Fabrication of multiple height microprobes using UV lithograhy on timed-development-and-thermal-reflowed photoresist

Abstract

A three dimensional (3-D) microprobe array with multiple heights has been fabricated using the timed-development-and-thermal-reflow (TDTR) process and an additional UV lithography process. After the TDTR process, the reflowed polymer profiles between the substrate and a micro wall are differing as a function of the development time and the surface properties of the side wall such as hydrophobicity and the contact angle between the wall and the reflowed polymer, resulting in a convex, linear, and concave shape. A polymeric micro slab array with continuously varying heights and a micropillar array with multiple heights, where the overall surface profile follows the reflowed surface after the TDTR step are successfully demonstrated. As an application, a 2 x 5 microprobe array with linearly changing multiple heights and metallic signal traces has been fabricated for 3-D neural probing and stimulation. Three different microprobe sets with a pillar diameter of 40μm and a different probe height range of 381µm to 482μm, 97μm to 164μm, and 21μm to 60µm, have been also demonstrated. DC resistance property of a probe has been tested.