Application Of Ferroelectric Polymer In Organic Electronics

Spontaneous polarization,which can be switched under external electric field,is the most attractive characteristics in ferroelectric polymers.To serve as a natural electric field,the controllable spontaneous polarization is widely utilized in binary system data storage,high-efficient solar cells,and so on.Here,we focus on the applications of ferroelectric polymers in organic ferroelectric memory,functional insulator-semiconductor interface,and bionic electronics.The main contents in this thesis are listed below:1.To improve the performance of ferroelectric polymer based memory devices,including reducing energy consumption and increasing storage speed,it is important to reduce the energy barrier of polarization switching.By breaking parts of the ferroelectric phases,one could reduce the stability of spontaneous polarization and increase the domain wall energy,which will result in reduced energy barrier.Specifically,by doping small amount of CFE or blending the terpolymer P(VDF-TrFE-CFE)in copolymer P(VDF-TrFE),the coercive field,which reflects the energy barrier,of the polymers reduce around 50%.There is another way to meet the similar performance.Terpolymer P(VDF-TrFE-CFE)exhibits ultra-low coercive field yet unstable spontaneous polarization,while stable ferroelectricity with low coercive field can be induced through nanoimprinting lithograph of the terpolymer thin film.2.Different from piezoelectric effect,flexoelectric effect,induced through strain gradient,also donates to the electro-mechanical conversion.Recently,it is found that flexoelectric effect can be amplified at nanoscale.The induced flexoelectric field can lead to polarization switching in ferroelectric film.In our research,to study the flexoelectric effect in P(VDF-TrFE)film,theoretical analysis is applied to evaluate the magnitude of flexoelectric field.It is found that the spontaneous polarization of ferroelectric polymer can also be switched by force,which can be regarded as a novel way for flexible electronic information storage.3.For field-effect transistor,the polarization on the dielectrics-semiconductor interface would affect the conductivity of the semiconductor.Meanwhile,we know that the polarization of ferroelectric polymer can happen to change under stimulation of mechanical force or heat.Here,through utilizing coupling between dipoles in ferroelectric polymer and carriers in the semiconductor,we design three types of transistors free from gate electrodes.(a)The device can serve as an ultra-sensitive force transducer;(b)By using the terpolymer instead of the copolymer,we propose a novel phase change memory based on the irreversible ferroelectric-paraelectric phase change in the terpolymer;(c)We find that the light-induced conductivity increase becomes stable in ferroelectric polymer-semiconductor device after removal of the light.It open a new way of the device as a light-controllable memory.4.We propose an artificial retina fabricated from blends of ferroelectric polymer and azo-containing polymer,which can directly convert light into electric polarization.Molecular motion in azo-containing polymer can be induced by illumination,as a consequence,strain can be induced within ferroelectric polymer,leading to the polarization change.Besides,we also connect the device to nerve cells to investigate the signal communication between them.It is intriguing that the cells can respond to the light-induced polarization change.Our research demonstrates the potential that the polymer blend film can directly replace the natural retina for helping the blinds to recover their vision.5.P(VDF-TrFE-CFE)exhibits controllable polarization under external electric field stimulation.In general,the high magnitude and increased time of applying electric field can lead to relative stable polarization in the terpolymer,while low magnitude and short time of applying electric field result in polarization rapidly decayed after removing the electric field.The whole procedure is similar with human memory.The terpolymer based memory has potential to using in artificial intelligence devices.