WO2009078522A1

WO2009078522A1 - Field emission type back light unit

Info

Publication number: WO2009078522A1
Application number: PCT/KR2008/003932
Authority: WO
Inventors: Jin Woo Jeong; Yoon Ho Song; Dae Jun Kim
Original assignee: Electronics And Telecommunications Research Institute
Priority date: 2007-12-17
Filing date: 2008-07-03
Publication date: 2009-06-25
Also published as: KR20090065266A

Abstract

A field emission display, more particularly, a field emission-back light unit having high field emission efficiency is provided. The field emission-back light unit includes an upper substrate and a lower substrate, which are spaced apart from and face each other, an anode electrode and a phosphor layer, which are formed on the upper substrate, a cathode electrode formed on the lower substrate, a plurality of field emitters formed on the cathode electrode and spaced apart from one another, and a metal gate substrate disposed between the upper substrate and the lower substrate to induce electron emission from the field emitter, and having an opening through which the emitted electron passes. At least one surface of the metal gate substrate is coated with a secondary electron-generating material capable of generating secondary electrons by collision of the emitted electrons.

Description

Description FIELD EMISSION TYPE BACK LIGHT UNIT

Technical Field

[I] The present invention relates to a field emission display, and more particularly, to a field emission-back light unit having improved field emission efficiency. Background Art

[2] Generally, flat panel displays may be classified into emissive displays and non- emissive displays.

[3] The emissive displays include a plasma display panel (PDP) and a field emission display (FED), and the non-emissive displays include a liquid crystal display (LCD).

[4] While the LCD has advantages of light weight and low power consumption, it cannot create an image by self-emission, but only by light entering from outside. Thus, the image created by the LCD cannot be observed in a dark place. To solve this problem, a back light unit is installed at a back surface of the LCD.

[5] Conventionally, as a back light unit, a cold cathode fluorescent lamp (CCFL), which is a linear light source, and a light emitting diode (LED), which is a spot light source, are mainly used.

[6] However, such back light units are complicated and expensive, and consume a large amount of power according to reflection and transmission of light due to the light source disposed at a side thereof. Particularly, as the LCD becomes larger, uniform brightness becomes difficult to ensure.

[7] For these reasons, in recent time, a field emission-back light unit having a flat emission structure has been developed. Such a field emission-back light unit consumes less power and exhibits relatively uniform brightness in a wide range of an emission region, compared to the conventional back light unit using a CCFL.

[8] Generally, in a field emission-back light unit, a cathode substrate having a field emitter and an anode substrate having a phosphor are disposed to face and be spaced a specific distance apart from each other, and vacuum-packed. An electron emitted from the field emitter collides with the phosphor of the anode substrate, so that light is emitted by cathodoluminescence of the phosphor.

[9] A structure of the conventional field emission device will now be described with reference to FIG. 1.

[10] FIG. 1 illustrates a conventional field emission device having a top-gate triode structure.

[I I] Referring to FIG. Ia, the field emission device using a dielectric thin film as a gate insulator 102 may have an emitter 104 formed by printing after formation of a gate and may be easily surfaced- treated, because of a low-height gate insulator 102. However, the emitter 104 and an electrode structure may be damaged due to occurrence of arc, and a production cost increases due to necessity of lithography.

[12] To solve these problems, a field emission device having a high-height gate insulator

102 formed of a thick dielectric or a dielectric mash substrate as in FIG. Ib was developed. The field emission device having a structure as in FIG. Ib is less likely to be damaged by the arc, so that a high voltage can be relatively easily applied thereto. However, the field emission device having a structure as in FIG. Ib has to have an emitter 104 and be surfaced- treated before formation of a gate structure, and an electron emitted from the emitter 104 collides with the gate insulator 102 to cause the charge accumulation. Moreover, it is difficult to form a thick gate insulator 102 in formation of a large-sized device.

