Flexible Ferroelectric Thin Films And Their Prototype Devices Research

Ferroelectrics are non-centrosymmetric polar materials,possessing various practical application functions.With the development of the modern scientific technology and the increasing diversified demand for people’s lives,flexible sensors,flexible electronic screens and wearable devices turn into the mainstream products in next-generation,as a result,how to apply the ferroelectric materials to flexible electronic devices has become the new research hot-topic.Traditional perovskite ferroelectric materials possess excellent properties,contributing to its backbone state of the national economy.Nonetheless,most of the inorganic ferroelectric materials are inflexible,with strong rigidity and high brittleness,imposing the bottleneck and challenge in flexible electric devices applications.On the other hand,organic ferroelectric materials are naturally flexible,non-toxic,with lightweight and can be prepared economically.The research has risen rapidly in this decade and achieved considerable progress.However,in general,organic ferroelectric materials are weak in functionality,which restricts the further development of high performance flexible electronic devices as well.The dissertation begins with a traditional high-performance PbZr0.52Ti0.48O3 perovskite-type ferroelectric thin film,trying to make the rigid film flexible."One-step method with flexible substrate" method for preparing thin film has been introduced and the stable ferroelectric property in bending process has been illuminated,the remarkable improvement for piezoelectric property mechanism being announced.Additionally,selecting intrinsic flexible organic ferroelectric thin films,trying to add functionality to the flexible thin films.We find outstanding electric properties of C3N2H5ClO4 thin film,and further elucidates the ferroelectric performance and electric-optical coupling effect of multiple polar axis C7H13NO·HCl thin film.The dissertation,which is divided into three explicit parts,strives to make a leap forward in flexible ferroelectric thin film for prototype devices,and as a consequence,provide some help for their industrialization development.Firstly,we employed the "flexible substrate,one-step" method for fabricating flexible PbZr0.52Ti0.4sO3 ferroelectric thin film and found its stable ferroelectric property in bending states.Finally,we revealed the mechanism for piezoelectric property enhancement effect:PbZr0.52Ti0.48O3 bulk materials manifest superior functionality,but they are generally hard and brittle,with the maximum tolerance for strain<1%.In terms of this situation,we used 10μm thickness flexible mica substrate to prepare large-scale and high quality flexible Mica/PbZr0.52Ti0.48O3thin film.We found the strain is ≤5%and no influence to the micron order structure of prewritten ferroelectric domain when thin film was bent in 1.4 mm radius.It possessed with the saturated polarization of～60 μC cm-2 and a dielectric tenability of～90%.Then we clarified the stability of ferroelectric anti-fatigue property of the thin film.We found there was no obviously weaken in the ferroelectric properties after 10000 times bending action in 2.2 mm radius and 1010 times anti-fatigue memory testing.The possible anti-fatigue mechanism has been demonstrated,that is the thin film and the substrate are combined in atomic level via "one-step"method preparation,resulting in lower level of defects.Additionally,we found d33 of PbZr0.52Ti0.48O3 thin film was about 1200pm V-1 and clarified the mechanical coupling between PZT and flexible mica substrate realized via the d31 piezoelectric tensor,where the substrate bending induced by thin film transverse strain contributed to the equivalent piezoelectric constant of the thin film.Secondly,we developed a new kind of fabrication method for single crystal-like C3N2H5ClO4 ferroelectric thin film and discovered the excellent ferroelectric property and remarkably enhanced piezoelectric property:Organic ferroelectric materials are intrinsically flexible.We applied spin coating method at room-temperature for thin film preparation,where the Van der Waals played a vital role for single-crystal-like thin film structure.No strictly lattice matching was demanded in this method like inorganic ferroelectric thin film growth and large-scale and high quality C3N2H5ClO4 thin film with(0-1-1)and(1 0-1)preferential orientations has grown.We presented the important factors for growth and the film preferential growth mechanism was expounded as well.In addition,we found the stability of ferroelectric property in large compressive and tensile strain.By the observation of ferroelectric domain evolution at different temperature,we certified the stability and retentivity of ferroelectric property.Last,by the comparison with PFM data of inorganic ferroelectric film,we testified the enhanced microcosmic piezoelectric property of C3N2H5ClO4 ferroelectric thin film,which was due to the small elastic constant of thin film and the lighter camper effect from the flexible substrate.Thirdly,we found the outstanding ferroelectric properties and electric-optical coupling effect in(R)-(-)-3-hydroxlyquinuclidinium chloride(C7H13NO·HCl)transparent flexible ferroelectric thin film at room temperature:C7H13NO·HCl is transparent chiral material with multiple ferroelectric polar axis,which is inherently flexible as well.Spin coating method was used for film fabrication.We found the distinct effect of ferroelectric domain reversal dominated by domain wall energy at room temperature,and the thin film in each polarization direction possessed the different resistive states.Next,we developed the high-performance ferroelectric memory with a large on/off ratio of～26.6.It showed anti-fatigue memory property and stability after 1 000 times ferroelectric polarization switching.In addition,we found thin film angle-dependent optical behaviors with polarized light,revealing the mechanism of electro-optic coupling effect between dipole and electromagnetic wave perpendicular to the liner light propagation.Based on the above discussion,the dissertation will introduce the detailed research work on the flexible inorganic and organic ferroelectric thin film.We emphasize on the physical mechanism,property advantage and the potential application.We hope the dissertation will be helpful for ferroelectric materials research and its flourish development on the way.