Overcoming Acoustoelectric Material Limits of Piezoelectric Resonators using Epitaxial Aluminum Nitride

Advanced wireless communication systems require compact and effective filters in the 6-40 GHz frequency range. These frequencies are beyond the capacity of conventional surface acoustic-wave resonators, and are challenging for bulk acoustic-wave resonators. This is mainly because higher frequencies require thinner resonators, but the electrical and mechanical properties of aluminum-nitride thin films deposited by conventional sputtering technique degrade at sub-micrometer thicknesses. Taking advantage of epitaxial aluminum nitride developed for ultraviolet photonics and high-speed electronics, we have explored aluminum-nitride film-bulk acoustic resonators (FBARs) which can operate in the thickness-extension mode up to 40 GHz. These FBARs also provide the unique opportunity for monolithic integration with nitride-based semiconductor and superconductor devices in the future.