High Temperature Semiconductor Pressure Sensor for Automobiles 860473

A semiconductor pressure sensor for automobiles which could be used up to 300°C was investigated. Conventional diffused type silicon semiconductor pressure sensors (1)* have a problem that they cannot be operated above the ambient temperature of 125 °C because of the appearance of thermal output voltage caused by large leakage current of pn junction. This sensor investigated in the present work has a new type of polycrystalline silicon on insulator (P-SOI) structure. A highly oriented polycrystalline silicon semiconductor thin film is used as a piezoresistive strain gage, which is electrically isolated from a silicon (110) diaphragm by a crystalline insulator thin film of CaF₂ deposited on the surface of a silicon substrate. This type of structure makes it possible for the sensor to operate stably up to 300°C having a value of gage factor as large as that of a single crystalline silicon, differently from the diffused type silicon pressure sensor.