Patent Application
20070018552
This application claims the benefit of Korean Application No. 2005-66380, filed Jul. 21, 2005, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein by reference.
1. Field of the Invention
Aspects of the present invention relate to an electron emission device, an electron emission type backlight unit, and a flat display apparatus having the same, and more particularly, to an electron emission device with improved electron emission efficiency and light-emitting uniformity, an electron emission type backlight unit employing the electron emission device, and a flat display apparatus having the electron emission type backlight unit.
2. Description of the Related Art
Generally electron emission devices can be classified into electron emission devices using a thermionic cathode and electron emission devices using a cold cathode as an electron emission source. Electron emission devices that use a cold cathode as an electron emission source include field emitter array (FEA) type devices, surface conduction emitter (SCE) type devices, metal insulator metal (MIM) type devices, metal insulator semiconductor (MIS) type devices, ballistic electron surface emitting (BSE) type devices, etc. Aspects of the present invention relate to the FEA type device.
An FEA type electron emission device uses the principle that, when a material having a low work function or a high β function is used as an electron emission source, the material readily emits electrons in a vacuum due to an electric potential. FEA devices that employ a tapered tip structure formed of, for example, Mo, Si as a main component, a carbon group material such as graphite, diamond like carbon (DLC), etc., or a nano structure such as nanotubes, nano wires, etc., have been developed.
FEA type electron emission devices can be classified into top gate types and under gate types according to the arrangement of cathode electrodes and gate electrodes. FEAs can also be classified into two-electrode, three-electrode, or four-electrode type emission devices according to the number of electrodes.
Studies have been conducted into ways of using an electron emission device as a backlight unit of a non-emissive display device.
Referring to
The electron emission device 2 includes a base substrate 10 that faces and is parallel to the front substrate 90, a cathode electrode 20 formed in strips on the base substrate 10, a gate electrode 30 that is formed in strips and is parallel to the cathode electrode 20, and electron emission layers 40 and 50 respectively formed around the cathode electrode 20 and the gate electrode 30. An electron emission gap G is formed between the electron emission layers 40 and 50 surrounding the cathode electrode 20 and the gate electrode 30.
A vacuum, that is, a pressure lower than the ambient air pressure, is maintained in the space between the front panel 1 and the electron emission device 2, and a spacer 60 is placed between the front panel 1 and the electron emission device 2 in order to sustain the pressure generated by the vacuum between the front panel 1 and the electron emission device 2 and to secure a light-emitting space 103.
In the above-described electron emission type backlight unit 3, electrons are emitted from one of the electron emission layers 40 and 50, that is, from the electron emission layer 40 that is formed at the cathode electrode 20 by an electric field generated between the gate electrode 30 and the cathode electrode 20. The emitted electrons travel toward the gate electrode 30 initially and then are attracted by the strong electric field of the anode electrode 80 and move toward the anode electrode 80.
However, an electric field formed between the anode electrode 80 and the cathode electrode 20 interferes with the electric field formed between the gate electrode 30 and the cathode electrode 20, and thus a diode discharge, that is, electron emission and electron acceleration occurring at the same time due to the electric field of the anode electrode 80, is likely to occur.
In addition, due to the light-emitting characteristic of phosphor materials, during a predetermined period of time in which light is emitted by electrons that are incident on a phosphor material, other incident electrons cannot contribute to light emission. Thus light-emitting efficiency is not improved by increasing incident electrons on the phosphor layer 70 beyond this saturation level, and also electron emission by a high anode voltage is detrimental from an energy efficiency aspect. In other words, electrons must be emitted stably and efficiently by a low gate voltage and at the same time the emitted electrons must be uniformly accelerated by a strong anode voltage. However, when electrons are emitted due to a strong anode voltage, efficient electron emission and light emission become impossible.
Thus an electron emission type backlight unit having a new structure in which an electric field between the anode electrode 80 and the cathode electrode 20 can be blocked is desired.
Aspects of the present invention provide an electron emission device and an electron emission type backlight unit having a new structure using the electron emission device in which an electric field between an anode electrode and a cathode electrode is effectively blocked, and electrons are emitted continuously and stably due to a low gate voltage, thereby improving light-emitting uniformity and light-emitting efficiency.
Aspects of the present invention also provide a flat display apparatus employing the electron emission type backlight unit.
According to an aspect of the present invention, there is provided an electron emission device comprising: a base substrate; an insulating layer that is formed on a surface of the base substrate; a cathode electrode formed on the insulating layer; a gate electrode formed on the base substrate, separated from the cathode electrode, and higher, extending farther from the base substrate, than the cathode electrode; and an electron emission layer that is electrically connected to the cathode electrode and disposed to face the gate electrode.
While not required in all aspects, the electron emission layer may be formed on both sides of the cathode electrode.
