Alexander A. Ned

Operation of α(6H)-SiC pressure sensor at 500°C

Abstract 6H-SiC piezoresistive pressure sensors have been batch fabricated and tested up to 500 °C in atmosphere. At 1000 psi, the full-scale outputs of a typical sensor are 40.66 and 20.03 mV at 23 and 500 °C, respectively. The full-scale linearity of − 0.17% and hysteresis of 0.17% compare favorably with current silicon technology. No significant degradation in the performance characteristics is observed when the sensors are operated for 10 h at 500 °C. The temperature coefficient of gage factor (TCGF) exhibits negative values of − 0.19 and − 0.11%/ °C at 100 and 500 °C, respectively. Excellent control of the diaphragm thickness is the result of a stabilized electrochemical etching process. The micromachining of bulk 6H-SiC eliminates the thermal-mismatch problem inherent in micromachined heterostructures. This work demonstrates batch manufacture and operation of 6H-SiC pressure sensors for temperatures beyond those of conventional silicon technology.

Characterization of highly doped n- and p-type 6H-SiC piezoresistors

Highly doped (/spl sim/2/spl times/10/sup 19/ cm/sup -3/) n- and p-type 6H-SiC strain sensing mesa resistors configured in Wheatstone bridge integrated beam transducers were investigated to characterize the piezoresistive and electrical properties. Longitudinal and transverse gauge factors, temperature dependence of resistance, gauge factor (GF), and bridge output voltage were evaluated. For the n-type net doping level of 2/spl times/10/sup 19/ cm/sup -3/ the bridge gauge factor was found to be 15 at room temperature and 8 at 250/spl deg/C. For this doping level, a TCR of -0.24%//spl deg/C and -0.74%//spl deg/C at 100/spl deg/C was obtained for the n- and p-type, respectively. At 250/spl deg/C, the TCR was -0.14%//spl deg/C and -0.34%//spl deg/C, respectively. In both types, for the given doping level, impurity scattering is implied to be the dominant scattering mechanism. The results from this investigation further strengthen the viability of 6H-SiC as a piezoresistive pressure sensor for high-temperature applications.

Operation of /spl alpha/(6H)-SiC pressure sensor at 500/spl deg/C

6H-SiC piezoresistive pressure sensors operational at 500/spl deg/C, were batch fabricated and tested. The full scale output (FSO at 1000 psi) was 40.66 mV and 20.03 mV at 23/spl deg/C and 500/spl deg/C, respectively, The full-scale linearity of -0.17% and hysteresis of 0.17% compared favorably with current technology. No serious degradation was observed when operated for ten hours at 500/spl deg/C, The temperature coefficient of resistance (TCR), was -0.25%//spl deg/C and -0.05%//spl deg/C at 100/spl deg/C and 500/spl deg/C, respectively, The temperature coefficient of gauge factor (TCGF) exhibited negative values of 0.19%//spl deg/C and -0.11%/spl deg/C at 100/spl deg/C and 500/spl deg/C, respectively, This work demonstrated batch manufacturing and operation of pressure sensors for temperatures beyond silicon technology.

Electrical characterization of annealed Ti/TiN/Pt contacts on N-type 6H-SiC epilayer

We report results of the electrical characteristics of in vacuo deposited Ti/TiN/Pt contact metallization on n-type 6H-SiC epilayer as function of impurity concentration in the range of 3.3/spl times/10/sup 17/ cm/sup -3/ to 1.9/spl times/10/sup 19/ cm/sup -3/. The as-deposited contacts are rectifying, except for the highly doped sample. Only the lesser doped remains rectifying after samples are annealed at 1000/spl deg/C between 0.5 and 1 min in argon. Bulk contact resistance ranging from factors of 10/sup -5/ to 10/sup -4/ /spl Omega/-cm/sup 2/ and Schottky barrier height in the range of 0.54-0.84 eV are obtained. Adhesion problems associated with metal deposition on pre-processed titanium is not observed, leading to excellent mechanical stability. Auger electron spectroscopy (AES) reveals the out diffusion of Ti-Si and agglomeration of Ti-C species at the epilayer surface. The contact resistance remains appreciably stable after treatment in air at 650/spl deg/C for 65 h. The drop in SBH and the resulting stable contact resistance is proposed to be associated with the thermal activation of TiC diffusion barrier layer on the 6H-SiC epilayer during annealing.

Characterization of Ti/TiN/Pt contacts on n-type 6H-SiC epilayer at 650/spl deg/C

We report results of electrical characteristics of Ti/TiN/Pt contact metallization on n-type 6H-SiC epilayer as a function of impurity concentration in the range of 3.3/spl times/10/sup 17/ cm/sup -3/to 1.9/spl times/10/sup 19/ cm/sup -3/. The as-deposited contacts were rectifying, except for the highly doped sample. Only the lesser doped remained rectifying after samples were annealed at 1000/spl deg/C between .5 to 1 minute in argon. Bulk contact resistance ranging from factors of 10/sup -5/ to 10/sup -4/ /spl Omega/-cm/sup 2/ and Schottky barrier height in the range of 0.74 to 1.07 eV were obtained. The contact resistance remained appreciably stable after heat treatment at 650/spl deg/C in air for sixty-five hours. Adhesion problems associated with metal deposition on pre-processed titanium layer was not observed, indicating excellent mechanical stability. Auger electron spectroscopy (AES) revealed the out-diffusion of titanium-silicon species and probable formation of titanium carbide as the new interface layer with the 6H-SiC epilayer.

High Accuracy, High Temperature Pressure Probes for Aerodynamic Testing

This paper presents a ruggedized high accuracy, extremely miniature pressure transducer suitable for numerous applications where size, accuracy and environmental conditions are of critical importance. High transducer accuracy was achieved by using a highly sensitive piezoresistive pressure sensor in conjunction with high resolution digital electronics for sensor output amplification and correction. The paper presents various ways that this transducer can be packaged to make it suitable for flow measurements in both wind tunnels and real world application such as gas turbine engines testing. These methods include miniature differential transducers, miniature 5-hole probes, and pressure rakes. Data from these various configurations are presented showing excellent response over temperature and flow regimes. I. Introduction he technology developed and discussed in this paper was originally developed for Wind Tunnel Applications, where typical flight performance studies using hypervelocity wind tunnel test articles involve the measurement of very low pressures at elevated temperatures. These initial installations were used for static and quasi-static measurements only. After the success 8 of these initial measurements it was decided to extend the use of the sensing and amplifier technologies into the more demanding regime of flow measurements. There are many areas where accurate flow measurement is critical: wind tunnel, ground based engine testing, and flight test can all benefit from high accuracy miniature flow measurement techniques. Many of these applications require both high temperature and high accuracy in order to be useful to the design engineer. We present in this paper a miniature pressure transducer developed specifically to address these instrumentation challenges. Test results are presented and potential benefits, in terms of measurement accuracy and cost savings, are discussed.