Description

FLAT LAMP DEVICE FOR TFT-LCD USING CARBON NANO

TUBE

Technical Field

[1] The present invention relates to a flat lamp device for TFT-LCD using a carbon nano tube, and more particularly to a flat lamp device capable of eliminating an afterimage problem in which an image is not clearly changed to a slow response time of a liquid crystal in a TFT-LCD panel, and also giving a high uniformity with a low power consumption.

[2]

Background Art

[3] Generally, a separate backlight module is required to display images on a screen because a TFT-LCD panel is not an active light emitting device. As one of the backlight modules, a CCFL backlight module for TFT-LCD is always turned on regardless of on/off states of a liquid crystal when the TFT-LCD is driven. That is, the backlight is always in a turned-on state, and as a liquid crystal is turn on or off, the light passes through the liquid crystal to display predetermined images on the screen.

[4] When the light from the backlight is interrupted or transmitted, a time delay is caused due to the slow response time of the liquid crystal, resulting in undesirable light leakage. Therefore, this causes an after-image problem in which an image is not clearly changed but faintly displayed on the screen. This problem is more serious when an image changes rapidly or a rapidly moving object is displayed on the screen.

[5]

Disclosure of Invention Technical Problem

[6] Accordingly, the present invention is designed to solve the problems of the prior art, and therefore it is an object of the present invention to provide a flat lamp device for TFT-LCD capable of eliminating an after-image in which an image is not clearly changed due to a slow response time of a liquid crystal in a TFT-LCD panel.

[7] Also, it is an object of the present invention to provide a flat lamp device for TFT-

LCD having high uniformity and low power consumption.

[8]

Technical Solution

[9] In order to accomplish the above object, the present invention provides a flat lamp device using a carbon nano tube, which is used as a backlight of a TFT-LCD panel, the flat lamp device including: a cathode electrode; a plurality of carbon nano tubes

installed on the cathode electrode; a mesh-type grid electrode installed over the carbon nano tubes to induce electron emission from the carbon nano tubes and having openings through which the emitted electrons pass; an anode electrode installed over the grid electrode and accelerating electrons emitted from the carbon nano tubes; a phosphor layer formed on a lower surface of the anode electrode and colliding with the accelerated electrons to emit light; and a controller for applying a voltage pulse to the cathode electrode in response to on/off states of a liquid crystal of the TFT-LCD so that the phosphor layer emits light.

[10] Preferably, the controller applies a voltage pulse to the cathode electrode for a period shorter than a frame time of the liquid crystal so that the phosphor layer can emit light for a period shorter than the frame time in one frame.

[11] More preferably, the cathode electrode includes a plurality of split electrodes which are electrically driven independently.

[12] Also, the split electrodes are preferably grouped in predetermined numbers to form electrode blocks, and the electrode blocks are driven independently.

[13] Additionally, the split electrodes is preferably driven sequentially or crossly, or a plurality of the split electrodes are driven in parallel.

[14] Here, the flat lamp device for TFT-LCD preferably includes a lower glass substrate installed on a lower surface of the cathode electrode; an upper glass substrate installed on an upper surface of the anode electrode; a frit installed between the upper glass substrate and the lower glass substrate to seal a space between the upper glass substrate and the lower glass substrate int a vacuum and having a lower melting temperature than the glass substrate; and a spacer for supporting the upper glass substrate and the lower glass substrate to maintain a gap between the upper and lower glass substrates.

[15] Preferably, the split electrodes are driven by a voltage pulse only once or at least two times in one frame.

[16] Preferably, in the cathode electrode, the split electrodes is split either horizontally or vertically, or both partitioned horizontally and vertically.

[17] Also, the split electrodes are preferably operated to turn on the flat lamp device with an intermediate brightness level.

[18]

Brief Description of the Drawings

[19] These and other features, aspects, and advantages of preferred embodiments of the present invention will be more fully described in the following detailed description, taken accompanying drawings. In the drawings:

[20] FIG. 1 is a cross-sectional view schematically showing a flat lamp device for TFT-

LCD using a carbon nano tube according to one preferred embodiment of the present

invention.

[21] FIG. 2 is a top view schematically showing a lower glass substrate and an electron supply source of the flat lamp device as shown in FIG. 1.

[22] FIG. 3 is a top view schematically showing a grid electrode and a spacer of the flat lamp device of FIG. 1.

[23] FIG. 4 is a top view schematically showing an upper glass substrate, an anode electrode and a phosphor layer of the flat lamp device of FIG. 1.

