Seong-Deok Ahn

Characterizations of Fine-pitched Carbon Nanotube Pixels for Field Emitter Arrays

Fine-pitched carbon nanotube (CNT) pixels for field emitter arrays were patterned using a lift-off process. Compared with the conventional screen-printing method, this lift-off process provides a small feature size of 195 µm×80 µm pixels in emitter arrays. The field emission properties of patterned pixels are highly dependent on surface morphology. The buried carbon nanotubes from the surface barely contribute to field emission in a low electric field range. By using a proper formulation of carbon nanotube slurry for emitters in the patterning layer, we were able to obtain carbon nanotube pixels in which most of carbon nanotubes protruded from the surface layer of patterns after a final heat treatment, to burn out the organic binders at 300°C. Their turn-on field was determined to be less than 2.2 V/µm and the current density was 3.2 mA/cm2 at 3.7 V/µm. This lift-off process has the potential for use as an inexpensive patterning method for fine-pitched emitter array on a large substrate.

Surface Morphology Improvement of Metalorganic Chemical Vapor Deposition Al Films by Layered Deposition of Al and Ultrathin TiN

The surface morphology of aluminum (Al) films grown by metalorganic chemical vapor deposition (MOCVD) has been improved by inserting a 1.0-nm-thick titanium nitride (TiN) layer between 90-nm-thick Al layers. For multilayered Al/TiN film depositions, dimethylaluminum-hydride (DMAH) and tetrakis(dimethylamido)titanium (TDMAT) are used as metalorganic precursors. For uniform and conformal TiN layers 1.0-nm-thick atomic layer deposition (ALD) was carried out in the same reaction chamber as the Al MOCVD. The surface morphology of the films was evaluated by measuring the optical reflectance. In the early stage of Al MOCVD, the reflectance versus film thickness curve shows a rapid decrease because of the scattering of incident light from the Al nuclei, and then it increases sharply to a maximum reflectance until the completion of island coalescence. However, it monotonically decays again with Al thickness due to the nonuniform grain growth. By inserting a 1.0 nm TiN layer on the Al layer at the maximum reflectance, the reflectance is restored again to the peak reflectance in the manner of a sinusoid waveform. Moreover, the multilayered Al/TiN films have a strong (111) preferred crystal orientation, and small and uniformly sized Al grains, which are expected to result in higher electromigration resistance. Therefore, the combined deposition technique with Al MOCVD and TiN ALD is considered a promising candidate to make Al MOCVD suitable for future microelectronic applications.

Cross-sectional transmission electron microscopy of carbon nanotubes-catalyst-substrate heterostructure using a novel method for specimen preparation

We report on cross-sectional transmission electron microscope (TEM) observations using a novel TEM specimen preparation. The processes of the method are presented in detail. In this approach, carbon nanotubes (CNTs) can be conserved in the state in which they were correlated with the substrate during the growth. The results directly confirm that the CNTs grow in a base-growth mode. Chemical analyses on the cross-section of the structures were also carried out. A new type of bulk defect or void was observed for the first time.

Low-Voltage Operating Triode-Type Field Emission Displays Controlled by Amorphous-Silicon Thin-Film Transistors

Fully vacuum-sealed triode-type active-matrix field emission display (AMFED) having an active-matrix cathode on soda-lime glass substrate was designed and fabricated. Each pixel in the active-matrix cathode has the monolithically integrated structure of an amorphous–silicon thin-film transistor (a-Si TFT) and triode-type field emitter array with conical Mo-tips just on the drain of the a-Si TFT. Experimental data indicate that the emission currents of the fabricated active-matrix cathode could be successfully controlled by the a-Si TFT gate voltage. We demonstrated that an emitting image of a moving picture from the fully vacuum-sealed 2-inch AMFEDs could be achieved by switching the low bias-voltage of the a-Si TFT gate to a value below 25 V.

X-Ray Photoelectron Spectroscopy Studies of Titanium Nitride Barrier Metals Prepared by Low-Pressure Metalorganic Chemical Vapor Deposition.

