Study of Low Temperature Deposition of Nanocrystalline Diamond Films on ZnO/LiNbO3 Layered Structures Suitable for Waveguiding Layer Acoustic Wave Devices

Abstract

In this article, the nanocrystalline diamond (NCD) film low temperature deposition process on ZnO/Si, ZnO/LiNbO3, and ZnO/IDTs/LiNbO3 substrates is investigated aiming at obtaining layered structures suitable for waveguiding layer acoustic wave (WLAW) devices. The NCD synthesis is performed at 250 °C by using a distributed antenna array (DAA) microwave system operating in H2/CH4/CO2 gas mixture at low pressure (<1 mbar). Since the ZnO layer is etched during the NCD growth process, the deposition of a thin AlN layer of few hundred nanometers in thickness on the considered substrates is performed and is shown to be effective as a protective layer. Diamond growth on AlN‐coated ZnO/Si substrates emphasizes the ability of the DAA reactor to synthesize NCD films with properties similar to those obtained on silicon substrates. Besides adherent NCD films up to 300 nm thickness are synthesized on AlN‐coated ZnO/LiNbO3 substrates but stress in the layered structure appears during the plasma process. Finally, the feasibility of a NCD/AlN/ZnO/IDTs/LiNbO3 layered structure, suitable for WLAW devices, is successfully demonstrated, even if the NCD film adherence must be further improved on the inter‐digital transducers (IDTs) finger zone.