SAW filter with AIN on diamond

摘要

Diamond surface acoustic wave (SAW) has been used to boost the frequency of thin film filters made of piezoelectric materials[1-3,13,14]. Many designs have been tested and with significant results, in particular, AIN on diamond (AlNoD) as the interface for transmitting Rayleigh wave was studied extensively [4-12,16-21]. However, in all cases, nano crystalline or microcrystalline AlN coatings were deposited, typically by sputtering or CVD, on polycrystalline diamond film. The diamond film itself may contain nano or micro grains that are deposited by CVD [4,5,7]. The presence of extensive grain boundaries in AlN can attenuate rapidly the propagation of Rayleigh wave. Moreover, the bonding between loose atomic packing of AlN and tight lattice of diamond is weak so much of the mechanical energy is dissipated as heat. In fact, the energy loss is much higher than energy transmitted during the resonating process. In this research, we attempted to improve the matching of atoms at the interface of AlNoD by doping AlN lattice with boron atoms. The shrinking of the lattice may allow more atoms are aligned at the interface. Moreover, a method of coupling single crystal AlN on single crystal diamond is proposed. Such a coupling can maximize the signal-to-noise ratio of the resonating AlNoD at the same time minimize the insertion loss of the SAW filter.