Substrate removal structures for AlScN/diamond surface acoustic wave resonators

A new method to prepare AlScN/diamond structure was proposed to fabricate high frequency surface acoustic wave (SAW) resonators. The AlScN/diamond structure was prepared by growing a diamond layer on the AlScN surface and removing the Si substrate. Highly c-axis oriented AlScN thin films with 2.37° full width at half maximum (FWHM) on the X-Ray rocking curve of the (002) peak were deposited by reactive ion assisted sputtering. This method solved the problem of high roughness synthetic diamond worsening sputtered AlScN quality without using polishing. A high electromechanical coupling coefficient (Keff2), 4.31 %, was obtained from the 2.77 GHz SAW devices of AlScN/diamond structure, and its insertion loss is 15.46 dB. The AlScN/diamond SAW devices exhibit lower insertion loss and higher Keff2 in comparison to AlScN/Si devices. The proposed AlScN/diamond structure fabrication process showed a feasibility of mass production of high frequency SAW resonators with excellent performance.