More-than-Moore Microacoustics: A Scalable Fabrication Process for Suspended Lamb Wave Resonators

TL;DR

This paper introduces a scalable fabrication process for suspended Lamb wave resonators using Deep Ultraviolet Photolithography, achieving high frequency, good uniformity, and potential for mass production in RF applications.

Contribution

It presents a novel process flow combining DUV photolithography, anti-reflective coatings, and ion beam etching for scalable production of high-frequency Lamb wave resonators.

Findings

Resonance frequencies up to 7.5 GHz achieved

Electromechanical coupling up to 8% measured

Wafer surface deviation of the S0 mode kept below 1%

Abstract

Deep Ultraviolet (DUV) Photolithography is currently used to fabricate mass-scale integrated circuits (ICs). Its high throughput and resolution could benefit large-scale RF MEMS production for the telecommunication market. We present a process flow to fabricate suspended acoustic resonators using DUV Photolithography. This method allows for scalable production of resonators with critical dimensions of 250 nm and alignment accuracy of less than 100 nm. We show how photoresists and anti-reflective coatings integrate with the process, help with deposition quality and resolution, and how Ion Beam Etching allows for vertical sidewalls of the resonators. We measure resonance frequencies (fr) up to 7.5 GHz and electromechanical couplings up to 8%, and we investigate the uniformity of this process by analyzing the deviation of fs over the wafer surface for four main resonance modes. We show that the deviation of the S0 mode can be kept below 1%. These results indicate the suitability of this process for quick scale-up of Lamb wave resonator technology, bridging the gap from research to industry.