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This paper reports a micromachined Pirani gauge with dual heat sinks that can be integrated with microelectromechanical systems (MEMS) devices inside a vacuum package to monitor long-term pressure changes and stability inside the package. The Pirani gauge utilizes small gaps (<1 μm) between its heater and two thermal heat sinks to obtain large dynamic range (20 mtorr to 2 torr) and high sensitivity (3.5×105 (K/W)/torr). The gauge is 2×2 mm2 in size, is fabricated using the dissolved wafer process (DWP) on a glass substrate, and utilizes dielectric bridges for signal routing. Measurements show the low end of the dynamic range can be extended by reducing the gap distance between the heater and thermal sinks, which matches well with analytical modeling. This gauge shows an uncertainty of 50 μtorr and a detectable leak rate of 3.1×10-16 cm3/s, assuming a common micropackage volume of 1.6×10-5 cm3, which represents at least four orders of magnitude improvement over traditional leak testing.
Date of Publication: Nov. 2005