Piezoresistive Position Microsensors with PPM Accuracy

Abstract Present work demonstrates the applicability of MEMS devices with multiple embedded flexures and sidewall piezoresistors for precise multi-Dimensional position monitoring. Particularly, applications requiring high accuracy monitoring of vector quantities such as: force, position or displacements, are targeted. In this paper, some particular results on applicability of sidewall piezoresistive MEMS for 1D, 2D and 3D position monitoring are reported. The presented MEMS are monolithic contact devices made of single crystal silicon, comprising of two rigid parts which are able to move relatively to each other. These rigid parts are connected with one or multiple flexures with integrated sidewall piezoresistors, capable of responding to relative displacements of the movable part. The separate flexures are designed to act differently in response to the movement stimulus, thus the sensor signals are non-proportional to each other. The set of linear equations characterizing the simultaneous dependence of sensor signals on their movement in all three directions are used for accurate calculation of the position. The sensitivities and travel ranges in each direction can vary with the layout of the exploited flexures. The contact points of all flexures and actuated members are closely located and permanent during the sensor lifespan. The envisaged multi-Dimensional position sensors reveal an extremely high ppm resolution and accuracy. The impact of additional factors on the sensor accuracy are analysed and briefly discussed.