While not required in all aspects, the gate electrode may be surrounded by an insulating layer.
While not required in all aspects, the cathode electrode may be formed to have a protrusion with a predetermined length and width facing the gate electrode, and the electron emission layer is formed on the protrusion, and a concave may be formed in the gate electrode, corresponding to the shape of the protrusion of the cathode electrode.
While not required in all aspects, the cathode electrode may be formed to have a concave with a predetermined length and width facing the gate electrode, and the electron emission layer is formed in the concave. A protrusion may be formed on the gate electrode, corresponding to the shape of the concave of the cathode electrode.
While not required in all aspects, the cathode electrode may be formed to have a curved surface having a predetermined curvature facing the gate electrode, and the electron emission layer is formed on the curved surface. The curved surface may be convex or concave toward the gate electrode, and the gate electrode may be formed to have a curved surface corresponding to the curved surface formed in the cathode electrode.
While not required in all aspects, plane surfaces of the cathode electrode and the gate electrode may be continuously curved. The electron emission layer may be discontinuously formed on a lateral side of the cathode electrode.
According to an aspect of the invention, the gate electrode may be formed to be closer to the base substrate and the anode electrode than the cathode electrode is to the base substrate and the anode electrode.
While not required in all aspects, the electron emission layer may comprise an electron emission material selected from a carbon type material and a nano type material, wherein the carbon type material is selected from the group consisting of carbon nanotubes, graphite, diamond, and diamond-like carbon, and the nano type material is selected from the group consisting of nanotubes, nanowires, nanorods, and nanoneedles.
According to another aspect of the present invention, there is provided an electron emission type backlight unit comprising: a front substrate comprising an anode electrode and a phosphor layer; a base substrate separated from the front substrate; an insulating layer formed on a surface of the base substrate; a cathode electrode formed on the insulating layer; a gate electrode that is formed on the insulating layer, separated from the cathode electrode, and extending farther from the base substrate than the cathode electrode; an electron emission layer that is formed on a lateral side of the cathode electrode and faces the gate electrode; and a spacer maintaining a distance between the front substrate and the base substrate.
According to another aspect of the present invention, there is provided a flat display device comprising: a backlight unit comprising: a front substrate comprising an anode electrode and a phosphor layer; a base substrate separated from the front substrate; an insulating layer formed on a surface of the base substrate; a cathode electrode formed on the insulating layer; a gate electrode that is formed on the insulating layer, separated from the cathode electrode, and extending farther from the base substrate than the cathode electrode; an electron emission layer formed on a lateral side of the cathode electrode facing the gate electrode; and a spacer maintaining a distance between the front substrate and the base substrate; and a non-emissive display device that is formed in front of the electron emission type backlight unit to control light supplied from the electron emission device to realize an image.
While not required in all aspects, the non-emissive display device may be a liquid display device.
Additional aspects and/or advantages of the invention will be set forth in part in the description which follows and, in part, will be obvious from the description, or may be learned by practice of the invention.
These and/or other aspects and advantages of the invention will become apparent and more readily appreciated from the following description of the embodiments, taken in conjunction with the accompanying drawings of which:
Reference will now be made in detail to the present embodiments of the present invention, examples of which are illustrated in the accompanying drawings, wherein like reference numerals refer to the like elements throughout. The embodiments are described below in order to explain the present invention by referring to the figures.
Referring to
The front panel 101 includes a front substrate 90, an anode electrode 80 disposed on a lower surface of the front substrate 90, and a phosphor layer 70 disposed on a lower surface of the anode electrode 80.
The electron emission device 102 includes a base substrate 110 disposed at a predetermined interval from and parallel to the front substrate 90 whereby the vacuum space 103 is formed between the front panel 101 and the electron emission device 102, an insulating layer 130 formed on a surface of the base substrate 110, a cathode electrode 120 formed on the insulating layer, a gate electrode 140 that is formed on the insulating layer 130, separated from and parallel to the cathode electrode 120, and is higher than the cathode electrode 120, and an electron emission layer 150 disposed at a side of the cathode electrode 120 to face the gate electrode 140.
The anode electrode 80 applies a high voltage that is necessary to accelerate electrons emitted from the electron emission layer 150 so that the electrons collide with the phosphor layer 70 at a high velocity. The phosphor layer 70 is excited by the electrons and subsequently changes from a high energy level to a low energy level, thus emitting visible light.
While not required in all aspects, the electron emission layer 150 may be disposed entirely on a lateral surface of the cathode electrode 120.
