Gerhard Kroetz

Silicon compatible materials for harsh environment sensors

The wide bandgap semiconductors silicon carbide and diamond and the material system Silicon On Insulator (SOI) are compared regarding their suitability as silicon compatible materials to extend the application fields of micromachined sensors to harsh environment conditions especially to high temperatures. The harsh environment conditions are specified by analyzing the demands of automotive and aerospace applications. The physical properties of the material systems are discussed and their technological stage of development is evaluated, especially with respect to the compatibility to standard silicon processes. Furthermore, the commercial availability of the different materials in the form of substrates is considered and a forecast of future developments is attempted. As an example of a harsh environment sensor, a combustion pressure sensor is presented and characterized.

A high temperature pressure sensor prepared by selective deposition of cubic silicon carbide on SOI substrates

Abstract A high temperature pressure sensor with 3C–SiC piezoresistors as sensing elements was prepared. For the first time the sensing elements were structured by selective deposition of 3C–SiC on a patterned Si/SiO 2 surface. To ensure dielectric isolation SOI substrates were used. The effectiveness of the selective deposition process is demonstrated by REM-photographs. Characterisation of the sensing elements shows the good crystal quality of the sensing elements as indicated by the gauge factor of −18 at room temperature which decreases to −10 at 200°C. As a benefit of the deep dry etching process the related sensitivity is 3.5 mV/V bar at room temperature decreasing to 2.1 mV/V bar at 200°C for a 100-μm thick circular center boss diaphragm.

Selective growth of high-quality 3C-SiC using a SiO2 sacrificial-layer technique

Abstract The selectivity of a LPCVD growth process for cubic silicon carbide with respect to the underlying substrate was investigated, and a highly selective growth process on structured Si/SiO 2 substrates was found at temperatures above 1150°C. The temperature dependence of this effect was systematically studied. In the temperature range between 1075–1150°C, polycrystalline SiC was grown on SiO 2 surfaces. At temperatures above 1150°C, no growth on SiO 2 occurred, whereas high-quality 3C-SiC layers were deposited onto the opened SiO 2 mask areas. This was shown by REM pictures and by removal of the SiO 2 layers in wet HF-etchant after the deposition. The selectively deposited 3C-SiC-structures were grown at a rate of 4.4 μm/h.