Effects of Thermal Treatment on DC Voltage-Driven Color Conversion in Organic Light-Emitting Diode.

A DC voltage-dependent color-tunable organic light-emitting diode (CTOLED) was proposed for lighting applications. The CTOLED consists of six consecutive organic layers: the hole injection layer, the hole transport layer (HTL), two emission layers (EMLs), a hole blocking layer (HBL), and an electron transport layer (ETL). Only one metal-free phthalocyanine (H2Pc) layer with a thickness of 5 nm was employed as the EML in the CTOLED on a green organic light-emitting diode (OLED) structure using tris (8-hydroxyquinoline) aluminum (III) (Alq3). The current density-voltage-luminance characteristics of the CTOLEDs before and after thermal treatment were characterized and analyzed. Several Gaussian peaks were also extracted by multipeak fitting analysis of the electroluminescent spectra. In the CTOLED before thermal treatment, green emission was dominant in the entire voltage range from low to high voltages, and blue and infrared were emitted simultaneously and at relatively low intensities at low and high voltages, respectively. In the CTOLED after thermal treatment, the dominant color conversion from blue to green was observed as the applied voltage increased, and the infrared emission was relatively low over the entire voltage range. By simulating the CTOLED with and without traps at the H2Pc interface using a technology computer-aided design simulator, we observed the following: 1. After thermal treatment, the CTOLED emitted blue light by exciton generation at the H2Pc-HBL interface because of the small electron transport through the H2Pc thin film due to the dramatic reduction of traps in the low-voltage regime. 2. In the high-voltage regime, electrons reaching the HBL were transferred to Alq3 by resonant tunneling in two quantum wells; thus, green light was emitted by exciton generation at the HTL-Alq3 interface.

Electrical Coupling and Simulation of Monolithic 3D Logic Circuits and Static Random Access Memory.

In order to simulate a circuit by applying various logic circuits and full chip using the HSPICE model, which can consider electrical coupling proposed in the previous research, it is investigated whether additional electrical coupling other than electrical coupling by top and bottom layer exists. Additional electrical coupling were verified through device simulation and confirmed to be blocked by heavily doped source/drain. Comparing the HSPICE circuit simulation results using the newly proposed monolithic 3D NAND (M3DNAND) structure in the technology computer-aided design (TCAD) mixed-mode and monolithic 3D inverter (M3DINV) unit cell model was once more verified. It is possible to simulate various logic circuits using the previously proposed M3DINV unit cell model. We simulated the operation and performances of M3DNAND, M3DNOR, 2 × 1 multiplexer (MUX), D flip-flop (D-FF), and static random access memry (SRAM).

Highly Conductive PEDOT:PSS Films with 1,3-Dimethyl-2-Imidazolidinone as Transparent Electrodes for Organic Light-Emitting Diodes.

Highly conductive poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) ( PEDOT: PSS) films as transparent electrodes for organic light-emitting diodes (OLEDs) are doped with a new solvent 1,3-dimethyl-2-imidazolidinone (DMI) and are optimized using solvent post-treatment. The DMI doped PEDOT: PSS films show significantly enhanced conductivities up to 812.1 S cm(-1) . The sheet resistance of the PEDOT: PSS films doped with DMI is further reduced by various solvent post-treatment. The effect of solvent post-treatment on DMI doped PEDOT: PSS films is investigated and is shown to reduce insulating PSS in the conductive films. The solvent posttreated PEDOT: PSS films are successfully employed as transparent electrodes in white OLEDs. It is shown that the efficiency of OLEDs with the optimized DMI doped PEDOT: PSS films is higher than that of reference OLEDs doped with a conventional solvent (ethylene glycol). The results present that the optimized PEDOT: PSS films with the new solvent of DMI can be a promising transparent electrode for low-cost, efficient ITO-free white OLEDs.

Fabrication Characterization of 1Ce10ScSZ Electrolyte Prepared by Co-Precipitation and Hydrothermal Treatment for Solid Oxide Fuel Cells.

Nanocrystallite ceria-doped scandia-stabilized zirconia (1Ce10ScSZ) powders are prepared using a combination of co-precipitation and hydrothermal treatments. Power density of 1.0 W cm(-2) is obtained at 1.6 A cm(-2) and 800 °C due to the drastic reduction of ohmic and polarization resistance in the SOFC cell.

Growth Behavior of High Density Al2O3 Layer Prepared by Using Cyclic Chemical Vapor Deposition Technology.

