JP3125337B2 - Image display device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a thin image display device such as a color display device.

[0002]

2. Description of the Related Art Conventionally, as a thin display device,
For example, Japan Display (JAPAN DISP)
LAY '86 P512-515) has proposed a microchip type display device using a micro cold cathode as an emission source. This display device is
As shown in FIG. 8, a substrate 51 is formed by a semiconductor manufacturing process.
The conical cathode 52 made of molybdenum or the like having a diameter of 1.0 μm or less is used as an emission source, and an electrode 53 provided below the cathode 52 and an insulating material provided so as to surround the cathode 52. The gate electrode 55 formed on the layer 54 and the gate electrode 55 form an XY matrix, and are configured to perform a so-called XY drive.

In this display device, for example, as shown in FIG.
When a negative electric field of about (relative voltage between the cathode 52 and the gate electrode 55) is applied, field emission occurs, and an electron beam is extracted from the tip of the cathode 52. An image is displayed by selectively irradiating the electron beam on a fluorescent screen 57 formed on the inner surface of the glass panel 56 by XY driving.

[0004]

However, in the time region where the luminance signal does not enter (the region indicated by a in FIG. 9), the electric field on the cathode surface is zero, and the local temperature rise of the phosphor due to the electron beam incidence causes The generated gas is left to be adsorbed on the cathode 52. For this reason, even if the luminance signal is applied again and the potential of the cathode 52 becomes -20 V, the work function may increase as shown in FIG. 10 and the electron beam may not be emitted. Further, even when the electron beam is being emitted, the work function increases, or the work function fluctuates in accordance with the adsorption and desorption of the residual gas, and becomes unstable. As a result, the electron beam becomes unstable, and the luminance deteriorates.

Accordingly, the present invention has been proposed in view of the above-mentioned conventional circumstances, and provides an image display device capable of stabilizing an electron beam, improving luminance and improving image quality. With the goal.

[0006]

In order to achieve the above-mentioned object, the present invention provides a method for applying a negative electric field such that the potential of a micro-cold cathode becomes negative with respect to the potential of a gate electrode. In an image display device for extracting an electron beam and irradiating a phosphor with the electron beam to display an image, when no negative electric field is applied, the potential of the minute cold cathode becomes positive with respect to the gate electrode, and the absolute value is A positive electric field that is four times the negative electric field is applied continuously or intermittently, and adsorption of a gas generated from the phosphor to the minute cold cathode is suppressed.

[0007]

According to the present invention, the positive electric field is applied to the minute cold cathode continuously or intermittently when no negative electric field is applied, so that the positive electric field is applied to the cathode even when the electron beam is not emitted. In this state, adsorption of the gas generated from the phosphor onto the cathode is prevented. Therefore, the surface of the cathode is always cleaned, and a stable emission of the electron beam becomes possible, so that the luminance can be stabilized.

[0008]

Embodiments of the present invention will be described below with reference to the drawings. The image display device according to the present embodiment includes:
As shown in FIG. 1, it is configured to include a front panel 1 having a phosphor stripe formed on an inner wall surface and a cathode panel 2 serving as an emission source. The front panel 1 has an inner wall surface 3a of a glass plate 3 facing an emission source.
Has a transparent anode electrode (not shown) of ITO (indium tin oxide) or the like, and red (R), green (G), and black (BK) phosphor stripes 4 are provided on the transparent anode electrode in a predetermined manner. The fluorescent screen is formed by forming the fluorescent screen.

On the other hand, the cathode panel 2 is constituted by arranging a plurality of pixels formed of minute cold cathodes in a matrix. As shown in FIG. 2, the micro cold cathode includes a cathode 6 serving as an emission source, a gate electrode 7 for extracting an electron beam from the cathode 6, a control line 8 for applying a potential to the cathode 6, and a control line 8 and an insulating layer 9 for insulating the gate electrode 7 from each other, and these are formed on a base plate 10 made of glass by a semiconductor manufacturing process.

The cathode 6 is formed as a small conical protrusion having a diameter of 1.0 μm or less by, for example, molybdenum, tungsten, lanthanum hexaboride (LaB ₆ ), or the like. This emits an electron beam. These cathodes 6 constitute one pixel as an aggregate composed of several to several tens, and are provided in a matrix corresponding to each dot of the phosphor. On the other hand, the gate electrode 7
Are formed on an insulating layer 9 formed so as to surround the periphery of the cathode 6 in an arc shape. At the position corresponding to each cathode 6, an electron beam is applied from the tip of each cathode 6 to the phosphor. An arc-shaped electron beam emission hole 7a for emission toward the stripe 4 is formed.
The gate electrodes 7 are arranged so as to form a matrix structure with the control lines 8.
The cathodes 6 of an assembly composed of several tens are made to face each other.

