JPH0756776B2 - Impregnated type cathode - Google Patents

Description

TECHNICAL FIELD The present invention relates to an impregnated cathode which has been attracting attention as a high current density cathode for high definition display tubes, picture tubes and image pickup tubes.

[Conventional technology]

In the conventional cathode, as described in Japanese Patent Application No. 59-133149, a thin film made of a refractory metal and Sc or an oxide of Sc or both is provided on the electron emission surface of a heat resistant porous substrate.

[Problems to be solved by the invention]

In the above-mentioned conventional cathode, the element constituting the thin film, particularly the oxidation state of W, is not taken into consideration, and the degree of oxidation of W changes depending on the vacuum atmosphere and the like when forming the thin film.

An object of the present invention is to artificially control the oxidation state of W.

[Means for solving problems]

The above-mentioned object is achieved by introducing a well-controlled oxidizing gas or vapor such as oxygen gas or water vapor during the deposition of the thin film in the production of the conventional cathode. The above object can also be realized by using W powder or a plate that has been previously oxidized as a target during vapor deposition of the sputter.

[Action]

The electron emission characteristics of the impregnated cathode are governed by the work function of the cathode surface. The work function is determined by the arrangement of atomic groups on the outermost surface of the cathode.

The outermost surface of the cathode coated with the mixed thin film of W and Sc ₂ O ₃ ideally has a monolayer composed of Ba, Sc and O. The constituent elements of this monolayer, Sc and O, are replenished from the mixed coating thin film, and Ba is supplied from the normal impregnated cathode of the base, and during the operation of the cathode, the supply and evaporation of these elements are in equilibrium and a steady state is achieved. Become.

Of these, O is replenished by the decomposition of W oxide (WO ₃ ) and Sc ₂ O _{3 in} the thin film. In particular, the presence of W oxide is indispensable because a large amount of O is required at the initial formation of the monolayer.

After forming the thin film, W
Oxide is easily formed on the surface, but the thickness of this oxide layer is extremely thin and cannot be a sufficient source of O 2 supply. The present invention controls and artificially forms the W oxide.

〔Example〕

An embodiment of the present invention will be described below with reference to FIG. First
The drawing is a cross-sectional view schematically showing an impregnated cathode according to the present invention. In the figure, reference numeral 1 is a cathode material pellet (1.4φ), which is a porous W substrate 2 having a porosity of 20 to 25%.
And holes 3 are formed. As the porous substrate, Mo, Ir, Pt, Re or the like and alloys thereof may be used.
BaCO ₃ , CaCO ₃ , and Al ₂ O ₃ are used as electron emission materials in the holes _3.
Was mixed in a molar ratio of 4: 1: 1 to impregnate. Note that materials having different molar ratios or electron emission materials to which different materials are added may be used. The pellet 1 may be attached to the Ta cup 4, and then the Ta cup 4 may be laser-welded to the Ta sleeve 5. Instead of laser welding, a brazing material may be used. The heating of the cathode is performed using a heater 7 in which the W core wire 6 is coated with alumina. The above is the source of Ba supply. The amount of replenishment of Ba depends on the heating temperature, but it is necessary to change the molar ratio of the electron emitting material or to add an activator such as Zr, Hf, Ti, Cr, Mn, Si and Al in the base material. It can also be adjusted. As a Sc ₂ O ₃ supply source, a thin film 8 made of W and Sc ₂ O ₃ having a thickness of 10 nm to 1 μm was deposited by a vacuum sputtering deposition method. Instead of W, a metal such as Mo, Re, Pt, Ir, Ta, or an alloy thereof may be used.

Prior to the sputter deposition in vacuum, the oxygen partial pressure in the sputter deposition container was adjusted to 1 × 10 ⁻⁵ to 1 × 10 ⁻⁴ Torr.
High purity (99.9%) oxygen is introduced through the gas introduction device,
The partial pressure was measured with a small mass spectrometer mounted in the container.

By this operation, W in the thin film 8 can be oxidized. It is also possible to introduce a partial pressure of oxygen measured in advance from the middle of the sputtering deposition to oxidize only a part of the thin film 8. As the introduced gas, an oxidizing gas other than oxygen can be used.

Using such a cathode, a saturation current density was measured by applying a high-voltage pulse having a width of 5 μS and a repetition rate of 100 Hz to the anode in a cathode / anode bipolar system. The result is the second
Shown in the figure.

In the figure, 9 is the characteristic of the cathode coated with a thin film of W and Sc ₂ O _{3 according} to the present invention.

In the figure, 10 is the characteristic of the cathode without the oxidation treatment of the thin film. Note that 11 in the figure shows the characteristics of the cathode not coated with a thin film.

〔The invention's effect〕

According to the present invention, a monomolecular layer composed of Ba, Sc and O can be stably supplied to the outermost surface of the cathode, so that a cathode having excellent electron emission characteristics can be obtained with good reproducibility.

[Brief description of drawings]

FIG. 1 is a cross-sectional view schematically showing an embodiment of the impregnated cathode of the present invention, and FIG. 2 is a diagram comparing electron emission characteristics of the cathode of the present invention and a conventional impregnated cathode. 1 ... Cathode pellet, 2 ... W substrate, 3 ... Hole, 4 ... Ta
Cup, 5 ... Ta sleeve, 6 ... W core wire, 7 ... Alumina coating, 8 ... Thin film, 9 ... Electron emission characteristics of impregnated cathode according to the present invention, 10 ... Conventional impregnated type in which thin film is not oxidized. Electron emission characteristics of cathode, 11 ... Electron emission characteristics of impregnated cathode without thin film coating.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Susumu Sasaki 1-280 Higashi Koigakubo, Kokubunji, Tokyo Inside Central Research Laboratory, Hitachi, Ltd. (56) References JP 61-91822 (JP, A) JP 61 -13526 (JP, A) JP-A-59-203343 (JP, A)

Claims (3)

[Claims] 1. A group consisting of a substrate made of a heat-resistant porous body, an electron-emitting substance containing barium impregnated in the pores of the substrate, and scandium and a scandium oxide formed on the surface of the substrate. An impregnated cathode comprising a thin film containing at least one selected and tungsten, the thin film containing an oxide of tungsten. 2. The oxide of tungsten is obtained by oxidizing tungsten in the thin film by introducing an oxidizing gas at the time of forming the thin film. Impregnated cathode. 3. The impregnated cathode according to claim 1, wherein the thin film has a thickness of 10 nm to 1 μm.