JPH11213862A - Cathode substrate and method of manufacturing the same - Google Patents

Abstract

(57) [Problem] To provide a cathode substrate having sufficient ion impact resistance under high voltage and high frequency conditions, good electron emission characteristics, and good low temperature operability. SOLUTION: A porous tungsten substrate is formed by sintering, and holes of the porous tungsten substrate are melt-impregnated with an electron emitting substance. A scandium oxide thin film layer and a tungsten thin film layer are sequentially formed on a porous cathode substrate by sputtering. The impregnated cathode assembly 1 having the porous cathode substrate 4 mounted thereon is incorporated into a cathode ray tube, and activated at a temperature of 1200 to 1300 ° C. for 1 to 2 hours in an activation step. The porous cathode substrate 4 has tungsten, scandium and oxygen on the electron emission surface side,
It has a scandium thin film. The scandium thin film has a scandium atom concentration having a positive concentration gradient from the surface on the electron emission surface side in the depth direction.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a cathode substrate capable of operating at a high current density and a method of manufacturing the same.

[0002]

2. Description of the Related Art In recent years, there has been a demand for the development of a color picture tube with an increased number of scanning lines and improved resolution, and a picture tube for an ultra-high frequency, and also an improvement in luminance of a projection tube and the like.

In order to cope with the improvement of the resolution or the luminance, it is necessary to greatly increase the density of the emission current from the cathode as compared with the prior art.

An impregnated cathode has a higher emission current density than an oxide cathode, and is used for an electron tube such as an image pickup tube, a traveling wave tube, or a klystron.

On the other hand, in the field of color picture tubes, impregnated cathodes have been limited to special applications such as HD-TV tubes and ED-TV tubes, but have recently been used for large color picture tubes and the like.

In such an impregnated cathode structure, porous cathode having a porosity of, for example, 15% to 20% is used for the cathode structure, and barium oxide (BaO), calcium oxide, etc. An electron emitting material such as (CaO) and aluminum oxide (Al ₂ O ₃ ) is impregnated to form an electron emitting surface. Further, a metal coat type impregnated cathode structure provided with a metal thin film layer such as iridium (Ir) is formed on the electron emission surface of the cathode substrate by a thin film forming means such as a sputtering method. The impregnated cathode assembly is mounted in an electron tube and heated by a heater to diffuse, for example, barium (Ba) or oxygen (O) impregnated into the impregnated cathode assembly. The formation of the electric double layer on the electron emission surface on the surface of the substrate enables high-density current emission.

Here, as such an impregnated cathode structure for an electron tube, a scandium-based impregnated cathode structure has recently been receiving attention.

On the other hand, the impregnated type cathode structure for an electron tube is formed in a compact structure as compared with the conventional structure for the purpose of power saving. It cannot be sufficiently impregnated.

In general, the life characteristics of an impregnated cathode assembly are governed by the amount of evaporation of barium, which is a main component of an electron-emitting substance. As a result, the required long life characteristics cannot be obtained.

[0010] For these reasons, there is a strong demand for the development of an impregnated cathode assembly capable of operating at a low temperature and at a high current density. As such a cathode, scandium oxide (Sc2
03) is dispersed, or a scandium-based impregnated cathode structure in which a scandium (Sc) compound is adhered to the surface of the cathode substrate has been developed. The operating temperature of the scandium-based impregnated cathode structure is 900, for example. From ℃ to 1000 ℃, the emission current density is several tens A / cm ² .

When a scandium-based impregnated cathode structure is applied to a diode, a pulse width of 5 μsec and a frequency of 50 H
In the evaluation of the pulsed emission current of z, the emission current density can be obtained about 10 times that of the conventional metal-coated impregnated cathode assembly, and a significant improvement in emission current is expected.

However, in the case of a high-frequency pulse, for example, the frequency is set to 15.75 kHz which is generally used in a picture tube or the like.
If z, only a radiation current equivalent to that of the conventional metal coat type can be obtained. In other words, in the scandium-based impregnated cathode assembly, sufficient emission can be obtained even at a relatively low cathode temperature under low duty operating conditions, but when operating in a high duty region, this low temperature operation effect decreases. There is no remarkable difference between the characteristics of the metal-coated impregnated cathode structure and the scandium-based impregnated cathode structure.

