Papers by Author: Srihari Rajgopal

Abstract: We report two improvements of our all-silicon carbide (SiC) micromachined capacitive diaphragm-based pressure sensors: Ti/TaSi2/Pt contact metallization to enhance temperature cycling durability and a 0.5 μm-thin sensing gap to further improve sensor sensitivity. Three sensors with 0.5 μm and 1.5 μm sensing gaps were packaged individually in high temperature ceramic packages and characterized to designed (static) pressures of 2.1 MPa (300 psi), 3.4 MPa (500psi) and 6.9 MPa (1000 psi) up to 550°C. For the 3.4 MPa range sensor (0.5 μm gap, 70 μm diaphragm radius), a sensitivity of 0.06 fF/Pa and a nonlinearity of 2.0% was obtained at 550°C in contact mode operation. In comparison, the 2.1 MPa range sensor (1.5 μm gap, 95 μm diaphragm radius) demonstrated a sensitivity of 0.07 fF/Pa and a nonlinearity of 4.6% at 550°C in contact mode operation. The 6.9 MPa range sensor (1.5 μm gap, 70 μm diaphragm radius) demonstrated a sensitivity of 0.03 fF/Pa and a nonlinearity of 4.0% at 500°C, also in contact mode.

Abstract: A polycrystalline silicon carbide (poly-SiC) surface-micromachined capacitive accelerometer is designed, fabricated and tested. Leveraging the superior thermo-mechanical and chemical resistance properties of SiC, the device is a first step toward cost-effective implementation of a new class of extreme environment accelerometers, for example for high temperature vibration and shock measurements, even thought this initial work is at room temperature. The accelerometer described herein is designed for a range of 5000 g and a bandwidth of 18 kHz, specifications consistent with commercially available piezoelectric devices for high-level mechanical impact measurements. Test results demonstrate the sensor achieving a resolution of 350 mg/√Hz at 1kHz with a sensitivity of 12 μV/g and a bandwidth of 10 kHz at room temperature.