Novel C-MOS compatible monolithic silicon gas flow sensor with porous silicon thermal isolation

A novel C-MOS compatible silicon gas flow sensor using porous silicon for t hermal isolation has been designed and fabricated. The small sensor size co mbined with the very good thermal isolation by porous silicon assure fast r esponse, with a time constant of the order of 1.5 ms. The principle of oper ation is based on heat transfer from a polysilicon resistor to the fluid an d the detection of the flow-induced temperature difference by A1/polysilico n thermopiles, integrated at both sides of the heater. The sensor has been evaluated in nitrogen flows from 0 to 0.4 m/s. The sensitivity per heating power is 6.0 mV/(m/s)W and the responsivity is 0.65 V/W. The noise equivale nt power and the minimum detectable velocity are 1.5 X 10(-8) W/Hz(1/2) and 4.1 X 10(-3) m/s, respectively. The chip size is 1.1 mm X 1.5 mm. (C) 1999 Elsevier Science S.A. All rights reserved.