The reason for this is that in the low-duty operation, the supply of barium, oxygen and scandium diffused from the pores of the porous substrate of the cathode substrate is sufficient, so that the electric current is discharged on the electron emission surface of the cathode substrate. Although the layers are kept,
In high-duty operation, this electric double layer is destroyed by ion bombardment. Therefore, the difference between the scandium-based cathode, which was superior in the low-duty operation region, and the metal-coated type in the high-duty operation region,
This is thought to be due to the slow diffusion rate of scandium. When the surface of the scandium-based impregnated cathode structure was analyzed by Auger electron spectroscopy, it was found that scandium on the surface disappeared when subjected to ion bombardment, and that it took time for the electron emission to recover to a favorable scandium concentration. Was.

In order to make the scandium-based impregnated cathode exhibit sufficient ion bombardment resistance under high voltage and high frequency operating conditions, oxygen constituting an electric double layer on the electron emission surface, A structure described in, for example, JP-A-63-91924 is known as an improved surface in which scandium and barium exhibit an extremely fast recovery after ion bombardment. Japanese Patent Application Laid-Open No. 63-91924 discloses tungsten (W), tungsten dioxide (WO).
₂ ) Simultaneously sputtering scandium oxide (Sc ₂ O ₃ ) on the surface of the cathode substrate on the electron emission side to form a composite oxide thin film such as Sc ₂ W ₃ O 12, Sc ₆ WO _12, etc. Oxide f at cathode operating temperature
free Sc can be effectively released, and this free Sc
Due to the high diffusion rate of e Sc, the ion impact resistance has been improved, but these improvements have not yet reached practical use.

[0015]

As described above, the conventional scandium-based impregnated cathode assembly cannot provide sufficient ion impact resistance under high voltage and high frequency conditions. That is, there is a problem that when subjected to ion bombardment in high-frequency operation, recovery of lost scandium is slow, and low-temperature operability is reduced.

The present invention has been made in view of the above problems, and has sufficient ion impact resistance even under high voltage and high frequency conditions, has good electron emission characteristics, and has good low temperature operability. An object of the present invention is to provide a cathode substrate and a method for manufacturing the same.

[0017]

According to the present invention, there is provided an electron emitting surface impregnated with an electron emitting material, and at least one of a metal scandium, a scandium compound, and a scandium alloy, wherein the scandium atom concentration is at least in a certain depth section. A scandium thin film layer having a positive concentration gradient from the electron emission surface side in the depth direction.

The scandium atom concentration of the scandium thin film layer in the cathode substrate has a positive gradient from the electron emission side toward the depth direction, and the diffusion of scandium is from the high concentration region to the low concentration region in proportion to the concentration gradient. Since scandium diffuses from the inside of the cathode base toward the electron emission surface side and is actively supplied with scandium, and the thermal diffusion of scandium during operation reduces the concentration gradient on the cathode surface, The life is prolonged by using the internal scandium as a scandium supply source due to the concentration gradient.

Further, the present invention provides a method of forming a scandium thin film layer containing any of metal scandium, a scandium compound and a scandium alloy on the surface of a cathode substrate, forming the scandium thin film layer, and then forming a high melting point metal refractory metal thin film. The layer is formed, and the cathode substrate on which the refractory metal thin film layer is formed is heated at a high temperature.

In the activation step for activating the electron tube, for example, the cathode substrate must be operated in the residual gas and is subjected to ion bombardment. At the initial stage of the activation step, a scandium thin film layer weak to ion bombardment is formed. Provided inside the refractory metal thin film layer, the scandium thin film layer can pass through the activation process without being subjected to ion bombardment. However, at the end of the activation step, scandium atoms can appear on the surface on the electron emission side.

Further, after forming the refractory metal thin film layer, the thickness of the scandium thin film layer containing any of the previously formed metal scandium, the scandium compound and the scandium alloy is equal to or less than the film thickness of the scandium metal, the scandium compound and the scandium alloy. After forming the scandium thin film layer containing the above, the scandium thin film layer is formed, and then the refractory metal thin film layer is formed with a thickness equal to or less than the thickness of the previously formed refractory metal thin film layer.

