Characterization of Group Ill-Nitride Based Surface Acoustic Wave Devices for High Temperature Applications

摘要

In this study, aluminum nitride (AlN) and gallium nitride (GaN) thin films have been grown via metal organic vapor phase epitaxy (MOVPE) on silicon and sapphire substrates. Samples were annealed at temperatures ranging from 450 to 1000 ℃ in atmosphere. AlN and GaN thin film quality has been characterized before and after annealing using scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS) and atomic force microscopy (AFM). Surface acoustic wave (SAW) devices with titanium/platinum interdigital transducers (IDTs) designed to operate at the characteristic frequency and fifth harmonic have been realized using traditional optical photolithographic processes. SAW devices on GaN were thermally cycled from 450 to 850 ℃. The S_(21) scattering parameter of SAW devices was measured before and after thermal cycling by a vector network analyzer (VNA). An approach for the suppression of electromagnetic feedthrough (EF) to improve device performance is discussed. Feasibility of 5th harmonic excitation for GHz operation without sub-micron fabrication is also investigated. SAW devices have also been fabricated on the more traditional SAW substrate, lithium niobate (LiNbO_3), and device response was compared with those on AlN and GaN at room temperature.