A micro sensor chip of High-field Asymmetric Waveform Ion Mobility Spectrometry(FAIMS) was designed and fabricated by inductively coupled plasma(ICP) etching on the both sides of silicon and double silicon-glass bonding,with dimensions of 18.8 mm×12.4 mm×1.2mm.The sample ions were created at ambient pressure by VUV lamp ion source,which was equipped with a 10.6 eV photo discharge lamp(λ=116.5 nm).The 2-pentanone was adopted to illustrate the influences of high-field rectangular asymmetric waveform voltage amplitude,frequency and carrier gas flow rate on the performance of FAIMS sensor chip.The experiment results showed that with the frequency or carrier gas flow rate increasing,or voltage amplitude decreasing,the FAIMS sensitivity increases,and that the resolution decreases with the increasing of the frequency or flow rate.The FAIMS simulation results based on the SIMION software was in agreement with the experimental results.The FAIMS detection sensitivity experiment showed that the FAIMS sensor chip can detect positive and negative ions simultaneously,and has detection sensitivity as low as 0.1 ppm for acetic acid.
TANG FeiLI HuaWANG XiaoHaoYANG JiZHANG LiangWANG Fan
An array micro Faraday cup ion detector for FAIMS (High-field Asymmetric Waveform Ion Mobility Spectrometry) was introduced, with which the size of the FAIMS system was reduced. With simple structure, good stability, low noise, large measurements range, this detector can work under the condition of atmospheric pressure. The array micro Faraday cup was composed of gate electrode, sensitive electrode and shielding electrode. The sensitive electrode was made of tens of crossing silicon columns with diameter of 200 μm. It was fabricated through typical MEMS technology, which was compatible completely with plane FAIMS. It was shown from FLUENT simulation result that the resistance to gas motion was low and the flow field distribution was helpful for full absorption of the ion in this array design. Through electricity simulation, the method to reduce interference on the detection signal of the micro Faraday cup was given out. Connecting with KEITHLEY 237 ampere meter, the noise level of the array micro Faraday cup was lower than 0.5 pA. The output signal of the acetone sample measured by experiment was about 210 pA. Through contrast experiment, the design parameter of the micro Faraday cup was obtained primarily. This array micro Faraday cup can meet the requirements of the FAIMS system.
TANG Fei, WANG XiaoHao, ZHANG Liang & YAN ZiLin State Key Laboratory of Precision Measurement Technology and Instruments, Department of Precision Instruments and Mechanology, Tsinghua University, Beijing 100084, China
