Gold microelectrodes fabricated by a print-and-imprint method using laser-drilled polyimide through-hole masks

Abstract

Multiple sets of gold (Au) four-terminal microelectrodes comprising 100 μm-scale pad electrodes and 20 μm-wide lead lines were fabricated on a silicon substrate by a print-and-imprint method involving laser drilling and screen printing. Laser drilling of 12.5 μm-thick polyimide (PI) sheets with a picosecond-pulse laser enabled the fabrication of PI membranes with designed patterns of through holes. The through holes had a frustum shape, and the average hole diameters on both the laser entry and exit sides of the PI films enlarged with an increase in the applied repetition rate. The hole patterns designed with submicrometer position accuracy were prepared using a linear motor stage. Liquid ultraviolet (UV)-curable resin, exhibiting a high viscosity (11.0 Pa s) and a high dry-etching resistance to argon (Ar) ion beam milling after UV curing, was placed onto a substrate surface as droplets by screen printing, corresponding to the hole patterns of the PI through-hole masks. The average volume of the liquid droplets could be tuned in the range of 0.02–0.54 pl, which depended on the volumes of the laser-drilled frustum holes. The volumes of liquid resin necessary to fill the mold recesses were adjusted site-selectively by the number of resin droplets printed on a metal-deposited substrate surface. Fluorescence microscopy with a fluorescent dye-doped resin indicated that the imprinted resist patterns had a residual layer thickness in the range of 15–28 nm. The Au electrodes with a 30 nm-thickness could be fabricated by subsequent Ar ion beam milling and removal of a sacrificial metal layer.