Combined effect of the membrane flatness defect and real dimension gauges on the sensitivity of a silicon piezoresistive pressure sensor

Presents a new approach to the sensitivity loss of a silicon piezoresistive pressure sensor. The loss origin is due to the parallelism defect of the two sides of the membrane cumulated to the real dimensions of the gauges, considered usually as being as points. The work we present deals with the modelling of a structure, realised by micro-electronic techniques and chemical etching, containing four piezoresistors of the P type connected in Wheatstone bridge. We modelled, firstly, the parallelism defects of a square membrane, secondly the effects of real dimension gauges according to their positions on the membrane. Then we examined their combined effects on the sensitivity of the sensor. The lack of flatness collected experimentally for a 30 /spl mu/m membrane thickness is less than 1%, however, it gives rises to an over-estimation of sensitivity of about 1.5%. If only the real dimensions of the gauges are considered an over-estimation of the sensitivity of approximately 10% is made for a 100 /spl mu/m gauge length.