Double-gated microtip emitters for brighter field-emission displays

Reducing the aperture of the beams emitted by microtips is important to increase the luminance of field-emission displays. Double-gated microtip emitters have been fabricated where the second gate is used to focus the beam emitted by the tip under the action of the attracting field produced by the first gate. The first gate is designed in a volcano shape to shield the apex of the tip from the second gate that is recessed under the level of the first one. This is rendered possible by using a thin rf sputtered SiO 2 layer with very good dielectric properties between the two gates. The beam aperture is reduced from 25° to 7° when the second gate is biased at a voltage 15 V lower than the tip. No reduction in emitted current is observed when the second gate is biased at that voltage, which results in an eightfold increase in current density.