Patent GB-1297127-A (GB)
IPC: H01J31/12
Filed: 1969-12-11
Abstract: 1297127 Cathode ray display tubes; electron multipliers PHILIPS ELECTRONIC & ASSOCIATED INDUSTRIES Ltd 11 Dec 1969 [14 Dec 1968] 60553/69 Heading H1D An electron source has a planar uniformly emissive surface the source having a channel plate, electron emitter device on the input face, and supply means for driving the plate in the saturation mode. A second channel plate (29) (Fig. 2, not shown) may be on the output side having channels of length l and diameter d such that l/d is at least equal to sin α/sin # sin (α + #), where α is the angle between the axis of the first plate and the second plate input surface, # is the angle between this surface and the axis of the second plate and α + # < 180 degrees. Saturation operation compensates non uniform emission at the emitting layer, the number of outgoing electrons no longer being a function of the number of electrons emitted and depending on plate resistance, and length/diameter ratio of the passages (e.g. 50). The electron emitting device may be a flat thermionic cathode a short distance from the plate or integral therewith, or may be a field emission device, the plate electrode also serving for field emission or a photocathode. The emitting material may be applied to the input electrode and advantageously a small quantity may enter a small distance into the channels. The electron kinetic energy varies as the last collision distance from the output face which determines the K.E. spread, the spread being smaller the more saturated, or with second plate 29 whose passage diameters need not equal those of plate 27, may have a common electrode with that plate, and operates at as low a voltage as possible compatible with multiplier operation; the plates being inclined to ensure at least one collision in plate 29. Alternatively a magnetic field may be provided, preferably at right angles to the single plate or may be used with the two plate system, e.g. 2 mm. long permanent magnets (34), (35) ensure at least one collision in the last 2 mm. (Fig. 3, not shown). Electron source 2 comprises conductor 4 (e.g. 1 mm. Al), porous insulating layer 5 (e.g. few microns thick Al 2 O 3 ), glass matrix 7 (e.g. 10 mm. thick with 2300 passages/cm.<SP>2</SP> of 200 Á diameter) Cr-Ni conductors 6,8, the passage walls of 500 M#/cm.<SP>2</SP> by reducing treatment for instance and a secondary emission coefficient 3 to 4 at right angle incidence, and phosphor layer 10 may be on glass base 11. Voltages are instanced. Second plate (29) may be 2 mm. thick, 20 M#/cm.<SP>2</SP>, plate (27), with slightly fewer passages at 2200/ cm.<SP>2</SP>, conductors 26, 30 of Cr-Ni to the glass followed by Au, Au having better conductivity but adhering less well, conductor (28) being similarly formed on each plate, and porous layer (25) of MgO, voltages being instanced. A channel length/diameter ratio of 50/sin 75 degrees = 52 will saturate (75 degrees being the angle between the interface and plate (27) axis. 50 V. across plate (29) and length/diameter ratio of 10 ensures multiplier operation, and a ratio #3À7 ensures at least one collision, while K.E. spread may be 50 eV.