The recent increase in transportation costs and the push for cleaner emissions demands advancements in aerospace technology. The current instrumentation used in aerospace applications is costly, and indirect measurement approaches are often employed due to the inability to locate sensors in harsh environments. Health monitoring technologies for the development of a distributed sensor network can be utilized to improve engine efficiencies and reduce emissions while maintaining safety. This paper reviews the recent advancements in silicon carbide (SiC) process technologies and demonstrations of SiC sensors and electronic circuits in hostile environments, which supports the use of SiC technology for health and performance monitoring of aerospace systems. Further development of this technology can ultimately improve the performance, reliability, and emissions of aerospace systems. However, challenges still remain for the realization of a distributed sensor network for harsh environment applications such as aerospace.

Harsh Environment Silicon Carbide Sensors for Health and Performance Monitoring of Aerospace Systems: A Review

Extreme temperature semiconductor integrated circuits (ICs) are being developed for use in the hot sections of aircraft engines and other harsh-environment applications well above the 300 °C effective limit of silicon-on-insulator IC technology. This paper reviews progress by the NASA Glenn Research Center and Case Western Reserve University (CWRU) in the development of extreme temperature (up to 500 °C) integrated circuit technology based on epitaxial 6H-SiC junction field effect transistors (JFETs). Simple analog amplifier and digital logic gate ICs fabricated and packaged by NASA have now demonstrated thousands of hours of continuous 500 °C operation in oxidizing air atmosphere with minimal changes in relevant electrical parameters. Design, modeling, and characterization of transistors and circuits at temperatures from 24 °C to 500 °C are also described. CWRU designs for improved extreme temperature SiC JFET differential amplifier circuits are demonstrated. Areas for further technology maturation, needed prior to beneficial system insertion, are discussed. Optical micrograph of a 500 °C durable 6H-SiC JFET differential amplifier IC chip fabricated at NASA prior to packaging. Digitized waveforms measured during the 1st (solid black) and 6519th (dashed grey) hour of 500 °C operational testing show no change in output characteristics.

Extreme temperature 6H-SiC JFET integrated circuit technology

This paper reports a research prototype of a low-cost, miniature, mass-producible sensor for measurement of high-pressure at operating temperatures of 300–600 °C, e.g., in-cylinder engine pressure monitoring applications. This all-silicon carbide (SiC) capacitive sensor, i.e., a SiC diaphragm on a SiC substrate, takes advantage of the excellent harsh-environment material properties of SiC and is fabricated by surface micromachining. The sensor is packaged in a high-temperature ceramic package and characterized under static pressures of up to ∼5 MPa (700 psi) and temperatures of up to 574 °C in a custom chamber. An instrumentation amplifier integrated circuit is used to convert capacitance into voltage for measurements up to 300 °C; beyond 300 °C, the capacitance is measured directly from an array of identical sensor elements using a LCZ meter. After high-temperature soaking and several tens of temperature/pressure cycles, packaged sensors continue to show stable operation. For monitoring the dynamic cylinder pressure in the combustion chamber, the sensor is packaged in a custom probe and inserted into the cylinder head of a research internal combustion engine. The sensor efficacy is verified against the reference probe used for monitoring pressure in the research engine.

A silicon carbide capacitive pressure sensor for in-cylinder pressure measurement

A monolithic bipolar operational amplifier (opamp) fabricated in 4H-SiC technology is presented. The opamp has been used in an inverting negative feedback amplifier configuration. Wide temperature ...

/pdf/a-monolithic-500-degrees-c-operational-amplifier-in-4h-sic-2euwgixujd.pdf

A Monolithic, 500 degrees C Operational Amplifier in 4H-SiC Bipolar Technology

This letter reports fabrication and testing of integrated circuits (ICs) with two levels of interconnect that consistently achieve greater than 1000 h of stable electrical operation at 500 °C in air ambient. These ICs are based on 4H-SiC junction field-effect transistor technology that integrates hafnium ohmic contacts with TaSi2 interconnects and SiO2 and Si3N4 dielectric layers over $\sim 1$ - $\mu \text{m}$ scale vertical topology. Following initial burn-in, important circuit parameters remain stable within 15% for more than 1000 h of 500 °C operational testing. These results advance the technology foundation for realizing long-term durable 500 °C ICs with increased functional capability for sensing and control combustion engine, planetary, deep-well drilling, and other harsh-environment applications.

