Search

Free-form factor optoelectronics is becoming more important for various applications. Specifically, flexible and transparent optoelectronics offers the potential to be adopted in wearable devices in displays, solar cells, or biomedical applications. However, current transparent electrodes are limited in conductivity and flexibility. This study aims to address these challenges and explore potential solutions. For the next-generation transparent conductive electrode, Al-doped zinc oxide (AZO) and silver (AZO/Ag/AZO) deposited by in-line magnetron sputtering without thermal treatment was investigated, and this transparent electrode was used as a transparent organic light-emitting diode (OLED) anode to maximize the transparency characteristics. The experiment and simulation involved adjusting the thickness of Ag and AZO and OLED structure to enhance the transmittance and device performance. The AZO/Ag/AZO with Ag of 12 nm and AZO of 32 nm thickness achieved the results of the highest figure of merit (FOM) (Φ550 = 4.65 mΩ−1) and lowest roughness. The full structure of transparent OLED (TrOLED) with AZO/Ag/AZO anode and Mg:Ag cathode reached 64.84% transmittance at 550 nm, and 300 cd/m2 at about 4 V. The results demonstrate the feasibility of adopting flexible substrates, such as PET, without the need for thermal treatment. This research provides valuable insights into the development of transparent and flexible electronic devices. [ABSTRACT FROM AUTHOR]

Bottom-gate thin-film transistors (TFTs) with n-type amorphous indium-gallium-zinc oxide (a-IGZO) active channels and indium-tin oxide (ITO) source/drain electrodes were fabricated. Then, an ultraviolet (UV) nanosecond pulsed laser with a wavelength of 355 nm was scanned to locally anneal the active channel at various laser powers. After laser annealing, negative shifts in the threshold voltages and enhanced on-currents were observed at laser powers ranging from 54 to 120 mW. The energy band gap and work function of a-IGZO extracted from the transmittance and ultraviolet photoelectron spectroscopy (UPS) measurement data confirm that different energy band structures for the ITO electrode/a-IGZO channel were established depending on the laser annealing conditions. Based on these observations, the electron injection mechanism from ITO electrodes to a-IGZO channels was analyzed. The results show that the selective laser annealing process can improve the electrical performance of the a-IGZO TFTs without any thermal damage to the substrate. [ABSTRACT FROM AUTHOR]

Transparent and flexible electronics are emerging technologies with the potential to enable new applications. However, to ensure high‐performance transparent electronics, post‐processing such as thermal annealing and vacuum plasma treatment is necessary, which are difficult to apply to polymer‐based flexible substrates. This study analyzed the feasibility of applying selective Ar plasma jet treatment at atmospheric pressure to transparent flexible electronics. When atmospheric Ar plasma treatment is applied to transparent flexible aluminum‐doped zinc oxide (AZO), it showed a maximum 83.1% improvement in sheet resistance while maintaining a high transmittance performance, of over 70%. To verify the mechanism behind the surface treatment effect using atmospheric Ar plasma, comprehensive analyses are performed using atomic force microscopy, X‐ray diffraction, and X‐ray photoelectron spectroscopy, which confirmed that the effect is due to oxygen vacancy formation caused by ion bombardment and thermal diffusion. The application of atmospheric plasma treatment to a patterned transparent flexible AZO device resulted in a reduction in contact resistance, and it is confirmed that the performance improvement effects can be retained for >500 h by applying additional passivation. [ABSTRACT FROM AUTHOR]

The vacuum process using small molecule-based organic materials to make organic photodiodes (OPDIs) will provide many promising features, such as well-defined molecular structure, large scalability, process repeatability, and good compatibility for CMOS integration, compared to the widely used Solution process. We present the performance of planar heterojunction OPDIs based on pentacene as the electron donor and C60 as the electron acceptor. In these devices, MoO3 and BCP interfacial layers were interlaced between the electrodes and the active layer as the electron- and hole-blocking layer, respectively. Typically, BCP played a good role in suppressing the dark current by two orders higher than that without that layer. These devices showed a significant dependence of the performance on the thickness of the pentacene. In particular, with the pentacene thickness of 25 nm, an external quantum efficiency at the 360 nm wavelength according to the peak absorption of C60 was enhanced by 1.5 times due to a cavity effect, compared to that of the non-cavity device. This work shows the importance of a vacuum processing approach based on small molecules for OPDIs, and the possibility of improving the performance via the optimization of the device architecture. [ABSTRACT FROM AUTHOR]

