BRIEF DESCRIPTION OF THE DRAWINGS
The invention can be more fully understood by reading the subsequent detailed description and examples with references made to the accompanying drawings, wherein:
FIG. 1 is a cross section of a conventional field emission display device;
FIGS. 2A-2B are cross sections schematically illustrating a method for fabricating a FED device using an adhesive film attached to the field emitters of the lower substrate;
FIG. 3A is a cross section of a conventional method of laser activation to create carbon nanotube (CNT) emitters with uniform orientation;
FIG. 3B is a cross section of the field emission display device activated by laser treatment of FIG. 3A;
FIG. 4A is a fabrication flowchart of a FED panel according to an embodiment of the invention;
FIG. 4B is a flowchart showing the surface treatment and activation of FIG. 4A;
FIGS. 5A-5C are cross sections showing fabrication of a substrate structure for a field emission display (FED) device according to an embodiment of the invention;
FIGS. 6A-6B are schematic views illustrating free radical oxidization treatment and supercritical CO2 fluid treatment of the cathode substrate according to an embodiment of the invention; and
FIG. 7 is a cross section of a CNT-FED device according to an exemplary embodiment of the invention.
DETAILED DESCRIPTION OF THE INVENTION
The following description is of the mode of carrying out the invention. This description is made for the purpose of illustrating the general principles of the invention and should not be taken in a limiting sense. The scope of the invention is best determined by reference to the appended claims.
The invention is related to an FED panel and surface treatment methods thereof. The cathode substrate is activated by methods combining free radical oxidization and supercritical carbon dioxide fluid cleaning to improve uniformity and stability of the FED panel. A plurality of cathode substrates can be treated simultaneously to purify and modify surface properties of the field emitters without producing potential contaminants. Furthermore, surface properties of carbon nanotube powders can be modified according to a embodiment, thereby improving uniformity and stability of the FED panel.
FIG. 4A is a fabrication flowchart of a FED panel according to an embodiment of the invention. In step 310, a lower substrate of the FED panel is formed. In step 320, an upper substrate of the FED panel is formed. In step 330, the lower substrate and the upper substrate are assembled and sealed in a vacuum, thus the field emission display device is completed.
Step 310 of forming a lower substrate of the FED device comprises synthesizing field emitter powders (ex. CNT) (step 301) by, for example, arc discharge, chemical vapor deposition (CVD), or laser ablation. The field emitter powders are gathered in a container. The field emitter powders are mixed into a field emitter paste in step 303. Next, in step 304, a patterned cathode structure is formed by screen printing the field emitter paste on a substrate. Surface treatment and activation (step 305) are performed on the patterned cathode structure. The patterned cathode structure is sintered or fired (step 306) to complete the lower substrate of the field emission display (FED) device.
Step 320 of forming an upper substrate of the FED device comprises forming a conductive layer or electrode on a substrate (step 312). Next, in step 314, a patterned anode structure is formed on the substrate and sintered (step 316). A fluorescent layer is formed on the anode structure to complete the upper substrate of the field emission display (FED) device.
FIG. 4B is a flowchart showing the surface treatment and activation of FIG. 4A. The surface treatment and activation comprises loading a cathode structure substrate in a reaction chamber (step 410). Subsequently, a free radical oxidization surface treatment (step 420) is performed. The step of free radical oxidization surface treatment can optionally comprise UV treatment (425a), O3 treatment (425b), or UV/O3 treatment (425c). After the free radical oxidization surface treatment, the cathode structure substrate is transferred to a supercritical CO2 fluid reaction chamber in step 430. Subsequently, a supercritical CO2 fluid cleaning treatment is performed. The cathode structure substrate is loaded in a supercritical CO2 fluid reaction chamber. After the pressure and temperature of the supercritical CO2 fluid reaction chamber and addition ratio of the modifier are set, the supercritical CO2 fluid is conducted into the chamber to clean cathode structure substrate (steps 440 and 450). After the cleaning step is completed, the pressure and temperature of the reaction chamber are reduced followed by removal of the cathode structure substrate from the supercritical CO2 fluid reaction chamber (steps 460 and 470).
