The barrier-modulated tap: a new SAW detection method in silicon

A method to detect surface acoustic waves (SAW) in a ZnO-SiO₂ Si layered structure is proposed. The detector consists of two p ⁺ electrodes implanted in an n-type epilayer, thus forming a lateral p⁺-n-p⁺ structure. The p⁺ electrodes are reverse-biased to deplete the gap between the electrodes. When the depletion regions of the two p⁺-n junctions meet, a lateral current flows. Its magnitude is determined by the potential barrier in the gap. The electric field accompanying a traveling SAW penetrates into the depleted gap and modulates the potential barrier and therefore the biased detector current. The output current signal depends on the bias conditions of the detector current. This novel detector can be used to realize current-controlled taps in programmable filters. Monolithic test devices operating at a frequency of 80 MHz were realized in a ZnO-SiO₂-Si layered structure with a 9-μm-thick epilayer of 20 Ω cm, a 0.1-μm-thick oxide layer, and a 10-μm-thick ZnO layer