During operation, the concentration gradient near the cathode surface decreases due to the thermal diffusion of scandium. However, a scandium thin film layer is provided inside as a supply source, and the scandium thin film layer serving as the supply layer is provided in the depth direction. A plurality of scandium thin-film layers are provided such that the thickness of each scandium thin-film layer becomes thicker toward the inner layer, and the thickness of the high-melting-point thin-film metal layer between each scandium thin-film layer is also increased according to the inside, so that the interval between each scandium thin-film layer is internally. Scandium is supplied to the surface on the electron emission side for a longer period of time by using the concentration gradient as a driving force, so that scandium can be supplied for a long period of time and the life is extended.

Further, the scandium thin film layer and the high melting point thin metal layer are formed by repeating a plurality of times.

[0024] And also, the metal scandium, scandium compounds and scandium thin layer containing scandium alloy comprises scandium oxide (Sc ₂ 0 _3), the refractory metal film layer, is intended to include tungsten (W).

[0025]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, an impregnated cathode structure according to an embodiment of the present invention will be described with reference to the drawings.

As shown in FIG. 1, the impregnated cathode assembly 1
A cup-shaped fixing member 3 having a cylindrical cathode sleeve 2 open at both ends and having a concave surface facing upward on the same plane as the opening is provided inside one end of the cathode sleeve 2. A porous cathode base member 4 having an electron emission surface impregnated with an electron emitting substance on its upper surface is fixed in the fixing member 3, and a heater for heating the porous cathode base member 4 is provided in the cup-shaped fixing member 3 in the cathode sleeve 2. 5 are provided. Note that the porous cathode substrate 4 is made of porous tungsten (W),
The pores are impregnated with scandium (Sc) and, for example, barium oxide (BaO), calcium oxide (CaO), and aluminum oxide (Al ₂ O ₃ )
The electron emitting material is impregnated in a molar ratio of aO: CaO: Al ₂ O ₃ = 4: 1: 1. The porous cathode substrate 4 has tungsten (W), scandium (Sc), and oxygen (O) on the electron emission surface side and also has a scandium thin film, and the scandium thin film has a scandium atom concentration of the electron emission surface. Has a positive concentration gradient from the surface on the side toward the depth direction. In addition, the cathode sleeve 2
Outside the cylindrical holder 6 at a predetermined distance from the outer peripheral surface.
Is disposed coaxially with the cathode sleeve 2, an opening 7 is formed in the upper surface of the cylindrical holder 6, and a plurality of, for example, three strip-shaped straps 8 are attached to the opening 7. The strap 8 holds the cathode sleeve 2. Further, an overhang 9 protruding inward is formed in the opening 7 of the cylindrical holder 6, and an L-shaped support member is formed on the overhang 9, with a shielding cylinder 11 coaxial with the cathode sleeve 2. 3 at 12
It is attached at the point. In addition, these supports 12
Alternating with the strap 8 in the opening 7.

Further, the impregnated cathode structure 1 is
The first cathode 16 and other grids (not shown) are held together by a bond glass 17, and the porous cathode substrate 4 is disposed so as to face an irradiation hole 18 formed in the first grid 16 to form an electron gun 19. Mounted inside the electron tube.

Next, a method for manufacturing the porous cathode substrate 4 will be described.

First, a porous tungsten substrate having a porosity of about 17% and having tungsten particles having a particle diameter of 3 μm is formed by sintering, and BaO: CaO: Al ₂ O ₃ = The mixture of electron emitting materials in a molar ratio of 4: 1: 1 is melt impregnated by heating at 1700 ° C. for about 10 minutes in an H ₂ atmosphere.

Then, a scandium oxide thin film layer and a tungsten thin film layer are sequentially formed on the porous cathode substrate by sputtering. First, using scandium oxide (Sc ₂ O ₃ ) as a target material, 1 vol. % Oxygen (O ₂ ) mixed with argon (A
Using r), scandium oxide is sputtered to a thickness of 10 angstroms according to the conditions of the sputtering rate measured in advance. Subsequently, using tungsten (W) as a target material, argon (Ar) is used as a sputtering gas.
And tungsten is sputtered to a thickness of 200 angstroms in accordance with the conditions of the sputtering rate similarly measured in advance.

