| Summary: | 碩士 === 國立清華大學 === 材料科學工程學系 === 93 === In last few decades, the applications of thin film have become more and more widely. In order to guarantee the long-term operation according to their specification, mechanical properties of thin film are highly desirable. Unfortunately, as the scale level of film structure decreasing, it becomes increasingly difficult to measure its mechanical properties.
Bulge test is a useful method for characterize mechanical properties in thin films. In bulge test, a pressure is applied to the backside of the thin film uniformly, making the free-standing thin film to deflect. By measuring the pressure applied and the deflection height of the thin film, a Pressure vs. deflection height curve can be obtained and mechanical properties of the film are determined from the curve fitting process. In bulge test, the accuracy of the measurement is significantly influenced by the sample geometry. The process of free-standing thin film fabrication will be described in this thesis. A big advantage of this test over other micromechanical test lies in the relatively simple stress-strain state in the sample since the stress state in the film is biaxial.
We apply bulge test to measure mechanical properties of polymeric thin film with thickness from several tenth to several hundredth nanometer. In this thesis, the polymeric thin film we tested is mr-I 8030 (Micro Resist Technology) which is used in nanoimprint lithography. The results are compared with data obtain by nanoindentation. The Young’s moduli measured by nanoindentation are about 20% to 50% greater than those measured by bulge test. This result can be viewed as the effect of substrate and the densification of thin film material under indent point.
We also introduce a method to estimate Poisson ratio of thin film material. Poisson ratio, ν, can be calculated from the relationship between biaxial modulus and plane strain modulus. This idea can be carried out by conducting bulge test on square and long rectangular free-standing thin films.
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