• Proceedings of the Korean Vacuum Society Conference
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• 2013.02a
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• pp.597-597
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• 2013

The resistive switching behaviors of Pt nanodisk on Nb-doped SrTiO3 single-crystal have been studied with conductive atomic force microscopy in ultra-high vacuum. The nanometer sizes of Pt disks were formed by using self-assembled patterns of silica nanospheres on Nb-doped SrTiO3 single-crystal semiconductor film using the Langmuir-Blodgett, followed by the metal deposition with e-beam evaporation. The conductance images shows the spatial mapping of the current flowing from the TiN coated AFM probe to Pt nanodisk surface on Nb：STO single-crystal substrate, that was simultaneously obtained with topography. The bipolar resistive switching behaviors of Pt nanodisk on Nb：STO single-crystal junctions was observed. By measuring the current-voltage spectroscopy after the forming process, we found that switching behavior depends on the charging and discharging of interface trap state that exhibit the high resistive state (HRS) and low resistive state (LRS), respectively. The results suggest that the bipolar resistive switching of Pt/Nb:STO single-crystal junctions can be performed without the electrochemical redox reaction between tip and sample with the potential application of nanometer scale resistive switching devices.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2010.06a
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• pp.370-370
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• 2010

The effects of adding higher-valence impurities on the bipolar resistive switching characteristics of Pt/$NiO_{1+x}$/TiN MIM stacks and physical properties were investigated. $NiO_{1+x}$ films with 14% W deposited at 20% oxygen partial pressure exhibited the bipolar resistance switching characteristics in Pt/$NiO_{1+x}$/TiN MIM stacks, while $NiO_{1+x}$ films with 8.2% W show unipolar resistance switching behavior. The relationship of W-doping and the crystallinity was studied by X-ray diffraction. The metallic Ni contents and $WO_x$ binding states with W amount was investigated by XPS. Our result showed that the metallic Ni, $WO_x$ binding states, and crystallinity in $NiO_{1+x}$ played an important role on the bipolar resistive switching.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.24 no.9
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• pp.710-712
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• 2011

In this study, we fabricate resistive switching random access memory (ReRAM) devices constructed with a Al/$HfO_2$/ITO structure on glass substrates and investigate their memory characteristics. The hafnium oxide thin film used as a resistive switching layer is sputtered at room temperature in a sputtering system with a cooling unit. The Al/$HfO_2$/ITO device exhibits bipolar resistive switching characteristics, and the ratio of the high resistance (HRS) to low resistance states (LRS) is more than 60. In addition, the resistance ratio maintains even after $10^4$ seconds.

• Proceedings of the Materials Research Society of Korea Conference
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• 2007.11a
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• pp.63.2-63.2
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• 2007

• JSTS:Journal of Semiconductor Technology and Science
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• v.8 no.1
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• pp.80-84
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• 2008

We systematically investigated the resistive switching properties of thin $TiO_2$ films on Pt/Ti/$SiO_2$/Si substrates that were embedded with a Co ultra thin layer. An in-situ sputtering technique was used to grow both films without breaking the chamber vacuum. A stable bipolar switching in the current-voltage curve was clearly observed in $TiO_2$ films with an embedded Co ultra thin layer, addressing the high and low resistive state under a bias voltage sweep. We propose that the underlying origin involved in the bipolar switching may be attributed to the interface redox reaction between the Co and $TiO_2$ layers. The improved reproducible switching properties of our novel structures under forward and reverse bias stresses demonstrated the possibility of future non-volatile memory elements in a simple capacitive-like structure.

• Journal of Applied Reliability
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• v.16 no.1
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• pp.1-6
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• 2016

Purpose: Fluorine doped tin oxide (FTO) bottom electrode for $Ta_2O_5$ based RRAM was studied to apply for transparent resistive switching memory devices owing to its superior transparency, good conductivity and chemical stability. Methods: $ITO/Ta_2O_5/FTO$ (ITF) and $ITO/Ta_2O_5/Pt$ (ITP) devices were fabricated on glass and Si substrate, respectively. UV-visible (UV-VIS) spectroscopy was used to examine transparency of the ITF device and its band gap energy was determined by conventional Tauc plot. Electrical properties, such as electroforming and voltage-induced RS characteristics were measured and compared. Results: The device with an FTO bottom electrode showed good transparency (>80%), low forming voltage (~-2.5V), and reliable bipolar RS behavior. Whereas, the one with Pt electrode showed both bipolar and unipolar RS behaviors unstably with large forming voltage (~-6.5V). Conclusion: Transparent and conducting FTO can successfully realize a transparent RRAM device. It is concluded that FTO electrode may form a stable interface with $Ta_2O_5$ switching layer and plays as oxygen ion reservoir to supply oxygen vacancies, which eventually facilitates a stable operation of RRAM device.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.29 no.7
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• pp.400-403
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• 2016

