Surface acoustic wave filters on diamond layered structures

Abstract

<p>Surface acoustic wave (SAW) devices are an enabling technology for high-performance wireless communication systems. They are able to meet performance specifications that are beyond the scope of competing technologies, particularly in the front-end of the receivers, and establish the ultimate performance that is achievable. Current spectrum congestion is forcing a move to higher operating frequencies, and this is leading to a search for low-cost SAW devices that are able to operate at frequencies above 2 GHz. To this end, there has been considerable interest in devices that employ the high acoustic velocity of diamond. Diamond, however, is not piezoelectric, and it must be layered with other materials such as zinc oxide (ZnO) to permit the electrical generation and detection of acoustic waves. There is therefore a need for modeling tools that accurately predict the behaviour of multi-layered SAW substrates in the presence of surface transducers and reflectors. This Thesis presents a study of SAW propagation and generation under infinite periodic grating structures on multi-layered ZnO/Diamond substrates. The study is based on the space harmonic method (SHM) and predicts the SAW behaviour under both open and shorted surface electrodes. Dispersion diagrams are obtained around the first Bragg wavenumber and stopbands of finite bandwidth are observed. The method is then extended to the generation of SAWS by interdigital transducers. Admittance curves and static capacitances are calculated. The physical propagation behaviour of ZnO/Diamond multi-layered substrates is also investigated. The displacement distributions and the standing wave patterns are calculated within each layer. The energy contained in each layer is computed for different propagation modes and different ZnO layer thicknesses. The results are interpreted within the framework of the coupling-of-modes (COM) theory. The COM parameters are derived for the first and second Sezawa modes as a function of aluminum and zinc oxide thicknesses. The results and the COM parameters can be directly used in the design of SAW devices. The established analytical treatments can be easily applied to other multi-layered substrates with an arbitrary configuration including additional layers.</p>