Monotonic and fatigue testing of spring-bridged freestanding microbeams application for MEMS

TL;DR

This study introduces a novel micro-tensile testing method for freestanding thin films in MEMS, demonstrating its application on gold, copper, and tantalum nitride films to understand their mechanical behaviors.

Contribution

The paper presents a new electroplating spring-bridge micro-specimen and testing setup for accurate monotonic and fatigue testing of sub-micron freestanding thin films in MEMS.

Findings

Gold, copper, and tantalum nitride films were successfully tested.

The testing method provides precise mechanical behavior data for MEMS materials.

Fabrication process for micro-specimens was detailed and reproducible.

Abstract

Microelectromechanical systems (MEMS) technologies are developing rapidly with increasing study of the design, fabrication and commercialization of microscale systems and devices. Accurate knowledge on the mechanical behaviors of thin film materials used for MEMS is important for successful design and development of MEMS. Here a novel electroplating spring-bridge micro-tensile specimen integrates pin-pin align holes, misalignment compensate spring, load sensor beam and freestanding thin film is demonstrated and fabricated. The specimen is fit into a specially designed micro-mechanical apparatus to carry out a series of monotonic tensile testing on sub-micron freestanding thin films. Certain thin films applicable as structure or motion gears in MEMS were tested including sputtered gold, copper and tantalum nitride thin films. Metal specimens were fabricated by sputtering; for tantalum nitride film samples, nitrogen gas was introduced into the chamber during sputtering tantalum films on the silicon wafer. The sample fabrication method involves three steps of lithography and two steps of electroplating copper to hold a dog bone freestanding thin film. Using standard wet etching or lift off techniques, a series of microtensile specimens were patterned in metal thin films, holes, and seed layer for spring and frame structure on the underlying silicon oxide coated silicon substrate. Two steps of electroplating processing to distinct spring and frame portion of the test chip. Finally, chemical etched away the silicon oxide to separated electroplated specimen and silicon substrate.