Basic Research on Combinatorial Evaluation Method for Coefficient of Thermal Expansion
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Basic Research on Combinatorial Evaluation Method for Coefficient of Thermal Expansion Yuko Aono1, Seiichi Hata2, Junpei Sakurai1, Ryusuke Yamauchi1, Hiroyuki Tachikawa1, and Akira Shimokohbe1 1 Precision and Intelligence Laboratory, Tokyo Institute of Technology, R2-37, 4259 Nagatsuta, Midori-ku, Yokohama, 226-8503, Japan 2 Frontier Collaborative Research Center, Tokyo Institute of Technology, S2-8, 4259 Nagatsuta, Midori-ku, Yokohama, 226-8503, Japan ABSTRACT The coefficient of thermal expansion (CTE) is one of the most important material properties for many applications such as actuators driven by heat or structure over a wide temperature. The CTE of an alloy depends on its composition, and combinatorial methods are very effective for researching new alloys. A CTE evaluation method, which can be applied to small samples (1×1 mm2) in a thin film library, is proposed in this paper. The thermal behavior of a bi-layer cantilever couple was used for the evaluation, and the Young’s modulus, which is also an important property, was simultaneously obtained. Firstly, one bi-layer cantilever was fabricated and agreement of the thermal behavior with the theoretical behavior was confirmed. The estimated error generated by the measurement device (CCD camera) resolution was then analyzed. The results indicate that combinatorial evaluation does not enable an accurate evaluation of Young’s modulus, but does allow the CTE be accurately determined.
INTRODUCTION Recently, many micromechanical systems (MEMS) actuators have been developed. Some of these actuators utilize the thermal behavior of a material, and require nano-level precision, so that thermal expansion is very important for these devices [1,2]. The coefficient of thermal expansion (CTE) is one of the primary values that describe the thermal behavior of materials. The CTE of alloys depend on the material composition, but this dependence has not been systematically investigated, to a sufficient extent; therefore, this dependence was investigated using the combinatorial method. The combinatorial method is a systematic material investigation method. Samples of various compositions are deposited on one substrate, and this is referred to as a library, and each sample of the library is evaluated, so that desirable materials with certain composition can be found efficiently [3,4]. A combinatorial arc plasma deposition (CAPD) device was developed which has three arc plasma guns that are set in three directions, so that a continuous compositionally-grated thin film is made from three elements. This thin film is divided into 33×33 samples (1 sample size is 1×1 mm2) for use as a thin film library as shown in Figure 1 [5]. The object of this research is a fundamental CTE evaluation that can be applied to the thin film combinatorial method. There are three objectives in using a thin film library for this CTE evaluation;
1. Evaluation using small, within 1×1 mm2, thin film structures, 2. High-throughput evaluation, 3. Obtaining relative values in a library. A micrometer
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