The vacuum space 103 between the front panel 101 and the electron emission device 102 is maintained at a lower pressure than the ambient air pressure, and the spacer 60 is disposed between the front panel 101 and the electron emission device 102 to sustain the vacuum pressure between the front panel 101 and the electron emission device 102 and to partition the vacuum space 103. Generally, the spacer 60 is formed of insulating material such as ceramics or glass that is not electrically conductive. Electrons may be accumulated during the operation of the electron emission type backlight unit 100 on the spacer 60, and to emit these accumulated electrons, the spacer 60 may be coated with a conductive material.
The cathode electrode 120 and the gate electrode 140 form an electric field so that electrons can be easily emitted from the electron emission layer 150. The insulating layer 130 insulates the electron emission layer 150 and the gate electrode 140. The height of the gate electrode 140 is set such that the gate electrode 140 is closer to the base substrate 110 and to the anode electrode 80 than the cathode electrode 120. Thus the electron emission layer 150 is disposed in a more uniform gate electric field. Also, the gate electrode 140 may be surrounded by the insulating layer 130 to prevent a short circuit between the cathode electrode 120 and the gate electrode 140.
Hereinafter, materials of components that constitute the electron emission backlight unit 100 will be described.
While not required in all aspects, the front substrate 90 and the base substrate 110 are board members having a predetermined thickness and may be formed of a quartz glass, a glass including an impurity such as a small amount of Na, a flat glass, a glass substrate coated with SiO2, an oxide aluminum substrate or a ceramic substrate.
While not required in all aspects, the cathode electrode 120 and the gate electrode 140 may be formed of general electrically conductive materials. Examples of the general electrically conductive materials include a metal (e.g., Al, Ti, Cr, Ni, Au, Ag, Mo, W, Pt, Cu, Sn, Sb, In or Pd) and alloys thereof, a conductive material made of either metal (e.g., Pd, Ag, RuO2, or Pd—Ag) or its oxide and glass, a transparent conductive material such as indium tin oxide (ITO), In2O3 or SnO2, and a semiconductor material such as polysilicon.
Electron emission materials that are formed in the electron emission layer 150 and emit electrons due to an electric field may be any electron emission material that has a small work function and a high β function. Specifically, carbon type materials such as carbon nanotubes (CNT), graphite, diamond and diamond-like carbon or nano materials such as nanotubes, nano wires, nanorods, or nanoneedles are preferable. CNTs particularly have good electron emission properties and can be driven at a low voltage. Therefore devices using CNTs as an electron emission layer can be applied to a larger electron emission display device.
According to an aspect of the present invention, the electron emission type backlight unit 100 operates as follows.
A negative voltage is applied to the cathode electrode 120 and a positive voltage is applied to the gate electrode 140 so that electrons can be emitted from the electron emission layer 150 formed on the cathode electrode 120. Also, a strong positive voltage is applied to the anode electrode 80 to accelerate the electrons emitted toward the anode electrode 80. Thus electrons are emitted from electron emission materials that form the electron emission layer 150 and travel toward the gate electrode 140 and then are accelerated toward the anode electrode 80. The electrons accelerated toward the anode electrode 80 collide with the phosphor layer 70 formed on the anode electrode 80 and thus generate visible light.
Since the gate electrode 140 is formed to be higher than the cathode electrode 140, the electric field formed by the anode electrode 80 can be prevented from interfering with the electric field between the cathode electrode 120 and the gate electrode 140. Thus, it is easy to control the anode electrode 80 and the gate electrode 140 such that the anode electrode 80 only accelerates the electrons and the gate electrode 140 emits the electrons, thereby maximizing the light-emitting uniformity and the light-emitting efficiency of the phosphors and preventing diode discharge.
Hereinafter, other example embodiments of the electron emission device 102 illustrated in
As illustrated in
Referring to
As illustrated in
Also, as illustrated in
Furthermore, as the current density increases, the amount of the generated visible light increases due to the characteristic of CL type phosphors, but at a predetermined saturated current density, the intensity of the visible light generated does not increase any more. Accordingly, forming as many electron emission layers as possible is not always efficient, and thus it may be preferable to discontinuously form an electron emission layer to secure an appropriate surface area of the electron emission layer.
As illustrated in
Also, as illustrated in
Also, as illustrated in
The shape of the protrusions formed in the cathode electrode 120 and the gate electrode 140 is not limited to a rectanglular shape as illustrated in
According to an aspect of the invention, the electron emission backlight unit 100 having the above-described configurations may be used as a back light unit (BLU) of a non-emissive display device such as a liquid crystal display (LCD), and in this case, the cathode electrode 120 and the gate electrode 140 are disposed substantially parallel to each other. Also, the phosphor layer 70 may include phosphors emitting visible light with a desired color, or red, green, and blue light emitting phosphors at an appropriate rate to obtain white light.
Referring to
The electron emission type backlight unit 100 receives power supplied via a connection cable 104 and emits visible light V through a front panel 90 disposed in front of the electron emission device, thereby supplying visible light V toward the LCD device 700.
