PCT No. PCT / JP97 / 01976 Sec. 371 Date Feb. 20, 1998 Sec. 102(e) Date Feb. 20, 1998 PCT Filed Jun. 10, 1997 PCT Pub. No. WO97 / 49108 PCT Pub. Date Dec. 24, 1997Problems with a conventional
cathode for electronic tubes arose because metals composing the substrate were subjected to heat deformation, resulting in a relatively lage drift of cutoff
voltage. The present invention diminishes the heat deformation of the substrate to obtain a
cathode with a small drift of cutoff
voltage. Particularly, heat expansion coefficients can be made uniform while metals in the
metal layer are prevented from diffusing into the substrate. This is done by incorporating the same metals present in the
metal layer into the metals composing the substrate, thereby supressing deformation of the substrate.