DE1614768A1 - Photo-conductive screen for picture-taking tubes - Google Patents

Description

DDSS ELO ORF 10 ~. H OMBE RGER S TRA SS E 5 10. 2. 1967

rm.ba

16U768 ~ ^{E 1 to}

Tokyo Shibaura Electric Co. Ltd. - Kawasaki-shi - Japan

Photoconductive screen for image pickup tubes

The invention relates to photoconductive devices such as e.g. photoconductive screens for image pick-up tubes, photoconductive cells and other devices and a Method of making the same.

Photo-conductive screens for image pick-up tubes are usually used formed from photoconductive materials that have a dark resistance greater than 10 ohm-cm. For now available photoconductive materials meeting the above dark resistance values but are very rare. Photoconductive screens made from conventional photoconductive materials, such as antimony trisulfide and lead oxide are produced, have a limited spectral response, as a photoconductive material against radiation is only sensitive in a particular spectral range. Accordingly, a single photoconductive material cannot capture the desired broad spectral range of wavelengths. For example, a screen made of ßleioxyd is despite its high sensitivity to the blue range of visible light is not sufficiently sensitive to that Red area so that it is not suitable for red channel pick-up tubes color television can be used.

In order to overcome the difficulties described above, it has been proposed to manufacture photoconductive screens from a mixture of two or more photoconductive materials, such as having different spectral response characteristics, for example a mixture consisting of lead oxide, which is sensitive to the blue range of visible light , and lead sulfide which is sensitive to the red area.

009886/1732

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A screen made of such a mixture offers considerably improved distribution of spectral sensitivity, but its electrical characteristics as a photoconductive screen for the television camera tube are inferior because of the lead sulfide of the dark resistance below 10 ⁷ omega-cm, so that it is useful for practical use is not useful.

A second alternative method has been proposed, a multilayer screen by stacking layers produce different photoconductive materials that have different spectral response characteristics, such as stacking a red light sensitive antimony trisulfide layer 0.1-0.5µ thick and one blue light-sensitive amorphous selenium layer with a thickness of 2 to 5 #u. With such a layer structure should however, the first layer exposed to light, in the above example, the antimony trisulfide layer is sufficient be thin so that the incident light can pass through enough and the next layer in the example the amorphous selenium layer can reach with the result that the first layer does not absorb the incident light in sufficient quantity Can absorb dimensions. Although the second layer absorbs blue light sufficiently, it is opposite to that Residual red light not absorbed by the first layer is insensitive and incident light cannot be fully utilized will. Furthermore, photoconductive materials of low resistance values cannot be used in this structure and hence a reduced dark current required for photoconductive devices cannot be expected.

Accordingly, it is an object of the invention to provide a photoconductive To create apparatus which has sufficient sensitivity to a desired spectral range and which allows low dark currents.

009886/1732

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21 121 February 10, 1967 rm.ba /

Another object of the invention is to provide a method of making such a device.

According to the invention there is a novel photoconductive Device of a plurality of adjacent first layers of a photoconductive material, the one having a spectral response range and a plurality of second layers of another photoconductive material which has a different spectral response range and / or an insulating material, with the second layers between the adjacent first layers or layered together with the first layers according to a certain order are and each of the first and second layers has a thickness less than 2 ai, so that the incident Light can penetrate and is gradually absorbed by the subsequent layers. The device is made by alternately evaporating layers of a photoconductive material by means of a mechanical arrangement that have a special spectral response distribution and layers of another photoconductive material, which has a different spectral response distribution and / or an insulating material, the vapor deposition from separate Evaporation units takes place.

BATH ORIGINAL

009886/1732 -Gi-

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The invention will now be described with reference to the accompanying drawings:

Figure 1

is a longitudinal section of an image pickup tube with a photoconductive screen, which has the has male of the invention.

Figure 2 - is an enlarged partial section showing the in

Figure 1 illustrated photoconductive screen illustrated.

Figure 3 - is an elevational section showing an apparatus for

Production of the photoconductive screen shown in FIG. 2 is illustrated.

Figure 4 a
and 4 b

show a variant of the device for producing the screen shown in FIG. 2, FIG 4 a is an elevation section of the device and FIG. 4 b is a plan view of one contained in the device Closure element is.

Figure 5

is a scheme in which the relative sensitivity as a function of the wavelength characteristic between the photoconductive device according to the invention and a conventional one Device is compared.

