Study On Fabrication And Performence Of Thermal Flow Sensor

In automotive,aerospace and other related fields,intake of air need to be monitored and well controlled in order to improve the efficiency of the engine.The thermal flow sensor is one of the methods to achieve accurate gas flow measurement.Compared with traditional flow sensor,the thermal flow sensor has great advantages in size,reliability and accuracy.In this paper,the simulation and fabrication of thermal flow sensor with large range(0m/s-15m/s)were mainly carried out.The thermal flow sensor which consisting of the substrate hollow structure,insulating layer,metal film resistors,protective layer was designed.The simulation and fabrication of the thermal flow sensor were discussed in detail and the sensor was tested.In order to design thermal flow sensor with large measurement range and high sensitivity,the thermal flow sensor was simulated by the FLUENT module of the ANSYS.First,the heat of the heating resistor transferred to the substrate was simulated.The simulation results showed that the hollow size of the silicon substrate was 2400?m×520?m.The surface temperature distribution of the sensor was simulated and analyzed with different gas flow rates.The result showed when the temperature difference at 167?m away from both sides of the heating resistor the temperature difference reaches the maximum and the measurement range was optimized.When the environmental thermal resistor was arranged 700?m upstream of the heating element,the influence from the heating resistance was minimized.The thickness of the protective layer is optimized as 300 nm.Platinum was used as metal film resistive material,and the resistance and size of the metal film was determined.In order to obtain the metal film resistors with good quality,DC magnetron sputtering was used to fabricate the metal thin film resistive layer on the surface of silicon nitride substrate.The effects of sputtering power and air pressure on the resistivity and deposition rate was studied.The deposition rate of Pt and Ti increased with increasing sputtering power and decreased with increasing air pressure.The resistivity of Pt thin films decreased with increasing air pressure initially and then increased.The optimized fabrication parameters of Pt thin films were as follows: the sputtering pressure is 0.4Pa,the power is 100 W,the sputtering rate is 34nm/min,the film thickness is 250 nm,and the resistance temperature coefficient(TCR)is 1.78×103ppm/?.And the thermal flow sensor was fabricated on silicon substrate and PI substrate,respectively.The sensors with different thickness of insulating layer were tested.The results showed that different thickness of insulating layer has little effect on the sensitivity of the thermal flow sensor.The sensor on PI substrate has better heat insulation performance,and the output signal is larger than that on silicon substrate.The variation of the signal increased with increasing heating voltage,and the heating voltage was finalized to be 13 V.