Ferroelectric HfO_(2)-based materials for next-generation ferroelectric memories

Ferroelectric random access memory(FeRAM)based on conventional ferroelectric perovskites,such as Pb(Zr,Ti)O_(3)and SrBi_(2)T_(2)O_(9),has encountered bottlenecks on memory density and cost,because those conventional perovskites suffer from various issues mainly including poor complementary metal-oxide-semiconductor(CMOS)-compatibility and limited scalability.Next-generation cost-efficient,high-density FeRAM shall therefore rely on a material revolution.Since the discovery of ferroelectricity in Si:HfO_(2)thin films in 2011,HfO_(2)-based materials have aroused widespread interest in the field of FeRAM,because they are CMOS-compatible and can exhibit robust ferroelectricity even when the film thickness is scaled down to below 10 nm.A review on this new class of ferroelectric materials is therefore of great interest.In this paper,the most appealing topics about ferroelectric HfO_(2)-based materials including origins of ferroelectricity,advantageous material properties,and current and potential applications in FeRAM,are briefly reviewed.

New‑Generation Ferroelectric AlScN Materials

Ferroelectrics have great potential in the field of nonvolatile memory due to programmable polarization states by external electric field in nonvolatile manner.However,complementary metal oxide semiconductor compatibility and uniformity of ferroelectric performance after size scaling have always been two thorny issues hindering practical application of ferroelectric memory devices.The emerging ferroelectricity of wurtzite structure nitride offers opportunities to circumvent the dilemma.This review covers the mechanism of ferroelectricity and domain dynamics in ferroelectric AlScN films.The performance optimization of AlScN films grown by different techniques is summarized and their applications for memories and emerging in-memory computing are illustrated.Finally,the challenges and perspectives regarding the commercial avenue of ferroelectric AlScN are discussed.

Simulation of electric properties of MFIS capacitor with BNT ferroelectric thin film using Silvaco/Atlas

Metal-ferroelectric-insulator-silicon(MFIS) capacitors with Bi3.15Nd0.85Ti3O12(BNT) ferroelectric thin film were simulated using a commercial software Silvaco/Atlas,and the effects of applied voltage and insulator layer on capacitance-voltage(C-V) hysteresis loops and memory windows were investigated. For the MFIS capacitors with CeO2 insulator,with the increase of applied voltage from 2 V to 15 V,the C-V loops become wider and memory windows increase from 0.15 V to 1.27 V. When the thickness of CeO2 layer increases from 1 nm to 5 nm at the applied voltage of 5 V,the C-V loops become narrower and the memory windows decrease from 1.09 V to 0.36 V. For MFIS capacitors with different insulator layers(CeO2,HfO2,Y2O3,Si3N4 and SiO2),the high dielectric constants can make the C-V loops wider and improve the capacitor's memory window. The simulation results prove that Silvaco/Atlas is a powerful simulator for MFIS capacitor,and they are helpful to the fabrication of MFIS nonvolatile memory devices.

Ferroelectric-gated ReS_(2)field-effect transistors for nonvolatile memory

Ferroelectric field-effect transistors(FeFET)with nondestructive readout capability have emerged as an attractive candidate for next-generation nonvolatile memory technology.Herein,we demonstrate ferroelectric-gated nonvolatile memory featuring a top gate architecture by combining multi-layer ReS_(2)with ferroelectric poly(vinylidene fluoride-trifluoroethylene)(P(VDF-TrFE))copolymer films.The ReS_(2)FeFET using hBN as substrate shows a large memory window of~30 V.Repeated write/erase operations are successfully performed by applying pulse voltage of±25 V with 1 ms width to the ferroelectric P(VDF-TrFE),and an ultra-high write/erase ratio of~107 can be achieved.Furthermore,the ReS_(2)FeFET shows stable data retention capability of longer than 2,000 s and reliable endurance of greater than 2,000 cycles.These characteristics highlight that such ferroelectricgated nonvolatile memory has great potential in future non-volatile memory applications.

