US 2870360 A
Description (OCR text may contain errors)
Jan-20, 1959 -M. KNGU. mL 2,870,360
ELECTRONSTORAGE DEVICE Filed Jan. 15, 1954 ORNEY United States 'Patent' z,s70,360 ELECTRON SToRAGE DEVICE Y Max Knoll, Princeton, N. J., and Paul Rudnick, Fort Wayne, Ind., assignors, by mesneyassignments,` to the- United States of America. as yrepresented by the Secretary of the Army Application January 15, 1954, SerialNo; 404,3322 6 Claims.v (Cl. 313468) In general, a storage tube is an electron tube into whichl information can be introduced and then extracted at a later time. In a charge-controlled ystorage tube the information is retained byv static electric charges. Such charges are generally retained on a homogeneous insulating surface, on an insulating coating over a conducting mesh, or on an array of discrete insulated areas for definite periods of time, as needed. It is desirable that the resistance of the storing material remain as high as possible even at higher temperatures.
The action of establishing a charge -pattern corresponding to an input signal is known as writing; The-retentive feature of this actionmay also be referred to as storing. Retention of the stored charge pattern for a period of time is accomplished by means of the insulating properties Of the surface of a target electrode. In a viewing storage tube provision is made for the formation of a visible imagecorresponding to the pattern of stored charges.
The generation of an electrical or visual output signal corresponding to the stored charge pattern is known as reading. Erasing takes place by the removal `of a pre-- viously stored charge pattern with the aid of some controllable process such as secondary emission or photoconductivity, and may be accomplished by the writing beam.
In certain types of storage tubes the storage insulator is located close to some major source of heatv such as a large-area thermionic cathode. At the high temperatures there found, most insulating materials tend to lose their effectiveness in storingelectric charges. In these cases increased temperature produces an exponential de'- crease'of specific resistance vof the material and the stored charges leak off.
It is therefore an object of this invention toprovide y an improved electronic device for the storage and visual presentation of information, in which the insulating ma-v terial serving to store the information may be operated at high temperature and still be capable of retaining information for a useful length of time.
A further object of this invention is to provide for use in a storage tube an improved insulating material which can retain a stored charge for a longer period than can other storage material under changing ambient'temperatures.
. The objects of the invention may be realized throughy an embodiment which makes use of a polymeriz'ed surface film formed over a' storage target electrode.- The-polymerized surface film may be formeddirectly voverthe conducting base of a target electrode or over the usual layer of magnesium'uoride, silica or otherinsulator used as the storage element in an electronic storage device;
Thisiilm is of a hydrocarbon nature, polymerizedgfand'- is formed by electron bombardment of a target electrode in a suitable yrareiied hydrocarbon atmosphere.
2,870,360 Patented Jan. 20, 1959 ICC elevational sectionalfview of a vviewing storage tube, in
accordance with the invention. i
Referring to the drawing, a viewing type storage tube 10 is shown having an evacuated, substantially cylindrical envelope 20, for example, a glass bulb. Positioned within the cylindrical envelope 20fis a large Vthermionic cathodem 21 held in place by anelectrically conducting ,cathodeV support 22 and so disposed near one end of the envelope 20 as to be capable of `'emitting a wide viewingbeamof electrons toward the other endof the envelope. .Heate r, element 23 is positioned within the thermionic cathode21` sufficiently close to the thermionic cathode v21 to heatV it efficiently. The storage Vtarget electrode 24,' is held, in
place adjacentv to the thermionic cathode by electrically conducting target supports 25 .and 26..
The storage target electrode 24 associated with this invention may be any of the ,usual types. lts surface may be homogeneous ornmeshed. The holespacing of the mesh is determined by the amount of resolution Vdesired. It may be made of woven wires or formed by etching or electroplating. The invention, however, will be more fully vand easily understood from a detailed description of a single type of target surface and for this purpose an y electro-formed mesh approximately .001 of an inch thick and with about 200 grid openings per linear inch has beenf chosen. Each cross-grid 30, in this embodiment of then target structure, is of suchsize as to form apertures 31 which are equal incombinedarea to approximately 50% of the total target surface.
The usual storage layer 32, which may be magnesium fluoride, silica or some other suitable insulator, is there shown formed over each cross-grid 30. For purposes of clarity, storage layer 32 thicknessl has been considerably exaggerated. According tov this invention a polymerized hydrocarbon'iilm 33 is deposited on the target electrode 24 over the usual storage layer 32.
