JP4741449B2 - Cold cathode, cold cathode array and field emission display - Google Patents

Description

  The present invention relates to a cold cathode, a cold cathode array, and a field emission display, and in particular, a cold cathode capable of reducing an electron beam diameter and increasing electron emission efficiency, and a cold cathode array using the same The present invention relates to a field emission display.

  Field emission displays (FEDs) are being put into practical use as display devices that can replace CRTs or liquid crystal display devices. However, high-definition display, ensuring adequate luminance, and electron emission Increased efficiency is required.

Various types of cold cathodes have already been proposed for use in FEDs. From the viewpoint of electron emission efficiency, attention is paid to cold cathodes in which carbon-based materials such as carbon nanotubes (hereinafter referred to as CNT) are formed on the cathode electrode. (For example, refer to Patent Document 1).

  FIG. 13 is a partial sectional view (a) of an FED using a cold cathode disclosed in Patent Document 1 and a top view (b) of the cold cathode.

The cold cathode includes a substrate 301, a cathode electrode 302 installed on the substrate 301, a CNT 303 formed on the cathode electrode 302, and a gate electrode 305 installed on the substrate 301 via an insulator 304. including.

  A strong electric field is formed at the tip of the CNT 303 by the voltage applied between the cathode electrode 302 and the gate electrode 305, and electrons are emitted from the tip of the CNT 303 in the form of a beam.

  This electron beam reaches the anode electrode 307 formed on the back surface of the front substrate 306 placed at an appropriate distance from the cold cathode, and causes the fluorescent paint 308 applied to the anode electrode 307 to emit light.

Also, if the electrons emitted from the CNT have a velocity component in the horizontal direction, the electron beam diverges, causing a decrease in resolution and occurrence of crosstalk. Therefore, a cold cathode in which a focus electrode is provided above the gate electrode. Has already been proposed (see Non-Patent Document 1, for example).
JP-A-2005-243607 ([0040], FIG. 7) YW Jin, et al, "A Study on the Driving Property of Double Gated Triode-Type Field Emission Display using Carbon Nanotube Emitter" Proc. Euro Display '02, pp.229-232, 2002

However, the cold cathode disclosed in Patent Document 1 does not have a focus electrode, so that not only the electron beam diameter is increased, but also CNT is emitted because it is formed only at the center of the cathode electrode. There was a problem that current was small.

  Further, although the cold cathode disclosed in Non-Patent Document 1 can focus the electron beam by the focus electrode, there is a problem that the electron emission efficiency decreases when the focusing is strengthened.

  The present invention has been made to solve the conventional problems, and provides a cold cathode, a cold cathode array, and a field emission display capable of reducing the electron beam diameter and improving the electron emission efficiency. The purpose is to do.

[First invention]
The cold cathode of the present invention is a cold cathode disposed at a predetermined distance from the anode electrode , the cathode electrode disposed on an insulating substrate, and the opening disposed on the cathode electrode and exposing the cathode electrode A first insulating material having a gate electrode having an opening that is disposed on the first insulating material and exposing the cathode electrode; and an opening that is disposed on the gate electrode and exposes the cathode electrode. a second insulating material is disposed on the second insulating material, seen including a focus electrode having an opening that exposes the cathode electrode, and a carbon-based material formed on the cathode electrode, the carbon The system material is formed in a partial region deviated from the center of the cathode electrode on the cathode electrode .

  With this configuration, the electron beam diameter can be reduced and the electron emission efficiency can be improved.

[Second invention]
In the cold cathode of the present invention, the opening of the gate electrode exposing the cathode electrode is a circle, and the partial region includes a projected circle of the opening of the gate electrode onto the exposed portion of the cathode electrode, and the gate one closed area sandwiched between the circle, which is located 1.0 by following predetermined multiple distance predetermined center side of the projection circle distance between the upper surface of the lower surface of the electrode and the cathode electrode It may be a partial area.

[Third invention]
Cold cathode of the present invention, the angle anticipating the partial area from the center of the projection circle onto the cathode electrode of the opening of the pre-Symbol gate electrode may be under 180 degrees or.

