Electric lamp and discharge devices: systems – Cathode ray tube circuits – Cathode-ray deflections circuits
Reexamination Certificate
2003-09-02
2004-11-02
Philogene, Haissa (Department: 2821)
Electric lamp and discharge devices: systems
Cathode ray tube circuits
Cathode-ray deflections circuits
C315S368110, C315S368150, C313S364000, C313S497000, C313S387000
Reexamination Certificate
active
06812654
ABSTRACT:
FIELD OF INVENTION
The present invention relates to a field emission device, an electron gun, a cathode ray tube apparatus, and a method of producing a cathode ray tube.
BACKGROUND ART
In recent years, flat display panels have started to be rapidly spread in the market. However, in the field of televisions of about 32 inches intended for home use, displays with cathode ray tubes (hereinafter “CRT”) still have an edge, with all things considered such as price and performance.
CRTs are provided with an electron gun as an electron emission source.
Conventional electron guns include a thermal cathode made up of a nickel cylinder in which a heater is placed, whose outer surface is covered with oxide that is mainly composed of barium oxide (BaO).
In the electron gun, an oxide layer will emit electron beams by being applied heat from the heater of the thermal cathode.
Displays are required to have a high-resolution performance, in order to deal with environmental changes such as full-scale introduction of terrestrial digital broadcasting. In order to realize a high-resolution performance in CRTs, it is necessary to improve current density at the thermal cathode. In fact, an extent of improvement required for the current density is great as much as by 6 to 10 times the normal thermal cathode currently used for CRTs.
There have already been attempts for improving current density at the thermal cathode, such as by technically improving materials, which, however, are reaching the physical limit. That is, with CRT, it has come to a point where it is difficult to dramatically improve the current resolution.
On the other hand, research and development has started recently attempting to replace the thermal cathode with a cathode equipped with a field emission device.
A cathode equipped with a field emission device is characterized by inherently having high current density compared to a thermal cathode, therefore has been used for some products such as electron microscopes.
The field emission device has a structure in which a cathode electrode and an extraction electrode, both being a thin film, are formed in the stated order on a substrate, and having at least one emitter being a protrusion in a shape of cone on the cathode electrode. The extraction electrode has an opening above the emitter, and is electrically insulated from the cathode electrode by an insulating layer formed between the extraction electrode and the cathode electrode.
The cathode including this field emission device emits electron beams towards the anode (towards the screen in a CRT), by being applied voltage that exceeds a threshold value between the extraction electrode and the cone-shape emitter. The luminance is adjusted by altering the voltage to be applied.
The aforementioned cathode can operate with high current density, which was not possible with the thermal cathode. Furthermore, the CRT equipped with such a cathode in its electron gun has excellent characteristics in luminance and resolution.
Here, it is noted that the conventional CRTs have a problem in that, even with use of a field emission device as their cathode, the profile of electron beam on the screen (spot profile) will be distorted towards the edge of the screen. Such distortion in electron beams is more pronounced with higher luminance.
This problem with CRTs regarding the distortion of the spot profile of the electron beam is detailed with
FIG. 14
as follows.
FIG. 14
is a plan view showing a spot profile of the electron beam on each area of the CRT screen.
The spot profile of the electron beam, being largely affected by the horizontal deflection magnetic field generated by the deflection yoke, is changed according to an area of the screen which is irradiated with the electron beam as shown in FIG.
14
.
As depicted in
FIG. 14
, in the center of the screen, the spot profile P
1
is yielded in a perfect circle form; and on the edges of the screen (either left or right of the screen in FIG.
14
), the spot profile P
2
is yielded in a laterally-long oval form.
Furthermore, in corner parts of the edges of the screen (either upper or lower parts), the spot profile P
3
is yielded in an oval form being long in a slanting direction.
The aforementioned distortion in spot profiles of the electron beam is generated since the collision angle of the electron beam on the screen is different according to each position of the screen. This is because the electron beam emitted from the electron gun comes into collision with the screen, after being deflected by the deflection magnetic field that is a combination of a horizontal deflection magnetic field and a vertical deflection magnetic field.
The electron beam having distortion in a horizontal direction, in particular, will greatly deteriorate an effective resolution of a CRT.
As shown in
FIG. 14
, the spot profile of the electron beam is largely affected by the horizontal deflection magnetic field of a deflection yoke.
In order to solve this problem, an electron gun whose electron lens is equipped with a quadrupole lens has been proposed. However, such electron gun is problematic because of the cost increase due to the increase in parts.
Under such circumstances, Japanese Laid-open Patent Application H07-147129 disclosed a technology for improving the distortion in spot profiles without using a quadrupole lens.
The structure of the cathode disclosed by this prior art is shown in FIG.
15
.
In
FIG. 15
, three electron emission areas
515
a
,
515
b
, and
515
c
are formed on a surface of a substrate
511
. The form of each electron emission area is as follows: the electron emission area
515
a
that positions in the center has a perfect circle form; and the electron emission areas
515
b
and
515
c
, each positioning at top and bottom, have a crescent form. A cathode electrode
512
a
is connected to the electron emission area
515
a
positioning in the center, and a cathode electrode
512
b
is connected to the other electron emission areas
515
b
and
515
c
. The cathode electrode
512
b
is electrically separate from the cathode electrode
512
a.
This cathode emits electron beams directed to the center of the screen, only from the electron emission area
515
a
, and emits electron beams directed to the edge areas of the screen, from all the electron emission areas
515
a
,
515
b
, and
515
c
. That is, this cathode is able to emit the electron beam having a perfect circle form, for the center of the screen, and to emit the electron beam having an oval form which is long in a vertical direction, for the edge areas of the screen.
Although the disclosed technology is able to improve the distortion of the electron beam to some extent, it cannot perform an appropriate correction to the distortions created throughout the screen, because the forms of the electron emission areas are limited to two patterns, either a perfect circle form or an oval form which is long in a vertical direction. More specifically, the aforementioned technology is not able to either perform a correction for horizontally distorted spot profiles, or an appropriate correction according to each position at the screen.
Furthermore, the cathode, having a field emission device, has a problem that the electron emitting performance will decrease as an elapse of driving time of the device.
When the degree of vacuum in the CRT is low, the electron emitted from the field emission device comes into collision with the gas remaining within the tube, thereby generating ions, and the generated ions come into collision with the surface of the field emission device, resulting in the device being damaged. The device damaged in the above way will have degraded electron emission performance, and will cause luminance deterioration.
As seen in the above, one reason causing the deterioration in the device is the generation of ions due to the low degree of vacuum within the CRT. Generally, the degree of vacuum in a CRT is about 10
−5
(Pa). Currently, a great improvement cannot be expected in the vacuum degree due to a limitation in the production proc
Kawase Toru
Koga Keisuke
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