A diamond substrate suitable for 5GHz SAW device application

SAW characteristics of various layer structures of SiO₂/IDT/AlN/diamond substrates that employ 2nd mode of wave (Sezawa mode) were studied both theoretically and experimentally. It was found that the SiO₂/IDT/AlN/diamond substrate would allow using thicker metal IDT in SAW device designs than other SAW substrates and also would have zero TCF characteristic at room temperature. SAW phase velocity and electromechanical coupling coefficient of the SiO₂/IDT/AlN/diamond substrate are 11150m/s and 0.5%, respectively. Fabricated 1-port SAW resonators using the diamond substrate showed Q of 660 at 5.4 GHz anti-resonance frequency. Frequency drift over temperature range of -25°C to 80°C was about 90 ppm that is even less than the ST-Quartz SAW substrate. In the end of paper, a 5 GHz band stop type SAW filter design is presented. It is shown that 30 MHz wide stopband at 6 dB rejection level can be achieved while keeping the passband insertion loss just in -0.76 dB.