Channel Plate Display Device Having Positive Optical Feedback

Abstract

Display device comprising a cathode-luminescent layer, a plurality of electron multiplier elements, and a plurality of individually energisable cathodes. The cathodes are photo-cathodes and an optical feedback path is provided between said luminescent layer and said photo-cathodes through said electron multiplier elements.

Description

BACKGROUND OF THE INVENTION

This invention relates to a display device comprising a plurality of selectively energisable display elements.

One class of such devices employs an array of glow-discharge paths in an inert gas atmosphere as the display elements. These paths may be arranged for example as a so-called "bar-matrix" or as a rectangular array of dots such as is described, for example, in U.S. Pat. No. 1,224,306. Energising selected combinations of the elements can cause, for example, any alpha-numeric character to be displayed. It is desirable in the interests of economy and reliability that the addressing circuitry for the elements be fabricated in integrated circuit form, this being particularly so when the number of display elements in the device is large. This is, however, difficult to do when gas-discharge elements are employed, because the striking voltage of such discharges is larger than the voltage capability of present-day integrated circuits.

SUMMARY OF THE INVENTION

It is an object of the invention to provide an alternative form of device which does not suffer from this disadvantage.

The invention provides a display device comprising a plurality of selectively energisable display elements each comprising a channel electron multiplier element, an individual photo-cathode adjacent the input of said element, and cathodo-luminescent material situated in a path for electrons from the output of said element, said photo-cathode being sensitive to electromagnetic radiation emitted by said material in response to electron bombardment and being situated in a path for said radiation from said material.

Switching of each element of such a device off and on may be achieved by making the corresponding photo-cathode either a few volts positive or a few volts negative, respectively, relative to the input of the corresponding multiplier element. Thus the switched voltage need only be small and, moreover, the switched current may be negligible.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of an array of photo-cathode substrates in the relative positions they will occupy in a completed display device;

FIG. 2 is a plan view of part of a display device in a partly finished state; and

FIG. 3 is a cross-section of the finished device of FIG. 2 taken along the line III--III, together with a channel electron multiplier plate and a viewing window.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

In FIG. 1 an array of cathode substrates 1 together with supply leads 2 are formed from a sheet of a glass-sealing alloy such as nickel-iron by photo-etching. Parts 3 of the plate interconnecting the supply leads are left in situ for the moment in order to maintain the substrates 1 in their correct positional relationship.

In FIG. 2 a block 6 of electrically insulating material for example that available under the Registered Trade Mark "Fusite K" has been moulded around the assembly of FIG. 1 so that the supply leads project therefrom. Shallow cavities 7 have been formed in the top face 9 of block 6, these cavities each terminating at an individual photo-cathode substrate 1. A ridge 16 completely encircles the cavities 7 and is separated from the main portion of the top face of the block 6 by a step on which rests a metal frame 4, for example again of nickel iron, which is led out through the ridge 16 at 5. An exhaust tube 12 terminates in a hole 13 opening into the upper surface 9 of the block 6.

Photo-cathode material 10 (FIG. 3) is then deposited in the cavities 7, the remainder of the upper surface 9 of the block 6 being masked while this is carried out. A channel electron multiplier plate 11 is then placed in the space surrounded by the ridge 16, the plate 11 being provided with metal flanges 14 and 15, the flange 14 contacting the frame 4 and the flange 15 resting on the top of the ridge 16. The plate 11 may be manufactured by a method described in U.S. Pat. 1,064,072 and each major surface thereof is coated with an electrically conductive layer (not shown) which layers contact the flange 14 and 15 respectively. These layers may be of vapour-deposited nickel-chromium and the major surfaces on which they are provided extend perpendicular to the channels in the plate.

The flange 15 is sealed all round to the top of the ridge 16 by a suitable solder glass (not shown) and a clear or translucent viewing window plate 17 is similarly sealed to an electrically insulating spacer 19 which is itself sealed to the flange 15. A thin layer 18 of cathodo-luminescent material has been previously deposited on a transparent electrically conductive layer (not shown) e.g., of tin oxide itself deposited on the underside of the window plate 17. Electrically conductive supply strips (not shown) welded or otherwise secured to the flange 15 and the transparent electrically conductive layer form current supply conductors thereto.

After sealing, the device is pumped through the tube 12 so that the pressure inside is below 10.sup.-.sup.4 torr and the photo-cathodes are then activated. The metal 3 interconnecting the conductors 2 is removed.

The cathodo-luminescent material 18 is chosen to match the spectral sensitivity of the photo-cathodes 10, i.e., the photo-cathodes 10 are sensitive to at least part of the emission spectrum of the material 18. Thus, if the material 18 is that known as "P 31" the photo-cathodes 10 may be the type known as "S 11". An optical path exists between each photo-cathode 10 and the corresponding part of the layer 18 so that, if electrons from a given photo-cathode 10 reach and are multiplied in the plate 11 to bombard part of the layer 18, some of the resulting electromagnetic radiation emitted by the layer 18 returns to the relevant photo-cathode 10 to sustain the electron emission. The fact that the channels in the plate 11 are perpendicular to the major surfaces of the plate assists this optical feedback.

