Capacitive pressure-responsive devices and their fabrication

摘要

A method for making capacitive silicon pressure sensors and pressure switches with high long-term stability involves fabrication by wafer bonding of a silicon substrate wafer with another silicon wafer where a highly boron-doped diaphragm is defined by a self-aligned doping process through a window defined on an insulating layer. The long-term stability of the device is secured by anisotropically etching the window, e.g. by reactive ion etching, so as to create vertical window walls. The flatness of the diaphragm can be secured by the provision of an insulating film on the backside of the substrate wafer that compensates the stress on the silicon diaphragm created by the insulating layer present between the two wafers. The cavity formed by the window may contain gas or it may be evacuated in which case the fabrication method may also involve a process step facilitating the evacuation of the cavity and sealing the same using metal employed for making electrical connections.