Evidence for reversible oxygen ion movement during electrical pulsing:enabler of emerging ferroelectricity in binary oxides

Ferroelectric HfO_(2)-based materials and devices show promising potential for applications in information technology but face challenges with inadequate electrostatic control,degraded reliability,and serious variation in effective oxide thickness scaling.We demonstrate a novel interface-type switching strategy to realize ferroelectric characteristics in atomic-scale amorphous binary oxide films,which are formed in oxygen-deficient conditions by atomic layer deposition at low temperatures.This approach can avoid the shortcomings of reliability degradation and gate leakage increment in scaling polycrystalline doped HfO_(2)-based films.Using theoretical modeling and experimental characterization,we show the following.(1)Emerging ferroelectricity exists in ultrathin oxide systems as a result of microscopic ion migration during the switching process.(2)These ferroelectric binary oxide films are governed by an interface-limited switching mechanism,which can be attributed to oxygen vacancy migration and surface defects related to electron(de)trapping.(3)Transistors featuring ultrathin amorphous dielectrics,used for non-volatile memory applications with an operating voltage reduced to±1 V,have also been experimentally demonstrated.These findings suggest that this strategy is a promising approach to realizing next-generation complementary metal-oxide semiconductors with scalable ferroelectric materials.

Ferromagnetic and ferroelectric two-dimensional materials for memory application

The discoveries of ferromagnetic and ferroelectric two-dimensional(2D)materials have dramatically inspired intense interests due to their potential in the field of spintronic and nonvolatile memories.This review focuses on the latest 2D ferromagnetic and ferroelectric materials that have been most recently studied,including insulating ferromagnetic,metallic ferromagnetic,antiferromagnetic and ferroelectric 2D materials.The fundamental properties that lead to the long-range magnetic orders of 2D materials are discussed.The low Curie temperature(Tc)and instability in 2D systems limits their use in practical applications,and several strategies to address this constraint are proposed,such as gating and composition stoichiometry.A van der Waals(vdW)heterostructure comprising 2D ferromagnetic and ferroelectric materials will open a door to exploring exotic physical phenomena and achieve multifunctional or nonvolatile devices.

Two-dimensional In_(2)Se_(3):A rising advanced material for ferroelectric data storage

Ferroelectric memory is a promising candidate for next-generation nonvolatile memory owing to its outstanding performance such as low power consump-tion,fast speed,and high endurance.However,the ferroelectricity of conven-tional ferroelectric materials will be eliminated by the depolarization field when the size drops to the nanometer scale.As a result,the miniaturization of ferroelectric devices was hindered,which makes ferroelectric memory unable to keep up with the development of integrated-circuit(IC)miniaturization.Recently,a two-dimensional(2D)In2Se3 was reported to maintain stable ferro-electricity at the ultrathin scale,which is expected to break through the bottle-neck of miniaturization.Soon,devices based on 2D In2Se3,including the ferroelectric field-effect transistor,ferroelectric channel transistor,synaptic fer-roelectric semiconductor junction,and ferroelectric memristor were demon-strated.However,a comprehensive understanding of the structures and the ferroelectric-switching mechanism of 2D In2Se3 is still lacking.Here,the atomic structures of different phases,the dynamic mechanism of ferroelectric switching,and the performance/functions of the latest devices of 2D In2Se3 are reviewed.Furthermore,the correlations among the structures,the properties,and the device performance are analyzed.Finally,several crucial problems or challenges and possible research directions are put forward.We hope that this review paper can provide timely knowledge and help for the research commu-nity to develop 2D In2Se3 based ferroelectric memory and computing technol-ogy for practical industrial applications.

