Diamond-based SAW oscillator at 1GHz

Diamond with ZnO thin films appears as an appropriate material system for high power GHz SAW devices. For the purpose of oscillator applications with extremely low phase noise, a resonator on this material base has been developed. The first Sezawa mode was selected for our device application. The geometric parameters were 900 nm for the ZnO thickness, 100 nm for the Al electrodes, and 9.43 μm for the IDT period. For the enhancement of the resonator Q-factor different loss contributions have been analyzed including the ZnO dielectric and ohmic losses, the leakage into the Si substrate below the diamond, and the effective reduction of Q-factor by laterally inhomogeneous SAW properties. A longitudinally coupled resonator with 61 finger IDTs and an aperture of 42 wavelengths was used to build an oscillator loop containing a phase shifter, a SiGe amplifier, and a 10 dB coupler. The oscillator frequency was 1.008 GHz, the tuning range 2 MHz, the power consumption 0.48 W, the noise floor was -171 dBc at 1 MHz offset from the carrier. The loading power for the SAW resonator was 24 dBm.