Manfred Poppinger

Silicon pressure sensor with frequency output

Abstract The silicon pressure sensor with frequency output presented in this work is based on CMOS ring oscillators designed with the aid of semicustom standard cells and fabricated using a standard IC process. The ring oscillators are integrated on a square silicon diaphragm with center boss and make use of the piezoresistive effect in the MOS field-effect transistors of the circuit. For this structure the pressure sensitivity and its cross sensitivity with supply voltage are presented. On the subject of signal conditioning, the frequency ratio (Φ) of two oscillators is studied with respect to the compensation of the zero output cross sensitivities. Furthermore, the advanced sensor signal Φ - 1/Φ is introduced which offers a number of crucial benefits compared to the simple frequency ratio. Finally, the pressure sensitivity of the sensor is simulated coupling the mechanical stress in the diaphragm calculated by finite element analysis with the electrical simulation of the ring oscillator frequency performed by SPICE.