KR100800568B1 - Field emission device and method for driving the same - Google Patents

Abstract

A field emission device and a method for driving the same are provided to ensure the operation stability of the field emission device by preventing over current in an anode electrode. A field emission device includes a lower substrate(11), gate and cathode electrodes(12_1-12_4,13_1-13_4), an emitter, an upper substrate(21), and an external voltage source. The lower substrate includes plural driving areas. The gate and cathode electrodes, which are located in the lower substrate, are electrically separated from each other. The emitter is formed on at least one of the gate and cathode electrodes. The upper substrate, which is disposed opposite to the lower substrate, includes an anode electrode. The external voltage source supplies pulse voltages to at least one of gate and cathode electrodes. The brightness of the driving areas is adjusted by adjusting the ratio of an on-time period to an off-time period. The pulse voltages are supplied during the on-time period and the pulse voltages are not supplied during the off-time period.

Description

Field emission device and driving method thereof {FIELD EMISSION DEVICE AND METHOD FOR DRIVING THE SAME}

1 is a plan view of a field emission device according to embodiments of the present invention.

FIG. 2 is an enlarged view of region A of FIG. 1.

3 is a cross-sectional view taken along the line II ′ of FIG. 2.

4 shows waveforms of pulse voltages used to drive a field emission device according to embodiments of the present invention.

FIG. 5 is an enlarged view of region B of FIG. 4.

♧ Explanation of Reference Numbers for Main Parts of Drawing

11: lower substrate

12_1, 12_2, 12_3, 12_4: gate electrode

13_1, 13_2, 13_3, 13_4: cathode electrodes

14 emitter

21: upper substrate

22: anode electrode

30: inverter

40: controller

The present invention relates to a field emission device, and more particularly to a method for driving the field emission device.

Liquid crystal display devices have been widely used in display devices in the computer or television field because of their light weight and low power consumption. However, the liquid crystal display itself does not form an image by emitting light and can form an image only after receiving uniform light from the rear. Providing such light is a backlight, and researches for using a field emission device as the backlight have been actively conducted.

The field emission device may be classified into a bipolar tube type and a tripole type tube according to the structure thereof. The triode type field emission device typically has a lower substrate in which a gate electrode and a cathode electrode are disposed in parallel, and an upper substrate in which an anode electrode is disposed. It includes. An emitter is disposed on the gate electrode and the cathode electrode. The tripolar field emission device may be driven by providing a pulse voltage to the gate electrode. That is, when a pulse voltage is provided to the gate electrode, electrons are emitted from the emitter, and the phosphor on the anode is excited and emitted by the emitted electrons.

The amount of electrons emitted to the anode electrode may increase in proportion to the substrate size and the intensity of the pulse voltages provided to the anode electrode and the gate electrode. In particular, when the size of the substrate increases, when a pulse voltage is provided to the gate electrode, driving is not stably performed because a large amount of electrons are instantaneously emitted to the anode electrode by the field emission phenomenon. For example, an excessively high peak current flows through a series resistor provided to prevent overcurrent from flowing to the anode electrode, thereby lowering a voltage provided to the anode electrode. As a result, the brightness and efficiency of the field emission device can be reduced, and an inverter capable of withstanding high current during driving is required, thereby increasing the manufacturing cost.

In addition, since the conventional backlight used in the liquid crystal display is always turned on at the maximum brightness, excessive power is consumed, and it is against the demand for improvement in the contrast ratio of the liquid crystal display.

Embodiments of the present invention provide a field emission device capable of partially adjusting luminance and a driving method thereof.

Embodiments of the present invention provide a field emission apparatus and a driving method thereof, which can partially improve contrast ratio.

Embodiments of the present invention provide a field emission apparatus and a driving method thereof that can be stably driven.

Field emission apparatus according to embodiments of the present invention comprises: a lower substrate; Gate electrodes positioned on the lower substrate and electrically isolated from each other; Cathode electrodes disposed on the lower substrate and electrically isolated from each other; An emitter positioned on at least one of the gate electrodes and the cathode electrodes; An upper substrate disposed to face the lower substrate and having an anode electrode; And an external power supply for providing pulse voltages to at least one of the gate electrodes and the cathode electrodes. The lower substrate may be divided into a plurality of driving regions, and the luminance of the driving regions may be adjusted by adjusting a ratio between on-time sections in which the pulse voltages are provided and off-time sections in which the pulse voltages are not provided. have.

