US3448317A - Semi-conductive device for reducing distortion in electron optics - Google Patents

Description

June 3, 1969 w. HEIMANN ET AL 3,448,317

SEMI-CONDUCTIVE DEvIcE FOR REDUCING DISTORTION IN ELECTRON OPTICS Filed March 23, 1966 h ALTER HE/Mfl/l A/ & 770 S 66 522157? INVENTORS av yi fifiZi/mf United States Patent 3,448,317 SEMI-CONDUCTIVE DEVICE FOR REDUCING DISTORTION IN ELECTRON OPTICS Walter Heimann, Wiesbaden-Dotzheim, and Otto Scherzer, Darmstadt-Niederramstadt, Germany, assignors to W. Hiemann, doing business as Forschungslaboratorium, Prof. Dr.-Iug. W. Heimann, Wieshaden-Dotzheim, Germany Filed Mar. 23, 1966, Ser. No. 541,910 Claims priority, application Germany, Mar. 26, 1965, 45 635 Int. Cl. H013 29710, 31/26, 39/00 US. Cl. 313-89 11 Claims ABSTRACT OF THE DISCLOSURE The present invention relates to a semi-conducting support for use with electron optics, and more particularly to such a support which is to be combined with a photocathode.

When it is desired to reproduce a plane surface by means of an electron optics, or electronic lenses, aberration results which causes increasing defocusing and loss of sharpness and resolution toward the edge of the screen. The reason for this aberration is, that the axial beams are much shorter than the beams directed to the edges of the screen. To avoid this difliculty, it has been proposed to form the screen on a surface which is concave with respect to the cathode. This reduces the difficulties and increases the sharpness. On the other hand, if optical irivestigation of the screen is then desired, for example if the surface is a photo cathode of an electron-optical image converter, the light optics must be designed for a curved surface, which is expensive and difficult. To obtain depth of field, the aperture available must be decreased and thus the light intensity available for observation is limited. It is also possible to form a fluorescent screen with a curved surface, to reduce aberration, which, however, again substantially increases the difiiculty with optical observation of the screen.

Proposals to change the electron optics, in order to in fiuence the sharpness of the images at the edges of the screen, have not resulted in practical solutions.

It is an object of the present invention to provide a semi-conducting support for the cathode, by which edge aberration and unsharpness is avoided.

Briefly, in accordance with the present invention, a semi-conducting support of said carrier plate for use in combination with electron optics is formed on a carrier plate, and an electrical potential is applied thereover in a radial direction by electrodes applied as layers and separated except at their center by an insulating or semiconducting material. At least one of the electrode layers is transparent and extends over the surface and is arranged in such a way, or is of such material and it has a predetermined resistance, so that a potential gradient is established in a radial direction, from the edge of the surface or screen toward-s the center where the electrodes are connected together, when the electrodes are connected to a source of potential. The potential drop at the center Patented June 3, 1969 is thus different from the potential drop at the edge, by

a few volts.

The potential drop from the edge of the center may be linear, or non-linear with respect to radial distance. A photo emission cathode may be applied directly over the electrode layer, or the electrode layer itself may be of a material which has the desired photo cathode effects, besides having the resistant characteristic-s above referred to. In order to avoid a shadow of a lead from the center of the support plate, one of the electrodes can be formed as a transparent screen layer, separated from the other electrode or the resistance material by an insulating layer from which a center has been left off, for example by masking, so that the electrodes come together at the center for an electrical connection avoids the shadow otherwise resulting from a lead to the center.

By suitably choosing the specific resistance of the layers applied to the surface of the support plate, an appropriate potential drop is obtained to the layer and aberations can be avoided; by making the potential drop nonlinear, it is also possible to introduce, artificially, desired distortions.

The transparent conductive layers may be tin oxide, SnO as an insulating layer, SiO, silicon oxide, or SiO may be used, which are evaporated on the support plate.

