| 摘要 |
PROBLEM TO BE SOLVED: To provide an electron tube with a cathode having an electron emissive material layer 15 capable of preventing decrease in the electron emission amount while maintaining excellent high density current operation characteristics. SOLUTION: In an electron tube with a cathode having an electron emissive material layer 15 on the surface of a cathode metal base plate 14, the electron emissive material layer 15 has the three layer structure of a first layer 17 made of an alkali earth metal oxide formed on the surface of the cathode metal base plate 14, a second layer 18 made of an alkali earth metal oxide containing a rare earth metal oxide formed on the surface of the first layer 17, and a third layer 19 made of an alkali earth metal oxide formed on the surface of the second layer 18. The second layer 18 maintains free barium (Ba) in the high concentration state by catching the free barium (Ba) with the rare earth metal oxide, and the third layer 19 shows excellent high current density operation characteristics and electron emission characteristics at the same time since the material not contributing to electron emission, such as the rare earth metal oxide, does not contain. |
