US2178233A - Cathode ray tube - Google Patents

Description

Oct. 31, 1939.

L KLATZOW 2,178,233

CAIHODE RAY TUBE Filed June 11, 1957 INVENTOR L' KLATZOW ATTO RN EY am Oscar, 1939 2,178,233

U ITED STATES PATENT OFFICE 2.11am Y Leonard Klatacw, Bayswater, London, England,

anlgnortolilecttic thlllatcallndultriqlllmited, Hayes, lllddleaex, England, a British oom- P Application June 11, 1837, Serial No. 147,619

7 InGreat Britain 25, 1938 i 9 Claims. (Illa-27.5) I o This invention relates to cathode ray tubes emtion of the metal layer to the mosaic screen as ploying photo-electric mosaic screens. referred to above.

Cathode ray tubes of this kind are employed in A further object of the present invention is to television systems, an image of the object for provideanimproved methodofproducinga cath- '5 transmission being projected upon the mosaic ode ray tube employing a photo-sensitive mosaic screen which is scanned by a, cathode ray to proscreen'in which the amount of silver or other suitduce picture signals for transmission, able metal which is deposited on the screen for In the manufacture of such tubes a support the purpose above-mentioned can be correctly such as a plate of mica or other suitable material determined.

10 is mounted within the tube, such mica plate hav- According to one feature of the invention, a 1 ing a layer of silver provided thereon which is cathode ray tube is provided having within the subsequently heated to uch a, tem erature that envelope one or more sources of silver or other the layer of silver aggregates into minute globules, suitable metal such as tantalum, molybdenum, Associated with the mica sheet is a conductive iron, tung t n, Pl n k c p 8 1 signal plate which,'in conjunction with the silver is so disposed in relation to the mosaic screen or 15 globules, forms a. multiplicity of small condensers. a support on which said screen is formed and The aggregated silver layer is subsequently photoapab of being at 50 at t e Silver 0 ot er sensitised so that on the projection of an image metal can be evaporated on to the screen or the on to the mosaic screen so formed, the minute ai S pport durin manufacture of the tube or condensers acquire electrostatic charges accordsu eq e ly during e fe thereof. 20 ing to the photo-electrons emitted in dependence According to n th r fe ur the i v n -1 H on the light and dark portions of the image, these comprises a method of producing cathode ray minute condensers being restored to a datum potubes employing photo-electric mosaic screens in tential on scanning the screen with the cathode an evacuated envelope and in whicha thin layer 5 ray. of silver or other suitable metalis adapted to be The silver surface which is applied to the mica deposited over substantially the whole of that suris usually formed thereon prior to assembling the face of the screen on which the elements are mica support in the tube, formed, comprising the step of determining, after In the specification of British Patent No. evacuation and sealing of the envelope, the cor- 458,586, it has been suggested to apply a thinrect amount of metal to be deposited by project- 30 layer 01' metal over substantially the whole of the ing an image on to the screen, scanningthe screen surface of the mosaic screen on which the phototo produce picture signals, reproducing picture electric mosaic elements are formed. Such a signals and causing the metal to be deposited on method serves to improve the insulation between to the screen during production of the picture 5 the photo-electric elements of a mosaic screen signals, and'until the reproduced picture acquires 5 and additionally the photq-sensitivity of the mo-' the requireddegree of sharpness. After the corsaic screen is improved without increasing the, rect amount of metal is deposited, the tube may amount of secondary emission obtained when the be subsequently heated at a temperature of the Y screen is bombarded with an electron beam. order of 100 degs. to 200 degs. 0., and in cases 40 The quantity of silver or other suitable metal where silver is employed as the metal, satisfactory 40 which is deposited on the mosaic screen has to be results are obtained at temperatures between 170 regulated very carefully, since, if too little metal degs. and 180 degs. C. y is deposited, no effect on the insulation is ob- The'present invention; therefore, provides a tained, while if too much silver is deposited, the cathode ray tube in which the initial deposit of insulation is decreased, since the metal in such silver or other suitable metal can be applied to the as circumstances provides a conductive path bemica or other support for the screen while the tween the elements. With a tube having an inlatter is mounted in position in the tube and also correct amount of deposited silver or other suitprovides a construction of tube in which a deable metal, pictures reproduced from signals obposit of silver or other metal can be applied to tained from such a tube exhibit a marked lack of the photo-sensitised elements while the tube is in 50 detail and sharpness. operation for the above mentioned purpose.

