Chung-Hoo Park

Diffuse dielectric anomaly in perovskite-type ferroelectric oxides in the temperature range of 400–700 °C

The diffuse dielectric anomaly by the dielectric relaxation found at the high-temperature region of 400–700 °C was investigated in perovskite-type ferroelectric oxides such as BaTiO3, (Pb,La)TiO3, and (Pb,La)(Zr,Ti)O3 ceramics. We observed that the diffuse dielectric anomaly in perovskite oxides was strongly affected by oxygen-related processing parameters. We have modified the Debye relaxation equation by introducing the mobile dipole of the thermal motion of oxygen vacancies in order to explain the temperature-dependent behavior of the diffuse dielectric anomaly. A relationship between the dielectric polarization/relaxation and the electrical conduction by the thermal motion of oxygen vacancies was microscopically suggested to explain the origin of the diffuse dielectric anomaly found at 400–700 °C in perovskite-type ferroelectric oxides.

Hydrogen-induced ferromagnetism in ZnCoO

We have investigated experimentally the effects of n-type impurities such as Al and H on the magnetic properties of ZnCoO. The carrier density changes slightly upon the introduction of hydrogen but increases significantly in the case of Al. A measurement of magnetic circular dichroism indicates that, of the two impurities, only H induces ferromagnetism in ZnCoO. Our experimental data suggest that, unlike Al, H plays an important role in the enhancement of ferromagnetic spin-spin interactions that goes much beyond a carrier-mediated effect.

A study of indium tin oxide thin film deposited at low temperature using facing target sputtering system

Abstract Indium tin oxide (ITO) thin films, for electroluminescent display electrodes, must be of low resistivity and high transparency. In this study, a facing target sputtering system was used to fabricate this film in order to improve its electrical and optical properties. Temperature was one of the most critical factors during fabrication. Scanning electron microscopy (SEM) and X-ray diffraction XRD were used to analyze the surface morphology and structure of ITO thin films. It was concluded that the ITO films deposited between 50 and 200 °C were polycrystalline. Under 50 °C, the ITO films were amorphous or had mixed amorphous and crystalline phases. After post-annealing, the amorphous ITO films could become crystalline, and therefore, the electrical property of amorphous ITO films could be effectively improved. In this research, an ITO film with the resistivity as low as 1.99×10−4 Ω cm and transparency above 85% within the visible wavelengths 400∼800 nm, was obtained after vacuum annealing at 300 °C for 2 h, while deposited at a working pressure 0.1333 Pa, percentage oxygen flow rate 22.7% in Ar+O2 gas mixture, substrate temperature 75 °C, and input DC power 50 W for 30 min. The corresponding deposition rate for this film was 22 nm/min.

ASYMMETRY IN FATIGUE AND RECOVERY IN FERROELECTRIC PB(ZR, TI)O3 THIN-FILM CAPACITORS

We investigate the fatigue and refreshment by dc-electrical field of the electrical properties of Pt/Pb(Ti,Zr)O3/Pt ferroelectric capacitors. We find an asymmetry in the refreshment, that is, the fatigued state can be refreshed by application of negative high dc voltage to the top electrode, but no refreshment is measured by positive dc-voltage application. We also find that the fatigue can be prevented by driving the capacitor asymmetrically.

Surface-discharge characteristics of MgO-thin films prepared by reactive RF unbalanced magnetron sputtering

Abstract The performance of a.c. plasma display panels (PDP) is influenced strongly by the surface glow-discharge characteristics on the MgO-thin films. This paper deals with the surface glow-discharge characteristics and some physical properties of MgO-thin films prepared by reactive RF planar unbalanced magnetron sputtering in connection with a.c. PDP. The samples prepared with the d.c. bias voltage of −10 V showed lower discharge voltage, lower erosion rate by ion bombardment, higher optical transparency and higher crack resistance in the annealing process than those samples prepared by conventional magnetron sputtering or E -beam evaporation.

A new method to reduce addressing time in a large AC plasma display panel

To replace the dual scan system by single scan in large ac plasma display panel (PDP), the addressing time should be reduced by modifying cell structure and/or driving circuits. Moreover, the luminance of the PDP can also be increased with the decrease in the addressing time. In this paper, we suggest the bus and address electrodes with triangular protruding tips in order to reduce the addressing time. Moreover, the addressing time of the ac PDP with these electrodes was investigated experimentally with address and display period separated (ADS) driving method. The experimental results show that the addressing time can be reduced more than 30% compared with the conventional type by modifying the electrodes without reducing the luminance of the PDP.

Improvement of addressing time and its dispersion in AC plasma display panel

In order to improve the addressing time and its dispersion, we have applied different addressing voltage at each cell such as progressively increasing pulse voltage instead of constant one which is used in conventional driving method. The experimental results show that the addressing time and its dispersion for a given cell driven by new method maintained almost constant value regardless of scanning sequence. Moreover, the addressing time can be reduced about 30% compared with conventional driving method without cross-talk and mis-firing.

Effects of MgO annealing process in a vacuum on the discharge characteristics of AC PDP

This paper deals with the relationships between various annealing conditions in a vacuum and the surface glow discharge characteristics on the MgO thin film prepared by e-beam evaporation method. The minimum discharge inception voltage is obtained for the sample annealed at 400°C for about 2 h in a clean vacuum. Above the annealing temperature of 430°C, cracks are founded on the MgO film, which results in higher discharge voltage. Moreover, the lower the annealing pressure, the lower the discharge voltage. The main factors that improves the discharge characteristics by annealing process is considered to be due to both the morphology changes or crystal structure of the MgO thin films and pumping impurities in the MgO film during the annealing process.

Electro-optical characteristics of plasma display panel with Mg1−xSixO protecting thin films deposited by an electron-beam evaporation method

The effect of Si doping in MgO has been investigated in order to improve the material properties of the MgO protecting layer in plasma display panels. A small amount of Si was added to the MgO pellet while the MgO layer was being deposited by using an electron-beam evaporation method. Both the surface characteristics of the protecting layer and the electro-optical properties of 4in. test panels were investigated, such as firing and sustain voltages, luminous efficacy, addressing jitter, and image sticking. The firing voltage is minimized when the Si concentration is 0.03%∼0.04%, where the luminous efficacy increases up to 35% compared with that of the conventional MgO film, and the boundary image sticking also shows good characteristics around the Si concentration level by 0.04%.

A study on the new type sustaining electrode showing high luminous efficiency in AC PDPs

In order to improve the luminous efficiency of ac plasma display panel (PDP), a new bridge type sustaining electrode is suggested. The luminous efficiency of the ac PDP with suggested new sustaining electrodes is improved about 30% compared with that of conventional sustaining electrodes. Furthermore, the suggested ac PDP is maintained almost the same luminance with the conventional ones, and this type has a merit of free alignment between front and rear panels.