The device operates as follows. A steady positive potential of the order of 1 Kv is applied to the flange 15 relative to the flange 14, and hence to the side of the plate 11 facing the luminescent layer 18 relative to the other side of this plate. A steady positive potential of e.g. 3 - 5 Kv is also applied to the conductive layer on which the luminescent layer 18 is deposited, relative to the flange 15. Any electrons, therefore, which are incident on the side of the multiplier plate 11 which faces the photo-cathodes 10 are multiplied in the plate, emerge from the other side thereof, and are accelerated towards the layer 18 which luminesces under their influence to give a display visible through the window 17 and also which activates at least that photo-cathode 10 which lies opposite the luminescing part of the layer 18. Thus the effect is self sustaining provided any electron emitted by a photo-cathode 10 can reach the input face of the plate 11. Whether or not this occurs is easily regulated by making small adjustments to the potential of each photo-cathode 10 relative to that of the input surface of the plate 11. Thus if the potential of a given photo-cathode is equal to or more negative than the input surface of the plate 11 a display occurs on the layer 18 at a position opposite that photo-cathode (there will normally be some stray electrons and/or photons to initiate the effect). On the other hand if the potential of that photo-cathode is raised to a few, e.g. 2-5, volts positive relative to the input surface of the plate 11 any electrons emitted therefrom will be prevented from reaching the input fo teh plate 11 and the luminescing area corresponding thereto will be extinguished. Thus a display can be obtained from any part of the layer 18 corresponding to a photo-cathode 10, and this display can be switched on and off by varying the potential of that photo-cathode by a few volts. Moreover the photo-current from each photo-cathode need only be very small so that the photo-cathode can be switched by means of integrated circuits.

With an array of photo-cathodes as described groups can be energised to display single letters or figures together with a decimal point: obviously the use of a larger array enables more complicated displays, such as groups of letters and/or figures, to be obtained.

In order to obtain maximum resolution it will be appreciated that the spacings between the plate 11 and both the photo-cathodes 10 and the layer 18 should be as small as possible, provided they are not so small that electrical breakdown occurs.

If desired, discrete areas of phosphors which are cathodo-luminescent in different colours may be provided in the layer 18, each colour, such as red, green and blue, being energisable by activating a different photo-cathode. In this way a multicoloured display may be obtained.

With large-area devices employing a large number of photo-cathode elements 10 an addressing system of the cross-bar type is preferably used for the individual display elements. Such a system may be formed by depositing an electrically conductive strip on the input surface of the plate 11 opposite each row or column of photo-cathode elements 10 and interconnecting the photo-cathode substrates 1 of each column or row respectively, for example by replacing the individual leads 2 to each substrate by strips which extend thorugh the block 6 in the column or row direction, which strips are exposed in each cavity 7.

It should be noted that U.S. Pat. No. 3,622,828 discloses a display device comprising a plurality of selectively energisable display elements each comprising a channel electron multiplier element, an individual photo-cathode adjacent the input of said element, and cathodo-luminescent material situated in a path for electrons from the output of said element, said elements forming a channel electron multiplier plate. However, in this known device the photo-cathodes are flooded with light from an external source to produce electron emission therefrom.

Claims

What I claim is:

1. A display device comprising a plurality of selectively energisable display elements each comprising a channel electron multiplier element, an individual photo-cathode adjacent the input of said element, and cathodo-luminescent material situated in a path for electrons from the output of said element, said photo-cathode being sensitive to radiation emitted by said cathodo-luminescent material in response to electron bombardment and being situated in a path for said radiation from said material.

2. A device as claimed in claim 1, wherein said multiplier elements form a channel electron multiplier plate having its channels substantially perpendicular to its major surfaces.

3. A display device, comprising:

a layer of cathodo-luminescent material which emits electromagnetic radiation in response to electron bombardment;

a channel plate electron multiplier positioned adjacent one side of said layer to selectively bombard said layer with electrons from the output face thereof and to receive at the output face thereof electromagnetic radiation from said layer, the channels of said channel plate being sufficiently straight to pass therethrough from the output face to the input face thereof at least some of said received electromagnetic radiation, and

an array of selectively energizable photo-cathodes positioned adjacent the input face of said channel plate to selectively supply electrons to said channel plate and to receive electromagnetic radiation passing back through said channel plate from said layer, said photo-cathodes emitting electrons in response to said received electromagnetic radiation, thereby providing positive feedback.

4. The display device defined in claim 3 wherein said photo-cathodes are selectively energized by individually controlling the voltage potentials between said photo-cathodes and the input face of said channel plate, an individual photo-cathode being selectively energized by lowering the voltage potential thereof relative to the input face of said channel plate and de-energized by raising said voltage potential relative to the input face of said channel plate.