Secondary sensitivities and stability of ultrasensitive silicon pressure sensors

Experimental results on the characterization of secondary effects in boron-doped silicon membranes are presented. Capacitive pressure sensors were fabricated with and without a variety of dielectrics on the diaphragms and were tested over pressure and temperature. The temperature coefficient of sensitivity (TCS) and zero pressure temperature coefficient of offset (TCO) were found to be as much as an order of magnitude higher than previously reported values; this is due to the strong dependence of pressure sensitivity on internal stress and the large mismatches in thermal expansion coefficients between silicon and dielectrics. Creep and fatigue affected the offset by <0.2% full scale, and the change in pressure sensitivity was insignificant; hysteresis observed on all devices was also <0.2% full scale. The results indicate that it may be possible to extend the pressure range by an order of magnitude, which would increase the resolution from 10 to 16 b.<>