HfO_x薄膜阻变特性及机理研究

采用射频磁控溅射法在Pt/Ti/SiO2/Si衬底上制备了Ta/HfOx/Pt三明治结构,对其电学性能和化学成分进行了分析。结果表明,Ta/HfOx/Pt结构具有明显的双极电阻转变特性,高低阻比(ROFF/RON)约26,并且具有良好的重复性与保持性,循环次数超过了200次。通过XPS和R-T数据分析证实,电场作用下HfOx层中因氧的逸出以及铪的富集所形成的铪导电细丝的生长、断裂和再生是该器件发生电阻转变的主要机制。     

Resistive Switching Characteristics of Al2O3/ZnO Bilayer Thin Films for Flexible Memory Applications

Unipolar resistive switching behaviors of the ZnO and Al2O3/ZnO films fabricated on flexible substrates by pulse laser deposition were studied in this paper. The films were deposited at room temperature without post-annealing treatment during the process. X-ray diffraction results indicated that ZnO film has a dominant peak at (002). Scanning electron microscopy observation showed a columnar grain structure of the ZnO film to the substrate. The bilayer device of Al2O3/ZnO films had stable resistive switching behaviors with a good endurance performance of more than 200 cycles, high resistive switching ratio of over 103 at a read voltage of 0.1 V, which is better than that of the single oxide layer device of ZnO film. A possible resistive switching filamentary mode was demonstrated in this paper. The conduction mechanisms of high and low resistance states can be explained by space charge limited conduction and Ohmics behaviors. The endurance of the bilayer (BL) device was not degraded upon bending cycles, which indicates the potential of the flexible resistive switching random access memory applications.     

Resistive Switching Mechanisms ofV-Doped$hboxSrZrO_3$Memory Films

The resistive switching behaviors of sputtered V-doped$hboxSrZrO_3$(V:SZO) memory films were investigated in this letter. The current states of the memory films were switched between high current state (H-state) and low current state (L-state). The resistance ratio of the two current states was over 1000 at a read voltage. The switching mechanism from L- to H-state corresponds to the formation of current paths. However, this mechanism from H- to L-state is thought to be due to the fact that the defects present in the V:SZO film randomly trap electrons, and hence, the current paths are ruptured. The conduction mechanism of the H-state is dominated by ohmic conduction, whereas the L-state conduction is dominated by Frenkel–Poole emission. The polarity direction of the resistive switching is an intrinsic property of the$hboxSrZrO_3$oxides. The V:SZO films with high uniformity and good stability are expected to be used in nonvolatile memory.     

磁控溅射法制备LiTaO3薄膜及其结晶性能研究

用射频磁控溅射法在Pt/Ti/SiO₂/Si(100)基片上沉积了LiTaO₃薄膜,并在氧气气氛中不同温度下进行退火。采用SEM、XRD、XPS等表征方法分析了薄膜的结晶性能、各元素化学价态和元素原子百分比。结果表明,经700℃退火处理1h得到的薄膜结晶性能最好,在(104)晶向上具有强烈的择优取向性。薄膜退火温度的升高导致薄膜中Li空位缺陷和O空位缺陷减少。研究表明,薄膜中O/Li的原子比对结晶性能有着非常明显的影响,原子值越接近晶体化学计量比,结晶性能越好。     

High-Throughput Screening Thickness-Dependent Resistive Switching in SrTiO3 Thin Films for Robust Electronic Synapse

The functionalities and applications of oxide thin films are highly dependent on their thickness. Most thickness-dependent studies on oxide thin films require the preparation of independent samples, which is labor-intensive and time-consuming and inevitably introduces experimental errors. To address this challenge, a general strategy based on high-throughput pulsed laser deposition technology is proposed to precisely control the thin-film thickness in local regions under similar growth conditions. The as-proposed synthesis strategy is demonstrated using typical complex oxide materials of SrTiO₃ (STO). Consequently, high-throughput STO thin films with nine gradient thicknesses ranging from 10.1 to 30.5 nm are fabricated. Notably, a transition from the unipolar to the bipolar resistive switching mode is observed with increasing STO thickness. Moreover, a physical mechanism based on the heterostructure-mediated redistribution of oxygen vacancies is employed to interpret the transition between the two memristive patterns. The screening of STO thin films with different resistive switching behaviors revealed that the STO thin film with a thickness of 20.3 nm exhibit excellent conductance modulation properties under the application of electrical pulses as well as significant reliability for the emulation of various synaptic functions, rendering it a promising material for artificial neuromorphic computing applications.     

