Design and manufacturing of a pressure sensor with capacitive readout, CMOS compatible

Abstract

A capacitive differential pressure sensor which is CMOS compatible is designed and realized. The device consists of a variable capacitor made by silicon bulk and surface micromachining. The upper electrode is a diaphragm in a sandwich of polyimide and metal. The bottom electrode is placed on a silicon substrate and is formed by Cr/Au deposition. The sensor has a 5 /spl mu/m air gap as a dielectric. It is made from monocrystalline silicon by means of micromachining methods. It has an area of 800/spl times/800 /spl mu/m and a thickness of about 7 /spl mu/m. The sensor can be integrated on one chip with a pre-amplifier circuit and is designed and simulated using the MEMCAD 4.8 software. In MEMCAD, we designed the 2D and 3D models, according with the technological manufacturing processes. We simulated the capacitance of the sensor depending on the applied relative pressure. A sensitivity /spl Delta/C/C of about 60% is achieved for a differential pressure of 1 atm. The results of the analysis show that the sensor can be used at relative pressures between 0 and 1.6 atm. The scale of pressures can be enlarged easily by increasing the air gap or by changing the thickness of the polyimide diaphragm. The manufacturing of the device is briefly described, but the focus lies primarily on the design and simulation of the sensor.