Research Of Nc-Si/c-Si Heterojunction MOSFETs Pressure-magnetic Mutli-sensor

With the development of technology,we usually need to measure parameters of pressure,temperature,magnetic field,humidity,acceleration,velocity of liquid,etc.at the same time,and these parameters are used in the fields of spaceflight,industry production,medicine,military affairs and so on.In many different application fields, due to the limits to adapting to environment,volume,cost and function,we need to pay much attention to miniaturization,multifunction,integration and all-in-one widely.The paper adopted CMOS technology and MEMS technology to design and fabricate MOSFETS pressure-magnetic multi-sensor taken nc-Si/c-Si heterojunetion as source and drain,and mainly researched the following five aspects:1.Fabrication and characteristics research on ne-Si thin filmsWe fabricated single crystalline and polyerystalline nc-Si thin films by LPCVD at 620℃,and then adopted Raman,XRD,SEM and AFM,etc.to do token research about micro-structure of the nc-Si thin films.The token result showed:when thickness of the thin films was 30.7nm,sizes of crystalline grains were 5～8nm,and orientation was <111>,orientation and polycrystalline characteristics were obvious with increasing thickness of the thin films,polycrystalline orientations of the deposited thin films were <111>,<220>and <311>,good orientation was <111>.Intensity of X-ray diffraction crests increased with annealing temperature for nc-Si thin films with the same thickness. The paper adopted nc-Si thin films with film thickness 30.7nm to fabricate MOSFETs pressure-magnetic multi-sensor,which took nc-Si/c-Si heterojunction as source and drain.2.Basic theory analysis of the MOSFETs pressure-magnetic multi-sensorThe paper presented basic theory analysis about the MOSFETs pressure-magnetic multi-sensor,which was based on the basic theory of JFET pressure-magnetic multi-sensor presented by Dianzhong Wen professor,the basic theory analysis of the MOSFETS pressure-magnetic multi-sensor concluded four conditions:When additional pressure P=0,additional magnetic field strength B=0;When the additional pressure P≠0, the additional magnetic field strength B=0;When the additional pressure P=0,the additional magnetic field strength B≠0;When the additional pressure P≠0,the additional magnetic field strength B≠0,etc.3.Design of pressure-magnetic sensitivity structure on the nc-Si/c-Si heterojunction MOSFETs pressure-magnetic multi-sensorAfter polishing double sides of n-type <100> p-Si wafer with high resistivity,we designed Wheatstone bridge constituted by four nc-Si/c-Si heterojunction p-MOSFET channel resistors on different positions of squared silicon membrane(6mm×6mm) by CMOS technology and MEMS technique,in order to achieve pressure-sensitivity structure of the nc-Si/c-Si heterojunction MOSFETs pressure-magnetic multi-sensor, and be able to complete the measurement to the additional pressure P.Two ohm-contact Electrodes,which were taken as Hall output on double sides of the channel situated 0.7L from the source,were fabricated by adopting nc-Si/c-Si heterojunction p-MOSFET of the Wheatstone bridge,so that nc-Si/c-Si heterojunction p-MOSFET Hall magnetic sensor could be constituted and the measurement for the additional magnetic field strength B could be achieved.In order to improve sensitivity characteristics of the magnetic sensor,we adopted two nc-Si/c-Si heterojunctions p-MOSFET Hall fan-out in series in Wheatstone bridge.4.Basic structure and fabrication technology of the nc-Si/c-Si heterojunction MOSFETs pressure-magnetic multi-sensorThe paper considered characteristics of pressure and magnetic sensors of the nc-Si/c-Si heterojunction MOSFETs pressure-magnetic multi-sensor at the same time, based on that to design and present basic structure of the nc-Si/c-Si heterojunction MOSFETs pressure-magnetic multi-sensor.Adopting CMOS technology and MEMS technique achieved fabrication of integration all-in-one and packaging for chip of the pressure-magnetic multi-sensor.5.Characteristics experimental result of the nc-Si/c-Si heterojunction MOSFETs pressure-magnetic multi-sensorThe paper mainly showed basic characteristics experimental result about the nc-Si/c-Si heterojunction MOSFETs pressure-magnetic multi-sensor from the following four respects:(1) When the additional pressure P=0,the additional magnetic field strength B=0:The paper adopted CMOS technology to achieve fabrication of the p-MOSFET device taken nc-Si/c-Si heterojunction as source and drain,when VDS and V_GS were constant,channel current I_DS of the nc-Si/c-Si heterojunction p-MOSFET was inversely proportional to length-width(L:W) ratio.(2) When the additional pressure P≠0,the additional magnetic field strength B=0:When thickness of squared silicon film and operating voltage V_DD were constant for the sensor,full range(160kPa) outputs of the nc-Si/c-Si heterojunction MOSFETs pressure sensor were directly proportional to length-width ratio of the channel.When thickness of squared silicon membrane was 75μm and operating voltage V_DD was -1.5V, full range output of 6SD MOSFETs pressure sensor with L:W ratio 6:1 was 21.04mV, and sensitivity was 0.132mV/kPa,linearity was 0.589%F.S,hysteresis was 0.412%F.S, precision was 0.82%F.S,temperature coefficient of sensitivity was-1550ppm/℃.(3) When the additional pressure P=0,the additional magnetic field strength B≠0:The paper adopted additional biased voltage V_GS of gate to adjust conducting channel equivalent resistors of the nc-Si/c-Si heterojunction p-MOSFET Hall device,so that different potentials V_OH were close to zero outputs,in the same operating circumstance,adopting additional biased voltage V_GS to adjust zero to different potentials could improve sensitivity compared with adjusting zero of compensation circuit to different potentials.When different potentials was adjusted zero and operating voltage V_DS was constant,sensitivity of the nc-Si/c-Si heterojunction p-MOSFET Hall magnetic sensor was directly proportional to channel W:L ratio,after adopting compensation circuit to adjust zero to different potentials,when V_DS=-7.0V,absolute sensitivity of the nc-Si/c-Si heterojunction p-MOSFET Hall magnetic sensor with L:W ratio 2:1 was 21.26mV/T,linearity was 0.156%F.S,repeatability was 1.719%F.S, hysteresis was 0.247%F.S,precision was 1.834%F.S;magnetic sensitivity for the nc-Si/c-Si heterojunction p-MOSFET Hall magnetic sensor with L:W ratio 4:1 was 13.88mV/T,when different potentials were adjusted zero by additional biased voltage V_GS of the gate,magnetic sensitivity was 16.48mV/T;When two fan-out of nc-Si/c-Si heterojunction p-MOSFET Hall device with L:W ratio 4:1 were in series,magnetic sensitivity of Hall fan-out of the magnetic sensor was 22.74mV/T,which was improved by about 64%compared with sensitivity of single nc-Si/c-Si heterojunction p-MOSFET Hall magnetic sensor.(4) When the additional pressure P≠0,the additional magnetic field strength B≠0:Experimental result showed that input-output experimental characteristics curves of the nc-Si/c-Si heterojunction p-MOSFET Hall pressure-magnetic multi-sensor would change with additional pressure and magnetic field.The nc-Si/c-Si heterojunction MOSFETs pressure-magnetic multi-sensor designed and fabricated in the paper,can achieve the measurements for pressure and magnetic field,and owns super characteristics of pressure sensitivity and magnetic sensitivity,and also achieve the integration and all-in-one for measurement of pressure-magnetic.