CHARACTERIZATIONS OF METALLIZED PLASTIC MEMS Charles Chu, Mark Bachman, Yuh-Min Chiang, Fernando Gonzales, G. P. Li Department of Electrical and Computer Engineering, University of California at Irvine, Irvine, CA 92697-2625 ABSTRACT Metallization of plastic devices is of interest to newer non-silicon based MEMS which are being developed for biomedical and other applications. The electrical properties of the metallization will depend, in part, on the material on which they are patterned, and the method of deposition. Of interest are the electrical characterizations during usage which must be studied to allow plastic MEMS designs to proceed wisely. Flexible microdevices may develop open circuits or shorts after excessive bending; joule heating may adversely affect the plastic substrates, leading to failure. We present some experimental studies on electrical characterization of metallized plastics as it relates to various processing conditons and usage scenarios. INTRODUCTION Polymer-based MEMS are of interest for fabricating biomedical devices. Such devices currently employ the use of molding or stamping to create microchannels for fluidic delivery in plastic materials. Example applications are capillary electrophoresis chips and the so called "lab on a chip", where chemicals are delivered to specific reaction chambers at specific times and in a predetermined order [1, 2]. A natural addition to such chips is the deposition of conductive traces and metals to deliver electrical energy for on-chip sensors or actuators. The use of conductive traces in plastic is not new-they have been successfully deployed in flexible circuits for many years [3, 4]. However, these tend to be rather thick conductive traces, on the order of several tens of microns thick. For plastic MEMS devices (which are only a few tens of microns high), very thin layers of conductive traces are required. Such thin layers (a few thousand angstroms) are required to allow for precise patterning, and to enable sealing of fluidic layers. An example device is shown in Figure 1. For biomedical applications, the surface chemistry of the material may be of great importance, and this should be taken into account when determining a metallization procedure [5]. If a metallization process changes the surface chemistry of the polymer, it may negate the reason the polymer was chosen. Furthermore, surface treatments required for metallization may make the plastic unsuitable for subsequent application of biological materials such as antibodies [3, 4]. In general, one hopes for a metal deposition (and subsequent patterning) approach which minimizes the chemical activity on the surface of the polymer. Figure 1: Capillary electrophoresis chip made from gold, silicone and polystyrene. 97 Mat. Res. Soc. Symp. Proc. Vol. 605 © 2000 Materials Research Society