Fabrication of SHF range SAW devices on AlN/Diamond-substrate

Preparation of piezoelectric AlN thin films on diamond substrates, and their application to SHF SAW devices are discussed. It is confirmed that DC-TFTS method enable to prepare highly c-axis oriented AlN films on polycrystalline diamond substrates. The AlN surface was smooth enough to fabricate fine electrodes with the width of the order of sub-microns. Transversal filters working around 5 GHz were fabricated to characterise SAW propagation on the Al-electrodes/AlN/diamond-substrate structure. The theory and measurements of the devices suggested that the largest reflectivity of Al-grating is achieved when the thickness of electrodes is about 0.20 p for the AlN thickness is 0.85 p, where p is the grating electrode pitch. Considering the facts, a one-port resonator was fabricated, which has relatively thick electrodes in order to realise high Q-factor. The measured Q-factor and capacitance ratio of the resonator were 650 and 155, respectively. It is seen from these results that the optimisation of the thickness for the electrodes as well as AlN films is very important to develop high performance SHF SAW devices using Al-electrode/AlN/diamond-substrate structure.