The structure, organization and operation of the invention will now be described more specifically in the following detailed description with reference to the accompanying drawings, in which:

FIG. 1 illustrates, in schematic form, an electron-optical image transducer and, in FIG. 1a, the kind of distortion observable;

FIG. 2 shows an image converter similar to FIG. 1 with a concave cathode and, in FIG. 2a, the image to be desired;

FIG. 3 is a vertical cross sectional view through an arrangement of the screen in accordance with the present invention;

FIG. 4 is a partial plan view of the central portion of the screen in FIG. 3; and

FIG. 5 illustrates, in schematic form, a screen in accordance with a modified form of the invention.

Referring now to the drawings: the electron-optical transducing system comprises, generally, an electronic system 20, and an optical system 30. An electronic image 21 (FIG. 1) will appear, by projections through an electronic lens system not further illustrated, as the electronic image 22 on the reproduction screen 10. The rays on the margin, 25, having to travel a greater distance than the central rays 24, are imperfectly focused and therefore blurr the edge of the image. If the rays from the margin of the cathode pass the other zones of the lens, they cause the distortion shown in FIG. la.

If now the cathode is made concave, as shown at 11, FIG. 2, then the rays all pass through the middle of the lens and the length of travel of the axial rays 24 is not much larger than that of the peripheral rays 25 and the image 23 will not be distorted, or at least will be distorted to a degree which is much less than that of the system of FIG. 1. An undistorted graph is shown in FIG. 2a. Of course, if an optical projection of the raster 23, as illustrated by the optical system 30, is intended to be done on the curved cathode 11, then difiiculties arise because the focus of the optical system 30 will be accurate and sharp only with respect to any particular position along the curved screen 11. To compensate for the differences in distance between axial light beams and peripheral light beams, extremely complicated and expensive optics have to be used.

A raster as shown in FIG. 2a can be obtained, in accordance with the present invention, with a fiat transducing cathode by imposing a radially extending electrical field thereon. A glass plate which may be circular, for example, has a transparent conductive layer 1 applied thereto. Layer 1 does not extend to the entire circumference of the disk but rather only over a portion thereof, up to a metal ring 2 which has an electrical lead 3a applied thereto, for example by extending through glass plate 5. A transparent insulating layer 4, for example formed of SiO or SiO is applied over layer 1, for example by evaporation, in such a manner that the metallic ring 2 and the conductive layer 1 are just covered. The insulating layer 4 has a central portion thereof removed; this can be achieved for example, by putting a mask over the center, during evaporation. Preferably, the center aperture of the insulating layer 4 is toothed or star shaped as shown in FIG. 4. Thus, an electrical connection to conductive layer 1 can be established at the center.

Transparent conductive layer 1a is then applied over insulating layer 4. Again, layer 1a may be evaporated over the insulating layer. Layer 1a is connected to a metallic ring 3 arranged at the outside of plate 5, which ring 3 is again connected to connection 3a. An electrical potential, placed between rings 2 and 3 by means of battery 3b, in which ring 2 is connected to the negative side and ring 3 to the positive, will cause a regularly extending potential gradient to result across the face of layer 1a. The layers 1, 1a have some resistance. Depending upon the value of the potential applied, aberrations as shown in FIG. 1a are compensated more or less; by making the source 3b variable, complete compensation to obtain a raster in accordance with FIG. 2a can be obtained; by changing the voltage even more, overcompensation, that is distortion similar again to FIG. 1a but with a bending of beams inwardly, can be obtained. Layers 1, 4, and 1a can be held very thin, so thin that the difference in thickness (shown exaggerated in FIG. 3) at the center is not noticeable. Layer 1a, may, in itself, form a photo cathode, or have other photo cathode material evaporated thereon or otherwise applied thereto.

