Gallium Nitride on Silicon Carbide Platform for Integrated Acoustic Devices

: Toward Monolithic Integration of Active/Passive RF Components

Abstract

Wireless communication systems have overreached the scalability of the current technology far beyond due to increasing the number of operating frequencies, the required radio frequency (RF) components, and high-frequency electronics to meet the demand of the end-users. The most viable solution for this problem is the monolithic integration of active/passive RF with integrated circuits (IC) and RF power amplifiers (PA). Gallium Nitride (GaN) on Silicon Carbide (SiC) is one of the most commonly used semiconductor platforms in high-power, high-frequency electronics. In addition, GaN is a piezoelectric material that has excellent electromechanical properties and low acoustic losses. These qualities make GaN-on-SiC a perfect platform for the monolithic integration of acoustic RF (passive) and high-power RF (active). The monolithic integration of active and passive RF would not only reduce parasitic and matching constraints, but also enable high-compact and efficient clocks, delay lines, and RF filters for timing applications, wireless communications, and signal processing.
This thesis emphasises compact acoustic RF devices and considerations that must be taken into account for the viability of the monolithic integration. In particular, we present guiding and manipulating GHz frequency acoustic waves in μm-scale waveguides and resonators through strong transverse confinement. The low-loss sound routing in on-chip waveguides opens up new degrees of freedom to manipulate RF signals on a chip. In addition, we show that the GaN-on-SiC platform supports low-loss acoustics by demonstrating acoustic microring resonators with frequency-quality factor (fQ) products approaching 4x10^13 Hz, exceeding the Akhieser damping limit of GaN. Furthermore, we use this platform to demonstrate spiral delay lines with RF delays of 2.5 μs, which is an equivalent of 750 m electromagnetic delay.

Date of Award	23 Jan 2024
Original language	English
Awarding Institution	University of Bristol
Supervisor	Krishna Coimbatore Balram (Supervisor)