Patent Application
20070187245
1. Field of the Invention
The present invention relates to a method for fabricating a field emission display, especially to a method for fabricating nanotube electron emission source by scanning-matrix type electrophoresis deposition.
2. Description of Prior Art
The field emission display uses cathode electron emitter to generate electron by electrical field. The emitted electron excites phosphor on anode plate for illumination. The field emission display has compact size and flexible viewable area. The field emission display does not have view angle problem encountered in LCD.
Conventional triode field emission display includes an anode structure and a cathode structure. There is a spacer disposed between the anode structure and the cathode structure, thereby providing a space and a support for the vacuum region between the anode structure and the cathode structure. The anode structure includes an anode substrate, an anode conducting layer, and a phosphorus layer. The cathode structure includes a cathode substrate, a cathode conducting layer, an electron emission layer, a dielectric layer and a gate layer. The gate layer is provided a voltage difference to induce the emission of electrons from the electron emission layer. The conducting layer of the cathode structure provides a high voltage to accelerate the electron beam, such that the electron beam can have enough kinetic energy to impinge and excite the phosphorous layer on the anode structure, thereby emitting light. Accordingly, in order to maintain the movement of electrons in the field emission display, a vacuum apparatus is required to keep the vacuum degree of the display being below 10−5 torr. Therefore, the electrons can have appropriate mean free paths. Meanwhile, the pollution and toxication of the electron emission source and the phosphorous layer should be prevented from happening. Furthermore, in order for the electrons to accumulate enough energy to impinge the phosphorous powder, a space is required between the two substrates. Consequently, the electrons can be accelerated to impinge the phosphorous layer, thereby exciting the phosphorous layer and emitting light therefrom.
The electron emission layer is composed of carbon nanotubes. Since carbon nanotubes, proposed by Iijima in 1991 (Nature, 354, 56 (1991)), comprises very good electronic properties that can be used to build a variety of devices. The carbon nanotubes also has a very large aspect ratio, mostly larger than 500, and a very high rigidity of Young moduli larger than 1000 GPn. In addition, the tips or defects of the carbon nanotubes are of atomic scale. The properties described above are considered an ideal material for building electron field emitter, such as an electron emission source of a cathode structure of a field emission display. Since the carbon nanotubes comprise the physical properties described above, a variety of manufacturing process can be developed, e.g. screen printing, or thin film processing.
However, the art of manufacturing the cathode structure employs carbon nanotubes as an electron emission material, which is fabricated on the cathode conducting layer. The manufacturing process can employ chemical vapor deposition (CVD) process, or any kind of process that can pattern the photosensitive carbon nanotube solution on any pixel of the cathode conducting layer. Moreover, the cathode structure can also be manufactured by coating the carbon nanotubes solution while incorporating with a mask, or depositing the carbon nanotubes on the cathode conducting layer by an electrophoresis method. However, it is still difficult to fabricate nanotube in the cathode electrode in each pixel by above-mentioned processes. Especially for large-size FED display.
Recently, an electrophoresis deposition process is proposed, for example, US pre-grant publication No. 2003/0102222 discloses an electrophoresis deposition process. An alcohol suspension for nanotube is prepared and charger such as Mg, La, Y and Al is used to form an electrophoresis solution. The cathode electrode substrate to be deposited is connected to an electrode in the electrophoresis solution. A DC or AC voltage is applied to provide electrical field in the electrophoresis solution. The charger is dissolved in the electrophoresis solution and attached to the nanotube powder. The electrical field will facilitate the nanotube powder to deposit on an electrode. This electrophoresis deposition process can easily deposit the nanotube on the electrode layer without the limit of forming triode field emission display on electrode. Therefore, the electrophoresis deposition process is extensively used on the fabrication of cathode plate.
However, in prior art electrophoresis deposition process, a sacrifice layer (or protection layer) is formed for the gate electrode and dielectric layer to expose the patterned cathode area. whereby the nanotube is only deposited on the cathode electrode instead of gate electrode to prevent short circuit between the cathode electrode and the gate electrode. The sacrifice layer is removed after electrophoresis deposition process to removed unwanted nanotube. Moreover, Japan Patent No. 2001020093 discloses an electrophoresis deposition process, where bumps are formed in specific area of cathode and electrical field is provided between the bump and the anode. Therefore, the nanotube can be formed in the specific area and tends to concentrate on the electrode area. The applicant also provides an anode structure for ease patterning and the electrophoresis deposition can be concentrated.
The above-mentioned prior art provide anode (cathode) to form electrical field to confine the electrophoresis deposition area. However, precise calculation is needed. This will influence reliability of the electrophoresis deposition process. For high-resolution display panel, the unit electrophoresis area is smaller. The point-to-point electrical field is influenced by adjacent electrical field. The point-to-point electrical field in a matrix is difficult to achieve in electrophoresis deposition process.
