A constant-temperature gas flowmeter with a silicon micromachined package

Abstract

A micromachined flowmeter based on convective heat transfer from hot, heavily doped polycrystalline silicon bridges was designed, fabricated, packaged, and tested. The flowmeter consists of two basic sensing units: one is exposed to the flow while the other acts as a reference. A silicon cap with a micromachined laminar-flow channel is placed on top of the sensor chip to confine the flow. The polysilicon bridge resistors operate at a constant temperature under the control of external circuits. An output signal voltage of 35 mV is obtained for air flow in the range of 0-100 SCCM at an average device temperature of 250 degrees C. The applied heating power is 8 mW.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>