[13] In addition, in order to improve efficiency, brightness and uniformity of the field emission device having the top-gate triode structure described above, an aperture ratio, i.e., a ratio of a gate hole to the total area of the device, should be increased. However, it is not easy to increase the aperture ratio because of a ratio of a diameter of a gate opening to a height of a gate insulator and a structural characteristic of a gate electrode.

[14] Thus, a field emission-back light unit which has high field emission efficiency and can be easily formed in a larger size is needed. Disclosure of Invention

Technical Problem

[15] The present invention is directed to a field emission-back light unit having high field emission efficiency.

[16] Other objects of the present invention will be understood with reference to the following descriptions and exemplary embodiments of the present invention. Technical Solution

[17] One aspect of the present invention provides a field emission-back light unit, including: an upper substrate and a lower substrate, which are spaced apart from and face each other; an anode electrode and a phosphor layer, which are formed on the upper substrate; a cathode electrode formed on the lower substrate; a plurality of field emitters formed on the cathode electrode and spaced apart from one another; and a metal gate substrate disposed between the upper substrate and the lower substrate to induce electron emission from the field emitter, and having an opening through which the emitted electron passes, wherein at least one surface of the metal gate substrate is coated with a secondary electron-generating material capable of generating secondary electrons by collision of the emitted electrons.

Advantageous Effects [18] As described above, the present invention can improve field emission efficiency with a secondary electron, which is generated from a secondary electron-generating material coated on a metal gate substrate inducing electron emission. Brief Description of the Drawings

[19] FIG. 1 illustrates a conventional field emission device having a top-gate triode structure;

[20] FIG. 2 is a schematic view of a field emission-back light unit according to an exemplary embodiment of the present invention; and

[21] FIGS. 3 to 6 illustrate generation of secondary electrons depending on shapes of an opening formed in a metal gate substrate according to exemplary embodiments of the present invention. Mode for the Invention

[22] In the following description, it is to be noted that a detailed description of the known function and configuration of the present invention will be omitted if it is deemed to obscure the subject matter of the present invention. The terms described below, as terms defined considering their functions in the present invention, can be different depending on a user or operator s intention, or a practice. Thus, the definition should be made on the basis of the contents throughout this specification.

[23] In general, a conventional field emission device having a top-gate triode structure and used as a back light for a liquid crystal display has a gate structure using a dielectric thin film or a dielectric substrate as an insulator, and has problems of damage of an electrode structure due to arc occurring in application of high voltage, and an increase in production cost caused by a lithography process. To solve these problems, the present invention provides a field emission-back light unit which is easily formed in a large size and has high field emission efficiency by using a metal substrate having an opening through which an electron beam emitted from an emitter can pass as a gate electrode, and the gate electrode coated with a material for facilitating generation of a secondary electron so as to generate the secondary electron due to collision of some electron beams emitted from the emitter with the material.

[24] Hereinafter, exemplary embodiments of the present invention will be described with reference to the accompanying drawings in detail.

[25] FIG. 2 is a schematic view of a field emission-back light unit according to an exemplary embodiment of the present invention. Referring to FIG. 2, the field emission-back light unit according to the exemplary embodiment of the present invention includes a lower substrate 210 as a cathode substrate, a cathode electrode 212 formed on the lower substrate 210, a field emitter 214 formed on the cathode electrode 212, an upper substrate 220 as an anode substrate, an anode electrode 222 formed on the upper substrate 220, a phosphor layer 224 formed on the anode electrode 222, a metal gate substrate 232 coated with a secondary electron-generating material 234, and spacers 242 and 244.

[26] The lower substrate 210 is spaced apart from and faces the upper substrate 220, and maintains a specific distance therebetween by the spacer 242 formed between the lower substrate 210 and the metal gate substrate 232, and the spacer 244 formed between the upper substrate 220 and the metal gate substrate 232. The lower substrate 210 and the upper substrate 220 may be glass substrates.

[27] The cathode electrode 212 may be formed on the lower substrate 210, and formed of a metallic material or a transparent conductive material. The transparent conductive material may be indium tin oxide (ITO), indium zinc oxide (IZO) or indium tin zinc oxide (ITZO).

