A Pirani vacuum sensor has been fabricated by the silicon micromachining technique. A square glass membrane was formed on (100) silicon substrate with a platinumhyphen;film resistor coated. The membrane is suspended by its four leads extended to the corners of an etched cavity. This structure can provide both low thermal loss through leads to the substrate and large active area for gaseous heat conduction. It thus can be used as a highly sensitive vacuum sensor. The fabricated sensor has shown a linear response of pressure from 8times;10minus;5to 6 Torr with constanthyphen;temperature operation. It is found that the lowhyphen;pressure limit of the vacuum sensor was caused by the noise of the instrument used in the experiment. A new terminology called lsquo;lsquo;noise equivalent pressurersquo;rsquo; thus is definable due to this finding. The physical limit of the noise equivalent pressure is analyzed. Optimization of the device structure and the noise equivalent pressure are also discussed in detail. A new method of ambienthyphen;temperature compensation is also proposed and analyzed here.
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