Forming-Free Unipolar Resistive Switching in BiFe0.95Co0.05O3 Films

We report the forming-free unipolar resistive switching effects in polycrystalline BiFe_0.95Co_0.05O₃ films which were spin-coated on ITO/glass substrates by a chemical solution deposition method. The resistive ratio of the high resistive state (HRS) to the low resistive state (LRS) is more than 2 orders of magnitude. The conduction of the HRS is dominated by the space-charge-limited conduction mechanism, while Ohmic behavior dominates the LRS, which suggests a filamentary conduction mechanism. The oxygen vacancies are considered to play an important role in forming the conducting filaments.     

氧化镍溶胶-凝胶薄膜阻变特性研究

用溶胶-凝胶法在1TO基片上旋涂制备了NiO薄膜,通过对ITO/NiO薄膜/GaIn器件进行伏安特性测试,研究了溶胶浓度、退火、层数以及Cu掺杂等对其电学特性的影响.结果表明:所制备NiO薄膜具有良好可重复双极电阻开关特性.其中,2％Cu掺杂0.2 mol/L溶胶、双层、400℃退火1h制备的薄膜,阈值电压较低,约0.8 V;而开关比受以上因素影响不明显,约3× 102.分析发现薄膜高阻态的荷电输运符合空间电荷限制导电机制,而低阻态为欧姆特性,阻变开关机理为阈值电场及焦耳热导致的氧空位细丝的形成与断裂.     

Bipolar Resistive Switching of Single Gold-in-Ga(2)O(3) Nanowire

We have fabricated single nanowire chips on gold-in-Ga(2)O(3) core-shell nanowires using the electron-beam lithography techniques and realized bipolar resistive switching characteristics having invariable set and reset voltages. We attribute the unique property of invariance to the built-in conduction path of gold core. This invariance allows us to fabricate many resistive switching cells with the same operating voltage by simple depositing repetitive metal electrodes along a single nanowire. Other characteristics of these core-shell resistive switching nanowires include comparable driving electric field with other thin film and nanowire devices and a remarkable on/off ratio more than 3 orders of magnitude at a low driving voltage of 2 V. A smaller but still impressive on/off ratio of 10 can be obtained at an even lower bias of 0.2 V. These characteristics of gold-in-Ga(2)O(3) core-shell nanowires make fabrication of future high-density resistive memory devices possible.     

The Multiferroic Properties of Zn Doped BiFeO3 Thin Films

BiFe_1?x Zn _x O₃ thin films (x=0, 0.05, 0.1, 0.2, and 0.3) were prepared on LaNiO₃ buffered surface oxidized Si substrates using pulsed laser deposition. The effect of Zn dopants on the structural, electrical, magnetic properties, and exchange bias on NiFe layers for BiFeO₃ thin films has been systematically investigated. X ray diffraction and Raman spectra show that BiFe_1?x Zn _x O₃ thin films have polycrystalline rhombohedral structure with Zn concentration smaller than 5 %, and a large amount of the impurity phase of Bi₂Fe₄O₉ with further increasing Zn concentration above 10 %. With 5 % Zn doping in BiFeO₃, the film quality is improved with larger grain size, better ferroelectricity, and larger magnetization. The exchange bias of BiFe_1?x Zn _x O₃ on a 3.6 nm thick NiFe layer drastically decreases with increasing Zn doping concentration, and totally disappears with the Zn concentration larger than 10 %, indicating that the canted antiferromagnetic spin structure of BiFeO₃ was suppressed with increasing the Zn doping concentration.     

