WO2007011117A1

WO2007011117A1 - Field emission device

Info

Publication number: WO2007011117A1
Application number: PCT/KR2006/002535
Authority: WO
Inventors: Dong Wook Yang
Original assignee: Iljin Diamond Co., Ltd
Priority date: 2005-07-18
Filing date: 2006-06-29
Publication date: 2007-01-25
Also published as: KR100710592B1; KR20070010238A

Abstract

The present invention relates to a field emission device; and, more particularly, a field emission device capable of preventing leakage current between electrodes while improving unstable light emitting characteristics. A field emission device of the present invention, including: a front substrate and a rear substrate disposed by being separated at a predetermined distance from each other; an anode formed on the front substrate; a fluorescence material formed on the anode; a plurality of electrode members placed on the rear substrate by being separated at a predetermined distance from each other; and an emitter formed on at least one among the electrode members, wherein the electrode members are composed of at least four electrode members, each electrode formed alternately, and the emitters of each electrode member are separated from each other. By forming an emitter having more than four individual electrode members, the electric field emission device in accordance with the present invention has advantages as follows: At first, it can prevent a leakage current between electrodes, even if a gap between the electrodes is smaller than that of the conventional dual emitter triode structure and a lateral gate method; and Secondly, it can obtain more natural images than applied to an LCD (Liquid Crystal Display) backlight, even if individual electrodes are formed at the same distance as that of the conventional method.

Description

Description FIELD EMISSION DEVICE

Technical Field

[1] The present invention relates to a field emission device; and, more particularly, a field emission device capable of preventing leakage current between electrodes while improving unstable light emitting characteristics.

[2]

Background Art

[3] Generally, a currently utilized filed emission device such as a field emission type backlight, an FEFL(Field Emission Flat Lamp) and a field emission display utilizes an acute cold cathode on behalf of a hot cathode used in a conventional cathode ray tube as a means for discharging an acceleration electron to excite a fluorescent material. That is, the electrons due to a quantum mechanical tunnel effect are discharged by concentrating high electric field on an emitter forming the cold cathode. The U.S patent 3,970,887 by Donald O. Smith et. al teaches a structure to emit the electrons by forming a Si micro tip on a semiconductor substrate and by applying an electric filed to the Si micro tip through a gate electrode, however, since the electric field emission device of such method employs material with a high work function used for the micro tip, there exist problems that gate voltage for emitting the electrons is significantly high and the micro tip is easily damaged.

[4] Accordingly, a diamond film is spotlighted as the emitter, recently researches for a

CNT(Carbon Nano Tube) which emits the electrons even in the low electric field about a tenth of the electric field of the diamond film for emitting the electron have been actively studied.

[5] There are required for large light emitting area, high luminance, long life and simplification of process regardless of the emitter in order to utilize the device practically.

[6] Diode or triode structure exists in a conventional field emission device. In the diode structure, a method allows the electrons to excite and emit the fluorescent material by extracting the electrons from the field emission material by applying a high voltage between the anode electrode and the cathode electrode. However, although the diode structure has advantages that a manufacturing cost is low, a manufacturing process is easy and a light emitting area is large, but there are problems that a driving voltage is high and a luminance to be emitted stably is low and luminous efficiency is low.

[7] The field emission devices for the triode structure are disclosed in Korea public patent No. 2000-74609, United States of America patent 5,773,834 and Korea public patent Nos. 2001-84384 and 2004-44101. In the triode structure, to discharge the electron from the field emission matter, a gate electrode as an auxiliary electrode is separately formed from the cathode at a distance from several tens of nano meters to several millimeters. Consequently, the emitted electron excites the fluorescent substance of the anode so as to emit light by applying the high voltage to the anode and the cathode. This triode structure has the advantages of significantly lowering driving voltage and securing high luminance but there are problems such as relatively high cost for manufacturing, long manufacturing time, and small light emitting area.

[8] Fig. 1 represents a lateral gate type field emission device disclosed in Korea publication patent No. 2004-44101. Referring to Fig. 1, the cathode 10 is formed on a surface of a rear substrate 5, the emitter made of CNT is placed on a top surface of the cathode 10 with a predetermined gap, and the gate electrode 25 is adjacent to the rear substrate 5 by media of an insulation layer 15. The lateral gate type field emission device is composed of an anode 35 composed of a fluorescent material layer 30 and ITO (Indium Tin Oxide) by facing the rear substrate 5 and a front substrate 40.