In this paper, growth behavior of high density Al2O3 which was prepared by using cyclic chemical vapor deposition (C-CVD) system has been systematically investigated. Tri-Methyl-Aluminum (TMA) and oxygen (02) plasma was used as source precursor and reactant, respectively. Unlike the conventional ALD system that source precursor and reactant was injected alternatively that was separated by inert gas purge step, TMA and 02 was mixed and co-fed into the process chamber simultaneously, followed by purge step. To obtain high density and defects-free Al2O3 layer, source precursor feeding time and the number of deposition cycles dependence on the thickness of C-CVD grown Al2O3 layer were investigated. We found that thickness of Al2O3 layer was increased almost linearly as the number of cycles increased which are typical characteristics of CVD. On the other hand, self-limiting phenomenon was observed in thickness as source feeding time increased which showed saturation of the thickness as source feeding time further increased. Using the optimized C-CVD process conditions, density of 3.298 g/cm3 was obtained in 100 nm thick Al2O3 layer whereas that of ALD Al2O3 was 3.192 g/cm3. The C-CVD grown Al2O3 layer effectively prevents water vapor from diffusing into active layer of organic light emitting diodes, which shows C-CVD grown Al2O3 layer can be applied to water vapor permeation barrier layer in organic light emitting diodes.

Fabrication Characteristics of Silicon Nanowires via the Electrochemical Electroless Etching Method.

A silicon nanowire structure was fabricated using the electrochemical electroless etching method, involving electroless plating and the electrochemical etching process. The reflection of the absorption layer with the nanowires' structure was about 5%, which is better than a bulk-type solar cell (10%).

Suppression of Cross Contamination in Multi-Layer Thin Film Prepared by Using Rotating Hexagonal Sputtering Cathode.

In this study, single- and multi-layered thin films were prepared on a glass substrate using a newly developed rotating hexagonal sputtering cathode in a single chamber. The rotatinghexagonal sputtering cathode can install up to six different sputtering targets or six single targets in a cathode. Using the rotating hexagonal cathode, we prepared a single-layered AZO film and a multi-layer film to evaluate the performance of hexagonal gun. Cross-contamination, which is often observed in multi-layer thin film preparation, was suppressed to nearly zero by controlling process parameters and revising hardware. Energy-saving effects of five-layered glass were also verified by measuring the temperature.

Optical Properties of Hybrid Inorganic/Organic Thin Film Encapsulation Layers for Flexible Top-Emission Organic Light-Emitting Diodes.

Inorganic/organic hybrid thin film encapsulation layers consist of a thin Al2O3 layer together with polymer material. We have investigated optical properties of thin film encapsulation layers for top-emission flexible organic light-emitting diodes. The transmittance of hybrid thin film encapsulation layers and the electroluminescent spectrum of organic light-emitting diodes that were passivated by hybrid organic/inorganic thin film encapsulation layers were also examined as a function of the thickness of inorganic Al203 and monomer layers. The number of interference peaks, their intensity, and their positions in the visible range can be controlled by varying the thickness of inorganic Al2O3 layer. On the other hand, changing the thickness of monomer layer had a negligible effect on the optical properties. We also verified that there is a trade-off between transparency in the visible range and the permeation of water vapor in hybrid thin film encapsulation layers. As the number of dyads decreased, optical transparency improved while the water vapor permeation barrier was degraded. Our study suggests that, in top-emission organic light-emitting diodes, the thickness of each thin film encapsulation layer, in particular that of the inorganic layer, and the number of dyads should be controlled for highly efficient top-emission flexible organic light-emitting diodes.

Thermal stability of atomic layer deposited Ru layer on Si and TaN/Si for barrier application of Cu interconnection.

The thermal stability of thin Ru single layer and Ru/TaN bilayers grown on bare Si by plasma enhanced atomic layer deposition (PEALD) have been studied with Cu/Ru, Cu/Ru/TaN structures as a function of annealing temperature. To investigate the characteristics as a copper diffusion barrier, a 50 nm thick Cu film was sputtered on Ru and Ru/TaN layers and each samples subjected to thermal annealing under N2 ambient with varied temperature 300, 400, and 500 degrees C, respectively. It was found that the single 5 nm thick ALD Ru layer acted as an effective Cu diffusion barrier up to 400 degrees C. On the other hand ALD Ru (5 nm)/TaN (3.2 nm) showed the improved diffusion barrier characteristics even though the annealing temperature increased up to 500 degrees C. Based on the experimental results, the failure mechanism of diffusion barrier would be related to the crystallization of amorphous Ru thin film as temperature raised which implies the crystallized Ru grain boundary served as the diffusion path of Cu atoms. The combination of ALD Ru incorporated with TaN layer would be a promising barrier structure in Cu metallization.

