Deuk Seok Chung

FULLY SEALED, HIGH-BRIGHTNESS CARBON-NANOTUBE FIELD-EMISSION DISPLAY

A fully sealed field-emission display 4.5 in. in size has been fabricated using single-wall carbon nanotube (CNT)-organic binders. The fabricated displays were fully scalable at low temperature, below 415u200a°C, and CNTs were vertically aligned using paste squeeze and surface rubbing techniques. The turn-on fields of 1 V/μm and field emission current of 1.5 mA at 3 V/μm (J=90u200aμA/cm2) were observed. Brightness of 1800 cd/m2 at 3.7 V/μm was observed on the entire area of a 4.5 in. panel from the green phosphor-indium–tin–oxide glass. The fluctuation of the current was found to be about 7% over a 4.5 in. cathode area.

Application of carbon nanotubes to field emission displays

Abstract Large-area field emission displays were fabricated with single-wall carbon nanotube emitters. A carbon nanotube paste was prepared and screen-printed to form an electron emission layer on a glass-based substrate. Carbon nanotube-based field emission displays fabricated by thick film processing were successfully integrated to demonstrate moving color images. They revealed excellent field emission characteristics of a threshold electric field of approximately 2 V/μm. We have also investigated triode-type field emission display structures to achieve high-gray scale and high brightness. In the triode structure, it was observed that electron emission from carbon nanotube emitters was controlled by modulation of gate voltages.

Fabrication of triode-type field emission displays with high-density carbon-nanotube emitter arrays

Abstract Triode-type carbon-nanotube field emission displays (CNT-FEDs) with the 5″. diagonal were fabricated using screen printing as well as thin film processing. We developed a photosensitive paste including single walled CNTs for screen printing. CNT emitter dots with the diameter of 5xa0μm were defined inside gate holes with a diameter of 10xa0μm by screen printing the CNT paste and a subsequent backside photolithography. CNTs were exposed to erect on the surface by development, serving as electron emitters. A thick Ni wall structure was electroplated just above gate electrodes to suppress diode emission caused by an anode potential and to improve focusing of electron beams. An onset gate voltage for emission was as low as 40–45xa0V. Under an optimum design of a FED panel, R, G, B colors were satisfactorily separated. Our vacuum-sealed CNT-FED demonstrated full color moving images with high brightness and good color purity at a video-speed operation.

Field emission from 4.5 in. single-walled and multiwalled carbon nanotube films

Field emission properties of 4.5 in. flat panel displays in a diode type panel using single-walled (SWNTs) and multiwalled carbon nanotube tips (MWNTs) were characterized and compared. The panel, fabricated by a slurry squeezing and surface rubbing technique, enables the generation of more emission sites by removing materials on the surface. The turn-on field of MWNTs decreased from 6.4 to 3 V/μm by treatment of the surface, and that of SWNTs also decreased, from 4.5 to 2 V/μm. The density of aligned MWNTs is approximately 2/μm2, whereas the aligned SWNTs were uniformly distributed, with densities of 5–10/μm2. As a result, SWNT films show higher emission uniformity than MWNT films. A gradual degradation over time was observed in both MWNTs and SWNTs. The current stability curve of the SWNTs decreased about 20%, while that of the MWNTs decreased less than 10%.

Carbon-Nanotubes for Full-Color Field-Emission Displays

A 4.5-inch fully sealed carbon-nanotube field-emission display with a 200-µm narrow gap was fabricated on glass using paste squeezing and surface rubbing techniques. The fabricated displays were fully scalable at low temperatures below 415°C and showed very high luminance of 1800 cd/m2 at 4 V/µm. The degradation of emission currents for single-wall carbon nanotubes was less than 10% in electrical aging tests. Large field-enhancement factors and low turn-on voltages (1.5–3 V/µm) were attributed to well-aligned carbon nanotubes on substrates and a large number density of carbon nanotubes of 5–10/µm2, which was confirmed by high-resolution electron microscopy. Although localized states exist for various tip morphologies, which was calculated by density-functional tight-binding calculations, the contribution from such states was found to be negligible.

Carbon nanotube field emitter arrays having an electron beam focusing structure

An electron beam focusing structure was incorporated into the gated field emitter arrays where the emitters were screen-printed carbon nanotubes. The focusing structure was comprised of 8-μm-thick bulky SiOx focus gate insulator and Cr focus gate, and exhibited negligible leakage between the gate and the focus gate. In current–voltage measurements, it is found that the anode current strongly depends on both the focus gate and the anode bias voltages. Electron beams were focused well at the anode with a slight overfocusing effect, which is due to the wide electron beam divergence from carbon nanotubes. A new focusing structure based on the simulation is proposed to overcome the overfocusing.

Carbon Nanotube-Based Field-Emission Displays for Large-Area and Full-Color Applications.

Single-wall carbon nanotubes (SWNTs) were applied to electron emitters of field-emission displays (FEDs). Large-area FED devices with SWNT emitters were successfully fabricated in a diode mode using screen printing to demonstrate moving color images. They revealed excellent field-emission characteristics of a threshold electric field of approximately 2 V/µm. We have also investigated triode-type FED structures to achieve a high gray scale and high brightness. It was observed that electron emission from carbon nanotube emitters was controlled by the modulation of gate voltages.

Building a backlight unit with lateral gate structure based on carbon nanotube field emitters.

This paper describes the fabrication of a backlight unit for liquid crystal display based on printed carbon nanotube field emitters with lateral gate and additional mesh structures. The device architecture has been optimized through field emission characterization and supporting numerical simulation. The emission current depends strongly on the cathode-gate gap, mesh position, and mesh bias. Direct observation of luminous images on a phosphor screen reveals that the electron beams undergo a noticeable shrinkage along the lateral direction with increasing anode bias, which is in good agreement with the simulation results. We suggest and demonstrate a modified structure equipped with double emitter edges leading to approximately 20% improved phosphor efficiency (34.4 lm W(-1)) and luminance (9600 cd m(-2)), compared to those from a single edge structure.

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.

Optimization of electron beam focusing for gated carbon nanotube field emitter arrays

We fabricated gated field emitter arrays with a novel focusing structure of electron beams, where the focusing electrode concentrically surrounded each gate hole. Carbon nanotube emitters were screen printed inside an amorphous-Si concave well far below the gate. It was theoretically and experimentally verified that the concave well structure effectively focused the emitted electron beams to their designated phosphor pixels by modulating focusing gate voltages. For the vacuum packaged field emission displays with the pixel specification fitting high-definition televisions, color reproducibility of approximately 71% was achieved at the brightness of 400 cd/m/sup 2/.