2022-058 – Deep Smooth Etching to Realize Scalable RF MEMS in Lithium Niobate

Abstract

Background
Lithium niobate (LiNbO3, or LN) makes an excellent material of choice for a wide range of applications due to its exceptional piezoelectric, electro-acoustical, electro-optical, and non-linear optical properties. Different crystalline orientations of LN are heavily utilized for applications in surface-acoustic-wave (SAW) resonators, optical filters, optical sensors, modulators, transducers, optical waveguides, Q-switch lasers, oscillators, and more. At the nanoscale and micro-scale, device performance is often constrained by the fabrication quality of processed LN films. Unlike many semiconductors and dielectric materials, LN substrates are complex to process and are notoriously difficult to etch. Typically, a long plasma dry-etch is required to obtain high-aspect-ratio or deep etching profiles in LN substrates. Thus, there is a need for a successful LN etching process that manages factors including substrate heating, redeposition of the etching products and mask materials, and durability of the mask materials over the etching process.

Technology Description
Researchers at the University of New Mexico and Sandia National Laboratories have collaborated to develop a robust etching method to realize the first three-dimensional (3D) piezoelectric phononic crystals and high-quality stacked lithium niobate resonators. Such procedures propose to employ epitaxial transfer and lift-off and deposition techniques to build up laminated thin-film piezoelectric lithium niobate (LN) alternated with amorphous silicon. Interferometric lithography, wet and dry electron cyclotron resonance (ECR) etching, and contact lithography, can be used to etch layer-by-layer as the structure is stacked up, thus realizing pristine 3D phononic crystal at XBAND frequencies. This inductively coupled plasma dry etch process can obtain a deep etching profile in LN with minimum roughness and vertical sidewalls. In addition, quality metal masks can be achieved. Periodic interruption steps can be included in the plasma dry etch procedure followed by a chemical cleaning between each cycle to avoid thermal effect and minimize byproduct redeposition during the long etching process.

Website

https://unm.flintbox.com/technologies/D0F10825B4354A529DB08983E5B16FC9

Advantages

  • Deep etching in lithium niobate that obtains vertical sidewalls with minimal roughness
  • Avoids thermal effect and minimizes byproduct redeposition
  • Improved bonding process with increased surface energy and removal of contaminants

Potential Applications

  • High density radio frequency systems
  • Waveguide-based optical devices
  • Surface acoustic wave devices
  • Memory units and neuromorphic systems
  • Exotic nonlinear phononics

Contact Information

Name: Andrew Roerick

Email: aroerick@innovations.unm.edu

Phone: 505-277-0608