[24] FIG. 5 is a circuit view showing the flat lamp device of FIG. 1.

[25] FIG. 6 is a graph showing a voltage pulse applied to the cathode electrode of the flat lamp device of FIG. 1.

[26]

Best Mode for Carrying Out the Invention

[27] Hereinafter, preferred embodiments of the present invention will be described in detail referring to the accompanying drawings. Prior to the description, it should be understood that the terms used in the specification and appended claims should not be construed as limited to general and dictionary meanings, but interpreted based on the meanings and concepts corresponding to technical aspects of the present invention on the basis of the principle that the inventor is allowed to define terms appropriately for the best explanation. Therefore, the description proposed herein is just a preferable example for the purpose of illustrations only, not intended to limit the scope of the invention, so it should be understood that other equivalents and modifications could be made thereto without departing from the spirit and scope of the invention.

[28] FIG. 1 is a cross-sectional view schematically showing a flat lamp device for TFT-

LCD using a carbon nano tube according to one preferred embodiment of the present invention, and FIG. 2 is a top view schematically showing a lower glass substrate and an electron supply source of the flat lamp device.

[29] Referring to FIG. 1 and FIG. 2, the flat lamp device 100 for TFT-LCD includes a cathode electrode 12; a plurality of carbon nano tubes 15 installed on the cathode electrode 12; a grid electrode 18 installed over the carbon nano tubes 15; an anode electrode 20 installed over the grid electrode 18; a phosphor layer 21 formed in a lower surface of the anode electrode 20; and a controller (not shown) for applying a voltage pulse to the cathode electrode 12 in response to on/off states of a liquid crystal of the TFT-LCD.

[30] The cathode electrode 12 is formed on a surface of the lower glass substrate 10. An

AC power source is connected to the cathode electrode 12.

[31] Preferably, the cathode electrode 12 is composed of a plurality of split electrodes

12', 12", 12'" which are electrically driven independently. The split electrodes

12', 12", 12'" are independently driven under the control of the controller (not shown). Also, the split electrodes 12', 12", 12'" may be bound by a predetermined number to form electrode blocks, which may be driven independently of each other by the controller. The controller will be described in detail later.

[32] More preferably, the split electrodes 12', 12", 12'" are obtained by splitting the cathode electrode 12 either horizontally or vertically, or both horizontally and vertically. That is, FIG. 2 shows that the cathode electrode 12 is split horizontally, but the cathode electrode 12 may be also split horizontally or vertically, or both horizontally and vertically.

[33] A plurality of independently formed electron supply sources are provided on the cathode electrode 12. The electron supply sources include a plurality of carbon nano tubes 15 for emitting electrons. An insulator 13 and a semiconductor layer 14 for maintaining constant electron emission are formed on the cathode electrode 12.

[34] The insulator 13 serves as a barrier for controlling flow of electrons to improve electron emission uniformity and serves to shield the cathode electrode 12. The insulator 13 is preferably composed of SiNx, and for example, formed with a thickness of about 50 D or less.

[35] The insulator 13 is formed as a single film over the entire area of the split electrodes

12', 12", 12'". Alternatively, the insulator 13 may be composed of a plurality of insulators independently patterned at regular intervals so that they can be formed within a region where the semiconductor layer 14 is formed.

[36] The semiconductor layer 14 also serves to improve electron emission uniformity, and it is preferably composed of amorphous silicon such as SiO and for example, y formed with a thickness of about 200 D or less. The semiconductor layer 14 is formed on the insulator 13. The semiconductor layer 14 is composed of a plurality of semiconductor layers which are independently patterned at regular intervals.

[37] A plurality of carbon nano tubes 15 are formed on the semiconductor layer 14, and a catalytic metal layer 16 is then laminated onto the semiconductor layer 14 for the purpose of growth of the carbon nano tubes 15. Preferably, the catalytic metal layer 16 is composed of Ni, Co, Fe or alloys thereof, and an adhesive layer 17 is interposed between the catalytic metal layer 16 and the semiconductor layer 14 in order to enhance an adhesion force of the catalytic metal layer 16, wherein the adhesive layer 17 is, for example, composed of at least one of Ti, TiN, Ta, TaN, WNx and TiW.

[38] Though not described in detail herein, the insulator 13, the semiconductor layer 14 and the catalytic metal layer 16 may be formed according to conventional semiconductor manufacturing processes using photolithography, screen printing or ink-jet methods, and the carbon nano tube 15 may be formed according to various methods such as plasma-enhanced chemical vapor deposition (PECVD), adhesion methods

using a mixture of a solvent and an adhesive, or the like.

