Patent Application
20070187246
1. Field of the Invention
The present invention relates to a field emission display, and more particular to an electrophoretic deposition technology for manufacturing electron field emitters for pixels by dot-matrix sequential electrophoretic carbon nanotubes.
2. Description of Prior Art
In a field emission display referred by this invention, an electric field is used for driving a cathode electron emitter to produce electrons, and the electrons excite phosphors of an anode plate, such that the phosphors produce photons to emit light. The field emission display has lightweight and thin features, and the size of an effective display area can be made according to the manufacturing process and product requirements. Furthermore, the field emission displays do not have the viewing angle issue occurred in the flat panel displays.
The structure of a prior art triode field emission display includes an anode plate, a cathode plate, and a spacer installed between the anode plate and the cathode plate for providing an interval with a vacuum area between the anode plate and the cathode plate as a support between the anode plate and the cathode plate. The anode plate includes an anode substrate, an anode conducting layer, and a phosphors layer, and the cathode plate includes a cathode substrate, a cathode conducting layer, an electron field transmitter layer, a dielectric layer, and a gate layer, wherein the gate layer provides a potential difference to draw electron emissions of the electron field transmitter layer, and the high voltage provided by the anode conducting layer accelerates the electron beams, so that the electrons have sufficient kinetic energy to impinge the phosphors layer on the anode plate to excite the phosphors to emit light. Thus, when the electrons are moving in the field emission display, it requires a vacuum equipment to maintain the display at a vacuum level lower than 10 to 5 torrs, such that the electrons can obtain a good mean free path, while avoiding contaminations and infections to the electron field transmitter and phosphors area To provide sufficient energy for electrons to impinge the phosphors, an appropriate gap is maintained between the two plates, so that the electrons can have enough space for their acceleration to impinge the phosphors and maximize the effect of producing lights.
The so-called electron field transmitter layer uses carbon nanotubes as its major components. Since carbon nanotube was introduced by Sumio Iijima in 1991 (Nature, Vol. 354, p 56 (1991)), the carbon nanotube has very high electronic characteristics and thus it is used extensively in various different electronic components, and the carbon nanotube comes with a high aspect ratio greater than 500 and a high rigidity with a Young's Modulus greater than 1000 GPn, and the tip or recession of the carbon nanotube is exposed at an atomic level. The aforementioned characteristics are considered ideal for being used as a material for making electron field transmitters, such as an electron field transmitter used for a cathode plate of a field emission display. Since carbon nanotubes have the aforementioned physical properties, therefore they can be designed for different manufacturing processes such as screen printing or thin film process and used for patterning electronic components.
In the so-called cathode plate manufacturing technology, the carbon nanotube is used as the material for making electron field transmitters and is manufactured on the cathode conducting layer, and the manufacturing method includes a chemical vapor deposition (CVD) to directly grow carbon nanotubes onto the cathode electrode layer of each cathode pixel, or uses a photosensitive carbon nanotube solution to be patterned onto the cathode conducting layer of each pixel, or coats a carbon nanotube solution accompanied with a masking process. However, the electron field transmitter structure of the foregoing triode field emission display adopts carbon nanotubes which are applied to the cathode electrode structure of each pixel, and such manufacturing process still has issues on its manufacturing costs and limitations on its three-dimensional structure, and more specifically it is difficult to achieve the evenness for large-size electron field transmitters.
Recently, a so-called electrophoretic deposition (EPD) technology disclosed in U.S. Pat. Publication No. 2003/0102222 prepares an alcohol suspension by employing carbon nanotubes and uses magnesium, lanthanum, yttrium, or aluminum ion salts as secondary salts (chargers) to produce the electrophoresis solution, and connects the cathode electrode with the electrophoresis solution for the electrophoretic deposition, such that an AD or DC voltage is supplied to form an electric field in the solution, and the ions in the secondary salt solution are attached on the carbon nanotube phosphors. The electrophoretic mobility produced by the electric field assists depositing the carbon nanotubes onto a specific electrode, so that the carbon nanotubes can be deposited and patterned onto the electrode. The aforementioned technology is called electrophoretic deposition technology, which can deposit carbon nanotubes onto an electrode layer easily, and also can avoid the limitation of the cathode structure on the triode field emission display, and thus this technology can be used extensively for manufacturing the cathode plate structure.
Since the prior art electrophoretic deposition can only deposit carbon nanotubes onto a cathode electrode without depositing the carbon nanotubes on the gates that will electrically connect the gates with the cathode electrode, therefore a sacrificial layer or a protective layer is usually installed between the gate and the dielectric layer to expose the patterned cathode electrode area before performing the electrophoretic deposition, and then the protective layer as well as any unnecessary carbon nanotubes remained in regions that do not require carbon nanotubes are removed to avoid improper electrical connections. Another prior art disclosed in Japan Pat. Publication No. 2001020093 forms a protrusion at the anode electrode corresponding to a specific region of the cathode in an electrophoresis. Since the protrusions form a specific electric field to the corresponding cathode electrode, the carbon nanotubes in the solution can be deposited in the specific region and the deposited carbon nanotubes can be centralized at the specific electrode layer region. A further prior art disclosed by the present inventor's previous patent application teaches a simple and easy way of making patterned electrophoresis anode structure to effectively centralize the electrophoretic deposition regions of an anode plate device.
