Electrically Modulated Microtransfer Molding for Fabrication of Micropillar Arrays with Spatially Varying Heights

The ability to generate a large area micropillar array with spatially varying heights allows for exploring numerous new interesting applications in biotechnology, surface engineering, microfluidics, and so forth. This Letter presents a clever and straightforward method, called electrically modulated microtransfer molding (EM3), for generating such unique microstructures from a silicon mold arrayed with microholes. The key to the process is an application of electrically tunable wettability caused by a spatially modulated voltage, which electrohydrodynamically drives a photocurable and dielectric prepolymer to fill the microholes to a depth depending on the voltage amplitude. Using EM3, micropillar arrays with stepwise or continuously varying heights are successfully fabricated, with the diameter scalable to 1.5 mu m and with the maximum height being equal to the depth of the high-aspect-ratio (more than 10:1) microholes.