Mi Hye Yi

Solvent‐Free Directed Patterning of a Highly Ordered Liquid Crystalline Organic Semiconductor via Template‐Assisted Self‐Assembly for Organic Transistors

Highly ordered organic semiconductor micropatterns of the liquid-crystalline small molecule 2,7-didecylbenzothienobenzothiophene (C10 -BTBT) are fabricated using a simple method based on template-assisted self-assembly (TASA). The liquid crystallinity of C10 -BTBT allows solvent-free fabrication of high-performance printed organic field-effect transistors (OFETs).

New amorphous semiconducting copolymers containing fluorene and thiophene moieties for organic thin-film transistors

New amorphous semiconducting materials consisting of fluorene-based thiophene copolymers, poly(2-(5-(9,9-dibutyl-9 H-fluoren-2-yl)-3-hexylthiophen-2-yl)-5-(3-hexylthiophen-2-yl)thieno[3,2-b]thiophene) P1 and poly(2-(5-(9,9-dibutyl-9 H-fluoren-2-yl)-4-hexylthiophen-2-yl)-5-(4-hexylthiophen-2-yl)thieno[3,2-b]thiophene) P2, have been successfully synthesized via a palladium-catalyzed Suzuki coupling reaction. The number-average molecular weights (Mn) of P1 and P2 were found to be 18 300, and 15 800, respectively. These polymers dissolve in common organic solvents such as chloroform, chlorobenzene, and toluene. The UV-vis absorption maxima of P1 and P2 appeared at 436 and 427 nm in solution and 441 and 431 nm in the film state, respectively. X-Ray diffraction (XRD) analysis showed no reflection peaks indicating amorphous collections of randomly oriented polymer chains. Atomic force microscopy (AFM) images of P1 and P2 showed amorphous film morphologies. Field-effect transistor mobilities of stable amorphous OTFTs of P1 and P2 under ambient conditions have been achieved up to 5.4 × 10−4 cm2V−1 s−1 and 1.6 × 10−4 cm2V−1 s−1, respectively. The high stability and mobility of fluorene-based thiophene copolymers in the amorphous state make them a new family of promising candidates for organic thin-film transistors.

Printed Cu source/drain electrode capped by CuO hole injection layer for organic thin film transistors

Using conductive functional ink comprising Cu/CuO core–shell nanoparticles, we present the printed Cu source/drain electrode surrounded by a CuO hole injection layer for organic thin-film transistors. The inherent CuO hole injection layer facilitates the transistor with electrical performance comparable to that of a transistor based on a vacuum deposited Au electrode, without additional physical or chemical treatments for obtaining an energetically compatible interface between the electrode and p-type organic semiconductor.

Poly(imide-benzoxazole) gate insulators with high thermal resistance for solution-processed flexible indium-zinc oxide thin-film transistors

We prepared a poly(imide-benzoxazole) gate insulator for solution-processed flexible metal oxide thin-film transistors (TFTs). The electrical insulating property of the poly(imide-benzoxazole) gate insulator is maintained up to at least 350 °C. The 350 °C-annealed indium-zinc oxide (IZO) TFT with the poly(imide-bezoxazole) gate insulator showed excellent TFT performance with the field-effect mobility of 9.2 cm2 V−1 s−1 and the on/off current ratio of 1.5 × 106. A flexible IZO TFT with the poly(imide-bezoxazole) gate insulator was also fabricated directly on a flexible Kapton substrate. The flexible IZO TFT with the poly(imide-bezoxazole) gate insulator could be operated during bending. Before bending, the mobility and on/off current ratio were 4.1 cm2 V−1 s−1 and 4.7 × 105, respectively. During bending with a radius of 10 mm, the mobility was maintained and the on/off current ratio was slightly decreased to 3.2 × 105.

Surface modification of a polyimide gate insulator with an yttrium oxide interlayer for aqueous-solution-processed ZnO thin-film transistors.

We report a simple approach to modify the surface of a polyimide gate insulator with an yttrium oxide interlayer for aqueous-solution-processed ZnO thin-film transistors. It is expected that the yttrium oxide interlayer will provide a surface that is more chemically compatible with the ZnO semiconductor than is bare polyimde. The field-effect mobility and the on/off current ratio of the ZnO TFT with the YOx/polyimide gate insulator were 0.456 cm(2)/V·s and 2.12 × 10(6), respectively, whereas the ZnO TFT with the polyimide gate insulator was inactive.

