Application of twin-beam structures for estimation of material properties and sensor fabrication

This paper discusses the application of the recently proposed twin-beam structure for fabrication of piezoresistive sensors and also for estimation of material properties. Instead of using common methods to isolate the piezoresistors from the structure by means of an insulating thin film or by reverse-biased junctions, the twin-beam structure relies on mechanical coupling to confine the current within the piezoresistors. Consequently, this technique can be used in cases where it is not possible to employ the common techniques for fabrication of piezoresistors, such as many standard microelectromechanical systems (MEMS) fabrication processes. Material properties can be estimated using the experimental results from devices that employ twin-beam structures and the calculated mechanical parameters. Using the twin-beam structure, the piezoresistive coefficient of the top polysilicon layer (Poly2) in the multi-user MEMS processes (MUMPs) process is calculated to be around -10.65 x 10(-11) Pa-1, which corresponds to a gauge factor of -19.4. The design of a magnetic field sensor with a twin-beam structure is also discussed.