Titanium nitride (TiN) films prepared by means of low-pressure metalorganic chemical vapor deposition (LP-MOCVD) with the tetrakis-dimethyl-amino titanium (TDMAT) and ammonia, attempting for producing conformal barrier metals for ultra-large scale integrated devices, are studied by means of X-ray photoelectron spectroscopy (XPS) in conjunction with Ar ion bombardment. In the detailed analysis of XPS spectra of the C 1 s region composed of two peaks corresponding to the chemical bondings of hydrocarbon and Ti-C, it is found that the relative intensity ratio between two peaks can be a direct measure of film properties, and that the chemical bonding of hydrocarbon dominates as the film thickness increases and the deposition temperature decreases.

Integration and characterization of amorphous silicon thin-film transistor and Mo-tips for active-matrix cathodes

We have designed and monolithically integrated amorphous silicon thin-film transistor (a-Si TFT) with Mo-tip field emitter arrays (FEAs) on glass substrate for active-matrix cathodes (AMCs) in field-emission display (FED) application. In our AMCs, a light shield layer of metal was introduced to reduce the photo leakage and back channel currents of a-Si TFT. The light shield was designed to have the role of focusing grid to focus emitted electron beams from the AMC on the corresponding anode pixel by forming it around the Mo-tip FEAs as well as above the a-Si TFT. The thin film depositions in a-Si TFTs were performed at a high temperature of above 360/spl deg/C to guarantee the postvacuum packaging process of cathode and anode plates in FED. Also, a novel wet etching process was developed for n/sup +/-doped-a-Si etching with high etch selectivity to intrinsic a-Si and good etch controllability and was used in the fabrication of inverted stagger TFT with a very thin active layer. The developed a-Si TFTs had good enough performance to be used as control devices for AMCs with Mo-tip emitters. The fabricated AMCs exhibited very effective aging process for field emitters.

Gated carbon nanotube emitters grown on silicon trench wells with a sidewall spacer for stable vacuum microwave devices

We present the gated carbon nanotubes (CNTs) emitters grown on silicon trench wells with a sidewall spacer for the application of vacuum microwave devices. The side wall spacer enables us to fabricate a highly stable gated CNT emitter. The developed CNT emitter can be. applicable. to the pre-bunched electron beam sources for microwave amplifier tubes.

Transparent Fingerprint Sensor System for Large Flat Panel Display

In this paper, we introduce a transparent fingerprint sensing system using a thin film transistor (TFT) sensor panel, based on a self-capacitive sensing scheme. An armorphousindium gallium zinc oxide (a-IGZO) TFT sensor array and associated custom Read-Out IC (ROIC) are implemented for the system. The sensor panel has a 200 × 200 pixel array and each pixel size is as small as 50 μm × 50 μm. The ROIC uses only eight analog front-end (AFE) amplifier stages along with a successive approximation analog-to-digital converter (SAR ADC). To get the fingerprint image data from the sensor array, the ROIC senses a capacitance, which is formed by a cover glass material between a human finger and an electrode of each pixel of the sensor array. Three methods are reviewed for estimating the self-capacitance. The measurement result demonstrates that the transparent fingerprint sensor system has an ability to differentiate a human finger’s ridges and valleys through the fingerprint sensor array.

Wireless Power Transmission to Organic Light Emitting Diode Lighting Panel with Magnetically Coupled Resonator

We are successful to lit the organic light emitting diode (OLED) lighting panel through the magnetically coupled wireless power transmission technology. For the wireless power transmission, we used the operation frequency 932 kHz, specially designed double spiral type transmitter, small and thin receiver on the four layered printed circuit board, and schottky diodes for the full bridge rectifier. Our white OLED is a hybrid type, in which phosphorescent and fluorescent organics are used together to generate stable white color. The total efficiency of power transmission is around 72%.

Effects of organic binders on field emission properties in patterned carbon nanotube pixels

We fabricated field emitter arrays on thin-metal electrodes by using carbon nanotube (CNT). The turn-on fields of CNT emitters patterned by photolithography and lift-off process were 4.2 V//spl mu/m and 2.2 V//spl mu/m, respectively. The lower turn-on field for the latter was due to the thinner residue covering the surface of CNT emitters after final heat treatment.