A high-temperature resistant polyimide gate insulator surface-modified with a YOx interlayer for high-performance, solution-processed Li-doped ZnO thin-film transistors

We report here a fully aromatic polyimide film with excellent electrical insulating properties and thermal stability. To use the polyimide as a gate insulator for high-performance solution-processed metal oxide thin-film transistors, the surface of a 350 nm thick polyimide film was modified with a 25 nm thick yttrium oxide interlayer. The YOx/polyimide gate insulator showed excellent gate insulating properties with a dielectric constant of 3.2 at 10 kHz and a leakage current density of 3.3 × 10−10 A cm−2 at 2 MV cm−1 after the 300 °C annealing process. We prepared solution-processed Li-doped ZnO thin-film transistors with the prepared gate insulators. After the surface modification with the interlayer, the field-effect mobility of the 300 °C annealed Li-doped ZnO thin-film transistor increased from 0.1 cm2 V−1 s−1 to 4.9 cm2 V−1 s−1.

Environmentally Stable Transparent Organic/Oxide Hybrid Transistor Based on an Oxide Semiconductor and a Polyimide Gate Insulator

We fabricated environmentally stable and transparent organic/oxide hybrid transistor on a glass substrate using the conventional photolithography. The obtained device, which was composed of an In-Ga-Zn-O active layer/soluble polyimide (KSPI) organic insulator, showed a mobility of 6.65 cm2/Vs, a subthreshold swing slope of 350 mV/decade, a threshold voltage (VT) of 3.10 V, and an on-off ratio of 3.9 × 109. The transistor also showed good uniformity characteristics and was found to be environmentally stable for 90 days under ambient conditions.

Synthesis and characterisation of photopolymerisable liquid crystals based on the π-extended fluorene core and their corresponding non-reactive analogues

We have synthesised a series of new reactive mesogens with photopolymerisable di-acrylates and their corresponding non-reactive analogues based on the π-conjugated aromatic core, fluorene (F)-di-[thiophene (T)-benzene (B)], using the Stille and Suzuki coupling reaction. The effect of lateral alkyl chains on the 9-position of the central fluorene moiety as well as α, ω- side alkyl chains attached to the π-conjugated aromatic core on the mesomorphism was investigated by utilising differential scanning calorimetry (DSC) and polarising optical microscopy (POM). A wide angle X-ray scattering (WAXS) study at the various temperatures was also carried out to reveal phase structures. Photopolymerisable di-acrylates connected directly to the rigid aromatic core showed higher phase transition temperatures, probably due to the induced dipole moment in comparison with those of a non-reactive methyl–ether counterpart.

Mesomorphic phase transition behaviour of photopolymerisable liquid crystalline triphenylene ether compounds

This report discusses the preparation and the unusual mesomorphism of three homologues of photopolymerisable triphenylene ether compounds. These homologues showed ‘a cold crystallisation’ on heating differential scanning calorimetry curves, and this phenomenon is attenuated with increase methylene units, spacers between the triphenylene core and the terminal photopolymerisable acrylate group. Classical textures of hexagonal columnar (Colh) mesophase were observed by polarising optical microscopy for all three photopolymerisable mesophase compounds described here. Also described is the mesomorphism of their intermediates, hydroxylalkoxytriphenylenes. In some cases, the discotic columnar hexagonal mesophases were confirmed by wide angle X-ray scattering techniques.

Novel Crosslinked PVA Without Photoinitiator for Organic Passivation Layers of Pentacene Thin-Film Transistors

We report a new polyvinyl alcohol (PVA)-tetraethoxysilane (TEOS) hybrid layer to protect an organic thin-film transistor (OTFT). PVA/TEOS hybrid thin film was successfully fabricated through hydrolysis and condensation mechanism. The surface roughness of PVA/TEOS film was measured by atomic force miscroscophy (AFM) and it showed a good surface roughness with a root-mean-squae value of about 0.23 nm. Thermally crosslinked PVA with TEOS was successfully adaped as a solution processable passivation layer for pentacene TFT. In case of well known photo-crosslinked PVA/ammonium dichromater (ADC) passivation, extremely large initial performance drop (almost 52% mobility drop) was observed after passivation. PVA/TEOS hybrid passiavtion, however, no significant initial performance drop was found after passivation process. In addition, pentacene TFT with PVA/TEOS passivation layer exhibited very stable TFT operation with almost no field mobility drop or threshold voltage shift up to 980 h.