MICROMACHINED MASS FLOW SENSOR WITH CONDENSATION PREVENTION AND METHOD OF MAKING THE SAME

摘要

The design and manufacture method of a silicon mass flow sensor made with silicon Micromachining MEMS, Micro Electro Mechanical Systems) process for applications of gas flow measurement with highly humidified or liquid vapors is disclosed in the present invention. The said silicon mass flow sensor operates with an embedded heater and an adjacent control temperature sensor beneath the integrated calorimetric and thermal dissipative sensing thermistors. When the condensation takes place at the surface of the said silicon mass flow sensor, the embedded heater shall be turned on to elevate the temperature of the supporting membrane or substrate for the sensing thermistors. The elevated temperature shall be adjusted to above the vaporization temperature with the feedback data of the adjacent temperature sensor such that the surface condensation due to the presence of the liquid vapors in a gas flow can be effectively eliminated.

主权项

1. A silicon mass flow sensor has the capability to continuously and accurately measure has flow rate or gas flow speed with extended measurement range where the gas medium is highly humidified or has water vapors or liquid vapors. The silicon mass flow sensor comprising
a silicon substrate having a thermally isolated membrane structure a set of thermistors for a calorimetric or a thermal dissipative mass flow sensing; a temperature sensor placed on the silicon substrate for the measurement of environmental temperature; and a membrane heating source embedded inside t le thermally isolated membrane structure:
wherein the thermally isolated membrane structure contains a mechanical and thermal robust membrane fir supporting the membrane structure;wherein the thermally isolated membrane structure contains a multilayered components and each function layer is separated with an electrically inert but thermally robust layer;wherein the set of thermistors includes a micro heater, an upstream and an downstream thermistor.wherein the membrane heating source embedded inside the membrane structure has a precise temperature control and has the capability to elevate the temperature of the membrane structure above concerned water or other liquid droplet condensation temperature;wherein the set of thermistors that serve as the sensing elements for mass flow measurement are placed above the membrane heater with an insulation layer in between;wherein a top surface passivation layer has abrasive robustness with thermal conductive efficiency;wherein a thermal isolation cavity beneath the membrane structure utilized gaswherein there are a number of pressure balance openings on the membrane. structure for the mass flow measurement at various pressure.