Electron emission device and electron emission display having beam-focusing structure using insulating layer

An electron emission device and/or display using the same includes a beam-focusing structure. The beam-focusing structure has a first insulating layer formed on a plate. The first insulating layer has a thickness, and is formed with a first hole. A first electrode is formed on the first insulating layer and extending into the first hole. An emission portion is formed in the first hole and connected to the first electrode. A second insulating layer is formed on the first electrode and is also formed with a second hole through which the emission portion is at least partially exposed. A second electrode is formed on the second insulating layer. In the electron emission device and/or the display, an electric field between the first electrode and the second electrode causes the emission portion to emit an electron beam and focuses the electron beam from the emission portion.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to and the benefit of Korean Patent Application No. 10-2004-0037549, filed May 25, 2004 in the Korean Intellectual Property Office, the entire content of which is incorporated herein by reference.

BACKGROUND

1. Field of the Invention

The present invention relates to an electron emission device, and more particularly, to an electron emission device and an electron emission display having a beam-focusing structure using an insulating layer.

2. Discussion of Related Art

Generally, an electron emission device can be classified into a hot cathode-type and a cold cathode-type. The hot cathode-type and the cold cathode-type employ a hot cathode and a cold cathode as an electron emission portion, respectively.

Also, a cold cathode-type electron emission device can have a structure such as a field emitter array (FEA), a surface conduction emitter (SCE), a metal insulator metal (MIM), a metal insulator semiconductor (MIS), a ballistic electron surface emitting (BSE), etc.

The electron emission device having the FEA structure is based on a principle that when a material having a low work function and/or a high beta(β)-function is used as an electron emission portion in a vacuum, electrons are easily emitted from the material due to an electric field difference. Such electron emission device having the FEA structure employs a tip structure mainly containing molybdenum (Mo), silicon (Si), a carbon material (e.g., graphite, diamond-like carbon (DLC), etc.), and/or a nano material (e.g., a nanotube, a nanowire, etc.) as the electron emission portion.

The electron emission device having the SCE structure is provided with an electron emission part in which a first electrode and a second electrode opposing each other are formed on a first plate, and a conductive layer is formed between the first electrode and the second electrode. The conductive layer is formed with a minute crack or gap, thereby forming the electron emission part. Such electron emission device is based on a principle that the electron emission part formed by the minute crack or gap emits electrons when electric current flows through a surface of the conductive layer by applying voltage to the first and second electrodes.

The electron emission device having the MIM or MIS structure includes an electron emission portion having a metal-insulator-metal structure or a metal-insulator-semiconductor structure, and is based on a principle that electrons are emitted from the metal or the semiconductor of high-electric potential to the metal of low-electric potential when a voltage is applied between the metal and the metal or between the metal and the semiconductor.

The electron emission device having the BSE structure is based on a principle that electrons travel without sputtering when the size of a semiconductor is smaller than a mean free path of the electrons contained in the semiconductor. Such electron emission device includes an electron supplying layer made of a metal or a semiconductor and formed on an ohmic electrode, an insulator formed on the electron supplying layer, and a thin metal layer formed on the insulator, so that the electrons are emitted when a voltage is applied between the ohmic electrode and the thin metal layer.

The foregoing electron emission devices are employed in electron emission displays, backlights, lithography electron beams, etc.

In the aforementioned electron emission devices, the electron beam emitted from the electron emission portion spreads in a voltage-applied direction. Therefore, there is a need for a focusing electrode to focus the electron beam. An example of an electron emission device with the focusing electrode is disclosed in Korean Patent Publication No. 2002-32208. Hereinafter, the conventional electron emission device with the focusing electrode will be described with reference toFIGS. 1 and 2.

FIG. 1is a schematic plan view of a conventional electron emission device with a horizontal focusing electrode.

