Monolithical integration of polymer-based microfluidic structures on application-specific integrated circuits

Abstract

In this paper, a concept for a monolithically integrated chemical lab on microchip is presented. It contains an ASIC (<b>A</b>pplication <b>S</b>pecific <b>I</b>ntegrated <b>C</b>ircuit), an interface to the polymer based microfluidic layer and a Pyrex glass cap. The top metal layer of the ASIC is etched off and replaced by a double layer metallization, more suitable to microfluidic and electrophoresis systems. The metallization consists of an approximately 50 <i>nm</i> gold layer and a 10 <i>nm </i>chromium layer, acting as adhesion promoter. A necessary prerequisite is a planarized ASIC topography. SU-8 is used to serve as microfluidic structure because of its excellent aspect ratio. This polymer layer contains reservoirs, channels, mixers and electrokinetic micro pumps. The typical channel cross section is 10<i>&#956;m</i>•10<i>&#956;m</i>. First experimental results on a microfluidic pump, consisting of pairs of interdigitated electrodes on the bottom of the channel and without any moving parts show a flow of up to 50<i>&#956;m </i>per second for low AC-voltages in the range of 5 V for aqueous fluids. The microfluidic system is irreversibly sealed with a 150<i>&#956;m </i>thick Pyrex glass plate bonded to the SU-8-layer, supported by oxygen plasma. Due to capillary forces and surfaces properties of the walls the system is self-priming. The technologies for the fabrication of the microfluidic system and the preparation of the interface between the lab layer and the ASIC are presented.