Young Rae Cho

Diameter-controlled growth of carbon nanotubes using thermal chemical vapor deposition

The diameter and the growth rate of vertically aligned carbon nanotubes (CNTs) are controlled by modulating the size of catalytic particles using thermal chemical vapor deposition (CVD). The size of iron catalytic particles deposited on silicon oxide substrate is varied in a controlled manner by adjusting the condition of ammonia pretreatment. We found an inverse relation between the diameter and growth rate of carbon nanotubes. As the diameter increases, the compartment layers of bamboo-shaped carbon nanotubes appear more frequently, which is suitably explained by the base growth mechanism.

Photolithography-based carbon nanotubes patterning for field emission displays

Carbon nanotubes (CNTs) emitters were successfully patterned in small pixels (50×50 μm2) by using photolithography process on a hard metal electrode for field emission displays (FEDs) application. The CNTs particles in the patterned pixels were uniformly distributed on 2-inch diagonal substrates. The maximum diameter of CNTs particles could be controlled less than 20 μm. After patterning and heat treatment process below 300°C, most of CNTs bundles on the cathode electrode were aligned perpendicular to the substrates. The threshold electric field of emission for patterned CNTs was about 4.2 V μm−1 and the field enhancement factor derived from the Fowler–Nordheim plots of the electron emissions was about 100 000 in the high voltage region. This newly developed process can be applicable to field emitter arrays for high resolution FEDs.

Micro-etching technology of high aspect ratio frameworks for electronic devices

High aspect ratio glass frameworks for spacer applications in the vacuum electronic devices were fabricated by photolithography. The material for the framework was photoetchable glass which has good mechanical and electrical insulating properties. The photoetchable glass was exposed to ultraviolet light, with a wave length of 312 nm, through a chrome mask. After heat treatment, the glass was etched in 10% hydrofluoric acid using ultrasonic agitation. The final dimensions of the glass framework were greatly dependent on the mask patterns and ultraviolet light exposure conditions. The framework surface was affected by the tilting of the glass surface with respect to the ultraviolet light source during the exposure process. In this work, glass frameworks, having a surface step of about 300 μm, were obtained by tilting 11°. An aspect ratio of 30 was obtained using photoetchable glass of 1000 μm thickness.

L‐3: Late‐News Paper: Active‐Controlled Diode Emitters with Thin‐Film Transistor and Carbon Nanotubes for FED Applications

A new cathode technology of active-controlled diode emitters with a-Si high-voltage TFTs and carbon nanotubes (CNTs) is suggested for field emission displays (FEDs). The a-Si TFT controlled electron emissions from the multiwall CNTs actively, resulting in great improvement in emission stability and the possibility of low voltage matrix-addressable operations of diode type cathodes. This technology can provide a new breakthrough in FEDs.

Dependence of substrate deflection on spacer pitch in emissive flat panel displays

To obtain optimum spacer configurations in the panel for flat panel display application, the stress and deflection distributions in the substrates were calculated by the finite element method. For the panels having different configurations of spacers, such as shape and distance between spacers, the dependence of substrate deflection on these variables were calculated and measured. The spacing of spacers was varied from 5 to 40 mm in the vacuum-sealed panel, where the face and base plates were made of soda lime glasses having thicknesses of 1.1 mm. The results of deflection values in the substrate agree closely between those by the simulation and experimental measurement for the ball-type spacer. Also in comparison of spacers using the bar-type and ball-type, the maximum stress and deflection values are always smaller in the former than the latter. When the spacer pitch is below 15 mm, the maximum substrate deflection is below 5 μm for both types of spacers.

P- 41: A Novel Patterning Technology of Fine-pitched CNT Pixels for Field Emitter Arrays

A novel patterning technology of fine-pitched carbon nanotube (CNT) pixels on a thin metal has been developed by lift-off process for field emitter arrays (FEAs). The lift-off method provides even smaller CNT pixels compared with those made by conventional screen-printing and photolithography processes. SEM images demonstrated that the smallest pitch and the size of patterned pixels were 15 μm × 15 μm and 7 μm × 7 μm, respectively. After patterning and heat treatment process at 300°C, most of CNT bundles on the cathodes were aligned perpendicular to the substrate. The density of CNT bundles in the patterned pixels was 10–20/μm2. The turn-on field of patterned CNTs was less than 2.5 V/μm and the current density was 3.2 mA/cm2 at 3.5 V/μm.

Active‐matrix cathodes though integration of amorphous silicon thin‐film transistor with triode ‐and diode‐type field emitters

Abstract Amorphous silicon thin‐film transistors (a‐Si TFTs) were incorporated into Mo‐tip‐based triode‐type field emitters and diode‐type ones of carbon nanotubes for an active‐matrix cathode (AMC) plate of field emission displays. Also, we developed a novel surface‐treatment process for the Mo‐tip fabrication, which gleatly enhanced in the stability of field emission. The field emission currents of AMC plates on glass substrate were well controlled by the gate bias of a‐Si TFTs. Active‐matrix field emission displays (AMFEDs) with these AMC plates were demonstrated in a vacuum chamber, showing low‐voltage matrix addressing, good stability and reliability of field emission, and highly uniform light emissions from the anode plate with phosphors. The optimum design of AMFEDs including a‐Si TFTs and a new light shield/focusing grid is discussed.