A Mems Electrostatic Particle Transportation System

We demonstrate here an electrostatic MEMS system capable of transporting particles 5-10pm in diameter in air. This system consists of 3-phase electrode arrays covered by insulators (Figs. I , 2). Extensive testing of this system has been done using a variety of insulation materials (silicon nitride, photoresist, and Teflon), thickness (012pm), particle sizes (11 Opm), particle materials (metal, glass, polystyrene, spores, etc), waveforms, frequencies, and voltages. Although previous literature [ 1-21 claimed it impractical to electrostatically transport particles with sizes 5-10pm due to complex surface forces, this effort actually shows it feasible (as high as 90% efficiency) with the optimal combination of insulation thickness, electrode geometry, and insulation material. Moreover, we suggest a qualitative theory for our particle transportation system which is consistent with our data and finite-element electrostatic simulations. regime the electrostatic forces that can be exerted on the particle are of the same magnitude as the adhesive forces between the particle and the solid surface. Numerous researchers have noted this size range cutoff; for example, Novick et a1 [2] have noted that the sub 10pm range presents a different regime where surface adhesive forces and particle charging hinder the successful engineering of a robust particle transport system. The goal of this work then, is to reexamine this difficult task and design a dielectrophoretic (DEP) particle transportation system [3-51 capable of moving particles below 10pm in air with low voltages. Our work emphasizes a three-phase electrode array with specific insulative films. It is found that these films enable us to not only repeatably demonstrate motion for 5 and 8 uni particles, but reveal a novel phenomenon the strong dependence of particle transportation efficiency with film thickness. In addition, computer simulation of DEP force on the particle is consistent with our observations and hypothesis. INTRODUCTION FABRICATION The ability to transport and manipulate particles in air is desirable in many instruments such as airborne particle samplers, particle sorters, and electrostatic particlecleaning apparatuses. There are many different ways to transport particles larger than 10 pm such as forced air jets, centrifuges and other mechanical means. However for particles ranging from 1 to 10 pm, there is still no efficient way to transport them because complex surface forces, instead of gravitational force, dominate. This attribute has long been a bottleneck for the development of automated airborne pollutant samplers for biological spores, dust particles, and chemical agents because their sizes fall into the 1-10 ym range. In the past, successful transportation of sub 10 pm particles has been accomplished in the liquid medium, but not on a solid surface in air. In air, Moesner and Higuchi [3] and Balachandran et a1 [4] have demonstrated motion of larger particles with voltages up to a few kV. Unfortunately, in the sub 10 pm The particle transportation chip was developed in using standard microfabrication processes. The process basically consists of depositing two insulation layers and two conductive layers for a three-phase network of electrodes. A cross-sectional view of a finished electrode panel is shown below. (Fig. 1)