Tunable acoustic delay lines based on thermally controlled single-phase unidirectional transducers

Abstract

This Letter presents a tunable acoustic delay line (ADL) based on thermally controlled single-phase unidirectional transducers, fabricated on a 1 μm thick scandium-doped aluminum nitride (Al0.7Sc0.3N) thin film. The ADL operates at a center frequency (fc) of 715 MHz, determined by the lithography of the top electrode. The bottom electrode functions as a resistive structure, enabling localized heating under a DC voltage (VDC), which induces frequency shifts (Δfc) at one or both radio frequency ports. Experimental results show a maximum tuning range of 16 MHz, with a modulation efficiency of 0.2 MHz/mW, accompanied by a 3.7 dB increase in insertion loss (IL). Furthermore, the device exhibits good recovery characteristics, with both IL and 3-dB bandwidth nearly returning to their original values after removal of VDC. The integration of a heater with single-phase unidirectional transducers in this work demonstrates promising potential for applications in acoustic information processing, sensing, and signal manipulation.