An Improved Performance Poly-Si Pirani Vacuum Gauge Using Heat-Distributing Structural Supports

Abstract

A new micro-Pirani vacuum gauge that employs a ladder-shaped structure with two parallel bridges and crosslinks in between has been designed and fabricated. This design enhances the physical performance of the gauge by increasing structural rigidity, thus allowing for longer beams and a wider selection of materials, and by allowing for better heat distribution across the sensor - therefore improving the full-scale range of sensor response. Furthermore, this Pirani gauge can be fabricated in a one-, two-, or three-mask process without postprocessing steps such as KOH etching. In a CMOS-compatible process, poly-Si 4 times 2 times 250-mum and 4 times 2 times 1000-mum Pirani gauges with the ladder structure were fabricated and tested with pressure ranges from 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-3</sup> to 50 torr (0.133 to 1 times 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> Pa) and 5 times 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-2</sup> to 760 torr (6.67 to 1.01 times 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">5</sup> -Pa atmospheric pressure) and with resolutions of approximately 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-3</sup> and 5 times 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-2</sup> (0.133 to 6.67 Pa), respectively. Constant temperature circuitry and thermoelectric temperature stabilization would further extend the range of operation and the resolution of these devices. Furthermore, these sensors operate at very low powers ranging from 300 to 600 muW depending on their geometry and pressure measurement range.