Although the present electrophoretic deposition method limits and reduces the electrophoretic deposition area, yet the prior art also provides a voltage to the cathode plate and the anode plate to form an electric field, and thus a meticulous computation or design is required for producing the electric field to maximize the effective regions, or else a poor applicability for the high-resolution panels may result. The unit area of the electrophoresis region so produced will become smaller, and the point-to-point electric field so produced will be affected by the electric field in the neighborhood and thus making it difficult to achieve the expected effect. Although the point-to-point electrophoretic deposition technology is employed, an electric field is produced at the same time, so that the electric fields of adjacent pixels will interfere with each other easily, and the dot-matrix point-to-point electrophoretic deposition effect can no longer be maintained.
In view of the foregoing shortcomings of the prior art, the inventor of the present invention based on years of experience in the related industry to conduct experiments and modifications, and finally invented a method of manufacturing carbon nanotube electron field emitters by do-matrix sequential electrophoretic deposition
Therefore, the present invention is to provide an alternating electrophoretic deposition technology to improve the electrophoretic deposition effect on the regions of a dot-matrix structure, so that the electrophoresis time can be focused on the electrophoretic deposition of a pixel only to centralize the electrophoretic deposition region and simplify the design of the anode plate and the electric field produced by the electrophoresis. The invention enhances the current density used for the electrophoresis and greatly lowers the equipment cost and reduces the power consumption for manufacturing large panels, and the present invention also improves the operating safety.
Accordingly, a method of manufacturing carbon nanotube electron field emitters by do-matrix sequential electrophoretic deposition according to the invention comprises the following steps:
An anode of a power supply is connected to a plurality of anode electrodes of an anode plate and a cathode of a power supply is connected to a switch unit, and the switch unit is connected to a plurality of cathode electrodes of a cathode plate, and the plurality of cathode electrodes and the plurality of anode electrodes are perpendicular to each other, and a signal generator is connected to an input end of the plurality of switch units, and the cathode plate and the anode plate are parallel with each other and placed in an electrophoresis tank.
The anode of the power supply outputs a voltage to the plurality of anode electrodes of the anode plate, and the signal generator produces a pulse signal outputted to the plurality of switch units. During the electrophoretic deposition process, only one switch unit is electrically connected, and the rest of the switch units is electrically disconnected, and the electrically connected switch unit applies a pulse signal produced by the signal generator to a cathode electrode of the cathode plate, such that the cathode electrode is electrically connected, and only one pixel forms a potential different with an electric field between the electrically connected cathode electrode and anode electrode, and the cathode electrode forms carbon nanotubes disposed at positions for depositing an electron field transmitter.
When one of the electrically connected cathode electrodes of the cathode plate goes through the electrophoresis process, the electrically connected switch unit counts the time, so that if the time counted by the switch unit is up, the electric power supplied to the cathode electrode will be disconnected to allow the next switch unit to be connected electrically and the rest of the switch unit will remain disconnected, and such sequence will apply to the next cathode electrode for continuing the electrophoretic deposition process.
The features of the invention believed to be novel are set forth with particularity in the appended claims. The invention itself however may be best understood by reference to the following detailed description of the invention, which describes certain exemplary embodiments of the invention, taken in conjunction with the accompanying drawings in which:
The technical characteristics, features and advantages of the present invention will become apparent in the following detailed description of the preferred embodiments with reference to the accompanying drawings.
Referring to
In the manufacturing method, a cathode plate 1 is prepared first, and the cathode plate 1 has a or 32 pieces of longitudinally aligned cathode electrodes 11, and the plurality of cathode electrodes 11 are semi-finished structures with a finished gate and a manufactured sacrificial layer, and the sacrificial layer is intended for preventing sediments (such as gates and dielectric layers) remained on the regions without going through the electrophoretic deposition, and the film of the sacrificial layer is removed after the electrophoretic deposition process is completed, and a semi-finished substrate of the cathode plate 1 provides a×b or 32×32 pixels.
An anode plate 2 is prepared, and a plurality of anode electrodes 21 of the anode plate 2 are manufactured and disposed transversally on an insulating board and perpendicular to the plurality of cathode electrodes 11, and correspond to the pixels of b or 32 pieces of anode electrodes 21 provided by the cathode plate 2, wherein the insulating board could be a glass substrate having a plurality of anode electrodes 21 produced on the glass substrate by screen printing or lithography.
The plurality of anodes 31 of the scanning power supply 3 are connected to the plurality of anode electrodes 21 of the anode plate 2 for providing a pulse voltage to each anode electrode 21 sequentially, and the cathode 32 is connected to the input end of the plurality of switch units 4, and the output end of the switch unit 4 is connected to the plurality of cathode electrodes 11 of the cathode plate 1.
