Very low (~0.125 mV) shifts in offset voltage were achieved in silicon carbide (SiC) piezoresistive pressure sensors during thermal cycling between 25 and 500 °C for 500 hours. It resulted in reduced measurement error to ~ 0.36 % and ~ 0.9 % of the full-scale output at 25 and 500 °C, respectively. The reduction in the offset shift was the result of the advancement made in controlling the intermetallic diffusion and microstructural phase changes within the contact metallization. The low offset voltage results provide critical figures of merit needed for quantifying the measurement error and correction when the SiC pressure sensors are used. The results demonstrate more robust and reliable SiC pressure sensors operating with significantly reduced FSO errors at 500 °C.
This paper presents a review of recent results of silicon carbide (SiC) piezoresistive pressure transducers that have been
demonstrated to operate up to 600 °C. The results offer promise to extend pressure measurement to higher temperatures
beyond the capability of conventional semiconductor pressure transducers. The development also provides three
immediate significant technological benefits: i) wider frequency bandwidth (overcomes acoustic attenuation associated
with pitot tubes), ii) accuracy (improved stable output at high temperature), and iii) reduced packaging complexity (no
package cooling required). Operation at 600 °C provides immediate applications in military and commercial jet engines
in which critical static and dynamic pressure measurements are performed to improve engine performance (i.e., reduced
emission and combustor instabilities) and improved CFD code validation. The pressure sensor is packaged by a novel
MEMS direct chip attach (MEMS-DCA) technique that eliminates the need for wire bonding, thereby removing some
reliability issues encountered at high temperature. Generally, at 600 °C the full-scale output (FSO) of these transducers
drops by about 50-65 % of the room temperature values, which can be compensated for with external signal
High temperature sensors and electronics are necessary for a number of aerospace propulsion applications. The Sensors
and Electronics Branch at NASA Glenn Research Center (NASA GRC) has been involved in the design, fabrication,
and application of a range of sensors and electronics that have use in high temperature, harsh environment propulsion
environments. The emphasis is on developing advanced capabilities for measurement and control of aeropropulsion
systems as well as monitoring the safety of those systems using Micro/Nano technologies. Specific areas of work
include SiC based electronic devices and sensors; thin film thermocouples, strain gauges, and heat flux gauges;
chemical sensors; as well as integrated and multifunctional sensor systems. Each sensor type has its own technical
challenges related to integration and reliability in a given application. These activities have a common goal of
improving the awareness of the state of the propulsion system and moving towards the realization of intelligent engines.
This paper will give an overview of the broad range of sensor-related development activities on-going in the NASA
GRC Sensors and Electronics Branch as well as their current and potential use in propulsion systems.