Residual Stress Anisotropy In Thin-Film Lithium Niobate For Stress-Managed MEMS

TL;DR

This study experimentally characterizes residual stress anisotropy in thin-film lithium niobate, revealing orientation-dependent stress-free directions that enable the fabrication of long, stable MEMS beams.

Contribution

First experimental mapping of in-plane residual stress anisotropy in TFLN, linking orientation and thickness to stress management and beam stability in MEMS.

Findings

Identified stress-free orientations near 55° and 125° for thicker films.

Achieved long suspended beams up to 2 cm without collapse.

Demonstrated stress anisotropy as a design tool for MEMS stability.

Abstract

In this work, we present the first experimental study of residual stress and post-release beam deflection in 128-degree Y-cut thin-film lithium niobate (TFLN) on Si, revealing pronounced stress anisotropy with in-plane orientation. Using optical profilometry with curvature fitting, we extract the stress gradient (sigma1) and generate orientation-resolved stress maps across multiple film thicknesses (100 nm, 220 nm, and 460 nm). For films in the 220 to 460 nm range, we identify stress-free in-plane orientations near approximately 55 degrees and 125 degrees, enabling extremely flat suspended beams. In contrast, ultra-thin 100 nm films exhibit shifted stress-free orientations near approximately 20 degrees and 160 degrees. Leveraging these orientations, we demonstrate very long suspended beams up to 2 cm in length, 10 micrometers in width, and 460 nm in thickness without collapse. These results establish in-plane stress anisotropy and thickness selection in TFLN as practical design levers for mechanically stable, scalable, and stress-managed microelectromechanical systems (MEMS).