Abstract: A Wheatstone bridge flowmeter is formed on a base substrate with a fluid passageway formed over or through a top surface of the base substrate. Resistors forming the Wheatstone bridge and a heater are arranged in a linear physical arrangement along the passageway, such that two resistors on one side of the Wheatstone bridge are sequentially upstream of the heater and two resistors on the other side of the Wheatstone bridge are sequentially downstream of the heater, establishing a sequential arrangement along the fluid passageway of two of the resistors, the heater and the other two resistors. Heating of the fluid by the heater creates a differential in the temperatures of the resistors, thereby changing the output sensing voltages across the Wheatstone bridge.

Abstract: A Wheatstone bridge flowmeter is provided with a flow channel on a top surface of the base substrate, with two resistors of the Wheatstone bridge in thermal communication with the flow channel. One resistor in the flow channel, on one side of the Wheatstone bridge, has a negative coefficient of resistance (NTC) and the other resistor in the flow channel, on the other side of the Wheatstone bridge, has a positive coefficient of resistance (PTC). At least two of the resistors in the Wheatstone bridge are mounted in at least one cavity space, so that one resistor on each side of the Wheatstone bridge is in thermal isolation from the flow channel, thereby allowing sensing of voltages across the Wheatstone bridge according to fluid flow through the flow channel.

Abstract: The microflow sensor includes a base wafer having opposed upper and lower surfaces, and a cap wafer, also having opposed upper and lower surfaces. The base wafer and the cap wafer may be formed from a semiconductor material. A flow sensing element is embedded in the upper surface of the base wafer. The flow sensing element may be any suitable type of flow sensing element, such as a central heater and at least one temperature-sensitive element. A flow channel is formed in the lower surface of the cap wafer and extends continuously between first and second longitudinally opposed edges of the cap wafer. The lower surface of the cap wafer is bonded to the upper surface of the base wafer such that fluid flowing through the flow channel passes above and across the sensing element.