Optical properties of electrochemically deposited ZnO thin films on colloidal crystal film of SiO2 microspheres.

The optical properties of electrochemically deposited ZnO thin films on colloidal crystal film of SiO2 microspheres structures were studied. Colloidal crystal film of SiO2 microspheres were self-assembled by evaporation using SiO2 in solution at a constant 0.1 wt%. ZnO in thin films was then electrochemically deposited on to colloidal crystal film of SiO2 microspheres. During electrochemical deposition, the content of Zn(NO3)2 x 6H2O in solution was 5 wt%, and the process's conditions were varied between of 2-4 V and 30-120 s at room temperature, with subsequent heat-treatment between 200 and 400 degrees C. A smooth surface and uniform thickness of 1.8 microm were obtained at 3 V for 90 s. The highest PL peak intensity was obtained in the ZnO thin film heat-treated at 400 degrees C. The double layered ZnO/SiO2 colloidal crystals showed clearly better emission properties than the SiO2/ZnO and ZnO structures.

Growth behavior of iridium on Si substrates prepared by plasma enhanced atomic layer deposition.

Growth behavior of iridium (Ir) thin film on Si substrates prepared by plasma enhanced atomic layer deposition (PEALD) was systematically studied. Ir(EtCp)(COD) and oxygen was employed as a precursor and reactant, respectively. To obtain optimal conditions for depositing nanometer scale Ir thin film, deposition temperature, cycle dependence and precursor feeding time dependence were studied. Uniform 12 nm thick Ir layer with sharp interface was grown at the temperature range of 330-360 degrees C at the fixed deposition cycles of 300. The grown Ir film showed linear properties as a function of deposition cycles which is a typical self-limiting characteristic of ALD. The XRD patterns revealed that IrOx was not formed due to relatively low partial pressure of oxygen. The optimal conditions obtained for 12 nm thick Ir thin film were 330 degrees C of deposition temperature, 300 deposition cycles, and 10 sec of precursor feeding time.

Preparation of pentacene thin film deposited using organic material auto-feeding system for the fabrication of organic thin film transistor.

In this study, pentacene organic thin film was prepared using newly developed organic material auto-feeding system integrated with linear cell and characterized. The newly developed organic material auto-feeding system consists of 4 major parts: reservoir, micro auto-feeder, vaporizer, and linear cell. The deposition of organic thin film could be precisely controlled by adjusting feeding rate, main tube size, position and size of nozzle. 10 nm thick pentacene thin film prepared on glass substrate exhibited high uniformity of 3.46% which is higher than that of conventional evaporation method using point cell. The continuous deposition without replenishment of organic material can be performed over 144 hours with regulated deposition control. The grain size of pentacene film which affect to mobility of OTFT, was controlled as a function of the temperature.

Synthesis of bimetallic nanoparticles and their application to growth of multiwalled carbon nanotube forest.

We synthesized bimetallic nanoparticles and used them to grow CNTs with an atmospheric-pressure plasma-enhanced chemical vapor deposition system. FePt and FeCo bimetallic nanoparticles were synthesized by the bottom-up high-temperature polyol process using a simple centrifugal method. The diameter of synthesized nanoparticles ranged from 2 to 5 nm with high uniformity, as measured with a transmission electron microscope. The CNTs synthesis was carried out on bimetallic nanoparticles as a catalyst using acetylene as a carbon source gas. The CNT forests grown exhibited a maximum height of 96 microm, which is relatively high compared with other growth technologies. A forest of highly pure multiwalled CNTs with diameters of 10-20 nm was successfully synthesized on a bimetallic nanoparticle catalyzed substrate. As the growth temperature increased, the quality of CNTs improved remarkably, indicating that the graphitization could be controlled by varying the growth temperature. Furthermore, the oxygen plasma pre-treatment of dispersed bimetallic nanoparticles before CNTs growth could contribute to the production of highly pure CNTs. By TEM measurements, we observed that pure multiwall CNTs without defects or amorphous carbon could be synthesized.

Decrease in work function of transparent conducting ZnO tin films by phosphorus ion implantation.

To confirm the possibility of engineering the work function of ZnO thin films, we have implanted phosphorus ions into ZnO thin films deposited by radio-frequency magnetron sputtering. The fabricated films show n-type characteristics. It is shown that the electrical and optical properties of those thin films vary depending sensitively on the ion dose and rapid thermal annealing time. Compared to as-deposited ZnO films, the work-function of phosphorus ion-implanted ZnO thin films is observed to be lower and decreases with increasing ion doses. It is likely that the zinc or oxygen vacancies are firstly filled with the implanted phosphorus ions. With further increased ions, free electrons are generated as Zn2+ sites are replaced by those ions or interstitial phosphorus ions increase at the lattice sites, the fermi level by which approaches the conduction band and thus the work function decreases. Those films exhibit the optical transmittance higher than 85% within the visible wavelength range (up to 800 nm).

