近年来,随着微电子学的不断进步,电子器件正朝着小型化、集成化的趋势发展.但是在纳米尺度下,表面效应和尺寸效应将变得不可忽略,这便制约了传统块体铁电材料在现代工业中的应用.因此,没有小尺寸效应限制并且有着稳定自发极化的二维铁电材料成为了材料科学领域研究的重点之一.本文首先从铁电材料的分类出发,将其分为二维非范德华铁电材料和二维范德华铁电材料,并列举了各类别中已被实验报道的铁电材料,讨论了它们的发展和研究现状,并阐述了它们内在的极化机制和新奇的物理特性.这些新的二维铁电材料有望在未来的纳米级铁电应用中发挥重要的作用,使电子器件的高度集成成为可能.然后,本文综述了二维铁电器件的最新研究进展,包括铁电场效应晶体管(ferroelectric field effect transistor,FeFET)、铁电隧道结(ferroelectric tunnel junction,FTJ)和铁电突触,总结了各种器件性能,并阐述了相应的工作原理.最后,对二维铁电材料领域进行了展望,提出我们需要在理论模型、材料制备、电子器件的稳定性和界面效应等方面开展更深入研究的观点.
Recent advances in two-dimensional ferroelectric materials
With the continuous progress of microelectronics,electronic devices are developing towards miniaturization and integration.However,Moore's Law has been challenged when the device size gradually shrinks.The difficulties encountered in highly integrated devices mainly come from the following aspects.(1)Physical limit problem:When the device size is smaller than the electron wavelength of the transistor(usually less than 10 nanometers),the quantum effect and tunneling effect will occur.The performance and stability of the device are affected.(2)Thermal effect:The power density of the device will increase with the decrease of the device size,which can lead to overheating of the device.Therefore,searching for new materials has become one of the hotspots in the field of materials science.Ferroelectric materials are one kind of important functional materials,which have a novel intrinsic physical mechanism and rich characteristics(such as piezoelectricity,pyroelectricity,nonlinear optical effect,etc.),so that it has a wide range of application prospects in electronic devices and information storage technology.However,with the trend of highly integrated electronic devices,the surface effect and size effect cannot be ignored,which restrict the application of bulk ferroelectric materials in modem industry.Therefore,two-dimensional ferroelectric materials without finite size effects and with stable spontaneous polarization have attracted great attention.In this review,the development and research status of two-dimensional ferroelectric materials is discussed.Two-dimensional ferroelectric materials are classified.(1)Non-van der Waals ferroelectric materials:Including perovskite oxides,Bi2O2Se and HfO2 materials.By shielding the depolarization field effect or enhancing the driving force,they can be made to exhibit ferroelectric properties in the two-dimensional limit.(2)van der Waals ferroelectric materials:Including indium copper thiophosphate,indium selenide,tin telluride,molybdenum telluride and tungsten telluride.Their ferroelectric properties mainly come from charge transfer or electron hybridization,and they realize polarization reversal through ion shift or atomic distortion.This review also presents the application and latest research progress of two-dimensional ferroelectric material innovative devices,including(1)ferroelectric field effect transistors(FFEs):Ferroelectric materials usually have the property of self-polarization.When using ferroelectric materials instead of traditional oxides as the dielectric layer of FETs,the polarization induced electric field can adjust the channel conductivity,thereby achieving non-volatile ferroelectric storage.(2)Ferroelectric tunnel junctions(FTJs):The FTJ is a heterostructure consisting of a ferroelectric thin film as a barrier layer,with electrodes sandwiched on both sides.The atomically thin van der Waals ferroelectric materials are also suitable materials for tunneling barrier layers of FTJs.(3)Ferroelectric synapses:Ferroelectric materials have unique non-volatile polarization characteristics,and the plasticity of polarization is very similar to that of biological synapses.Although significant research progress has been made,ferroelectric synapses are still in the stage of principle verification and further research is needed in the future.Finally,an outlook on the field of 2D ferroelectric materials is provided.In general,the exploration of 2D ferroelectric materials is still in its early stage.Further work includes establishing and improving theoretical models,developing efficient preparation methods,delving into the durability and stability of 2D ferroelectric devices,and studying and analyzing the interface effects between two-dimensional ferroelectric materials and other materials.
ferroelectricityvan der Waals layered materialferroelectric field effect transistorferroelectric tunnel junctionferroelectric synapse
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