Patent Application
20050231090
The present invention relates in general to a field-emission display and a method of fabricating the same, and more particular, to a method and a structure that introduce a fourth electrode (converging electrode) to a conventional triode field-emission display.
Flat panel displays such as field-emission display (FED), liquid crystal display (LCD), plasma display panel (PDP) and organic light emitting diode display (OLED) have become more and more popular in the market. Lighter and thin are the common features of flat panel displays. According to specific characteristics such as dimension and brightness, some of the above are suitable for small dimension display panel such as cellular phone and personal data assistant (PDA), some are suitable for medium or large size display such as the computer and television screens, or some are even suitable for ultra-large size display such as the outdoor display panel. The development trend of various displays is to obtain high image quality, large display area, low cost and long life time.
The field-emission display is a very newly developed technology. Being self-illuminant, such type of display does not require a back light source like the liquid crystal display. In addition to the better brightness, the viewing angle is broader, power consumption is lower, response speed is faster (no residual image), and the operation temperature range is larger. The image quality of the field-emission display is similar to that of the conventional cathode ray tube (CRT) display, while the dimension of the field-emission display is much thinner and lighter compared to the cathode ray tube display. Therefore, it is foreseeable that the field-emission display may replace the liquid crystal display in the market. Further, the fast growing nanotechnology enables nano-material to be applied in the field-emission display, such that the technology of field-emission display will be commercially available.
The conventional electron emission layer is typically in the form of a spike structure (as shown in
Recently, a carbon nanotube has been proposed by Iijima. Having high aspect ratio, high machine strength, high chemical resistance, abrasion resistance, low threshold electric field, the carbon nanotube has been popularly studied and applied as an electron emission source. As known in the art, the field electron emission is facilitated by applying a high electric field to a surface of a material to reduce the thickness of energy barrier of the material, such that electron can be ejected from the surface of the material to become a free electron according to quantum-mechanical tunneling effect. The current of the field electron emission can be increased by reducing the work function of the material surface. As the free electron is generated by the electric field, a heat source is not required, and the field electron emission apparatus is sometimes referred as a cold cathode.
The carbon nanotube has been continuously improved and applied to continuously enhance electron emission of a field-emission display. Currently, the carbon nanotube can be fabricated by a thick-film process (such as screen printing or spray printing). Referring to Chinese (Taiwanese) Patent Publication No. 502495, the carbon nanotube can be directly patterned on the cathode conductive layer 22 to form the electron emission layer 23 thereon. Thereby, the conventional triode field-emission display is not limited to the high-cost thin-film process. The carbon nanotube electron emission source provides a high electron emission efficiency (with a current density of 10 μA/cm2 and a threshold voltage of 1.5 V/μm, and a current density of 10 mA/cm2 under an electric field of 2.5 V/μm) which achieves perfect dynamic display effect with a lost cost driving circuit. Even so, each electron emission source unit is constructed of a plurality of carbon nanotubes, such that the electron beam generated thereby within the distance between the anode and the cathode is similar to that generated by the spike field-emission source. Therefore, the cross section of the collected electron beam 26 diverges while approaching the anode as shown in
To resolve the color purity or image resolution issue, the area of the electron emission source is reduced or partitioned into a plurality of smaller units, such that the electron beam 26 generated thereby is similar to the area of the corresponding phosphors layer 13 excited thereby. However, the reduction in cross section results in a lower efficiency of electron emission or reduced unit area of the corresponding phosphors layer 13, such that the space between neighboring phosphors layer 13 is increased, and the image resolution is degraded.
Another method to resolve the issue is to provide an adjustable voltage between the gate electrode 25 and the cathode conductive layer 22. In addition to electron drainage, the gate layer 25 can also control the cross section of the electron beam by adjusting the voltage. This type of design results in a lower efficiency of electron generation and a more complex circuit design. Further, the response time of the picture is increased, and the image quality is lowered.