It is one of the objects of the present inven- In order that the said invention may be clearly tion to provide an improved construction of cathunderstood and readily carried into efiect, the I ode ray tube with a view to facilitating manufacsame will now be more fully described with referture of the mosaic screen or to facilitate applicaence to the accompanying drawing in which: so

ray tube constructed in accordance with the invention and suitablefor carrying into eflect the method hereinbefore referred to, and

Fig. 2 is a front elevation of the support employed for the metal sources shown in Fig. 1.

As shownin Fig. 1, the reference numeral I indicates the envelope of the tube which is provided with a bulbous portion and a tubular portion in which a cathode ray gun of known form is provided. In Fig. 1 only the cathode 2 and the first and second anodes 3 and l of the cathode 'gun are shown. A support 5 of mica or other suitable material is mounted in the tube and associated therewith is a conductive signal plate 6, a lead from which is brought to the exterior of the tube for connection to an amplifier whereby the picture signals obtained on scanning the mosaic screen which is formed on the 'mica support 5 can be amplified prior to transmission. The surface of the mica support 5 opposite to the surface adjacent to the signal plate 6 is provided with a layer of metal, preferably silver.

In accordance with one feature of the invention, for the purpose of applying the initial deposit of silver or other metal to the mica support 5, one or more sources of metal are provided inside the envelope I. In order to enable a uni- 1 form deposit of metal over the whole. area of the screen more than one metal source is provided and in accordance with the preferred form of the invention two metal sources of silver are provided in the tube, one of which isshown in Fig.

but maintain the'supports 8 substantially at right 1. These silver sources-are each in the form of a helix 1 of tungsten wire mounted on a support 8, the support being preferably made of mica and mounted substantially at right angles to the plane of the screen support 5. As shown in Fig. 2 each support 8 carries an additional helix 9 the purpose of which will be hereinafter referred to. Each helix is provided with a coating of silver either by electro-depositing the silver thereon or by applying the silver by other suitable processes, such as by cathode sputtering. The helices may be connected in. series and brought to external contacts whereby they can be connected to a suitable source of heating current so that on'heating the helices the silver is vaporated onto the surface of the support 5. The

support 8 may be shaped as shown in Fig. l in order substantiallyto prevent deposition of the silver on the parts where silver is not required, particularly onto that part of the tube through which the image is projected. The two sources are mounted adiacent to the vertical edges of the support 5 and are arranged as shown in Fig. 2. This figure illustrates the construction of a supporting frame for the helices, the frame being arranged to be collapsibleso that it can be inserted through a narrow opening in the envelope I and erected in the form shown in Fig. 2. As

stated above, the supports-8 are preferably made of mica and at their upper edges they are provided with metal plates I0 riveted thereto, the

upper ends of the-supports 8 being maintained when in the erected position at the required distance apart by a strut II the ends of which are provided with metal plates l2 riveted thereto and attached tothe plates, II by flexible metal strips Illa. V

The strips |0a permitthe framework to be collapsed on moving the supports 8 outwardly,

angles to the strut II when erected. The helices 1 are mounted on the supports 8 through the order to aid in maintaining the framework in the required position. It will be seen that metal sources are placed on the outer surfaces of the supports 8 so that on projection of the image for transmission on to the screen 5, there islittle possibility of shadows being formed on the screen due to the presence of the metal sources.

In practice, sufilcient silver will be applied to the helices 1 so that on evaporating the whole of the silver deposited thereon, the required amount of silver will be applied to the support 5. By the arrangement described, the elements can be mounted within the tube prior to the deposition of silver on to thesupport 5, thus facilitating manufacture and avoiding possibility of damage compared with the known construction on which the support is provided with its deposition of silver prior to mounting within the tube.

In another form of the invention, instead of employing a number of metal sources for providing uniformity in the deposited layer, an annulus or other suitably-shaped source may -be provided substantially surrounding the said screen. Further, instead of plating or otherwise coating the aforesaid helices with silver, beads of silver or other suitable metal may be provided within the convolutions of the helices. In

- seals will be required compared with a construction in which all the filaments or meshes are. heated separately. The grids, instead of having metal mechanically attached thereto, may be electro-plated with the required metal or may have the metal evaporated thereon. Alternative ly, metal plates, to which the required metal is attached or which are plated with the required adapted to be heated by eddy currents to evap-.

. orate the metal.

