Electrodeposition of Refractory Metals in Medium-Temperature Molten Salts

LIGA process, a microfabrication technique consisting of a lithography and an electroforming, has attracted considerable attention. The authors believe that electrodeposition of refractory metals such as W, Mo, Ta in molten salts is a very promising method for the electroforming step of LIGA process owing to their high hardness and high mechanical-strength. If this method is realized, it would extremely contribute to the technical development of the Micro-Electro-Mechanical Systems (MEMS). Senderoff and Mellors have obtained refractory metals in fluoride melts at 700-850°C[1, 2]. Katagiri et al. have obtained W metal at 350-450°C using ZnCl2-NaCl and ZnBr2-NaBr melts[3, 4]. However, LIGA process requires the electroforming step under 250 °C due to the limit of heat resistance of a resist sheet made of polymethylmethacrylate (PMMA). Electrodeposition of refractory metals in molten salts under 250 °C has not been reported so far. The aim of the present work is to obtain refractory metals by electrodeposition in molten salts at mediumtemperatures around 250 °C.