[ Fourth Invention]
The cold cathode array of the present invention is a cold cathode array in which a plurality of any of the above-mentioned cold cathodes are arranged , wherein the formation area of the carbon-based material of each cold cathode is from the center of the cathode electrode on the cathode electrode. It has a configuration biased in the same direction .

  With this configuration, when a plurality of cold cathodes are applied to one subpixel, it is possible to avoid an increase in the dot diameter of the subpixel.

[ Fifth Invention]
The field emission display of the present invention has a configuration using the cold cathode array as a sub-pixel.

  With this configuration, the luminance, resolution, and luminous efficiency of the field emission display can be improved.

The present invention provides a cold cathode, a cold cathode array, and a field emission display capable of reducing an electron beam diameter and improving electron emission efficiency by forming a carbon-based material in a partial region of a cathode electrode. Can be provided.

  Hereinafter, embodiments of a cold cathode, a cold cathode array, and a field emission display according to the present invention will be described with reference to the drawings.

  In this specification, the electron beam diameter means the maximum interval of the arrival positions of electrons emitted from one cold cathode to the anode electrode.

A cold cathode 10 according to an embodiment of the present invention includes a cathode electrode 12 disposed on an insulating substrate 11 and a cathode electrode 12 as shown in an XX sectional view (a) and a top view (b) of FIG. A first insulating material 13 having an opening that is disposed above and exposing the cathode electrode 12, a gate electrode 14 that is disposed on the first insulating material 13 and has an opening that exposes the cathode electrode 12, and on the gate electrode 14 A second insulating material 15 that is disposed and has an opening that exposes the cathode electrode 12, a focus electrode 16 that is disposed on the second insulating material 15 and has an opening that exposes the cathode electrode 12, and the cathode electrode 12 is formed. CNT17 which is a carbon-based material.

  The anode electrode 19 disposed at a predetermined distance from the cold cathode 10 is formed on the lower surface of the front substrate 18, and the fluorescent paint 20 is applied to the lower surface of the anode electrode 19.

The CNTs 17 are formed in the partial region R of the cathode electrode 12 that is deviated from the center of the cathode electrode 12.

In the partial region R, the anode current induced in the anode electrode 19 by the electron emitted from one CNT 17 formed in the projection region of the opening of the gate electrode 14 onto the exposed portion of the cathode electrode 12 has a maximum value. The first curve drawn by the formation position of one CNT 17 and the formation position of one CNT 17 that induces an anode current whose anode current is a predetermined number of times that is 1.0 or less of the maximum value. It is desirable to be a partial region of a closed region sandwiched between the second curve to be drawn.

  The opening of the gate electrode 14 exposing the cathode electrode 12 is a circle, and the partial region R has an angle at which the center of the projected circle on the cathode electrode 12 of the opening of the gate electrode 14 looks at the closed region is 180 degrees or less. It is an area.

At this time, as shown in FIG. 1B, the partial region R is a part of the projected circle whose angle θ that the center O of the projected circle on the cathode electrode 12 of the opening of the gate electrode 14 is expected to be 180 degrees or less. The arc a, the arc a, and a distance (α · h) which is a predetermined number α times 1.0 or less of the distance h between the lower surface of the gate electrode 14 and the upper surface of the cathode electrode 12, A _first line segment d that connects _one end point A _{1 of} the inner arc b, arc a and the center O of the projected circle, and a second line segment that connects the other end point A ₂ of the arc a and the center O. This corresponds to the area surrounded by e.

  When a voltage is applied between the cathode electrode 12 and the gate electrode 14, electrons are emitted from the tip of the CNT 17, but the electric field applied to the tip of the CNT 17 is weak at the center of the projection circle and becomes stronger toward the periphery.

If Figure 2 is formed with one CNT17 in the projection circle center O of the anode current i _a and the projection circle cold cathode 10 is induced in the anode electrode 19 by the emission current i _e and the emission current i _e radiate The horizontal axis represents the distance r from the center O of the projected circle, and the vertical axis represents the emission current i _e and the anode current i _a .

