JPH04370635A - Image display device - Google Patents

Abstract

PURPOSE:To stabilize the electron beams and to realize the improvement of the brightness and the high quality of the picture image by applying a positive electric field to a minute cold cathode continuously or intermittently when a negative electric field is not applied. CONSTITUTION:By applying a negative electric field, electron beams are drawn out from the front end of a minute cold cathode which furnishes cathodes 6, gate electrodes 7, control lines 8, and insulating layers 9, and the electron beams are radiated to a phosphor 4 to display an image on an image display device. In such an image display device, a positive electric field of 4V/Angstrom or higher is applied continuously or intermittently to the cathodes 6, constantly when the negative electric field is not applied. As a result, a gas generated from the phosphor stripe 4 is never adsorbed to the cathodes 6 even when the device is not being driven, and the purity of the surfaces of the cathodes 6 is secured constantly. Consequently, the electron beams can be stabilized, the brightness can be stabilized, and a high quality of image can be secured.

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

[Prior Art] Conventionally, as a thin display device,
For example, Japan Display (JAPAN DIS)
A microchip type display device using a minute cold cathode as an emission source has been proposed in PLAY '86 P512-515). As shown in FIG. 8, this display device uses a conical cathode 52 made of molybdenum or the like with a diameter of 1.0 microns or less formed on a substrate 51 by a semiconductor manufacturing process as an emission source.
An electrode 53 provided under this cathode 52 and the cathode 52
The gate electrode 55 formed on the insulating layer 54 surrounding the periphery of the gate electrode 55 forms an X-Y matrix, and is configured to perform so-called X-Y driving.

In this display device, for example, as shown in FIG. 9, -20V (
When a negative electric field of the order of magnitude (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 this electron beam onto a fluorescent screen 57 formed on the inner surface of the glass panel 56 by X-Y driving.

0004

[Problem to be Solved by the Invention] However, in the time domain where there is no luminance signal (the region indicated by a in FIG. 9), the electric field on the cathode surface is zero, and due to the local temperature rise of the phosphor due to the electron beam incidence. The generated gas is left to be adsorbed by the cathode 52. Therefore, even if the luminance signal is applied again and the potential of the cathode 52 becomes -20V, the work function increases as shown in FIG. 10, and there is a possibility that the electron beam will not be emitted. Further, even when an electron beam is being emitted, the work function increases or fluctuates as residual gas is adsorbed or desorbed, resulting in instability. As a result, the electron beam becomes unstable and the brightness deteriorates.

SUMMARY OF THE INVENTION The present invention was proposed in view of the above-mentioned conventional situation, and it is an object of the present invention to provide an image display device that stabilizes an electron beam and makes it possible to improve brightness and improve image quality. With the goal.

[0006]

[Means for Solving the Problems] In order to achieve the above object, the present invention draws out an electron beam from the tip of a minute cold cathode by applying a negative electric field, and irradiates the electron beam onto a phosphor to display an image. The image display device is characterized in that a positive electric field is applied continuously or intermittently to the minute cold cathode when the negative electric field is not applied.

[0007]

[Operation] In the present invention, since a positive electric field is continuously or intermittently applied to the minute cold cathode when no negative electric field is applied, a positive electric field is applied to the cathode even when an electron beam is not emitted. This prevents gas generated from the phosphor from being adsorbed onto the cathode. Therefore, the cathode surface is constantly cleaned, making it possible to emit stable electron beams and stabilizing the brightness.

[0008]

Embodiments Hereinafter, embodiments to which the present invention is applied will be described with reference to the drawings. The image display device of this embodiment is
As shown in FIG. 1, the device includes a front panel 1 having phosphor stripes formed on its inner wall surface, and a cathode panel 2 serving as an emission source. The front panel 1 has an inner wall surface 3a of the glass plate 3 facing the emission source.
A transparent anode electrode such as ITO (indium tin oxide) (
Illustration is omitted. ), and red (R), green (G), and black (BK) phosphor stripes 4 are formed in a predetermined pattern on this transparent anode electrode to constitute a fluorescent screen.

On the other hand, the cathode panel 2 is constructed by arranging a plurality of pixels made of minute cold cathodes in a matrix. As shown in FIG. 2, the microcold cathode consists of 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 this control line. 8 and an insulating layer 9 that insulates the gate electrode 7, and these are formed on a base plate 10 made of glass by a semiconductor manufacturing process.

