KR20060121910A - Well formation - Google Patents

Abstract

Composition of carbon nanotubes (CNTs) are produced into inks that are dispensable via ink jet deposition processes. The CNT ink is dispensed into wells formed in a cathode structure.

Description

Well Formation {WELL FORMATION}

This patent application claims the priority of US Provisional Patent Application No. 60 / 50,454, filed September 12, 2003. This patent application is directed to United States Provisional Patent Application No. 60 / 343,642; 60 / 348,856; And US Patent Application No. 10 / 269,577, which claims priority of 60 / 369,794.

The present invention relates to the deposition of carbon nanotubes with CNT ink in well structures.

Cathode uniformity is an important factor in commercializing field emission displays (FED). Carbon nanotube (CNT) materials have high potential as cathode materials for future FEDs. Uniform and selective CNT deposition on a substrate over a large substrate is one of the major issues in the FED manufacturing process. A typical means of growing carbon nanotubes on a substrate is to use chemical vapor deposition (CVD) techniques using catalytic activation. This technique requires a relatively high growth temperature, which increases the manufacturing cost. It is difficult to achieve a film with uniformity over a large area. Other methods, such as screen-printing or dispensing, have been developed to deposit CNTs in paste or ink compositions. The composite consists of CNT powder mixed with conductive or non-conductive particles, in some cases carriers or vehicles and binders. The size and shape of the pattern formed by this technique is nonuniform from spot to spot resulting in a non-uniform effective emission area for each pixel or subpixel. In addition, edge ejection from printed or dispersed CNT composite inks or pastes commonly results in non-uniform performance of the CNT cathode, making the cathode manufacturing process unpredictable.

For FED applications, depositing the same amount of CNTs on each pixel or sub-pixel with a uniform effective emission area is a major goal of achieving a uniform emission current from each pixel or sub-pixel. In other words, ideally CNT deposition is the final step in the manufacture of the cathode, in particular the triode structure. Once the CNT cathode is provided, no additional wet etch process or etch process should be applied to the CNT cathode surface, which may degrade cathode performance.

For a clearer understanding of the invention, the present invention refers to the following detailed description taken in conjunction with the accompanying drawings.

1A is a side view of one embodiment of a well structure.

1B shows a well structure incorporating gate electrodes.

1C shows a metal grid electrode mounted after depositing CNTs in the wells.

2A shows a cathode electrode printed using a screen-printing process.

2B shows an insulator layer printed using a screen-printing process.

3A shows filling the wells with CNT ink.

3B shows the diffusion of CNT ink in the wells.

3C shows drying of the CNT ink.

4A shows one embodiment of a CNT ink inner well structure.

4B shows another embodiment of a CNT ink inner well structure.

5 shows a portion of a field emission display constructed in accordance with an embodiment of the invention.

6A illustrates a portion of a diode structure constructed in accordance with an embodiment of the invention.

6B shows a digital image of field emission from a cathode made using an embodiment of the present invention.

Figure 7 shows the I-V characteristics of the CNT ink prepared in accordance with an embodiment of the present invention.

In the following detailed description, various specific details are provided to aid the understanding of the present invention. However, those skilled in the art may implement the present invention without these specific details. For example, well-known circuits are shown in block diagram form in order not to obscure the present invention from unnecessary description.

Embodiments of the Invention A process for uniformly depositing CNTs in well structures as shown in FIG. 1A is provided. The well structure has four or more months (or one month in the case of round holes) to form a hole. Also, the well structure may be used as a gate, a triode structure in which a grid electrode is deposited on top of an insulator prior to CNT deposition (shown in FIG. 1B), or a metal grid is mounted after CNT deposition in the well (shown in FIG. 1C). being). The metal grid can be used to modulate the current from the CNT material located inside the well structure, as shown in FIG. 1C. These embodiments (FIGS. 1B and 1C) require a CNT material inside the well structure. Each well may correspond to a respective pixel or sub-pixel. In some cases, several well structures may be part of a pixel or sub-pixel from each other.

Well structures may be prepared using thick film processes for low-resolution applications such as screen printing (FIGS. 2A and 2B), or thin film processes for high-resolution well structures. The cathode electrode is printed using screen-printing. The conductive cathode electrode can be patterned on the substrate. The electrode line can be formed by etching a pattern from a thin film of conductive metal deposited on a substrate using various techniques available in the art (eg, evaporation, sputter, CVD, etc.). The etch pattern is formed using one of several lithography techniques (eg, optical lithography, e-beam lithography, embossing, etc.). Photo-active pastes such as DuPont Fodel ^™ can be used to form the cathode electrode. The insulator layer can be printed using screen-printing. In addition, the wall of the well structure may be printed using a dispersion (including ink jet printing) technique, or formed by sand or bead blasting techniques commonly used in the plasma display industry. Photo-active pastes such as DuPont Fodel ^™ can be used to form insulator wall structures. 2A and 2B show the fabrication of well structures. Various materials can be used for the substrate, including insulating materials (glass and ceramics), semiconductor materials (Si), or conductive materials (metal sheets or foils, pure metals or metal alloys), or combinations of these materials. Low cost glass substrates may be used in flat panel display applications.