The large viewing beam of electrons which is emitted by the thermionic cathode 21 during operation is focused magnetically by a field from a focusing coil 36 to impinge on the luminescent viewing screen 38, at the end of the cylindrical envelope 20 opposite to a thermionic cathode 21, through the grounded aluminum layer 39. The aluminum layer 39 lies directly over the luminescent yviewing screen 38 and over a largepartof the inner cylindrical surface of the envelope 20.
The writing gun'is placed within` the neck.61 of the lmage storage tube 10 and so disposed as to be in a position -to emit a beam of electrons. 62 in the directit'nn-y of the storage target electrode 24. The electron gun 60 comprises a cathode electrode 63, a control kelectrode 64,
a first accelerating kelectrode 66, a focusing electrode- 68, and a second acceleratingelectrode 69. 'I'he foregomg electrodes form the electron beam 62 emanating from the cathode 63 of the gun 60 into. a sharply defined and focused beam. Separate pairs of deflection plates 72 and 74`are provided for electrostatically deecting the beamin the desired manner.
:The viewing storage tube shown in the drawing containsbo-th an electronic storage system and elements whlch Vmalte the stored information visible for-an appreciable time from outside the tube. During operation, the largethermionic cathode 21'emits electrons substantially unlformly over itsl whole surface in a large beam which 1s focused magnetically by the field from focusing coil 36- onto `the luminescent viewing screen 38. In the absence of any modulation by the storage targety electrode 24, the bombarded area of the screen is ofunifo'rm brightness;
During a writing cycle,.withthe thermionic cathode 21` switched to ground potential through: the switch 76, as y the writing gun 60 scans the insulating film 33, it forms a pattern of charge or potential on the exposed surface of film 33 by any of the various known methods of modulation for storage tubes in which an incoming signal is fed to the control grid 64, as described in the book Storage Tubes and Their Basic Principles by Knoll and Kazan and published in 1952 by John Wiley and Sons. Suitable operating voltages are shown in the drawing. The storage target electrode may be set at a potential of zero to 100 volts depending upon the geometry of the particular tube. Then, during the reading part of the cycle, with the large thermionic cathode at -5,000 volts with respect to ground, in regions of film 33 left with a relatively high negative charge with respect to the thermionic cathode 21, the apertures 31 in the target electrode 24 will be closed to electrons from thermionic cathode 21 by the field from this high negative charge and will produce no luminescence on screen 38. In regions which are relatively highly positive, all available electrons from the thermionic cathode 21 will penetrate the apertures 31 in the target electrode 24 and will be focused on the luminescent viewing screen 38, giving highlights to the picture or other pattern of information. Regions at intermediate potentials will allow smaller electron currents from the thermionic cathode 21 to penetrate the target electrode 24 and bombard the luminescent viewing screen 38, yielding half-tones. Thus the incoming electrical signal is converted into a visible picture containing desired information, which will persist until the next writing cycle leaves a different pattern on the insulating film 33. The new and important feature of this device is the polymerized hydrocarbon film 33 which makes possible the storage of charge or potential patterns on an insulator in relatively close proximity to the hot cathode, as required in a storage tube of this type. It also makes possible other advantages which will be described.
Glass side tubes 77 and 78 are employed only during the process of forming the polymerized layer 33 over the target electrode 24 and are sealed off close to the envelope 2f) before actual operation of the viewing storage tube 10. A few drops of oil 80, preferably of low vacuum pressure (Octoil, for example) such as is used n oil diffusion vacuum pumps7 are left deposited in the glass bottle 79 the opening to which is controlled by valve-stopper 81.
Polymerization lof a hydrocarbon film over a storage target electrode may conveniently be accomplished at room temperature. The storage target electrode is so disposed within the evacuated envelope of a storage tube as to facilitate bombardment by an electron gun. An oil diffusion pump is continuously operated to maintain a pressure of 10r5 mm. of mercury. If an electron gun, similar to the writing gun 60 in the neck of the image storage tube 10 is chosen, it is operated at the voltages shown in Figure l except for the control grid which is maintained at-SOOO volts. Under these conditions an unfocused electron beam of approximately 1 milliampere will be swept across the surface of the storage target electrode. A polymerized hydrocarbon film 0.1 micron thick would be formed over a storage target electrode approximately 3 cm. in diameter in approximately 24 hours or less depending on the residual gas pressure within the tube. The use of an inexpensive electron spray gun which is capable of emitting an unfocused beam of 1GO milliamperes reduces the time of formation of the film to approximately minutes. In the region of the values here used the rate of growth of the film is substantially linear' with beam current intensity.
