Duk-Young Jeon

Thickness effect on secondary electron emission of MgO layers

Two series of MgO thin layers having various thicknesses were prepared on the Si substrate by electron-beam evaporation and by spin coating of MgO precursor solutions. We found that the magnitude of the secondary electron emission (SEE) yield of the MgO films strongly depends on the film thickness and the sample bias voltage. We ascribed it to the electric field through the insulating MgO layer, which allowed fast supply of electrons from the Si substrate to the surface. The mechanism of electron supply can be explained either as an acceleration through the MgO layer that becomes partially conductive upon primary electrons bombardment (radiation induced conductivity), or as a tunneling through the non-irradiated region of the insulating layer where the primary electrons cannot reach deeply into the sample with a certain penetration depth. The maximum SEE yield of the each MgO film on the Si substrate was observed when the penetration depth of primary electrons was close to the thickness of the MgO film, if the applied electric potential to the sample was low. Under a strong electric potential, the relationship between the penetration depth of primary electrons and the thickness of MgO films is not observed. It suggests the existence of the non-irradiated region, where electron supply is allowed by electron tunneling. Therefore, the magnitude of SEE yield for the thin insulating layer is strongly related to the detailed mechanism of electron supply, which is determined by the thickness of the insulating layer and the applied bias voltage to the sample during the SEE process.

Design and fabrication of scanning mirror for laser display

A 1500mm � 1200 mm silicon scanning mirror for laser display has been designed and fabricated by deep inductively coupled plasma reactive ion etching (ICPRIE) and flip chip bonding technology. It is a vertically driven electrostatic scanner and composed of two structures having vertical comb fingers. The upper structure is composed of a scanning mirror plate, two torsion bars, a supporting frame and vertical comb fingers. The lower structure is composed of vertical comb fingers, a supporting frame, gold signal lines and pads on the Pyrex glass substrate. The comb fingers are etched by ICPRIE and assembled by flip chip aligner bonder. This scanning mirror can be used for laser display as a galvanometric vertical scanner. # 2002 Elsevier Science B.V. All rights reserved.

Fabrication of silicon optical scanner for laser display

A new fabrication process of vertically driven electrostatic scanner for laser display is presented. This scanner is composed of two structures having vertical combs. The combs are etched by ICP RIE and assembled by eutectic bonding aligner.

Laser TV for home theater

The laser TV using blue, green diode-pumped solid state lasers and a red diode laser is developed. The wavelengths of the blue, green and red are 457 nm, 532 nm and 648 nm, and the output powers are 350 mW, 700 mW and 500 mW, respectively. The power levels of lasers are adjusted for white color balance. The polygon mirror and the galvanometer are used for horizontal scanning and vertical scanning, respectively. The image size of 80 inches with high-brightness and VGA resolution (640 X 480 Progressive scanning) is obtained. The acousto-optic modulator (AOM) is fabricated for laser beam modulation, for which the carrier frequency of 350 MHz for XGA resolution is applied. TeO2 crystal, which is cut at Brewster angle, is used as an optical medium and LiNbO3 is attached as a transducer. In order to get a compact size, low cost, low-power consumption and lightweight, a scanning mirror using MEMS technology is fabricated by the size of 1500 micrometers X 1200 micrometers . This scanning mirror can be used as a galvanometric vertical scanner for laser TV.

Dependency of luminescence properties of Y2O3: Eu on the activator incorporation degree and lattice parameter

— Samples of yttrium oxide doped with trivalent europium have been prepared by ceramic techniques, under different synthesis conditions; barium chloride (BaCl2) and sodium tetraborate (Na2B4O7) were tested as flux. The improvement of the luminescence properties dependency on the substitution of Eu3+ for Y3+ in the host lattice under electron and UV excitations is demonstrated. The lattice parameter as a quantitative assessment of activator incorporation degree is proposed. The obtained results are discussed with respect to the employed processing method.