热蒸发紫外LaF3薄膜光学性能和结构表征

在不同的沉积温度下,用热蒸发方法在熔融石英(JGS1)上制备了LaF3单层薄膜。分别采用分光光度计测量了薄膜样品的透射率和反射率光谱,反演得出薄膜的折射率和消光系数;采用原子力显微镜(AFM)观察了样品的表面形貌,并通过表面粗糙度计算得出总积分散射损耗;采用X射线衍射仪(XRD)测试了薄膜的晶体结构,由衍射谱图拟合得到衍射峰的半峰全宽,进而计算出薄膜晶粒的平均尺寸。实验结果表明,随着沉积温度的升高,LaF3薄膜的结晶状况明显变好,晶粒尺寸逐渐变大,膜层变得更加致密,薄膜的光学常数和折射率不均匀性均呈线性变化。沉积温度的增加对薄膜表面粗糙度的影响不明显,散射损耗在光学损耗中所占比例较小,所以光学损耗的变化主要由吸收损耗引起。     

Preparation of Surfactants Directed PANI/In2O3 Nanocomposite Thin Films and Its NH3-Sensing Properties

Polyaniline/indium oxide (PANI/In2O3) nanocomposite thin films have been prepared in water-dispersed medium with the presence of different surfactants by an in-situ self-assembly technique. A cationic surfactant TTAB (tetradecyltrimethylammonium bromide) and a non-ionic surfactant tween- 20 (poly (ethylene oxide) (20) sorbitan monolaurate) are used as additives. The nanocomposites and thin films are characterized by Fourier transform infrared (FTIR), transmission electron microscopy (TEM), and scanning electron microscopy (SEM), respectively. The optical properties reveal the interaction between PANI/In2O3 nanocomposites and surfactants, and PANI/In2O3 thin films prepared in the presence of surfactants exhibits the finer nanofiber than the surfactants free PANI/In2O3 thin film. The ammonia (NH3) gas-sensing characteristic of PANI/In2O3 thin films and the effect of different surfactants on the gas-sensing property are studied. The results indicated that the film processed in the presence of TTAB has the highest gas sensitivity among all the prepared films.     

ReSe2薄膜的盐助生长及其光电特性研究

二硒化铼(ReSe2)因具有较好的红外光响应和各向异性特性而成为近年来的研究热点.采用盐辅助化学气相沉积技术,在SiO2/Si衬底上成功合成了大面积的单层ReSe2薄膜,其尺寸达到80μm.采用拉曼光谱(Raman)、光致发光光谱(PL)、原子力显微镜(AFM)和X射线光电子能谱(XPS)等手段对制备的ReSe2薄膜样品进行了形貌、光谱、厚度和元素成分的表征,结果表明所制备的ReSe2薄膜晶体质量高.基于单层ReSe2薄膜构筑了场效应晶体管,系统研究了其光电特性,结果显示器件的响应时间达毫秒级.     

WO3/SnO2复合薄膜的制备及光电性能

采用水热法和电化学沉积法,成功制备了包覆有SnO₂纳米颗粒的WO₃纳米棒阵列薄膜,退火处理后形成WO₃/SnO₂异质结复合薄膜。通过改变SnO₂的沉积时间得到了复合薄膜的最佳制备条件。采用XRD,FESEM对WO₃/SnO₂复合薄膜的物相和形貌进行了分析,通过电化学工作站对WO₃/SnO₂复合薄膜的光电性能进行了研究,结果表明,电沉积时间为120 s时,WO₃/SnO₂复合薄膜具有最小的阻抗,且在0.6 V的偏压下光电流密度为0.46 mA/cm²,相比于单一WO₃纳米棒薄膜,表现出更好的光电化学性能。     

Effect of Top Electrode Material on Resistive Switching Properties of ZrO2 Film Memory Devices

The influence of top electrode material on the resistive switching properties of $hbox{ZrO}_{2}$-based memory film using Pt as a bottom electrode was investigated in this letter. In comparison with $hbox{Pt/ZrO}_{2}/hbox{Pt}$ and $hbox{Al/ZrO}_{2}/hbox{Pt}$ devices, the $hbox{Ti/ZrO}_{2}/hbox{Pt}$ device exhibits different resistive switching current–voltage $(I$– $V)$ curve, which can be traced and reproduced by a dc voltage more than 1000 times only showing a little decrease of resistance ratio between high and low resistance states. Furthermore, the broad dispersions of resistive switching characteristics in the $hbox{Pt/ZrO}_{2}/hbox{Pt}$ and $hbox{Al/ZrO}_{2}/hbox{Pt}$ devices are generally observed during successive resistive switching, but those dispersions are suppressed by the device using Ti as a top electrode. The reliability results, such as cycling endurance and continuous readout test, are also presented. The write-read-erase-read operations can be over $hbox{10}^{4}$ cycles without degradation. No data loss is found upon successive readout after performing various endurance cycles.      

