Design,Fabrication And Application Of The Flexible Capacitive Sensors

To meet the growing demands of flexibility and miniaturization for new electronic devices,this thesis project is focused on the development of a new type of flexible pressure sensor,specifically including the preparation or modification of related materials,and assembling testing devices.By optimizing the electrode preparation methods and fabrication the dielectric films with different microstructure through a template method,a type of flexible capacitive pressure sensors was prepared.The electrode performance and the effect of the film microstructure on the sensor sensitivity were also studied to realize the detection of simple pressure signals.Following is the main studies.1.The preparation of flexible electrodeUsing trimethylamine(TMA)to modify the surface of polyimide(PI)and then electroless copper plating,we prepared the copper flexibility electrode that shows larger conductivity and lower moisture absorption when comparing with that prepared through traditional surface treatment with aqueous KOH.The detailed mechanism of this surface modification of PI was also studied.2.The fabrication of flexible microstructured polydimethylsiloxane(PDMS)thin filmWe used the template developed by self-organization of microspheres on the surface to obtain the PDMS thin film with a uniform micro-nano porous structure.Furthermore,by changing the size of the microsphere template,we can alter the size(500~850 nm)and morphology of the resulting porous structure on the PDMS film.In the case of 500 and 750 nm microspheres,the corresponding porous structures on PDMS have a secondary nanostructure with roughness of 30~50 nm.3.The capacitive pressure sensor based on the microstructured PDMSThe sensor based on microstructured dielectric film was fabricated,with a basic sandwich structure of two electrodes having a dielectric film in between.Mechanical sensitivity and electrical performance of the sensor were tested according to its working principle.In addition,we studied the influence of the microstructure of dielectric layer on the sensor sensitivity.The main innovation points of this research include: i.developed a new surface treatment method to modify polyimide,based on which a metal electrode with suitable performances was obtained;ii.designed and fabricated microstructured PDMS dielectric thin layer and obtained the capacitive pressure sensors using this PDMS film and metal-electrode.Our study indicates that after the treatment of PI for 6 h using TMA,3~5 min electroless copper plating,the resulting electrode layer has a thickness of 0.6~1.0 ?m?m,a square resistance of 3~5 ?/?.The average conductivity of the metal layer is almost at the same magnitude of the pure copper.Through optimizing and selecting different microstructured dielectric/electrode layer,the best sensitivity of 2.7 kPa-1 can be achieved with the PDMS flexible sensor.