15-GHz Epitaxial AlN FBARs on SiC Substrates

Epitaxial AlN thin-film bulk acoustic resonators (FBARs) on SiC substrates with first-order thickness extensional modes of 15-17 GHz are demonstrated. For the 15 GHz epi-AlN FBARs, the quality factor <tex-math notation="LaTeX">Q_max≈ 443 </tex-math> , electromechanical coupling coefficient <tex-math notation="LaTeX">k_eff^2≈ 2.3% </tex-math> , and <tex-math notation="LaTeX">f· Q ≈ 6.65~THz </tex-math> figure of merit achieved are among the highest in the Ku-band (12-18 GHz). A clean primary mode with a high quality factor enables such epi-AlN FBARs to be utilized in Ku-band acoustic filters with clean bands and steep rejection. Because such epi-AlN FBARs share the same SiC substrate and epitaxial growth as AlN/GaN/AlN quantum well high-electron-mobility-transistors (QW HEMTs), they are well suited for monolithic integration with HEMT low noise amplifiers (LNAs) and power amplifiers (PAs).