As shown therein, the conventional electron emission device includes a plurality of micro-tips1respectively formed inside a plurality of gate holes2, a gate electrode3formed above the micro-tips1and determining an emitting direction of electrons emitted from each micro-tip1, and a focusing electrode4to focus the electrons emitted from the micro-tips1.

In the conventional electron emission device, to enhance a focusing effect, a distance between at least one of the micro-tips1used as an emitter and the gate electrode3should be short, and, at the same time, a distance between the gate electrode3and the focusing electrode4should also be short. Because of this, the fabricating process for the conventional electron emission device is difficult. Also, when the focusing electrode4is horizontally arranged, the number of emitters per unit surface area is limited.

FIG. 2is a sectional view of a conventional electron emission device with a vertical focusing electrode.

As shown inFIG. 2, the conventional electron emission device includes a plate202, a first insulator203, a gate electrode204, an emitter205, a cold cathode206, a second insulator207, a focusing electrode208and a metal mesh210. In this electron emission device, in order to focus an electron beam from the emitter205, a voltage of −40V is applied to the focusing electrode208and a voltage of 80V is applied to the gate electrode204. Here, the voltage applied to the gate electrode204serves to control the amount of beam current.

Such conventional electron emission device with the vertical focusing electrode is excellent in focusing the electron beam, but has a complicated fabricating process because the insulator formed on the gate electrode should be thick with a thickness of a few μm to a few hundreds μm, thereby lowering a yield thereof.

SUMMARY OF THE INVENTION

Accordingly, it is an aspect of the present invention to provide an electron emission device and an electron emission display having a beam-focusing structure using an insulating layer, which is not only excellent in focusing an electron beam but also has a simple fabricating process.

Another aspect of the present invention is to provide an electron emission device and an electron emission display using the same in which the electron emission device is fabricated by a simple, low-cost process, and is improved in focusing efficiency.

In one embodiment of the present invention, an electron emission device includes: a first insulating layer formed on a plate, having a predetermined thickness, and formed with a first hole; a first electrode formed on the first insulating layer and extending into the first hole; an electron emission portion located in the first hole and connected to the first electrode; a second insulating layer formed on the first electrode and formed with a second hole through which the electron emission portion is at least partially exposed; and a second electrode formed on the second insulating layer, wherein an electric field between the first electrode and the second electrode causes the electron emission portion to emit an electron beam and focuses the electron beam from the electron emission portion.

In one embodiment of the present invention, an electron emission display includes: first and second plates opposing each other, and having a space therebetween; a first insulating layer formed on the first plate, having a predetermined thickness, and formed with a first hole; a cathode electrode formed on the first insulating layer and extended into the first hole; an electron emission portion located in the first hole and connected to the cathode electrode; a second insulating layer formed on the cathode electrode and formed with a second hole through which the electron emission portion is at least partially exposed; a gate electrode formed on the second insulating layer; and a display part formed on the second plate and displaying a picture based on electrons emitted from the electron emission structure, wherein an electric field between the cathode electrode and the gate electrode causes the electron emission portion to emit an electron beam and focuses the electron beam from the electron emission portion.

According to an embodiment of the invention, the thickness of the first insulating layer ranges from about four to six times larger than the thickness of the electron emission portion. Here, the thickness of the first insulating layer can be increased in proportion to a distance between the electron emission portion and an inner wall of the first hole.

According to an embodiment of the invention, the first electrode (or the cathode electrode) is formed on the inner wall of the first hole and surrounds the electron emission portion.

According to an embodiment of the invention, the first insulating layer and the second insulating layer differ in their etching rates. Thus, the inner wall of the first hole is formed substantially perpendicular onto the plate, and an inner wall of the second hole slopes with respect to the plate.

According to an embodiment of the invention, the electron emission portion includes a nanotube material, a carbon nanotube (CNT) material, a nanowire material, a fullerene (C60) material, a diamond-like carbon (DLC) material, and/or a graphite material.

According to an embodiment of the invention, the cathode includes an indium tin oxide (ITO) material.

