Design of a novel micromachined capacitive engine oil pressure sensor

A novel capacitive pressure sensor based on surface micromachining technology is designed and simulated. The sense element is a parallel plate capacitor with one electrode fixed to the substrate, and the other suspended on a polysilicon diaphragm. In the presence of an oil pressure, the silicon diaphragm is deflected downward, which also displaces the suspended electrode downward. The sensor structure is in such away that due to the suspended electrode displacement, the effective area between two plates is changed, and therefore the capacitance is changed. It must be mentioned that the effective area as well as the gap between the capacitor plates vary with the applied pressure. However, the nonlinearity due to gap variation is about 9.46%. The dimensions of the sense element are 1.5 mm/spl times/1.5 mm, which consists of 25 cells: in a 5 columns and 5 rows manner. The total active area is 1.1 mm/spl times/1.1 mm. The capacitance varies between the 11.455-24.72pF, when the pressure varies in the range of 4-60psi. The minimum sensitivity of this sensor is about 0.135 pF/psi. The purposed fabrication process steps consist of only 4 masks. Also, the deposition of the different layers is done with a good self-alignment.