A novel architecture for a lab-on-a-chip is presented. The architecture consists of a microfluidic system including integrated optical sensors and thin film transistors. The concept is based on the TFA (Thin Film on ASIC) technology that was developed at University of Siegen. The device consists of two substrate plates that are sandwiched together using oxygen plasma bonding. The thicker bottom plate contains the contacts to the microfluidic channels, while the thinner top plate contains the microfluidic system. The top plate is bonded face down onto the bottom substrate, and, on its reverse side, hydrogenated amorphous silicon (a-Si:H) based pin-diodes and thin film transistors (TFTs) are deposited for optical detection and data transfer. The pin-diodes and the TFTs are manufactured by PECVD (Plasma Enhanced Chemical Vapor Deposition) from silane, ammonia and dopant gases at temperatures around 200°C. Sputtered ZnO:Al is used as semitransparent front contact for the diodes, while Al and Cr are used as contacts to the transistors. The TFTs are used as switches to read out an array of pin-diodes. Experimental results for an electrokinetic microfluidic pump and the a-Si:H devices are reported. Further developments and potential applications for microanalysis are outlined.
In this paper, a concept for a monolithically integrated chemical lab on microchip is presented. It contains an ASIC (Application Specific Integrated Circuit), 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 nm gold layer and a 10 nm 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 10μm•10μm. 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 50μm per second for low AC-voltages in the range of 5 V for aqueous fluids. The microfluidic system is irreversibly sealed with a 150μm 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.