Study On The Fabrication And Properties Of Constant Conductance Element Using 1D Nanofluidic Channels

Standard conductance element(SCE)used to offer micro-flow gas,is an important measuring tools for in-situ calibrations of ionization gauges(IGs)and quadrupole mass spectrometers(QMSs),and its performance directly affects the accuracy of vacuum measurement.At present,the commonly used SCE exists many problems,such as the shape and size of leak are not controllable,the leak rate is uncertain,the gas of the leak doesn't correspond with theoretical result.Nevertheless,most novel SCE are usually sealed with Torr-Seal,which may results in large outgassing rate.Aiming at the existing problems of traditional SCE,we presented a constant conductance element using 1D nanofluidic channels in this paper.Such nanofluidic channels with a depth of~100nm were developed as a leak element,where the fluidic channels were etched on silicon wafer by reactive ion etching and then enclosed by direct silicon bonding.A tight lamination between the chip and the vacuum flange was achieved using indium gasket sealing,and outgassing measurement result indicates indium sealing can replace glue sealing and eliminate the influence of outgassing effectively.Two leak elements with different amount of parallel channels were fabricated and their values were characterized by the difference method.The results demonstrate that:(1)the gas flow through these leak elements realizes molecular flow at pressures ranging from high vacuum up to 10~5 Pa for helium,argon,and nitrogen;(2)the conductance of the leaks with same channels is approximately proportional to the inverse square root of the molecular mass;(3)the conductance of the leak elements behave in reasonable agreement with their theoretically calculated conductance with relative errors of approximately 5.4%and 29.9%,respectively.The uncertainty of the conductance measurement is estimated and the combined uncertainty is less than 9.8%.We propose a new constant conductance element that allows simple calibration and possesses controllable feature dimension,constant conductance and a wide leak rate range.To achieve different flow conductance,the size and quantity of the channels etched on silicon wafers could be changed.Meanwhile,the constant conductance element can be used as predictable leak elements for other gases when we just know the conductance for helium.