Optimization of AlN thin layers on diamond substrates for high frequency SAW resonators

AlN/diamond heterostructures are very promising for high frequency surface acoustic wave (SAW) resonators. In their design, the thickness of the piezoelectric film is one of the key parameters. On the other hand, the film material quality and, hence, the device performance, also depend on that thickness. In this work, polished microcrystalline diamond substrates have been used to deposit AlN films by reactive sputtering, from 150 nm up to 3 μm thick. A high degree of the c-axis orientation has been obtained in all cases. SAW one port resonators at high frequency have been fabricated on these films with a proper combination of the film thickness and transducer size. ► We deposit AlN on Diamond substrates by sputtering for high-frequency applications. ► The thickness of the AlN film influences on the crystal quality. ► The deposit of AlN on diamond has been optimized for different film thicknesses. ► The crystal quality for AlN films on diamond improves as its thickness increases. ► The layers were used to process SAW resonators operating above 10 GHz.