Deposition growth direction Loading (a) In-plane type Deposition growth direction Loading (b) Out-of-plane type Figure 5: Schematic images of columnar structure aligned towards the growth direction in the elecroless deposited Ni-P amorphous alloy thin film. growth direction. The difference in KQ values and fracture surfaces between these two specimens suggests that there is some ordering towards the growth direction. Actually, anisotropic magnetic properties have been often observed for sputtered and deposited amorphous thin films [10]. Consequently, there may exist some columnar type domain structures oriented towards the deposition growth direction as schematically shown in Fig. 5. Actually, such a columnar structure was observed for electro-deposited amorphous Fe-P alloys [11]. If there is such a columnar structure aligned towards the growth direction, the cantilever specimens have an anisotropy. This may be one reason that the KQ of the out-of-plane specimen is higher compared to that of the in-plane specimen. CONCLUSIONS Fracture tests have been performed on micro-sized cantilever beam specimens prepared from an electroless plated Ni-P amorphous alloy thin film. Two types of specimens with different crack growth directions, which are perpendicular and parallel to the deposition growth directions, were prepared to investigate anisotropic fracture behavior of the thin film. Fracture behavior is different between the two types of specimens. As KIC values were not obtained because the criteria of plane strain were not satisfied for this micro-sized specimen, the provisional fracture toughness KQ values were measured. The KQ value of the specimen with crack propagation direction being parallel to the deposition growth direction was 7.3 MPam1/2, while that with crack propagation direction perpendicular to the deposition growth direction was 4.2 MPam1/2. This result suggests that the electroless plated Ni-P amorphous alloy thin film has anisotropic fracture properties. It is important to consider the anisotropic fracture behavior when designing actual MEMS devices using electroless deposited amorphous films. Acknowledgment – This work was partly supported by the Grant-in-Aid for Scientific Research (B) (2) No. 12555186 from the Ministry of Education, Science, Sports and Culture, Japan. REFRENCES 1. Lewis D. B. and Marshall, G. W. (1996) Surface and Coating Tech., 78, 150. 2. Ichikawa, Y., Maekawa, S., Takashima, K., Shimojo, M., Higo, Y. and Swain, M. V. (2000). In: Materials Science of Microelectromechanical Systems (MEMS) Devices II, pp. 273-278, deBoer, M. P., Heuer, A. H., Jacobs, S. J. and Peeters, E., (Eds). The Materials Research Society, Pennsylvania.
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