Surface acoustic wave devices for processing and storing signals

Abstract

A surface acoustic wave device utilizing a piezoelectric substrate capable of propagating traveling acoustic waves along a surface thereof and a semiconductive substrate positioned adjacent such surface, the latter substrate having an array of Schottky diodes and associated islands of highly resistive material, such as polycrystalline silicon material, disposed in the surface thereof opposite the piezoelectric substrate to form an interaction region. Application of a signal uniformly over the interaction region will charge the diodes uniformly and an acoustic wave traveling along a selected surface of the piezoelectric substrate will interact with the uniformly applied signal to alter the charging pattern of the Schottky diode array in accordance therewith to produce a corresponding altered conductivity pattern stored in the semiconductor substrate and representing the interaction of the uniformly applied signal and the traveling wave signal. A second signal can thereupon be propagated along the piezoelectric substrate to interact with the stored altered conductivity pattern to provide either correlation or convolution operation depending on the direction of propagation thereof along the piezoelectric surface. Improvement in the stored signal to noise ratio can be obtained by applying the signal to be stored and the uniformly applied signal a selected number of times over a selected time interval to maximize the charge on the diodes so that when the stored signal is read out the signal to noise ratio at read-out is also improved. Further, a plurality of signals can be simultaneously stored in substantially the same space in the semiconductor substrate by tilting the direction of propagation thereof or by using coded wavefront patterns thereof to provide orthogonal beams which prevent interaction, or cross-talk, therebetween.