For practical purposes a storage layer of the thickness of 0.1 to 10.0 microns has been found effective. In general, for storage tubes layers of a thickness of 0.1 to 100 microns are used.
If an oil diEusion pump is used for the purpose of evacuating the glass envelope suicient oil vapor is present in the atmosphere of the partially evacuated envelope for the formation of the polymerized hydrocarbon film. Where a mercury diffusion pump is used it may become necessary to introduce some oil vapor through the side tube 78 connected to the bottle 79 into which has been deposited a few drops of some oil of low vacuum pressure.
The polymerized film may be formed either over the surface of some other insulating layer such as silica or magnesium uoride; or it may equally effectively beformed directly on the bare conducting base of the storage target electrode.
Similarly, the polymerized hydrocarbon lm may beformed over the storage target electrode Within a bell jar. If done in this manner the same conditions prevail as would prevail under those circumstances where the film is formed in the envelope of the storage tube. An electron gun is prequired and is so disposed and activated that it can bombard a storage target electrode with a beam of adequate current intensity. Care must be taken however in removing the target electrode from the bell jar to prevent contamination.
Thus, by electron bombardment within a suitable atmosphere containing small amounts of oil vapor, a hydrocarbon film will be polymerized upon the surface of a storage target electrode making it a highly effective insulator for storage purposes.
The hydrocarbon film may be used as a storage element in all kinds of charge controlled storage tubes and its use is not limited to the storage tube 10 described in the drawing herein. The use of the hydrocarbon iilm as a storage element carries with it other definite advantages. Storage tubes with a higher degree of vacuum can thus be produced. The higher temperature required for processing of such tubes does not disintegrate the hydrocarbon film. Other insulating storage materials frequently are evaporated in such processes.v Also, images may be stored for long periods of time under high temperature. Furthermore, with the storagey grid at 220 C. the retention time of a polymerized film has been observed to be ten times longer than that of uncoated silica at the same temperature. Television projection storage tubes of the transmission control type could be made to yield brighter images as neither the higher voltages nor the higher temperatures there required would lower the effectiveness of the polymerized hydrocarbon storage element.
What is claimed is:
l. An electron storage device comprising an electron gun for producing a beam of electrons along a path, an electrically conductive target electrode mounted transversely of said path, a layer of insulating material on said target electrode, and a polymerized film formed on the said layer of insulating material.
2. An electron storage device comprising an electron gun for producing a beam of electrons along a path, an electrically conductive target electrode mounted transversely of said path, a layer of insulating material on said target, and a polymerized hydrocarbon film formed on the said layer of insulating material.
3. An electron storage device comprising an electron gun for producing a beam of electrons along a path, an
r electrically conductive target electrode mounted transversely of said path, a layer of insulating material on said target and facing said gun, and a polymerized hydrocarbon film formed on the said layer of insulating material.
4. An electron storage device comprising an evacuated envelope, an electron gun within said envelope for the production of a beam of electrons along said path, an electrically conductive target electrode mounted within said envelope transversely to the said path, an insulating coating on the surface of said target electrode, and a polymerized lm formed on said insulating coating.
5. An electron storage tube comprising an evacuated envelope, an electron gun within the said envelope for the production of a beam of electrons along a path, a meshed electrically conductive target electrode mounted within said envelope transversely to the said path, and a polymer ized hydrocarbon lm on said meshed target electrode.
6. A target electrode, for an electron storage device, comprising an electrically conductive target base, a layer of insulating material on said electrically conductive target base and a polymerized hydrocarbon'iilm on said layer of insulating material.
References Cited in the tile of this patent UNITED STATES PATENTS Jones Oct. 31, Knoll et al Nov. 21, Schulze Oct. 15, Klemperer Dec. 31, Sukumlyn May 5, Ross Sept. 21, Aichele July 27, Rudner Dec. 27,