Hanul Moon

Resistive Switching Characteristics of Sol–Gel Zinc Oxide Films for Flexible Memory Applications

Unipolar resistive switching devices are investigated for nonvolatile memory applications in a metal-insulator-metal structure in which the insulator layer is based on sol-gel-derived zinc oxide (ZnO) films prepared by a simple spin-coating process followed by thermal annealing. Fast programming ( les 50 ns) and a high off-to-on resistance ratio ( ges 104) is demonstrated. The influences on the switching behaviors according to the crystallinity of the ZnO films are studied as a function of the annealing temperature. In addition, the devices are fabricated on a flexible plastic substrate and exhibit excellent durability upon repeated bending tests, demonstrating their potential for flexible low-cost memory devices.

Nanoscale Electronics: Digital Fabrication by Direct Femtosecond Laser Processing of Metal Nanoparticles

For various applications in the electronics industry, the fabrication of electrically conductive nanoand micropatterns has become important. Conventional vacuum metal deposition and photolithography processes are widely used for high-resolution metal patterning of microelectronics. However, those conventional approaches require expensive vacuum conditions, high processing temperatures, many steps, and toxic chemicals to fabricate one layer of a metal pattern. Furthermore, it is almost impossible to change the design of the expensive photomask once it is fabricated. For these reasons, the development of alternative maskless, direct, high-resolution patterning techniques to fabricate conductive microand nanopatterns at atmospheric pressure and low temperature without using vacuum deposition or photolithography has attracted wide attention in recent years. One of the most promising alternatives is the direct patterning of solution-deposited metal nanoparticles (NPs). The development of metal NP solution ink enabled 1) an inexpensive solution-based metal deposition approach without using expensive vacuum deposition and 2) a low-temperature metal deposition process, which allows using heat-sensitive and inexpensive polymer as the substrate. Examples of NP-inkbased direct metal patterning include screen printing, [ 1 ] direct nanoimprinting, [ 2 , 3 ] microcontact printing, [ 4 , 5 ] inkjet printing, [ 6 , 7 ]

Synthesis of ultrathin polymer insulating layers by initiated chemical vapour deposition for low-power soft electronics

Insulating layers based on oxides and nitrides provide high capacitance, low leakage, high breakdown field and resistance to electrical stresses when used in electronic devices based on rigid substrates. However, their typically high process temperatures and brittleness make it difficult to achieve similar performance in flexible or organic electronics. Here, we show that poly(1,3,5-trimethyl-1,3,5-trivinyl cyclotrisiloxane) (pV3D3) prepared via a one-step, solvent-free technique called initiated chemical vapour deposition (iCVD) is a versatile polymeric insulating layer that meets a wide range of requirements for next-generation electronic devices. Highly uniform and pure ultrathin films of pV3D3 with excellent insulating properties, a large energy gap (>8 eV), tunnelling-limited leakage characteristics and resistance to a tensile strain of up to 4% are demonstrated. The low process temperature, surface-growth character, and solvent-free nature of the iCVD process enable pV3D3 to be grown conformally on plastic substrates to yield flexible field-effect transistors as well as on a variety of channel layers, including organics, oxides, and graphene.

Towards Gigahertz Operation: Ultrafast Low Turn‐on Organic Diodes and Rectifiers Based on C60 and Tungsten Oxide

Ultrafast organic diodes with low turn-on voltage based on a junction between C60 and WO3 are proposed. The high electron mobility of C60 layers and the optimal work function of hexamethyldisilazane (HMDS)-treated WO3 layers together provide ideal diode characteristics including high rectification ratio and low turn-on voltage. Ultrahigh frequency (UHF) compatible rectifiers with a low voltage drop are demonstrated with the C60/WO3 diodes.