The porous cathode substrate 4 thus produced
The impregnated cathode assembly 1 equipped with is assembled into a cathode ray tube,
In the activation step, activation is performed at a temperature of 1200 ° C. to 1300 ° C. for 1 hour to 2 hours. The temperature and time here need to be finely adjusted in consideration of the heat history in the preceding and subsequent steps.

Using this cathode ray tube, a pulse having an applied voltage of 300 V, a pulse width of 5 μsec, and a pulse period of 50 Hz was applied to the porous cathode substrate 4 and the first grid 16, and the characteristics were evaluated by the operation of a diode.

The resulting emission current density was 120 A / cm ₂ at a cathode operating temperature of 1300 K and 3 at 1150 K.
It is 0 A / cm ₂ , and the emission current density obtained with a conventional cathode ray tube is about 20 A / cm ₂ at an operating temperature of 1300 K. Therefore, even if the operating temperature is lowered by 100 K, a performance higher than the conventional one can be obtained.

Further, this cathode ray tube is operated at a cathode operating temperature of 11
A life test was performed by continuously operating the cathode ray tube at 50 K under the normal use conditions, but no deterioration in the characteristics of the cathode ray tube was observed even after 5000 hours.

The thickness of the scandium oxide thin film layer is 1
The same effect can be obtained if the thickness is in the range of 0 to 50 angstroms, more preferably 10 to 20 angstroms, and the thickness of the tungsten thin film layer is in the range of 100 to 500 angstroms, more preferably 100 to 200 angstroms. Obtainable.

If the scandium oxide thin film layer is too thin, the initial electron emission characteristics deteriorate, and at the same time, the life of the cathode is shortened. Conversely, if the scandium oxide thin film layer is too thick, the scandium concentration on the surface of the porous cathode substrate 4 will be too high, and the electron emission characteristics will deteriorate. On the other hand, if the tungsten thin film layer is too thin, an effective scandium concentration gradient cannot be formed. If the tungsten thin film layer is too thick, an extremely high temperature or a long time is required to cause scandium to appear on the surface, which makes production difficult.

Next, the porous cathode substrate 4 of another embodiment will be described.
A method of manufacturing the device will be described. In addition, about composition,
This is the same as the porous cathode substrate 4 of the impregnated cathode assembly 1 shown in FIG.

First, a porous tungsten substrate having a porosity of about 17% and containing tungsten particles having a particle diameter of 3 μm is formed by sintering, and BaO: CaO: Al ₂ O ₃ = The mixture of electron emitting materials in a molar ratio of 4: 1: 1 is melt impregnated by heating at 1700 ° C. for about 10 minutes in an H ₂ atmosphere.

Then, a scandium oxide thin film layer and a tungsten thin film layer are formed on the porous cathode substrate by sputtering. First, using scandium oxide (Sc ₂ O ₃ ) as a target material, 1 vol. % Oxygen (O ₂ ) mixed with argon (A
Using r), scandium oxide is sputtered to a thickness of 20 angstroms according to the conditions of the sputtering rate measured in advance. Subsequently, using tungsten (W) as a target material, argon (Ar) is used as a sputtering gas.
And tungsten is sputtered to a thickness of 800 angstroms according to the conditions of the sputtering rate similarly measured in advance. Further, under the same conditions, scandium oxide is formed with a thickness of 10 Å which is smaller than the previous film thickness, and tungsten is formed with a film thickness of 400 Å which is also smaller than the previous film thickness.

The porous cathode substrate 4 thus produced
The impregnated cathode assembly 1 equipped with is assembled into a cathode ray tube,
In the activation step, activation is performed at a temperature of 1200 ° C. to 1300 ° C. for 1 hour to 2 hours.

Then, the operating characteristics of the diode were evaluated under the same conditions as described above.

The resulting radiant current density was 70 A / cm ₂ at a cathode operating temperature of 1300 K and 30 A at 1200 K.
A / cm ₂ .

Further, the cathode ray tube is operated at a cathode operating temperature of 12
A life test was carried out by continuously operating the cathode ray tube at the operating condition of 00K, but no deterioration in the characteristics of the cathode ray tube was observed even after 8000 hours.

