Research Of Flexible Pressure Sensor Based On Organic Electrochemical Transistor Structure

In recent years,flexible pressure sensors,as the important sensing devices in the fields of artificial intelligence,internet of things,and robotics,have been given lots of attention from researchers.Compared with traditional rigid sensors,flexible sensors are light,soft,deformable?including bendable,compressed,stretched,or twisted?,and have superiority in man-machine interaction.Thus flexible sensors,as current research hotspots in academia and industry,are widely used in wearable devices,medical rehabilitation equipment,and soft robots.In order to solve the problem of the weak output signal of some existing flexible pressure sensors,flexible organic transistors,with functions of anti-interference and amplifying the output signal,are used in the sensors.However,current organic transistor-based flexible pressure sensors generally use organic field-effect transistors?OFETs?,which have the disadvantages of high operating voltage,high power consumption,and low output signal.All of these are not conducive to the application of flexible pressure sensors.Compared with organic field-effect transistors,organic electrochemical transistors?OECTs?have the advantages of low operating voltage,low power consumption,and strong output signals.However,the gate medium materials are electrolyte solutions generally,which are easy to drip or leak when subjected to external forces,making OECTs difficult to apply to flexible pressure sensors.In this thesis,we proposed a new structure of OECT,which used gelatin methacryloyl hydrogel instead of the electrolyte solution as the gate medium to solve the problem of the electrolyte solution dripping easily,and we also applied the structure of OECT to construct the flexible pressure sensor.Theoretical and experimental researches results show that the flexible pressure sensor based on OECT structure has the advantages of low operating voltage,low power consumption,and strong output signal.In addition,the sensitivity,output current,and power consumption of the flexible pressure sensor based on OECT structure can be adjusted by the gate voltage controlling.The main research contents of this thesis are as follows:?1?We theoretically analyzed the relationship between the output current and related parameters of OECTs.The ion circuit and the electronic circuit were split to establish the theoretical model of the output current,gate capacitance,drain voltage,and gate voltage.In addition,the relationship of the modulation effect,the hole density and hole mobility of the semiconductor material was theoretically researched.What's more,the OECTs were prepared,the output characteristics as well as transfer characteristics were tested.We also researched the effect of the gate equivalent capacitance on the output current,and the effect of the electrolyte solution concentration on the modulation state.The researches results show that the increase in gate voltage reduces the output current,and the OECT enters the saturation state when the gate voltage is 0.6 V.The increase in hole density of semiconductor materials increases the output current,the increase in hole mobility inhibits the modulation effect,the increase in gate capacitance reduces the output current,and the high concentration electrolyte solution makes the OECT have better controllable performance.?2?The gelatin methacryloyl hydrogels containing hexadecyltrimethylammonium bromide electrolyte solution were prepared and used for OECT construction.Combined with theoretical analysis,the transfer and output characteristics of the OECT based on the electrolyte hydrogel were experimentally researched.The results show that the replacement of the electrolyte solution with hydrogel ensures the OECT to work in the dehydrated environment,the output current is controlled by the gate voltage and the OECT enters the saturation state when the gate voltage is 0.8 V.?3?We designed and fabricated the flexible pressure sensor based on the OECT structure.The surface of the electrolyte hydrogel was designed as the miniature pyramids structure,contacted with the gate electrode.The modulation effect made the output current sensitive to pressure.We also theoretically analyzed the influence of pressure on the gate capacitance,the relationship between the output current and pressure,the influence of the gate voltage on the sensitivity.The results show that the increase in pressure causes the increase in capacitance and the decrease in output current;the increase in gate voltage increases the sensitivity of the sensor.The flexible pressure sensor based on the OECT structure was prepared by ultraviolet light polymerization,thermal curing,and other processes.Combined with theoretical researches,the experiments of transfer characteristics,output characteristics,response to step pressure,minimum detection limit,and stability were carried out.And the effects of gate voltage,pyramid size on sensitivity,response time were analyzed experimentally.The results show that the output current of the flexible pressure sensor is controlled by the gate voltage,and the pressure promotes the modulation effect.In addition,the sensor has the good resolution to the step pressure,the minimum detection limit is 20 Pa,the maximum sensitivity is 2.1 k Pa^-1,the minimum response time is 0.8 s,and the sensor has good stability within 150 pressure cycles.Compared with other flexible pressure sensors based on organic transistor structure,the flexible pressure sensor based on OECT structure in this thesis has low operating voltage?within 0.8 V?,low power consumption?down to 2.1?W?,strong output signal?up to the order of milliamps?,and the gate voltage can be adjusted to balance the relationship between the output signal and power consumption.