Figure 6

Fig. 13 is a diagram in which the residual image signal or the lag as a function of the time characteristic between the photoconductive device according to the invention and a conventional device is compared.

BAD ORiGfNAL

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In Figure 1, an image pickup tube is indicated generally by reference number 10 and consists of an evacuated cylindrical jacket 11, the coaxially an electron gun enveloped, which consists of a cathode 12, a grid electrode 13, a first acceleration electrode 14, a second acceleration electrode 15 and a sieve electrode 17. An end plate 18 closes the end of the jacket 11, at the end remote from the cathode 12, the end of which inner surface is coated with a transparent conductive film 19 made of, for example, tin oxide. The conductive one Film 19 is electrically connected to a signal electrode 20 and is on the opposite of the electron gun 16 Side provided with a multilayer photoconductive which forms the invention and which is indicated generally at 32 and their manufacture will be described in detail later.

As can be seen in more detail from FIG. 2, the multilayered photoconductive structure 32 consists of a large number of first and second layers 30 and 31 lying next to one another, the layering being achieved, for example, by first vapor deposition of a layer 30 of a photoconductive material on the photoconductive film 19 , which is particularly sensitive to visible light in the short wave range such as lead oxide in a thickness of 0.8 ax followed by the vapor deposition of a second layer 31 of another photoconductive material that is particularly sensitive to visible light in the long wave range such as ßleisulfid with a Thickness of 0.2 ii and the repeated alternating vapor deposition of two of these photoconductive materials until the thickness of the layer reaches 10 μ . The layer structure 32 can have a thickness in the range of 3-20 μm, the thickness of the individual layers preferably being less than 2 μm .

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When the image pickup tube 10 is operated, an electron beam 34 from the electron gun 16 accelerated by the acceleration electrodes 14 and 15 and bundled and deflected by . bundling and deflection coils, not shown, whereby the photoconductive layer 32 forming the screen is scanned will. If no light falls on the screen 32, the surface of the screen scanned by the electron beam 34 is shown in FIG held at about the same potential as the cathode. As soon as light reaches the screen 32, the screen is excited so that that depending on the intensity of the incident light, its resistance is reduced and corresponding electrical signals are produced by the electron beam scanning the screen.

The manufacturing method of the aforementioned multilayer photoconductive screen will now be described with reference to Figure 3, in which a preferred construction of the device for Production of the photoconductive multilayer screen is shown.

The device consists of a bell 40 which is gas-tight on the peripheral annular edge 42 of a support element 41 is attached by means of a rubber seal 43, so that a general at 56 marked gas-tight boiler is formed. Inside the gas-tight vessel 56 is a coaxial, disk-like, rotating support member 46 is arranged, which is attached to a vertical shaft 45, which is rotatable under sealing goes through the support element 41 to the outside of the boiler 56 and a drive device such as motor 44 is coupled to the rotor. The disk-like rotating support member 46 is in this form with circular openings 47 of the same diameter, arranged symmetrically with respect to the axis of the shaft 45, the center of the openings 47, for example, 8 cm from the center of the disc like support element 46 is removed. Overlying each of the openings is a layer 48 which is the faceplate of the image pickup tube forms. Above the pads 48 is a pad heater 49 arranged, for example from a chrome

Nicke! Draht bestent 009886/1732 _ _{f; 4} _ _BAD ORIGINAL

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Directly below the supports 48 is a corresponding one Number of evaporation devices in this form of training 2 arranged. One marked 50 consists of a platinum container containing lead oxide and the other 51 from a quartz container which contains lead sulfide and is surrounded by a heating coil 52. The platinum container 50 and the Heat coils 52 are electrically connected to associated lines 54, which are sealed gas-tight from the support element 41 come out and are stripped from this by an insulating device, such as ceramic ring elements 53. Each of the vaporizing devices 50 and 51 is made of, for example, glass in order to prevent it from being vaporized photoconductive material is scattered and occupies all of the space inside the gas-tight vessel.

