Thermal and Electrical Conductivities of Nanocrystalline Nickel Microbridges

DC electrical self-heating (Joule heating) is exploited to characterize the thermal behavior of Ni microbridges. The temperature rise of the devices due to self-heating is monitored using an infrared microscope for current densities up to 10⁵ A/cm². The obtained temperature profiles reveal significant heating at the bases of the microbridges. Simulations are performed in order to extract the thermal conductivity of the electroplated Ni thin film from the experimental data. The thermal conductivity is found to be 78.8 W/m · K or 13% less than that of bulk Ni. As current flows through the microbridges, they deflect upward, significantly changing the system response and pull-in voltage required for actuation. Additionally, the electrical resistivity and specific electrical contact resistances between the microbridges and the anchor points are reported. The electroplated Ni is found to have an electrical resistivity of 9.7 μΩ · cm which agrees with other values in the literature for thin-film Ni. By combining the electrical and thermal measurements, it is possible to determine the phonon and electron contributions to thermal conductivity. Although demonstrated on Ni films, this technique can be applied to any metallic film without modification. Such characterization of transport properties of constituent materials is important in the modeling of microelectromechanical systems and enables device performance to be predicted with improved accuracy.