Electrostatic micro gas pumping for micro gas chromatography systems---Fabrication and experiments.

In a micro gas chromatography (mu-GC) system, micro-fabricated pumps are used to load gases to be sampled into a pre-concentrator, which increases the concentration of the targeted gases before injecting a plug into a separation column. In order for the system to function well, a continuous pumping of the sampling gas is important. In this research, electrostatic gas pump is realized with two controlling passive check valves. The actuator consists of an upper flexible conducting diaphragm and an annular-cavity shaped fixed electrode. The diaphragm has a Cr/Au/Cr layer sandwiched with ∼2.2 um thick Polyimide (PI) film, which is a structural and electric insulation layer. The bottom cavity silicon surface is p++ doped, and a dry SiO 2 is thermally grown on it to sustain high electric field for full zipping. Two unidirectional polyimide valves are used to control the gas flows. These valves are treated with hydrophobic CFn surface at the valve seat/membrane touching interface to reduce the in-use stiction and opening valve pressure. For the pump to perform as designed, the diaphragm has to fully zip and the inlet/outlet valves need to open and close as the diaphragm actuates. As an actuation compresses gas, the outlet valve should open with the inlet valve closed so that the gas flows out. As the diaphragm releases, the outlet valve closes and the inlet valve open, and the gas flows into the chamber. The volume of the pump chamber is 2∼6mul, and the full zipping actuation occurred at a voltage of 55∼270V depending on a diaphragm thickness. The valves have a conductance of larger than 1 sccm/kPa and a leakage of less than 0.002 sccm with opening pressures of 0.3∼3.48 kPa. The overall performance of a pump with two valves is investigated by pneumatic actuation as well as electrostatic actuation. The electrostatic actuation with two passive valves tends to suffer in-use stiction, and challenges and suggestions are made to overcome these problems. Successfully developed devices are tested with various actuation voltages and various duty cycles, and corresponding stroke volume and flow rates are measured.