Low Temperature Properties of Low-Loss Macroscopic Lithium Niobate Bulk Acoustic Wave Resonators

TL;DR

This study explores the low-temperature behavior of lithium niobate bulk acoustic wave resonators, revealing high quality factors and defect-related loss mechanisms that limit performance, with implications for future material improvements.

Contribution

It provides the first detailed analysis of cryogenic loss mechanisms in macroscopic lithium niobate BAW resonators, highlighting defect-related dissipation effects.

Findings

Achieved a maximum quality factor of 8.9 million in BAW modes

Observed anomalous self-induced absorption and transparency effects

Identified impurities and defects as key loss mechanisms

Abstract

We investigate gram scale macroscopic bulk acoustic wave (BAW) resonators manufactured from plates of piezoelectric lithium niobate. The intrinsic competing loss mechanisms were studied at cryogenic temperature through precision measurements of various BAW modes. Exceptional quality factors were measured for the longitudinal BAW modes in the 1-100 MHz range, with a maximum quality factor of 8.9 million, corresponding to a quality factor $\times$ frequency product of 3.8 $\times 10^{14}$ Hz. Through measurements of the acoustic response to a strong drive tone, anomalous self induced absorption and transparency effects are observed. We show that such observations can be explained by microscopic impurities and defect sites in the crystal bulk by the use of a non linear model of acoustic dissipation. The losses associated with these defects provide the ultimate limit of resonator performance, which could be improved in the future if more pure samples were available.