Secondary electron emission for layered structures

Semiempirical theory for secondary electron emission is extended to cover the layered structure. Secondary electron emission for the two-layered structure, i.e., a thin film on a substrate, is calculated and compared with the experiment. Good agreement between the two indicates the usefulness of this theory for the layered structure.

Double- to single-hump shape change of secondary electron emission curve for thermal SiO2 layers

Secondary electron emission yields (SEEYs) were measured for silicon oxides which were thermally grown on doped silicon substrates. Generally, SEEY curves can be described by the so-called universal curve, i.e., one hump with a monotonic increase (decrease) before (after) the hump. However, we found that our thick oxide layers exhibited double-hump shaped SEEY curves instead of single-hump shaped curves. Additionally, we were able to change the shape of a SEEY curve with two humps to a curve with one hump, or vice versa, by varying the experimental parameters. This change in curve shape can be explained if we consider the competition between the oxide layer thickness and the electron’s penetration depth, the charge accumulation due to emission of secondary electrons, and charge traps created during thermal oxidation at the same time.

Fabrication and characterization of electrically tunable high-Tc superconducting resonators incorporating barium strontium titanate as a tuning material

We have made the electrically tunable microstrip resonators by using both high-Tc superconducting and dielectric films. The two-pole resonators employ a dielectric barium strontium titanate film on their centre in the form of flip chip. The superconducting YBa2Cu3Oy (YBCO) and dielectric Ba0.1Sr0.9TiO3 were deposited on the CeO2-buffered sapphire substrate and LaAlO3 substrate, respectively, by a pulsed laser deposition technique. Variations of the relative permittivity, r, and dielectric loss tangent, tan, of the Ba0.1Sr0.9TiO3 were studied as a function of the applied dc bias at liquid-nitrogen temperature. The tunability, defined as C(0 V)/C(100 V), and loss tangent of the resonators were measured to be ~1.9 and 1.5 × 10-2 (at 100 V), respectively.

Synthesis of ZnS Phosphor Particles in Exothermic Frontal Waves

In this study, temperature profiles and combustion velocities of a Zn + S system in the presence of sodium halide (SH) as an inert diluent were investigated by combining combustion experiments with the thermocouple measurement technique. Flammability limits were determined experimentally by determining the limiting concentrations of sodium halides for which combustion can be initiated and propagated throughout the reaction pellet. The limiting concentration of NaCl was found to be higher than those of NaF and NaI, indicating that NaCl might be a more effective diluent for the Zn + S system. All reaction mixtures were characterized by low combustion temperature in the range 800–1350 °C and burning velocities in the range of 0.024–0.095 cm/s. Depending on the combustion temperature, this synthetic route provides single-phase modified zinc sulfide powders of sphalerite and wurtzite. ZnS samples doped with halogen ions (H–) produced sky-blue emission (470 nm) under 340 nm excitation. ZnS samples codoped with Mn2+ ions showed a red shift (588 nm) under 356 nm excitation. The relative emission intensity of ZnS:Mn2+ phosphor increased as much as 3 times in the NaF → NaI → NaCl range.

Electrostatic force microscopy study on the domain switching properties of the Pb(Zr0.2Ti0.8)O3 thin films with different crystallographic orientations for the probe-based data storage.

The domain switching properties of the ferroelectric Pb(Zr(0.2)Ti(0.8))O(3) (PZT) thin films with two types of crystallographic orientations were investigated by electrostatic force microscopy (EFM). The crystallographic orientations of the PZT thin films were random on the (111)Pt/MgO(100) and c-axis preferred on the (100)Pt/MgO(100), respectively. When dc bias was applied to the films for writing in micro-scale area, electrostatic force images showed that the domain switching was hard in the PZT thin films with random orientation, while the pattern could clearly be written in the PZT films with c-axis orientation. The differences in the domain switching properties of each PZT thin film were investigated in the crystallographic orientations point of view, and the domain switching dynamics were also measured by investigating the nano-sized dot switching behavior with respect to the width of the applied voltage pulse.