Kyunghun Kim

Al2O3/TiO2 nanolaminate thin film encapsulation for organic thin film transistors via plasma-enhanced atomic layer deposition.

Organic electronic devices require a passivation layer that protects the active layers from moisture and oxygen because most organic materials are very sensitive to such gases. Passivation films for the encapsulation of organic electronic devices need excellent stability and mechanical properties. Although Al2O3 films obtained with plasma enhanced atomic layer deposition (PEALD) have been tested as passivation layers because of their excellent gas barrier properties, amorphous Al2O3 films are significantly corroded by water. In this study, we examined the deformation of PEALD Al2O3 films when immersed in water and attempted to fabricate a corrosion-resistant passivation film by using a PEALD-based Al2O3/TiO2 nanolamination (NL) technique. Our Al2O3/TiO2 NL films were found to exhibit excellent water anticorrosion and low gas permeation and require only low-temperature processing (<100 °C). Organic thin film transistors with excellent air-stability (52 days under high humidity (a relative humidity of 90% and a temperature of 38 °C)) were fabricated.

The Origin of Excellent Gate‐Bias Stress Stability in Organic Field‐Effect Transistors Employing Fluorinated‐Polymer Gate Dielectrics

Tuning of the energetic barriers to charge transfer at the semiconductor/dielectric interface in organic field-effect transistors (OFETs) is achieved by varying the dielectric functionality. Based on this, the correlation between the magnitude of the energy barrier and the gate-bias stress stability of the OFETs is demonstrated, and the origin of the excellent device stability of OFETs employing fluorinated dielectrics is revealed.

A Lattice-Strained Organic Single-Crystal Nanowire Array Fabricated via Solution-Phase Nanograting-Assisted Pattern Transfer for Use in High-Mobility Organic Field-Effect Transistors.

A 50 nm-wide 6,13-bis(triisopropylsilylethynyl) pentacene nanowire (NW) array is fabricated on a centimeter-sized substrate via a facile nanograting-assisted pattern-transfer method. NW growth under a nanoconfined space adopts a lattice-strained packing motif of the NWs for strong intermolecular electronic coupling, and thus a NW-based organic field-effect transistor shows high field-effect mobility up to 9.71 cm(2) V(-1) s(-1) .

Unified film patterning and annealing of an organic semiconductor with micro-grooved wet stamps

A unified patterning and annealing approach was successfully demonstrated for 5,11-bis(triethylsilylethynyl)-anthradithiophene (TES-ADT) films spun-cast on polymer-treated SiO2 dielectrics. First, rubbery polydimethylsiloxane (μ-PDMS) stamps with microscale periodic grooves were swollen in 1,2-dichloroethane and then softly placed onto amorphous-like TES-ADT films. In this case, the film sides physically in contact with the wet stamps were quickly absorbed into the PDMS matrix while the non-contact area formed highly-ordered phases by the solvent-annealing effect. The resulting patterns of TES-ADT contained discernable crystallites, where the grain sizes drastically decreased and their shapes transformed from spherulites to optically featureless ones with a decreasing line width from 100 to 2.5 μm. Unlike ordinary systems containing spherulitic domains, the 2.5 μm line-confined TES-ADT patterns contained layer-stacked crystallites but an optically invisible grain boundary, yielding an unexpectedly high field-effect mobility of 2.60 cm2 V−1 s−1 in organic field-effect transistors (OFETs), with narrow deviations less than 8% (averaged from 42 devices). The results suggest that the well π-overlapped grains and their smooth connections are key factors to achieve high performance multi-array OFET applications.

Repurposing compact discs as master molds to fabricate high-performance organic nanowire field-effect transistors

Organic field-effect transistors (OFETs) have been developed over the past few decades due to their potential applications in future electronics such as wearable and foldable electronics. As the electrical performance of OFETs has improved, patterning organic semiconducting crystals has become a key issue for their commercialization. However, conventional soft lithographic techniques have required the use of expensive processes to fabricate high-resolution master molds. In this study, we demonstrated a cost-effective method to prepare nanopatterned master molds for the fabrication of high-performance nanowire OFETs. We repurposed commercially available compact discs (CDs) as master molds because they already have linear nanopatterns on their surface. Flexible nanopatterned templates were replicated from the CDs using UV-imprint lithography. Subsequently, 6,13-bis-(triisopropylsilylethynyl) pentacene nanowires (NWs) were grown from the templates using a capillary force-assisted lithographic technique. The NW-based OFETs showed a high average field-effect mobility of 2.04 cm2 V-1 s-1. This result was attributed to the high crystallinity of the NWs and to their crystal orientation favorable for charge transport.

Nanowires: A Lattice-Strained Organic Single-Crystal Nanowire Array Fabricated via Solution-Phase Nanograting-Assisted Pattern Transfer for Use in High-Mobility Organic Field-Effect Transistors (Adv. Mater. 16/2016)

S. H. Kim, S. G. Hahm, C. E. Park, and co-workers fabricate a 50 nm-wide organic single-crystalline nanowire array on a centimeter-sized substrate via a facile roll-to-plate process, as described on page 3209. Nanowire growth in a nano-confined space adopts a lattice-strained and single-crystalline packing motif, which can be harnessed for strong intermolecular electronic coupling. Thus, nanowire-based field-effect transistors show extremely high field-effect mobilities up to 9.71 cm(2) V(-1) s(-1) .