Studies On The Ferroelectricity Of Two-dimensional Layered Material ?-In₂Se₃ And Ferroelectric Devices Application

Room-temperature ultrathin ferroelectrics are crucial for building high-density non-volatile memory.In the past decades,conventional ferroelectric thin films,for example,the complex ferroelectric perovskite oxide,received enormous research efforts.However,limited by the possible critical size effect or the ferroelectricity vanishing below a critical film thickness,there is a great challenge when developing modern nonelectronic devices based on the conventional ferroelectric thin film.Two-dimensional(2D)van der Waals(vdW)material,which is with naturally stable layered structure,innate surface chemistry,and weak inter-layer interaction,adds an excellent material foundation for achieving two-dimensional ferroelectricity at the atomic-scale limit thickness and also provides a research platform for the development of next-generation multi-functional devices.Currently,the in-plane(IP)ferroelectricity has been realized in the single layer of SnTe crystal[1].However,the more useful room-temprature out-of-plane(OOP)ferroelectricity found in CuInP2S6 can only be maintained above 4 nm[2].?-In2Se3,a layered semiconductor material,has been widely concerned due to its simple structure and stable ferroelectricity at room temperature.More importantly,its unique intercorrelated IP and OOP ferroelectricity are possible to achieve the OOP ferroelectricity in single layer limitation[3].The layered 2D ferroelectrics provide the opportunity and possibility for further miniaturization of nanoelectronics as well as developing novel flexible electronics.In this article,we first review the research background of conventional ferroelectrics.This thesis is mainly devoted to the study of the ferroelectricity of a-In2Se3.The contents of the thesis include:Chapter 1 We will first review the relevant background of traditional ferroelectric research,secondly introduce the research progress of two-dimensional ferroelectrics and the application of ferroelectrics in electronic devices,and finally look forward to the development of two-dimensional ferroelectrics.Chapter 2 Related experimental programs and technical introductions.The first part is to introduce the working principle and data error analysis of piezoelectric power microscope(PFM);the second part is the preparation and characterization of the sample;the third part is the preparation technology and operation precautions of the electrode.Chapter 3 Experimental exploration and research on the ferroelectricity of a-In2Se3 at room temperature.Based on PFM,we verified a stable ferroelectric domain structure in the a-In2Se3 thin layer.The operation of writing/reading ferroelectric domains and the single-point polarization test also verified the controllable inversion of ferroelectric polarization.Also,by statistical comparison of sample thickness and piezoelectric response signal strength,we found no significant correlation between the two.Finally,we show the ferroelectric stripe domain structure observed in the a-In2Se3 thin layer.Chapter 4 We prepared an a-In2Se3 thin-layer ferroelectric capacitor,the device exhibits the rectification effect of the diode,and the rectification direction can be changed by switching the polarization direction.Chapter 5 Based on the out-of-plane ferroelectricity of a-In2Se3,we designed and fabricated a ferroelectric gate field effect transistor to verify the non-volatility of ferroelectric domains,demonstrating a prototype ferroelectric memory device based on layered ferroelectric materials.Chapter 6 We summarize the research results of the experimental part of the paper.