[28] At least one field emitter 214 is formed on the cathode electrode 212, and preferably, a plurality of field emitters 214 are formed to be spaced a specific distance apart from one another.

[29] The field emitter 214 may be formed of an electron emission material having an excellent electron emission characteristic, which includes a carbon nano tube, a carbon nano fiber and a carbon-based synthetic material.

[30] The anode electrode 222 is formed on the upper substrate 220, and the phosphor layer 224 is disposed on the anode electrode 222. The anode electrode 222 may also be formed of a transparent conductive material, such as ITO, IZO or ITZO.

[31] The metal gate substrate 232 serves as a gate electrode inducing electron emission from the field emitter 214, and maintains a specific distance apart from the upper and lower substrates 220 and 210 by the spacers 242 and 244.

[32] A plurality of openings 236 are formed in the metal gate substrate 232, wherein the opening 236 may be formed to correspond to a location of the field emitter 214.

[33] The secondary electron-generating material 234 which facilitates the generation of a secondary electron due to collision of electron beams emitted from the field emitter 214 is coated on at least one surface of the metal gate substrate 232. While FIG. 2 shows that the secondary electron-generating material 234 is coated on a bottom surface of the metal gate substrate 232 and a side surface thereof adjacent to the opening 236, the secondary electron-generating material 234 may be also coated on a top surface of the metal gate substrate 232, if necessary. Further, to generate more secondary electrons due to the collision of the electron beams, a width of the field emitter 214 may be formed larger than a diameter of the opening 236. In addition, to prevent accumulation of charges in the secondary electron-generating material 234 having general insulator s characteristics, the secondary electron-generating material 234 may be coated only on the side surface of the metal gate substrate 232 adjacent to the opening 236. Meanwhile, the secondary electron-generating material 235 may include magnesium oxide (MgO).

[34] An emission mechanism of the field emission-back light unit having the above- described structure according to the exemplary embodiment of the present invention will now be described.

[35] Some electrons emitted form the field emitter 214 pass through the opening 236 and collide with the phosphor layer 224, and the others emitted collide with the secondary electron-generating material 234 coated on the metal gate substrate 232 and generate secondary electrons. Here, more secondary electrons are generated according to an acceleration voltage between a gate and a cathode.

[36] The secondary electron generated as such is combined with an electron emitted from the field emitter 214, and the combined result passes through the opening 236 and collides with the phosphor layer 224, such that light is emitted.

[37] In the structure described above, secondary electrons are generated using electrons which leak through a gate electrode, i.e., the metal gate substrate 232, so that an amount of electrons passing through the opening 236 is increased, and thus emission efficiency is improved.

[38] Here, the secondary electron-generating material coated on the metal gate substrate

232 may be coated as thin as possible to prevent the accumulation of charges.

[39] FIG. 3 illustrates generation of secondary electrons in a metal gate substrate having an opening with a rectangular longitudinal-section according to an exemplary embodiment of the present invention.

[40] Referring to FIG. 3a, an opening 236 with a rectangular longitudinal- section is formed in a metal gate substrate 232, and a secondary electron-generating material 234 is coated on a side surface of the metal gate substrate 232 adjacent to the opening 236 and a bottom surface of the metal gate substrate 232.

[41] Some electron beams 301, i.e., the flow of electrons emitted from a field emitter 214, pass through the opening 236 without collision with the metal gate substrate 232, and the other electron beams collide with the secondary electron-generating material 234 coated on the metal gate substrate 232 so as to generate secondary electrons e.

[42] The secondary electrons e generated as such pass through the opening 236 together with the electron beams emitted from the field emitter 214, and go to an anode electrode.

[43] If necessary, the secondary electron-generating material 234 may be coated only on a side surface of the metal gate substrate 232 adjacent to the opening 236, or only on a bottom surface of the metal gate substrate 232.

