We report the enhancement of the electroluminescent property of top emitting organic light emitting diodes ͑TEOLEDs͒ using thermally evaporated copper oxide ͑CuO x ͒ as a hole injection layer ͑HIL͒ between UV ozone-treated silver ͑Ag͒ anodes and 4,4Ј-bis͓N-͑1-naphthyl͒-N-phenylamino͔biphenyl ͑␣-NPD͒. The operation voltage of TEOLEDs at 1 mA/cm 2 decreased from 6.2 to 5.0 V as a 2 nm thick CuO x layer was used as the HIL. ␣-NPD layers were separately in situ deposited on both Ag and thermally evaporated CuO x -coated Ag ͑Ag/CuO x ͒ and their interface dipole energies were quantitatively determined using synchrotron radiation photoemission spectroscopy. Secondary electron emission spectra revealed that the work function of Ag/CuO x is higher by 0.53 eV than that of Ag. The corresponding interface dipole energies were −0.93 eV for Ag and −0.88 eV for Ag/CuO x . As a result, CuO x plays a role in reducing the hole injection barrier from 1.63 to 0.96 eV, resulting in a decrease in the turn-on voltage of TEOLEDs.
Integrating circuits into organic light emitting diode displays require fabrication of polycrystalline silicon (poly-Si) based thin-film transistors (TFTs) on glass substrates. In this work we evaluated the use of high pressure annealing (HPA) process of poly-Si films in H2O atmosphere to improve TFT characteristics via reducing defect density in poly-Si films. We attempted to develop a HPA process at temperatures below 600°C without causing any glass distortion and reducing the throughput. The HPA-treated poly-Si film was analyzed using various spectroscopic methods such as Raman, x-ray photoelectron spectroscopy, and transmission electron microscope, and the evaluation of the characteristics of TFTs fabricated by such poly-Si films was made. The heating at 550°C with 1MPa H2O vapor increased the carrier mobility from 8.5to20cm2∕Vs and reduced the absolute value of the threshold voltage from 9.6to6.5V, as compared with the conventional solid phase crystallization (SPC) process. The sub-threshold swings also decreased from 1.2to0.8V/decade. Since the realization of good performance in poly-Si depends on the defect density, the poly-Si formed by a combined process of SPC and HPA may be well suited for fabrication of poly-Si TFTs for flat panel displays such as liquid crystal display and active matrix organic light emitting diode that require circuit integration on panels.
We replace Indium Tin Oxide (ITO) with an MgO nano-facet Embedded WO(3)/Ag/WO(3)(WAW) multilayer for electrodes of high efficiency OLEDs. WAW shows higher values for transmittance (93%) and conductivity (1.3×10(5) S/cm) than those of ITO. Moreover, WAW shows higher transmittance (92.5%) than that of ITO (86.4%) in the blue region (<500 nm). However, due to the large difference in refractive indices (n) of glass (n=1.55) and WO(3) (n=1.95), the incident light has a small critical angle (52°). Thus, the generated light is confined by the glass/WAW interface, resulting in low light outcoupling efficiency (~20%). This can be enhanced by using a nano-facet structured MgO (n=1.73) layer and a ZrO(2) (n=1.84) layer as a graded index layer. Using these optimized electrodes, ITO-free, OLEDs with various emission wavelengths have been produced. The luminance of OLEDs using MgO/ZrO(2)/WAW layers is enhanced by 24% compared to that of devices with ITO.
The growth and delamination mechanism of cubic boron nitride (c-BN) film on silicon substrate was investigated with Fourier transform infrared (FTIR) spectroscopy and transmission electron microscopy (TEM). c-BN films were prepared by the helicon wave plasma chemical vapor deposition process on (100) Si. The film deposited under the intense impact of energetic ions is usually delaminated from the substrate after deposition. It is found that moisture in the air, as well as severe compressive stress in the film, contribute to film delamination. From FTIR and TEM characterization, a model for the delamination mechanism of c-BN film is suggested. Based on the delamination mechanism, several kinds of remedies such as post-annealing and post-N2 plasma treatment were carried out to improve the adhesion. The effects of these respective remedies on the adhesion of c-BN film are also discussed.
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