[9] In a conventional field emission device for the triode structure including the lateral gate method, since the electrons are not discharged from the gate electrode 25, non- uniformity occurs in luminance, and since the electrons are only discharged from the emitter 20 placed on the top surface of the cathode 10, a lifetime is shortened and luminance is reduced due to a heavy load on the emitter 20.

[10] Fig. 2 is a construction diagram of Korea patent application No. 2004-70871 which is previously filed by the applicant of the present invention. In Fig. 2, the first electrode 105 and the second electrode 110 are placed on a top surface of the rear substrate 100, and also the emitter 115 is placed on a top surface of the first electrode 105 and the second electrode 110. This is a structure obtained by particularly removing a difference between the gate electrode and the cathode by forming the emitter 115 on the first electrode 105 and the second electrode 110. In other words, the first electrode 105 and the second electrode 110 become the gate electrode or the cathode according to the driving voltage. Hence the increment of light emitting area and light emitting efficiency, uniform light emission, high luminance, and long lifetime can be achieved.

[11] Fig. 3 is a plane view of the rear substrate 110 of the field emission device of Fig. 2.

As shown in Fig. 3, the first electrode member 105 and the second electrode member 110 are formed in a rake-shape crossing each other. The electrons are discharged from the emitter 115 placed on each electrode by alternately applying voltage having different polarities from each other to the first electrode member 105 and the second electrode member 110, respectively. As mentioned above, since the electrons are discharged from both of two electrodes, higher current density is obtained at the same electric field in comparison with the field emission device of the conventional lateral gate triode structure. Undoubtedly, it is possible to use one of the first electrode member 105 and the second electrode member 110 as the gate electrode.

[12] However, while the field emission devices of Figs. 2 and 3 overcome problems of the prior arts, increasing light emitting area and luminance and reducing manufacturing cost, they have a problem of generating a leakage current and electric arc when a gap between the electrodes is reduced for the purpose of increasing efficiency.

[13]

Disclosure of Invention Technical Problem

[14] The present invention has been proposed in order to overcome the above-described problems in the related background art. It is, therefore, an object of the present invention to provide a field emission device capable of preventing a leakage current between electrodes and improving an unstable light emitting characteristic by forming an emitter having more than four individual electrodes.

[15]

Technical Solution

[16] In accordance with one aspect of the present invention, there is provided a field emission device, including a front substrate and a rear substrate disposed by being separated at a predetermined distance from each other, an anode formed on the front substrate, a fluorescence material formed on the anode, a plurality of electrode members placed on the rear substrate by being separated at a predetermined distance from each other and an emitter formed on at least one among the electrode members, wherein the electrode members are composed of at least four electrode members, each electrode is formed alternately, and the emitters of each electrode member are separated from each other.

[17] Hereinafter, a preferred embodiment of the present invention will be described in detail with reference to the accompanying drawings. Above all, terms or words used in the specification and claims are not limited to usual or encyclopedical meaning, but the present invention should be understood by the meaning or concept matching to the technical sprits of the present invention on the basis of such principles that the scope of the term can be properly defined to explain the present invention with the best method by the inventor. Thus, since the embodiments described in the present specification and construction described on the accompanying drawings are only the preferred embodiments, but do not represent for all technical aspects of the present invention, it should be understood that various equivalents and modification examples exist for replacing with the technical aspects of the present invention at the time of filing the present invention.

[18] Advantageous Effects

[19] By forming an emitter having more than four individual electrode members, the electric field emission device in accordance with the present invention has advantages as follows: At first, it can prevent a leakage current between electrodes, even if a gap between the electrodes is smaller than that of the conventional dual emitter triode structure and a lateral gate method; and Secondly, it can obtain more natural images than applied to an LCD(Liquid Crystal Display) backlight, even if individual electrodes are formed at the same distance as that of the conventional method.

