Yun-Hyuk Choi

Characteristics of Double-Gate Ga–In–Zn–O Thin-Film Transistor

A Ga-In-Zn-O thin-film transistor with double-gate structure is reported. Enhancement-mode operation that is essential to the constitution of a low-power digital circuitry is easily achieved when the upper and lower gate electrodes are tied together. The saturation mobility and the subthreshold swing are improved from 3.65 cm2/(V·s) and 0.44 V/dec to 18.9 cm2/(V·s) and 0.14 V/dec, respectively, compared with the single-gate structure. We can modulate the threshold voltage of either gate by adjusting the bias on the other gate.

Highly conductive polymer-decorated Cu electrode films printed on glass substrates with novel precursor-based inks and pastes

Novel inks and pastes based on a copper(II) formate tetrahydrate precursor were formulated with controllable viscosities in the range 5000–10 000 cP for use in printed electrodes. In particular, the addition of ethyl cellulose increased the adhesion of the printed paste films to the glass substrates. For the facile fabrication of electrodes with improved performance, the formulated pastes were printed on glass substrates under ambient conditions by a doctor-blade method. The printed films were thermally sintered at 170–250 °C in air and subsequently reduced under a formic acid atmosphere. The phase and microstructural evolution of the electrode films were systematically investigated by X-ray diffraction (XRD) and cross-sectional, focused ion beam scanning electron microscopy (FIB-SEM) in each processing step. Highly adhesive, polycrystalline Cu electrode films decorated by ethyl cellulose with a vermicular microstructure and large interconnected pore channels were well formed on the glass substrates. The electrode films sintered for 1 min in air and then reduced for 5 min under formic acid atmosphere at 250 °C showed the lowest electrical resistivity of ∼8 μΩ cm (electrical conductivity of ∼125 000 Ω cm−1, equivalent to ∼22% of bulk Cu), despite their maximum porosity of 27.31%.

P-214: Ultra Thin-Film Encapsulation for AMOLED Displays

A 5.4-inch AMOLED display was prepared using the combination of ultra thin film encapsulation steps with alternative organic and inorganic hybrid multi-layers. Organic layers for smoothing and improved adhesion were prepared by polyurea condensation with vapor deposition polymerization. Al2O3 inorganic layers were sequentially deposited on organic layers by sputtering. All processes were performed at room temperature. After optimization of the organic and inorganic layer deposition process, device operating lifetime performance was over 85%, as compared with glass encapsulation, and the transmittance of thin film multilayered structure was over 90% in the visible region.

Cobalt oxide polymorph growth on electrostatic self-assembled nanoparticle arrays for dually tunable nano-textures

We report on a method for surface nano-texturing on a plastic substrate. Nano-objects with a silica nanoparticle core and a textured cobalt oxide crown are created with selectable density on the plastic substrate. The resulting dual morphology is easily tuned over large areas, either by changing the parameters directing nanoparticle deposition through electrostatic self-arrangement for nano-object density control, or the parameter directing cobalt oxide deposition for shape control. The entire process takes place at room temperature, with no chemicals harmful to the plastic substrate. The ready modulation of the dual morphology is used to control the wettability properties of the plastic film, which is covered by nano-objects.