prove that the sensor’s performance is repeatable, with negligible hysteresis. Compared to conventional silicon piezoresistive sensors, this new sensor is more viable in high-temperature environments.
Benefits
- Direct measurement eliminates the need for lookup tables or temperature compensation techniques.
- Simultaneous on-chip measurement of pressure and temperature improves accurate correlation of results.
- Real-time translation of pressure as function of temperature has been demonstrated to 800°C.
- Use of a single sensorreduces production and assembly costs, and eases path toward IC integration.
- Small footprint allows use of the same pressure tap for both sensors, as opposed to separate taps.
Applications
- Nuclear power: monitors pressure at high temperature
- Aircraft: monitors engine health to control safety and optimize combustion efficiency
- Aerospace: enables feedback control to watch for thermo-acoustic instabilities
- Engine Simulations (general): provides data to validate computational fluid dynamic codes used in engine model prediction
Similar Results
Advanced Gas Sensors and High-Temperature Pressure Sensors
In conjunction with academia and industry, NASA's Glenn Research Center has developed a range of microelectromechanical systems (MEMS)-based and SiC-based microsensor technologies that are well-suited for many applications. The suite of technologies includes (1) hydrogen and leak detection sensors; (2) emissions sensor arrays; (3) SiC high- temperature pressure sensors; and (4) high-temperature contact pads for wire bond connections.
Currently used to protect astronauts on the International Space Station, the hydrogen and leak detection sensors have many Earth-based applications as well. They can function as a single-sensor unit or as part of a complete smart sensor system that includes multiple sensors, signal conditioning, power, and telemetry. The system can comprise sensors for hydrocarbons, oxygen, temperature, and pressure. The emissions sensor array features a gas-sensing structure that detects various combustion emission species (carbon monoxide, carbon dioxide, oxygen, hydrocarbons, and nitrogen oxides) over a wide range of concentrations. In addition, the emissions sensor array remains highly sensitive and stable while providing gas detection at temperatures ranging from 450 to 600°C, as does the SiC high-temperature pressure sensor. These new sensors provide a combination of responsiveness and durability that offers great value for a wide range of applications and industries.
Advanced Hydrogen and Hydrocarbon Gas Sensors
In conjunction with academia and industry, NASA's Glenn Research Center has developed a range of microelectromechanical systems (MEMS)-based and Silicon Carbide (SiC)-based microsensor technologies that are well-suited for many applications. The suite of technologies includes hydrogen and hydrocarbon leak detection sensors; emissions sensor arrays; and high-temperature contact pads for wire bond connections.
Currently used to protect astronauts on the International Space Station, the hydrogen and leak detection sensors have many Earth-based applications as well. They can function as a single-sensor unit or as part of a complete smart sensor system that includes multiple sensors, signal conditioning, power, and telemetry. The system can comprise sensors for hydrogen, hydrocarbons, oxygen, temperature, and pressure. The emissions sensor array features a gas-sensing structure that detects various combustion emission species (carbon monoxide, carbon dioxide, oxygen, hydrocarbons, and nitrogen oxides) over a wide range of concentrations. In addition, the emissions sensor array remains highly sensitive and stable while providing gas detection at temperatures ranging from 450 to 600°C. These new sensors provide a combination of responsiveness and durability that offers great value for a wide range of applications and industries.
Capacitive Pressure Sensor System and Packaging
Pressure sensors play an important role in engine maintenance and monitoring systems by diagnosing problems before they happen. To capture the most accurate data, however, these sensors must be placed directly on an engine. In order to withstand extreme temperature and vibration, traditional pressure sensor technologies are bulky and complex, lacking the on-board control of microsystem technologies. Glenn's new capacitive pressure sensor system and packaging is the first of its kind to achieve high-temperature capability while maintaining miniaturization.
This novel system consists of a Clapp-type oscillator that is fabricated on a high temperature alumina substrate. It comprises a silicon carbide (SiC) nitride pressure sensor, a metal-semiconductor field-effect transistor, and one or more chip resistors, wire-wound inductors, and SiC metal-insulator-metal (MIM) capacitors. The pressure sensor is located in the tank circuit of the oscillator so that a variation in pressure causes a change in capacitance, thus altering the resonant frequency of the sensing system. The chip resistors, inductors, and MIM capacitors have been characterized at temperature and operational frequency, and exhibit less than 5% variance in electrical performance. The system, which can be installed with a borescope plug adaptor in an on-wing operating engine, has been extensively tested and proven to operate reliably under extreme conditions. Its compact size, wireless capability, and ability to provide real-time in-situ data acquisition make this technology a game-changer in next-generation maintenance and monitoring systems.
N Channel JFET Based Digital Logic Gate Structure
In 2010, NASA Glenn Research Center secured a patent for an innovative approach to SiC component production (described in U.S. Patent 7,688,117) that enabled the development of logic gates using only epitaxial resistors and N channel JFETs. This allowed for the production of pulse and edge triggered latches through the use of inverting and combinatorial logic. This innovation was improved upon in 2013 and a second patent was issued. In the modified version of this technology, epitaxial resistors are used as loads and level shifters to create useable logic blocks with N channel JFETs. The resistive level shifter can be designed at the output of the basic gate structure, or at the input, which means that the device can be considered a lone follower transistor with its source node as the output of the gate. The basic logic gate can be configured as a driver for oscillator circuits, allowing for time bases and simple digitizers for resistive or reactive sensors.
By removing the level shifter from the output of the gate structure, this new adaptation boasts a simplified source-coupled gate topography, which makes more real estate available for other circuit functions. Furthermore, by replacing multiple paths to the ground (level shifter strings) with a single path to the ground, power is saved and the device operates more efficiently.
Robust High Temperature SiC Op Amps – Practical Fabrication
The technology is part of a new generation of NASA Glenn SiC integrated circuits with unprecedented durability in the field of high-temperature electronics. For robust operational amplifiers based on SiC Junction Field Effect Transistors (JFETs), this novel compensation method mitigates issues with threshold voltage variations that are an effect of die location on the wafer. Modern high-temperature op amps on the market fall short due to temperature limits (only 225°C for silicon-based devices). Previously, researchers noted that multiple op amps on a single SiC wafer had different amplification properties due to different threshold voltages that varied spatially as much as 18% depending on the circuit's distance from the SiC wafer center. While 18% is okay for some applications, other important system applications demand better precision. By applying this technology to the amplifier circuit design process, the op amp will provide the same signal gain no matter its position on the wafer. The compensation approach enables practical signal conditioning that works from 25°C up to 500°C.
