Publications (17)48.71 Total impact
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Article: High Current Density and Nonlinearity Combination of Selection Device Based on TaO(x)/TiO(2)/TaO(x) Structure for One Selector-One Resistor Arrays.
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ABSTRACT: We demonstrate a high-performance selection device by utilizing the concept of crested oxide barrier to suppress the sneak current in bipolar resistive memory arrays. Using a TaO(x)/TiO(2)/TaO(x) structure, high current density over 10(7) A cm(-2) and excellent nonlinear characteristics up to 10(4) were successfully demonstrated. On the basis of the defect chemistry and SIMS depth profile result, we found that some Ta atoms gradually diffused into TiO(2) film, and consequently, the energy band of the TiO(2) film was symmetrically bent at the top and bottom TaO(x)/TiO(2) interfaces and modified as a crested oxide barrier. Furthermore, the one selector-one resistor device exhibited significant suppression of the leakage current, indicating excellent selector characteristics.ACS Nano 08/2012; 6(9):8166-72. · 10.77 Impact Factor -
Article: Low-power and controllable memory window in Pt/Pr0.7Ca0.3MnO3/yttria-stabilized zirconia/W resistive random-access memory devices.
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ABSTRACT: Yttria-stabilized zirconia (YSZ) layers of various thicknesses were designed and introduced before Pr0.7Ca0.3MnO3 (PCMO) film was deposited on W bottom electrodes with a submicron via-hole structure. By changing the thickness of the YSZ barrier layer (3, 5, 9, and 13 nm), a tunable memory window can be realized while low power consumption (P(max) < 4 microW) is maintained. Resistive switching (RS) in a Pt/PCMO/YSZ/W stack with a thin YSZ layer can be ascribed to an oxidation/reduction reaction caused by a ring-type PCMO/W contact, while RS with a thick YSZ layer may be related to oxygen migration across the YSZ layer between the PCMO film and the W bottom electrode and the increase (decrease) of the effective tunnel barrier height of the YSZ layer. Excellent RS behavior characteristics, such as a large R(HRS)/R(LRS) ratio (> 10(3)), die-to-die uniformity, sweeping endurance, and a retention time of more than 10(3) s, can be obtained by optimizing the thickness of YSZ layer.Journal of Nanoscience and Nanotechnology 04/2012; 12(4):3252-5. · 1.56 Impact Factor -
Article: Effect of Thermal Barrier on Reset Operations in Filament-Type Resistive Memory
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ABSTRACT: We have investigated the effect of a Ge<sub>2</sub>Sb<sub>2</sub>Te<sub>5</sub> (GST) thermal barrier on the reset operations in TiN/Cu/SiC/Pt devices. When the GST film was introduced as a thermal barrier, the device showed a lower reset voltage and a lower reset current than a device without the GST layer. In particular, the reset speed of the device with the GST layer was significantly faster at room temperature compared to the device without the GST layer. We attribute the improved resistive switching to the GST thermal barrier, which induces thermally assisted electrochemical reduction of the Cu filament.IEEE Electron Device Letters 12/2011; · 2.85 Impact Factor -
Article: Excellent Selector Characteristics of Nanoscale for High-Density Bipolar ReRAM Applications
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ABSTRACT: We herein present a nanoscale vanadium oxide (VO<sub>2</sub>) device with excellent selector characteristics such as a high on/off ratio (>; 50), fast switching speed (<; 20 ns), and high current density (>; 10<sup>6</sup> A/cm2). Owing to extrinsic defects, a large-area device with a 20-nm-thick VO<sub>2</sub> layer underwent an electrical short. In contrast, after scaling the device active area (<; 5 × 10<sup>4</sup> nm<sup>2</sup>), excellent switching uniformity was obtained. This can be explained by the reduced defects and the metal-insulator transition of the whole nanoscale VO<sub>2</sub>. By integrating a bipolar resistive random access memory device with the VO<sub>2</sub> selection device, a significantly improved readout margin was obtained. The VO<sub>2</sub> selection device shows good potential for cross-point bipolar resistive memory applications.IEEE Electron Device Letters 12/2011; · 2.85 Impact Factor -
Article: Diode-less bilayer oxide (WO(x)-NbO(x)) device for cross-point resistive memory applications.