The structure and operation of the LCD device 700 will be described hereinafter with reference to
The electron emission type backlight unit 100 illustrated in
Meanwhile, the LCD device 700 includes a front panel 505, and a buffer layer 510 is formed on the front panel 505, and a semiconductor layer 580 is formed on the buffer layer 510 in a predetermined pattern. A first insulating layer 520 is formed on the semiconductor layer 580, a gate electrode 590 is formed in a predetermined pattern on the first insulating layer 520, and a second insulating layer 530 is formed on the gate electrode 590. After the second insulating layer 530 is formed, the first and second insulating layers 520 and 530 are etched using a dry etching method or other similar process and thus a portion of the semiconductor layer 580 is exposed, and a source electrode 570 and a drain electrode 610 are formed in a predetermined area including the exposed portion of the semiconductor layer 580. After the source electrode 570 and the drain electrode 610 are formed, a third insulating layer 540 is formed, and a planarization layer 550 is formed on the third insulating layer 540. A first electrode 620 is formed on the planarization layer 550 in a predetermined pattern, and a portion of the third insulating layer 540 and the planarization layer 550 is etched, and thus a conductive path between the drain electrode 610 and the first electrode 620 is formed. A transparent base substrate 680 is separated from the front panel 505, and a color filter layer 670 is formed on a lower surface 680a of the base substrate 680. A second electrode 660 is formed on a lower surface 670a of the color filter layer 670, and a first alignment layer 630 and a second alignment layer 650 that align a liquid crystal layer 640 are formed in the area where the surfaces of the first electrode 620 and the second electrode 660 face each other. A first polarization layer 500 is formed on a lower surface of the front panel 505, a second polarization layer 690 is formed on a upper surface 680b of the base substrate 680, and a protection film 695 is formed on a upper surface 690a of the second polarization layer 690. A spacer 560 that partitions the liquid crystal layer 640 is formed between the color filter layer 670 and the planarization layer 550.
The LCD device 700 operates as follows. A potential difference is formed between the first and second electrodes 620 and 660 due to an external signal controlled by the gate electrode 590, the source electrode 570, and the drain electrode 610, and the liquid crystal layer 640 is aligned by the potential difference, and the visible light V supplied from the backlight unit 100 is shielded or transmitted according to the alignment of the liquid crystal layer 640. The transmitting light passes the color filter layer 670 and is colored to realize an image.
According to the current embodiment of the present invention, illustrated in
A flat display apparatus including the above described electron emission device and the electron emission type backlight unit includes a backlight unit with increased brightness and life span, and thus the brightness of the image and life span of the display apparatus can also be increased.
According to an embodiment of the present invention, the electron emission device having the above-described configuration can be used as an image display device. In this case, the electron emission device may have a structure in which the gate electrode 140 and the cathode electrode 120 are formed in strips and cross each other, which is advantageous for applying signals to realize an image. For example, when the cathode electrode 120 is formed in strips extending in one direction, the gate electrode 140 may be formed of a main electrode crossing the cathode electrode 120 and a branch electrode extending from the main electrode to face the cathode electrode 120. The arrangement of the cathode electrode 120 and the gate electrode 140 may be exchanged as shown in
As described above, according to an aspect of the present invention, an upper end of the gate electrode 140 is disposed closer to the anode electrode 80 than the cathode electrode is to the anode electrode 80 such that an electric field of the anode electrode 80 is prevented from interfering with the electric field between the cathode electrode 120 and the gate electrode 140. Thus electron emission and acceleration becomes easy to control such that the anode electrode 80 only accelerates the electrons and the electrons are emitted from the gate electrode 140, thereby obtaining light-emitting uniformity and maximizing the light-emitting efficiency of the phosphors. Also, the electron emission device can be manufactured by a simple process.
Also, since a lower end of the gate electrode 140 is closer to the base substrate 680 than the cathode electrode 120 according to an aspect of the present invention, the electron emission layer 150 is located in a more uniform electric field and uniform electron emission can occur in the electron emission layer 150.
Also, curved surfaces, protrusions, or grooves are formed in the cathode electrode 120 and the gate electrode 140, which are formed in strips according to an aspect of the present invention, and thus the surface area of the electron emission layer 150 is increased, thereby increasing the electron emitting efficiency.
Meanwhile, when a backlight unit is formed using an electron emission device according to aspects of the present invention, a display apparatus employing the backlight unit can have improved brightness and light-emitting efficiency.
Although a few embodiments of the present invention have been shown and described, it would be appreciated by those skilled in the art that changes may be made in this embodiment without departing from the principles and spirit of the invention, the scope of which is defined in the claims and their equivalents.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2005-66380 | Jul 2005 | KR | national |
