A CMOS compatible thermal accelerometer without solid proof mass, based on porous silicon thermal isolation

A Si thermal accelerometer without solid proof mass has been developed and characterized. The device is CMOS compatible and consists of a polysilicon heater and two thermopiles, situated symmetrically on each side of a heater. A thick porous silicon (PS) layer assures thermal isolation from the Si substrate. The operating principle is based on the movement induced thermal convection variations between the heater and the hot thermopile contacts, which is caused by the movement of the hot air on top of the heater relative to the sensor die. The porous silicon thermal accelerometer (PSTA) was tested in a specially designed vibration system for different frequencies and accelerations. In each case, the response was compared to a commercial accelerometer. Appropriate read out electronics were fabricated in order to reduce the noise of the thermopiles and to amplify the signal. The dependence of the response on applied power and the surrounding environment was also studied.