Oxygen vacancies are a major factor that controls the electrical characteristics of the amorphous indium-gallium-zinc oxide transistor (a-IGZO TFT). Oxygen vacancies are affected by the composition ratio of the a-IGZO target and the injected oxygen flow rate. In this study, we fabricated three types of a-IGZO TFTs with different oxygen flow rates and then investigated changes in electrical characteristics. Atomic force microscopy (AFM) was performed to analyze the surface morphology of the a-IGZO films according to the oxygen gas rate. Furthermore, X-ray photoelectron spectroscopy (XPS) analysis was performed to confirm changes in oxygen vacancies of a-IGZO films. The optimized a-IGZO TFT has enhanced electrical characteristics such as carrier mobility (μ) of 12.3 cm2/V·s, on/off ratio of 1.25 × 1010 A/A, subthreshold swing (S.S.) of 3.7 V/dec, and turn-on voltage (Vto) of −3 V. As a result, the optimized a-IGZO TFT has improved electrical characteristics with oxygen vacancies having the highest conductivity. [ABSTRACT FROM AUTHOR]

To obtain high transparecy conductive films (TCFs), graphene embedded indium tin oxide (ITO) TCFs (ITO-graphene-ITO) were formed (I-G-I), using ITO sputtering, and the exfoliation/transfer process of chemical vapor deposition (CVD) grown graphene. Compared with ITO-graphene (I-G), I-G-I TCFs showed degradation in transmittance, and in figure of merits(FOM) despite enhanced conductivity. After annealing, both transmittance and conductivity improved; however, were not dependent on the embedded graphene multilayers in the I-G-I structure. From the Raman spectra results, it was possible to investigate degradation of the graphene layers' 2D structures, caused by sputtering damage which occurred during the deposition of ITO onto the I-G structure. [ABSTRACT FROM AUTHOR]

For the direct formation of two-dimensional (2D) tungsten disulfide (WS2) thin films with higher productivity and lower process temperature than conventional chemical vapor deposition (CVD), WS2 thin films were deposited on a sapphire glass substrate by direct current (DC) sputtering and subsequent rapid thermal processing (RTP). From the optical investigation by atomic force microscopy (AFM), it was possible to stable surface and observe more improvements at higher RTP temperatures irrespective of sputtering power. Hall measurements showed higher resistivity and lower carrier density at higher DC sputtering power in spite of the constant carrier mobility. Raman spectrum results showed lateral vibration of tungsten and sulfur atoms at temperatures above 700 °C. The directly formed WS2 thin films showed the improvements in structural and electrical characteristics as a semiconductor layer. [ABSTRACT FROM AUTHOR]

For the realization of high conductive and transparent electrodes on flexible substrates, indium tin oxide(ITO), Ag, and ITO were sequentially deposited on polyethylene terephthalate(PET) and a Q-switched Nd:YVO4laser was used for direct etching of the ITO–Ag-ITO films. Considering the complementary relationship between transmittance and conductivity, Ag was deposited for different sputtering times and the laser etched results were also compared and analyzed. Considering the laser etched shape, the ITO–Ag-ITO electrodes were patterned with the optimized laser beam condition. From the current-voltage characteristics and multi-meter measurement, much lower resistances were obtained from electrically isolated ITO-Ag-ITO electrode. [ABSTRACT FROM PUBLISHER]

Nb2O5films were deposited with pulsed DC magnetron sputter which is versatile and provides the ability to deposit thin film of oxide compounds with high deposition rate. Current measurement data from the metal-insulator-semiconductor (MIS) structure followed Schottky emission mechanism andreverse current characteristics were analyzed with oxygen flow rate variation. Low frequency noise measurements have been carried out with MIS samples at the forward conduction region. The experimental noise data have been successfully explained by the random walk model. The effect of O2flow rate of deposition process on low frequency noise has also been investigated and analyzed. [ABSTRACT FROM AUTHOR]

