Single-Crystal Multilayer Nitride, Metal, and Oxide Structures on Engineered Silicon for New-Generation Radio Frequency Filter Applications

Molecular beam epitaxy is used for growth of structures with ScAlN for radio frequency filter applications. The nitride layers are grown directly on Si substrates for surface acoustic wave resonators, Lamb acoustic wave resonators, and on an epitaxial Mo on Er₂O₃ buffer layer on Si for film bulk acoustic resonators (FBARs). The crystal structure of the ScAlN layer is defined by Sc concentration. It can vary from wurtzite to hexagonal. Good crystal quality of the Mo layer results in low sheet resistance which is very close to that of the bulk material. Enhanced electroacoustic performance is achieved in fabricated acoustic devices. A Lamb acoustic wave resonator with ScAlN grown directly on Si demonstrates a high coupling factor (4.8%) and figure of merit (Q × k_t ²) (9.1) at a resonance frequency of 9.02 GHz. A fundamental resonance frequency 4.32 GHz is achieved for an FBAR device fabricated using the structure with the nitride layer on an epitaxial metal electrode. At the 4.32 GHz resonance frequency, the extracted figure of merit of the resonator is 10.6.