The cathode 6 is made of, for example, molybdenum, tungsten, or lanthanum hexaboride (LaB6).
It is formed as a minute conical protrusion with a diameter of 1.0 microns or less, and an electron beam is emitted from the tip of the protrusion by applying a negative electric field. These cathodes 6 constitute one pixel as a collection of several to several dozen cathodes, and are provided in a matrix to correspond to each dot of the phosphor. On the other hand, gate electrode 7
is formed on an insulating layer 9 formed around the cathode 6 in an arc shape, and an electron beam is emitted from the tip of each cathode 6 to a position corresponding to each cathode 6. An arc-shaped electron beam emitting hole 7a is formed to emit the electron beam toward the stripe 4. The gate electrode 7 and the control line 8 are arranged to form a matrix structure, and the several to
The cathodes 6 of the assembly consisting of several tens of cathodes are arranged 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 X-Y driving 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 irradiated onto the phosphor stripe 4, causing the phosphor dots to emit light. Brightness I at this time
As shown in equation (1), depends exponentially on the work function ψ of the cathode surface. Therefore, it is essential to stabilize the work function ψ in order to stabilize the brightness. I=a・exp(−ψ/bF)...Equation (1) (however,
ψ represents a work function, F represents a surface electric field, and a and b each represent a constant. ) Further, the work function ψ easily changes depending on the surface coverage r of the residual gas covering the cathode surface, as shown in FIG. Note that the surface coverage r and the current i have a correlation as shown in FIG. 5, and as the coverage increases, the current value decreases. On the other hand, adsorbed gas (CO, H2, O2)
As shown in Table 1, when the radius of curvature of the cathode tip is 100 angstroms, the voltage is 4.0 V/angstrom (
It has the property of detaching from the surface of the cathode by applying a positive electric field greater than (the relative voltage between the cathode 6 and the gate electrode 7). Therefore, by applying an electric field of this value to the cathode 6 as needed, the surface of the cathode 6 can be kept clean. Note that the electric field changes depending on the radius of curvature of the cathode, so it is appropriately selected depending on the size of the cathode 6.

0012

[Table 1]

From the above, in order to stabilize the brightness, it is necessary to reduce the residual gas adsorption on the cathode surface as much as possible, suppress the change in the work function ψ as much as possible, and remove the residual gas. It is necessary to apply a positive electric field. Therefore, in this embodiment, based on the above viewpoint, as shown in FIG. A positive electric field of 4 V/Angstrom or more should be applied to prevent adsorption of residual gas. In reality, it is +80V which corresponds to 4V/Angstrom.
Apply an electric field. In this way, even when the device is not driven, gas generated from the phosphor is not adsorbed to the cathode 6, and the electron beam can be stabilized.

Alternatively, as shown in FIG.
A positive electric field of 4 V/angstrom or more may be applied intermittently between the brightness signal S1 and the next brightness signal S2. In this case, the cleaning pulse P of about 10 msec can sufficiently clean the cathode. Note that when the cleaning pulse is applied intermittently, the pulse height of the luminance signal can be smaller than when the electric field is continuously applied.

In addition, as shown in FIG. 7, the voltage applied to the cathode 6 is set between the positive and negative pulses, and both the positive pulse and the brightness pulse have the same pulse height, and the brightness signal S1 and the next brightness signal are similarly A positive electric field of 4 V/angstrom or more may be applied intermittently during S2.

As described above, by applying the cleaning pulse continuously or intermittently, the surface of the cathode 6 can be constantly cleaned, and the electron beam can be stabilized. Therefore, fluctuations in brightness, etc. can be eliminated, and higher image quality can be expected. Further, it is also possible to stabilize the brightness of the pixel itself constituted by the cathode 6.

[0017]

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

[Brief explanation of drawings]

FIG. 1 is a schematic cross-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 of a small cold cathode, partially cut away.

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

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

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

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

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

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

FIG. 9 is a timing chart diagram showing a conventional driving method.

FIG. 10 is a characteristic diagram showing changes in current value and voltage over time in a conventional image display device.

[Explanation of symbols]

1...Front panel 2...Cathode panel 4...phosphor stripe 6...Cathode 7...Gate electrode

Claims (1)

[Claims] 1. An image display device that extracts an electron beam from the tip of a minute cold cathode by applying a negative electric field, and irradiates the electron beam onto a phosphor to display an image, wherein when the negative electric field is not applied, an electron beam is extracted from the tip of the minute cold cathode. An image display device characterized in that a positive electric field is applied continuously or intermittently.