Study On Silicon Machined Thermal Distribution Flow Sensor

The gas flux is the important parameter in manufactory industry and scientific research. With the development of fine chemistry and medical biological analysis, the precision and veracity in gas flow measurement are highly required. The gas flow sensor fabricated by microfabrication and IC technique has the advantage of small volume, wide measurement range, rapid response and low price. So, it has been received much attention. In this paper, a thermal distribution gas flow sensor was fabricated via microfabrication technique. The properties of the sensor are analysized detailedly.Based on the principle of thermal distribution on flow sensor and the result of finite element analysis, the format of gas flow sensor was designed. The SiO₂ and Si₃N₄ insulation membrane were fabricated via heat oxidation and LPCVD method to improve the stability of the gas flow sensor. The heat insulating silicon cup was etched at the back of silicon via KOH wet etching method to form the efficient heat field. The Pt thin membrane micro heater and temperature sensor was fabricated by RF sputtering to form the heat field and detect the temperature of the sensor. The SiO₂ passivation film was fabricated by electron beam evaporation to block the environmental influence to the metal films. Totally 10 temperature sensors were fabricated in the chip, three pairs of which are used to measure the gas flux and the others of which are to measure the working condition of silicon chip. The gas flow channel with different thinkness was etched in glass material, which is conncted to slicon substrate to compose the gas flow sensor chip. In addition, the control and detecting circuit system was build including temperature and voltage collection, signal amplification, A/D conversion, micro single chip, keyboard control, LCD display and serial port communication. Take the advantage of C++ Builder software, the applied program interface in PC was designed and realize the graphic display of temperature data and flux data in real time and save the analyzed data.The results show that the fabricated Pt membrane has good heating efficiency and TCR. By calibrating the gas flow sensor with three thick gas channels, three measurement ranges (2ml/min～4000ml/min, 0.8ml/min～2800ml/min and 0.4ml/min～1300ml/min) were obtained. The fabricated gas flow sensor has relative high sensitivity and large measurement range.