Hee-Ok Kim

Beneficial effect of hydrogen in aluminum oxide deposited through the atomic layer deposition method on the electrical properties of an indium–gallium–zinc oxide thin-film transistor

ABSTRACT Described herein is the role of hydrogen in aluminum oxide (Al2O3) gate dielectrics in amorphous indium–gallium–zinc oxide (a-InGaZnO or a-IGZO) thin-film transistors (TFTs). Compared to a-IGZO TFTs with a low-temperature (150°C) Al2O3 gate dielectric, a-IGZO devices with a high-temperature (250–300°C) Al2O3 gate dielectric exhibit poor transistor characteristics, such as low mobility, a high subthreshold slope, and huge hysteresis. Through DC and short-pulsed current–voltage (I–V) measurements, it was revealed that the degradation of the transistor performance stems from the charging and discharging phenomenon at the interface traps located in the interface between the a-IGZO semiconductor and the Al2O3 gate insulator. It was found that the low-temperature Al2O3 atomic layer deposition processed film contains a higher density of hydrogen atoms compared to high-deposition-temperature films. The study results show that a high concentration of hydrogen atoms can passivate the defect sites in the interface and bulk, which produces excellent transistor characteristics. This study demonstrated that hydrogen has a beneficial effect on the defect passivation for oxide TFTs.

Switchable subwavelength plasmonic structures with phase-change materials for reflection-type active metasurfaces in the visible region

In this work, a switchable plasmonic structure is proposed for reflection-type spatial light modulation in the visible range with subwavelength resolution. This structure is based on a metallic grating in which each resonant cavity couples the incident light into a gap surface plasmon mode and then reflects the light modulated in the cavity. By incorporating an ultrathin layer of the phase-change material Ge2Sb2Te5 at the entrance of the cavity, the optical modulation characteristic of the structure can be switched between two modes. Numerical investigations are conducted to verify the proposed structure, with the focused analysis of two common types of binary modulations: amplitude-only and phase-only modulations.

Effect of hydrogen diffusion in an In–Ga–Zn–O thin film transistor with an aluminum oxide gate insulator on its electrical properties

We fabricated amorphous InGaZnO thin film transistors (a-IGZO TFTs) with aluminum oxide (Al2O3) as a gate insulator grown through atomic layer deposition (ALD) method at different deposition temperatures (Tdep). The Al2O3 gate insulator with a low Tdep exhibited a high amount of hydrogen in the film, and the relationship between the hydrogen content and the electrical properties of the TFTs was investigated. The device with the Al2O3 gate insulator having a high H content showed much better transfer parameters and reliabilities than the low H sample. This is attributed to the defect passivation effect of H in the active layer, which is diffused from the Al2O3 layer. In addition, according to the post-annealing temperature (Tpost-ann), a-IGZO TFTs exhibited two unique changes of properties; the degradation in low Tpost-ann and the enhancement in high Tpost-ann, as explained in terms of H diffusion from the gate insulator to an active layer.

Development of high-resolution active matrix spatial light modulator

Abstract. We developed a high-resolution active matrix spatial light modulator on a glass substrate. To integrate a switching device on the glass substrate, we designed a high-performance oxide thin-film transistor with a minimum channel length of 1  μm and a maximum processing temperature of 380°C. To drive a large number of data lines, we used multiple source drivers and data drivers as well. For an optical modulation, we optimized a liquid crystal of a high anisotropic refractive index of 0.25 with a cell gap of 2.5  μm, which was effectively operated until pixel pitch is 1.6  μm. Hologram was successfully reconstructed by fabricated SLM with 7-μm pixel pitch. For the other approach for a high-resolution spatial light modulator, we tested a phase change material of Ge2Sb2Te5 [GST]. The variation of refractive index between a polycrystalline phase and an amorphous phase of the GST film is used for a hologram reconstruction. By optimizing the underlying oxide thickness, we can show a color hologram without color filters.

InZnO/AlSnZnInO Bilayer Oxide Thin-Film Transistors With High Mobility and High Uniformity

In this letter, high-performance InZnO/AlSnZnInO (IZO/ATZIO) bilayer thin-film transistors (TFTs) with an inverted staggered back channel etch structure are presented. The channel width and the length were both 6 μm, which is small enough to be adapted to a high-resolution display backplane. High field-effect mobility (μFE) over 60 cm2/Vs was obtained from the structure with 8-nm IZO channel insertion between the gate dielectric and the ATZIO layer. The device shows good controllability in light of TFT operation. The subthreshold slope, turn-ON voltage (VON), and ON/OFF ratio were 0.16 V/decade, -1.52 V, and 5×109, respectively.

Rewritable full-color computer-generated holograms based on color-selective diffractive optical components including phase-change materials

We propose rewritable full-color computer-generated holograms (CGHs) based on color-selective diffraction using the diffractive optical component with the resonant characteristic. The structure includes an ultrathin layer of phase-change material Ge2Sb2Te5 (GST) on which a spatial binary pattern of amorphous and crystalline states can be recorded. The CGH patterns can be easily erased and rewritten by the pulsed ultraviolet laser writing technique owing to the thermally reconfigurable characteristic of GST. We experimentally demonstrate that the fabricated CGH, having a fine pixel pitch of 2 μm and a size of 32.8 × 32.8 mm2, reconstructs the three-dimensional holographic images. In addition, the feasibility of the rewritable property is verified by erasing and rewriting part of the CGH.