Measurement conditions are as follows.
Gate electrode potential = 0 volts, cathode electrode potential = -50 volts Focus electrode potential = -50 volts, anode electrode potential = 1000 volts Distance between gate electrode and anode electrode = 1 millimeter Distance between gate electrode and cathode electrode = 3 micron Meter Distance between gate electrode and focus electrode = 1.2 micrometers Gate electrode opening radius = 2.5 micrometers Focus electrode opening radius = 3.0 micrometers

As shown in the graph of FIG. 2, when one CNT 17 is formed at a distance r = 2.2 micrometers from the center O of the projection circle, the anode current i _a is 0.04 nanoamperes and r = 2.5 micrometers. anode current i _a at the time of forming one CNT17 meters becomes 0.4 nA.

From the above, the projected line p of the opening of the gate electrode 14 on the exposed part of the cathode electrode 12 and the distance h (= 3 micrometers) between the projected line p and the lower surface of the gate electrode 14 and the upper surface of the cathode electrode 12 are 0. It can be seen that a sufficient anode current can be obtained if the CNTs 17 are formed in an annular region surrounded by a line separated from the center O side by a distance of 0.3 micrometers, which is 1 time.

FIG. 3 is a trajectory diagram of the electron beam of the cold cathode 10 in which the CNTs 17 are formed in the annular region between the outer circumference circle with a radius of 2.5 micrometers and the inner circumference circle with a radius of 2.2 micrometers. a) shows a case where the focus voltage is high (−45 volts), and (b) shows a case where the focus voltage is low (−50 volts).

  As can be seen from FIG. 3, when the focus voltage is high (−45 volts), the electron beam diameter at the anode electrode 19 is larger than when the focus voltage is low (−50 volts).

  FIG. 4 is a graph showing the relationship between the focus voltage and the electron beam diameter. The horizontal axis represents the focus voltage, and the vertical axis represents the electron beam diameter. 4 that the electron beam diameter at the anode electrode 19 increases as the focus voltage increases.

  FIG. 5 is a graph showing the relationship between the focus voltage, the emission current, the anode current, and the electron emission efficiency η. The horizontal axis represents the focus voltage, the left vertical axis represents the current, and the right vertical axis represents the electron emission efficiency. represents η. Here, the emission current and the anode current are converted into average current values per CNT 17 in the annular region.

  Although it is preferable that the electron beam diameter is small in order to achieve high definition, as shown in FIG. 5, when the focus voltage is excessively lowered, the anode current decreases rapidly and the electron emission efficiency η also decreases abruptly. .

  When displaying a high-definition video on a 25-inch diagonal display device, or when displaying a super-high-definition video on a 50-inch diagonal display device, the electron beam diameter should be approximately 100 micrometers or less with a range of 1 mm. Is preferred.

When the electron beam diameter is 100 micrometers, the focus voltage is -52.7 volts, the emission current is 1.353 nanoamperes, the anode current is 0.023 nanoamperes, and CNT17 is formed in the entire annular region. In this case, the electron emission efficiency η is reduced to 1.7%.

Therefore, in the present invention, in order to reduce the electron beam diameter without excessively reducing the focus voltage, the CNT 17 is formed in a part of the annular region.

FIG. 6 is a graph showing a relationship between an angle θ (degree) (hereinafter, referred to as a center angle θ) at which the center O of the projected circle looks into the annular region forming the CNT 17 and an electron beam diameter (micrometer), The horizontal axis represents the center angle θ, and the vertical axis represents the electron beam diameter.

From this graph, in order to set the electron beam diameter to 100 micrometers, when the focus voltage V _f is −45 volts, the center angle θ of the annular region is 2 degrees, and the focus voltage V _f is −50 volts. It turns out that the center angle θ of the annular region may be selected as 54 degrees.

FIG. 7 is a graph showing the relationship between the center angle θ (degrees) of the annular region forming the CNT 17 and the emission current I _e and anode current I _a , where the horizontal axis represents the center angle θ and the vertical axis represents the current ( Nanoampere).

