Heated silicon semiconductor sensor for diverse gases including hydrocarbons, has monocrystalline, floating silicon bridge carrying gas sensitive element

摘要

A monocrystalline silicon bridge (3) carries the gas sensitive element (8). The bridge is supported, whilst floating freely in the region of the gas sensitive element. An Independent claim is included for the method of manufacturing the corresponding sensor. Parts of the silicon layer are made porous, whilst the region below, in monocrystalline silicon, is protected from this change. Having formed the element on the monocrystalline region, the region made porous is removed, leaving the bridge. A further claim is made for the method of sensor operation. It is heated to a temperature at which hydrogen is split off from molecules to be detected. The temperature of the bridge is reduced and the electrical capacity of the element is measured. Preferred features: The element is on one side of the bridge, with an empty space (10) on the other. The bridge is held by its two ends, floating between them. It is a silicon substrate, especially p-type Si, with a recess or indentation beneath it. The element is a metal oxide layer and/or a gas-sensitive field effect transistor. The bridge includes or is constructed from phosphorus-implanted regions of n-type Si. At edges on one side of the bridge, highly-doped regions of n+ Si are located, to form electrical contacts. On one or more sides of the bridge, there are meandering heating elements, made of platinum. The bridge comprises or carries a gate oxide and a gate electrode. The gate oxide is silica and/or the gate electrode is platinum. The sensor is formed by one or more metal oxide sensors and/or one or more gas sensitive field effect transistors. In the method of manufacture, which is further detailed, standardized process steps are used. In the method of operation, the bridge is heated and cooled for cyclic detection of hydrocarbon.