Sensitivity and stress effects of composite membranes with micro/macro porous silicon for pressure sensor applications

Abstract

Since porous silicon (PS) has a lower Young's Modulus as compared to silicon, Silicon/Porous Silicon (Si/PS) composite membranes are expected to show higher sensitivity as compared to membranes of silicon alone. In this paper we discuss the fabrication and testing of Si/PS composite membranes where a part of the silicon membrane depth is converted into PS. Composite membranes with Si/ microPS and Si/ macroPS were fabricated with varying porosity and same thickness. The composite membranes with micro PS show higher sensitivity than composite membranes with macro PS. Formation of microporous and macroporous silicon produces stress on the membrane varying with the porosity. The variation in compressive stress on the membrane with porosity for both micro and macro PS has been studied by measuring the deformation of the composite membrane with a surface profiler and the stress is found to be larger for microPS. The compressive stress results in an increase in the offset voltage by more than an order of magnitude for composite membranes with porosity above 50% as compared to one with a single crystalline silicon one. Though the composite membranes exhibit saturation and hysteresis at higher pressures, the response is linear and repeatable at pressures below 1 bar making this a viable option for sensing low pressures.