From this graph, when the focus voltage V _f is −45 volts and the center angle θ is 2 degrees, the emission current I _e is 0.007 nanoamperes, the anode current I _a is 0.002 nanoamperes, and the focus voltage V It can be seen that when _f is −50 volts and the center angle θ is 54 degrees, the emission current I _e is 0.194 nanoamperes and the anode current I _a is 0.035 nanoamperes.

That is, when the focus voltage V _f is −50 volts, the first arc, which is a part of a projected circle of the opening of the gate electrode 14 onto the cathode electrode 12 and the center angle θ is 54 degrees, A distance α · h = 0.3 micrometers which is a predetermined number α = 0.1 times 1.0 or less of the distance h = 3 micrometers between the lower surface of the gate electrode 14 and the upper surface of the cathode electrode 12 from the arc of A portion surrounded by a second arc separated by only the center side, a line segment connecting one end point of the first arc and the center O, and a line segment connecting the other end point of the first arc and the center O If the CNTs 17 are formed in the annular region R ₅₀ , the electron emission efficiency η can be improved from 1.7% when the CNTs 17 are formed over the entire annular region to 18%.

When the focus voltage V _f is −45 volts, the first arc, which is a part of a projected circle of the opening of the gate electrode 14 onto the cathode electrode 12 and the center angle θ is 2 degrees, A distance α · h = 0.3 micrometers which is a predetermined number α = 0.1 times 1.0 or less of the distance h = 3 micrometers between the lower surface of the gate electrode 14 and the upper surface of the cathode electrode 12 from the arc of A portion surrounded by a second arc separated by only the center side, a line segment connecting one end point of the first arc and the center O, and a line segment connecting the other end point of the first arc and the center O If the CNT 17 is formed in the annular region R ₄₅ , the electron emission efficiency η can be improved from 1.7% when the CNT 17 is formed in the entire annular region to 29%.

  When one sub-pixel (three sub-pixels displaying red, green, and blue constitutes one pixel) with one cold cathode, the image quality deteriorates due to variations in the cold cathode. By using the cold cathode array in which the cold cathodes are arranged in an array as one sub-pixel, it is possible to improve image quality degradation due to variations in the cold cathode.

However, it is necessary to consider that the CNT formation region of the cold cathode constituting the cold cathode array is directed in the same direction and the dot diameter of the subpixel is not increased.

FIG. 8 is a top view and an XX cross-sectional view of a 3 × 5 cold cathode array, and the CNT formation region of each cold cathode is set in the 3 o'clock direction.

The vertical diameter (H) and the horizontal diameter (W) of the dot of the subpixel composed of the electron beam emitted from the cold cathode array composed of n × m cold cathodes are expressed by [Equation 1].

  FIG. 9 shows an example of a sub-pixel, for example, applying a Bayer arrangement that displays green in the upper left and lower right cold cathode arrays, red in the upper right cold cathode array, and blue in the lower left cold cathode array. Can do.

FIG. 10 shows another example of a subpixel. FIG. 10A shows a case where circular cold cathodes are used, and CNTs are formed in the direction of 12:00 of each cold cathode. FIG. 10B shows a case where rectangular cold cathodes are used, and CNTs are formed in the direction of 3 o'clock of each cold cathode.

  FIG. 11 is a top view of the cold cathode according to the present invention, and the cold cathode may be rectangular as shown in (a) and (b), or may be hexagonal as shown in (c). However, the side may be a waveform as shown in (d).

Further, in the CNT 17, the anode current induced in the anode electrode 19 by the electrons emitted from one CNT 17 formed in the projected region of the opening of the gate electrode 14 on the exposed portion of the cathode electrode 12 has the maximum value. a first curve one formation position of CNT17 the draw, the anode current second curve and sandwiched by closed area drawn by one formation position of CNT17 of inducing an anode current of 10% of the maximum value be formed in the partial region R is sufficient, it may be formed in a region other than the partial region R.

  FIG. 12 is a perspective view for explaining the structure of a field emission display (FED) 100 using a cold cathode array according to the present invention. The cold cathode array 21 and the front substrate 22 have a predetermined thickness (for example, Adhered to the top and bottom of a 1 mm spacer (not shown) to maintain a vacuum inside.