In operation, the container 50 is filled with 320 mg of powdered lead oxide, while the container 51 is filled with 80.mg of powdered lead Lead sulfide is filled. The pads 48 are then heated to a temperature between 98 and 200 ° C., for example 150 ° C through the heating element 49. Thereafter, the interior of the gas-tight vessel 56 is an oxygen atmosphere at a low pressure between 2 χ 10 ~ and 3 χ

-1 "-2

For example, 10 mm Hg exposed to 5 × 10 mm Hg. The most suitable value for the pressure mentioned is determined experimentally. The containers 50 and 51 are then heated to approx. 900 ° C and approx. 700 ° C, respectively. After the lead oxide and lead sulfide is completely melted by the heating, the bearing support member 4b is rotated at a speed of, for example, 15 rpm During the rotation of the bearing support member 46 which runs above the support element 46 are 48 alternately with Bleioxydschichten of 0.8 η Thick and lead sulfide layers of 0.2µ thick each coated. For example, a photoconductive multi-layer structure with a thickness of 10μ can be achieved if the support element 4t is rotated> 10μ before it is switched off. Thus, the thickness of a layer and that of the multilayer structure

009886/1732 ^BAD

■ 16U768

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are determined by the speed and the number of Revolutions of the support element and the evaporation conditions.

As with the device described above, the apparatus generally designated 61 in FIG. 4 a consists of a bell 64, which is attached to a support element 62 by means of a rubber seal 63 is attached that the apparatus is gas-tight. Inside the gastight Kessels 61 is a coaxial stationary seat support member 68 arranged, the upper part of which is a disk-like element with a concentric annular opening 69 is provided, over which a support 83 is brought, which forms the face plate of the image pickup tube.

A disk-like closure element 67 is also arranged below the circular opening 69 and concentrically therewith in which a notch, as shown in Figure 4b, is cut and which is rotatable under sealing through the Support element 62 on the outside of the gas-tight vessel 61 and is coupled to the rotor of a motor 65. As with the device described above, there is a platen heater 70 arranged above the support 83. Below, as well as in the vicinity of the closure element 67 is a plurality of Evaporation devices arranged. With this apparatus are two such devices arranged and provided offset by a certain distance, as in the apparatus described above, one consisting of a platinum container 71 containing lead oxide and the other consisting of a quartz container 72 containing lead sulfide and is surrounded by a heating coil 73. The platinum container 71 is electrically connected to associated lines 80 , and 81 connected from the gas-tight vessel 61 via an insulating device such as ceramic ring members 78 and 79 are led out, through which they are stripped from the support element, while the heating coil 73 is electrical is connected to associated lines 76 and 77, which in a similar manner via ceramic ring elements 74 and 75 from the gastight boiler b1 are brought out.

009886/1732 - « ⁶ - bad original

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-G-T-

In operation, the platinum container is powdered with 320 mg Lead oxide and the quartz container 72 filled with 80 mg of lead sulfide. Then the opening located in the upper part of the disk-shaped element of the support device 68 is opened 69 brought a support 83, a transparent glass plate, which is on the side lying on the evaporation unit with covered by a transparent conductor. Then the The temperature of the support 83 is brought to a temperature between 90 and 200 ° C., for example 150 ° C., by the heating element 70. The gas-tight vessel 61 is then pumped out of air and oxygen is supplied at a low pressure between 2 × 10 mm Hg

-1 -2

up to 3x10 mm Hg, for example 5x10 mm Hg. The platinum container is then heated to 900.degree. C. and the quartz container 72 to approx. 700.degree. After the lead oxide and lead sulfide are completely melted by the heating, the closure element 67 is rotated by actuation of the motor 65 at a speed of, for example, 15 rpm. Once the closure member is in turn 67, the support 83 is alternately coated with Bleioxydschichten of 0.8 u thickness and lead sulfide layers of 0.2, u thickness, and indeed during the alternate periods during which the notch of the locking element 67 via the evaporation device 71 and 72 goes. As in the embodiment described above, the photoconductive multilayer structure can be stacked with a thickness of 10 µm if the shutter member 67 is rotated 10 χ before it is turned off. The desired thickness can be regulated by properly adjusting the speed and number of turns of the closure element and the evaporation conditions, the size of the notch in the closure element and other operating conditions,

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0008 8671732

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By defining the evaporation rates of individual photoconductive materials and the evaporation times can make the thickness of each layer or the multilayer structure constant be, with the repeatability of the photoconductive Characteristics is very good. As the individual photoconductive materials evaporate from different evaporation devices one can also achieve that each layer of the multilayer structure has a desired thickness by properly adjusting the temperature of the evaporation device, thereby controlling the photoconductive properties of the photoconductive structure such as spectral responsiveness and sensitivity can be controlled.