[44] Here, to prevent accumulation of charges in the secondary electron-generating material 234 as descried above, the secondary electron-generating material 234 may be coated only on the side surface of the metal gate substrate 232 adjacent to the opening

236, which is illustrated in FIG. 3b. [45] Alternatively, the secondary electron-generating material 234 may be coated on the bottom and top surfaces of the metal gate substrate 232, and the side surface of the metal gate substrate 232 adjacent to the opening 236, which is illustrated in FIG. 3c. [46] To generate more secondary electrons e, a width of the field emitter 214 may be formed larger than a diameter of the opening 236, which is not dependant on a location of the secondary electron-generating material 234. [47] FIG. 4 illustrates generation of secondary electrons in a metal gate substrate having an opening with a reverse-tapered longitudinal-section according to another exemplary embodiment of the present invention. [48] Referring to FIG. 4a, an opening 236 with a reverse-tapered longitudinal- section may be formed in a metal gate substrate 232, and a secondary electron-generating material

234 is coated on a bottom surface of the metal gate substrate 232. [49] Like the structure of FIG. 3a, some electron beams 301, i.e., the flow of electrons emitted from a field emitter 214, pass through the opening 236 without collision with the metal gate substrate 232, and the other electron beams collide with the secondary electron-generating material 234 coated on the metal gate substrate 232 and generate secondary electrons e. [50] Compared to the structure of FIG. 3a, an area of a side surface of the metal gate substrate 232 on which the secondary electron-generating material 234 is coated is larger, so that more secondary electrons e can be generated. [51] If necessary, the secondary electron-generating material 234 may be coated only on a side surface of the metal gate substrate 232 adjacent to the opening 236, or only on a bottom surface of the metal gate substrate 232. [52] Here, to prevent accumulation of charges in the secondary electron-generating materials 234 as described above, the secondary electron-generating material 234 may be coated only on the side surface of the metal gate substrate 232 adjacent to the opening 236, which is illustrated in FIG. 4b. [53] Alternatively, the secondary electron-generating material 234 may be coated on bottom and top surfaces of the gate substrate 232, and the side surface of the metal gate substrate 232 adjacent to the opening 236, which is illustrated in FIG. 4c. [54] A width of the filed emitter 214 may be formed larger than a diameter of the opening

236 to generate more secondary electrons e, which is not dependant on a location of the secondary electron-generating material 234. [55] FIG. 5 illustrates generation of secondary electrons in a metal gate substrate having an opening with a tapered longitudinal- section according to still another exemplary embodiment of the present invention. [56] Referring to FIG. 5a, an opening 236 with a tapered longitudinal-section may be formed in a metal gate substrate 232, and a secondary electron-generating material 234 may be coated on a bottom surface of the metal gate substrate 232, and a side surface of the metal gate substrate 232 adjacent to the opening 236.

[57] Like other exemplary embodiments, some electron beams 301, i.e., the flow of electrons emitted from a field emitter 214, pass through the opening 236 without collision with the metal gate substrate 232, and the other electron beams collide with the secondary electron-generating material 234 coated on the metal gate substrate 232, and generate secondary electrons e.

[58] Compared to other exemplary embodiments described above, the structure of FIG. 5a can reduce a loss of electron beams which leak through the metal gate substrate 232.

[59] If necessary, the secondary electron-generating material 234 may be coated only on the side surface of the metal gate substrate 232 adjacent to the opening 236, or only on the bottom surface of the metal gate substrate 232.

[60] Here, to prevent accumulation of charges in the secondary electron-generating materials 234 as described above, the secondary electron-generating material 234 may be coated only on the side surface of the metal gate substrate 232 adjacent to the opening 236, which is illustrated in FIG. 5b.

[61] Alternatively, the secondary electron-generating material 234 may be coated on the bottom and top surfaces of the metal gate substrate 232, and the side surface of the metal gate substrate 232 adjacent to the opening 236, which is illustrated in FIG. 5c.

[62] A width of the field emitter 214 may be formed larger than a diameter of the opening

236 to generate more secondary electrons e, which is not dependant on a location of the secondary electron-generating material 234.