Prolonged 500 °C Demonstration of 4H-SiC JFET ICs With Two-Level Interconnect

A family of fully-integrated differential amplifiers was designed and fabricated in 6H-SiC, n-channel JFET integrated-circuit technology. A single-stage amplifier with resistor loads has gain-bandwidth of ∼2.8 MHz, and differential-mode gain that varies by less than 1 dB from 25–600°C. A two-stage amplifier with current-source loads and common-mode feedback in 1st-stage, and resistor loads in 2nd-stage has gain-bandwidth of 1.4 MHz, and differential-mode gain of 69 dB at 576°C, with just 3.6 dB gain-variation from 25–576°C.

Fully-monolithic, 600°C differential amplifiers in 6H-SiC JFET IC technology

Silicon Carbide JFET Integrated Circuit Technology for High-Temperature Sensors

This paper reports the characterization and modeling of differential amplifiers constructed using integrated 6H-Silicon Carbide (SiC) depletion-mode n-channel JFETs operating at temperatures up to 450degC, along with off-chip passive components. The 3-stage amplifier has a differential voltage gain of -50 dB and a unity-gain frequency of -200 kHz at 450degC, limited by test parasiticus. With further improvements in the related interconnect technology, the JFET technology reported here would enable analog sensor interface circuits operating at temperatures as high as 600degC for use in data acquisition from high-impedance microsensors.

Characterization of Silicon Carbide Differential Amplifiers at High Temperature

This paper introduces a high-temperature fully monolithic high gain-bandwidth 6H-SiC transimpedance amplifier for capacitive sensor interfacing. The amplifier achieves a gain of 235 kΩ and a bandwidth of 0.61 MHz at room temperature. Results from the proof-of-concept measurements performed with variable capacitors demonstrate the functionality of differential capacitive sensing across a wide temperature range, up to 450 °C. The amplifier also exhibits a stable gain with respect to power supply variations. At elevated temperatures, the amplifier exhibits increasing gain with decreasing bandwidth, as expected. At 450 °C, the gain and bandwidth are 774 kΩ and 0.17 MHz, respectively. This is the first report that demonstrates the capacitive sensing capability of a SiC transimpedance amplifier, and represents a critical step toward the goal of integrating a sensing element with its interface circuit in a single monolithic device for operation at extreme temperatures.

A Fully Monolithic 6H-SiC JFET-Based Transimpedance Amplifier for High-Temperature Capacitive Sensing

This paper presents silicon carbide sensor interface circuits and techniques for MEMSbased sensors operating in harsh environments. More specifically, differential amplifiers were constructed using integrated, depletion-mode, n-channel, 6H-SiC JFETs and off-chip passive components. A three-stage voltage amplifier has a differential voltage gain of ~50 dB and a gainbandwidth of ~200 kHz at 450oC, as limited by test parasitics. Such an amplifier could be used to amplify the signals produced by a piezoresistive Wheatstone bridge sensor, for example. Design considerations for 6H-SiC JFET transimpedance amplifiers appropriate for capacitance sensing and for frequency readout from a micromechanical resonator are also presented.

Amita C. Patil

Papers

Fully-monolithic, 600°C differential amplifiers in 6H-SiC JFET IC technology

Silicon Carbide JFET Integrated Circuit Technology for High-Temperature Sensors

Characterization of Silicon Carbide Differential Amplifiers at High Temperature

A Fully Monolithic 6H-SiC JFET-Based Transimpedance Amplifier for High-Temperature Capacitive Sensing

Silicon Carbide Differential Amplifiers for High-Temperature Sensing