[39] The grid electrode 18 has a mesh shape in which openings are formed so that the electrons emitted from the carbon nano tube 15 can pass through the opening, preferably with porosity of 50 % or more. More preferably, the grid electrode 18 is installed to be spaced at a distance of 0.1 to 10 D from the cathode electrode 12.

[40] Also, a plurality of spacers 19 are interposed between the lower glass substrate 10 and the upper glass substrate 11, which face each other, in order to maintain a constant distance between the lower and upper glass substrates 10, 11. More preferably, the spacers 19 may be formed integrally with the grid electrode 18 for the purpose of easy assembling of a flat lamp device, as shown in FIG. 3.

[41] As shown in FIG. 4, an anode electrode 20 is formed on the entire lower surface of the upper glass substrate 11, preferably at a point spaced at a distance of 1 to 1,000 D from the grid electrode 18. The anode electrode 20 is formed of transparent electrode materials such as InSnOx, InOx or ZnOx.

[42] A phosphor layer 21 colliding with the electrons emitted from the carbon nano tube

15 to give the light is provided on a lower surface of the anode electrode 20. The phosphor used herein includes sulfides or oxides as a main component, and phosphors that emit red, green, blue, or other various color lights may be considered according to its use.

[43] The lower glass substrate 10 and the upper glass substrate 11 are adhered to each other by means of frit 22. That is, the frit 22 is applied to edges of the lower glass substrate 10 and the upper glass substrate 11, and heat-melted under a vacuum condition to attach the lower and upper glass substrate 10,11 to each other. The frit 22 is made of adhesive materials having a lower melting temperature than that of the glass substrates 10, 11. As an alternative, the following method may be used: heating the lower and upper glass substrates 10, 11 to a melting temperature of the frit 22 under an atmospheric pressure to attach them to each other; making an inner space between the lower glass substrate 10 and the upper glass substrate 11 to a vacuum state through an exhaust pipe (not shown) previously formed in the cathode electrode 12, the anode electrode 20 or the frit 22; and closing the exhaust pipe.

[44] Preferably, a vacuum degree of the inner space is enhanced by inserting a getter 23 into the inner space before the adhesion of the substrates 10, 11, and then heating the getter 23 with a laser to activate the getter 23 after the adhesion of the substrates 10, 11, thereby removing residual gases from the inner space.

[45] Also, an emission improving film 24 may be preferably further attached to the top of the upper glass substrate 11 for homogeneous light emission.

[46] In the drawings, reference numerals 12a, 12b, 12c, 26 and 27 represent pads for applying a voltage to the cathode electrodes 12', 12", 12'", the grid electrode 18, the

anode electrode 20, respectively.

[47] The controller applies a voltage pulse to the cathode electrode 12 in response to on/ off states of a liquid crystal. That is, the controller applies a voltage pulse to the cathode electrode 12 to allow light emission of the phosphor layer 21 when the liquid crystal is in a turned-on state.

[48] Preferably, the controller applies a voltage pulse to the cathode electrode 12 for a period shorter than a frame time of the liquid crystal so that the phosphor layer 21 can emit light for a period shorter than one frame time in one frame. For this purpose, the controller receives a synchronizing signal (a control signal) outputted from a timing controller of TFT-LCD. Alternatively, the controller may also receives the synchronizing signal along with a signal transmitted to a liquid crystal to extract a synchronizing drive signal.

[49] Although the phosphor layer 21 is allowed to emit light for a period shorter than a frame time in one frame through this controlling procedure, it is not recognized by human eyes. This is based on the same principle that users do not recognize that CRT displays an image in one frame using a scan method.

[50] Hereinafter, an operation procedure of the flat lamp device 100 according to the preferred embodiment of the present invention will be described in detail.

[51] First, a voltage pulse as shown in FIG. 6 is applied to the cathode electrode 12 and the grid electrode 18. For example, a voltage of 100 V or below having a positive value on the basis of the cathode electrode 12 is applied between the cathode electrode 12 and the grid electrode 18, and a high voltage of 10 kV or below is applied to the anode electrode 20. If the voltage is applied in the same manner as described above, electrons are emitted from the carbon nano tube 15. The emitted electrons are accelerated towards the phosphor layer 21 by the high voltage applied to the anode electrode 20. Then, the accelerated electrons collide with the phosphor layer 21, and therefore a fluorescent material is allowed to emit the light.

