Silicon Microsensors for Severe Environment Using SOI Technology

Abstract

Si-On-Insulator (SOI) structure is an attractive material not only for VLSI but also for sensor applications. In SOI sensors, the top Si layers can be used as a piezoresistor or a hall-sensor, and SiO₂ is used as perfect electric isolation at high temperatures. Epitaxially stacked SOI structures such as Si/Al₂O₃/Si structures can be used as a sensor material, which is formed by epitaxial growth of Al₂O₃ on Si substrates and epitaxial growth of Si on Al₂O₃/Si. By this epitaxial method, the thicknesses of Si and insulator layers are easily controlled and optimized for sensor applications. Multi-SOI structures like a Si/insulator/Si/insulator/Si structure can be formed, which are also interesting structures for micromachining. In this paper, pressure sensors, an accelerometer, and a magnetic sensor using SOI structure for high temperature application are presented. The advantages of SOI structure in sensor applications are also demonstrated showing examples of actual sensor devices and their characteristics.