The pulse voltages may include gate pulse voltages provided to the gate electrodes and cathode pulse voltages provided to the cathode electrodes, and the external power source independently provides the gate pulse voltages and the cathode pulse voltages. can do. The off-time periods may be greater than a period of the pulse voltages and less than 1 second. The gate electrodes and the cathode electrodes may be arranged in a lateral gate type, a normal gate type, or an under gate type.

The pulse voltages may include gate pulse voltages provided to the gate electrodes and cathode pulse voltages provided to the cathode electrodes, and the external power source supplies the gate pulse voltages and the cathode pulse voltages to the driving region. Can be provided independently. The gate pulse voltages and the cathode pulse voltages may have different on-time intervals according to the driving regions. The gate pulse voltage and the cathode pulse voltage provided in the same driving region may have the same on-time interval.

A method of driving a field emission device according to embodiments of the present invention includes: a lower substrate; Gate electrodes positioned on the lower substrate and electrically isolated from each other; Cathode electrodes disposed on the lower substrate and electrically isolated from each other; An emitter positioned on at least one of the gate electrodes and the cathode electrodes; An upper substrate disposed to face the lower substrate and having an anode electrode; And an external power source providing pulse voltages to at least one of the gate electrodes and the cathode electrodes, wherein the lower substrate is divided into a plurality of driving regions. The brightness of the driving regions may be adjusted by adjusting a ratio between on-time sections in which the pulse voltages are provided and off-time sections in which the pulse voltages are not provided.

Adjusting the brightness may include providing the gate pulse voltages and the cathode pulse voltages independently of the gate electrodes and the cathode electrodes. The off-time periods may be greater than a period of the pulse voltages and less than 1 second. The pulse voltages may be provided to have a phase difference.

The pulse voltages may include gate pulse voltages provided to the gate electrodes and cathode pulse voltages provided to the cathode electrodes, and adjusting the brightness may include the gate pulse voltages and the cathode pulse voltages. And providing independently to the drive regions. The gate pulse voltages and the cathode pulse voltages may be provided to have different on-time intervals according to the driving regions. The gate pulse voltage and the cathode pulse voltage provided in the same driving region may be provided to have the same on-time interval.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. However, the present invention is not limited to the embodiments described herein and may be embodied in other forms. Rather, the embodiments introduced herein are provided so that the disclosure may be made thorough and complete, and to fully convey the spirit of the present invention to those skilled in the art.

Although terms such as first, second, etc. are used herein to describe various elements, the elements should not be limited by such terms. These terms are only used to distinguish the elements from one another.

Hereinafter, a lateral gate type field emission device is described as an embodiment of the present invention. However, the present invention is not limited thereto and may be applied to other types of field emission devices such as a normal gate type and an under gate type field emission device.

1 to 3, a field emission apparatus according to embodiments of the present invention is described. The field emission device 1 includes a lower substrate 11 and an upper substrate 21. Gate electrodes 12_1, 12_2, 12_3 and 12_4 and cathode electrodes 13_1, 13_2, 13_3 and 13_4 are disposed on the lower substrate 11. Each of the gate electrodes 12_1, 12_2, 12_3 and 12_4 and the cathode electrodes 13_1, 13_2, 13_3 and 13_4 may have a stripe shape. In addition, the stripes of the gate electrode and the stripes of the cathode electrode may be alternately arranged one by one. The widths of the gate electrodes 12_1, 12_2, 12_3, 12_4 and the cathode electrodes 13_1, 13_2, 13_3, and 13_4 are 150 μm, respectively, and the cathode electrodes adjacent to the gate electrodes 12_1, 12_2, 12_3, and 12_4. The interval between the fields 13_1, 13_2, 13_3, and 13_4 may be 50 μm.

Emitter 14 may be disposed on the central portion of gate electrodes 12_1, 12_2, 12_3, 12_4 and / or cathode electrodes 13_1, 13_2, 13_3, 13_4. Emitter 14 may have a stripe shape. The width of the emitter 14 may be 100 μm. Thus, the spacing between the emitter 14 and the cathode electrodes 13_1, 13_2, 13_3, 13_4 on the gate electrodes 12_1, 12_2, 12_3, 12_4 and the emitter on the cathode electrodes 13_1, 13_2, 13_3, 13_4 An interval between the 14 and the gate electrodes 12_1, 12_2, 12_3, and 12_4 may be 75 μm. The emitter 14 may be formed by applying a paste including carbon nanotubes by screen printing.