Investigation on growth behavior of CNTs synthesized by atmospheric pressure plasma enhanced chemical vapor deposition system on Fe catalyzed substrate.

We have studied growth behavior of carbon nanotubes (CNTs) on iron (Fe) catalyzed substrate using newly developed atmospheric pressure plasma enhanced chemical vapor deposition (AP-PECVD) system. To investigate the improved growth performance with simple equipment and process on large scale, a new AP-PECVD system containing different concept on downstream gas was designed and manufactured. As a catalyst, either sputtered or evaporated Fe thin film on SiO2/Si substrate was used and acetylene gas was used as a carbon source. We observed growth behavior of CNTs such as height, rate and density were strongly affected by plasma power. The maximum height of 427 microm and 267 microm was synthesized under RF plasma power of 30 W for 30 min and 40 W for 3 min, respectively. The growth rate dramatically increased to 6.27 times as plasma power increased from 30 to 40 W which opens the possibility the mass production of CNTs. By SEM and TEM observation, it was verified the grown CNTs was consists of mixture of single-wall and multi-wall CNTs. The graphitization ratio was measured to be 0.93, indicating that the graphitized CNTs forest was formed and relatively high purity of CNTs was synthesized, being useful for nano-composite materials to reinforce the strength. From our experiments, we can observe that the height and growth rate of CNTs is strong function of plasma power.

Preparation of phosphorus doped hydrogenated microcrystalline silicon thin films by inductively coupled plasma chemical vapor deposition and their characteristics for solar cell applications.

Intrinsic and phosphorus-doped hydrogenated microcrystalline silicon (microc-Si:H) films were prepared using inductively coupled plasma chemical vapor deposition (ICP-CVD) method. Structural, electrical and optical properties of these films were studied as a function of silane concentration, ICP source power and PH3/SiH4 gas ratio. Characterization of these films from Raman spectroscopy and X-ray diffraction revealed that the conductive film exists in microcrystalline phase embedded in an amorphous network. The condition of electrical properties (sigma(d): approximately 10(-7) S/cm, sigma(ph): approximately 10(-4) S/cm) and activation energy (0.55 eV), satisfied with properties of intrinsic microc-Si:H, was obtained at 1200 W of ICP power and 2% of silane concentration, respectively. At PH3/SiH4 gas ratio of 0.09%, dark conductivity has a maximum value of approximately 18.5 S/cm and optical bandgap also a maximum value of approximately 2.39 eV. The deposition rate was not satisfactory (4.9 angstroms/s) at same condition.

Decrease in work function of boron ion-implanted ZnO thin films.

We have fabricated boron ion-implanted ZnO thin films by ion implantation into sputtered ZnO thin films on a glass substrate. An investigation of the effects of ion doses and activation time on the electrical and optical properties of the films has been made. The electrical sheet resistance and resistivity of the implanted films are observed to increase with increasing rapid thermal annealing (RTA) time, while decreasing as the ion dose increases. Without any RTA process, the variation of the carrier density is insensitive to the ion dose. With the RTA process, however, the carrier density of the implanted films increases and approaches that of the un-implanted ZnO film as the ion dose increases. On the other hand, the carrier mobility is shown to decrease with increasing ion doses when no RTA process is applied. With the RTA process, however, there is almost no change in the mobility. We have achieved the optical transmittance as high as 87% within the visible wavelength range up to 800 nm. It is also demonstrated that the work function can be engineered by changing the ion dose during the ion implantation process. We have found that the work function decreases as the ion dose increases.

Work function increase of Al-doped ZnO thin films by B+ ion implantation.

The work function of an Al-doped ZnO (AZO) thin film can be increased via B+ ion implantation from 3.92 eV up to 4.22 eV. The ion implantation has been carried out with the ion dose of 1 x 10(16) cm(-2) and ion energy of 5 keV. The resistance of the B+ implanted AZO films has been a bit raised, while their transmittance is slightly lowered, compared to those of un-implanted AZO films. These behaviors can be explained by the doping profile and the resultant band diagram. It is concluded that the coupling between the B+ ions and oxygen vacancies would be the main reason for an increase in the work function and a change in the other properties. We also address that the work function is more effectively alterable if the defect density of the top transparent conducting oxide layer can be controlled.