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ABSTRACT: The combination of a threshold switching device and a resistive switching (RS) device was proposed to suppress the undesired sneak current for the integration of bipolar RS cells in a cross-point array type memory. A simulation for this hybrid-type device shows that the matching of key parameters between switch element and memory element is an important issue. Based on the threshold switching oxides, a conceptual structure with a simple metal-oxide 1-oxide 2-metal stack was provided to accommodate the evolution trend. We show that electroformed W-NbO(x)-Pt devices can simultaneously exhibit both threshold switching and memory switching. A qualitative model was suggested to elucidate the unique properties in a W-NbO(x)-Pt stack, where threshold switching is associated with a localized metal-insulator transition in the NbO(x) bulk, and the bipolar RS derives from a redox at the tip of the localized filament at the WO(x)-NbO(x) interface. Such a simple metal-oxide-metal structure, with functionally separated bulk and interface effects, provides a fabrication advantage for future high-density cross-point memory devices.Nanotechnology 11/2011; 22(47):475702. · 3.98 Impact Factor -
Article: Parallel memristive filaments model applicable to bipolar and filamentary resistive switching
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ABSTRACT: The concept of memristive filaments (MFs) is introduced, which is based on the memristors developed by the Hewlett–Packard group. The effects of key parameters on electrical properties are elucidated. The current–voltage features of bipolar and filamentary resistive switching are reproduced by using a parallel MF model with dynamic growth and rupture of multiple MFs. This model can be extended and adapted to most nanosized transition metal oxide memristors.Applied Physics Letters 09/2011; 99(11):113518-113518-3. · 3.84 Impact Factor -
Article: Analog memory and spike-timing-dependent plasticity characteristics of a nanoscale titanium oxide bilayer resistive switching device.
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ABSTRACT: We demonstrated analog memory, synaptic plasticity, and a spike-timing-dependent plasticity (STDP) function with a nanoscale titanium oxide bilayer resistive switching device with a simple fabrication process and good yield uniformity. We confirmed the multilevel conductance and analog memory characteristics as well as the uniformity and separated states for the accuracy of conductance change. Finally, STDP and a biological triple model were analyzed to demonstrate the potential of titanium oxide bilayer resistive switching device as synapses in neuromorphic devices. By developing a simple resistive switching device that can emulate a synaptic function, the unique characteristics of synapses in the brain, e.g. combined memory and computing in one synapse and adaptation to the outside environment, were successfully demonstrated in a solid state device.Nanotechnology 06/2011; 22(25):254023. · 3.98 Impact Factor -
Article: Effect of Scaling -Based RRAMs on Their Resistive Switching Characteristics
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ABSTRACT: We investigated the effect of scaling down the device area of WO x resistive random-access memory (RRAM) devices on their switching characteristics. Device dimensions were successfully scaled down to 50 nm using a via-hole structure with additional Al<sub>2</sub>O<sub>3</sub> sidewall process. As compared to the microscale devices, the nanoscale devices exhibited a distinct switching mechanism and better memory performance, such as improved switching uniformity, larger memory window, and stable endurance characteristics for up to 10<sup>7</sup> cycles. This improvement can be explained by a uniform interfacial switching mechanism in nanoscale device; this is in contrast with the defect-induced filamentary switching mechanism observed in microscale devices. In this way, the intrinsic switching properties of RRAMs were obtained by scaling down of the device area, indicating that RRAMs hold considerable promise for future applications.IEEE Electron Device Letters 06/2011; · 2.85 Impact Factor -
Article: Excellent State Stability of Cu/SiC/Pt Programmable Metallization Cells for Nonvolatile Memory Applications
