This application claims priority to and the benefit of Korean Patent Application No. 10-2004-0068520 filed on Aug. 30, 2004 in the Korean Intellectual Property Office, the entire content of which is incorporated herein by reference.
1. Field of the Invention
The present invention relates to an electron emission device, and in particular, to an electron emission device which has an improved structure of a focusing electrode for focusing electron beams and an insulating layer for supporting the focusing electrode, and a method of manufacturing the same.
2. Description of Related Art
Generally, electron emission devices are classified into a first type where a hot cathode is used as an electron emission source, and a second type where a cold cathode is used as the electron emission source.
Among the second type of electron emission devices there are known: a field emitter array (FEA) type, a surface conduction emission (SCE) type, a metal-insulator-metal (MIM) type, and a metal-insulator-semiconductor (MIS) type.
The FEA type electron emission device is based on the principle that when a material having a low work function or a high aspect ratio is used as the electron emission source, electrons are easily emitted from the material under a vacuum atmosphere due to an electric field. A sharp-pointed tip structure based on molybdenum (Mo) or silicon (Si), or a carbonaceous material, such as carbon nanotube, graphite and diamond-like carbon, has been developed to be used as the electron emission source.
The electron emission device using the cold cathode basically has first and second substrates forming a vacuum region, with electron emission regions formed on the first substrate together with driving electrodes for controlling the emission of electrons from the electron emission regions. Phosphor layers are formed on the second substrate together with an electron accelerating electrode for effectively accelerating the electrons emitted from the electron emission regions toward the phosphor layers, causing light emission or image display.
With the above-structured electron emission device, where the electrons emitted from the electron emission regions are migrated toward the second substrate while being widely diffused, the electrons hit the target phosphor layers as well as the neighboring incorrect phosphor layers, thereby deteriorating the screen color purity. Accordingly, approaches have been developed to induce the trajectory of electron beams to the target direction, and enhance the device characteristics.
In this regard, it has been proposed that a focusing electrode should be introduced to control the electron beams. The focusing electrode is usually placed at the topmost area of the electron emission structure while surrounding the electron emission regions. An insulating layer is disposed between the driving electrodes and the focusing electrode to prevent an electrical short circuit between the driving electrodes and the focusing electrode. Furthermore, the insulating layer spaces the focusing electrode from the electron emission regions with a predetermined height. Opening portions are formed at the insulating layer and the focusing electrode while exposing the electron emission regions on the first substrate, thereby allowing the passage of electron beams.
A wet etching is mainly used to form opening portions at the insulating layer. The wet etching, where the target to be etched is dipped in an etching solution, involves an isotropic etching characteristic. Greater the depth of the insulating layer to be etched is, the opening width becomes enlarged. Accordingly, it is difficult with the wet etching process to form opening portions with a high vertical to horizontal ratio.
With the known FEA type electron emission device, electron emission regions are formed on the cathode electrodes, and a first insulating layer and gate electrodes are formed on the cathode electrodes with opening portions exposing the electron emission regions. A second insulating layer and a focusing electrode are formed on the first insulating layer and the gate electrodes. In this case, when the second insulating layer and the first insulating layer are sequentially etched to form opening portions at the respective insulating layers, the second insulating layer is continuously etched even after the formation of the opening portions thereof until the opening portions of the first insulating layer are formed.
Consequently, the opening portion of the second insulating layer is larger in width than that of the first insulating layer, and, as such, the opening portion of the focusing electrode is larger in width than that of the gate electrode. With this structure, the focusing electrode is placed apart from the trajectory of electron beams, and hence, the electron beam focusing efficiency is deteriorated.
Furthermore, as the focusing electrode is placed at the plane higher than the electron emission region, the electron beam focusing efficiency becomes enhanced. However, since it is difficult to form opening portions with a high vertical to horizontal ratio at the second insulating layer, there is a limit to increasing the height of the focusing electrode.
In one exemplary embodiment of the present invention, there is provided an electron emission device which has a focusing electrode placed closer to the trajectory of electron beams to enhance the electron beam focusing efficiency, and displays a high resolution screen image by forming opening portions with a high vertical to horizontal ratio at an insulating layer for supporting the focusing electrode, and a method of manufacturing the same.
In an exemplary embodiment of the present invention, the electron emission device includes a substrate, cathode electrodes formed on the substrate, and electron emission regions electrically connected to the cathode electrodes. Gate electrodes are formed over the cathode electrodes while interposing a first insulating layer. The gate electrodes have a plurality of opening portions exposing the electron emission regions on the substrate. A focusing electrode is formed over the first insulating layer and the gate electrodes while interposing a second insulating layer. The focusing electrode has opening portions corresponding to the opening portions of the gate electrodes with a size smaller than that of the latter.
