Silicon SAW devices and electromagnetic feedthrough

Surface acoustic wave (SAW) devices in a ZnO-SiO₂-Si layered structure, with the interdigital pattern at the ZnO-SiO₂ interface, exhibit a higher electromagnetic feedthrough than SAW devices in (nonconductive) piezoelectric substrates. Feedthrough between the input and output transducers mainly takes place through the conductive silicon substrates and can therefore not be adequately eliminated, even with a good packaging technique. Well-known measures, compatible with standard IC processes, to reduce this feedthrough are discussed and experimental results are shown. A simple configuration to further reduce the electromagnetic feedthrough is introduced, in which the silicon substrate is covered with a grounded, metal layer. Since a thermally grown SiO₂ layer can no longer be obtained, IC-compatible materials, such as SiO₂ (sputtered) or Si₃ N₄ (plasma-deposited) are used as a dielectric layer. Experimental results show an extra 10-15 dB reduction in electromagnetic feedthrough