# Phononic band structure engineering for high-Q gigahertz surface acoustic wave resonators on lithium niobate

## TL;DR

This paper introduces a design methodology for high-Q gigahertz surface acoustic wave resonators on lithium niobate, utilizing phononic band structure engineering to achieve high confinement, low loss, and small mode size, advancing quantum and signal processing applications.

## Contribution

The paper presents a novel phononic band structure engineering approach to create compact, high-Q gigahertz SAW resonators on lithium niobate with record high fQ products and minimal mode area.

## Key findings

- Q factors exceeding 2×10^4 at room temperature
- Mode area as low as 1.87 λ^2
- fQ product greater than 10^13

## Abstract

Phonons at gigahertz frequencies interact with electrons, photons, and atomic systems in solids, and therefore have extensive applications in signal processing, sensing, and quantum technologies. Surface acoustic wave (SAW) resonators that confine surface phonons can play a crucial role in such integrated phononic systems due to small mode size, low dissipation, and efficient electrical transduction. To date, it has been challenging to achieve high quality (Q) factor and small phonon mode size for SAW resonators at gigahertz frequencies. Here, we present a methodology to design compact high-Q SAW resonators on lithium niobate operating at gigahertz frequencies. We experimentally verify out designs and demonstrate Q factors in excess of $2\times10^4$ at room temperature ($6\times10^4$ at 4 Kelvin) and mode area as low as $1.87 \lambda^2$. This is achieved by phononic band structure engineering, which provides high confinement with low mechanical loss. The frequency-Q products (fQ) of our SAW resonators are greater than $10^{13}$. These high-fQ and small mode size SAW resonators could enable applications in quantum phononics and integrated hybrid systems with phonons, photons, and solid-state qubits.

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Source: https://tomesphere.com/paper/1901.09080