[63] FIG. 6 illustrates generation of secondary electrons in a metal gate substrate having an opening with a longitudinal-section which has a tapered lower region, and a reverse- tapered upper region according to yet another exemplary embodiment of the present invention.

[64] Referring to FIG. 6, a metal gate substrate 232 has an opening 236 with a longitudinal-section having a tapered lower region and a reverse-tapered upper region, and a secondary electron-generating material 234 is coated on a bottom surface of the metal gate substrate 232 and a side surface thereof adjacent to the tapered lower region of the opening 236.

[65] Like other exemplary embodiments, some electron beams 301, i.e., the flow of electrons emitted from a field emitter 214 pass through an opening 236 without collision with the metal gate substrate 232, and the other electron beams collide with the secondary electron-generating material 234 coated on the metal gate substrate 232 and generate secondary electrons e. [66] The structure of FIG. 6a described above can reduce a loss of electron beams which leak through the metal gate substrate 232, like the structure of FIG. 5a. In addition, the structure of FIG. 6a facilitates the flow of the generated electrons e to an anode, compared to the structure of FIG. 5a.

[67] If necessary, the secondary electron-generating material 234 may be coated only on the side surface of the metal gate substrate 232 adjacent to the opening 236, or only on the bottom surface of the metal gate substrate 232.

[68] Here, to prevent accumulation of charges on the secondary electron-generating material 234 as described above, the secondary electron-generating material 234 may be coated only on the side surface of the metal gate substrate 232 adjacent to the opening 236, which is illustrated in FIG. 6b.

[69] Alternatively, the secondary electron-generating material 234 may be coated on the bottom and top surfaces of the metal gate substrate 232, and the side surface thereof adjacent to the opening 236, which is illustrated in FIG. 6c.

[70] A width of the field emitter 214 may be formed larger than a diameter of the opening

236 to generate more secondary electrons e, which is not dependent on a location of the secondary electron-generating material 234.

[71] While the invention has been shown and described with reference to certain exemplary embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined by the appended claims.

Claims

[1] A field emission-back light unit, comprising: an upper substrate and a lower substrate, which are spaced apart from and face each other; an anode electrode and a phosphor layer, which are formed on the upper substrate; a cathode electrode formed on the lower substrate; a plurality of field emitters formed on the cathode electrode and spaced apart from one another; and a metal gate substrate disposed between the upper substrate and the lower substrate to induce electron emission from the field emitter, and having an opening through which the emitted electron passes, wherein at least one surface of the metal gate substrate is coated with a secondary electron-generating material capable of generating secondary electrons by collision of the emitted electrons.

[2] The field emission-back light unit according to claim 1, wherein the opening is formed in a location corresponding to each field emitter.

[3] The field emission-back light unit according to claim 1, wherein the secondary electron-generating material is coated only on a side surface of the metal gate substrate adjacent to the opening.

[4] The field emission-back light unit according to claim 1, wherein the secondary electron-generating material is coated on a side surface of the metal gate substrate adjacent to the opening, and a bottom surface of the metal gate substrate.

[5] The field emission-back light unit according to claim 1, wherein the secondary electron-generating material is coated on a side surface of the metal gate substrate adjacent to the opening, and top and bottom surfaces of the metal gate substrate.

[6] The field emission-back light unit according to claim 1, wherein the opening has a rectangular, tapered or reverse-tapered longitudinal-section, or a longitudinal- section having a reverse-tapered upper region and a tapered lower region.

[7] The field emission-back light unit according to claim 1, wherein the secondary electron-generating material is MgO.

[8] The field emission-back light unit according to claim 1, further comprising: spacers formed between the upper substrate and the metal gate substrate, and between the lower substrate and the metal gate substrate.

[9] The field emission-back light unit according to claim 1, wherein the field emitter is formed of any one of a carbon nano tube, a carbon nano fiber and a carbon- based synthetic material.

[10] The field emission-back light unit according to claim 1, wherein the field emitter has a width larger than a maximum diameter of the opening.