A Thin-Film Piezo-Silicon Acoustoelectric Isolator with More than 30 dB Non-Reciprocal Transmission

Bulk acoustic wave (BAW) thin-film lithium niobate (LN)-silicon (Si) delay lines are presented that offer more than 30 dB of non-reciprocal transmission ratio enabled by the acoustoelectric (AE) effect. In this scheme, the interaction of drifting electrons and acoustic phonons turns the microacoustic waveguide into a strong isolator. By tailoring a heterostructure stack of LN and Si, up to ~22 dB of AE gain (160 μW) is measured at only ~4 mW of DC bias power, yielding an unprecedented high power-added efficiency of 4%. This is realized within a 4.3% fractional bandwidth and a spurious-free span of 400 MHz centered around 700 MHz. Furthermore, thermal analysis and measurement results support device operation under large and continuous bias, mostly due to the high thermal conductivity of Si. The increasing demand for nonreciprocal RF components such as isolators and circulators in rapidly growing areas, namely, 5G communications and quantum computing could render this platform a potentially suitable candidate for further investigations.