The resistive memory switching characteristics of resistive random access memory (ReRAM) using the amorphous GeSe thin film have been demonstrated at Al/Ti/GeSe/$n^+$ poly Si structure. This ReRAM indicated bipolar resistive memory switching characteristics. The generation and the recombination of chalcogen cations and anions were suitable to explain the bipolar switching operation. Space charge limited current (SCLC) model and Poole-Frenkel emission is applied to explain the formation of conductive filament in the amorphous GeSe thin film. The results showed characteristics of stable switching and excellent reliability. Through the annealing condition of $400^{\circ}C$, the possibility of low temperature process was established. Very low operation current level (set current: ~ ${\mu}A$, reset current: ~ nA) was showed the possibility of low power consumption. Particularly, $n^+$ poly Si based GeSe ReRAM could be applied directly to thin film transistor (TFT).

• Proceedings of the Korean Vacuum Society Conference
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• 2011.02a
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• pp.9-9
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• 2011

There has been strong demand for novel nonvolatile memory technology for low-cost, large-area, and low-power flexible electronics applications. Resistive memories based on metal oxide thin films have been extensively studied for application as next-generation nonvolatile memory devices. However, although the metal oxide-based resistive memories have several advantages, such as good scalability, low-power consumption, and fast switching speed, their application to large-area flexible substrates has been limited due to their material characteristics and necessity of a high-temperature fabrication process. As a promising nonvolatile memory technology for large-area flexible applications, we present a graphene oxide-based memory that can be easily fabricated using a room temperature spin-casting method on flexible substrates and has reliable memory performance in terms of retention and endurance. The microscopic origin of the bipolar resistive switching behaviour was elucidated and is attributed to rupture and formation of conducting filaments at the top amorphous interface layer formed between the graphene oxide film and the top Al metal electrode, via high-resolution transmission electron microscopy and in situ x-ray photoemission spectroscopy. This work provides an important step for developing understanding of the fundamental physics of bipolar resistive switching in graphene oxide films, for the application to future flexible electronics.

• Proceedings of the Korean Vacuum Society Conference
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• 2012.08a
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• pp.384-384
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• 2012

We report nonvolatile memory properties of poly (3, 4-ethylenedioxythiophene) (PEDOT) thin films grown by vapor phase polymerization using FeCl3 as an oxidant. Liquid-bridge-mediated transfer method was employed to remove FeCl3 for generation of pure PEDOT thin films. From the electrical measurement of memory device, we observed voltage induced bipolar resistive switching behavior with ON/OFF ratio of 103 and reproducibility of more than 103 dc sweeping cycles. ON and OFF states were stable up to 104 seconds without significant degradation. Cyclic voltammetry data illustrates resistive switching effect can be attributed to formation and rupture of conducting paths due to oxidation and reduction of PEDOT. The maximum current before reset process was found to be increase linearly with increase in compliance current applied during set process.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.29 no.5
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• pp.268-273
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• 2016

In this study, we observed current-voltage characteristics of the MIM (metal-insulator-metal) structure. The $WO_x$ material was used between metal electrodes as the oxide insulator. The structure of the $Al/WO_x/TiN$ shows bipolar resistive switching and the operating direction of the resistive switching is clockwise, which means set at negative voltage and reset at positive voltage. The set process from HRS (high resistance state) to LRS (low resistance state) occurred at -2.6V. The reset process from LRS to HRS occurred at 2.78V. The on/off current ratio was about 10 and resistive switching was performed for 5 cycles in the endurance characteristics. With consecutive switching cycles, the stable $V_{set}$ and $V_{reset}$ were observed. The electrical transport mechanism of the device was based on the migration of oxygen ions and the current-voltage curve is following (Ohm's Law ${\rightarrow}$ Trap-Controlled Space Charge Limited Current ${\rightarrow}$ Ohm's Law) process in the positive voltage region.