In another exemplary embodiment of the present invention, the electron emission device includes first and second substrates facing each other, cathode electrodes formed on the first substrate, and electron emission regions electrically connected to the cathode electrodes. Gate electrodes are formed over the cathode electrodes while interposing an insulating layer. The gate electrodes have a plurality of opening portions exposing the electron emission regions on the first substrate. A grid electrode is disposed between the first and the second substrates while being spaced apart from the first and the second substrates with a predetermined distance. The grid electrode has opening portions corresponding to the opening portions of the gate electrodes with a size smaller than that of the latter.
In a method of fabricating the electron emission device, cathode electrodes, a first insulating layer and gate electrodes are sequentially formed on a substrate. Opening portions are formed at the gate electrodes and the first insulating layer. A second insulating layer is formed by depositing two or more different kinds of insulating layers on the first insulating layer and the gate electrodes. The deposition is sequentially made from the insulating layer having a high etching rate with respect to an etching solution to the insulating layer having a low etching rate. A focusing electrode is formed on the second insulating layer, and opening portions are formed at the focusing electrode with a size smaller than the size of the opening portions of the gate electrodes. Opening portions are formed at the second insulating layer by etching the portions of the second insulating layer exposed through the opening portions of the focusing electrode. The opening portions of the second insulating layer are gradually enlarged in width as they proceed toward the substrate.
Referring now to
Specifically, cathode electrodes 6 are stripe-patterned on the first substrate 2 in a direction of the first substrate 2 (in the y axis direction). A first insulating layer 8 is formed on the entire surface of the first substrate 2 while covering the cathode electrodes 6. Gate electrodes 10 are stripe-patterned on the first insulating layer 8 while proceeding substantially perpendicular to the cathode electrodes 6 (in the x axis direction).
When the crossed regions of the cathode and the gate electrodes 6, 10 are defined as the pixel regions, at least one electron emission region 12 is formed on the cathode electrode 10 per the respective pixel regions. Opening portions 8a, 1Oa are formed at the first insulating layer 8 and the gate electrodes 10 corresponding to the electron emission regions 12 while exposing the electron emission regions 12 on the first substrate 2.
The electron emission regions 12 are formed with a material capable of emitting electrons when applied with an electric field under a vacuum atmosphere, such as a carbonaceous material and a nanometer-sized material. The electron emission regions 12 may be formed with carbon nanotube, graphite, graphite nanofiber, diamond, diamond-like carbon, C60, silicon nanowire, or a combination thereof.
A second insulating layer 14 and a focusing electrode 16 are formed on the gate electrodes 10 and the first insulating layer 8. Opening portions 14a, 16a are formed at the second insulating layer 14 and the focusing electrode 16 while exposing the electron emission regions 12 on the first substrate 2. The opening portions 16a of the focusing electrode 16 are in one to one correspondence with the electron emission regions 12 to surround the trajectory of the electron beams emitted from the respective electron emission regions 12 and increase the efficiency of focusing the electron beams.
It is illustrated in the drawings that the focusing electrode 16 is formed over the entire surface of the first substrate 2, but the focusing electrode 16 may be patterned with a plurality of portions. Furthermore, the focusing electrode 16 may be formed with a metallic layer through deposition, or with a thin metal plate having opening portions 16a formed through mechanical processing or etching.
In this embodiment, the focusing electrode 16 has opening portions 16a smaller than the opening portions 10a of the gate electrodes 10 to reduce the diameter of the electron beams passing through it. The second insulating layer 14 has a thickness larger than that of the first insulating layer 8 such that the focusing electrode 16 is placed at the plane higher than the electron emission regions 12.
The opening portion 16a of the focusing electrode 16 has a width as large as or larger than that of the electron emission region 12.
The opening portion 14a of the second insulating layer 14 is gradually reduced in width from the bottom surface thereof facing the gate electrodes 10 toward the top surface thereof overlaid with the focusing electrode 16. With the sectional view of the electron emission device, the opening portion 14a of the second insulating layer 14 is formed with an inclined sidewall having a predetermined inclination. The second insulating layer 14 stably supports the whole structure of the focusing electrode 16 to thereby increase the stability of the electron emission structure.
The second insulating layer 14 may have a multi-layered structure with different kinds of insulating layers involving different etching rates with respect to an etching solution. That is, the second insulating layer 14 may be of two or more layers. As shown in the embodiment of
In this embodiment, the opening portion of the second insulating layer 14 is shaped as an inverted funnel such that the width thereof is narrowed as it goes apart from the first substrate 2. The focusing electrode 16 is formed on the second insulating layer 14 with opening portions 16a being smaller in width than the corresponding opening portions 10a of the gate electrodes 10. In such a structure, the electrons travel straightly while passing through the opening portions 16a of the focusing electrode 16, and the focusing electrode 16 is placed closer to the trajectory of electron beams, thereby enhancing the efficiency of focusing the electron beams.