Low-Voltage High-Performance Pentacene Thin-Film Transistors With Ultrathin PVP/High-

Low-voltage and high-performance pentacene thin-film transistors with a hybrid gate dielectric consisting of ultrathin PVP (8 nm) and a high-κ HfLaO (20 nm) have been demonstrated. The hybrid gate dielectric exploits the advantages of both dielectrics, i.e., a good interface between the organic dielectric and channel material as well as the insulating properties of the inorganic metal-oxide, resulting in very low leakage current, hysteresis-free behavior, superior drain-current drivability, and successful operation at -2 V. The superior device performance is attributed to good intermolecular ordering and the large grain size of the pentacene channel layer formed on the hybrid dielectric.

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Colorless, highly transparent organic thin-film transistors (TOTFTs) with high performance are realized based on benzothieno[3,2-b]benzothiophene (BTBT) derivatives that simultaneously exhibit a wide energy gap and high transport properties. Multilayer transparent source/drain electrodes maintain the transparency, and ultrathin fluoropolymer dielectric layers enable stable, low-voltage operation of the proposed TOTFTs.

HfLaO Hybrid Gate Dielectric

A novel nanogap fabrication method using an electrochemical nanopatterning technique is presented. Electrochemical deposition of platinum ions reduces the microgap size to the sub-50-nm range due to the self-limited volume expansion of the electrodes. Additionally, the low crystallinity of platinum reduces the line edge roughness in the electrodes, whereas the high crystallinity of gold increases it. Current compliance, a buffered resistor, and a symmetric deposition strategy are used to achieve high reliability and practicality of nanogap electrodes. As a possible application, an organic thin-film transistor using the nanogap electrodes is also demonstrated.

Towards Colorless Transparent Organic Transistors: Potential of Benzothieno[3,2‐b]benzothiophene‐Based Wide‐Gap Semiconductors

Digital-mode organic vapor-jet printing (D-OVJP) is demonstrated by producing a series of organic vapor jets. D-OVJP not only inherits all the benefits of a conventional OVJP but also provides an advanced, straightforward control over organic deposition with a pixel-to-pixel precision. Digitally-controlled film thickness and high-performance thin-film transistors are demonstrated with D-OVJP, proving its potential applicability to organic electronics and related areas.

Nanogap Electrode Fabrication for a Nanoscale Device by Volume‐Expanding Electrochemical Synthesis

With the emergence of wearable or disposable electronics, there grows a demand for a flash memory realizable on various flexible substrates. Nevertheless, it has been challenging to develop a flash memory that simultaneously exhibits a significant level of flexibility and performance. This is mainly due to the scarcity of flexible dielectric materials with insulating properties sufficient for a flash memory, which involves dual dielectric layers, respectively, responsible for tunneling and blocking of charges. Here we report ultra-flexible organic flash memories based on polymer dielectrics prepared by initiated chemical vapor deposition. Using their near-ideal dielectric characteristics, we demonstrate flash memories bendable down to a radius of 300 μm that exhibits a relatively long-projected retention with a programming voltage on par with the present industrial standards. The proposed memory technology is then applied to non-conventional substrates, such as papers, to demonstrate its feasibility in a wide range of applications.Flexible flash memory is crucial to modern electronics, but its fabrication is challenging in the absence of suitable dielectric materials. Here, Lee et al. realize organic memory with retention over 10 years using tunneling and blocking dielectric layers prepared by initiated chemical vapor deposition.

Digital-Mode Organic Vapor-Jet Printing (D-OVJP): Advanced Jet-on-Demand Control of Organic Thin-Film Deposition

Organic vapor-jet printing, a maskless direct printing method, is used to fabricate high-performance pentacene thin-film transistors. By combining the optimal carrier gas temperature and the surface treatment of gate dielectrics, a mobility of 0.46 (±0.03) cm2 V-1 s-1 and an on-off ratio greater than 107 are achieved. Morphological analyses indicate that the relatively high carrier gas temperature and low surface energy of the dielectric surface are the keys in achieving the level of performance comparable to that of devices based on conventional technologies.