HIGH-TEMPERATURE PRESSURE SENSOR USING DOUBLE SOI STRUCTURES WITH 2 AL2O3 FILMS

A high temperature pressure sensor using double silicon-on-insulator (SOI) structures stacked by double heteroepitaxial growth, Si//gamma-Al2O3//Si//gamma-Al2O3//Si-substrate stacked structures, has been developed. This sensor consists of a thin rectangular diaphragm and a single-element four-terminal piezoresistor produced by micromachining technology with a standard IC process. The diaphragm size is 360 x 1080 mum and 5 mum in thickness. The diaphragm thickness was precisely controlled by the Al2O3 films of the first SOI layer. A second Al2O3 film on the first SOI layer was used as a dielectrically isolated single-element four-terminal piezoresistor that was placed at the center of the diaphragm. The pressure sensitivity was 6.5 mV/V kgf/cm2 for 1 kgf/cm2 full scale pressure range. The thermal sensitivity shift was less than 2.7% in the temperature range from 20 to 300-degrees-C. These values are acceptable for many applications, and indicate that the sensor can be operated stably up to temperatures as high as 300-degrees-C.