Hyunsang Hwang

Reproducible hysteresis and resistive switching in metal-CuxO-metal heterostructures

Materials showing reversible resistance switching between high-resistance state and low-resistance state at room temperature are attractive for today’s semiconductor technology. In this letter, the reproducible hysteresis and resistive switching characteristics of metal-CuxO-metal (M-CuxO-M) heterostructures driven by low voltages are demonstrated. The fabrication of the M-CuxO-M heterostructures is fully compatible with the standard complementary metal-oxide semiconductor process. The hysteresis and resistive switching behavior are discussed. The good retention characteristics are exhibited in the M-CuxO-M heterostructures by the accurate controlling of the preparation parameters.

Three-Dimensional Integration of Organic Resistive Memory Devices

Since the discovery of conducting polymers [ 1 ] , organic-based electronics such as organic light-emitting diodes, transistors, photovoltaics, and memory devices have been spotlighted as potentially innovative devices given their easy and lowcost fabrication by spin-coating or ink-jet printing, and their fl exibility. [ 2–15 ] Among these, organic memories have been extensively investigated for data-storage application. [ 11 , 14 , 16–21 ]

Analog memory and spike-timing-dependent plasticity characteristics of a nanoscale titanium oxide bilayer resistive switching device.

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.

Rewritable Switching of One Diode–One Resistor Nonvolatile Organic Memory Devices

[*] Prof. T. Lee, B. Cho, T.-W. Kim, S. Song, Y. Ji, M. Jo, Prof. H. Hwang, Prof. G.-Y. Jung Department of Materials Science and Engineering Gwangju Institute of Science and Technology 1 Oryong-Dong, Buk-Gu Gwangju 500-712 (Korea) E-mail: tlee@gist.ac.kr Prof. T. Lee, Prof. H. Hwang Department of Nanobio Materials and Electronics Gwangju Institute of Science and Technology 1 Oryong-Dong, Buk-Gu Gwangju 500-712 (Korea)

Excellent Selector Characteristics of Nanoscale

We herein present a nanoscale vanadium oxide (VO₂) device with excellent selector characteristics such as a high on/off ratio (>; 50), fast switching speed (<; 20 ns), and high current density (>; 10⁶ A/cm2). Owing to extrinsic defects, a large-area device with a 20-nm-thick VO₂ layer underwent an electrical short. In contrast, after scaling the device active area (<; 5 × 10⁴ nm²), excellent switching uniformity was obtained. This can be explained by the reduced defects and the metal-insulator transition of the whole nanoscale VO₂. By integrating a bipolar resistive random access memory device with the VO₂ selection device, a significantly improved readout margin was obtained. The VO₂ selection device shows good potential for cross-point bipolar resistive memory applications.

\hbox{VO}_{2}

The hygroscopic nature of lanthanide oxides such as Pr2O3, Sm2O3, Gd2O3, and Dy2O3 was characterized by means of x-ray photoelectron spectroscopy and its effect on the electrical characteristics of the compounds was investigated. Among the four samples, Pr2O3 was found to be the most reactive with water which can be attributed to the relatively large ionic radius and lower electronegativity of Pr. In contrast, Dy2O3 was the least reactive with water. A direct correlation between the hygroscopicity and electronegativity of lanthanide elements was found. With increasing hygroscopicity, a significant growth of interfacial oxide with annealing temperature was observed. A clear understanding of the nature of hygroscopic effects and the optimization of process flow will be needed for future high-k gate dielectric application.

for High-Density Bipolar ReRAM Applications

Nonvolatile and reversible bistable and multistable resistance states of polycrystalline SrTiOx thin film were studied. The pulse-laser-deposition method was employed to grow the film, and the clear resistance switching was observed under dc bias sweep and voltage pulses. More than two controllable resistance states were observed by applying voltage pulses. These reversible states have a resistance difference by nearly two orders of magnitude, and we verified that this sharp resistance switching takes place at the metal-oxide interface. Excellent reliability characteristics, such as endurance cycles of up to 105 times and data retention time of up to 106s at 125°C demonstrate the promise of SrTiOx film for future nonvolatile random access memory applications.

Effect of hygroscopic nature on the electrical characteristics of lanthanide oxides (Pr2O3, Sm2O3, Gd2O3, and Dy2O3)

The resistance switching behavior and switching mechanism of nonstoichiometric zirconium oxide thin films were investigated for nonvolatile memory application. The Pt/ZrO/sub x//p/sup +/-Si sandwich structure fabricated by reactive sputtering shows two stable resistance states. By applying proper bias, resistance switching from one to another state can be obtained. The composition in ZrO/sub x/ thin films were confirmed from X-ray photoelectron spectroscope (XPS) analysis, which showed three layers such as top stoichiometric ZrO/sub 2/ layer with high resistance, transition region with medium resistance, and conducting ZrO/sub x/ bulk layer. The resistance switching can be explained by electron trapping and detrapping of excess Zr/sup +/ ions in transition layer which control the distribution of electric field inside the oxide, and, hence the current flow.

Reversible resistive switching of SrTiOx thin films for nonvolatile memory applications

The electrical and physical characteristics of oxynitride grown in N/sub 2/O gas ambient have been studied. The dielectric growth rate in N/sub 2/O was found to be highly controllable and lower than that in O/sub 2/. Auger electron spectroscopy studies of oxynitride show a nitrogen-rich layer near the Si-SiO/sub 2/ interface. Compared with the control oxide, the oxynitride shows excellent electrical characteristics such as excellent diffusion barrier to dopant (BF/sub 2/), a significant reduction in interface state generation, less electron trapping, and much larger charge-to-breakdown under Fowler-Nordheim stress. A significantly lower threshold voltage shift and degradation of subthreshold swing under hot electron stress were also observed. These improvements can be explained by the nitrogen incorporation at Si-SiO/sub 2/ interface. This new oxynitride shows good promise for future ULSI application.<<ETX>>

Resistance switching of the nonstoichiometric zirconium oxide for nonvolatile memory applications

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/TiO2/TiN selection device to a Pt/TiO2−x/TiO2/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.