Myungchul Jun

Uniform Graphene Quantum Dots Patterned from Self-Assembled Silica Nanodots

Graphene dots precisely controlled in size are interesting in nanoelectronics due to their quantum optical and electrical properties. However, most graphene quantum dot (GQD) research so far has been performed based on flake-type graphene reduced from graphene oxides. Consequently, it is extremely difficult to isolate the size effect of GQDs from the measured optical properties. Here, we report the size-controlled fabrication of uniform GQDs using self-assembled block copolymer (BCP) as an etch mask on graphene films grown by chemical vapor deposition (CVD). Electron microscope images show that as-prepared GQDs are composed of mono- or bilayer graphene with diameters of 10 and 20 nm, corresponding to the size of BCP nanospheres. In the measured photoluminescence (PL) spectra, the emission peak of the GQDs on the SiO(2) substrate is shown to be at ∼395 nm. The fabrication of GQDs was supported by the analysis of the Raman spectra and the observation of PL spectra after each fabrication step. Additionally, oxygen content in the GQDs is rationally controlled by additional air plasma treatment, which reveals the effect of oxygen content to the PL property.

Competitive device performance of low-temperature and all-solution-processed metal-oxide thin-film transistors

In this Letter, we described a solution-processed indium-gallium-zinc oxide thin-film transistors (TFTs) with a solution-processed aluminum oxide phosphate gate dielectric, fabricated at a maximum annealing temperature under 350 °C to be applicable to conventional fabrication process of flat-panel displays (FPDs). The solution-processed TFTs exhibited competitive device characteristics under 350 °C, including a field-effect mobility of 4.50 cm2/Vs, an on-to-off current ratio of ∼109, a threshold voltage of 2.34 V, and a subthreshold gate swing of 0.46 V/dec, making them applicable to the future backplane of FPDs.

Terahertz time-domain measurement of non-Drude conductivity in silver nanowire thin films for transparent electrode applications

We have investigated the complex conductivity of silver nanowire thin films using terahertz time-domain spectroscopy. Maxwell-Garnett effective medium theory, which accounts for the effective complex conductivity of silver nanowires, is presented in detail theoretically and experimentally. The conductivity of nanowires exhibits a characteristic non-Drude response in which the applied terahertz field is polarized in the longitudinal nanowire direction. The non-Drude responses of the silver nanowires are explained by the Gans approximation and the Drude-Smith model, and both agree well with the experimental data. Our results provide a basis for further explorations of charge carrier dynamics in nanowire-based transparent electrode applications.

Highly Reliable Depletion-Mode a-IGZO TFT Gate Driver Circuits for High-Frequency Display Applications Under Light Illumination

We proposed and fabricated a depletion-mode amorphous indium-gallium-zinc-oxide thin-film transistor gate driver without any additional signals. The proposed gate driver successfully exhibited a high-voltage output pulse without distortion at a clock frequency of 100 kHz, which is enough to drive a high-frequency panel with a frame rate of ~360 Hz and a resolution of full high definition. The experimental and simulation results showed that the gate driver would be highly reliable under light illumination. Also, the output waveform of the gate driver was not distorted after 240-h driving under 450-nm illumination with an intensity of 1 mW/ cm2 at 60°C.

9.3: Control of Threshold Voltage in Back Channel Etch Type Amorphous Indium Gallium Zinc Oxide Thin Film Transistors

Tuning the process pressure at the deposition of the passivation layers has been suggested in the way of controlling the threshold voltage of a-IGZO TFTs, making it possible to employ gate driver integration. It has showed that Vth linearly changes with the pressure ΔVth/ΔPressure∼3.5V/100Pa. A 3.2 inch WVGA AMLCD with integrated gate driver circuits were successfully demonstrated using the enhancement mode BCE type bottom gate a-IGZO TFTs.

A Novel Depletion-Mode a-IGZO TFT Shift Register With a Node-Shared Structure

We proposed and fabricated a new depletion-mode amorphous indium-gallium-zinc-oxide thin-film-transistor (TFT) shift register with a node-shared structure. The proposed shift register requires 14 TFTs, 3 clock lines, and 3 power source lines for two output pulses, whereas the previous shift registers consisted of more than 22 TFTs, 4 clock lines, and 6 power source lines. The experimental results showed that the proposed shift register successfully generated two output pulses at one stage without any distortion. The circuit area of the proposed shift register is reduced by about 30%, as compared with that of the previous one.

P‐20: Highly Stable Amorphous Indium Gallium Zinc Oxide Thin‐Film Transistors with N2O Plasma Treatment

Amorphous InGaZnO4 (a-IGZO) thin film transistors (TFTs) are promising devices in backplane technology. Since a-IGZO TFTs are very sensitive to the fabrication processes, they need stable process to keep their initial deposition properties. Herein we improved the stability of a-IGZO by applying N2O plasma. The stability characteristic of a-IGZO TFT was improved with N2O plasma. Vth shift was 1.5V for 10,000s under NBTS with illumination which was the best result in the world.

Compositional changes in the channel layer of an amorphous In–Ga–Zn-O thin film transistor after thermal annealing

In order to investigate the possible reason for the improved device performances of amorphous In–Ga–Zn-O (a-IGZO) thin film transistors after thermal annealing, changes in the elemental concentrations in the a-IGZO channel regions and related device performances due to thermal annealing were observed. It was found that thermal annealing introduces a substantial level of oxygen deficiencies in the channel layer accompanying significantly enhanced device performances. The improved device performances are attributed to the oxygen deficiency which is believed to be averaged over the entire structure to function as shallow donors increasing the carrier concentrations. Such a deduction was supported by the changes in the absorption spectra of the a-IGZO films with various thermal histories.

A Novel Four-Mask Low-Temperature Polycrystalline Silicon PMOS Thin-Film Transistor With Advanced Terrace Structure for AMOLED Application

We propose a novel four-mask low-temperature polycrystalline-silicon PMOS structure. In this letter, we obtain the utmost simplified thin-film transistor (TFT) structure by eliminating the storage doping, passivation, and anode photomask steps. The proposed four-mask structure has a self-aligned terrace structure whose lightly doped drain (LDD) and gate-overlapped LDD are formed with only one photomask step. The on current of the four-mask PMOS TFT with an advanced terrace structure is similar to that of the conventional seven-mask TFT, while the off current of the new structure is lower than that of the conventional seven-mask TFT.

26.4: Novel Driving and Panel Design of Frame Inversion Method for High Aperture Ratio in the Large Size and High Resolution LCD TV Panel

The 120Hz frame inversion driving FHD LCD TV panels were fabricated without image degradations seen such as the luminance gradient and the horizontal crosstalk. The panels had the higher aperture ratio because of the wider electrode space between the pixel and common electrode than conventional S-IPS. The novel driving method of gate-low-voltage-swing was used to remove the luminance gradient and the new panel design of divided-common-feeding was adopted to suppress the horizontal crosstalk. These technologies were very successful to achieve the high aperture ratio in the S-IPS panel without increase of the panel cost.