Patent ID: 8132455

Claim:
A robust micromachined thermal mass flow sensor comprising: a suspending polyimide membrane with double side passivation layers on both top and bottom surfaces of the polyimide membrane which is suspended on a silicon substrate; a heating element thermistor being connected to a microcontroller circuit with an ambient temperature sensing thermistor; a temperature sensing thermistor being disposed on upstream flow side of the heating element thermistor with an open slot on the suspending polyimide membrane; a temperature sensing thermistor being disposed on downstream flow side of the heating element thermistor with an open slot on the suspending membrane; wherein the passivation layer on the bottom surface of the polyimide layer contains silicon nitride; wherein the ambient temperature sensing thermistor being disposed in a region of no polyimide layer on the silicon substrate; and wherein the open slots on the suspending polyimide membrane between the heating element thermistor and the temperature sensing thermistors isolates transverse heat conduction from the heating element thermistor to the temperature sensing thermistors.