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Roles of oxygen interstitial defects located in the In-Ga-Zn-O (IGZO) thin films prepared by atomic layer deposition were investigated with controlling the cationic compositions and gate-stack process conditions. It was found from the spectroscopic ellipsometry analysis that the excess oxygens increased with increasing the In contents within the IGZO channels. While the device using the IGZO channel with an In/Ga ratio of 0.2 did not show marked differences with the variations in the oxidant types during the gate-stack formation, the device characteristics were severely deteriorated with increasing the In/Ga ratio to 1.4, when the Al

Device scaling of oxide-channel thin-film transistors (TFTs) toward sub-micrometer regime has been an urgent issue to realize higher-resolution displays and 3-D structured electronic devices. The channel-shortening effect is a serious problem in implementing the oxide TFTs with short channel lengths. In this work, the short-channel effects (SCEs) of the In-Ga-Zn-O (IGZO) TFTs were investigated with the variations in channel composition when the channel length was varied from 3 μm to 500 nm. Effective channel lengths were examined to decrease with increasing the In contents, in which the reduction of the effective channel length was estimated to be 240 and 720 nm when the In/Ga ratio increased 0.7 to 1.4. The drain bias-dependent roll-offs in turn-on voltages, which typically correspond to drain-induced barrier-lowering (DIBL), also showed significant channel composition dependence. When the In/Ga ratio within the channel increased from 0.2 to 1.4, the DIBL coefficients were estimated from 22 to 244 mV/V for the devices with a channel length of 1 μm. The channel composition-dependent variations in the effective channel length were suggested to result from the inter-diffusion and redox reactions at interfaces between the channel and electrode layers. Alternatively, the contact resistances were also examined to play major roles in determining the SCEs with scaling the devices, especially when the In contents decreased in the channel composition. Thus, properly controlling the channel composition can be concluded as such an important issue for compromising both technical strategies to reduce the channel resistance and to suppress the reduction of effective channel length.

Stretchable electronics have become essential for custom-built electronics, self-assembling robotics, and wearable devices. Although many stretchable electronics contain integrated systems, they still limit bulky connection systems. We introduce a new dual-functioned self-attachable and stretchable interface (SASI), allowing a direct and instant interconnection between rigid and soft electronics. The SASI consists of a sticky and stretchable substrate and surface-embedded serpentine conductors with the single-sided polyimide fabricated using the embedded transfer process. The adhesion property of the SASI is controlled by the mixed elastomer ratio. The resulting sticky and conductive SASI can instantly adhere to a metal surface and create conductive paths. The SASI serpentine conductors exhibit high stretchability (∼290%) and provide self-attachable, re-attachable, and low-resistant electrical contacts (0.85 ohms in 0.25 mm

Thin-film transistor (TFT)-driven full-color organic light-emitting diodes (OLEDs) with vertically stacked structures are developed herein using photolithography processes, which allow for high-resolution displays of over 2,000 pixels per inch. Vertical stacking of OLEDs by the photolithography process is technically challenging, as OLEDs are vulnerable to moisture, oxygen, solutions for photolithography processes, and temperatures over 100 °C. In this study, we develop a low-temperature processed Al2O3/SiNx bilayered protection layer, which stably protects the OLEDs from photolithography process solutions, as well as from moisture and oxygen. As a result, transparent intermediate electrodes are patterned on top of the OLED elements without degrading the OLED, thereby enabling to fabricate the vertically stacked OLED. The aperture ratio of the full-color-driven OLED pixel is approximately twice as large as conventional sub-pixel structures, due to geometric advantage, despite the TFT integration. To the best of our knowledge, we first demonstrate the TFT-driven vertically stacked full-color OLED., To realize organic light-emitting diodes (OLEDs) with improved resolution for display applications, a method for achieving high yield device fabrication is needed. Here, the authors report vertically-stacked transistor-driven full-color OLEDs with photolithography-processed intermediate electrodes.