When two scandium oxide thin film layers and two tungsten thin film layers are formed as described above,
The thickness of the scandium oxide thin film layer is 20 Å to 60 Å for the first layer, 10 Å to 30 Å for the second layer, and 400 Å to 1200 Å for the first layer of the tungsten thin film layer. 2
The same effect can be obtained by reducing the thickness in the range of 00 Å to 600 Å toward the surface side of the electron emission surface.

Further, a method of manufacturing a porous cathode substrate 4 according to another embodiment will be described. Note that this configuration also applies to the porous cathode substrate 4 of the impregnated cathode assembly 1 shown in FIG.
Is the same as

First, a porous tungsten substrate having a porosity of about 17% and containing tungsten particles having a particle diameter of 3 μm is formed by sintering, and BaO: CaO: Al ₂ O ₃ = The mixture of electron emitting materials in a molar ratio of 4: 1: 1 is melt impregnated by heating at 1700 ° C. for about 10 minutes in an H ₂ atmosphere.

Then, a scandium oxide thin film layer and a tungsten thin film layer are formed on the porous cathode substrate by sputtering. First, using scandium oxide (Sc ₂ O ₃ ) as a target material, 1 vol. % Oxygen (O ₂ ) mixed with argon (A
Using r), scandium oxide is sputtered to a thickness of 40 angstroms according to the conditions of the sputtering rate measured in advance. Subsequently, using tungsten (W) as a target material, argon (Ar) is used as a sputtering gas.
Is used, and tungsten is sputtered to a thickness of 1200 angstroms in accordance with the conditions of the sputtering rate similarly measured in advance. Further, under the same conditions, scandium oxide is formed to a thickness of 20 angstroms thinner than the previous film thickness, tungsten is similarly formed to a thickness of 800 angstroms smaller than the previous film thickness, and scandium oxide is formed to a thickness of the previous film thickness. A thinner film having a thickness of 10 angstroms is formed, and tungsten is similarly formed with a thinner film thickness of 400 angstroms than the previous film thickness.

The porous cathode substrate 4 thus produced
The impregnated cathode assembly 1 equipped with is assembled into a cathode ray tube,
In the activation step, activation is performed at a temperature of 1200 ° C. to 1300 ° C. for 1 hour to 2 hours.

Then, the surface distribution of the scandium atoms in the depth direction was measured by analyzing the surface of the porous cathode substrate 4 after passing through the activation step by Auger electron spectroscopy combined with ion etching. The atomic concentration of scandium is equal to the scandium (S
c) The signal intensity of tungsten (W) and oxygen (O) is multiplied by a predetermined sensitivity coefficient, and the intensity is determined from the ratio.

As a result, as shown in FIG. 2, it was recognized that there was a region where the concentration increased from the surface of the porous cathode substrate 4 in the depth direction. It is recognized that there are two regions where the density increases toward. That is, the region near the surface of the porous cathode substrate 4 disappears by diffusion in the latter half of the operating life, and the concentration gradient far from the surface of the porous cathode substrate 4 diffuses to the surface of the porous cathode substrate 4. It is thought that it becomes the driving force for scandium supply on the surface.

The operating characteristics of the diode were evaluated under the same conditions as described above.

The resulting emission current density was 50 A / cm ₂ at a cathode operating temperature of 1300 K and 30 A at 1200 K.
A / cm ₂ .

Further, this cathode ray tube is operated at a cathode operating temperature of 12
The life test was performed by continuously operating the cathode ray tube at 20 K under normal operating conditions, and the diode operating characteristics at an operating temperature of 1220 K were also evaluated.

As a result, as shown in FIG. 3, although the emission current density slightly varies from the start of the life test, the emission current density at the start of the life test is maintained until the test time reaches 10,000 hours.

When three scandium oxide thin film layers and three tungsten thin film layers are formed as described above,
The thickness of the scandium oxide thin film layer is 40 Å to 120 Å for the first layer and 20 Å for the second layer.
Angstroms to 60 Angstroms, the third layer is 10 Angstroms to 30 Angstroms,
The thickness of the tungsten thin film layer is 800 angstrom to 2400 angstrom for the first layer, 2
The same effect can be obtained by reducing the thickness of the third layer in the range of 200 to 600 angstroms toward the surface side of the electron emission surface within the range of 400 to 1200 angstroms.