In the production of a tube after the silver from the sources I is deposited on the support 5, the tube is heated atabout a temperature of 650 degs. C. to cause aggregation of. the silver. Such globules are subsequently oxidised in known manner and thereafter a photo-sensitive material, such as caesium, is introduced, preferably to a slight excess, so that the sensitivity of the mosaic screen so formed is-reduced slightly below the maximum sensitivity obtainable. The tube may then be heated for a short time at a temperature ofabout degs. C. after which it is sealed from the evacuating pump.

Where it is desired to apply a layer of sliver of other suitable metal over the surface of the metal may be provided within the envelope and mosaic screen in accordance with the speciflcatubeisdesignedsothattheinltiallnerofmetal toiormthemosaicscreenisappliedfl'omthe interior of the tube. it is then preferred topmvide the additional metal sourca I for electing the additional coating of metal in accordance with the aforesaid British patent. In Hg. 2 it willbeseenthateachsupportlcan'iestwo helices l and! both oi'whichareprovidedwitha' vaporisable metal, one of each pair of helices m employed for initially coating the support I while the other helix of'each pair is employed for provlding the additional metal layer. The helices I and 9 are so electrically connected that either set can be heated as desired. Alternatively, the sources of metal for the additional coating may be constructed in accordance with the modification hereinbefore referred to.

As stated above, when applying the additional layer of metal, it is diiilcult to r gulate the quantity depositedon the screen and in accordance with a further feature of the invention the cathode ray tube described, since metal sources are provided within the tube, is capable of being operated during deposition of the additional metal 2:! layer in order accurately to deposite the additional metal layer. In carrying this feature of the invention into eflect, the tube described is connected in circuit for operation and an image of an object is projected on to the screen 5 where- 30, by picture signals are generated on scanning the screen. The picture signals after amplification are fed to a receiving or monitoring tube and the helices or other sources of metal are heated until the picture reproduced in the monitoring tube acquires the required degree of sharpness. Heating of the helices is then discontinued. after which the tube may again be heated at a temperature of the order of 100 degs. to 200 degs. C. and, in most cases where the additional layer is silver, satisfactory results will be obtained at temperatures between 170 dogs. and 180 degs. C.

It will be understood that should the sensitivity of the tube decrease during its life, additional metal can be deposited on the screen to improve the sensitivity thereof without the necessity of breaking down the tube, since the required source of metal is provided within the tube.

In cases where the tube with the metal sources is only employed for the deposition of the initial metal layer, which is subsequently aggregated, it is preferred, as stated above, to apply to the helices or other metal sources only sufiicient silver or other metal to form the required thickness on the screen support. In some cases, however, more metal than is required for this initial layer may be provided so that the sources can subsequently be employed for providing the additional coating of metal on to the mosaic screen after the screen is photo-sensitised.

It will be appreciated from the above that the tube constructed in accordance with the invention enables silver or other suitable metal to-be applied to the support for the screen or to the mosaic screen when formed during the manufacture of the tubes, or, subsequently, during the life thereof, and, in addition, enables silver or other suitable metal to be deposited in accordance with the above described method.

Various modifications may be made in my invention without departing from the general features and embodiments thereof and I desire, therefore, that any and all of such modifications which fall fairly within vthespirit and scope of the hereinafter appended claims may be utilized.

I claim as my invention:

a 3 1. a method or producing when, tubes employing photo-electric mosaic screens in an' evacuated envelope and in which a thin layer of silver or other suitable metal is adapted to be deposited over substantially the whole of that surface of the screen on which the individual photo-electric elements of the mosaic are formed, comprising the step of determining, after evacuation and sealing of the envelope, the amount of metal to be deposited upon the photo-electric mosaic to increase the sensitivity and definition thereof to a maximum by projecting an image on to the screen, scanning the screen to produce picture signals, reproducing the 'picture signals and causing the metal to be deposited on to the screen during production of the picture signals, and continuing such deposition until the reproduced picture acquires the required degree of sharpness.

2. The method of preparing a photosensitive mosaic surface upon an electrode within a cathode ray tube wherein a cathode ray beam for scanning is developed which comprises the steps of depositing an insulating layer upon said electrode, depositing a continuous film of conductive material upon the insulating layer, thermally reducing the film to produce a mosaic surface comprising a plurality of electrically isolated formed particles each of substantially microscopic size, oxidizing the formed particles, photoelectrically sensitizing the formed particles, thermally removing the photoelectric deposit from areas intermediate the formed particles, tracing the developed cathode ray beam across the formed mosaic surface to produce signals representative of the surface condition, depositing additional conducting material upon the mosaic surface simultaneously with the scanning operation, limiting the period of deposition of the second conducting material in accordance with observations 'of the signals resulting from scanning, and subsequently heating the formed mosaic over a temperature range of the order of to 200 C.