Vertical channel thin film transistors (VTFTs) have been expected to be exploited as one of the promising three-dimensional devices demanding a higher integration density owing to their structural advantages such as small device footprints. However, the VTFTs have suffered from the back-channel effects induced by the pattering process of vertical sidewalls, which critically deteriorate the device reliability. Therefore, to reduce the detrimental back-channel effects has been one of the most urgent issues for enhancing the device performance of VTFTs. Here we show a novel strategy to introduce an In–Ga–Zn–O (IGZO) bilayer channel configuration, which was prepared by atomic-layer deposition (ALD), in terms of structural and electrical passivation against the back-channel effects. Two-dimensional electron gas was effectively employed for improving the operational reliability of the VTFTs by inducing strong confinement of conduction electrons at heterojunction interfaces. The IGZO bilayer channel structure was composed of 3 nm-thick In-rich prompt (In/Ga = 4.1) and 12 nm-thick prime (In/Ga = 0.7) layers. The VTFTs using bilayer IGZO channel showed high on/off ratio (4.8 × 109), low SS value (180 mV dec−1), and high current drivability (13.6 μA μm−1). Interestingly, the strategic employment of bilayer channel configurations has secured excellent device operational stability representing the immunity against the bias-dependent hysteretic drain current and the threshold voltage instability of the fabricated VTFTs. Moreover, the threshold voltage shifts of the VTFTs could be suppressed from +5.3 to +2.6 V under a gate bias stress of +3 MV cm−1 for 104 s at 60 °C, when the single layer channel was replaced with the bilayer channel. As a result, ALD IGZO bilayer configuration could be suggested as a useful strategy to improve the device characteristics and operational reliability of VTFTs.

From the very first time that graphene was used as a transparent electrode for OLED applications, the emergence of active-matrix (AM)-graphene OLED displays has been envisioned. Realizing this expectation, however, turned out to be difficult. Two obstacles are the growth and transfer of a large-area graphene film and the patterning of a graphene film into pixels. To solve these problems, a process of patterning a graphene film without surface contamination was developed. The fabrication of OLED panels by the patterned graphene anode on Gen 2(370 × 470 mm)-sized and flexible substrates was successfully demonstrated. In this work, oxide TFT arrays were combined as a switching backplane, and a pixelated graphene OLED was used as an emissive layer, to realize AM-graphene OLED displays. To explore the technical feasibility of flexible AM-graphene OLED displays, the aforementioned components were formed on a flexible substrate. For commercial-level production, all the processes that were used were chosen to be compatible with the conventional display processes.

Since the late 20th century, there has been rapid development in the display industry. Only 30 years ago, we used big cathode ray tube displays with poor resolution, but now most people use televisions or smartphones with very high‐quality displays. People now want images that are more realistic, beyond the two‐dimensional images that exist on the flat screen, and digital holography—one of the next‐generation displays—is expected to meet that need. The most important parameter that determines the performance of a digital hologram is the pixel pitch. The smaller the pixel pitch, the higher the level of hologram implementation possible. In this study, we fabricated the world‐smallest 3‐μm‐pixel‐pitch holographic backplane based on the spatial light modulator technology. This panel could display images with a viewing angle of more than 10°. Furthermore, a comparative study was conducted on the fabrication processes and the corresponding holographic results from the large to the small pixel‐pitch panels.

We developed a high definition holographic display with two different approaches. First approach is to adjust a wellknown display technology using a liquid crystal as an optical modulator. While merit of display technology is a large panel size, the challenge is to define a small pixel pitch and to reduce a crosstalk effect of a liquid crystal. Second approach is to adapt a silicon technology with a new optical modulator, Ge2Sb2Te5. Although we can easily define a small pixel pitch, we have to confront a small panel size. We will explain our solutions to overcome these issues.

Rubrene-based electrochemiluminescence (r-ECL) cells with two different solvent systems is prepared, one in a co-solvent system with a mixture of 1,2-dichlorobenzene and propylene carbonate (DCB : PC, v/v 3 : 1) and another in a single solvent system of tetrahydrofuran (THF), as the medium to form a liquid-electrolyte (L-El). By simply changing the solvent systems, from the co-solvent DCB : PC (v/v 3 : 1) to the single solvent THF, with the same amount of electrochemiluminescent rubrene (5 mM) and Li-based salt, a dramatically enhanced brightness of over 30 cd m−2 is observed for the r-ECL cell in L-ElTHF which is approximately 7-times higher than the brightness of 5 cd m−2 observed for the r-ECL in L-ElDCB:PC(v/v 3:1).

