Critical study of high-sensitivity pressure sensors with silicon/porous silicon composite membranes

Abstract

Since porous silicon (PS) has a much lower Young's modulus than single crystalline silicon, Si/PS composite membranes deflect more and can be used to fabricate pressure sensors with improved sensitivity. However, PS has some drawbacks, like weaker structural stability and being more susceptible to humidity due to its large surface-to-volume ratio. We discuss the fabrication and testing of Si/PS composite membrane pressure sensors with MicroPS and MacroPS of varying porosity. For the same porosity, the composite membranes with Si/MicroPS show higher sensitivity than Si/MacroPS. The sensor output is linear and repeatable at pressures less than 1 bar. The deformation of composite membranes measured up to 10 bar showed that it saturates at high pressure and is irreversible. Composite membranes also exhibit higher offset voltage than single crystal silicon membranes, which could be attributed to the stress developed in the membrane during PS formation and subsequent processing. The composite membrane pressure sensors were packaged on TO 39 headers, and the effect of humidity and temperature variation were investigated.