Hye-Yong Chu

Transparent Al–Zn–Sn–O thin film transistors prepared at low temperature

We have fabricated transparent bottom gate thin film transistors (TFTs) using Al-doped zinc tin oxide (AZTO) as active layers. The AZTO active layer was deposited by rf magnetron sputtering at room temperature. The AZTO TFT showed good TFT performance without postannealing. The field effect mobility and the subthreshold swing were improved by postannealing below 180u2009°C. The AZTO TFT exhibited a field effect mobility (μFET) of 10.1u2002cm2/Vu2009s, a turn-on voltage (Von) of 0.4 V, a subthreshold swing (S/S) of 0.6 V/decade, and an on/off ratio (Ion/Ioff) of 109.

High efficiency organic light-emitting devices with Al/NaF cathode

An organic light-emitting device (OLED) with an Al/NaF (1.5 nm) cathode exhibited a highly enhanced performance comparable to the one with the best Al/LiF cathode. This suggests that NaF can be an alternative to commonly used LiF interlayer for improved OLED performance. Photoelectron spectroscopy studies revealed that the intensity of the gap states and the amount of the valence band shift at Al/NaF/Alq3 interface surpassed those of Al/LiF/Alq3 interface, suggesting that the observed performance improvement is directly related with these features.

Tris-(8-hydroxyquinoline)aluminum-based organic light-emitting devices with Al/CaF2 cathode: Performance enhancement and interface electronic structures

The device characteristics and the interface electronic structures of organic light-emitting devices based on tris-(8-hydroxyquinoline)aluminum were investigated with Al/CaF2, Al/LiF, and Al-only cathodes. Similar to the Al/LiF cathode, the Al/CaF2 cathode greatly improved the performance of the device over the Al-only cathode. However, a photoelectron spectroscopy study revealed that despite the performance improvement, the evolution of the new peaks during the Al/CaF2 cathode formation closely resembled those of the Al-only cathode rather than the Al/LiF cathode.

Transparent Oxide Thin-Film Transistors Composed of Al and Sn -doped Zinc Indium Oxide

We have fabricated the transparent bottom gate thin-film transistors (TFTs) using Al and Sn-doped zinc indium oxide (AT-ZIO) as an active layer. The AT-ZIO active layer was deposited by RF magnetron sputtering at room temperature, and the AT-ZIO TFT showed a field effect mobility of 15.6 cm²/Vs even before annealing. The mobility increased with increasing the In₂O₃ content and postannealing temperature up to 250^degC. The AT-ZIO TFT exhibited a field effect mobility of 30.2 cm²/Vs, a subthreshold swing of 0.17 V/dec, and an on/off current ratio of more than 10⁹ .

The initial state of dark spots in degradation of polymer lighting-emitting diodes

Abstract The initial state of dark spots in polymer light-emitting diodes (PLEDs) with poly[2-methoxy-5-(2′-ethyl-hexyloxy)-1,4-phenylene vinylene] (MEH-PPV) layer as an emissive layer has been investigated by in situ measurement with the interferometer, fluorescence microscope, and other various analytical instruments. Degradation of the device initiates with the dark spot that is the non-emissive portion of the polymer layer. The cross-sectional profile of interferometer image of Al electrode changes with operating time from dip to con-shaped sharp peak. It is clear that the dark spot originates from the pinhole leading to the severe damages on the microstructure of the polymer layer, polymer/metal interface, and metal electrode. Interferometer is a powerful tool for the investigation of the short-term degradation behavior of the polymeric EL devices.

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.

Non-uniform sampling and wide range angular spectrum method

A novel method is proposed for simulating free space field propagation from a source plane to a destination plane that is applicable for both small and large propagation distances. The angular spectrum method (ASM) was widely used for simulating near field propagation, but it caused a numerical error when the propagation distance was large because of aliasing due to under sampling. Band limited ASM satisfied the Nyquist condition on sampling by limiting a bandwidth of a propagation field to avoid an aliasing error so that it could extend the applicable propagation distance of the ASM. However, the band limited ASM also made an error due to the decrease of an effective sampling number in a Fourier space when the propagation distance was large. In the proposed wide range ASM, we use a non-uniform sampling in a Fourier space to keep a constant effective sampling number even though the propagation distance is large. As a result, the wide range ASM can produce simulation results with high accuracy for both far and near field propagation. For non-paraxial wave propagation, we applied the wide range ASM to a shifted destination plane as well.

P‐20: Post‐Annealing and Passivations of Transparent Bottom Gate IGZO Thin Film Transistors

We have examined post-annealing and passivation for the transparent bottom gate IGZO TFT having an inverse co-planar structure. The oxygen-vacuum two step annealing enhanced the field effect mobility up to 18 cm2/Vs and the sub-threshold swing down to 0.2 V/dec. However, the hysterysis and the bias stability problems could not be solved just by post-annealing. Thus, we have passivated the bottom gate IGZO TFTs with organic and inorganic materials. Ga2O3, Al2O3, SiO2 and some polymer materials were effective materials for passivations. The hysterysis and the stability of the TFTs were remarkably improved by the passivations.

High-resolution TFT-LCD for spatial light modulator

SLM with very fine pixel pitch is needed for the holographic display system. Among various kinds of SLMs, commercially available high resolution LCoS has been widely used as a spatial light modulator. But the size of commercially available LCoS SLM is limited because the manufacturing technology of LCoS is based on the semiconductor process developed on small size Si wafer. Recently very high resolution flat panel display panel (~500ppi) was developed as a “retina display”. Until now, the pixel pitch of flat panel display is several times larger than the pixel pitch of LCoS. But considering the possibility of shrink down the pixel pitch with advanced lithographic tools, the application of flat panel display will make it possible to build a SLM with high spatial bandwidth product. We simulated High resolution TFT-LCD panel on glass substrate using oxide semiconductor TFT with pixel pitch of 20um. And we considered phase modulation behavior of LC(ECB) mode. The TFT-LCD panel is reflective type with 4-metal structure with organic planarization layers. The technical challenge for high resolution large area SLM will be discussed with very fine pixel.

Progress of dark spot and blister formation in polymeric lighting-emitting diodes

Abstract Progress of dark spot formation during the device operation in polymeric light-emitting diodes (PLEDs) with poly[2-methoxy-5-(2′-ethyl-hexyloxy)-1,4-phenylene vinylene] (MEH-PPV) layer as an emissive layer was clarified by in situ measurement with the interferomer and other various analytical instruments. According to the morphological change of the Al electrode, the dark spot in electroluminescent images was initiated by the pinhole. It is found that the pinhole in devices is one of critical factors in the formation of dark spots. Blister formation due to the detachment of ITO / polymer layers in PELDs was varied by the humidity level of environmental conditions during operation and irradiation time of the light before operation.