According to an embodiment of the invention, the display part includes a fluorescent layer formed on the second plate, and a thin metal film formed on the fluorescent layer. Alternatively, the display part includes a transparent electrode formed on the second plate, and a fluorescent layer formed on the transparent electrode. Further, the display part additionally includes a thin metal film formed on the fluorescent layer. Additionally, the display part additionally includes a dark region formed between the fluorescent layers.

According to an embodiment of the present invention, the electron emission display further includes a grid electrode provided between the first plate and the second plate and formed with a plurality of holes through which the electrons pass.

DETAILED DESCRIPTION

In the following detailed description, exemplary embodiments of the present invention are shown and described by way of illustration. Accordingly, the drawings and description are to be regarded as illustrative in nature, and not restrictive.

FIG. 3is a sectional view of an electron emission device having a beam-focusing structure according to an embodiment of the present invention.

Referring toFIG. 3, an electron emission device300includes a plate302, a first insulating layer304, a cathode electrode306, a second insulating layer308, a gate electrode310, and an electron emission portion320. The plate302may be formed of a transparent plate such as a vitreous plate.

The first insulating layer304is made of insulating material having a first etching rate and formed on the plate302. The first insulating layer304is formed with a first hole through which the plate302or a buffer layer (not shown) on the plate302, to be formed with the electron emission portion320, are exposed. An inner wall of the first hole is substantially perpendicular to a surface of the plate302. The thickness T1of the first insulating layer304is approximately four to six times larger than the thickness of the electron emission portion320. For example, in the case where the electron emission portion320has a thickness of about 2 μm, the first insulating layer304should have a thickness of about 10 μm.

The cathode electrode306may be made of transparent conductive material such as indium tin oxide (ITO) and formed on the first insulating layer304. The cathode electrode306extends to an inside of the first hole. In the first hole, the cathode electrode306is connected to the electron emission portion320. At this time, the cathode electrode306is connected to the electron emission portion320, covering the whole bottom area of the first hole or covering the inner wall and a portion of the bottom area of the first hole.

The second insulating layer308is made of insulating material having a second etching rate and is formed on the cathode electrode306. The second insulating layer308is formed with a second hole through which the cathode electrode306, at an area to be formed with the electron emission portion320, is exposed. An inner wall of the second hole slopes to cover a portion of the cathode electrode306formed on the inner wall of the first hole. The thickness T2of the second insulating layer308is appropriately selected in consideration of a breakdown voltage between the cathode electrode306and the gate electrode310. Further, the thickness of the second insulating layer308is appropriately selected in consideration of the thickness of the electron emission portion320and a space between the gate electrode310and the electron emission portion320. For example, in the case where the cathode electrode306is applied with a voltage of −80V and the gate electrode310is applied with a voltage of 70V, the second insulating layer308should have a thickness of about 15 μm. However, the thickness of the second insulating layer may vary according to the type and the characteristics of the insulating material.

The gate electrode310is formed on the second insulating layer308in a predetermined pattern. The gate electrode310is disposed for easily inducing the electron emission portion320to emit electrons.

The electron emission portion320is formed in the first hole and the second hole superposed on the first hole and is connected to the cathode electrode306. For example, the electron emission portion320is directly formed on the plate302and connected with the cathode electrode306on at least one side. InFIG. 3, the portion of the cathode electrode306surrounding the electron emission portion320in the first hole is relatively high, thereby enhancing a beam-focusing effect. Alternatively, the electron emission portion320can be formed on the cathode electrode306. The electron emission portion320can be made of nanotube (e.g., carbon nanotube (CNT)), nanowire, fullerene (C60), diamond-like carbon (DLC), and/or graphite materials.