The present invention is to provide a method for fabricating nanotube electron emission source by scanning-matrix type electrophoresis deposition. The electrophoresis deposition is performed in interleaving manner such that the electrophoresis deposition can be localized and the anode plate design can be simplified.
Accordingly, the present invention provides a method for fabricating nanotube electron emission source by scanning-matrix type electrophoresis deposition.
The anode ends of a power source are connected to anode strips of an anode plate. The cathode ends of the power source are connected to one input ends of signal amplifiers. The output ends of the signal amplifiers are connected to a plurality of cathode strips of a cathode plate. The anode strips are placed vertical to the cathode strips. A signal generator is connected to another input ends of the signal amplifiers. The anode plate and the cathode plate are placed parallel in the electrophoresis tank.
The voltage of the power source is output from anode ends of the power source to the anode strips. The signal generator sends pulse voltage signal to one of the signal amplifiers and amplified by the one of the signal amplifiers such that one of the cathode strip is conducted while the remaining cathode strips are not conducted, whereby only one electrical field is present for one pixel at one time and nanotube is formed at that pixel.
The next cathode strip is conducted successively and keeping the remaining cathode strips being non-conducted to fabricate nanotube electron emission source in scanning-matrix manner.
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:
With reference to
According to the method of the present invention, a cathode plate 1 is prepared with a rows (or 32 rows) of cathode strips 11 in longitudinal direction. The cathode strips 11 are already formed with gate and semi-finished sacrifice layer. The sacrifice layer is used to prevent unwanted deposition (such as gate, dielectric) on the non-electrophoresis deposition area. The sacrifice layer is removed after electrophoresis deposition process, Therefore, a×b (or 32×32) pixels can be provided on the semi-finished cathode plate 1.
Afterward, an anode plate 2 is provided, where a plurality of anode strips 21 is formed on an insulating plate in transverse direction and vertical to the cathode strips 11. Therefore, b columns (or 32 columns) of anode strips 21 can be provided for the cathode plate 1. The insulating plate can be a glass plate and the anode strips 21 can be formed by screen-printing or lithography.
A plurality of anode ends 31 of a scanning power source 3 is connected to each of the anode strips 21 to provide pulse voltage sequentially to the anode strips 21. A plurality of cathode ends 32 of a scanning power source 3 is connected to one end of signal amplifiers 4, and the signal amplifiers 4 are connected to the cathode strips 11. Another end of the signal amplifier 4 is connected to a signal generator 5. The scanning power source 3 provides sequential pulse voltage to the anode strips 21 and the signal generator 5 provides sequential signals to the cathode strips 11. The signal amplifier 4 provides signal amplification for the sequential signals of the signal generator 5.
With reference to
The cathode plate 1 and the anode plate 2 are placed in the electrophoresis tank 6 with 3-5 cm separation therebetween. The scanning power source 3 finishes a global area electrophoresis within a period of time, for example, within 1 second. Therefore scanning power source 3 sequentially sends pulse voltage of 120V to the anode strips 21 in the frequency of b or 32 Hz (duty=1/b or 1/32). The signal generator 5 sends a continuous square-wave signal to the signal amplifier 4. The signal amplifier 4 amplifies the continuous square-wave signal and sends the amplified continuous square-wave signal to the first one of the cathode strips 11, while the remaining cathode strips 11 are not conducted. Therefore, an electrical field is established between the first cathode strip 11 and the first anode strip 21 due to a potential difference. A nanotube can be fabricated on the position to be deposited with electron emission source on the first cathode strip 11. The remaining cathode strips 11 are conducted one by one and other cathode strips 11 are not conducted. In this manner, the electron emission source can be fabricated. The duty cycle for the cathode strips 11 are 1/a or 1/32 (frequency a or 32 Hz) or higher frequency. Therefore, the electrophoresis deposition is performed at the frequency of a×b (or 32×32). The electrophoresis deposition is 15 minutes and an electron emission source with 5-10 um thickness can be formed by one electrophoresis deposition operation.
The cathode strips 11a and the anode strips 21a are placed in the electrophoresis tank 6 with 3-5 cm separation therebetween and vertical to each other. The scanning power source 3a sends a lagged sequential signals to the anode strips 21a, where the sequential signal is pulse voltage signal of 120V. At the same time, the signal generator 5a generates a signal for outputting to the signal amplifiers 4a, where only one of the signal amplifiers 4a does not perform amplification and the remaining signal amplifiers 4a perform amplification. Therefore, the first cathode strip 11a is in low level while other cathode strips 11a are in high level, which level is the same as that of anode strips 21a. Therefore, nanotube will be formed on the first cathode strip 11a and can be formed on other cathode strips 11a successively.
To sum up, the scanning-matrix type electrophoresis deposition method according to the present invention has following advantages:
Although the present invention has been described with reference to the preferred embodiment thereof, it will be understood that the invention is not limited to the details thereof. 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.
