Preparation And Application Of Flexible Pressure Sensors Based On Conductive Nanomaterial

Flexible pressure sensor has attracted increasing research interest due to its potential applications in wearable healthcare monitors,electronic skins,biomedical diagnostics and so on.In order to realize the aforementioned technologies,flexible pressure sensors with high mechanical flexibility,high sensitivity,low detection limit,fast response and high working stability are required.Among the kinds of flexible pressure sensors,the flexible pressure sensors based on the capacitive and resistive sensing are easily to be fabricated and show outstanding performance,especially the short response time and high working stability,but the pressure sensitivity of common capacitive and resistive pressure sensors can’t meet the needs of application.To enhance their sensitivity,the electrodes and dielectric layers are generally micro-structured,but the preparation processes of micro-structures are usually fabricated by chemical etching or photolithography techniques,which are complex,time-consuming and difficult for scaling up production.In this study,a facile fabrication strategy was provided to form microstructure mould.Using the mould,the flexible electrode and dielectric layer with micro-array structure were prepared,and three kinds of capacitive or resistive flexible pressure sensor were fabricated.The main research contents are as the follows:1.Preparation and application of capacitive flexible pressure sensor based on flexible micro-array electrode.In this work,the pre-stretched PDMS film which was treated by plasma of dry low-pressure air shows spontaneous buckle surface stucture and was used to fabricate the micro-array mould.By several transfer processes,the bottom electrode was prepared via embedding AgNWs into PDMS film of micro-array structure.Polydimethylsiloxane（PDMS）substrate,coated with silver nanowires（AgNWs）,was used as the top electrode,and polyvinylidene fluoride（PVDF）was used as the dielectric layer.The flexible pressure sensor integrates the top electrode,dielectric layer and micro-array electrode in a sandwich structure.It is demonstrated that such sensors possess the superiorities of high sensitivity(2.94 kPa^-1),low detection limit（<3 Pa）,short response time（<50 ms）,excellent flexibility and stability.This simple process for preparing such sensors can also be easily scaled up to construct a pressure sensor array in identifying the location and the distribution of external pressure.In addition,this flexible pressure sensor exhibits good performance even in non-contact way,such as detecting voice vibrations and air flow.2.Preparation and application of capacitive flexible pressure sensor based on micro-array dielectric layer.Firstly,the flexible electrodes were simply prepared by transferring the vacuum filtration AgNWs film onto the PDMS substrate.Subsequently,using the aforementioned micro-array mould,the PDMS dielectric layer with micro-array structure were prepared by a series of transfer process.By integrating PDMS flexible electrodes and micro-array PDMS dielectric layer,the capacitive flexible pressure sensor was fabricated.The pressure response performances were systematically studied,and the results suggested that the pressure sensor possesses high sensitivity(2.04 kPa^-1),wide measure range（9000 Pa）,and low detection limit（<7 Pa）.The flexible capacitive pressure sensors can be used to measure the pressure of fingertips when an object was grabbed with fingers,and the pressure sensor array based on the flexible capacitive pressure sensor can be used to detect the spatial distribution of the applied external pressure.3.Preparation of resistive flexible pressure sensor based on micro-array electrode.Based on the work of first part,we prepared the AgNWs-embedded PDMS flexible electrode with micro-array structure,which was used as the top electrode.The flexible PDMS substrate coated with AgNWs film by vacuum filtration and transfer process was treated as bottom electrode.The resistive flexible pressure sensor was fabricated by intergrating the top electrode and bottom electrode.The preliminary test results demonstrated that the resistive flexible pressure sensor has excellent pressure response performances,and its maximum sensitivity was-2.6 kPa^-1.