Holographic display is known as the most realistic 3D display by creating real 3D image in front of observer. But there are tremendous technical hurdles in realizing electronic hologram. It is required to achieve very small pixel pitch SLM (spatial light modulator) for realizing electronic hologram using flat panel display. All the components of the unit pixel should be carefully redesigned and improved to maintaining same performance in spite of reduction of pixel pitch. The size of hologram image depends on the size of SLM. Therefore, the resolution of the SLM increases very fast as the reduction of pixel pitch in SLM. The driver chip and architecture should be developed to manage the large number of pixels with high speed. Novel unit pixel design for achieving 1μm pixel pitch will be presented. VST (vertically stacked transistor) structure will be introduced. In VST structure, the driving TFT is stacked on the data line. VST structure has the merits for reducing horizontal pixel pitch without introducing expensive high-definition lithography tool. The technology compatible with 0.5μm critical dimension can be used for fabrication of 1μm pixel pitch SLM. Alternative structure for achieving small pitch pixel is the adopting VTFT (vertical channel thin film transistor). VTFT means that the channel direction is vertical to SLM plane. The footprint of VTFT is very small, for required area is only the overlap region of active layer and source/drain layer. Cross-talk between adjacent pixels can interfere the rotation of LC molecule. This phenomenon will be very critical for accurate phase modulation for 1μm pixel pitch SLM. Novel concept for reducing cross-talk will be also presented with experimental results.

The ability to image pressure distribution over complex three-dimensional surfaces would significantly augment the potential applications of electronic skin. However, existing methods show poor spatial and temporal fidelity due to their limited pixel density, low sensitivity, or low conformability. Here, we report an ultraflexible and transparent electroluminescent skin that autonomously displays super-resolution images of pressure distribution in real time. The device comprises a transparent pressure-sensing film with a solution-processable cellulose/nanowire nanohybrid network featuring ultrahigh sensor sensitivity (>5000 kPa−1) and a fast response time (1000 dpi) pressure imaging without the need for pixel structures. Our approach provides a new framework for visualizing accurate stimulus distribution with potential applications in skin prosthesis, robotics, and advanced human-machine interfaces., Electronic skin that spatially maps pressure distribution through imaging shows limited performance despite improvements to data acquisition. Here, the authors report ultraflexible, transparent electroluminescent skin capable of high-resolution imaging of pressure distribution over 3D surfaces.

A phase modulation device was proposed for the implementation of hologram image for display applications. A Ge2Sb2Te5 (GST) film as thin as 7 nm was prepared between the ITO films to form the cavities corresponding a unit pixel. Nitrogen was incorporated into the GST for improving the thermal stability of the GST active region. The effects of the nitrogen doping on the physical properties of GST was investigated with the variations in doping amounts. The nitrogen incorporation was found to reduce the surface micro-roughness and to improve the thermal stability of the GST even after the crystallization by effectively suppressing the excessive grain growth. As results, the number of repeatable operations for the fabricated phase modulation device was evidently improved from 10 to 69 cycles when a 2.7-at% nitrogen was doped into the GST.

A new structure for a switchable mirror device based on reversible electrodeposition is proposed. This device does not contain Cu ions in the electrolyte and adapts a counter electrode. The feasibility of the device was evaluated with a WO3 film, which is a well-known electrochromic material, as a counter electrode. Even in the absence of Cu ions, the WO3 film facilitates a clean erase feature in the device. Furthermore, using a pre-deposited Ag film as a working electrode, Ag deposition can be driven at a substantially lower voltage than that in conventional devices. Moreover the deposition current decreases with the progress of Ag deposition, and stops after completion of the deposition process. The results clearly indicate that the tri-bromine ion, which makes the self-erasing circulation, is not generated during Ag deposition process. The new switchable mirror shows excellent bistability and size scale-up is possible because it does not consume continuous current in the mirror state. By appling the proposed technology, a switchable mirror device with a 7 cm × 9 cm active area was successfully fabricated.

Light-adaptable (LA) displays combining the advantages of reflective and emissive displays, are considered as the future of display technology. Electrochromic devices are potentially strong candidates for reflective-mode LA displays because of their high transmittance in the transparent state and low power consumption. However, the narrow viewing angle of these displays in relation to a hybrid structure of the LA display, is a technical barrier that must be overcome for the successful application of electrochromic devices to light-adaptable displays. In the present study, an electrochromic device with a self-diffusing function was developed for application to light-adaptable displays. Si3N4 scattering particles were incorporated in the TiO2 nanostructure-based electrochromic device. Efficient forward diffuse scatterings were obtained without deteriorating the total transmittance of the device. The contrast ratio and color gamut of the electrochromic device were dramatically improved because of the addition of the scattering particles.