The physical properties of supercritical fluid are similar to transition between gas phase and liquid phase. The supercritical fluid exhibits low viscosity, high diffusion coefficient, and low surface tension similar to gas phase, but further high density like liquid phase. Chemical properties of the supercritical fluid differ from gas phase and liquid phase, such as the supercritical CO2 fluid, thereby becoming organically soluble. The organic solubility of the supercritical CO2 fluid depends on temperature and pressure of the supercritical fluid. The organic solute in the supercritical CO2 fluid is precipitated with temperature and pressure reduction, producing gas phase CO2 which is recyclable.
FIGS. 5A-5C are cross sections showing fabrication steps of a substrate structure for a field emission display (FED) device according to an embodiment of the invention. Referring to FIG. 5A, a substrate 510 such as a glass substrate or a flexible substrate is provided. A conductive layer 512 is formed on the substrate 510.
Referring to FIG. 5B, the conductive layer 512 is patterned into a cathode electrode pattern 513 and a gate line pattern 514 by, for example, lithography or etching. Alternatively, a patterned conductive layer 512 can be screen printed on the substrate 510.
Referring to FIG. 5C, a field emitter 515 is formed on the cathode electrode pattern 513 by, for example, carbon nanotube paste screen printing, completing fabrication of the substrate with cathode structure. Note that the formation of the field emitter 515 can optionally comprise screen printing, micro-contact printing, ink-jet printing, electrophoresis deposition (EPD), or chemical vapor deposition (CVD). Furthermore, the field emitter can comprise a carbon nanotube (CNT), a carbon nanofiber (CNF), graphite, palladium oxide (PdO), polysilicon, diamond film, or carbon nitride (CxNy).
FIGS. 6A-6B are schematic views illustrating free radical oxidization treatment and supercritical CO2 fluid treatment of the cathode substrate according to an embodiment of the invention. Referring to FIG. 6A, the cathode substrate for the FED device is irradiated by a UV light source with a wavelength in a range of 185-254 nm. Preferably, the wavelength of the UV light source is 185 nm or 254 nm in about 3 min. The distance between the cathode substrate and the UV light source is about 0.2 cm. Alternatively, O3 can be conducted into the process chamber during UV irradiation, or simply conduct O3 gas performing free radical oxidization.
Subsequently, referring to FIG. 6B, the cathode substrate for the FED device is transferred into a processing chamber 650 full of supercritical CO2 fluid 620. After gas phase to supercritical fluid phase transition, the supercritical CO2 fluid becomes organically soluble. Operating pressure of the supercritical CO2 fluid is preferably controlled at about 3000 psi, and that of the supercritical CO2 fluid is preferably controlled at about 50° C. The supercritical CO2 fluid cleaning lasts about 5 min. More preferably, an additional modifier such as 7% n-propanol can improve the cleaning capability of the supercritical CO2 fluid.
FIG. 7 is a cross section of a CNT-FED device according to an exemplary embodiment of the invention. In FIG. 7, a CNT-FED device 700 comprises a lower substrate 701 and an upper substrate 702. A wall structure 750 or a rib structure separates the lower and upper substrates by a predetermined gap G. The lower and upper substrates are sealed in a vacuum. The lower substrate 702 includes a patterned cathode structure 710. A CNT thick film 715 is disposed on the patterned cathode structure 710 to serve as a field emitter. A dielectric layer 720 surrounding the patterned cathode structure 710 is disposed on the lower substrate 702. A gate electrode 730 is disposed on the dielectric layer 720.
An anode electrode 706 is disposed on the upper substrate 702. Red, green, and blue fluorescent layers 775 are alternatively disposed on the anode electrode 706. A black matrix 770 is disposed between the red, green, and blue fluorescent layers 775.
The invention provides a surface treatment method comprising free radical oxidization and supercritical CO2 fluid cleaning. The surface treatment method is applicable with FED devices comprising a horizontal triode structure, a vertical triode structure, or an undergate triode structure. The disclosed treatment deeply cleans the field emitter without leaving impurities or contaminants, resulting in increased brightness and improved display uniformity.
While the invention has been described by way of example and in terms of the embodiment, it is to be understood that the invention is not limited thereto. To the contrary, it is intended to cover various modifications and similar arrangements (as would be apparent to those skilled in the art). Therefore, the scope of the appended claims should be accorded the broadest interpretation so as to encompass all such modifications and similar arrangements.
Patent Application
20080014821