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ABSTRACT: We have investigated silicon carbide (SiC) as a new programmable metallization cell material for nonvolatile memory applications. Our Cu/SiC/Pt devices showed bipolar resistive switching; the conduction mechanisms can be explained by the formation of a Cu filament and Poole-Frenkel emission in the low-resistance and high-resistance states, respectively. In particular, our devices showed excellent state stability, e.g., nondestructive readout at various stress voltages, excellent retention characteristics at 150°C for 10<sup>4</sup> s, and stable memory operation at high ambient temperature. We attribute this state stability to the SiC's high chemical stability and the ability to act as a Cu diffusion barrier.IEEE Electron Device Letters 06/2011; · 2.85 Impact Factor -
Article: Multibit Operation of -Based ReRAM by Schottky Barrier Height Engineering
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ABSTRACT: We demonstrated multibit operation using a 250-nm Ir/TiO<sub>x</sub>/ TiN resistive random access memory by Schottky barrier height engineering. A Schottky barrier was formed by the interface between a high-work-function Ir top electrode and n-type TiO<sub>x</sub>. The conducting path, which was composed of oxygen vacancies, was generated in a low-resistance state, whereas a Schottky barrier was reproduced in a high-resistance state (HRS) due to the high concentration of oxygen by the electric field. By changing the reset operation voltage, we successfully engineered the Schottky barrier height, resulting in the modulation of the HRS current and demonstrating the feasibility of multibit applications.IEEE Electron Device Letters 05/2011; · 2.85 Impact Factor -
Article: New Set/Reset Scheme for Excellent Uniformity in Bipolar Resistive Memory
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ABSTRACT: We proposed a new set/reset operation scheme to improve the switching uniformity of filament-type resistive memory. By controlling the magnitude of the sweep voltage in the pulse-sweep mode at each set and reset operation, similar resistance of a conducting filament in a low-resistance state and a homogeneously dissolved conducting filament in high resistance state were obtained continuously. As compared with a normal operation scheme involving a fixed voltage, our new operation scheme exhibits dramatically improved switching uniformity. By combining the new operation scheme with a gradual reset operation, we successfully achieved a stable multibit operation.IEEE Electron Device Letters 04/2011; · 2.85 Impact Factor -
Article: TiO2-based metal-insulator-metal selection device for bipolar resistive random access memory cross-point application
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ABSTRACT: We report a simple metal-insulator-metal (MIM)-type selection device that can alleviate the sneak current path in cross-point arrays. By connecting a nanometer-scale Pt / TiO <sub>2</sub>/ TiN selection device to a Pt / TiO <sub>2- x </sub>/ TiO <sub>2</sub>/ W resistive random access memory (RRAM), we could significantly reduce read disturbance from unselected memory cells. This selection device could be easily integrated into an RRAM device, in which it suppressed the sneak current and significantly improved the readout margin compared to that obtained for an RRAM not using a selection device. The introduction of this MIM device can fulfill the requirement for an appropriate selection device for bipolar-type RRAM cross-point applications.Journal of Applied Physics 03/2011; · 2.17 Impact Factor -
Article: Nonvolatile resistive switching in Pr0.7Ca0.3MnO3 devices using multilayer graphene electrodes
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ABSTRACT: We report resistive switching in Pr0.7Ca0.3MnO3 (PCMO) devices using multilayer graphene (MLG) for nonvolatile memory applications. When MLG was used as a conducting electrode, PCMO device exhibited resistive switching with an on/off ratio of over two orders of magnitude and stable retention characteristics for over 104 s at 85 °C. Raman spectroscopy in both resistance states revealed increases in D and D′ peaks associated with defects and large shift in G peak position for high-resistance state. This was attributed to formation and dissolution of oxygenated graphene at the MLG/PCMO interface, resulting in resistive switching.Applied Physics Letters 01/2011; 98(3):032105-032105-3. · 3.84 Impact Factor -
Conference Proceeding: Diode-less nano-scale ZrOx/HfOx RRAM device with excellent switching uniformity and reliability for high-density cross-point memory applications