Indium tin oxide (ITO) films were deposited on glass substrates by in-line DC sputtering and were annealed at different temperatures in the main chamber of sputter. The post-annealing effects on the optical and electrical properties of the ITO films were investigated and analyzed by various measurement systems. The results show that a higher annealing temperature makes an improvement on the electro-optical properties of the ITO films. The resistivity of the ITO films was reduced from 8.90×10−4Ω·cm to 2.91×10−4Ω·cm and the transmittance was increased from about 76.91% to 82.15% after post annealing at 300 °C in vacuum. The post annealed ITO glass was used in the fabrication of resistive touch panel and it was possible to obtain the better linearity characteristics than those from the touch panel fabricated with non-annealed ITO glass. [ABSTRACT FROM AUTHOR]

Highlights: [•] Al-doped zinc oxide (AZO) film is deposited using the in-line pulsed-DC sputter. [•] Oxygen concentration is varied to optimize AZO films for Cu(In,Ga)Se2 solar cells. [•] The electrical, optical, and structure properties of AZO films are analyzed. [•] The optimized AZO film is obtained when it is deposited under pure Ar ambient. [ABSTRACT FROM AUTHOR]

We fabricated and investigated soluble, organic, thin-film transistors (OTFTs) containing ‘[6, 6]-phenyl-C61-butyric acid methyl ester (PCBM)’ as a semiconducting layer, and an organic dielectric buffer (cross-linked poly-4-vinylphenol) as a dielectric buffer-layer to improve electrical characteristics. The semiconducting layer of the devices was fabricated by the drop-casting method where PCBM was dissolved in three different solvents (odichlorobenzene, chloroform, and chlorobenzene). From the transfer and output characteristics of the PCBM OTFTs, a threshold voltage of 10 V, sub-threshold slope of 10 V/dec, on/off current ratio of 7.305 × 10 3, and field-effect mobility of 1.53 × 10 −2 cm 2/Vs were obtained; for PCBM using o-dichlorobenzene solvent and an organic dielectric buffer layer. It was also found that the hysteresis for the same device was improved conspicuously compared to the other devices, by the above-mentioned condition. [ABSTRACT FROM AUTHOR]

In this work, we present the results concerning the use of amorphous indium- gallium-zinc-oxide (a-IGZO) thin-film transistor (TFT) as a driving transistor of the flexible thermal and pressure sensors which are applicable to artificial skin systems. Although the a-IGZO TFT has been attracting much attention as a driving transistor of the next-generation flat panel displays, no study has been performed about the application of this new device to the driving transistor of the flexible sensors yet. The proposed thermal sensor pixel is composed of the series-connected a-IGZO TFT and ZnO-based thermistor fabricated on a polished metal foil, and the ZnO-based thermistor is replaced by the pressure sensitive rubber in the pressure sensor pixel. In both sensor pixels, the a-IGZO TFT acts as the driving transistor and the temperature/pressure-dependent resistance of the ZnO-based thermistor/pressure-sensitive rubber mainly determines the magnitude of the output currents. The fabricated a-IGZO TFT-driven flexible thermal sensor shows around a seven times increase in the output current as the temperature increases from 20 ?C to 100 ?C, and the a-IGZO TFT-driven flexible pressure sensors also exhibit high sensitivity under various pressure environments. [ABSTRACT FROM AUTHOR]

In order to reduce the extent of hydroxide and carbonate formation on (Mg, Ca)O protective layer during sealing step, panels were sealed while Ar-5H2 gas was flown between front and rear plates assembled. The gas was supplied up to a temperature below sealing took place. This processing scheme lowered firing and sustaining voltages of the panels significantly, demonstrating a practical way to seal the panel. [ABSTRACT FROM AUTHOR]