Referring now to
Referring now back to
An anode electrode 26 is formed on the phosphor layers 22 and the black layers 24 with a metallic material, such as aluminum. The anode electrode 26 receives a high voltage required for accelerating the electron beams, and reflects the visible rays radiated toward the first substrate 2 from the phosphor layers 22 to the side of the second substrate 4, thereby increasing the screen luminance.
The anode electrode may be formed with a transparent conductive material, such as indium tin oxide (ITO). In this case, the anode electrode is placed on the surface of the phosphor and the black layers directed toward the second substrate. The anode electrode may be patterned with a plurality of portions.
Spacers 28 are arranged between the first and the second substrates 2, 4, and the first and the second substrates 2, 4 are attached to each other at their peripheries using a low melting point glass, such as a glass frit. The inner space between the first and the second substrates 2, 4 is evacuated to be in a vacuum state, thereby constructing an electron emission device. The spacers 28 are arranged at the non-light emission area where the black layers 24 are placed.
The above-structured electron emission device is driven by applying predetermined voltages to the cathode electrodes 6, the gate electrodes 10, the focusing electrode 16 and the anode electrode 26. For instance, driving voltages with a voltage difference of several to several tens volts are applied to the cathode and the gate electrodes 6, 10, and a minus (−) voltage of several tens volts to the focusing electrode 16, whereas a plus (+) voltage of several hundreds to several thousands volts is applied to the anode electrode 26.
Accordingly, an electric field is formed around the electron emission regions 12 at the pixels where the voltage difference between the cathode and the gate electrodes 6, 10 exceeds a threshold value, and electrons are emitted from the electron emission regions 12. The emitted electrons are focused by the voltage applied to the focusing electrode 16 such that the diffusion angle thereof is reduced, and attracted by the high voltage applied to the anode electrode 26. The electrons are directed toward the second substrate 4, and collide against the corresponding phosphor layers 22, thereby causing light to be emitted from them.
In the above process, the electrons travel with excellent straightness while passing through the opening portions 16a of the focusing electrode 16 due to the reduced size thereof. The focusing electrode 16 is placed close to the trajectory of electron beams, thereby increasing the efficiency of focusing the electron beams.
Turning now to
Referring now to
The grid electrode 30 is disposed between the first and the second substrates 2, 4 while being spaced apart from them at a predetermined distance by upper and lower spacers 32, 34. Opening portions 30a are formed at the grid electrode 30 corresponding to the opening portions 10a of the gate electrodes 10 with a size smaller than the latter. The electron beam focusing effect due to the reduced size of the opening portions 30a of the grid electrode 30 is comparable to that of the previous embodiment, and hence, detailed explanation thereof will be omitted.
A method of manufacturing the electron emission device according to the first embodiment of the present invention will be now explained with reference to
As shown in
A conductive film is coated onto the first insulating layer 8, and patterned, thereby forming gate electrodes 10 proceeding perpendicular to the cathode electrodes 6, and forming opening portions 10a at the crossed regions thereof with the cathode electrodes 6.
As shown in
As shown in
When the sacrificial layer 38 is used to form the electron emission regions 12, the extension of the electron emission regions 12 over the cathode and the gate electrodes 6, 10 is inhibited to thereby prevent a possible short circuit between the two electrodes. The method of forming the electron emission regions 12 is not limited to the above.
As shown in
As shown in
As shown in
The portions of the second insulating layer 14 exposed through the opening portions 16a of the focusing electrode 16 are etched using an etching solution. Consequently, the opening portion formed at the insulating layer placed apart from the focusing electrode 16 has a width larger than that of the opening portion formed at the insulating layer placed close to the focusing electrode 16 such that the opening portions 14a of the second insulating layer 14 are shaped as an inverted funnel. The protective layer 42 covering the electron emission regions 12 is removed to thereby complete the electron emission structure shown in
The first substrate 2 with the above-described electron emission structure and the second substrate 4 with phosphor layers 22, black layers 24 and an anode electrode 26 are assembled in a body, and the inner space between the substrates 2, 4 is exhausted to thereby construct an electron emission device.
Although exemplary embodiments of the present invention have been described in detail hereinabove, it should be clearly understood that many variations and/or modifications of the basic inventive concept herein taught which may appear to those skilled in the art will still fall within the spirit and scope of the present invention, as defined in the appended claims.
Number | Date | Country | Kind |
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10-2004-0068520 | Aug 2004 | KR | national |