Very high frequency SAW devices based on nanocrystalline diamond and aluminum nitride layered structure achieved using e-beam lithography

Very high frequency surface acoustic wave (SAW) devices based on the AlN/diamond layered structure are fabricated by direct writing using e-beam lithography on the nucleation side of nanocrystalline diamond (NCD) films deposited by microwave plasma assisted chemical vapor deposition process. The NCD nucleation side is characterized from the point of view of microstructure, morphology and surface topography. Surface roughness as low as 6 nm is reached, which enhances the deposition of AlN film on this flat surface. The interdigital transducers IDTs made in aluminum with lateral resolution down to 600 nm are successfully patterned on the AlN/NCD layered structure with an adapted technological process. Experimental results show that the Rayleigh wave and the higher mode are generated. A high frequency around 4 GHz (mode 1) is obtained for the considered layered structure SAW device, exhibiting a phase velocity of 9200 m/s taking into account the wavelength of 2.4 μm. This value agrees well with calculated values determined from dispersion curves of phase velocity.