As described above, according to the invention it is possible a photoconductive multilayer screen by alternately To achieve build-up of lead oxide layers of 0.8 µm thick, which are sensitive to light of short wavelengths and layers of lead sulfide 0.2 µm thick, sensitive to long waves. Such a multilayer structure can the visible light in a wide range of the long wave range absorb effectively, as shown by curve A in FIG. As you can see from this figure can, the multilayer structure according to the invention is very sensitive to the long wavelength ranges, without that the sensitivity to the short wavelength ranges is reduced in comparison to the corresponding characteristic data of a conventional lead oxide screen, as shown in FIG Curve B shown. This means improved performance and broader application.

As can also be seen from FIG. 6, the lag of the photoconductive multilayer structure made of lead oxide-lead sulfide is improved to a great extent in accordance with the invention (see illustration of curve A ¹ in FIG. 6). In comparison with the same characteristics of a conventional photoconductive mixed structure made of lead oxide-lead sulfide (see curve B ¹ in FIG. 6).

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So far, lead sulfide could provide an ideal sensitivity. · Does not have compared to the long wavelength ranges for photoelectric conversion units for an image pickup tube can be used because its resistance is well below 10 ohm-cm. According to the invention can Lead sulphide in connection with lead oxide, which has a high resistance of over 10 ohm-cm, a multilayer structure can be used and the time constant in the direction of The thickness of the resulting multilayer structure can be greater than a lake. be made.

The above description was about making a Photoconductive multilayer structure made of lead oxide-lead sulfide. Similar effects are obtained from multilayer structures a combination of lead oxide layers and lead selenide layers a combination of lead acid layers and lead telluride layers and a combination of lead oxide layers and layers of a mixture of lead telluride and lead sulfide or lead sulfide and lead selenide etc.

The photoconductive materials made in accordance with this invention can be used include oxides, sulfides, selenides, Tellurides of lead, antimony, arsenic, copper, silver and cadmium and suitable mixtures of these compounds.

In the previous description, the lead oxide layer was used and the lead sulfide layer is each formed from pure substances. When ßleioxyd out with a contaminant element a group consisting of antimony, arsenic and bismuth is added, creating a photoconductive n-type layer and at the same time ßleisulfid with an impurity element from a group consisting of oxygen, silver, copper and thallium is added, creating a photoconductive e-type Layer arises, a photoconductive multilayer structure can

- G 9 009886/1732 'BADOHiGlNAL

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obtained from alternately n-p-n-p or

p-n-p-h ..... layers, with this structure the dark current is considerably reduced.

In the case of the aforementioned Αμ5 ^ ί ^ υη§5formen a photoconductive material was used which has good sensitivity to light in the shorter wavelength range and a photoconductive material which has good photosensitivity in the longer wavelength range. At this point it is also possible to obtain a photoconductive unit that is extremely sensitive to a desired spectral range by stacking layers of photoconductive material that has a relatively narrow spectral response range but good sensitivity and layers of another photoconductive material whose spectral response range is close to that of the first photoconductive material.

Furthermore, in the case of antimony triselenide, its more specific Resistance for television camera tubes is as low as, for example, Vidicon by alternating layers of very thin layers of such photoconductive material with low resistivity and also very thin Insulating layers of e.g. silicon monoxide in the layer structure a more effective electric field can be produced than if only a photoconductive layer of greater thickness is present so that generated free carriers can effectively contribute to conduction. Calcium fluoride can be used as an insulating material and magnesium fluoride as well as silicon monoxide can be used.

Although the above-described forms of training are shown in their application for photoconductive cells and image pickup tubes similar effects can also be obtained if the multilayer structure for photoconductive transducers like Light amplifiers can be used.

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In addition, the characteristics can be improved significantly if an additional photoconductive layer or layers on one side or on both sides of more than Photoconductive multilayer structure consisting of two materials be applied.

For example, on the lower layer, a layer of a mixture of lead oxide and a trace of an oxide or a sulfide of a trivalent metallic element such as antimony trisulfide are applied to the then the layer of the photoconductive multilayer structure Lead oxide-lead sulfide is evaporated, on which in turn a thin layer of a mixture consisting of lead oxide and one Trace of an oxide or a sulfide of a monovalent metallic element is applied, which improves the sensitivity which leads to darkness characteristics and other further characteristics.

It should be noted that various changes and Variations are possible without thereby departing from the scope of the invention is deviated from according to the attached claims. The above description and drawings are therefore only illustrative and in no way to be regarded as limiting the invention.