A gate voltage V _G is applied to the gate electrode 211 according to the scanning pulse, and a cathode voltage V _K is applied to the cathode electrode 212 according to the image signal.

A focus voltage V _F is always applied to the focus electrode 213, and an anode voltage V _A is always applied to the anode electrode 221 deposited on the front substrate 22.

The cold cathode 214 in which the gate voltage V _G is simultaneously applied to the gate electrode 211 and the cathode voltage V _K is simultaneously applied to the cathode electrode 212 enters an operating state and emits electrons, but these electrons are focused by the electric field generated around the focus electrode 213. And absorbed by the anode electrode 221.

  The electrons absorbed by the anode electrode 221 cause the phosphor 222 applied to the front substrate 22 to emit light.

  In the above embodiment, the size of the cold cathode is approximately 5 micrometers, but a cold cathode of this size can be manufactured by a thin film manufacturing technique such as vapor deposition or sputtering.

  In the case of an FED having a pixel size of 600 micrometers, a cold cathode having a size of about 100 micrometers can be applied. A cold cathode of this size should be manufactured by printing technology. Is possible.

As described above, the cold cathode according to the present invention can reduce the electron beam diameter and improve the electron emission efficiency by forming the CNT in the partial region of the cathode electrode that is deviated from the center of the cathode electrode. It becomes possible.

  As described above, the cold cathode, the cold cathode array, and the field emission display according to the present invention have the effect of reducing the electron beam diameter and improving the electron emission efficiency, and are effective as a display device or the like. It is.

Block diagram of cold cathode according to the present invention A graph showing the relationship between the emission current i _e and the anode current i _a and the distance r from the center O of the projected circle Trajectory diagram of electron beam of cold cathode according to the present invention Graph showing the relationship between focus voltage and electron beam diameter Graph showing the relationship between focus voltage, emission current, anode current, and electron emission efficiency η Graph showing the relationship between the center angle of the annular region and the electron beam diameter Graph showing the relationship between the central angle and the emission current I _e and the anode current I _a of the annular region Top view and XX cross section of 3x5 cold cathode array An example of a subpixel Other examples of subpixels Top view of cold cathode The perspective view for demonstrating the structure of FED using the cold cathode array which concerns on this invention Partial sectional view and top view of FED using conventional cold cathode

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Cold cathode 11 Insulating substrate 12 Cathode electrode 13 1st insulating material 14 Gate electrode 15 2nd insulating material 16 Focus electrode 17 Carbon nanotube (CNT)
18 Front substrate 19 Anode electrode 20 Fluorescent paint 21 Cold cathode array 100 Field emission display (FED)

Claims (5)

A cold cathode disposed at a predetermined distance from the anode electrode,
A cathode electrode disposed on an insulating substrate;
A first insulating material disposed on the cathode electrode and having an opening exposing the cathode electrode;
A gate electrode disposed on the first insulating material and having an opening exposing the cathode electrode;
A second insulating material disposed on the gate electrode and having an opening exposing the cathode electrode;
A focus electrode disposed on the second insulating material and having an opening exposing the cathode electrode;
And a carbon-based material formed on the cathode electrode, only including,
The cold cathode, wherein the carbon-based material is formed in a partial region deviated from the center of the cathode electrode on the cathode electrode . The gate electrode opening exposing the cathode electrode is a circle;
The partial region is predetermined as 1.0 or less of a distance between the projected circle of the opening of the gate electrode onto the exposed portion of the cathode electrode and the lower surface of the gate electrode and the upper surface of the cathode electrode. cold cathode according to claim 1 by a distance of a predetermined number of times and a circle located on the center side of the projection circle, a partial area of the closed area sandwiched between the. Before SL cold cathode according the center of the projection circle 請 Motomeko 2 angle Ru Ah under 180 degrees or looking into the partial region onto the cathode electrode of the opening of the gate electrode. A cold cathode array in which a plurality of cold cathodes according to any one of claims 1 to 3 are arranged,
The cold cathode array in which the formation area of the carbon-based material of each cold cathode is deviated in the same direction from the center of the cathode electrode on the cathode electrode. A field emission display using the cold cathode array according to claim 4 as a sub-pixel.

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