Multi-Layer ZnO Acoustic Transducers

The conversion loss of thin-film acoustic transducers can be very high for frequencies higher than 8 GHz. To improve the transduction efficiency, a multi-layer structure consisting of half-wave thick layers of two materials with different coupling constants can be used. One method to obtain such a structure is to grow thin films of a piezoelectric material such as ZnO while changing the crystallographic orientation of alternating films to modulate the mechanical coupling. We have fabricated multi-layer ZnO transducers with alternating crystal structure f or operation at 8 and 12 CHz. The performance of these transducers is compared with that of single-layer transducers and shown to be superior at frequencies between 8 and 12 GHz. The two-way conversion loss is between 10 and 20 dB for multilayer transducers operating at cryogenic temperatures for frequencies in the 8-12 GHz range.