Electric lamp and discharge devices – Cathode ray tube – Ray generating or control
Reexamination Certificate
2001-03-21
2004-01-20
Bradley, P. Austin (Department: 2833)
Electric lamp and discharge devices
Cathode ray tube
Ray generating or control
C313S309000, C313S351000
Reexamination Certificate
active
06680564
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a field emission type cold cathode structure (spindt type cathode structure) and an electron gun having the cathode, in particular to a field emission type cold cathode structure and an electron gun using the cold cathode which is capable of preventing electron emission error due to impurities etc. infiltrated into the cathode part.
2. Description of the Prior Art
FIG. 1
illustrates a structure of a standard CRT (Cathode Ray Tube) in accordance with the prior art.
As depicted in
FIG. 1
, the standard CRT (Cathode Ray Tube) comprises a glass container
1
, an electron gun
2
, an electron beam
3
, a deflection yoke
4
, and a fluorescent screen
5
, and it will now be described as below.
First, the electron gun
2
is installed at the end of the vacuum glass container
1
, the electron beam
3
generated from the electron gun
2
is deviated by the deflection yoke
4
generating a magnetic field, and the electron beam is emitted to the fluorescent screen
5
, accordingly the fluorescent screen
5
emits by being excited by the collision with the electron beam
3
.
And, when the described CRT (Cathode Ray Tube) is actually used, a certain image can be displayed by controlling the quantity of the electron beam in accordance with an input image signal, deviating the electron beam
3
two-dimensionally, and scanning it on the fluorescent screen
5
.
FIG. 2
illustrates a structure of a cathode used in an electron gun of a CRT in accordance with the prior art.
As depicted in
FIG. 2
, it comprises a nickel cylinder
6
, an emitter
7
, a heater
8
, and a steatite disk
9
. It will now be described.
First, the emitter
7
is installed at the front end of the nickel cylinder
6
, herein an oxide cathode constructed with Ba, Ca, Sr etc. is widely used.
In addition, a cathode of high electric current density fabricated by impregnating an emitter into a porous tungsten can be used also.
In addition, the heater
8
is installed inside of the nickel cylinder
6
, the electron beam is emitted from the emitter
7
to the vacuum. The cathode is mounted on the steatite disk
9
in order to make the assembly of the electron gun easier.
FIG. 3
illustrates a structure of a section of the electron gun used in the CRT in accordance with the prior art.
As depicted in
FIG. 3
, it comprises a first control electrode
10
, a second control electrode
11
, a third control electrode
12
, a fourth control electrode
13
, a free focus electron lens
14
, a main electron lens
15
, and a crossover of an electron beam
16
, it will now be described as below.
First, the first control electrode
10
and second control electrode
11
for controlling the electron beam are installed on the front of the emitter
7
installed on the cathode.
In addition, the third control electrode
12
and fourth control electrode
13
are placed in order to form the main electron lens
15
for making the electron beam
3
into a detailed spot beam on the fluorescent screen
5
.
In addition, the free focus electron lens
14
of the electron beam
3
is formed by the second control electrode
11
and third control electrode
12
.
Direction dependency of the electron beam density emitted from the cathode, namely, electric current density j(&thgr;) emitted from a normal line to a &thgr; direction about current density j(A/m
2
steradian) vertical direction to the fluorescent screen, can be described as below Equation 1.
j
(&thgr;)=
j
cos &thgr;
Herein, the j describes the current density vertical to the fluorescent screen.
In addition, the emitted electron is discharged with a certain statistical initial velocity distribution, ‘distribution of mark cell’ about the velocity distribution of gas molecules can be adapted to a temperature corresponding to a temperature of the cathode.
As described above, in order to focus the electron emitted from each point of the cathode on one point of the fluorescent screen, various structures are provided for a control electrode for forming the main electron lens
15
and a control electrode for guiding the electron beam to the main electron lens.
FIG. 4
illustrates a field emission type cold cathode structure in accordance with the prior art.
As depicted in
FIG. 4
, it comprises a substrate glass
101
, a base electrode
102
, an insulating layer
103
, a gate electrode
104
, an emitter chip, e.g. emitter tip,
105
, and an electron beam
106
, a power
107
. It can be described as below.
First, the emitter chip
105
constructed with a very small electric conductor (for example, molybdenum) having a cone shape is formed on the base electrode
102
formed on the substrate glass
101
.
The gate electrode
104
constructed with an electric conductor (for example, nickel) is formed on the front end of the emitter chip
105
so as to surround the emitter chip
105
.
And, the insulating layer
103
(for example, sio
2
) is placed between the base electrode
102
and electrode
104
in order to insulate them.
As described above, when a certain voltage Vg is applied from the power
107
between the base electrode
102
and gate electrode
104
, very strong field occurs on the front end of the emitter chip
105
, and electron (electron beam
106
) is emitted from the front end of the emitter chip
105
.
When the electron is emitted from the front end of the emitter chip
105
, the electron beam current as about 350 &mgr;A per 1 spot is required on the fluorescent screen, it is impossible to get the required electron beam current on the fluorescent screen with the one emitter chip
105
.
Accordingly, in order to get the required electron beam current, the cathode is constructed by forming the plurality of emitter chips
105
on the two dimensional plane.
FIG. 5
illustrates a section of a field emission type cathode structure including the plurality of emitter chips in accordance with the prior art, herein a reference numeral
51
describes impurities.
As depicted in
FIG. 5
, when the impurities having the conductivity are stuck to the emitter chip
105
by a certain cause, the base electrode
102
and gate electrode
104
are in short circuit states.
When the base electrode
102
and gate electrode
104
are in the short circuit states, at this time high current flows between the base electrode
102
and gate electrode
104
through the emitter chip
105
and impurities
51
. According to this, the voltage can not be applied between the emitter chip
105
and gate electrode
104
, therefore the electron is not emitted from the other emitter chip
105
.
In the prior art, there is the number of parts increase problem in the control electrode structure.
In addition, in the structure of the cathode in accordance with the prior art, because the electron is emitted by a heating method, although a main power of a television set is ON, a picture having good picture quality is not displayed on the CRT of the television set until the temperature of Ba reaches to the electron emission temperature.
In addition, in the CRT used for the general television, the required electron beam current is about 350 &mgr;A per one spot of the fluorescent screen, however the power for heating the cathode is required about 2 W, accordingly the electron emission efficiency is low.
In addition, in the prior art, when Ba as the electron emission material is used for a long time, it evaporates slowly by being heated, accordingly the electron emission efficiency deteriorates slowly.
In addition, in the prior art, because the electron emitted from the cathode surface is radiated from each point to each region and the initial velocity is irregular, in order to get the detailed electron beam spot on the fluorescent screen, the lots of control electrodes are required.
In addition, in the prior art, when the electron is emitted from the front end of the emitter chip
105
, because the electron beam current as about 350 &mgr;A per one spot on the fluorescent screen is required, it is impossible to get the required electron beam current on th
Bradley P. Austin
Fleshner & Kim LLP
Hammond Briggitte R.
LG Electronics Inc.
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