A New Test Structure to Determine the Poisson's Ratio of Thin Films Using Resonant Method
Date Issued
2005
Date
2005
Author(s)
Lu, Chih-Chan
DOI
zh-TW
Abstract
In this study, a novel crisscross-shaped micro test structure to characterize the Poisson's ratio of thin film materials is proposed. In micro-electro-mechanical-system （MEMS）fabrication technology, the surface micromachining means that the deposition, growth, and etching of thin films are processed on the surface of a substrate. The residual stress is one of the important issues to influence the behavior of thin films. This issue must be considered seriously when designing, fabricating, and analyzing the micro devices used film materials. The basic material properties, such as Young’s modulus and Poisson's ratio, are almost used in the analysis of residual stresses in practice. The material properties of thin films are usually different from those of bulk materials, and it is crucial to determine the mechanical properties of thin films to not only predict the performance but also enhance the reliability and yield of MEMS devices. There are very few investigations regarding the characterization of Poisson's ratio of thin films compared with Young’s modulus. This thesis starts with basic mechanics of materials and vibration analysis, and presents a novel crisscross-shaped test key to facilitate the measurement of the Poisson's ratio of thin films. Through exciting the microstructure and measuring the bending and torsional vibration modes, the Poisson's ratio can be determined directly. With the combination of test keys and optical measurement system which is electronic speckle pattern interferometry（ESPI）, they construct a measurement process, and are expected to provide a feasible way to extract the Poisson's ratio of thin film materials.
The primary advantage of this design is that it decouples the bending and torsional vibration modes without measuring the thickness of the thin films precisely, so it is easy and fast to measure the resonant frequencies, and to achieve the purpose of nondestructive measurement. This method is feasible for on-line inspection of mass production in MEMS industry. The detail theory and simulation will be explained clearly and the issues of design, fabrication, and experiment results are also proposed by using silicon on insulator（SOI）wafers as the substrates. The bulk and surface micromachining are included in fabrication process, and the rich experiences of using dry and wet etching techniques could be the dependable references for releasing MEMS devices afterward.
Subjects
薄膜
卜松比
微機電系統
機械性質
Thin films
MEMS
Mechanical properties
Type
thesis