Sunghoon Song

Tunable electronic transport characteristics of surface-architecture-controlled ZnO nanowire field effect transistors.

Surface-architecture-controlled ZnO nanowires were grown using a vapor transport method on various ZnO buffer film coated c-plane sapphire substrates with or without Au catalysts. The ZnO nanowires that were grown showed two different types of geometric properties: corrugated ZnO nanowires having a relatively smaller diameter and a strong deep-level emission photoluminescence (PL) peak and smooth ZnO nanowires having a relatively larger diameter and a weak deep-level emission PL peak. The surface morphology and size-dependent tunable electronic transport properties of the ZnO nanowires were characterized using a nanowire field effect transistor (FET) device structure. The FETs made from smooth ZnO nanowires with a larger diameter exhibited negative threshold voltages, indicating n-channel depletion-mode behavior, whereas those made from corrugated ZnO nanowires with a smaller diameter had positive threshold voltages, indicating n-channel enhancement-mode behavior.

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 ]

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)

Stable Switching Characteristics of Organic Nonvolatile Memory on a Bent Flexible Substrate

Organic-based electronics have received great attention due to their material variety and advantageous properties such as fl exibility, printability, and light-weightness. [ 1 , 2 ] Their low costs, based on their ease of fabrication and large-area processing capabilities, increase the merits of organic electronics even more. [ 3 , 4 ] Consequently, organic electronics, including organic solar cells, light-emitting diodes, thin-fi lm transistors, and memories, have been extensively investigated for the realization of practical device applications. [ 5–8 ] Among these, organic memories have emerged as an excellent candidate for the nextgeneration information storage media because of their potential application in fl exible memory devices. [ 8–18 ] There are different types of organic memories. They are distinguished as ferroelectric, [ 13 , 14 , 18 ] fl ash, [ 15 , 18 ] and resistive-type organic memories [ 16–18 ]

Passivation effects on ZnO nanowire field effect transistors under oxygen, ambient, and vacuum environments

We investigated the passivation effects on the electrical characteristics of ZnO nanowire field effect transistors (FETs) under the various oxygen environments of ambient air, dry O2, and vacuum. When the ZnO nanowire FET was exposed to more oxygen, the current decreased and the threshold voltage shifted to the positive gate bias direction, due to electrons trapping to the oxygen molecules at the nanowire surface. On the contrary, the electrical properties of the nanowire FET remained unchanged under different environments with passivation by a polymethyl methacrylate layer, which demonstrates the importance of surface passivation for ZnO nanowire-based electronic device applications.

Structural and Electrical Characterization of a Block Copolymer‐Based Unipolar Nonvolatile Memory Device

Electronic devices based on a series of synthesized block copolymers are demonstrated. In particular, a block copolymer system with a lamellar structure exhibits unipolar switching behavior. This study provides a simple strategy based on the adjustment of the block ratio in block copolymers to control the polymer morphology and thus the electrical and switching properties of polymer-based memory devices.

Realization of highly reproducible ZnO nanowire field effect transistors with n-channel depletion and enhancement modes

The authors demonstrate the highly reproducible fabrication of n-channel depletion-mode (D-mode) and enhancement-mode (E-mode) field effect transistors (FETs) created from ZnO nanowires (NWs). ZnO NWs were grown by the vapor transport method on two different types of substrates. It was determined that the FETs created from ZnO NWs grown on an Au-coated sapphire substrate exhibited an n-channel D mode, whereas the FETs of ZnO NWs grown on an Au-catalyst-free ZnO film exhibited an n-channel E mode. This controlled fabrication of the two operation modes of ZnO NW-FETs is important for the wide application of NW-FETs in logic circuits.

Electrical Properties of Surface-Tailored ZnO Nanowire Field-Effect Transistors

A review on the tunable electrical properties of ZnO nanowire field-effect transistors (FETs) is presented. The FETs made from surface-tailored ZnO nanowire exhibit two different types of operation modes, which are distinguished as depletion and enhancement modes in terms of the polarity of the threshold voltage. We demonstrate that the transport properties of ZnO nanowire FETs are associated with the influence of nanowire size and surface roughness associated with the presence of surface trap states at the interfaces as well as the surface chemistry in environments.

Electrical characterization of organic resistive memory with interfacial oxide layers formed by O2 plasma treatment

We studied organic resistive memory devices with interfacial oxide layers, the thickness of which depended on O2 plasma treatment time. The different interfacial oxide thicknesses sequentially changed the ON and OFF states of the final memory devices. We found that the memory devices that had undergone additional plasma treatment showed higher ON/OFF ratios than devices without the treatment, which was due to the relatively large OFF resistance values. However, a long oxidation process widened the threshold voltage distribution and degraded the switching reproducibility. This indicates that the oxidation process should be carefully optimized to provide practical high-performance organic memory.

Resistive Switching Characteristics of Solution-Processed Transparent TiO x for Nonvolatile Memory Application

We propose a solution-processed transparent TiO x -based resistive switching random access memory (ReRAM) device. Electronically active TiO x was prepared by sol-gel spin coating of a titanium(IV) isopropoxide precursor on an indium tin oxide-coated glass. The prepared TiO x film is completely transparent in the visible range and has an amorphous structure. The fabricated TiO x -based ReRAM device exhibits distinct resistive switching under consecutive dc voltage sweeps of ±2 V. The device also exhibits good memory performance, including fast switching speed with a pulse width of 1 μs, stable pulse endurance over 1000 cycles, and excellent retention characteristics at up to 125 °C. In addition, based on the log I - log V plot and X-ray photoelectron spectroscopy analysis, we postulate that the fabricated device is operated by the reversible formation/rupture of the conducting filament in the oxygen-deficient TiO x layer.