| 摘要 |
PURPOSE:To eliminate the face-anisotropy of radiation current, by constituting the tip of a cathode material chip theta which has the crystal face anisotropy in the work function or the Lichardson constant with a face having specific area and perpendicular to the direction of field. CONSTITUTION:The tip of a chip is made conical and the circular plane to have an area smaller than 0.25mm.<2>. With such a shape of chip, the beam is mainly radiated from the circular plane at the tip and scarcely radiated from the slope of chip. The wider the area of the plane at the tip of the chip is, the wider the radiation angle of the beam is, and it is more effective for an exposing device of an aperture projection pattern, but the brightness is reduced. For this reason, the area of the plane is made smaller than 0.25mm.<2>. Consequently, the face-anisotropy of the radiation current can be eliminated. |