[52] The application of the voltage pulse is controlled by the controller. The controller applies a voltage pulse to the cathode electrode 12 for a period shorter than a frame time of the liquid crystal, thereby allowing the phosphor layer 21 to emit light for a period shorter than the frame time in one frame. That is, a turned-on period when the voltage pulse is applied is included in the period while the liquid crystal is turned on, as shown in FIG. 6. The controller receives a synchronizing signal (a control signal) outputted from a timing controller of TFT-LCD, or receives the synchronizing signal along with a signal transmitted to a liquid crystal to extract a synchronizing drive signal, and then applies a voltage pulse to the cathode electrode 12.

[53] Hereinafter an operation procedure of the controller will be described in detail.

[54] In a 60Hz driving mode which is the most general mode for driving TFT-LCD, one

image, namely one frame, is displayed for 16.7 msec (1/60 sec) since 60 images are displayed per one second.

[55] The number of vertical drive lines are determined depending on resolution of an image. At this time, if the number of vertical drive lines is "n," it takes (16.7/n)msec to drive one vertical drive line. Accordingly, the lines are grouped into block units having the minimum number of "one line" to the maximum number of "n lines", if necessary, and then every block unit is turned on for a period shorter than the frame time in one frame.

[56] If the flat lamp device 100 is used as a backlight of TFT-LCD having a VGA resolution (640 pixelsx480 lines), each of pulses has a maximum pulse width of 34.8 μsec. If the 480 lines are divided into 3 blocks, each of the blocks has 160 lines, and therefore a driving time of one block is calculated to be 6.2 msec. 6.2 msec is calculated in consideration of a delay time when the lines are turned on/off.

[57] At this time, if the cathode electrode 12 is also divided into 3 groups, each of the split electrodes 12', 12", 12'" may be driven with a turned-on signal of 6.2 msec and a turned-off signal of 10.5 msec, during one frame time of 16.7 msec which is the sum. If the split electrodes 12', 12", 12'" is driven sequentially, a voltage pulse is applied to the first split electrode 12' for 6.2 msec, and then not applied for 10.5 msec, and a voltage pulse is applied to the second split electrode 12" for 6.2 msec after the first 6.2 msec, and the second split electrode 12" is then turned off for 10.5 msec. The third split electrode 12'" is also operated in connection with the first and second split electrodes 12', 12".

[58] In addition to the sequential driving mode as described above, the split electrodes

12', 12", 12'" may also be driven in a cross driving mode and a parallel driving mode. For example, in the cross driving mode, the third split electrode 12'" is driven after the first split electrode 12' is driven, and the second split electrode 12" is driven after the third split electrode 12'" is driven. In the case of the parallel driving mode, at least two of the split electrodes 12', 12", 12'" are driven at the same time.

[59] Also, the split electrodes 12', 12", 12'" may be driven by a voltage pulse once or at least two times in one frame. The controller may adjust a driving frequency of the split electrodes 12', 12", 12'" in one frame by controlling the cycle and delay time of a voltage pulse.

[60] Meanwhile, the brightness of irradiated light may be adjusted by controlling voltage differences between the grid electrode 18 and the cathode electrode 12, and between the cathode electrode 12 and the anode electrode 20. Accordingly, the split electrodes 12', 12", 12'" may be operated so that the flat lamp device can be turned on with any intermediate brightness.

[61] The light emitted from the phosphor layer 21 is emitted to a front surface through

the upper glass substrate 11, and preferably irradiated more uniformly while passing through the emission improving film 24.

[62] A circuit of the flat lamp device according to the present invention may be expressed, as shown in FIG. 5. The flat lamp device 100 may induce electron emission with a low voltage since it includes the grid electrode 18 between the cathode electrode 12 and the anode electrode 20. Also, influences between a plurality of the electrons supply sources may be minimized since they are formed in a parallel circuit and driven independently. A surface light source may be driven stably and a uniform surface emission may be accomplished due to the use of the grid electrode and the parallel circuit design of the electron supply source.

[63]

Industrial Applicability

[64] The flat lamp device for TFT-LCD using a carbon nano tube according to the present invention has the following advantages.

[65] First, it is possible to eliminate an after-image problem in which an image is not clearly changed due to a slow response time of a liquid crystal in a TFT-LCD panel.

[66] Second, there is provided a flat lamp device for TFT-LCD capable of reducing generation of heat by realizing high brightness with high uniformity and low electric power.