The aforementioned switch unit 4 is selected from either a timer or a timer operating with a switch, and the switch unit 4 has a timing function and its path can be set to be electrically connected or disconnected, and another input end of the switch unit 4 is connected to the output end of the signal generator 5 to complete the connections by the electrophoretic deposition, wherein the scanning power supply 3 provides a pulse voltage with a lag to each anode electrode 21 sequentially.
Referring to
The gap between the cathode plate 1 and the corresponding anode plate 2 is maintained at an interval of 3˜5 cm and placed in the electrophoresis tank 6, wherein the voltage of the scanning power supply 3 is supplied to complete a whole-area electrophoresis per cycle (such as a whole electrophoresis per second), and the scanning power supply 3 supplies a voltage to each of the plurality of anode electrodes 21 with a lag sequentially, and scans with a frequency b or 32 of each anode with a lag sequentially and each anode has a Duty=1/b or 1/32 of the positive pulse voltage 120V supplied to the plurality of anode electrodes 21a of the anode plate 2, and the signal generator 5 produces continuous square wave signals outputted to a plurality of switch units 4. By then, the first switch unit 4 is electrically connected, and the rest of the switch units 4 are electrically disconnected. The electrically connected switch unit 4 drives the signal generator 5 to generate square wave signals applied to the first cathode electrode 11. By then, the first cathode electrode 11 is electrically connected, and thus a potential difference of only one pixel of the first cathode electrode 11 and first anode electrode 21 is formed to produce an electric field signal during the electrophoresis period, so that a carbon nanotube is formed at a position for the cathode electrode 11 to deposit the electron field transmitter. During the electrophoretic deposition process, the first switch unit 4 counts the time synchronously. Once the time counted by a first switch unit is up, the switch unit 4 will stop timing, and will disconnect the electric power supplied to the first cathode electrode 11, so that the second switch unit 4 will be electrically connected and the rest of the switch units 4 will remain electrically disconnected. Such sequence will apply to the next cathode electrode 11 for continuing the electrophoretic deposition process, so as to complete the manufacture of the electron field transmitters of the cathode electrode 11. Each of the foregoing cathode electrodes 11 has a sequential change (or a higher frequency multiplication) with Duty= 1/32 or 1/a and sequentially scans with a lag for each cathode electrode 11 with a frequency equal to a or 32, and thus each pixel is scanned to perform an electrophoretic deposition with a frequency of a×b or 32×32 or its frequency multiplication, and the time for the electrophoresis counted by the switch unit 4 is set to 15 minutes, and each electrophoresis can produce an electron field transmitter structure with an even thickness of approximately 5˜10 um.
Referring to
The plurality of cathode electrodes 11a and anode electrodes 21a are perpendicular to each other and keep an interval of 3˜5 cm in between and these electrodes 1a, 21a are placed in the electrophoresis tank 6a. The scanning power supply 3a supplies electric power to each anode electrode 21a with a lag sequentially and scans each anode electrode 21a with a lag. The scanning power supply 3a provides a positive pulse voltage equal to 120V. By then, the signal generator 5a produces a signal outputted to the plurality of switch units 4a, wherein only the first switch unit 4a is electrically connected, and the rest of the switch units 4a remained electrically disconnected. Therefore, only one pixel forms a potential difference to produce an electric field between the first cathode electrode 11a and the first anode electrode 21a during the period of electrophoresis, so that the first cathode electrode 11a forms carbon nanotubes disposed at the positions for depositing an electron field transmitter, while the timer 41a of the switch unit 4a starts counting time. Once the time counted by the timer 41a is up, the switch 42a will immediately disconnect the power supplied to the first cathode electrode 11a, and allow the second switch unit 4a to be electrically connected and the rest of the switch units 4a remain electrically disconnected, so as to perform the electrophoretic deposition process for the next cathode electrode 11a sequentially, and scan the pixel of the next cathode electrode 11a sequentially.
In summation of the description above, the method of manufacturing carbon nanotube electron field emitters by do-matrix sequential electrophoretic deposition in accordance with the present invention has the following advantages:
1. The conducting wires on the electrodes of the cathode plate and the anode plate in the electrophoresis are installed alternately, so that the time of the electrophoresis focuses on a pixel for the electrophoretic deposition to centralize the electrophoretic deposition region.
2. The design of the invention provides a simpler and easier way to simplify the design of the anode plate in an electrophoresis. Unlike the complicated interactions of electric fields in the prior art, the electrophoresis process of the invention is simplified, such that the invention can produce a simplified electric field for the electrophoresis.
3. Since the electrophoresis gives better regions per unit area, and thus the current density for the electrophoresis is improved.
4. The current for a large-area electrophoresis is large, and thus the invention can lower the equipment cost, reduce the power consumption, and improve the operating safety.
The present invention is illustrated with reference to the preferred embodiment and not intended to limit the patent scope of the present invention. Various substitutions and modifications have suggested in the foregoing description, and other will occur to those of ordinary skill in the art. Therefore, all such substitutions and modifications are intended to be embraced within the scope of the invention as defined in the appended claims.