[20]

Brief Description of the Drawings

[21] Figs. 1 to 3 are diagrams showing a field emission device according to a prior art;

[22] Fig. 4 is a cross-sectional view depicting a field emission device in accordance with an embodiment of the present invention;

[23] Fig. 5 is a plane view representing a rear substrate of the field emission device in accordance with the embodiment of the present invention;

[24] Fig. 6 is a cross-sectional view describing a field emission device in accordance with another embodiment of the present invention;

[25] Fig. 7 is a cross-sectional view illustrating a field emission device in accordance with still another embodiment of the present invention;

[26] Fig. 8 is a view comparing the field emission device in accordance with the embodiments of the present invention with the conventional field emission device;

[27] Fig. 9 is an applied driving waveform diagram of the field emission device in accordance with the embodiments of the present invention;

[28] Fig. 10 is a comparison diagram comparing the field emission device in accordance with the embodiment of the present invention with the conventional device;

[29] Fig. 11 is a comparison diagram comparing the field emission device in accordance with the above-described another embodiment of the present invention with the conventional device;

[30] Fig. 12 is an applied driving waveform diagram of the field emission device in accordance with the above-described embodiment of the present invention;

[31] Fig. 13 is a comparison diagram comparing the field emission device in accordance with the above-described embodiment of the present invention with the conventional device; and

[32] Figs. 14 to 15 is an exemplary diagram depicting a driving circuit of the field emission device in accordance with the present invention.

[33]

[34] <Description of reference numerals for major parts of drawings> [35] 100: rear substrate 106: first electrode member

[36] 107: second electrode member 108: third electrode member

[37] 109: fourth electrode member 111, 112: insulating materials

[38] 115: emitter 200: front substrate

[39] 205: anode 210: fluorescence material

[40] 300: spacer 305: sealing agent

[41 ] 400: DC inverter 402: AC inverter

[42] 404, 406, 408: transformer

[43]

Best Mode for Carrying Out the Invention

[44] Fig. 4 is a construction diagram showing a field emission device in accordance with an embodiment of the present invention. In accordance with the field emission device of the present invention, a first electrode member 106, a second electrode member 107, a third electrode member 108 and a fourth electrode member 109 are formed on a rear substrate 100, and an emitter 115 is placed on a top surface of the electrode members

106, 107, 108 and 109. By forming the emitter 115 on all the electrode members 106,

107, 108 and 109, the electrode members 106, 107, 108 and 109 can be a gate or a cathode according to a driving voltage as a structure that practically removes a difference between the gate electrode and the cathode. By being formed as described above, a leakage current between the electrodes can be prevented and an unstable light- emitting characteristic can be improved. It is preferable that the rear substrate 100 can be made of glass, alumina (Al O ), quartz, plastic, and silicon (Si), but the glass substrate is more preferable.

[45] The electrodes 106, 107, 108 and 109 can be made of metal such as silver(Ag), chrome(Cr), copper(Cu), aluminum(Al), nickel(Ni), zinc(Zn), titanium(Ti), platinum(Pt), tungsten(W), or ITO(Indium Tin Oxide) and an alloy thereof, and it is appropriate to employ a printing method such as a screen printing method, but the electrode members 106, 107, 108 and 109 can be formed by using a method of sintering a metal powder or a thin film deposition method such as a sputtering, a vacuum deposition and a CVD(Chemical Vapor Deposition).

[46] The emitter 115 can be made of a carbon nano tube, diamond, DLC(Diamond Like

Carbon), fullerene, palladium oxide(PdO) or the like, but the carbon nano tube capable of emitting electrons even in a relatively low voltage is further preferable.

[47] A transparent electrode 205 and a fluorescence material 210 are formed on a front substrate and a spacer 300 maintaining a gap between the front substrate 200 and the rear substrate 100 exists. The front substrate 200 and the rear substrate 100 are sealed by a sealing agent such as a frit glass, thereby maintaining an inside space therebetween at a high vacuum in a degree of 10 torr. The front substrate 200 can be made of glass, quartz, plastic or the like, but the glass is further preferable. In addition, if all the rear substrate 100 and the front substrate 200 are made of plastic substrates, they can be used as a backlight of a flexible liquid crystal display.

[48] A transparent electrode 205 can be formed by depositing, coating or printing transparent conducting material such as ITO on the front substrate 200. A white fluorescence material such as oxide or sulfide obtained by mixing red, green, and blue fluorescence materials in a predetermined ratio is suitable for the fluorescence material 210 and the fluorescence material 210 can be formed by the screen printing method.

