GaN-based Periodic High-Q RF Acoustic Resonator with Integrated HEMT

This work demonstrates the first on-chip integration of a high overtone bulk acoustic resonator (HBAR) with a high electron mobility transistor (HEMT) using an epitaxial AlGaN/GaN/NbN heterostructure on a SiC substrate. This pairing combines the robust structure, periodic mode spacing, high mode density, and high quality factor (Q) of the HBAR with the amplification and nonreciprocal characteristics of the HEMT. From L-band to X-band, the HBAR exhibits among the highest Q and f×Q products reported with Q > 10⁴ and f×Q > 10¹⁴ at 295 K, and Q > 10⁶ and f×Q > 10¹⁵ at 20K. The drain-connected HEMT+HBAR pair demonstrates 34 dB On/Off ratio and 16 dB directional contrast (both at 3 GHz), while retaining the signature periodic spacing and mode density of the HBAR. HEMT+HBAR devices can be building blocks for comb filters, circulators, and sparse spectrum front-ends. The TMN/III-N heterostructure (with superconducting, semiconducting, and piezoelectric properties) and excellent cryogenic performance also indicates enormous potential as an integrated quantum platform for computation, communications, sensing, and metrology.