Effect of the silicon membrane flatness defect on the piezoresistive pressure sensor response

In this paper, we present a new approach of the sensitivity loss of a silicon piezoresistive pressure sensor. This loss of sensitivity is due to the lack of parallelism of the two membrane sides. An experimental topographical result of bottom membrane realised in LAAS, is simulated to quantify the effects on the gauges electrical responses and on the sensor sensitivity. A bridge of four piezoresistors forms our sensor. A flatness defect less than 1% obtained experimentally on 30 /spl mu/m membrane has lead to an electrical response loss around 3% of each gauges while the full bridge give 1.5% loss of sensitivity as a result of the simulation. These values increase significantly as the membrane thickness decreases. The irregularity of the surface could be an important source of information about the voltage offset.