Shang-hyeun Park

Carbon nanotube electron emitters with a gated structure using backside exposure processes

We have fabricated fully vacuum-sealed 5 in. diagonal carbon nanotube field-emission displays of a gated structure with reliable electron emission characteristics. Single-walled carbon nanotube tips were implemented into the gate structure using self-aligned backside exposure of photosensitive carbon nanotube paste. An onset gate electrode voltage for emission was about 60 V and the luminance as high as 510 cd/m2 was exhibited under an application of 100 V and 1.5 kV to gate electrode and anode, respectively.

Triode-type field emission array using carbon nanotubes and a conducting polymer composite prepared by electrochemical polymerization

We report a method to fabricate carbon nanotubes (CNT)/conducting polymer composite films for the application of CNTs to field emission displays. The composite was prepared by a combination of electrochemical polymerization of pyrrole and electrophoretic deposition of CNTs. We obtained a uniform CNT/conducting polypyrrole polymer composite film. The CNTs were mainly coated on protrusions of the polypyrrole film and emitted electrons without rubbing and stretching. We realized a triode-type field emission array (FEA) using the CNT/polypyrrol composite. This FEA showed that the emission current was modulated by gate voltage of 30 V. The film morphology and emission characteristics of the CNT/conducting polymer composite were studied using optical microscopy, scanning electron microscopy, and an emission test in vacuum.

High resolution phosphor screening method for full-color field emission display applications

A polyvinyl alcohol-slurry screening technology of phosphors was studied for field emission displays with a resolution up to supervideo graphics adapter. Phosphor lines were successfully patterned as narrow as 25 μm on 6 in. glass substrates. Process conditions such as spin coating speeds, exposure time, and shadow mask layout for photolithography were related to thickness and line resolutions of phosphor. Luminance characteristics of phosphors were optimized in terms of firing processes. For ZnS:Cu, Al, ZnS:Ag, Cl, and Y2O3:Eu phosphors, the firing temperature was optimized to be 400 °C. The nitrogen ambient during the cooling process improves the stability of phosphor surface.

Development of triode-type carbon nanotube field-emitter arrays with suppression of diode emission by forming electroplated Ni wall structure

Triode-type field-emitter arrays were developed by screen printing a photosensitive paste including single-walled carbon nanotubes. Ni wall structure (NWS) was electroplated to form a thick gate to suppress diode emission induced by strong electric strengths due to an anode potential and to focus electron beams to their destined color subpixels. It was observed in computer simulations, as well in experiments that the NWS with the optimum thickness was effective in reducing the diode emission and enhancing electron-beam focusing by modifying electrical potentials around the carbon nanotube emitters. Our fully sealed field-emission display panel using the field-emitter arrays with the NWS demonstrated full color moving images without serious diode emission and with satisfactory color separation.

Synthesis and modification of red oxide phosphors for low voltage excitation

New red oxide phosphors Y2O3:Eu3+,Si4+ and (Y,Gd)2O3:Eu3+,Si4+,Bi3+ are synthesized by a coprecipitation method. Relative cathodoluminescence (CL) brightness at low voltages (⩽1 kV) is analyzed. At the low voltage excitation, luminance of the synthesized phosphors is higher than that of other commercially available red phosphors Y2O2S:Eu3+ and Y2O3:Eu3+. In particular, the difference of relative brightness between the commercially available phosphors and the synthesized Y2O3:Eu3+,Si4+ is larger at low voltages (⩽500 V) than at higher voltages. The synthesized (Y,Gd)2O3:Eu3+,Si4+,Bi3+ phosphor gives the same level of brightness as that of Y2O3:Eu3+,Si4+ at voltages greater than 500 V. (Y,Gd)2O3:Eu3+,Si4+,Bi3+ is coated with a conductive material SnO2:Eu3+. The coating of SnO2:Eu3+ shows a considerable improvement in brightness without a color shift. The excellent luminescence characteristics of (Y,Gd)2O3:Eu3+,Si4+,Bi3+ coated with SnO2:Eu3+, studied using field emitter arrays, suggests that our synthesized...

