Ultra-compact analog thermo-acoustic phase shifter

Phase shifters are key enablers of beam steering, adaptive modulation, and reconfigurable filtering in modern wireless and acoustic systems. However, conventional electromagnetic (EM)-based phase shifters are fundamentally constrained in size and scalability by the wavelength-dependent nature of EM wave propagation, limiting their integration in compact and on-chip platforms, particularly at ultra-high frequencies (UHF). Here, we report a chip-scale thermo-acoustic (TA) phase shifter based on a suspended Z-cut lithium niobate (LiNbO 3 ) thin film, which achieves analog and compact phase modulation through localized heating. By exploiting the temperature dependence of elastic constants, the device modulates acoustic wave velocity without relying on EM wavelength-scale resonant structures. The platform supports both shear-horizontal (SH 0 ) and asymmetric (A 1 ) modes across six acoustic passbands from 0.5 to 3.5 GHz. The TA phase shifter demonstrates a phase response exceeding −118°/mW, with a 3-dB modulation bandwidth reaching 2.83 kHz, enabled by a closed-loop constant-temperature control circuit that stabilizes thermal response for high-speed operation. The device occupies a core area of 580 × 180 μm 2 , representing orders-of-magnitude miniaturization compared to EM counterparts for the same range of frequency. This work establishes thermo-acoustic modulation as a scalable and energy-efficient approach for compact, high-frequency phase control, advancing the development of integrated acoustic signal processors and next-generation reconfigurable RF front ends.