In the image display device configured as described above, an electric field is applied between the gate electrode 7 and the cathode 6 by XY driving of the gate electrode 7 and the control line 8,
An electron beam is extracted from the tip of the cathode 6. And
The extracted electron beam is applied to the phosphor stripe 4 to emit phosphor dots. Brightness I at this time
Depends exponentially on the work function の of the cathode surface, as shown by equation (1). Therefore, stabilizing the work function ψ is indispensable for stabilizing the luminance. I = a · exp (−ψ / bF) (1) where ψ represents a work function, F represents a surface electric field, and a and b represent constants, respectively. As shown in (1), it easily changes depending on the surface coverage r of the residual gas covering the cathode surface. The surface coverage r and the current i have a correlation as shown in FIG. 5, and the current value decreases as the coverage increases. On the other hand, adsorption gas (CO, H ₂ , O
₂ ) As shown in Table 1, the curvature radius of the cathode tip is 10
In the case of 0 angstrom, it has a property of being detached from the surface of the cathode by application of a positive electric field of 4.0 V / angstrom (relative voltage between the cathode 6 and the gate electrode 7). Therefore, the surface of the cathode 6 can be kept clean by applying an electric field of this value to the cathode 6 as necessary. Note that the electric field varies according to the radius of curvature of the cathode, and is appropriately selected according to the size of the cathode 6.

[0012]

[Table 1]

From the above, in order to stabilize the luminance, the residual gas adsorption on the cathode surface should be reduced as much as possible, the change of the work function ψ should be suppressed as much as possible, and the residual gas should be large enough to release the residual gas. It is necessary to apply a positive electric field. Thus, in this embodiment, when under no application of a negative electric field as shown in Figure 5 based on the above point of view, i.e. in a state that does not have luminance signals S ₁ and the luminance signal S _2, always the cathode 6V to prevent residual gas adsorption
/ Angstroms or more.
Actually, +80 V corresponding to 4 V / angstrom
Apply an electric field of In this way, even when the apparatus is not driven, the gas generated from the phosphor does not adsorb to the cathode 6 and the electron beam can be stabilized.

Alternatively, as shown in FIG.
₁ and the positive electric field of more than 4V / Å during the next luminance signal S ₂ may be configured to intermittently applied. In this case, a cleaning pulse P of about 10 msec can sufficiently clean the cathode. When the cleaning pulse is applied intermittently, the pulse height of the luminance signal can be smaller than when the electric field is applied continuously.

[0015] In addition, as shown in FIG. 7, taking the applied voltage to the cathode 6 in the middle of the positive and negative pulses, both positive pulse and intensity pulses equal pulse height, likewise luminance signals S ₁ and the next luminance positive electric field of more than 4V / Å between the signal S ₂ may be configured to intermittently applied to.

As described above, if the cleaning pulse is applied continuously or intermittently, the surface of the cathode 6 can be always cleaned and the electron beam can be stabilized. Therefore, fluctuations in luminance and the like can be eliminated, and higher image quality can be expected. Further, the brightness of the pixel itself constituted by the cathode 6 can be stabilized.

[0017]

As is clear from the above description, in the image display device of the present invention, the positive electric field is applied continuously or intermittently to the minute cold cathode when no negative electric field is applied. Adsorption of the gas generated from the phosphor to the cathode is prevented, and the surface of the cathode can be constantly cleaned. Therefore, the electron beam can be stabilized, the luminance can be stabilized, and high image quality can be expected.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view showing an example of an image display device to which the present invention is applied.

FIG. 2 is an enlarged perspective view of a main part showing a micro cold cathode partially broken away.

FIG. 3 is a characteristic diagram showing a relationship between a work function and a surface coverage.

FIG. 4 is a characteristic diagram showing a relationship between a current value and a surface coverage.

FIG. 5 is a timing chart illustrating an example of a method for driving an image display device to which the present invention has been applied.

FIG. 6 is a timing chart illustrating another example of the driving method of the image display device to which the present invention is applied.

FIG. 7 is a timing chart showing still another example of the driving method of the image display device to which the present invention is applied.

FIG. 8 is a schematic sectional view showing an example of a conventional image display device.

FIG. 9 is a timing chart illustrating a conventional driving method.

FIG. 10 is a characteristic diagram showing a temporal change of a current value and a voltage in a conventional image display device.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Front panel 2 ... Cathode panel 4 ... Phosphor stripe 6 ... Cathode 7 ... Gate electrode

Claims (1)

(57) [Claims] 1. The potential of a micro-cold cathode is changed to the potential of a gate electrode.
In an image display device that draws an electron beam from the tip of a minute cold cathode by applying a negative electric field that is negative with respect to the cathode, and irradiates the electron beam to a phosphor to display an image, when the negative electric field is not applied, the minute The potential of the cold cathode is
And the absolute value is 4 of the negative electric field.
An image display device , wherein a positive electric field that is twice as large is applied continuously or intermittently, and adsorption of a gas generated from a phosphor to the minute cold cathode is suppressed.