Study of temperature coefficient of frequency and electromechanical coupling coefficient of X band frequency SAW devices based on AlN/diamond layered structure

In this work, we report about the study of electromechanical coupling coefficient (K 2) and temperature coefficient of frequency (TCF) of SAW devices based on AlN/diamond layered structure intended for the X band (8GHz). SAW devices operating in the range of 8 GHz were realized by the combination of the high velocity of the AlN/diamond layered structure and the high lateral resolution obtained using e-beam lithography (EBL). Due to high electrical resistivity of the AlN film, interdigital transducers with sub-micronic resolution were patterned by an adapted technological EBL process. The analyses of structural and morphological of the diamond and AlN layers by X-ray diffraction, atomic force microscopy (AFM) were carried out. They showed the highly (002) preferential orientation of AlN film deposited on diamond layer and a very weak surface roughness of less than 1nm measured on the surface of AlN/diamond layered structure. The analysis of device performances in terms of K 2 and temperature stability were carried out and discussed. The dispersion of both parameters as a function of normalized thickness of AlN layer (kh(AlN)) was experimentally determined, and showed the obtaining of electromechanical coupling coefficient up to 1.4% for normalized thickness kh(AlN) varying between 3 and 5. Concerning the TCF, the recorder values show a quasi-parabolic behavior. This TCF behavior in such high frequencies will discussed taking into account the nature of the TCF of AlN and diamond layers separately.