Study And Fabrication Of Flexible MEMS Flow Sensor

Gas measuring is of great important in the fields of aerospace, energy,medical, food and automobile. Thermal mass flow meter has been widely usedbecause of its simple principle and wide measuring range. And also because itcause little disturbance of the gas. However, as the requirements of gas measuringbecome higher and the great development of semiconductor technology, flowsensors fabricated by MEMS technology begin to replace traditional metal-shellthermal flow sensor. Because MEMS flow senor has great advantages than thelatter in accuracy and power consumption. Also, the cost of fabrication is lowerby using MEMS technology. This paper designed a new type of flexible MEMSflow sensor. The material of the substrate is PI rather than bulk silicon in order toavoid etching cavity which is a complicate fabrication process. The PI substate ismade by FPC which is simple and highly reliable. And nickle is used as thermalmetal because of its high TCR.The vital parameters such as the wideness of the Ni film, the thickness of thePI substrate and the distance between heater and thermal metal unit are designedby mathematical model and simulation. The nickel is directly spur on the substateon which there is signal circuit. And the TCR of nickle film reach2450ppm/℃with heat treatment. This paper also gives the principle of test including testcircuit and program. We use PID algorithm to control the temperature of heater toget higher accuracy and less response time. The test shows that the sensor canreach the accuracy as±0.1m/s and even higher as±0.05m/s at the situationlow air speed which is a great advantage of MEMS flow sensor in measuringmicro-flow. The power consumption is also much lower than metal-shell ones asit is only24mW at zero point and45.7mW at10m/s flow speed.