Design Research Of MEMS Time-of-flight Mass Spectrometer Chip

The mass spectrometer is an analytical instrument,widely used in aerospace,bio-medical,emergency and food safety.With the development of China’s deep space exploration program,miniature mass spectrometers play an increasingly important role in space activities,either can be used to detect the surface of the gas composition of the planet or to monitor the environment in the space station.But a series of problems about space mass spectrometers still exist in terms of large size,high power consumption,large weight,which limits its further application in aerospace engineering.With the rapid development of microelectromechanical systems（MEMS）process technology,including etching,coating,encapsulation bond and so on,miniature mass spectrometers develop toward small size,low power,portable MEMS mass spectrometers.Based on micromachining process,this paper designs a MEMS time-of-flight mass spectrometer chip for gas detection in deep space,which has the characteristic of low power consumption,light weight,small size and meet the requirement of large payload capability in spacecraft.This design has three core components,including field emission electron source,ion transport and mass selector.This design allows the test gas into the ionization chamber by sampling system and ionization by electron impact.Then ions are extracted,focused and accelerated into mass selector to achieve detection because of different mass to charge ratio of ions.Field emission cathode is prepared by screen printing carbon nanotube and tested to obtain its emission properties.Analyzing law of the gate structure（L/l）and the gate-anode voltage ratio（Va/Vg）by electromagnetic simulation to obtain the best result of electron transfer.Analyzing electrode parameters of ion transport system,including voltage,distance spacing,opening width and so on,to obtain the best result of ion transfer.Then,analyzing and comparing respectively structure and voltage of linear and reflective time-of-flight mass selector to obtain the best result of ion selection.Obtaining the best structural parameters to this study by simulation of electromagnetism and ion optics:gate structure L/1=4,gate-anode voltage ratio Va/Vg=1-2 in the field emission electron source;Using einzel lens with five electrodes,voltage of ionization chamber is 100V,voltage of extraction electrode is Vi=30V,voltage of focusing electrode is V2=60V,distance spacing among extraction electrode,ionization chamber and focusing electrode is l₁=0.3mm,distance spacing of einzel lens with five electrodes is 12=0.3mm,exit width of ionization chamber and electrodes is d₁=d2=0.5mm;Using reflective time-of-flight mass selector,opening width is 0.5mm,exit electrode shape of mass selector is grid,voltage of mass selector is 0V.Decreasing the opening width of the field free drift zone and increasing the distance between field free drift zone and reflector at thier junction.The reflector includes six electrodes（0-150V）with potential difference of 30V and distance spacing of 0.6mm.The above analysis provides a reference design for MEMS time-of-flight mass spectrometer chip.