Research On Flexible Humidity Sensors Based On PTFE Microporous Membrane

Humidity is an important environmental parameter.Monitoring and controlling environmental humidity is of great significance to industrial and agricultural production and people's daily life.Therefore,the research of humidity sensor has attracted the attention of many researchers.There are many kinds of humidity sensors based on different mechanisms,such as resistive sensors,capacitive sensors,optical sensors,piezo-resistive sensors,surface acoustic wave sensors and so on.With the development of society and the arrival of the Internet of things era,people have put forward higher requirements for the performance of humidity sensors.In recent years,flexible electronic devices have developed rapidly in the fields of flexible display,flexible sensors,electronic skin,energy collection and so on,and have become a new research field.For flexible humidity sensors,researchers have done a lot of work,trying to fabricate humidity sensors on different flexible substrates.The substrates of common flexible humidity sensors include cellulose acetate,polyethylene terephthalate(PET),polydimethylsiloxane(PDMS),polyimide(PI)and so on.Polytetrafluoroethylene(PTFE)microporous membranes have many advantages like low cost,excellent mechanical properties,good thermal stability and chemical stability.A piece of PTFE microporous membrane has a large number of micron sized pores.The micropores allow gas to pass through but prevent liquid water from penetrating it.Therefore,PTFE films are breathable and waterproof.This is conducive to the diffusion of external air into sensitive materials of humidity sensors,and to quicken the response of humidity sensors.A capacitive humidity sensor and an impedance humidity sensor were designed and prepared with hydrophobic PTFE microporous membranes as the flexible substrate in this thesis.The main work is as follows:(1)Based on PTFE microporous membrane substrate,a flexible capacitive humidity sensor with polyimide as the humidity sensitive dielectric was proposed.Its structure and fabrication process were developed.The compatibility of PTFE microporous membrane working as a substrate of humidity sensors were studied.Finally,the static and transient tests of the capacitive humidity sensor were carried out,and the performance parameters such as sensitivity,hysteresis,response and recovery time were measured.In addition,the effect of microporous on the response and recovery time of the humidity sensor was verified.(2)Based on PTFE microporous membrane substrate,a flexible impedance humidity sensor with graphene oxide film as the humidity sensitive material was proposed.The structure and preparation process of the sensor were designed.According to the impedance spectrums of the sensor at different humidity,an equivalent circuit model of the sensor was established and the humidity sensing mechanism was studied.Finally,the static and transient tests of the impedance humidity sensor were carried out,and the performance parameters such as sensitivity,hysteresis,response and recovery time were measured and explained.In this thesis,the feasibility of using PTFE microporous membrane as a flexible substrate of humidity sensors was studied.Two different humidity sensors were designed and fabricated,and their performance parameters were measured.We hope to provide some useful information for the research of the flexible humidity sensors.