Current degradation mechanism of single wall carbon nanotube emitters during field emission

Electron emission current degradation is often observed from printed single wall carbon nanotube emitters during field emission process. After a highly imposed emission, structural deformation of emitters from thin crystalline nanotube bundle to thick amorphous-type carbon fiber was observed. This deformation seems to relate to the current degradation, deteriorating the efficiency of field emission either by increasing the resistance of emitters or by decreasing the field enhancement factor of emitter tips. Two possible mechanisms of structural deformation are internal structural transformation by Joule heating under excessively imposed emission current and continuous adsorption of carbon particles on actively working emitters.

Structure and Luminescence Properties of the ZnS:Cu, Al Phosphor for Low Voltage Excitation

The ZnS:Cu, Al phosphor has been studied for low voltage excitation field emission devices. To improve the cathodoluminescence (CL) brightness, the phosphor has been synthesized with iodide-type alkaline and alkali-earth metal as fluxes. Cul and AlF 3 were used as an activator and coactivator, respectively. The phosphor has been characterized in comparison with commercially available cathode ray tubes (CRTs) phosphor and conventionally prepared ones Newly synthesized ZnS:Cu. Al phosphor prepared with iodide-type fluxes has shown higher CL brightness than commercially available phosphor and conventionally prepared ones. The phosphor structure has been analyzed using scanning electron microscopy, X-ray diffraction, and transmission electron microscopy. From the analysis, the phosphor particles were composed of cubic and hexagonal phases. The cubic phase was much more formed when iodide-type fluxes were used. This cubic phase helps the phosphor to have high brightness at low voltage operations.

Modyfying device structure for high emission current for x-ray tube application from triode-type carbon nanotube cathode

The triode-typed field emission (FE) devices using carbon nanotube (CNT) emitters for the x-ray application were fabricated. For the stability of the device, the leakage current between cathode and gate, and the emission current to the anode electrode should be controlled. We realized that the thickness of insulating layer-gap distance between cathode and gate- and the space between the gate electrodes-electron path from cathode and anode- should be controlled for the ratio of the current from cathode to anode (Ia) to the current from cathode to gate (Ig). The ratio of Ia to Ig can be represented the device efficiency. The rectangular-mesh electrode and screen printed insulating layer were controlled for Ia/Ig. When the size of gate hole was the 50 by 700 um - the electrode size is 25 by 700 um - and the thickness of insulator layer was 65 μm, the maximum ratio of Ia/(Ia+Ig) was 0.63.

A carbon nanotube paste with high emission currnet for the X-ray tube

Field emission properties of CNTs(carbon nanotubes) have been investigated in the various field, such as flat panel display and x-ray sources. Especially, the x-ray tube which fabricated using the CNTs can be operated with low power consumption compare with filament-based x-ray tubes. The cold cathode - CNTs- can be operated at the lower voltage and the electron which coming out from the CNTs can be controlled easilly by focus electrode. And for high emission current, the device should be stable at the high operate voltage. The gate electrode-mesh-type electrode- can be layered by using glass frit and firing process. At this point, the mesh structure can be controlled for the higher adhesion force which is for the emission stability at the high voltage. The glass frit could be act effectively between mesh electrode and insulating layer because of the designed mesh structure.

Density control of carbon nanotubes for field emission display by control of catalytic layer diffusion

In this report, we have controlled the growth of multiwalled carbon nanotubes (MWNT) in terms of the populations and diameters by introducing a buffer layer between catalytic layer and amorphous silicon coated substrates. The carbon nanotubes growth with the chemical vapor deposition technique might produce interaction of the metallic catalyst with silicon layer, which could interrupt the catalytic effect. We will show how control of diffusion layer between the amorphous silicon and metal catalyst effectively control the formation of the silicide phase and consequently optimize the carbon nanotubes growth. It is performed on amorphous silicon coated glass by infrared radiation heated thermal chemical vapor deposition(CVD), using a gas mixture of carbon mono-oxide and hydrogen and Fe-Ni-Co alloy catalyst at temperatures as low as 480/spl sim/580/spl deg/C.