论文研究-Chemical Bond Polarity-driven Memristive Effects in Ge2Sb2Te5 Films.pdf

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化学键极性驱动的Ge2Sb2Te5薄膜忆阻效应,孙华军,谢松,本研究制备了基于Ge2Sb2Te5硫系化合物的忆阻器单元,忆阻器单元经过初始化操作后,忆阻功能材料Ge2Sb2Te5处于晶态和非晶态之间的中间状
国武技论文在线 http:/www.paper.edu.cn Fig 2 Resistances change of device cell after applying +0. 48V and-0. 48V voltage pulses as a function of cycling number(RH:R≈4) For better understanding the memristive effects of device, the I-V curves of full crystalline 70 GST(R<10) and full amorphous Gst(r2 10) statc in ccll wcrc mcasurcd in Fig 3 and Fig respectively. The I-V curve of full crystalline GST was approximately linear, the full amorphous state demonstrated common schottky barrier commutating. The I-V curve of nano-scale full amorphous GST films(r 10)shows in Fig.5, it demonstrated repeatedly"8 I-V loop without lectroforming process. Based on the Fig 3 and Fig 4, full amorphous or full crystalline state could 75 not demonstrate rcpcatcdly8I-V loop. But electroforming proccss can induce deposited amorphous films(full amorphous) to some intermediate state and realize nonlinear 8"I-V loop The"intermediate state"would be elucidated as partly ionized amorphous GSt in the following 10X10 4,0×1c 10x10 4.0X1C 2.0x10° 0x1C2 151.0-0.50.00.5101.5 4.6 4.3 0 03 0.6 Voltage(v) gev Fig 3 I-V curve of PCM cell in crystalline state Fig 4. I-V curve of PCm in amorphous state 3 国武技论文在线 http:/www.paper.edu.cn 1.D103 Polarity and strength induce ionic bonds incretin 10 5Dx10 0.0 t 5.0K10 Polarity and strength induce covalent bond increa sing 10 1.D10 200 200 Voltage (mV) voltageⅣV ig. 5 Polarity inverse I-V curve of nano-scale amorphous films Fig. 6 Schematic diagram of electric field impacts reversible transition of ionization and covalent linkage xpcrimcntal rcsults to somc extent give out cvidcncc to undcrstand mcmristivc behavior of 85 the GST or device. As we well know GSt films has amorphous and crystalline state nanosecond pulsed electrical or optical can realize each other reversible transformation. But the nonlinear"& loop in experimental resulis still existed in amorphous region by the judgment of resistance slate General filamentary conduction theory! 0- and solid-state electrolytes are not available for incrt clectrode tiw and stoichiometric Gc2 Sb2 Tcs compounds uscd in device ccll. Hencc wc nccd 90 new mechanism to understand the memristive behavior. Amorphous chalcogenide generally linked by plenty of covalent linkages and could be classified as covalently bonded materials, and a few vacancy and wrong linkages also were inside l, (6. Koloboy et al. D had proved bond length and intensity of gSt obvious change during the short -range order to long-range order transition by X-ray absorption fine-structure spectroscopy. Therefore it is credible that an initial electroforming 95 step can inpact partly covalent bonds to ionize to ionic bonds and result in resistance increasing to 10 orders of magnitude. One hand, GST ionization itself can improve conductivity, on the other hand, defects and cavity are filled with ionized free ion, it also improved the conductivity Ultimately all of them make the current nonlinear change and high conductive sate be formed Reverse polarity electric field can reversed ionic bonds to covalent bonds, so the low conductive 100 state can be formed. Schematic diagram of electric field impacting reversible ionization and covalent linkage process was showed in Fig. 6 Hence reversible covalent-electrovalent bands transform and competition is essential reason Full amorphous covalent bonds domain) or crystalline(electrovalent bond domain) state can not present memristive effect because the transform is fewness to be ignore by the principle of 105 statistics, so it can not demonstrate memristive effect. Nanoscale capacitor-like cell without electroforming step also demonstrated memristive effects. It can be understood as following Chat a low voltage can bring a enough huge electric field at nanoscale to induce reversible covalent-clectrovalent bands transform. Namely, with ccll sizc dccrcascd thc mcmristivc cffccts is more and more easy to realize and electroforming can be canceled. It again proves the theory of 110 reversible covalenl-electrovalent bands Transform is reliable lo clarify the memristive effect of GST-based devices Amorphous GSt films with electroforming process, demonstrated the memristive effect 4 国武技论文在线 http:/www.paper.edu.cn Polarity reverse electrical pulse can switch the high-and low-state, and rH/ri is about 4 times 1 15 full amorphous Gst and full crystalline GST could not demonstrate reduplicable8I-V loop Nanoscale amorphous films also demonstrated reduplicable memristive effect due to enough huge electric field impact. During the initial electroforming process, the electric field impact ionizations of gst and enough ionized bonds make it possible to switch the reversible covalent-electrovalent bands by the polarity and strength of the electric field, so the memristive effect of gst-based 120 devices is driven by the transition of chemical bond polarity IL.O. Chua Memristor- the missing circuit element[J IEEE Trans. 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Del losson, A Pauza Polarity-dependent reversible resistance switching in Ge-Sb-Te phase-change thin films[J]. Appl. Phys. Lett., 2007, 91(15): 152103-1-152103-3 160 化学键极性驱动的 薄膜忆 阻效应 孙华军12,谢松12,李人杰2 (1.华中科技大学,武汉光电国家实验室,430074; 165 2.华中科技大学,光学与电子信息学院,430074) 摘要:本研究制备了基于Ge2Sb2Te5硫系化合物的忆阻器单元,忆阻器单元经过初姱化操 作后,忆阻功能材料Ge2Sb2le5处于晶态和非晶态之问的中问状态,单元在该状态下表现 岀良好的忆阻效应,并表现出良好的高低阻开关状态转换。然而,未经初始化的非晶态(沉 国武技论文在线 http:/www.paper.edu.cn 积态)和完全晶态均不具有忆阻效应。导电原子力显微镜导电针尖Ge2Sb2Te5-电极构成的 170纳米尺度忆阻器类电容单元在非昌态下同样录现出忆阻器效应。根据实验结果,推断出硫系 化合物忆阻效应是由于经过初始化过程后,忆阻功能层Ge2Sb2Te5处于共价键和离子键共 存的中间状夵,电场强度冲击化学键极性发生转变,即共价键-离子键转变,并在电场极性 的调制下,哀现出忆阻效应。纳米尺度下的非晶态Ge2Sb2le5忆阻器单元的忆阻器效应是 于纳米尺度下巨大的电场冲击化学键极性转变引起 175关键词:忆阻效应;Ge2Sb2Te5;化学键 中图分类号:TN6

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