We present high-mobility back channel etch Al–In–Zn–Sn–O/In–Zn–O (IZO) double-layer channel thin-film transistors (TFTs). The field-effect mobility of 53.2 $\text{cm}^{2}/\text{V} \cdot \text{s}$ , threshold voltage of 0.5 V, and subthreshold swing of 0.15 V/decade were obtained with a thin IZO-inserted double-layer channel TFT. The positive bias stability was improved with an IZO-inserted double-layer channel. We fabricated 13-stage ring oscillators, which exhibited an oscillating frequency of 296 kHz at ${V} _{\text {DD}} = {20}$ . These results demonstrate that the proposed double-layer channel oxide TFT can be used for demanding applications such as backplane devices for ultrahigh resolution display.

Holographic projection displays provide high diffraction efficiency. However, they have a limited projection angle. This work proposes a holographic projection display with a wide angle, which gives an image of size 306 m m × 161 m m at 700 mm and reduced speckle noise. The solution uses single Fourier lens imaging with a frequency filter and hologram generation utilizing complex coding and nonparaxial diffraction. The experiment was performed with a 4K phase-only spatial light modulator (SLM) to prove the high efficiency of the developed numerical tools. Optical reconstruction shows high resolution and high image quality achieved from a single frame. Hence, displaying video at a full frame rate of the SLM is possible.

We fabricated high performance 2-µm-channel oxide thin-film transistors (TFT) on glass substrate for 7-μm-pixel-pitch spatial light modulator (SLM) panel for digital holographic applications. Furthermore, we succeeded in the demonstration of the sub-micron TFTs, which is an inevitable route to the next-generation spatial light modulation devices with near 1-μm pixel pitch.

We investigated the effect of back channel material which plays as a channel defining layer in vertical TFT for the application to the TFT of ultra-high resolution display. Although the IGZO vertical TFT with polyimide back channel has low mobility, it shows good on/off ratio higher than 107 , low gate leakage current, and hard saturation behavior with channel length of 1 um.

The mechanism of formation of metal–oxide–metal (M–O–M) bonds in solution-processed metal oxide semiconductors can vary depending on the types of precursors used. To date, metal-alkoxides or metal-chloride precursors have mainly been studied; therefore, efforts to improve the device characteristics of oxide thin-film transistors (TFTs) have been limited to these types of precursors. On the other hand, systematic studies to optimize the experimental conditions (e.g. thickness and annealing atmosphere) of oxide TFTs made by using new types of precursors have rarely been reported. In this study, we successfully demonstrate high-performance solution-processed Zn–Sn–O TFTs by using a metal-carboxylate precursor, tin(II) 2-ethylhexanoate, and optimizing the oxide thickness and thermal annealing conditions. To determine the optimum thickness of Zn–Sn–O, we prepared 3 types of active layers with different thickness combinations of ZnO and SnO2. In addition, we found that oxygen gas in the annealing process maximizes the formation of M–O–M bonds and decreases the number of trap sites in the thickness-optimized active layer, leading to dramatically enhanced device performances. As a result, the optimized Zn–Sn–O TFTs based on tin(II) 2-ethylhexanoate exhibit excellent mobility exceeding 22 cm2 V−1 s−1, which is an order of magnitude higher than that of the previously reported Zn–Sn–O TFTs based on the same precursor and very comparable to the mobility levels obtained from conventional solution-processed metal-oxide TFTs. We believe that our approach will enrich the current family of tin precursors and provide another option for resource-friendly, low-cost, and high performance Zn–Sn–O semiconductors.

As potential lighting-emitting devices, electrochemiluminescence (ECL) devices are promising in terms of device structure and fabrication and involve low processing cost compared to organic light-emitting devices (OLEDs). Herein, liquid electrolyte-based multi-colored ECL devices (ECLDs) were prepared with organic materials dissolved in electrolyte solution, which generated red, yellow, green, and blue emissions under an applied square-wave AC bias voltage. Among the four different emissive colors, yellow showed a strong and stable emission, which enabled quantitative measurements, including a luminance of 12 cd m−2 at 4.5 V.