3. The method of preparing a photosensitive mosaic surface upon an insulating target electrode within a cathode ray tube wherein a cathode ray beam for scanning is developed which comprises the steps of positioning the target electrode within the tube envelope, depositing a continuous film of conductive material upon the target electrode, thermally reducing the film to form a plurality of electrically isolated particles each of substantially microscopic size, oxidizing the formed particles, photoelectrically sensitizing the formed photoelectric mosaic surface, thermally removing the photoelectric deposit from areas intermediate the formed particles, tracing the developed cathode ray beam across the formed mosaic surface to produce signals representative of the surface condition, depositing additional conducting material upon the mosaic simultaneously with. the scanning operation, limiting the period of deposition of the second conducting material in accordance with observations of the signals resulting from scanning, and subsequently heating the formed mosaic over a temperature range of the order of 100 to 200 C.

4. The method of preparing a photosensitive mosaic surface upon an insulating target electrode within a cathode ray tube wherein a cathode ray beam for scanning is developed which comprises the steps of depositing a continuous film of conductive material upon the target electrode, thermally reducing the film to produce a mosaic surface comprising a plurality of elec- 5 trically isolated formed particles each of substantially microscopic size, oxidizing the formed particles, photoelectrically sensitizing the formed photoelectric mosaic surface, removing the photoelectric deposit from areas intermediate the formed particles, scanning the mosaic surface with the developed cathode ray beam, depositing additional conducting material upon the mosaic surface simultaneously with the scanning operation, limiting the period of deposition of the second conducting material in accordance with observations of the signals resulting from scanning, and subsequently heating the formed mosaic.

5. The method of improving the sensitivity of mosaic'electrode structures formed from photoelectrically sensitized isolated metallic particles supported upon a dielectric support base within an electron tube which comprises the steps of depositing a metal coating over predetermined portions of the activated mosaic surface, scan ning during pe 'ods of metal deposition, limiting the period of deposition of the metal, coating in accordance with observations of the signals resulting from scanning and subsequently heating at a low temperature.

6. The method of improving the sensitivity of a mosaic electrode structure formed from photoelectricaliy sensitized isolated electrically conducing metallic particles supported upon a dielectric support base. within an electron tube wherein a cathode ray beam for scanning is developed to form a mosaic surface which comprises the steps of tracing the developed cathode ray beam across the formed mosaic surface, depositing additional conducting material upon the mosaic surface simultaneous with the scan-'- ning operation, limiting the period of deposition of the second conducting material in accordance with observations of the signals resulting from scanning, and subsequently heating the base to a temperature within a temperature range of the order of 100? to 200 C.

7. The process of forming a mosaic light sensitive surface on anon-conducting-base within a cathode ray tube wherein a cathode ray beam for scanning is developed which comprises applying to the base a metallic coating, thermally converting the coating into a plurality of isolated metallic particles each microscopic in size to form a mosaic surface, photosensitizlng the individual isolated metallic particles, tracing the developed cathode ray beam across the formed mosaic surface, depositing an additional metallic coating upon the mosaic surface simultaneously with the scanning operation, limiting the period of deposition of the second conducting material in accordance with observations of the signals resulting from scanning, and subsequently heating the formed mosaic over a temperature range of the order of 100 to 200 C.

8. The process of forming a mosaic light sensitive surface upon a non-conducting base within an electron tube which comprises applying a metal compound to the base, reducing the compound to form a mosaic surface of isolated metallic particles microscopic in size by the application of heat, applying a layer of alkali metal upon the surface of the base, removing the alkali metal between the particles, depositing an additional metal compound coating over predetermined portions of the activated mosaic surface, scanning during periods of metal deposition, limiting the period of deposition of the additional metal coating in accordance with observations of the signals resulting from scanning and subsequently heating at a low temperature.

9. The method according to claim 1, wherein after such an amount of metal has been deposited .as will ultimately produce maximum sensitivity and definition, the tube is heated to a temperature on the order of 100 to 200 C.

LEONARD KLATzow.

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