Miniature thermal fluid flow sensors and batch methods of making same

TLDR: In this article, the thermal fluid flow sensors of the airfoil type are made in batch form by forming the thermal flow sensors on a thin sheet of material and bonding the sheet over an array of duct structures and dicing the individual sensors and duct structures apart.

Abstract: Miniature thermal fluid flow sensors of the airfoil type are made in batch form by forming the thermal fluid flow sensors on a thin sheet of material and bonding the sheet over an array of duct structures and dicing the individual sensors and duct structures apart In another embodiment, thin carrier sheet portions of a wafer bearing the thermal fluid flow sensors of the airfoil or grid type are supported by surrounding frame portions of the wafer The wafer is diced to separate the individual sensing chips The respective chips are mounted across respective fluid flow ducts For the airfoil type sensor, portions of the frame are broken away for undisturbed flow over the thin carrier and sensor In one thermal flow sensor configuration, a flow heater is disposed in between first and second thermal flow sensors in heat exchanging relation therewith A third thermal flow sensor is disposed upstream of the others out of heat exchanging relation with the heater for operation of the heater at a certain temperature above that sensed by the third sensor In the low flow regime, flow is measured by the difference between the outputs of the first and second sensors, whereas in the high flow regime, the power required to maintain the temperature of the heater serves as a measure of the flow