In the fabrication of zinc oxide thin film transistor(ZnO TFT), aluminum oxide(Al2O3) was deposited as gate insulator by using an oxygen atom neutral beam assisted deposition(NBAD) during e-beam evaporation. From the thickness of the Al2O3 layer evaporated with the oxygen NBAD process and the C-f measurement of metal-insulator-metal(MIM) capacitors fabricated with the NBAD Al2O3 layer, it was possible to conclude that the NBAD Al2O3 layer has a higher thickness and a higher dielectric constant at an acceleration beam energy of 300 eV as a result of the additional deposition of oxygen atoms during e-beam evaporation. The fabricated ZnO TFT with the NBAD Al2O3 gate insulator showed better electrical characteristics, such as a lower subthreshold swing and a higher on-off ratio, than those without any NBAD process. [ABSTRACT FROM PUBLISHER]

In this paper we have studied a low-temperature process of fabricating zinc oxide (ZnO) thin-film transistors (TFTs) on polyethylene terephthlate (PET) substrate. PET film has a lower glass transition temperature (Tg = 120°C) than costly Polyethersulphone (PES) film (Tg = 230°C). Therefore we applied a low-temperature cross-linked poly-vinylphenol (c-PVP) process to annealing at 110°C instead of the conventional c-PVP process (annealing at 165°C). The resulting TFTs based on oxide fabricated by the low-temperature process were similar in electrical characteristics to conventional TFTs. In addition, the ZnO TFTs fabricated by the low-temperature process exhibited a field-effect mobility of 0.075 cm2/Vs, a threshold voltage of 15 V and an on/off ratio of 1.7 × 105 respectively. [ABSTRACT FROM PUBLISHER]

A cold cathode fluorescent lamp (CCFL) and various color spectrum filters were used in the investigation of photoelectric characteristics of hydrogenated amorphous silicon thin film transistor(a-Si:H TFT). From the photo leakage currents of a-Si:H TFT for the transmitted backlights through the various color spectrum filters, it was possible to conclude the photo leakage currents are not directly related to the luminance of the transmitted backlights. The photoelectric characteristics were well described in terms of photon energy spectrums calculated from the photon energy and the energy transmittance of backlight through the color spectrum filters. [ABSTRACT FROM AUTHOR]

In the fabrication of transparent conductive oxide thin film transistor (TFT), an atomic layer deposited (ALD) zinc oxide (ZnO) and a cross-linked poly-vinyl-alcohol (c-PVA) were each used as active layer and gate insulating layer on poly-ethylene (PET) substrate respectively. Considering the transmittance and the deposition rate of the ALD ZnO at a low temperature without any damage on PET substrate, the ZnO layer was deposited at a temperature of 120°C on a spin-coated c-PVA layer. From the atomic force microscope (AFM) images, it was possible to conclude that the surface morphologies of ZnO deposited on a c-PVA layer was not inferior to those of ZnO deposited on bare-Si and that the c-PVA can be used as a gate insulator at 120°C. The fabricated ZnO TFT showed good electrical characteristics such as the mobility of 0.1 cm2/V · s, on-off current ratio of 4.5 × 104. [ABSTRACT FROM AUTHOR]

Abstract: Field emission properties of silicon field emitter arrays (Si-FEAs) with sputtered gate structures were described and analyzed about two different tip structures surrounded by volcano-shaped gates. The resulted field emission characteristics showed that some of the emitted electrons are diverted to the gate structure because of the asymmetrical geometry of fabricated Si-FEAs with volcano-shaped gate structures. However, although the gate structures of fabricated FEAs had fragile and non-uniform edged shapes as a result of the shadow effect during sputtering and lift-off process in ultrasonic bath, it was possible to obtain stable field emission properties as a result of electrical aging effects on the edge of the non-uniform gate electrode as well as the surface of silicon tip after repeated measurements. From the Fowler–Nordheim (F–N) plots and F–N equations, it was confirmed that the field enhancement factor was abruptly changed through the electrical aging and was more influenced in case of the volcano-shaped lateral tip structure. [Copyright &y& Elsevier]