A low-leakage 3-way silicon microvalve

Abstract

This thesis presents an electrostatically actuated silicon microvalve designed for use in a miniature gas chromatography system for sample preparation and injection. In contrast to prior art, this design combines an integrated low voltage electrostatic microactuator as well as tight sealing capability. The device uses only silicon and silicon dioxide, which allows it to be used in a gas chromatography system for a wide range of chemically compatible gases. Using a 3-way design, the valve can switch an input gas flow to either of two output ports, which helps reducing wafer space consumption if used in a valve array, by combining two 2-way on/off valves into one device. After a thorough discussion of prior art in microvalve technology, the design and modeling of the microvalve is presented. A detailed discussion of the microfabrication issues is given, along with a final process plan. One-sided prototype valves were fabricated and their performance was characterized. Leakage rates on the order of 10⁻⁶ atm-cc/sec have been measured. The prototype valves are capable of switching inlet pressures of typically 8 psi with open flow rates of 8 sccm Nitrogen at an operation voltage of 23 V.