The Effect Of Physical Parameters On The Performance Of MEMS Pirani Vacuum Guages

Vacuum packing is a crucial technology to make many MEMS devices work effectivelyand improve the performance. Then, it is a key researching subject to measure and monitorthe pressure in the vacuum cavity. There are advantages for MEMS Pirani vacuum gauge,such as high sensitivity, large test range, small size, little weight, thermal response quicklyand easily fitting to other MEMS devices with standard Silicon process. A kind of lateralsilicon MEMS Pirani vacuum gauge with high aspect ratio and dual heater sinks wassuccessfully made by our team. In the thesis, we design and made a lot of gauges withdifferent structure parameters, such as the heater with different length, width, thickness andthe space between heater and heater sinks. Then, base on the theory of gas thermalconductance on micro-scale and a lot of experiment data, the effect of structure parameters tothe performance were researched detailed.The parameter effect to the heater resistance was studied in this thesis. The resistanceimproved a lot with length increasing, width and thickness decreasing and fluctuated a littlewith space increasing, the resistance. Because of the processing problem of photolithographyand DRIE, the measured resistance of the one with large length and small is larger than theircalculated resistance; the measured resistance of the one with large space is smaller than itscalculated resistance. Then the silicon temperature-resistance characteristic was measured andanalyzed in this thesis and the resistance was tested by four-probe measurement methods. Theresult shows that the resistance was increased quickly with temperature raised from roomtemperature to215℃, and the relation between the resistance and temperature isapproximately linear above120℃and the data was fitted by nonlinear formula. The phenomenon of temperature response was also focused on this thesis. During thewhole pressure range, the temperature of major devices could be stable in10seconds with1.275mA. Then, only at10-3Pa, the temperature of the one with10μm idth and ith15μmwidth could be stable in30seconds and in10seconds at other pressure, too. So, the MEMSPriani vacuum gauge has quickly response.In this thesis, the vacuum sensing performance of the standard structure device wasmeasured and analyzed systematically. The measurement result shows that the curve ofresistance versus pressure is an S-shape. At the pressure between2Pa and55.14Pa, resistanceincreases quickly when pressure decreases, so this range is called high sensing range, itssensitivity SmHis259.23Ω/In(Pa). At the pressure between0.021Pa and2Pa, resistanceincreases but little slower than last range, so this range is called low sensing range, itssensitivity SmLis125.00Ω/In(Pa). At the pressure lower than0.021Pa, resistance increasesslowly, but is still linear. The average sensitivity is19.87Ω/In(Pa). At the pressure higher than100Pa, resistance increases slowly when pressure decreases, so its sensitivity is quite low. Sothe sensing range of the standard one is0.021Pa to55.14Pa.This thesis mainly focused on effect of different physical parameters to the sensitivity.The result shows that increasing the length, decreasing the width and thickness can promotethe sensitivity at sensing range, and the last two methods are more significant. Comparingwith the standard one, decreasing the width with40%can increase the SmLand SmHby198.5%and165.5%respectively, decreasing the thickness to half, can increase the SmLand SmHby118.8%and101.0%respectively. But, it is useless to promote the sensing range by changingthe space at micrometer scale. However, less the length and increasing the power can obtain awider sensing range.