退火温度对 BNST薄膜结构和性能的影响

采用射频磁控溅射法在Pt/Ti/LaAlO3(100)衬底上制备了BaO-Nd2O3-Sm2O3-TiO2系(BNST)薄膜.研究了退火温度对BNST薄膜结构、表面形貌和介电性能的影响.X线衍射仪(XRD)分析表明,随着退火温度的升高,晶粒逐渐长大.经850℃退火处理的BNST薄膜具有很好的结晶质量.原子力显微镜(AFM)分析表明,在一定范围内提高退火温度所制备的薄膜晶粒致密、大小均匀.LCR测试分析表明,在测试频率为100 kHz时,随着退火温度的升高,BNST薄膜介电常数有所增加,介电损耗则先降低,后增加.实验表明,经850℃退火处理,所制备的BNST薄膜的介电常数达37,介电损耗小于1.2‰.     

SnO_(2)缓冲层对VO_(2)薄膜微观结构与相变性能的影响北大核心

利用电子束蒸发法在Si衬底上制备了不同厚度的SnO_(2)缓冲层,并使用磁控溅射法制备出上层氧化钒薄膜,研究了SnO_(2)缓冲层厚度对于氧化钒薄膜微观结构、相组成以及相变性能的影响。结果表明,引入具有四方金红石结构的SnO_(2)缓冲层后,上层氧化钒薄膜的结晶性变好,随着SnO_(2)缓冲层厚度的增加,沉积的氧化钒薄膜中V^(4+)含量逐渐提高,氧化钒薄膜的平均晶粒尺寸增大,成膜质量变好;相变锐度有所降低,热滞回线宽度减小。这些结果表示SnO_(2)缓冲层的引入有利于在硅衬底上生长高质量且相变性能优越的VO_(2)薄膜。     

Ag/La0.67Sr0.33MnO3薄膜电阻开关特性的研究

采用脉冲激光沉积技术在SrTiO3（001）单晶衬底上制备出钙钛矿结构La0.67Sr0.33MnO3薄膜，利用X射线衍射仪与原子力显微镜表征其晶体结构与微观形貌，并对Ag/La0.67Sr0.33MnO3/SrTiO3结构的室温电脉冲诱发可逆变阻效应进行了分析讨论。该效应表现出良好的非挥发多值存储特性，有望应用于新型存储器、传感器、可变电阻等电子元器件的研制。     

Ag/La_(0.67)Sr_(0.33)MnO_3薄膜电阻开关特性的研究

采用脉冲激光沉积技术在SrTiO3(001)单晶衬底上制备出钙钛矿结构La0.67Sr0.33MnO3薄膜,利用X射线衍射仪与原子力显微镜表征其晶体结构与微观形貌,并对Ag/La0.67Sr0.33MnO3/SrTiO3结构的室温电脉冲诱发可逆变阻效应进行了分析讨论。该效应表现出良好的非挥发多值存储特性,有望应用于新型存储器、传感器、可变电阻等电子元器件的研制。     

二硫化钼薄膜的制备和性质研究

基于第一性原理,应用Materials Studio软件对2H-MoS2的能带结构、态密度、光学特性等进行了模拟研究.结果 表明:MoS2是间接带隙半导体,禁带宽度约为1.1275 eV;材料在紫外至可见光波段具有一定吸收,吸收系数随波长增加而减小,拉曼光谱在375和400 cm-1分别出现了E2g1和A1g两个振动模式.在39.5°,33.5°等位置处出现了(103),(101)等晶面的衍射峰.采用磁控溅射的方法,在石英衬底上制备了不同厚度的MoS2薄膜,发现该薄膜具有(101)择优取向,在375和407 cm-1处也分别出现了E2g1和A1g两个拉曼峰.随着厚度的增加,薄膜在可见光波段透过率下降,光学带隙向长波长移动,模拟结果与实验结果基本吻合.     