[49] The field emission device of the present invention includes a DC inverter 400 capable of generating power applied to the anode 205 on the front substrate for driving the same and an AC inverter 402 capable of generating power applied to each of the electrode members 106, 107, 108 and 109. An inner structure of the AC inverter 402 can apply various modifications to constructions of each electrode members 106, 107, 108 and 109 according to a size of the front substrate 200. In accordance with the field emission device of the present invention, by forming the four electrode members 106, 107, 108 and 109, the AC inverter 402 and the DC inverter 400 are operated. An AC inverter can be constructed by at least one.

[50] Fig. 5 is a plane view showing the rear substrate of the field emission device in accordance with the present invention. As shown in Fig. 5, each of the electrode members 106, 107, 108 and 109 is alternately formed in a rake shape, and electrons are emitted from the emitter 115 placed on each electrode member 106, 107, 108 and 109 by alternately applying voltages having different polarities from each other according to the phase difference of the electrode members 106, 107, 108 and 109. Since the electrons are emitted from all the electrode members 106, 107, 108 and 109, higher current density can be obtained in comparison with the conventional field emission device with a lateral gate triode structure. Insulating material 112 is formed on a portion overlapped by each electrode member one another.

[51] Fig. 6 is a construction diagram showing a field emission device in accordance with another embodiment of the present invention. A construction according to Fig. 6 is a method that is operated by making a pair of the first electrode member 106 and the third electrode member 108 and making a pair of the second electrode member 107 and the fourth electrode member 109, whereas a construction according to Fig. 4 is a method that is operated by making a pair of the first electrode member 106 and the second electrode member 107 and making a pair of the third electrode member 108 and the fourth electrode member 109. In the construction according to Fig. 6, since the electrons are emitted with making the pair of the first electrode member 106 and the third electrode member 108, gaps between each electrode members 106, 107, 108 and 109 can be formed nearly below a half in comparison with those of the conventional electrode members. And also, like Fig. 7, the leakage current between each electrode members 106, 107, 108 and 109 can be prevented more securely by forming the insulating material 111 between each of the electrode members 106, 107, 108 and 109. That is, if the gaps between each of the electrodes become narrower, it is achieved by mutually controlling a thickness, a height and an insulating component of the insulating material 111.

[52] Figs. 8a to 8c are diagrams comparing a driving method in accordance with a construction of the field emission device in Fig. 4 with driving methods according to prior arts. Fig. 8a represents a method for driving a conventional dual emitter; Fig. 8b represent a method for driving a quadruple emitter in accordance with embodiments of the present invention; and Fig. 8c represents a method for driving a conventional lateral gate. In addition, Fig. 8 shows that the driving methods shown in Figs. 8a to 8c are emitted at the same electrode distance. For the sake of convenience, the first electrode and the second electrode are represented by X and Y in Fig. 8a, respectively; the first electrode, the second electrode, the third electrode, and the fourth electrode are represented by Xl, X2, Yl and Y2, respectively in Fig. 8b; and the gate and emitter are represented by X and Y, respectively in Fig. 8c.

[53] Fig. 9 represents a driving waveform applied in response to times Tl, T2, T3 and

T4 in each structure of Fig. 8. The electron emission according to the driving waveform of Fig. 9 is equal to that of Fig. 10. Assuming that the same frequency is applied at the same electrode distance, the dual emitter of Fig. 8a and the quadruple emitter of Fig. 8b show the same number of the light emissions (8 times), and the lateral gate method of Fig. 8c shows a half of the number (4 times). Although the dual emitter method of Fig. 8a and the quadruple emitter method of Fig. 8b show the same number of light emission, it is shown that the quadruple emitter of Fig. 8b can emit the light continuously. Accordingly, the more excellent images are obtained than the conventional device when the quadruple emitter method according to the embodiment of the present invention is applied to the LCD backlight.

