Luo, J.K., Pritschow, M., Flewitt, A.J., Spearing, S.M., Fleck, N.A. and Milne, W.I.
Effects of process conditions on properties of electroplated Ni thin films for microsystem applications.
Journal of the Electrochemical Society, 153, (10), . (doi:10.1149/1.2223302).
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The properties of electroplated Ni thin films have been systematically investigated as a function of plating temperature and current density. The resistivity and its temperature coefficient remain unchanged on varying the process conditions, though the values of these properties are approximately three times and one-half of those of bulk Ni material, respectively. Optimal conditions of J = 2 mA/cm(2) and 60 degrees C were found for stress-free Ni thin films. The modulus of elasticity of the Ni films is as high as that of bulk Ni (210 GPa) when plated at high temperature and low current density, and then decreases linearly with increasing plating current density, down to 85 GPa at a plating current density of 30 mA/cm(2). It is believed that higher plating rates produced fine-grained structures of low density, leading to a high tensile stress and low modulus of elasticity, while lower plating rates produced a dense material with a modulus of elasticity close to that of bulk Ni and a compressive residual stress. A clear correlation between modulus of elasticity and the stress exists, which reveals that a material under high tensile stress may posses a low modulus of elasticity, and is not suitable for fabrication of microelectromechanical systems devices.
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