Experimental search for high-performance ferroelectric tunnel junctions guided by machine learning

Ferroelectric tunnel junction(FTJ)has attracted considerable attention for its potential applications in nonvolatile memory and neuromorphic computing.However,the experimental exploration of FTJs with high ON/OFF ratios is a challenging task due to the vast search space comprising of ferroelectric and electrode materials,fabrication methods and conditions and so on.Here,machine learning(ML)is demonstrated to be an effective tool to guide the experimental search of FTJs with high ON/OFF ratios.A dataset consisting of 152 FTJ samples with nine features and one target attribute(i.e.,ON/OFF ratio)is established for ML modeling.Among various ML models,the gradient boosting classification model achieves the highest prediction accuracy.Combining the feature importance analysis based on this model with the association rule mining,it is extracted that the utilizations of{graphene/graphite(Gra)(top),LaNiO_(3)(LNO)(bottom)}and{Gra(top),Ca_(0.96)Ce_(0.04)MnO_(3)(CCMO)(bottom)}electrode pairs are likely to result in high ON/OFF ratios in FTJs.Moreover,two previously unexplored FTJs:Gra/BaTiO_(3)(BTO)/LNO and Gra/BTO/CCMO,are predicted to achieve ON/OFF ratios higher than 1000.Guided by the ML predictions,the Gra/BTO/LNO and Gra/BTO/CCMO FTJs are experimentally fabricated,which unsurprisingly exhibit≥1000 ON/OFF ratios(~8540 and~7890,respectively).This study demonstrates a new paradigm of developing high-performance FTJs by using ML.

氧化铪基铁电薄膜的研究进展

氧化铪(HfO_(2))基铁电薄膜拥有稳定、独特的铁电极化,且与CMOS集成电路制造工艺的高度兼容性,成为下一代高密度、非易失性铁电存储器的重要候选材料,因而备受关注。首先探讨了HfO_(2)基铁电薄膜的不同制备方法,分析了脉冲激光沉积法、磁控溅射法、原子层沉积法等制备方法的特点。其次,阐述了退火处理、唤醒效应、底电极等因素对该类薄膜铁电性的影响,并对其铁电性的起源进行了介绍。此外,总结了HfO_(2)基铁电薄膜在铁电存储器、铁电隧道结、铁电场效应晶体管等领域的应用研究成果。最后对HfO_(2)基铁电薄膜研究中存在的问题及发展方向进行了总结与展望。

不同厚度铁电薄膜的制备及15nm Hf_(0.5)Zr_(0.5)O_(2)铁电晶体管性能研究

在铁电场效应晶体管(Ferroelectric Field Effect Transistor,FeFET)中,Hf_(0.5)Zr_(0.5)O_(2)(HZO)铁电薄膜的厚度是影响晶体管性能的关键参数。通过制备不同厚度铁电薄膜的铁电电容对其进行测试,选择最优厚度的铁电薄膜,设计制备一种15 nm Hf_(0.5)Zr_(0.5)O_(2)铁电薄膜的铁电晶体管——Si/HZO/W(MFS)栅极结构的铁电晶体管。它的剩余极化强度2Pr达到30μC·cm^(-2),具有高的循环稳定性和倍率性能,电压窗口达到1.2 V,在铁电存储器领域具有巨大的应用潜力。

铁电薄膜及铁电存储器研究

综述了铁电薄膜以及铁电存储器的发展,讨论了铁电薄膜制备方法、结构和物理性能表征,并结合作者的前期工作,详细讨论了用于铁电薄膜与硅衬底集成的导电阻挡层问题,指出了铁电薄膜研究中需重点解决的一些问题.