According to experiments, metal scandium,
A scandium thin film layer containing a scandium compound or a scandium alloy includes, in addition to metal scandium (Sc), scandium oxide (Sc ₂ O ₃ ), scandium hydride (ScH ₂ ), and rhenium scandium (Re-S).
c) An alloy or the like can also be used, and molybdenum (Mo) can be used for the high melting point metal thin film layer in addition to tungsten (W).

[0057]

According to the present invention, the scandium atom concentration of the scandium thin film layer in the cathode substrate has a positive gradient from the electron emission side to the depth direction, and the diffusion of scandium is high in proportion to the concentration gradient. Since the diffusion from the region to the low-concentration region, scandium diffuses from the inside of the cathode base toward the electron emission surface side, so that scandium can be positively supplied, and the concentration gradient on the cathode surface due to thermal diffusion of scandium during operation. Because the concentration decreases, scandium inside is used as a source of scandium due to the concentration gradient, so it shows sufficient ion impact resistance even under high voltage and high frequency conditions,
Good electron emission characteristics can be obtained, and low-temperature operability is improved while maintaining good electron emission characteristics, and the life can be extended.

In the activation step for activating the electron tube, for example, the cathode substrate must be operated in the residual gas and is subjected to ion bombardment. At the initial stage of the activation step, a scandium thin film layer weak to ion bombardment is formed. Provided inside the refractory metal thin film layer, the scandium thin film layer can pass through the activation process without being subjected to ion bombardment. At the end of the activation step, scandium atoms appear on the surface on the electron emission side, exhibit sufficient ion bombardment resistance even under high voltage and high frequency conditions, and have good electron emission characteristics. The low-temperature operability is improved while maintaining, and the life can be extended.

During operation, the concentration gradient near the cathode surface decreases due to thermal diffusion of scandium. However, a scandium thin film layer is provided inside as a supply source, and the scandium thin film layer serving as the supply layer is provided in the depth direction. A plurality of scandium thin-film layers are provided such that the thickness of each scandium thin-film layer becomes thicker toward the inner layer, and the thickness of the high-melting-point thin-film metal layer between each scandium thin-film layer is also increased according to the inside, so that the interval between each scandium thin-film layer is internally. Scandium can be supplied to the surface on the electron emission side for a longer period of time by using the concentration gradient as a driving force, so that scandium can be supplied for a long period of time and the life can be prolonged.

[Brief description of the drawings]

FIG. 1 is a partially cutaway side view showing an impregnated cathode structure according to an embodiment of the present invention.

FIG. 2 is a graph showing a scandium atom concentration distribution in a depth direction from the surface of another impregnated cathode assembly according to the first embodiment.

FIG. 3 is a graph showing a relationship between a life test time and a radiation current density of another impregnated cathode assembly according to the embodiment.

[Explanation of symbols]

 4 Porous cathode substrate

Claims (5)

[Claims] An electron emitting surface impregnated with an electron emitting material, and at least one of a metal scandium, a scandium compound, and a scandium alloy, wherein a scandium atom concentration is at least a depth section from the electron emitting surface side. And a scandium thin film layer having a positive concentration gradient in the direction. 2. A method for forming a scandium thin film layer containing any one of scandium, a scandium compound, and a scandium alloy on a surface of a cathode substrate, forming a scandium thin film layer, and then forming a refractory metal thin film layer of a refractory metal. A method for manufacturing a cathode substrate, comprising heating the cathode substrate having the refractory metal thin film layer formed thereon at a high temperature. 3. After forming the refractory metal thin film layer, the thickness of the scandium thin film layer containing any of the previously formed metal scandium, scandium compound and scandium alloy is equal to or less than the thickness of the scandium metal, scandium compound and scandium alloy. 3. A high melting point metal thin film layer having a thickness equal to or less than the thickness of the previously formed high melting point metal thin film layer after forming a scandium thin film layer containing the above. A method for producing a cathode substrate. 4. The method according to claim 3, wherein the scandium thin film layer and the high melting point thin metal layer are repeatedly formed a plurality of times. 5. A scandium thin film layer comprising a metal scandium, a scandium compound and a scandium alloy,
Includes a scandium oxide (Sc ₂ 0 _3), the refractory metal film layer, the manufacturing method of claims 2 to 4 cathode substrate according to any one characterized in that it comprises a tungsten (W).