Surface-wave interaction with the MOSFET

The silicon p-channel MOSFET has previously been characterized as a piezoresistive element. Since gmof the device varies with applied stress through modulation of surface-carrier mobility, it becomes of interest to examine the response of the device to acoustic surface waves induced in the silicon. The MOSFET has a geometry well suited for surface-wave detection since current flow is limited to the inversion layer and, in addition, the device can be fabricated with inversion layer dimensions less than λ/2 for surface waves of frequency less than 100 MHz. The devices can therefore be used to evaluate surface-wave propagation in any direction on a given silicon plane. The investigation also has practical aspects in that surface-wave detector arrays can find application as weighted tapped delay lines with weighting controlled by the application of various dc gate voltages.