MEMS-based High Field Asymmetric Waveform Ion Mobility Spectrometry Research

High-Field Asymmetric Waveform Ion Mobility Spectrometry(FAIMS)is an analytical technique based on the principle of non-linear electric field dependence of coefficient of mobility of ions for separation,and was originally conceived in the Soviet Union in the early 1970s.Being well developed over the past decades,FAIMS has become an efficient method for the separation and characterization of gas-phase ions at ambient pressure,often in air,to detect trace amounts of chemical species including explosives,toxic chemicals,chemical warfare agents and other compounds.However the resolution of FAIMS and ion separation capability remain relatively low and poor compared to other analytic techniques,improvement of ion separation and resolution become the most important issues for FAIMS applications.The development of High-Field Asymmetric Waveform Ion Mobility Spectrometry(FAIMS)is based on micro-electromechanical system(MEMS)technology,and the research divides into three parts:the chip design for FAIMS,circuit design for FAIMS and the front-end mechanical design.Two kinds of fabricated FAIMS chip is designed:based on DRIE and based on LIGA.Circuit design includes high frequency and high voltage RF power circuit,transimpendence amplifier,sensor control circuit and etc.The front-end mechanical design provides channel for gas ionized and separated.Based on above,the effect of above-ambient pressure varying from 1 to 3 atm on peak position,resolving power,peak width,and peak intensity are investigated theoretically and experimentally in purified air.It is demonstrated that ion Townsend-scale peak positions remain unchanged for a range of pressures investigated,implying higher the pressure is,stronger compensation and separation fields are needed within limits of air breakdown field.Increase in pressure is found to separate ions that couldn't be distinguished in ambient pressure.Increase in pressure can also result in the increase of peak intensity.