Micromachined thermal mass flow sensor with self-cleaning capability and methods of making the same
First Claim
1. A micromachined thermal mass flow sensor with self-cleaning components comprising:
- a suspending membrane with an resonant cavity underneath;
a heater thermistor being disposed on top of said suspending membrane;
an upstream temperature sensing thermistor being disposed on top of said suspending membrane;
a downstream temperature sensing thermistor being disposed on top of said suspending membrane;
a reference thermistor being disposed on top of a region of non-suspending membrane;
a top electrode being formed by in serial connecting said heater thermistor, said upstream temperature sensing thermistor, and said downstream temperature sensing thermistor by an external circuit; and
a bottom electrode being formed by a doped polysilicon layer or a metal layer which is disposed on a bottom surface of said resonant cavity;
wherein the self-cleaning components of said thermal mass flow sensor generate a mechanical vibration on said suspending membrane by modulating an electric voltage between said top and bottom electrodes of said resonant cavity such that foreign particles are detached and blown away by a gas flow from the top surface of said suspending membrane.
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Accused Products
Abstract
The current invention generally relates to Micro Electro Mechanical Systems (MEMS) thermal mass flow sensors for measuring the flow rate of a flowing fluid (gas/liquid) and the methods of manufacturing on single crystal silicon wafers. The said mass flow sensors have self-cleaning capability that is achieved via the modulation of the cavity of which the sensing elements locate on the top of the cavity that is made of a silicon nitride film; alternatively the sensing elements are fabricated on top of a binary silicon nitride/conductive polycrystalline silicon film under which is a porous silicon layer selective formed in a silicon substrate. Using polycrystalline silicon or the sensing elements as electrodes, an acoustic wave can be generated across the porous silicon layer which is also used for the thermal isolation of the sensing elements. The vibration or acoustic energy is effective to remove foreign materials deposited on top surface of the sensing elements that ensure the accuracy and enhance repeatability of the thermal mass flow sensing.
49 Citations
9 Claims
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1. A micromachined thermal mass flow sensor with self-cleaning components comprising:
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a suspending membrane with an resonant cavity underneath; a heater thermistor being disposed on top of said suspending membrane; an upstream temperature sensing thermistor being disposed on top of said suspending membrane; a downstream temperature sensing thermistor being disposed on top of said suspending membrane; a reference thermistor being disposed on top of a region of non-suspending membrane; a top electrode being formed by in serial connecting said heater thermistor, said upstream temperature sensing thermistor, and said downstream temperature sensing thermistor by an external circuit; and a bottom electrode being formed by a doped polysilicon layer or a metal layer which is disposed on a bottom surface of said resonant cavity; wherein the self-cleaning components of said thermal mass flow sensor generate a mechanical vibration on said suspending membrane by modulating an electric voltage between said top and bottom electrodes of said resonant cavity such that foreign particles are detached and blown away by a gas flow from the top surface of said suspending membrane. - View Dependent Claims (2)
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3. A micromachined thermal mass flow sensor with self-cleaning components comprising:
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a selectively formed porous silicon island with a dielectric film on top as electric insulation layer being provided on a silicon substrate as a thermally isolated area for flow sensor operation; a heater thermistor being disposed on a top surface of said porous silicon island; an upstream temperature sensing thermistors being disposed on the top surface of said porous silicon island; a downstream temperature sensing thermistors being disposed on the top surface of said porous silicon island; and a reference thermistor being disposed on a region of said silicon substrate other than said porous silicon island; wherein the self-cleaning components of said thermal mass flow sensor actuate as thermal source for an ultrasonic acoustic wave emitter, said heater thermistor and said temperature sensing thermistors by introducing a pulsed voltage source to elevate a temperature of said heater thermistor and said temperature sensing thermistors. - View Dependent Claims (4, 5, 6, 7, 8, 9)
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Specification