HVPSAW sensitivity to film properties for ZnO/diamond/Si structures

Over the past decade, improvements in the ZnO on diamond SAW (DSAW) thin film technology has demonstrated that the ZnO/diamond/Si structure is suitable for high frequency and high power SAW devices. In addition to high quality ZnO and diamond thin films, temperature compensation using SiO2 layers have been reported, with temperature performances that surpass those of ST-X quartz. With such favorable characteristics, 2 to 3.5 GHz DSAW resonator devices are now commercially available. This frequency range does not push the photolithographic process definition to the limit, since the phase velocities for the DSAW modes used typically ranges from 8 to 10 km/s. The high velocity pseudo SAW (HVPSAW) has phase velocities from 12 to 17.5 Km/s for the ZnO/diamond structure, making it very attractive in extending the frequency range of the DSAW devices for the next generation of communications equipment. The present work describes a sensitivity study of the HVPSAW properties with respect to the values of the ZnO and diamond film material properties. Using three different sets of material constants from the literature for both the diamond and the ZnO films, we show that the propagation loss minimum predicted for the HVPSAW varies up to 20% depending on the material constants used. It is thus essential that the films´ material constants be accurately characterized to predict the minimum propagation loss conditions. We show the results of calculations of ZnO film thicknesses needed to obtain minimum HVPSAW loss and we discuss the diamond film thickness requirements needed to avoid power losses into the silicon substrate. Simulations for different IDT and metal shorting planes structures are presented, resulting in coupling constants that range from 0.1 to 1.3%