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ABSTRACT: We report excellent switching uniformity and reliability of RRAM device with ZrO<sub>x</sub>/HfO<sub>x</sub> bi-layer films. Precise control of the oxygen vacancy concentration in HfO<sub>2</sub> layer was achieved by depositing thin Zr metal (2-15nm) layer. Scaling down active device area (φ=50 nm) and film thickness (<;2-5 nm) can significantly minimize the extrinsic defects-related non-uniform switching which was normally observed in large area (φ >;um) device, with higher active layer thickness (>;10 nm). Using back-to-back connection of two RRAM devices, we confirmed feasibility of a diode-free cross-point array with a wide readout margin and stable data reading. Considering excellent electrical and reliability characteristics of diode-free RRAM device, shows a great promise for future high density cross-point memory devices.Electron Devices Meeting (IEDM), 2010 IEEE International; 01/2011 -
Article: Effect of Scaling WOx-based RRAMs on their Resistive Switching Characteristics
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ABSTRACT: We investigated the effect of scaling down the device area of WOx resistive random-access memory (RRAM) devices on their switching characteristics. Device dimensions were successfully scaled down to 50 nm using a via-hole structure with additional Al2O3 sidewall process. As compared to the microscale devices, the nanoscale devices exhibited a distinct switching mechanism and better memory performance, such as improved switching uniformity, larger memory window, and stable endurance characteristics for up to 107 cycles. This improvement can be explained by a uniform interfacial switching mechanism in nanoscale device; this is in contrast with the defect-induced filamentary switching mechanism observed in microscale devices. In this way, the intrinsic switching properties of RRAMs were obtained by scaling down of the device area, indicating that RRAMs hold considerable promise for future applications.IEEE Electron Device Letters. 01/2011; 32:671. -
Article: Improved switching characteristics of perovskite oxide‐based resistance random access memory by high‐pressure oxygen annealing at low temperature
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ABSTRACT: We successfully fabricated perovskite oxide-based resistance random access memory (RRAM) with improved resistance switching characteristics, at a low temperature. A high-pressure oxygen-annealed (HPOA) W/Al/Pr0.7Ca0.3MnO3 (PCMO)/Pt device shows good memory characteristics such as device uniformity, endurance, and improved switching speed. X-ray photoelectron spectroscopy reveals large amounts of oxygen effectively incorporated into the PCMO layer during HPOA, enhancing the crystallization of PCMO at low temperature. X-ray diffraction analysis confirmed that an amorphous PCMO layer was converted to a polycrystalline structure. These results suggest that HPOA is a promising method for fabricating reliable perovskite oxide-based RRAM at a low temperature.Physica Status Solidi (A) Applications and Materials 10/2010; 208(1):202 - 205. · 1.46 Impact Factor -
Conference Proceeding: Effect of oxygen migration and interface engineering on resistance switching behavior of reactive metal/polycrystalline Pr0.7Ca0.3MnO3 device for nonvolatile memory applications
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ABSTRACT: An in-depth study on the resistive switching mechanism of perovskite oxide based device was performed. Compared with filament type resistive switching device, excellent switching uniformity was obtained due to controlled redox reaction at metal/oxide interface. Electromigration of oxygen ion under the bipolar electric filed can explain the switching behavior. Formation of ultrathin AlO<sub>x</sub> at the interface can guarantee excellent retention characteristics at 125°C. Compared with the large area (50 à 50 um<sup>2</sup>) memory cell, the nanoscale device (¿=50 nm) showed better memory performance such as faster switching speed, better uniformity, endurance, and retention characteristics.Electron Devices Meeting (IEDM), 2009 IEEE International; 01/2010
Top co-authors
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Institutions
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2010–2012
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Gwangju Institute of Science and Technology
- Department of Materials Science and Engineering
Kwangju, Gwangju, South Korea
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