As described above, the electron emission device ofFIG. 3according to an embodiment of the present invention includes the first insulating layer304, formed to have a predetermined pattern on the plate302, and the cathode electrode306formed on the first insulating layer304. The cathode electrode306forms a beam-focusing structure using the first insulating layer304. Here, the beam-focusing structure indicates that the cathode electrode306surrounds the electron emission portion320in the first hole of the first insulating layer304at a predetermined height. Such a beam-focusing structure allows the electron beam emitted from the electron emission portion320to react against a voltage, e.g., negative voltage applied to the cathode electrode306and to be focused into the center of the second hole (e.g., as inFIG. 5). Hence, the electron emission device according to an embodiment of the present invention has a simple structure but is excellent in focusing the electron beam.

FIG. 4is a partially sectional view of an electron emission display using the electron emission device having the beam-focusing structure according to an embodiment of the present invention, andFIG. 5illustrates a beam-focusing effect of the electron emission display ofFIG. 4.

Referring toFIG. 4, an electron emission display400includes an electron emission structure301, a display part331, and a spacer340. The spacer340is disposed between the electron emission structure301and the display part331, so that the electron emission structure301and the display part331are opposing each other with a space between them.

The electron emission structure301includes a first plate302′, a first insulating layer304′, a cathode electrode306′, a second insulating layer308′, a gate electrode310′, and an electron emission portion320′. The electron emission structure301is similar to a structure having a plurality of aforementioned electron emission devices300ofFIG. 3. However, inFIGS. 4 and 5, the electron emission portion320′ is formed on the cathode electrode306′ (rather than directly formed on the plate302ofFIG. 3). Therefore, descriptions of the electron emission structure301will be abbreviated to avoid repetitive descriptions.

The display part331may have various shapes, and hereinafter, one example thereof will be described. On the other hand, other examples thereof will be described with reference toFIGS. 7A and 7B.

The display part331includes a second plate332, an anode electrode334, and a fluorescent layer338. Additionally, the image realizer331may include a dark region336. The second plate332is formed of a transparent plate such as a vitreous plate.

The anode electrode334is formed on the second plate332, covering the whole area of the second plate332, or having a predetermined division shape (or pattern) such as a striped shape (or pattern) or the like. The anode electrode334can be made of a conductive transparent material such as ITO, or by making metal, such as chromium (Cr), aluminum (Al), molybdenum (Mo), copper (Cu), etc., thin and transparent.

The fluorescent layer338is formed on the anode electrode334with a striped shape (or in a striped pattern) or with a dotted shape (or in a dotted pattern). The fluorescent layer338includes a high-voltage fluorescent material or a low-voltage fluorescent material according to voltages applied to the anode electrode334. The florescent layer338should be made of a fluorescent material having excellent efficiency, life-span, and/or color purity.

The display part331further includes a dark region336. The dark region336is made of a conductive material having a dark color and formed to have a matrix shape (or pattern) or a striped shape (or pattern) on the anode electrode334. The dark region336forms a non-luminous region between luminous regions due to the fluorescent layer338. The dark region336can be abbreviated according to the type, structure and shape of the electron emission display400.

In addition, the electron emission display400should be sealed in a vacuum so as to increase a mean free path of the electrons; prevent a work function from changing due to gas particles absorbed into the electron emission portion; protect the electron emission portion from physical and chemical damage due to ionized gas particles; prevent a track of the electron beam from changing; and/or protect the fluorescent layer from damage due to vapor, oxygen, carbon monoxide, carbon dioxide, methane, etc.

Thus, as shown inFIG. 5, the electron emission display400according to an embodiment of the present invention includes the cathode electrode306′ of the beam-focusing structure using the first insulating layer304′, so that the electron beam emitted from the electron emission portion320′ is focused into the center of the hole by the voltage, e.g., negative voltage applied to the cathode electrode306′, thereby enhancing the beam-focusing effect.

Further, the electron emission display400according to an embodiment of the present invention can be, as shown inFIG. 4, fabricated by adding only a process of forming the first insulating layer304′ at a predetermined height on the plate302′ under the-cathode electrode306′. Thus, the fabricating process of the electron emission display400according to an embodiment of the present invention is simple as compared with the conventional display having the beam-focusing structure (e.g., the structure having a separate or dedicated focusing electrode).