ORIGINAL INSPECTED -At-

i, 009886/1732

Claims (1)

LlVJVlX February 10, 1967 rm.ba Tokyo Shibaura Electric Co. Ltd. - Kawasaki-shi - Japan Claims / 1) / A photoconductive device consisting of first ^ - "'Layers of a photoconductive material, the one has particular spectral responsiveness and second layers of another photoconductive material that has a different spectral response and / or insulating material, characterized in that each of said first and second layers has one Thickness of less than 2µ, any of the above first and second layer is composed of more than four layers, such that one layer adjoins the adjacent layer of a different material. - A 2 - 009886/1732 ΙΛ February 10, 1967 rm.ba Z) The photoconductive device according to claim 1, characterized in that said second layers of two or. ' several types of photoconductive materials exist. 3) The photoconductive device according to claim 1, characterized in, that the mentioned second layers of photoconductive Layers and / or insulating layers exist. 4) The photoconductive device according to claim 1, characterized, that the photoconductive materials of said first and second layers of oxides, sulfides, selenides, Tellurides consist of antimony, arsenic, copper, lead, silver and cadmium or mixtures of these. 5) The photoconductive device according to claim 1, characterized in, that said insulating material from a group consisting of silicon oxide, calcium fluoride and magnesium fluoride is chosen 6) The photoconductive device according to claim 1, characterized in that said apparatus is a screen for an image pickup tube is. 7) The photoconductive device according to claim 6, characterized in that that the photoconductive material of said first layers has a resistivity of more than 10 ohm-cm and the photoconductive material of said second layers have a specific resistance of less - '.. ■ - BATHROOM than -10 ¹¹ ohm-cm. 009886/1732 - A3- 21 121 February 10, 1967 rm.ba / £ 7 - A Jf - 8) A photoconductive screen for an image pickup tube, according to claim 6, characterized in that said screen is particularly sensitive to it Red light and two or more first layers of lead oxide and a corresponding element of the second Layers made of lead sulfide, each of the layers mentioned has a thickness of less than two microns and the aforementioned lead oxide and lead sulfide layers are alternately stacked on top of one another. 9) The fotokonduktive screen own. According to claim 8, characterized in that said first layers have a thickness of about 0.8 u, and the second layers comprise a thickness of about 0.2 u. 10) This photoconductive screen according to claim 8, characterized in that that said first layers have one type of conductivity and said zi \ reiten layers the opposite Have type of conductivity. 11) The photoconductive screen according to claim 10, characterized in that that said first layers have at least one impurity element selected from antimony-arsenic and bismuth and said second layers contain at least one impurity element selected from oxygen, silver, Contains copper and thallium. ■ A4 009886/1732 16H768 21 121 10. 2 * 1967 rm.ba ηψ -A4T- 12) A method of making multilayer photoconductive devices, _s can be characterized in that is placed a plurality of evaporation units on a support one or more conditions placed on a movable frame so that they are opposed to the evaporation units mentioned, said support as well as the evaporation devices mentioned are kept under low pressure, the supports above and those said evaporation units are heated and the position of the supports relative to the said IVferdampfungsaggregaten is constantly shifted so that the supports are repeatedly placed opposite each of the said evaporation units, so that one after the other that evaporated material from the said evaporation units are vaporized onto the said supports. 13) A method of making multilayer photoconductive devices according to claim 12, characterized in that a plurality of evaporation units, including at least one photoconductive material unit, are placed on a support in certain positions, a support is placed in a stationary frame so that it is opposite the said evaporation units, a rotating closure plate with a notch being interposed , the mentioned edition and those mentioned. Evaporation aggre gate, are kept under low pressure, said support and said evaporation units are heated and said rotating shutter plate is rotated so that successive thin layers are evaporated from the individual evaporation units during the time in which through the notch in the ge so-called rotating closure plate, a directly opposite relationship is established between the support and the vaporization unit . 00S386 / 1732 - A S - 21 121 February 10, 1967 rm.ba 14) A method for making a photoconductive multilayer structure from lead-chalcogen compounds according to claim 12, characterized in that initially a support by depositing a conductive Film is formed on a flat parallel plate, layers of lead oxide and layers of a compound of lead and at least one chalcogen element such as sulfur, selenium and tellurium on the said conductive Film in an oxygen atmosphere under a pressure of -3 -1 2 χ 10 mm Hg to 3 χ 10 mm Hg by heating the aforementioned Edition is layered at a temperature between 90 and 200 ° C. 15) A photoconductive device essentially as herein described with reference to the accompanying drawings. - end - 009886/1732