Referring to FIG. 5, a transparent conductive layer 8 is again applied to a glass carrier plate 5, as before. Layer 8 is connected, as before to lead 3a, and then to a battery 3b. A semi-conductive layer 7 is then deposited, for example vapor deposited over layer 8. Semi-conductive layer 7 has a high resistance layer 6 applied thereover; for purposes of connection, a ring 6a may be used, applied over layer 7. The resistance distribution of layer 6, taken vertically in FIG. 5, need not be homogeneous; on the contrary, the resistance distribution may be arranged in such a manner that when a potential is applied between layers 6 and 8, a suitable potential gradient results which is proportional to the radius in the center of the disk, and non-linear at the peripheral portion. The nonlinearity can readily be changed by varying the thickness of the applied layer 6 or of the semi-conductor layer 7 beneath, or changing the physical composition of either the applied layer 6, or the semi-conductive layer 7.

Distortion having outwardly bending lines as illustrated in FIG. la can thus be compensated perfectly so that a raster in accordance with FIG. 2a is obtained; higher order distortions, which sometime arise and cause undulating lines towards the peripheral region, can, by suitable choice of the resistance distribution of layer 6 or layer 7, be avoided entirely, when the distribution of resistance is made non-linear. Particularly, distortions of the fifth Seidel orders can be compensated in this summer. A desirable potential drop distribution, from the center portion of the surface toward the edge portion may vary, for example, with the square of the radius.

A suitable material for layers 1, 1a (FIG. 3) or layers 6, 8 (FIG. 5) is SnO A suitable material for semi-conductive layer 7 (FIG. 5) is an electron-conducting glass.

What is claimed is:

1. Semi-conductive support for use in combination with electron optics comprising a carrier plate;

first and second separated superposed electrodes applied to a surface of said carrier plate and extending essentially over the entire surface and adapted to be connected to a source of potential;

a layer of insulating material located between said electrodes and covering said first electrode except for a small center region to insulate and separate said electrodes from each other, except at the center, the unseparated center region of the electrodes forming an electrical connection between both electrodes to establish, upon connection of said electrodes to a voltage source, a potential gradient radially between the edge and said center region over the extent of said surface.

2. Support as claimed in claim 1, wherein one of said electrodes includes a composition of material forming a photo cathode.

3. Support as claimed in claim 1, wherein the resistance distribution with respect to the radial distance from the center of the surface of the electrodes establishing the potential gradient has a square law relationship so that the potential drop from edge portions to the center of the surface is substantially proportional to the square of the distance from the center.

4. Support as claimed in claim 1, wherein the resistance distribution with respect to the radial distance from the center of the surface of the electrodes and establishing the potential gradient is chosen so that the potential drop is non-linear and that the edge portions suppress distortions arising due to higher order aberrations.

5. Support as claimed in claim 1 including a layer of semi-conductive material covering one of said electrodes; the other of said electrodes being formed by a thin, transparent layer of high resistance material covering said layer of semi-conductive material.

6. Support as claimed in claim 1, wherein at least one of said electrodes is a transparent, thin conductive layer.

7. Support as claimed in claim 1, wherein said conductive layers include a layer of evaporated SnO 8. Support as claimed in claim 1, wherein said carrier plate and said means of establishing potential gradient forms a support for a photo cathode.

9. Support as claimed in claim 8, wherein the thickness of said high resistance material is non-uniform with respect to the radial distance from the center of the surface.

10. Support as claimed in claim 8, wherein the high resistance material is of non-uniform composition with respect to the radial distance from the center of the surface.

11. Support as claimed in claim 8', wherein the layer of semi-conductive material covering said first electrode has a non-uniform resistance distribution with respect to the radial distance from the center of the surface.

References Cited UNITED STATES PATENTS 3,118,084 1/1964 Havn et al. 313-78 X 3,155,872 11/1964 H avn et al. 315-23 3,260,876 7/1966 Manley et a1. 313-80 X 3,308,330 3/1967 C'harles 313-65 X 3,321,665 5/1967 Dye 315-169 2,622,219 12/1962 Schagen 313-65 2,908,835 10/1959 Weimer 313-65 3,048,728 8/1962 Beurle 313-94 X 3,204,142 8/1965 Dehaan et al 313-65 X 3,289,024 11/1966 Dehaan et al 313-65 JOHN W. HUCKERT, Primary Examiner.

A. J. JAMES, Assistant Examiner.

US. Cl. X.R.

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