Hereinafter, an electron emission display according to another embodiment of the present invention will be described with reference toFIG. 6.

FIG. 6is a sectional view of another electron emission display including an electron emission device having a grid electrode according to the another embodiment of the present invention, andFIGS. 7A and 7Bare sectional views of a display part applicable to the electron emission display according to an embodiment of the present invention.

Referring toFIG. 6, an electron emission display600includes an electron emission structure301, a display part331′, a spacer340′, and a grid electrode346. The spacer340′ is disposed between the electron emission structure301and the display part331′, so that the electron emission structure301and the display part331′ are opposing each other with a space between them.

The electron emission structure301includes a first plate302′, a first insulating layer304′, a cathode electrode306′, a second insulating layer308′, a gate electrode310′, and an electron emission portion320′. Such an electron emission structure301is similar to a structure having a plurality of aforementioned electron emission devices300. However, inFIG. 6, the electron emission portion320′ is formed on the cathode electrode306′ (rather than directly formed on the plate302ofFIG. 3). Therefore, descriptions of the electron emission structure301will be abbreviated to avoid repetitive descriptions.

The display part331′ includes a second plate332′, an anode electrode334′, a dark region336′ and a fluorescent layer338′. Such a display part331′ is similar to the above-mentioned display part331ofFIGS. 4 and 5. Therefore, descriptions of the display part331′ will be abbreviated to avoid repetitive descriptions.

The grid electrode346is appropriately provided above the gate electrode310′ or attached to the spacer340′. The grid electrode346includes a plurality of through-holes or a plurality of windows through which the electrons emitted from the electron emission portion320′ pass. The grid electrode346prevents the electron beam from colliding, not with the target fluorescent layer338′, but with the non-target fluorescent layer, thereby preventing the fluorescent layer338′ from representing unwanted colors. Further, the grid electrode346can be employed as a focusing electrode to focus the electron beam emitted from the electron emission portion320′. Such grid electrode346can include a sheet-type metal mesh.

Thus, the electron emission display600according to an embodiment of the present invention includes the grid electrode346, so that the electron emitted from the electron emission portion320′ is primarily focused by the beam-focusing structure of the cathode electrode306′ and then secondarily focused by the grid electrode346. Thus, the electron emission display600including both the cathode and grid electrodes306′,346has a good beam-focusing effect as compared with the conventional electron emission display basically having just the grid electrode.

In the foregoing embodiments, the electron emission display300,400,600includes a display part that displays a picture based on the electron emitted from the electron emission structure301and colliding with the fluorescent layer338,338′. Such display part is not limited to the foregoing description and may vary.

For example, as shown inFIG. 7A, the display part includes a second plate732, an anode electrode734formed on the second plate732, a fluorescent layer738formed on the anode electrode734, and a thin metal film742formed on the fluorescent layer738. Further, a dark region736shown inFIG. 7Amay be selectively formed on the anode electrode734. The anode electrode734can be in the form of a transparent plate. Here, the thin metal film742protects the electron emission structure301from damage due to an electric arc generated from the fluorescent layer738and can be also functioned as an anode electrode (e.g., a second anode electrode or an anode electrode that replaces the anode electrode734).

For example, as shown inFIG. 7B, the display part includes a second plate732′, a fluorescent layer738′ formed on the second plate732′, and a thin metal electrode744formed on the fluorescent layer738′. Here, the thin metal electrode744functions as the anode electrode. Such display part is adapted to a high-voltage electron emission display using thousands of volts or more.

As described above, the present invention provides an electron emission device and an electron emission display using the same, which forms a beam-focusing structure using an insulating layer, thereby making the electron emission device and the electron emission display using the same more easily fabricated and being excellent in focusing an electron beam.

Further, the present invention provides an electron emission display having an improved beam-focusing structure, thereby enhancing color representation or reproduction.