Various methods may be used to fill well structures with CNT ink or paste composites such as ink-jet printing, screen-printing, dipping, painting, blushing, spraying and spin-coating. Using a dispersing or ink-jet printing process, the dispersing head is moved relative to the substrate and prepared to disperse one or more drops of ink or paste using a computer program before moving to the next spot to deposit more material. Located in position (see FIG. 3A). In the following description, Musashi SHOTmini ^™ is used and other dispersers or ink-jet dispersers may be used. Depending on the model and type of disperser used, it is necessary to adjust the formulation. Once the fluid CNT-ink is placed in the well structure, the bottom of the well structure can be completely covered through a wetting process (see FIG. 3B). After drying or curing of the ink or paste, the CNTs remain in the pixel wall (see FIG. 3C). This process may require a heating or UV (ultraviolet) curing step, depending on the CNT ink material used. As a result, CNTs are contained within the well structure. Well structures can be made accurately using printing or dispersing techniques or using sand or bead blasting processes. Once the well structure has been made correctly, uniform CNT deposition can be made for each pixel using the process disclosed above. In addition, the well structure effectively prevents edge emission problems that can lead to non-uniform performance. The shape of the well may define the shape of the CNT cathode and the effective emission area for each pixel or sub-pixel.

In filling the wells uniformly, it is important to provide a uniform CNT-ink or CNT-paste and to control the volume of ink or paste in the wells. Due to the hydrophilicity or hydrophobicity of the CNT ink or paste and the substrate or well structure surface, CNTs can be formed along the well in different shapes as shown in FIGS. 4A and 4B. 5 shows a vacuum sealed CNT field emission display configured as a well-forming process as disclosed herein. The side wall spacer (wall spacer) and the inner spacer maintain the gap between the anode plate (phosphor screen) and the cathode plate after the vacuum sealed display is evacuated. Different CNT-based inks with good field emission properties are developed according to the process (s) of the present invention. Dispersers, inkjet printers, screen-printers and the like and combinations thereof may be used to fill the wells with relatively accurate volumes of CNT-inks.

It is important that after the CNT ink is deposited to form the cathode structure, no further post-deposition process, such as removal of a sacrificial layer that may damage the CNT ink, is performed. This sacrificial layer is centrally disclosed in the process disclosed in US Pat. No. 6,705,910. Damage to CNT inks can adversely affect field emission performance.

Examples of suitable means for filling a CNT-ink into a well of a pixel include, but are not limited to, dispersion, inkjet printing, screen-printing, spin-on-coating, bushing, dipping, and the like, and combinations thereof.

The following examples are not intended to unduly limit the scope of the invention but are provided for further explanation of the invention. The following shows an exemplary formulation of CNT-inks that can be used in accordance with the process of the present invention, wherein the field emission properties are obtained in various formulations.

Sample 1 (CNT-Ink 1):

1) Source Material: Single Wall Carbon Nanotubes (SWNT) are obtained from Kentucky, Lexington, CarboLex Inc. SWNTs have a diameter range of 1 nm (nanometer) to 2 nm and a length in the range of 5 μm (micrometer) to 20 μm. Single month, double-month, or multi-month carbon nanotubes (MWNT) prepared by other vendors and by other means can be used with similar results.

Other components of the resulting composites are included in the inorganic adhesive material. This inorganic adhesive material is obtained from Cotronics Corp., Brooklyn, NY under the name / identification of Resbond 989, which is a mixture of Al ₂ O ₃ particles, water, and an inorganic adhesive. Composites such as SiO ₂ containing other particles can be used. Such particles may be insulating, conductive or semiconducting. The particle size is less than 50 μm. The carriers in Lesbond 989 are believed to be water, but other carrier materials may be used, which may be organic or inorganic materials. Other materials, such as binders (eg, alkali silicates or phosphates), which enhance other properties of the material, may be provided in the composite in small amounts.

