Flexible Piezoresistive Sensors Based On 3D Porous Composite

With the development of science and technology,flexible force sensors play a vital role in all aspects of human life and has gradually become hot spots in scientific community.In order to meet the market demands,various types of flexible force sensors have emerged,including capacitive sensors,piezoelectric sensors,piezoresistive sensors.Compared with capacitive/piezoelectric sensors,piezo-resistive sensor has the advantages of simple sensing principle,low signal-to-noise ratio and stable sensing performance.Therefore,piezoresistive sensors have been widely used in a lot of fields.However,the common issues of resistive force sensors are that the preparation process is complex and costly,the sensitivity and stress response range are limited,and the cycle stability is poor.In order to solve the problem that the sensitivity and stress response range cannot be considered simultaneously,we uses simple and cheap methods to modify the conductive surface area of 3D structure,adjust the conductivity and Young's modulus of sensing materials and increase the contact resistance between sensing materials and electrodes.In addition,to solve the problem of poor cycling stability,we adopt three methods to improve the binding force between conductive material and flexible substrate during the process of fabrication,including semi-embedded of metal nanowires on the surface of flexible substrate,electrodeposition and heat treatment.The specific research contents are as follows:?1?The sensing performance was optimized by selecting different templates to increase the conductive surface area of 3D porous structure.To obtain different conductive surface area,nickel foam and square sugar were used as templates,respectively.The sensing performance showed that the maximum sensitivity of the sensor based on nickel foam as a template was 2.48 kPa^-1,the response range was 0-120 kPa.For the pressure sensor prepared with square sugar as template,the highest sensitivity was 6.24 kPa^-1,the response range was 0-160 kPa.It was attributed to the larger pore feature size of square sugar²00?m compared with that of Nickel foam⁵0?m.When square surge was used as template,the obtained3D porous composite has a larger conductive surface area,which can provide more conductive paths.In addition,the cycling stability of sensors could reached 3700cycles by half-embedded conductive material on surface of flexible substrate.Secondly,the conductive surface area of 3D porous structure was further improved by constructing porous multiscale structures.The sensing performance showed that the response range of flexible force sensor based on porous multiscale structure is 0-60 kPa.The sensitivity of the sensor is 28 kPa^-1 in the stress range of0-20 kPa and 12.7 kPa^-11 in the stress range of 20-60 kPa.Moreover,to further improve the cycling stability,the conductive material of sensor was replaced by conductive polymers?PPy?,and the electrodeposition method was used to increase the bonding force between the substrate and the conductive material.The sensor have a favorable repeatability over 16000 cycles.?2?In order to improve the sensing performance,we modulated the conductivity and young's modulus of sensing material.Different AgNWs/rGO porous composites were prepared by one-step hydrothermal method.The sensing performance showed that the sensor had the best sensing performance when the mass ratio of GO to AgNWs reached 2:1.The response range of the sensor is 0-75 kPa,the highest sensitivity is 25.5 kPa^-1.Compared with the sensing performance of flexible pressure sensing sensor based on carbon foam,the sensitivity of the composite sensor was increased by more than twice times and the response range was increased by more than 0.5 times.In addition,the sensor based on the optimized mass ratio had excellent cycle stability.The maximum relative current remains at 99%after 10,000 cycles under the stress of 3 kPa.?3?To further improve the sensing performance based on 3D porous composite sensor,we increase the interface contact resistance between sensing material and electrode.Porous carbon cloth is selected as the electrode of the flexible force sensor.The sensing performance showed that the maximum response stress of the sensor was 50kPa by using carbon paper as elecrodes,while with porous carbon cloth as the electrode,the maximum stress response can reach 500 kPa.The sensitivity can still reach 34 kPa^-1 in the stress range of 150-500 kPa,and has a low monitoring limit?1Pa?.Moreover,the sensor shows good cyclic stability after the heat treatment.The retention value of the maximum current remains at 99%after 10,000 cycles under a high stress of 35 kPa.In addition,the power consumption of the sensor is greatly reduced in the unstressed state by increasing the contact interface resistance,and the full flexibility of the pressure sensor was also realized by using carbon cloth as a electrode.In this paper,we focused on the problems which restricted the wide application of flexible piezoresistive sensor.We improved the sensing performance of flexible piezoresistive sensors from the aspects of modulating the physical characteristics of sensing materials,optimizing the structural design,et.al.,so that it can meet the application requirements in the field of intelligent equipment.