Gallium nitride phononic integrated circuits for future RF front-ends

Abstract

Achieving monolithic integration of passive acoustic wave devices, in particular RF filters, with active devices such as RF amplifiers and switches, is the optimal solution to meet the challenging communication requirements of mobile devices, especially as we move towards the 6G era. This requires a significant (≈ 100x) reduction in the size of the RF passives, from mm 2 footprints in current devices to tens of µm 2 in future systems. Applying ideas from integrated photonics, we demonstrate that high frequency (>3 GHz) sound can be efficiently guided in µm-scale gallium nitride (GaN) waveguides by exploiting the strong velocity contrast available in the GaN on silicon carbide (SiC) platform. Given the established use of GaN devices in RF amplifiers, our work opens up the possibility of building monolithically integrated RF front-ends in GaN-on-SiC.

Single-mode and ultra-broadband gigahertz surface acoustic waveguides on AlN-on-SiC substrates

“…In the non-propagating directions, these SAW waveguides confine SAWs in wavelength-scale structures, reducing the beamwidth of operating SAWs significantly and allowing SAWs to propagate freely on the substrate surface. There are three main types of SAW waveguides implemented so far: (a) phononic crystals (PnCs) waveguides [8][9][10][11], (b) suspended waveguides [12][13][14], and (c) ridge waveguides [15][16][17][18][19][20][21][22][23][24]. Their implementations mainly benefit from the progress of micro-nanofabrication technology for the piezoelectric substrates.…”

“…In the same GaN-on-sapphire substrate, Shen et al reported SAW mode conversions between quasi-Rayleigh to quasi-Love [22], Xu et al further improved their operating frequencies to several GHz [23]. In 2020, Dahmani et al realized the SAW ridge waveguides working over three GHz on a LiNbO 3 -on-sapphire substrate [24]. In 2021, Bicer et al realized similar SAW waveguides on a GaN-on-SiC substrate [21].…”