Electrical contact resistance performance of precious-metal-electroplated carbon nanotube films under micro loads

Radio frequency-microelectromechanical system (RF-MEMS) switches, which use physical Ohmic contacts, are recently focused for high performance in the high-frequency ranges. Typically, the contact areas of the electrodes in RF-MEMS switches are less than 0.01 mm(2), and they generate just very low normal loads of less than 1 mN. The limited real contact area of the electrodes leads to high electrical contact resistances and wear on the switches. Carbon nanotube (CNT) films, formed with many vertically aligned CNTs on a silicon substrate, are one candidate electrode material for RF-MEMS switches. However, CNT films have a high electrical contact resistance with metals. In this study, precious-metal electroplating (Ag, Au, Pt, Rh, and Cu) on CNT films was performed to decrease the electrical contact resistances of the films and increase their wear resistances. The contact resistances of the electroplated CNT films as a function of normal loads up to 1 mN were measured by phi 2 mm Cu balls. In this study, the Ag-electroplated CNT film with a hydrogen annealing had the lowest electrical contact resistance of 0.10 Omega. Durability experiments of cyclic connection switching were conducted under direct applied voltages of 3 V or 10 V between the films and Cu balls, and with a load of 1 mN for 3 x 10(5) cycles. The electrical contact resistance of the Ag-electroplated CNT film with the hydrogen annealing was stable during this durability experiment.