Eunkyoung Nam

Organic Light-Emitting Devices with In-Doped (4 at. %) ZnO Thin Films as the Anodic Electrode

We have investigated transparent conducting properties of using In-doped (4 at. %) zinc oxide (IZO) thin films deposited on glass substrate by pulsed DC magnetron sputtering at low processing substrate temperatures. As increase of the substrate temperature, IZO thin films with better c-axis orientations were grown in perpendicular to the substrate and work functions of IZO films slightly decrease. The optical properties showed high transmittance of higher than 85% in the UV–visible region and exhibited the absorption edge of about 350 nm. The electrical properties exhibited the low resistivity of 1.1 ×10-3 Ω cm and the high mobility of ~7.8 cm2 V-1 s-1. The organic light emitting diodes (OLEDs) with an IZO anode achieved a maximum luminance efficiency of 2.7 cd/A and external quantum efficiency of 0.47%, which are compared to the values of a control device fabricated on commercial ITO anode. These results indicate that IZO films hold promise for anodic electrodes in the OLEDs application.

Effects of Deposition Plasma Power on Properties of Low Dielectric-Constant Plasma Polymer Films Deposited Using Hexamethyldisiloxane and 3,3-Dimethyl-1-butene Precursors

We investigated the effects of deposition plasma power on the properties of plasma polymer films deposited by plasma-enhanced chemical vapor deposition using a mixture of hexamethyldisiloxane and 3,3-dimethyl-1-butene as the precursor, which are referred to as plasma polymerized hexamethyldisiloxane:3,3-dimethyl-1-butene (PPHMDSO:DMB) films. As the deposition plasma power was increased from 15 to 60 W, the relative dielectric constants k of PPHMDSO:DMB films, increased from 2.67 to 3.19. After annealing at 450 °C, the films deposited at a deposition plasma power of 15–60 W showed k values of 2.27–2.64. With increased deposition plasma power, the as-deposited and annealed films showed increased values of hardness and Youngs modulus. For as-deposited films, deposited at a plasma power of 15–60 W, the films showed a hardness of 0.13–2.0 GPa, and a modulus of 2.25–17.27 GPa. Annealed films, deposited at a plasma power of 15–60 W, showed a hardness of 0.05–2.07 GPa and a modulus of 1.66–14.4 GPa. The change in the k value and hardness of plasma polymer films as a function of deposition plasma power was correlated with fourier transform infrared (FT-IR) absorption peaks of C–Hx, Si–CH3, and Si–O related groups. The as-deposited and annealed PPHMDSO:DMB films showed decreased intensities of C–Hx and Si–CH3 peaks as the deposition plasma power increased. The reduction in the dielectric constant after annealing is mainly due to hydrocarbon removal in the film. Deconvolution of Si–CH3 bending peaks of PPHMDSO:DMB films was performed to relate mechanical properties to chemical structures. The relative oxygen content in the O–Si–(CH3)x structure is analyzed in detail. Improvements in hardness and modulus of our films are attributed to an increased amount of O3Si–(CH3) in the Si–CH3 structure.

A Triple-Layered Microcavity Structure for Electrophoretic Image Display

An electrophoretic display (EPD) cell with a triple-layered microcavity structure was fabricated using a convenient dry film resist. The inherent structural advantage arising from the function of the middle channel layer as a background colored state enabled the EPD to operate with two different-colored states by using a single type of electronic-ink particles, thereby eliminating the possible agglomeration of oppositely charged ink particles and supporting the potential application of the proposed structure to color the electronic paper. The preliminary operation of this new EPD structure was demonstrated as white and blue display states on a rigid glass exhibiting a contrast ratio of 1.5 : 1 with saturation voltages of + 30 and -30 V, respectively. Successful demonstrations on both the indium-tin-oxide-patterned glass and flexible polyethylene substrates are also provided.

LOW TEMPERATURE FABRICATION AND PHYSICAL PROPERTIES OF 5 at.% Ga-DOPED ZnO FILMS FOR TRANSPARENT ELECTRODE APPLICATIONS

Transparent conductive 5 at.% Ga-doped ZnO (GZO) thin films are deposited on a glass substrate by an asymmetrical bipolar-pulsed DC magnetron sputtering at various substrate temperatures. All the GZO films have nanocrystalline structure and compact surface morphology. A highly c-axis oriented GZO film was grown perpendicular to the substrate at the 200C. The measured work function of GZO film deposited at 200°C shows slightly lower value of 4.37 eV than a commercial ITO film of 4.6 eV. The GZO film showed the lowest sheet resistance of 35 Ω/□, a carrier concentration of 1.2 ×1021cm-3, a mobility of 9.9 cm2/Vs, and high optical transmittance of over 85% in the visible range. It indicates that the GZO films at 200°C can be promising as an alternative to ITO thin film for transparent electrode applications.

Performance Improvement of the Organic Light-Emitting Diodes by Using a LiF/Pyromellitic Dianhydride Stacked Cathode Interfacial Layer

A bilayered cathode interfacial structure consisting of lithium fluoride (LiF) and pyromellitic dianhydride (PMDA) was used between Al and tris-(8-hydroxyquinoline) aluminum (Alq 3 ) in the organic light-emitting diode (OLED), and a better performance enhancement compared to the OLED with a single LiF interfacial layer was achieved by using an optimal thickness combination of the bilayered interfacial structure (0.3 nm LiF/0.7 nm PMDA). The bilayered interfacial stucture with an optimum thickness combination decreased the parallel bulk resistance and lowered the electron injection barrier height between Al and Alq 3 according to the impedance and in situ ultraviolet photoelectron spectroscopy measurements, respectively.