Polycrystalline diamond film flow sensor

A batch-fabricated micromachined silicon flow sensor is developed. It incorporates a selectively deposited diamond film as a thermal element. The sensor consists of a boron-doped silicon heater resistor thermally coupled to a boron-doped silicon temperature sensing resistor by a free-standing diamond film. The flow sensor works by forcing a sufficient current through the heater resistor to maintain a constant temperature at the temperature sensing resistor. The power required to keep the sensor at a constant temperature is used to obtain the velocity of the flowing medium. As flow is increased, heat is removed from the diamond film, lowering the temperature of the sensor. This causes the circuit to increase the current to the heater. The sensor appears to be a promising structure for use in corrosive or abrasive environments as well as in general flow measurements.<>