Referring to FIG. 1, the lower substrate 11 may be divided into N driving regions Dn. In the present embodiment, the lower substrate 11 includes 84 driving regions Dn. However, in another embodiment of the present invention, the number of driving regions Dn may vary. Each of the driving regions Dn may be driven independently of each other. Hereinafter, as illustrated in FIG. 2, four driving regions D1, D2, D3, and D4 of the 84 driving regions are described as an example to easily describe the exemplary embodiment of the present invention.

Referring back to FIGS. 2 and 3, the gate electrodes 12_1, 12_2, 12_3, 12_4 and the cathode electrodes 13_1, 13_2, 13_3, 13_4 are respectively formed in the driving regions D1, D2, D3, and D4. Can be placed one by one. For example, the first gate electrode 12_1 and the first cathode electrode 13_1 may be disposed in the first driving region D1, and the second gate electrode 12_2 and the second cathode electrode 13_2 may be second driven. It may be disposed in the area D2. The third gate electrode 12_3 and the third cathode electrode 13_3 may be disposed in the third driving region D3, and the fourth gate electrode 12_4 and the fourth cathode electrode 13_4 may be disposed in the fourth driving region. It may be disposed at (D4).

The upper substrate 21 is disposed to face the lower substrate 11. The anode electrode 22 and the phosphor layer 23 may be disposed on the upper substrate 21 toward the lower substrate 11. The anode electrode 22 may be formed of a transparent conductive material such as indium tin oxide (ITO), and the phosphor layer 23 may be formed of a white phosphor in which RGB phosphors are mixed in a predetermined ratio.

The lower substrate 11 and the upper substrate 21 may face each other at regular intervals, for example, 6 mm intervals, with a spacer (not shown) therebetween, and a vacuum may be formed in the space therebetween so that electrons can be emitted. . The degree of vacuum may be 10 ⁻⁷ Torr.

The field emission device 1 provides pulse voltages to the gate electrodes 12_1, 12_2, 12_3, 12_4 and the cathode electrodes 13_1, 13_2, 13_3, 13_4, and provides a high DC voltage to the anode electrode 14. An inverter 30 may be included. In addition, the field emission device 1 may include a controller 40 for controlling the inverter 30.

2, 4 and 5, a method of driving a field emission device according to embodiments of the present invention will be described. The inverter 30 provides a direct current voltage of 8 kV to the anode electrode 22 under the control of the controller 40, the gate electrodes 12_1, 12_2, 12_3, 12_4 and the cathode electrodes 13_1, 13_2, 13_3, Gate pulse voltages GPV1, GPV2, GPV3 and GPV4 of 250V and cathode pulse voltages CPV1, CPV2, CPV3 and CPV4. The gate pulse voltages GPV1, GPV2, GPV3, and GPV4 and the cathode pulse voltages CPV1, CPV2, CPV3, and CPV4 may be rectangular. For example, the frequency, period T, and pulse width T _W of the square wave may be 5 kH, 200 Hz, and 1 Hz, respectively. In addition, the gate pulse voltages GPV1, GPV2, GPV3, and GPV4 and the cathode pulse voltages CPV1, CPV2, CPV3, and CPV4 may be sequentially provided to have a phase difference P _D. For example, the first gate pulse voltage GPV1 and the second gate pulse voltage may be sequentially applied to the first gate electrode 12_1, the second gate electrode 12_2, the third gate electrode 12_3, and the fourth gate electrode 12_4. GPV2, third gate pulse voltage GPV3, and fourth gate pulse voltage GPV4 may be provided, followed by a first cathode electrode 13_1, a second cathode electrode 13_2, and a third cathode electrode 13_3. ), The first cathode pulse voltage CPV1, the second cathode pulse voltage CPV2, the third cathode pulse voltage CPV3, and the fourth cathode pulse voltage CPV4 may be sequentially provided to the fourth cathode electrode 13_4. Can be.