2) Preparation and deposition of carbon nanotube mixture with Lesbond 989 on the substrate:

Polishing the mixture:

1 gram of CNT powder (40 wt%) and 1.5 grams of Lesbond (60 wt%) are injected together into the mortar. The mixture is ground using a pestle for at least 30 minutes so that the mixture looks like a gel, which means that the CNT and Al ₂ O ₃ particles do not separate from each other. Note that different weight ratios of CNT to Lesbond may be effective. In addition, water or other carrier materials may be added to the mixture and diluted to control viscosity. The mixture is then ready for deposition on the substrate.

Provision and curing of the mixture on the substrate:

Disperser (Model: SHOT mini ^™ ) manufactured by Musashi is used to deposit CNT ink mixtures into well structures. Other dispensing machines, including ink-jet methods, can be used. CNT materials are placed in each well structure by moving the dispersing head and / or substrate relative to each other and dispersing material dots at predetermined locations. The substrate is then dried at room temperature in air for about 10 minutes but may be dried (cured) in an oven at elevated temperature (above about 100 ° C.) to remove water more quickly. If a solvent is included in the organic material, a higher temperature may be set to remove the material. For example, it can be set up to 300 ° C. to remove the epoxy. The oven or curing vessel includes a vacuum pump to evacuate air from the oven and a vacuum is formed inside the oven during the drying / curing process. The oven or curing vessel may provide a gaseous environment or flow near the sample to further facilitate curing or drying. This gaseous environment or flow may or may not be partially or completely from an inert gas such as rare gas or nitrogen. Ultraviolet or infrared light may be used to assist the curing process. Surface activation processes (US Patent Application No. 10 / 269,577) can be applied to CNT cathodes to enhance field emission characteristics.

3) A sample is prepared for the next field emission test.

Sample 2 (CNT-Ink 1)

1) Purified 0.9 grams of single-month CNT from Iljin Nanotech Corp., Ltd., 5.7 grams of epoxy (ethylcellulose, 2- (2-butoxyethoxy) ethyl acetate, and 2- (2-butoxy) Ethoxy) ethanol), and 0.5 grams of glass frit are weighed and ground in mortar for 30 minutes using a pestle. Single month, dual month or multimonth CNT materials may be used and CNT materials from other vendors may be used.

2) Next 2 mL of thinner (terpineol) is added to the mortar. Other organic materials may also be used to control the viscosity of the CNT ink.

3) The resulting mixture is ground to mortar by hand for 30 minutes.

4) After grounding the mixture in mortar, a 3-roll mill is used immediately to further mix the paste that is formed for another 30 minutes. This process is used to uniformly disperse the mixture components and to provide a constant viscosity to the formed paste (CNT-Ink 2).

5) The CNT-Ink 2 formed is added to a syringe fixed to the Disperser (Musashi SHOTmini ^™ ) and ready for use.

Distributed process

The following describes a process for dispersing the CNT-ink of the present invention.

1) A reference substrate having the same thickness of the substrate to which the CNT-ink deposition of the present invention is preferably applied is used to detect whether the dot including the CNT-ink and the CNT-ink can be uniformly dispersed.

2) The spot size of the dispersed material comprising the CNT-ink depends on the viscosity, the disperser nozzle size and the gap (gap) between the nozzle and the substrate. The smaller the nozzle hole, the more sensitive the parameter of the gap between the nozzle and the substrate.

3) The disperser is programmed to adjust the substrate position and provide good alignment at the proper position (s).

4) Various programs are used for different dot patterns to fill the wells.

5) The dispersion volume of the CNT-ink can be adjusted by, for example, air pressure, spacing, suck-back vacuum, viscosity of the dispersion material, and the size of the nozzle aperture. The spacing and viscosity of the dispersing material are the most important parameters for constant dispersion because other parameters are easier to control. The spacing control depends on how the substrate planarization is made and the leveling of the X-Y table and may be precisely controlled by the height sensor.

Firing process

The following describes the firing process of the present invention provided for the removal of organic material from the CNT cathode of the present invention.

After the wells are filled, a firing process is required to remove organic material to the CNT cathode.

1) The substrate containing the CNT-ink of the present invention is baked in an oven at 100 ° C. for 10 minutes in air.

2) After baking, the substrate is placed in another nitrogen-flow oven for firing. First, the temperature is gradually increased to 315 ° C. (speed of 180 ° C./hour) and held at 315 ° C. for 10 minutes.

3) The temperature is then increased to 450 ° C. (same ramp rate of 180 ° C./hour) and fired at 450 ° C. for 10 minutes.

4) The temperature is gradually reduced to room temperature (same ramp rate of 180 ° C./hour), ie the substrate is cooled to room temperature.

Sample 3 (CNT-Ink 3)

1) 0.2 grams of CNT (single-month, purified from Iljin Nanotech Corp., Ltd.) is weighed using microbalance and placed in the jar. Single month, dual month or multi month CNT materials may be used or CNT materials from other vendors may be used.

