| 摘要 |
<p>PURPOSE:To prevent the exfoliation of an oxide film for langthening the longevity of a directly heating type cathode by roughening the surface, where an alkaline earth metal oxide is to be coated, of a base by providing finely concaved portions. CONSTITUTION:The upside of the base 1 is roughened by integrally providing a great number of finely concave portions 1a, and then the roughened surface is coated with alkaline earth metal oxide 2 to form a cathode. In this case, both sides of the base 1 are coated with a photoresisto, exposed to light through a desired pattern of a negative film, developed, and then subjected to an etching treatment using an acid in order to form finely concaved portions 1a on the upside of the base 1. Then, the remaining photoresisto is removed out to obtain a desirably formed rough surface only on the upside of the base 1. Thus, the exfoliation of the alkaline earth metal oxide can be exactly prevent because the surface to be coated with the alkaline earth metal oxide 2 is securely roughened, and therefore the longevity of the cathode can be lengthened and its reliability can be also raised.</p> |