The minimum value of the phase difference P _D of the gate pulse voltages GPV1, GPV2, GPV3, GPV4 and the cathode pulse voltages CPV1, CPV2, CPV3, CPV4 may be greater than or equal to the pulse width T _W. In addition, when the number of driving regions is N and the period of the pulse voltages is T, the phase difference P _D between the gate pulse voltages GPV1, GPV2, GPV3 and GPV4 and the cathode pulse voltages CPV1, CPV2, CPV3, CPV4. ) May be T / 2N. For example, the period T may be 200 Hz, and the minimum number of the 84-plane phase difference PD may be 200/168 (about 1.2 ms). In this case, the second gate pulse voltage GPV2 may be provided with a phase difference of 1.2 Hz with respect to the first gate pulse voltage GPV1, and the third gate pulse voltage GPV3 and the fourth gate pulse voltage GPV4 may be provided. The first gate pulse voltage GPV1 may be provided with a phase difference of 2.4 mA and 3.6 mA, respectively. In addition, the cathode pulse voltages CPV1, CPV2, CPV3, and CPV4 may be provided with phase differences of 100.8 mA, 102.0 mA, 103.2 mA, and 104.4 mA with respect to the first gate pulse voltage GPV1, respectively. The gate pulse voltages GPV1, GPV2, GPV3, GPV4 and the cathode pulse voltages CPV1, CPV2, CPV3, CPV4 are formed on the gate electrodes 12_1, 12_2, 12_3, 12_4 and the cathode electrodes 13_1, 13_2, 13_3. 13_4) may be reversed. In addition, the gate pulse voltages and the cathode pulse voltages provided to the driving regions may not be provided in all different phase differences depending on the driving regions, and the gate pulse voltages and / or the cathode pulse voltages provided to some driving regions may be The same phase difference can be provided.

 As such, as the gate pulse voltages GPV1, GPV2, GPV3, and GPV4 and the cathode pulse voltages CPV1, CPV2, CPV3, and CPV4 are sequentially provided, the first driving region D1 and the second driving region D2 are provided. ), The third driving region D3 and the fourth driving region D4 may be sequentially driven. In the case of providing a pulse voltage without dividing the lower substrate into a plurality of driving regions, the peak current of the anode is large as 120 mA, and the luminance and the efficiency of the field emission device are as low as 4500 mA / m2 and 48.3 mA / W, respectively. appear. However, according to the above-described driving method of the present invention, the peak current of the anode electrode 22 appears as low as 30 mA, and the luminance and efficiency of the field emission device are shown as large as 7600 mA / m 2 and 61.2 mA / W, respectively.

Referring again to FIGS. 2 and 4, waveform diagrams of the gate pulse voltages GPV1, GPV2, GPV3, GPV4 and the cathode pulse voltages CPV1, CPV2, CPV3, CPV4 are shown in the on-time intervals t _{ON. _1} , t _{ON _2} , t _{ON _3} , t _{ON _4} ) and off-time intervals (t _{OFF _1} , t _{OFF _2} , t _{OFF _3} , t _{OFF _4} ). The first gate pulse voltage GPV1 and the first cathode pulse voltage CPV1 are respectively provided to the first gate electrode 12_1 and the first cathode electrode 13_1 during the first on-time period t _{ON _1} . , During the first off-time interval t _{OFF _1} . The second gate pulse voltage GPV2 and the second cathode pulse voltage CPV2 are respectively provided to the second gate electrode 12_2 and the second cathode electrode 13_2 during the second on-time period t _{ON _2} , Not provided during the second off-time interval t _{OFF _2} . The third gate pulse voltage GPV3 and the third cathode pulse voltage CPV3 are respectively provided to the third gate electrode 12_3 and the third cathode electrode 13_3 during the third on-time period t _{ON _3} . It is not provided during the third off-time interval t _{OFF _3} . The fourth gate pulse voltage GPV4 and the fourth cathode pulse voltage CPV4 are respectively provided to the fourth gate electrode 12_4 and the fourth cathode electrode 13_4 during the fourth on-time period t _{ON _4} . It is not provided during the fourth off-time interval t _{OFF _1} .

The off-time periods t _{OFF _1} , t _{OFF _2} , t _{OFF _3} , t _{OFF _4 of the} driving regions D1, D2, D3, and D4 may be the same as or different from each other. On-time sections (t _{ON _1} , t _{ON _2} , t _{ON _3} , t _{ON _4} ) and off-time sections (t _{OFF _1} , t _{OFF _2} , t _OFF ) for each driving area _{_3} , t _{OFF _4} ) may be appropriately adjusted to adjust luminance for each driving region D1, D2, D3, and D4. The off-time intervals t _{OFF _1} , t _{OFF _2} , t _{OFF _3} , t _{OFF _4} may be applied to the gate pulse voltages GPV1, GPV2, GPV3, GPV4 and the cathode pulse voltages CPV1, CPV2, CPV3, CPV4. If it is smaller than the period, the correct luminance cannot be obtained, and if it is larger than 1 second, the screen may appear to be turned off, so the off-time interval t _{OFF _1-4} is used for the gate pulse voltages GPV1, GPV2, GPV3, and GPV4. And greater than the period of the cathode pulse voltages CPV1, CPV2, CPV3, CPV4 and less than 1 second.