Structural and Electrical Characters of Ba0.6Sr0.4TiO3/La0.5Sr0.5CoO3 Thin Films by Plus Laser Deposition

Epitaxial Ba0.6Sr0.4TiO3 (BST) thin films were deposited on LaAlO3 (LAO) substrates with the conductive metallic oxide La0.5Sr0.5CoO3 (LSCO) film as a bottom electrode by pulsed laser deposition (PLD). X-ray diffraction ~2 and Ф scan showed that the epitaxial relationship of BST/LSCO/LAO was [001] BST//[001] LSCO//[001] LAO. The atomic force microscope (AFM) revealed a smooth and crack-free surface of BST films on LSCO-coated LAO substrate with the average grain size of 120 nm and the RMS of 1.564 nm for BST films. Pt/BST/LSCO capacitor was fabricated to perform CapacitanceVoltage measurement indicating good insulating characteristics. For epitaxial BST film, the dielectric constant and dielectric loss were determined as 471 and 0.03, respectively. The tunabilty was 79.59% and the leakage current was 2.6310-7 A/cm2 under an applied filed of 200 kV/cm. Furthermore, it was found that epitaxial BST (60/40) films demonstrate well-behaved ferroelectric properties with the remnate polarization of 6.085 C/cm2 and the coercive field of 72 kV/cm. The different electric properties from bulk BST (60/40) materials with intrinsic paraelectric characteristic are attributed to the interface effects.     

微波等离子体化学气相沉积法制备C3N4薄膜的研究

本文采用微波等离子体化学气相沉积法（ＭＰＣＶＤ）,高纯Ｎ２（９９．９９９％）和ＣＨ４（９９．９％）作反应气体,在多晶Ｐｔ（９９．９９％）基片上沉积Ｃ３Ｎ４薄膜。Ｘ－射线能谱（ＥＤＸ）分析结果表明Ｎ／Ｃ原子比为１．０～１．４,接近Ｃ３Ｎ４的化学比;Ｘ射线衍射谱说明薄膜主要由β和α－Ｃ３Ｎ４组成;ＦＴ－ＩＲ谱和Ｒａｍａｎ谱支持Ｃ－Ｎ键的存在。     

Growth of Fe-Doped and V-Doped MoS2 and Their Magnetic-Electrical Effects

Magnetism in two-dimensional (2D) materials has attracted much attention recently. However, intrinsic magnetic 2D materials are rare and mostly unstable in ambient. Although heteroatom doping can introduce magnetism, the basic property especially the electrical-magnetic coupling property has been rarely revealed. Herein, both iron (Fe)-doped and vanadium (V)-doped MoS₂ films were grown by chemical vapor deposition. Through studying the structure and electrical property of Fe-doped and V-doped MoS₂, it was found that both Fe and V doping would decrease the electron concentration, exhibiting a p-type doping effect. Significantly, V-doped MoS₂ displays a p-type conduction behavior. Although the carrier mobility decreases after heteroatom doping, both Fe and V doping could endow MoS₂ with magnetism, in which the transfer curves of both MoS₂ transistors exhibit a strong magnetic-dependent behavior. It is found that the magnetic response of Fe-doped MoS₂ can be tuned from ~0.2 nA/T to ~1.3 nA/T, with the tunability much larger than that of V-doped MoS₂. At last, the magnetic mechanism is discussed with the local magnetic property performed by magnetic force microscopy. The typical morphology-independent magnetic signal demonstrates the formed magnetic domain structure in Fe-doped MoS₂. This study opens new potential to design novel magnetic-electrical devices.     

Effects of Heat Treatment on Thermoelectric and Infrared Properties of Bi2Te3 Films

In this work, Bi2Te3 films (250 nm) are fabricated on SiO2/Si substrates by radio frequency (RF) magnetron sputtering at room temperature, and the prepared films are annealed over the temperature range of 200 ℃ to 400 ℃. Crystallinity and electrical properties of the films can be tuned correspondingly. The power factors of Bi2Te3 films of 0.85 W/K2cm to 11.43 W/K2cm were achieved after annealing. The infrared reflectance measurements from 2.5 m to 5.0 m demonstrate that there is also a slight red-shift of the plasma oscillation frequency in the Bi2Te3 films. By means of plasmonic calculations, we attribute the red-shift of absorption peaks to the reduction of carrier concentration and the change of effective mass of Bi2Te3 films with the increased annealing temperature.     

Evolution of Electron Transport under Resistive Switching in Porphyrazine Films

Semiconductors - An analysis of the I–V characteristics makes it possible to determine the mechanisms of conduction corresponding to different states of the flow channels upon resistive...