[54] Fig. 11 shows diagrams comparing the driving method in accordance with the field emission device of Fig. 6 with those of the prior arts. A conventional dual emitter driving method is described in Fig. 1 Ia; a quadruple emitter driving method in accordance with the embodiment of the present invention is depicted in Fig. 1 Ib; and a conventional lateral gate driving method is shown in Fig. 11C. In addition, Figs. 1 Ia to l ie represent the light emission methods at a different electrode distance from each other. For the shake of convenience, the first electrode member and the second electrode member are represented by X and Y in Fig. 11a, respectively; the first electrode member, the second electrode member, the third electrode member, and the fourth electrode member are represented by Xl, X2, Yl and Y2, respectively in Fig. 1 Ib; and the gate and emitter are represented by X and Y, respectively in Fig. 1 Ic.

[55] Fig. 12 shows the applied driving waveform according to the times Tl, T2, T3 and

T4 in each of the structures of Fig. 11. The electron emission according to the driving waveform of Fig. 12 is equal to that of Fig. 13. Assuming that the same frequency is applied at the same electrode distance, the dual emitter of Fig. 11a and the quadruple emitter of Fig. 1 Ib show the same number of the light emissions (4 times), and the lateral gate method of Fig. 1 Ic shows a half of the number (2 times). Although the dual emitter method of Fig. 11a and the quadruple emitter method of Fig. 1 Ib show the same number of light emission, the quadruple emitter of Fig. 1 Ib can obtain the same number of the light emission with the half of frequency cycle of the dual emitter method of Fig. 11a. Therefore, the quadruple emitter method in accordance with the embodiment of the present invention increases the life span of the field emission device more than twice.

[56] The field emission device in accordance with the embodiment of the present invention is capable of adopting a driving method having various frequencies and duty ratios when applying a square wave and an AC wave. In other words, driving circuits of Fig. 14 to Fig. 15 can be adopted.

[57] Fig. 14 shows a driving circuit in accordance with the field emission device of the present invention. First, the power is applied to the AC inverter 402 from an input power supply 401. Thereafter, an irregular waveform is filtered at a power filtering member 402a, an power transformed into desired various shapes applied to a high voltage generation member 402d by using a power device at the power driving stage 402c through a power supply member 402b and a driving pulse is generated. The electric power applied to the high voltage generating member 402d is applied to the first electrode member 106, the second electrode member 107 and an transparent substrate (an anode substrate) 205 through a transformer to operate the field emission device. This can be also applied to the third electrode member 108 and the fourth electrode member 109, similarly.

[58] Fig. 15 is one embodiment showing the high voltage generating member 402d of the AC inverter 402. The high voltage generating member 402d of Fig. 15 represents such a state that each driving duty of the first electrode and the second electrode is 50%. As this is achieved by commonly grounding an intermediate potential of the AC wave to the DC inverter, the case as shown in Fig. 14 is operated by commonly grounding an intermediate tab region of a secondary coil of a pair of transformers 404 and 406 among construction elements consisting of the whole inverter to the DC inverter 400. It is preferable that the ground of the present invention employs a virtual grounding method so as to generate a stable output. [59] The driving circuits of Fig. 14 and Fig. 15 can be applied to the driving method of

Fig. 4 as well as to the driving method of Fig. 6. And also, it is obvious that the driving circuits can be applied although more than one AC inverter 402 is used.

[60] While the present invention has been described with respect to certain preferred embodiments, it will be apparent to those skilled in the art that various changes and modifications may be made without departing from the scope of the invention as defined in the following claims.

Claims

[1] A field emission device, comprising: a front substrate and a rear substrate disposed by being separated at a predetermined distance from each other; an anode formed on the front substrate; a fluorescence material formed on the anode; a plurality of electrode members placed on the rear substrate by being separated at a predetermined distance from each other; and an emitter formed on at least one among the electrode members, wherein the electrode members are composed of at least four electrode members, each electrode is formed alternately, and the emitters of each electrode member are separated from each other. [2] The field emission device as recited in claim 1, wherein each of more than four electrode members alternately changed into a cathode or a gate electrode together with adjacent electrodes to emit electrons. [3] The field emission device as recited in claim 1, wherein each of more than four electrode members is alternately changed into a cathode or a gate electrode together with electrodes next to adjacent electrodes. [4] The field emission device as recited in claim 1, wherein an insulator is formed between each of said more than four electrode members. [5] The field emission device as recited in claim 1, further comprising: a DC inverter applying power to the anode; and an AC inverter grounding an intermediate electric potential of an AC wave to the

DC inverter and applying the power to each of the electrode members.