HYBRID FABRICATION OF MICROFLUIDIC CHIPS BASED ON COC, SILICON AND TMMF DRY RESIST Kiril Kalkandjiev 1 , Roland Zengerle 1 and Peter Koltay 1,2 1 University of Freiburg - IMTEK, Germany 2 BioFluidiX, Freiburg, Germany ABSTRACT We describe the hybrid fabrication of silicon-plastic microfluidic chips based on machining of Cyclic Olefin Copolymer (COC), standard silicon process- ing and TMMF lithography. The combination of different processes enables an individual material selection leading to significant reduction of the manufacturing costs. We demonstrate the potential of the hybrid technology by manufacturing and testing a 24-channel TopSpot dispenser [1] which consists of an intermediate silicon layer, a COC interface and a TMMF sealing lid. Characterization studies show that TMMF lamination is ideally suited for the sealing of silicon microchannels showing numerous advantages over adhesive-based approaches, thermal and anodic bonding. INTRODUCTION In contrast to sensor devices manufactured in batches of thousands, BioMEMS devices are often requested in smaller numbers, which makes low- cost fabrication challenging. While silicon proc- esses go for higher densities and sub-micron struc- tures, the size of a typical microfluidic device is given by the relatively large interface that requires thicker materials for operation with laboratory-scale equipments [2]. As a result, polymer techniques have been adapted for the requirements of BioMEMS. The main advantages of polymers – lower cost compared to silicon and glass, wide range of available materials and suitability for pro- totyping and high-volume production, have been frequently pointed out [3-5]. On the other hand, silicon components have the advantage of higher accuracy as a consequence of the established MEMS processes. Silicon is the material of choice when components with high-aspect ratio, sharply defined edges or high mechanical stiffness are re- quired. It is furthermore advantageous when it comes to the integration of sensing or actuating elements [6]. Silicon micromachining is often combined with silicon-Pyrex anodic bonding to provide the chip with the necessary peripheral components. The machining of Pyrex, however, together with the anodic bonding and dicing of the stacked assembly is a time-consuming process that accounts for a very significant part of the manufacturing costs. At the same time, the properties of the Pyrex compo- nents and the high quality of the anodic bond are not necessarily required for a typical lab-on-a-chip. Thus, silicon-plastic hybrid integration approaches should be considered as an open alternative for cost saving. A major aspect of the hybrid integration is the precise alignment and liquid-tight bonding of components possessing different chemical nature. Usually, bonding of dissimilar materials is based on the use of adhesives. In microfluidics, however, direct bonding is more popular [7] but it is mostly restricted to materials of the same type. Few methods for direct silicon-plastic bonding such as localized heating with resistive heaters [8,9], plasma-assisted silicon-PDMS bonding [10], me- chanical interlocking [11] or bonding of polymer to a black-silicon surface [12] have been reported to be suitable for the fabrication of hybrid liquid-tight assemblies. In this paper, we describe an alternative fabrication technique using TMMF dry resist as a sealing lid for silicon microchannels and an adhesive tape (3M 9965) for bonding of the silicon core to a COC interface. Finally, we show the application of this technique to the manufacturing of 24-channel Top- Spot printheads used for the formation of microar- rays [1]. FABRICATION The printhead contains 24 reservoirs which can be filled with different samples using standard labora- tory equipment. Each reservoir is connected to a corresponding nozzle via a capillary microchannel. The nozzles are arranged in a 6x4 grid with a pitch of 500 µm. A one-to-one format conversion from the 4.5 mm pitched reservoirs to the microarray format is provided by the microchannels. A piezo- driven piston generates a pressure pulse by com- pressing an air chamber which causes the parallel ejection of a single droplet out of each nozzle (Fig. 1). Figure 1: A schematic cross-section and operation principle of the hybrid TopSpot printheads. 978-1-4244-5763-2/10/$26.00 ©2010 IEEE 400