The evaluation of Young's modulus and residual stress of nickel films by microbridge testings

Abstract

The variation of deflection and maximum stress of a nickel film microbridge with load was investigated over a wide range of length, thickness, elastic modulus and residual stress by both large and small deflection theories of microbridge testings. The limits of deflection and load for a microbridge to be deformed elastically were determined by the assumption that the maximum stress could not be more than the yield strength. Furthermore, the deflection and load limits of small deflection theory were decided by setting a threshold beforehand for the normalized deflection and maximum stress difference between large and small deflection theories. Based on the results above, the dimensions of the nickel microbridge samples were chosen and the deflection range suitable for the small deflection theory was calculated. The nickel film microbridge samples electroplated on a Si(100) substrate were fabricated by MEMS and the microbridge testings were conducted with a load and displacement sensing nanoindenter system. From small deflection theory, the Young's modulus and residual stress for the electroplated nickel films were calculated and the results were 190.5 GPa and 86.6 MPa, respectively.