The third method to resolve the above issue includes forming one or more than one set of control electrode between the cathode and the anode. The control gate provides a converging voltage or bias voltage to confine the cross section of the electron beam or deflect the electron beam, such that the electron beam can impinge the phosphors layer 13 at the predetermined position. However, such type of design requires complex fabrication process such as thin-film and lithography process and cannot meet with the requirement of large area display and mass production.
The present invention provides tetraode field-emission display and a method of fabricating the same. By disposing a gate layer and a converging electrode layer between an anode and a cathode, a tetraode structure is formed. The installation of the fourth electrode, that is, the converging electrode layer, the diverging range of the electron beam is effectively restricted. The cross section of the electron beam is thus effectively reduced to impinge on the phosphor layer at a predetermined location precisely without affecting the picture brightness, resolution and color purity. Further, the fabrication cost will not be increased.
The present invention also provides a tetraode field-emission display which includes a converging electrode layer formed by metal conductive plate and a gate electrode. The gate electrode and the converging electrode are disposed at two sides of the metal conductive layer to form a sandwich structure of mesh. The mesh can be fabricated by independent process and package with the anode plate in subsequent process. Therefore, the high cost of photolithography process and large thickness of the conventional structure are no longer required.
The present invention further provides a tetraode field-emission display and a method of fabricating the same. The fabrication process is much simpler, and such type of display can be fabricated by mass production.
The tetraode field-emission display provided by the present invention includes a mesh between an anode plate and a cathode plate. The mesh includes a sandwich structure of a gate layer and a converging electrode player formed on two opposing sides of an insulation layer. The mesh includes a plurality of apertures extending therethrough. Each of the apertures corresponds to a set of anode unit and cathode unit. The converging electrode layer of the mesh is facing the anode plate, such that the divergent range of the electron beam emitted by the electron emission source is restricted thereby.
These as well as other features of the present invention will become more apparent upon reference to the drawings therein:
Referring to
An equivalent isolation wall 44 or a spacer 34 is respectively installed between the cathode plate 40 and the gate layer 53, and the anode plate 30 and the converging electrode layer 51 to provide air conducting channel. In this embodiment, it is preferred to provide the isolation wall 44 between the cathode plate 40 and the gate layer 53 with the thickness about 10 μm to about 150 μm, for example. As shown, the isolation wall 44 is so positioned that the electron emission channel between the anode unit and the cathode unit will not be blocked thereby. Moreover, it is preferred to provide the spacer 34 between the converging electrode layer 51 and anode substrate 31.
The path of electron beam 6 is illustrated in
The method of fabricating the mesh 5 includes selecting a metal conductive plate that has a thermal expansion coefficient similar to that of the anode substrate 31 and the cathode substrate 41. For example, an iron, nickel and carbon composite plate with a thickness of about 150 μm and a thermal expansion coefficient of about 82×10−7 /° to about 86×10−7/° can be used as the metal conductive plate to prevent crack during vacuum package process due to thermal expansion difference. Laser or photolithography and etching process can be used for forming the apertures 54 through the metal conductive plate, such that the converging electrode layer 51 is formed. An insulation layer 52 is patterned or printed on one side of the converging electrode layer 51. For example, the glass coating paste DG001 produced by DuPond can be used to print the insulation layer 52 on the converging electrode layer 51. The thickness of the insulation layer 52 is preferably controlled between 10 and 100 μm. A conductive layer is then formed on the exposed side of the insulation layer 52 to serve as the gate layer 53. In this embodiment, silver conductive paste DC206 produced by DuPond can be used to print the gate layer 53 with a thickness controlled between 4 to 10 μm. Therefore, the mesh 5 is fabricated by independent process and applied to the display subsequently.
The apertures 54 can be configured with various shapes to obtain specific effect, for example, the inverse conical apertures 54′ as shown in
While an illustrative and presently preferred embodiment of the invention has been described in detail herein, it is to be understood that the inventive concepts may be otherwise variously embodied and employed and that the appended claims are intended to be construed to include such variations except insofar as limited by the prior art.
