Fabrication of a 4.4 GHz oscillator using SAW excited on epitaxial AlN grown on a Sapphire substrate

Surface Acoustic Wave (SAW) devices are still the preferred solution for the stabilization of on-board frequency source for radar control. The possibility for developing an oscillator delivering a frequency very close to the usual operating band of these devices is considered in this paper. Double-port SAW resonators are built on epitaxial Aluminum Nitride grown onto Sapphire to take advantage of one of the lowest visco-elastic loss material and a high structural quality piezoelectric layer to optimize the resonance of the acoustic wave device. Experimental test vehicles are built using electron-beam lithography, yielding devices operating near 4.5 GHz with Q factor in excess of 3000 and moderate insertion losses. These resonators are used to stabilized feedback loop oscillators yielding noise floor better than -150 dBc/Hz. Among the other possible application of these devices, high temperature sensors may be considered as the growth temperature of the layer is in the range 1000°C - 1600°C.