2) 0.2 grams of aluminum oxide nanoparticles are added to the jar. The particle size is in the range of 0.01-0.02 μm.

3) 5 mL of thinner (terpineol) is added. Other organic materials may be used to adjust the viscosity of the CNT ink.

4) Using a stirrer, the CNTs, aluminum oxide nanoparticles, and terpineol mixture are stirred for 3 hours.

5) After stirring, a 3-roll mill is used immediately to uniformly disperse the mixture components and provide additional mixing for 30 minutes to provide a constant viscosity to the resulting mixture (CNT-ink 3).

6) The CNT-Ink 3 formed is added to a syringe fixed to the Disperser (Musashi SHOTmini ^™ ) and ready for use.

Baking process

The cathode formed by dispersing the CNT-ink, such as CNT-ink 3, is baked in an oven at 230 ° C. for 30 minutes in air. The thinner may be evaporated at 230 ° C. without any residue or residue.

Sample 4 (CNT-Ink 4)

1) 0.2 grams of CNTs are weighed using a microbalance and placed in a jar.

2) Next 0.2 grams of aluminum oxide nanoparticles are added to the jar. Particle sizes range from 0.01-0.02 μm.

3) Next 5 mL of thinner (terpineol) is added to the jar. Other organic materials may be used to control the viscosity of the CNT ink.

2135가 단지에 첨가된다. Kasil은 기판에 대한 잉크 접착력을 강화시키기 위해 사용된다. 포타슘 실리케이트와 같은 다른 무기 물질이 사용될 수도 있다.4) then 1mL Kasil

2135 is added to the jar. Kasil is used to enhance ink adhesion to the substrate. Other inorganic materials may also be used, such as potassium silicate.

5) Using a stirrer, a mixture of CNTs, aluminum oxide nanoparticles, Kasil and thinner is stirred for 3 hours.

6) After stirring, a 3-roll miller is used immediately to uniformly disperse the mixture components and further mix the formed ink for 30 minutes to provide a constant viscosity to the resulting mixture (CNT-ink 4).

7) The CNT-ink 4 formed is ready for use in screen-printing.

Baking process

The CNT cathode formed by screen printing is baked in an oven at 100-300 ° C. for 30 minutes in air. After baking, usually only the inorganic material remains in the cathode.

Field emission results

Cathodes provided with different CNT-inks of the present invention are tested using a diode configuration as shown in FIG. 6A. The spacer thickness between the cathode and the anode is about 0.5 mm. The cathode is an ITO glass coated with phosphor. The field emission image from the cathode (CNT-Ink 2) formed by filling the well structure using the process disclosed herein for CNT-Ink 2 is shown in FIG. 6B. 22 pixels are provided in the sample. 7 shows I-V curves from various cathodes formed by different CNT-inks prepared as disclosed above.

In summary, CNT-inks are used to fill wells of pixels using methods such as, but not limited to, dispersion or screen-printing methods. Using this self-filling process, a uniform cathode is formed over each of the pixels or sub-pixels. In addition, edge-emission can be reduced or erased.

Although the invention and its advantages have been described in detail, various changes, substitutions and substitutions may be made without departing from the scope and spirit of the invention as defined by the appended claims.

Claims (12)

A composition comprising carbon nanotubes and an inorganic adhesive. A composition comprising carbon nanotubes, epoxy, glass frit, and thinner. A composition comprising carbon nanotubes, aluminum oxide nanoparticles, thinner. The method of claim 2, Wherein said epoxy is selected from the group consisting of ethyl cellulose, 2- (2-butaoxyethoxy) ethyl acetate, 2- (2-butaoxyethoxy) ethanol, and combinations thereof. A process for preparing a composition comprising contacting carbon nanotubes, an inorganic adhesive, and water. Contacting carbon nanotubes, epoxy, glass frit, and thinner. Contacting carbon nanotubes, aluminum oxide nanoparticles, and thinner. A process for preparing a composition comprising carbon nanotubes, aluminum oxide nanoparticles, thinner, and kasil. The method according to any one of claims 5 to 8, And dispersing said composition. The method of claim 9, Wherein said dispersing comprises dispersing, screen-printing, ink-jet printing, dipping, painting, bushing, spin-coating, spraying, and combinations thereof. A process of depositing a carbon nanotube (CNT) ink composition in a well formed in a cathode structure, The post deposition process is not performed on the cathode structure following the deposition of the CNT ink like composition. The method of claim 11, And wherein said post-deposition process removes a layer of material from said cathode structure.

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