Capacitive absolute pressure sensors with hybrid structure

A capacitive pressure sensor with a reference pressure chamber for absolute pressure measurement was fabricated in a hybrid form. This paper describes the summary, fabrication process and characteristics. The fabricated sensor chip has dimensions of 4.5 × 3.4 × 0.9 mm³, a diaphragm area of 1.7 × 1.7 mm², an electrode area of 1.5 × 1.5 mm², a diaphragm thickness of 65 μm and a gap of 1.5 μm between the electrodes. The principal characteristics are as follows: (1) since the pressure sensor chip and the capacitance detection IC chip are fabricated separately, the characteristics of both can easily be optimized and the fabrication is rather simple; (2) since the interior of the reference pressure chamber is hermetically sealed, the effect of humidity can be minimized; (3) since a thin p⁺ silicon cap is sealed using anodic bonding on the hole in the glass of the reference pressure chamber side, the terminal can be removed from the electrode on the glass side with a minimum parasitic capacitance to the silicon; and (4) the temperature characteristics of the pressure sensor can be minimized by changing the power supply voltage of the capacitance detection IC. The output sensitivity of the hybrid pressure sensor was −9.22 kHz/kgf/cm², the nonlinearity was −5.3 percent F.S., the thermal zero shift was −3.1 percent F.S. (5 to 45d̀C) and the thermal sensitivity shift was 3.8 percent F.S. (5 to 45d̀C).