Studying On Fabrication Of Flexible Pressure Sensors And Their Influence Factor Of Sensitivity

With the growing demand for booming artificial intelligence and the Internet of Everything?IoT?,flexible pressure sensors,as one of the most important sensing elements,have attracted much attention because of their promising applications in medically diagnosed wearable electronic devices.To distinguish external stimuli,the applied force was typically converted to an identifiable electrical signal or other responsive output signal by flexible pressure sensors.In a way,flexible sensors can help inanimate objects understand the"feelings"of human interactions and obtain biological signals such as blood pressure and body movement.Sensitivity,response time,detection limit?LOD?and stability are widely used to evaluate the performance of flexible pressure sensors in current research.According to the sensing mechanism,there are three typical types of flexible pressure sensors,including resistance,capacitance,piezoelectric.Among them,flexible capacitive and resistive pressure sensors have been widely studied because of their high sensitivity and low hysteresis.However,the sensitivity of ordinary flexible capacitive and resistive pressure sensors is not sufficient to meet the requirements of practical application.In order to improve the sensitivity of flexible sensors,the most convenient and effective way is to microstructure the sensor layer of the flexible pressure sensor.However,the preparation of microstructures usually uses complex and high-cost methods such as laser etching,which greatly limits the large-scale production of flexible pressure sensors.In this paper,we propose a method to improve the sensitivity of flexible pressure sensors by simplifying the process of microstructure preparation,and create a capacitive flexible pressure sensor and two resistive flexible pressure sensors,respectively,as follows:1.Capacitive flexible pressure sensor based on gold/polydimethylsiloxaneFirst,a uniform convex microstructure array was prepared by colloidal self-assembly,and then prepared flexible substrate with microstructure array was fabricated by two transfers,followed by spraying gold nanoparticles to prepare a flexible electrode with microstructure array.Then,we prepared the dielectric layer?PVDF?of different thicknesses by rotating the method,and assembled the two flexible electrodes and dielectric layers into a flexible pressure sensor.The sensor shows an ultra-high sensitivity of 30.2 kPa^-1?130Pa?,a low detection limit of 0.7 Pa,a fast response time of25 ms,and the stability of up to 100,000 cycles.The FEA results show that when external pressure is applied to the sensor,the synergy of the microarray structure on the electrode surface and the ultra-thin dielectric layer significantly increases the contact area and reduces the distance between the two electrodes,thereby increasing the sensitivity of the sensor.The flexible pressure sensor has been successfully used to monitor a variety of human biological signals and robot action signals,providing a development strategy for intelligent healthcare,automatic speech recognition?ASR?and language recognition.2.Resistive flexible pressure sensor based on copper nanowire/graphene/melamine foamFirst,we prepared an interconnected conductive network of copper nanowires?Cu NWs?and reduced graphene oxide?RGO?adsorbed on melamine?MF?skeletons by reducing graphene oxide and copper salts adsorbed to melamine foam,and then led electrodes at the upper and lower ends of the conductive foam to assemble into resistive flexible pressure sensors.The interconnected conductive networks of Cu NWs and RGO saline adsorbed on melamine?MF?skeletons resulted significant changes in the resistance of the sensor under external stimulation.X-ray diffraction analysis showed that,due to the presence of RGO,CuNWs in the sensor were barely oxidized after a month of exposure to air.The CuRGOMF sensor exhibits high sensitivity over both small and large compression pressures and excellent cycle stability after 5000 cycles.Finally,we successfully demonstrated the potential application of sensors for hand grip,mouse click,and pick and drop items.3.Resistive flexible pressure/stretch sensor based on carbon nanofibers and polybutadiene-styrene-butadieneFirst,the conductive material carbon nanofibers and polybutadiene-styrene-butadiene?SBS?were mixed to prepare conductive polymers,and then the conductive polymers were fabricated into flexible pressure sensor with an ultra-high sensitivity of769.2 kPa^-1,as low as 5 Pa detection limits and high reliability of more than 1000 cycles.In addition,due to SBS's excellent tensile performance,we prepared a non-structured flexible strain sensor with sensitivity of 105.6.The compressible and stretchable sensor has a wide range of applications in wearable medical monitoring devices,intelligent robot technology and human-machine interface.