Bi2O3薄膜的制备及其电阻开关特性的研究

电阻式存储器由于具有众多的优点有望成为最有前景的下一代高速非挥发性存储器的选择之一.实验利用射频磁控溅射法在重掺硅上沉积了Bi2O3薄膜,并对该薄膜的结晶状态和Au/Bi2O3/n+Si/Al结构的电阻开关特性进行了研究.XRD分析结果表明,射频磁控溅射法沉积所得的Bi2O3薄膜结晶性能好,(201)取向明显.I-V曲线测试结果表明,Au/Bi2O3/n+Si/Al结构具有单极性电阻开关特性.通过对不同厚度Bi2O3薄膜的Au/Bi2O3/n+Si/Al结构I-V特性比较发现,随着薄膜厚度的增加,电阻开关的Forming、Set和Reset阈值电压均随之增加.对于Bi2O3薄膜厚度为31.2 nm的Au/Bi2O3/n+Si/Al结构,其Forming、Set和Reset阈值电压均低于4 V,符合存储器低电压工作的要求.     

PLD法制备TiO2薄膜及电阻转变特性研究

采用脉冲激光沉积法（PLD）,以Pt(111)/Ti/SiO₂/Si为衬底,制备了具有电阻转变特性的TiO₂薄膜.X射线衍射（XRD）分析未发现明显的TiO₂结晶峰,薄膜呈纳米晶或非晶态.扫描电子显微镜（SEM）及原子力显微镜（AFM）分析表明,TiO₂薄膜表面平整、光滑致密.电学测试结果表明,TiO₂薄膜具有明显的单极性电阻转变特性,高低阻态比值达到10⁴.高阻态下薄膜的导电过程可用空间电荷限制电流模型解释,过程中存在软击穿现象.在此基础上,对薄膜中丝导电通道的产生及熔断过程进行了初步分析.     

Two-Phase Coexistence and Multiferroic Properties of Cr-Doped BiFeO3 Thin Films

Pure BiFeO ₃ (BFO) and Cr-doped BiFe _0.97 Cr _0.03 O ₃ (BFCO) thin films were successfully prepared on F-doped SnO ₂ conductive film (FTO)/glass (SnO ₂: F) substrates by a sol–gel method. The effect of Cr doping on the structure, ferroelectric, and ferromagnetic properties of the BFO and BFCO thin films have been investigated. X-ray diffraction, Rietveld refined X-ray diffraction (XRD) patterns, and Raman spectroscopy results clearly reveal that the BFCO thin film is characterized by the coexistence of two phases (trigonal and tetragonal). Moreover, the various leakage mechanisms of both thin films have also been studied. The improved ferroelectricity with remnant polarization (Pr) of about 2Pr = 68.68 μC/cm ² under an applied electric field of 1,181.8 kV/cm and enhanced ferromagnetism with saturation magnetization (M _s) of M _s = 0.93 emu/cm ³ have been observed in the BFCO thin film. The improved electrical properties of the BFCO thin film are ascribed to the coexistence of trigonal and tetragonal phase and high valence of Cr ⁶⁺, and the Fe–O ₆ octahedron distortion is enhanced due to the overlap and hybridization of Fe _3d/Cr _3d and O _2p orbits by Cr doping.     

Solid-Phase Epitaxy of BiFeO3 Films with Magnetoelectric Properties on Sapphire

Technical Physics Letters - The ferroelectric domain structure has been investigated in bismuth-ferrite rhombohedral phase films prepared on the rhombohedral plane of sapphire by solid-phase...     

不同厚度BiFeO_3薄膜的光电性质

利用溶胶-凝胶法制备BiFeO_3靶材,通过射频磁控溅射法在玻璃衬底上制备不同厚度的BiFeO_3薄膜,并研究不同厚度对其微观结构、铁电性、漏电流特性及薄膜折射率和消光系数的的影响。结果表明,随着薄膜厚度的增加,铁电性变好,薄膜折射率和消光系数增大,当电压较低时(U1/22),Poole-Frenkel机制在漏电特性中起主导作用,当电压较高(1/U0.25)时,FN隧穿起主导作用;通过拟合图谱计算出不同沉积时间的薄膜厚度及表面层厚度,结果与原子力显微镜测的数值基本一致。