A novel resonant pressure sensor with boron diffused silicon resonator

To improve the performance of the micro-machined resonant pressure sensor and simplify its fabrication process, a novel structure is proposed in which the boron diffused silicon (up to 15um thickness) and the bulk silicon are used as the resonant beam and pressure membrane respectively. The structural parameters were optimized through FEM to achieve the better sensitivity, and the relationships between the structural parameters and the sensitivity were established. Moreover, the fabrication processes were discussed to increase the product rate and the pressure sensor with the optimal structural parameters was fabricated by the bulk silicon MEMS processes. In order to enhance the signal of the sensor and make the closed-looped control of the sensor easily, electromagnetic excitation and detection was applied. However there is so high noise coming from the distributing capacitances between the diffused silicon layer and electrodes that reduce the signal to noise ratio of the sensor. Through the analysis of the micro-structure of the sensor, the asymmetrical excitation circuit was used to reduce the noise and then the detection circuit was designed for this sensor. The resonator of the sensor was packaged in the low vacuum condition so that the high quality factor (Q) with about 10000 can be achieved. Experimental tests were carried out for the sensor over the range of -80kPa to 100kPa, the results show that the sensitivity of the sensor is about 20kHz/100kPa, the sensitivity is 0.01%F.S. and the nonlinearity is about 1.8%.