Research Of Silicon Pulse Sensing And Detecting System By MEMS Technology

Pulse diagnosis is the most characteristic diagnosis method in traditional chinese medicine, which has the advantages of convenient, reliable and non-invasion. With the rapid development of the modern science and technology, collecting and processing information by scientific methods is an important means of pulse diagnosis providing objective information of diseases for patients. The design and fabrication of the pulse sensor is the objective research foundation of pulse diagnosis.The pulse sensors of the silicon cup and the cantilever beam structures have been designed and fabricated by using MEMS, CMOS and laser processing technologies, in which the nc-Si/c-Si heterojunction has been used as the source and drain of the MOSFETs. The pulse sensors can detect the tiny pulse signal accurately, which is small size, light weight, high sensitivity and good temperature characteristics. As the application of the pulse sensors, the nc-Si/c-Si heterojunction MOSFETs pulse detecting system has been fabricated. The methods of processing the pulse detecting results by using artificial neural network have been presented.On the basis of theoretical analysis, the force-sensitive structures of the nc-Si/c-Si heterojunction MOSFETs pulse sensors have been designed. The substrate material, the thickness of the silicon film, the position of the MOSFET channel resistance on the silicon film and cantilever beam have been determined. Four nc-Si/c-Si heterojunction p-MOSFETs have been designed on the rectangular silicon film of the silicon cup and the cantilever beam. The p-MOSFETs whose channel resistance has been used as force-sensitive resistance have been designed in a Wheatstone bridge configuration. When the silicon film and the cantilever beam are stimulated by the pulse pressure, the MOSFET channel resistance on the silicon film and the cantilever beam changes, and the output voltage of the Wheatstone bridge changes with the MOSFET channel resistance. Therefore, the pulse sensors can detect the human pulse.The nc-Si/c-Si heterojunction MOSFETs pulse sensor chips based silicon cup and cantilever beam have been fabricated on the n-type,<100> crystal orientation, double-side polished silicon wafer. The fabrication process and the photographs of the MOSFETs pulse sensors chips have been presented. To solve some problems of etching rate and quality in the etching technology for silicon cantilevers, a method which combines laser processing technology and MEMS technology is adopted to fabricate silicon cantilevers. The method makes the fabrication of silicon cantilevers simple, rapid and accurate, which avoiding the convex corner undercutting in etching of cantilevers. This study also provides a laser etching method for the fabrication of other microstructures.The characteristics of the fabricated nc-Si/c-Si heterojunction p-MOSFET, the static characteristics of the nc-Si/c-Si heterojunction MOSFETs pulse sensor based silicon cup, the characteristics of the nc-Si/c-Si heterojunction MOSFETs pulse sensor based cantilever beam and the temperature characteristics of the nc-Si/c-Si heterojunction MOSFETs pulse sensor based silicon cup have been studied, and the experimental results are as following.The electrical characteristics of the nc-Si/c-Si heterojunction p-MOSFET has been studied under the conditions of the applied pressure P=0, and the high and low temperature experiments of the nc-Si/c-Si heterojunction p-MOSFET in temperature range from-20℃to 60℃have been studied. The experimental results show that the channel current IDS of the nc-Si/c-Si heterojunction p-MOSFET has little change with temperature, and the variable quantity of channel current IDs decreases with increasing temperature. The channel resistance of the four nc-Si/c-Si heterojunction p-MOSFET slightly decreases with increasing temperature.The nc-Si/c-Si heterojunction MOSFETs pulse sensor based silicon cup has been experimentized using the constant voltage and the constant current power supply respectively, and the applied pressure range of the sensor is 0-160kPa. The experimental results show that the sensitivity of the nc-Si/c-Si heterojunction MOSFETs pulse sensor increases with the increasing of the supply voltage under the conditon of constant voltage power supply, the sensitivity is 0.6517 mV/kPa and the precision is 2.343 %F.S with-5.0V power supply; the sensitivity of the nc-Si/c-Si heterojunction MOSFETs pulse sensor increases with the increasing of the supply current under the conditon of constant current power supply, the sensitivity is 0.6381 mV/kPa and the precision is 2.281% F.S with 1.000mA current supply.The characteristics test of the nc-Si/c-Si heterojunction MOSFETs pulse sensor based cantilever beam has been studied. The experimental results show that the output voltage of sensor increases when the acceleration of the cantilever beam increases at a constant vibration frequency; the output voltage of sensor increases when the vibration frequency increases at a constant acceleration.The temperature characteristics test of the nc-Si/c-Si heterojunction MOSFETs pulse sensor based silicon cup has been studied at different temperatures. The experimental results show that the sensitivity of the nc-Si/c-Si heterojunction MOSFETs pulse sensor increases with decreasing temperature under the conditions of constant voltage and constant current power supply.The application example of the nc-Si/c-Si heterojunction MOSFETs pulse sensor has been presented. The general scheme of the nc-Si/c-Si heterojunction MOSFETs pulse detecting system and the design methods of the function modules have been presented. The detecting results of the MOSFETs pulse detecting system has been presented.The error back propagation neural network and the probabilistic neural network in artificial neural network have been used to process the detecting results of pulses, which can distinguish the pregnant woman. The method is different from the classification of pulse, whose advantage is accurately distinguishing the pregnant woman by the pulse characteristic parameters of the woman. The research will establish the foundation for the study on the human pulse information by scientific methods.To sum up, the fabrication method of the silicon pulse sensing and detecting system by MEMS technology is feasible. It is easy to be integrated and produced in a large scale. The study has great significance for the objective research of pulse diagnosis.