Fabrication of a novel resonant pressure sensor based on SOI wafer

Based on the silicon-on-insulator (SOI) silicon, a novel resonant pressure sensor for atmosphere pressure detection is designed and fabricated. The resonator suspended by four beams at four pedestals on the diaphragm is encapsulated between two glass lids. The diaphragm shape changes with the change of ambient gas pressure; thereby the resonator's nature frequency also is changes. To prevent the undesired etching of resonator during the wet etching, a protective process using silicon nitride and silicon oxide is adopted. Experiments show that after wet etching 10 hours in tetramethyl ammonium hydroxide (TMAH) solution, the resonator is successfully released. This protection technology shows a high practical value especially for the release of a movable microstructure by wet silicon etchants. Initial performance test results of the device yield a natural frequency of 9.932 KHz at atmospheric pressure and the Q-factor of 34 rising to over 7293 in high vacuum(<10 Pa). The relative pressure sensitivity of the sensor is measured to be 5.88% for a 10μm diaphragm.