铁电随机存储器的研究进展

铁电薄膜与半导体集成技术相结合而发展起来的铁电存储器,以其高密度、高速度、非易失性及抗辐射性而大大优于目前任何一种半导体存储器。该文介绍了铁电存储器的存储原理、特点、基本存储单元、研究进展、应用及存在的问题,并指出1T结构的铁电随机存储器(FRAM)将会成为下一代随机存储器。

铁电薄膜及铁电存储器的研究进展

铁电薄膜是具有铁电性且厚度尺寸为数纳米到数微米的薄膜材料,因其在非挥发性铁电随机存储器方面的潜在应用而受到广泛关注。综述了新型无铅、无疲劳Bi4Ti3O12(BIT)基铁电薄膜材料的制备和改性及性能表征方法,阐述了铁电薄膜的3种失效机制及铁电薄膜存储器的研究现状,最后提出了铁电薄膜及存储器今后可能的研究方向。

应用于非破坏性读出铁电存储器的MFIS FET制备及其特性

将 Zr O2 和 PZT的 sol- gel薄膜制备技术应用到非破坏性读出铁电存储器中 ,制作出应用 Al/ PZT/ Zr O2 / p- Si结构的 MFIS电容和单管 MFIS FET,研究了 MFIS电容的界面和存储窗口特性 ,结果表明 Zr O2 介质阻挡层和 Si衬底以及 PZT的附着良好 ,在± 5 V测试电压、1MHz测试频率下 ,存储窗口电压为 2 .6 V左右 ,与相应的铁电薄膜的正、负矫顽电压差值的比为 0 .8.对于宽长比为 5 0 0μm / 5 0μm器件 ,采用栅极与源极、漏极写入方式 ,± 10 V时在写入电压下得到理想的输入 -输出特性 ;小尺寸的 4 0μm/ 8μm器件在± 5

铁电场效应晶体管

介绍了铁电场效应晶体管 (FFET)的基本结构、存储机制、制作方法 ,综述其结构设计的改进、铁电薄膜在 FFET中应用的进展情况 ,探讨围绕铁电薄膜材料、过渡层、结构设计、不同成膜方法及工艺对 FFET存储特性的影响 ,对

MFIS结构的C-V特性

研究了运用 SOL- GEL方法制备的 Au/PZT(铅锆钛 ) /Zr O2 /Si结构电容即 MFIS(Met-al/Ferroelectric /Insulator/Semiconductor)电容的方法 ,并对其进行了 SEM、C- V特性测试及Zr O2 介质层介电常数分析 .研究了 C- V存储窗口 (Memory Window)电压与铁电薄膜和介质层厚度比的关系 ,得出 MFIS电容结构中最佳铁电薄膜和介质层厚度比为 7— 1 0左右 ,在外加电压- 5V- +5V时存储窗口可达 2 .52 V左右 .

不挥发铁电存储器的最新发展

铁电材料具有自发极化并可由外电场反转，因此可以构成一种不挥发存储器．铁电薄膜与半导体集成，产生铁电随机存储器，并将成为存储器技术的主体．

铁电场效应晶体管:原理、材料设计与研究进展

系统阐述了铁电场效应晶体管(FeFET)的工作原理,重点介绍了铁电层和缓冲层的材料设计的基本原理、主要的铁电层材料和缓冲层材料及其所对应的FeFET的器件性能.并介绍了基于FeFET的FeCMOS逻辑电路、FeNAND闪存电路、基于氧化物半导体和有机半导体的FeFET的最新研究成果.最后对FeFET的未来研究作出展望.

准分子激光制备多层铁电薄膜的C-V特性研究

采用脉冲准分子激光工艺,在p型Si(100)单晶基片上,成功地淀积了BIT、PZT/BIT和BIT/PZT/BIT等多层结构的铁电薄膜;采用低频阻抗分析仪,分析了它们的C-V特性曲线的记忆窗口,讨论了记忆窗口与频率的关系,记忆窗口与多层结构的关系。结果表明,三层结构铁电薄膜的C-V特性的记忆窗口优于双层和单层结构的铁电薄膜。

铁电存储技术

简要说明了铁电随机存储器的工作原理及特点 ,详细阐述了阻碍铁电存储技术发展的技术难点 ,重点讨论了铁电薄膜材料的疲劳机理 。