Thin film scandium tungsten cathode and preparation method thereof
Among many thermal-electron emission cathodes, scandium cathode currently has a relatively high emission level, and its low temperature and large current characteristics are obvious. However, its emission heterogeneity, poor process repeatability and insufficient ion bombardment resistance limit the wide use of scandium cathode in microwave vacuum electronic devices.
In order to overcome the above disadvantages of the poor ion bombardment resistance of the ordinary scandium cathode, the cathode researchers developed the top scandium cathode structure among the existing technologies. According to the different development methods and techniques, these cathodes can be divided into two types: "pressed type" and "thin film type".
"Thin film type" scandium cathode deposits a thin film of oxides or compounds containing scandium on the surface of ordinary diffusion cathode (" B "or" S "type). Their composition is W+Sc2O3, Sc2O3, W+Sc2W3O12, etc. In this way, the work function emitted by the cathode can be reduced to less than 1.5eV. The research on scandium cathode shows that Sc on the cathode surface has no contribution to emission if it exists in the state of element. Only when Sc is in the oxidation state can the emission work of the cathode be reduced in the subsequent activation process.
At present, rf sputtering and laser evaporation are used to form scandium films. However, the former will lead to the decomposition of scandium oxide in the target material, so it is necessary to fill the system with oxygen and strictly control the gas partial pressure, or adopt the post-oxidation process, or adopt Sc2O3, W, WO2 multi-target deposition method, etc., which makes the conditions for sputtering film formation (including the oxidation partial pressure, substrate temperature, post-oxidation temperature, Sputtering power distribution, etc.) becomes quite difficult to control. Although the laser evaporation method can make Sc maintain complete oxidation state in the film without introducing active gas into the system, and it also has good emission characteristics, but its production process is complex, poor controllability, and there is still a large distance from being widely used.
Tungsten and scandium are used as raw materials to prepare tungsten scandium target, and a thin film containing scandium is deposited on the cathode surface by sputtering, which has good controllability and repeatability.
The thin film scandium tungsten cathode consists of a cathode matrix, the lower part of which is a molybdenum shield cylinder, and the inner part of the shield cylinder is a thermal component, which is characterized in that the top surface of the cathode substrate is covered with synthetic scandium tungsten film.
We can produce molybdenum shield cylinder according to customer's requirement.