So far, specific embodiments of the present invention have been described. Those skilled in the art will appreciate that the present invention can be implemented in a modified form without departing from the essential features of the present invention. Therefore, the disclosed embodiments should be considered in descriptive sense only and not for purposes of limitation. The scope of the present invention is shown in the claims rather than the foregoing description, and all differences within the scope will be construed as being included in the present invention.

According to the exemplary embodiments of the present invention, luminance may be partially adjusted in a backlight used as a light source in a liquid crystal display, and the contrast ratio may be improved. For example, the dark portion of the screen of the liquid crystal display is darkened in the backlight, and the bright part of the screen of the liquid crystal display is brightened in the backlight, thereby improving the contrast ratio. Can be used efficiently.

According to embodiments of the present invention, the driving stability of the field emission device may be secured by preventing excessively large current from flowing to the anode electrode. Low-current drive inverters can be used to reduce manufacturing costs. The brightness and efficiency of the field emission device can be improved.

Claims (14)

Lower substrate; Gate electrodes positioned on the lower substrate and electrically isolated from each other; Cathode electrodes disposed on the lower substrate and electrically isolated from each other; An emitter positioned on at least one of the gate electrodes and the cathode electrodes; An upper substrate disposed to face the lower substrate and having an anode electrode; And An external power source providing pulse voltages to at least one of the gate electrodes and the cathode electrodes, The lower substrate is divided into a plurality of driving regions, And a luminance of the driving regions is adjusted by adjusting a ratio between on-time sections in which the pulse voltages are provided and off-time sections in which the pulse voltages are not provided. The method of claim 1, wherein the pulse voltages include gate pulse voltages provided to the gate electrodes and cathode pulse voltages provided to the cathode electrodes. And the external power supply independently provides the gate pulse voltages and the cathode pulse voltages. The field emission device of claim 1, wherein the off-time intervals are greater than a period of the pulse voltages and are less than 1 second. The field emission device of claim 1, wherein the gate electrodes and the cathode electrodes are arranged in a lateral gate type, a normal gate type, or an under gate type. The method of claim 1, wherein the pulse voltages include gate pulse voltages provided to the gate electrodes and cathode pulse voltages provided to the cathode electrodes. And the external power supply independently provides the gate pulse voltages and the cathode pulse voltages to the driving regions. The field emission device of claim 5, wherein the gate pulse voltages and the cathode pulse voltages have different on-time intervals according to the driving regions. The field emission device of claim 6, wherein the gate pulse voltage and the cathode pulse voltage provided to the same driving region have the same on-time interval. Lower substrate; Gate electrodes positioned on the lower substrate and electrically isolated from each other; Cathode electrodes disposed on the lower substrate and electrically isolated from each other; An emitter positioned on at least one of the gate electrodes and the cathode electrodes; An upper substrate disposed to face the lower substrate and having an anode electrode; And an external power source providing pulse voltages to at least one of the gate electrodes and the cathode electrodes, wherein the lower substrate is divided into a plurality of driving regions. In And adjusting brightness of the driving regions by adjusting a ratio between on-time sections in which the pulse voltages are provided and off-time sections in which the pulse voltages are not provided. The method of claim 8, wherein adjusting the brightness, And independently providing the gate pulse voltages and the cathode pulse voltages to the gate electrodes and the cathode electrodes. The method of claim 8, wherein the off-time periods are larger than a period of the pulse voltages and smaller than 1 second. The method of claim 8, wherein the pulse voltages are provided to have a phase difference. The method of claim 8, wherein the pulse voltages include gate pulse voltages provided to the gate electrodes and cathode pulse voltages provided to the cathode electrodes, Adjusting the brightness comprises independently providing the gate pulse voltages and the cathode pulse voltages to the drive regions. The method of claim 12, wherein the gate pulse voltages and the cathode pulse voltages are provided to have different on-time intervals according to the driving regions. The method of claim 12, wherein the gate pulse voltage and the cathode pulse voltage provided in the same driving region are provided to have the same on-time interval.

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