Modulation mask for an image display device

Abstract

A metal sheet is provided with a plurality of slots which are disposed in parallel rows and columns. Charge sensing pads are disposed on an insulating layer on one surface of the metal sheet with a separate pair of the charge sensing pads being in abutting relation and sandwiching a separate slot. The sensing pads include a portion which extends beyond the length of the slot and is of a material having a high secondary emission ratio. The sensing pads have a capacitance to the metal layer such that they can be electrically charged to a common voltage level which permits a substantially uniform maximum electrical charge to pass into each one of the slots when the abutting sensing pads are discharged by line electron sources. The charge sensing pads may be repetitively charged, i.e., brought back to the common level, through secondary emission from the portions of the pads which extend beyond the slots. A plurality of substantially parallel modulating electrodes are disposed on, but insulated from, the other surface of the metal sheet. Each one of the modulating electrodes extends around one of the parallel columns of slots. The modulating electrodes control the charge which exits from each one of the slots during a charge-discharge cycle. The modulating mask is suitable for use with line electron sources to form a display having desirable characteristics. The modulation mask can be used in conjunction with feedback multiplier line sources as long as high energy electrons are eliminated through the use of high energy electron filters.