This invention relates to an integrated electron-tube structure and in particular to a structure which may be employed for a cathode-ray tube or similar apparatus and which is adapted for the generation of an electron beam having high stability in the presence of mechanical interference.

An improved method is presented for constructing an electron tube from ceramic and metal materials using a process of reaction bonding to achieve vacuum-tight seals between the components. The method enables high alignment accuracy to be achieved with a simple assembly procedure.

Previously-known electron-tube structures used commonly in oscilloscope, video display or camera tubes employ a glass and metal construction method in which the electron-gun- assembly is supported by springs in the glass envelope. Although economical, this technique is unsatisfactory for high-stability applications and the glass tube-envelope may be prone to damage from shock. There exist further problems of material and process incompatibility with semiconductors where integrated- circuit target arrays are incorporated. A form of construction which has been used for so-called ruggedized tubes is dependent on the bonding together of metal electrodes and ceramic insulators in a vacuum-tight assembly requiring no outer envelope. The use of ceramic further allows higher process temperatures to be employed in manufacture, assisting in the achievement of a high vacuum and reducing the risk of contamination of semiconductor devices in the tubes.

A major disadvantage of the ceramic and metal structure is the high cost resulting from the complexity of the numerous metal-to-ceramic seals usually required for each tube. These seals are typically made by an appropriate brazing or high- temperature soldering process, the difficulty of which varies according to the shape of the parts to be joined. In many cases the metal parts have to be formed in such a way that

4 the seals are relieved of stresses ^' which could result in seal failure and which are caused by differences in thermal expansion coefficients of the materials. The resulting complex shapes may make precise alignment difficult.

According to the present invention there is provided an integrated electron-tube structure utilising a process of metal-to-ceramic reaction bonding to produce an assembly forming the whole or part of an electron tube and comprising a plurality of metal elements separated by and bonded to ceramic elements; the said ceramic and metal elements in combination providing the functional electrode means and insulator means of the said integrated electron-tube structure. It wi I I be apparent to those ski I led in the art that electrodes are commonly required to be made in various shapes and that the said shapes principally include planar and cylindrical and a combination ^' thereof.

The achievement of any desired shape in the present invention may be effected either by formation of a metal element, by a combination of metal elements, by a metal layer

« or coating applied to the whole or part of a ceramic element

or by a combination of one or more ceramic elements so metallized and one or more metal elements.

It is usual, but not essential, for a structure of this type to be circular and cylindrical in form. The bonds may be made vacuum-tight and the outer surface of the structure may then form the outer envelope, or part thereof, of the electron-tube. The ceramic elements may be conveniently cut from standard commercial tubing but, in some instances, it may be advantageous to mould the ceramic, for example, to form electrode shapes, which may then be suitably metallized, it is further possible to combine a structure as previously described with one or more other structures or assemblies, fabricated by reaction bonding or other means, fitted either as part of or internal to the tube envelope and attached by welding, screwing or other means. As an example, it has been found advantageous to manufacture a cathode-ray tube deflection- electrode structure by reaction bonding and fit this structure to an electron-gun structure fabricated separately by reaction bonding. The process of reaction bonding between some metals and ceramics is known. Copper and high-alumina ceramic have been found to be suitable materials for the present applications. Where appropriate, gold may be used in place of, or in combination with, copper in a single structure since reaction bonding occurs at sufficiently similar temperatures for both metals. Strong bonds are formed when the mating surfaces of the materials are ground and, for vacuum-tightness, polished. The elements to be bonded are stacked and aligned along an axis. They are then subjected to axial pressure whilst being

heated to a temperature slightly below the melting-point of the metal. In a multi-layer stack of elements, the bonding surfaces on successive layers should preferably align so that shear or bending stresses in the elements are avoided during the bonding process. Supplementary feed-through electrical connections in either ceramic or metal sections forming the outer tube envelope may also be formed simultaneously or separately by reaction bonding or commonly used brazing techniques. Embodiments of the present invention will now be described with reference to the drawings in which, for clarity and ease of comprehension only, the proportions and dimensions of component parts have been disregarded and in which:

Figure 1 is a diagram of a simple electrostatic lens according to the first embodiment of the invention, suitable for use in combination with other non-illustrated parts inside the vacuum envelope of a cathode-ray tube, for example;

Figure 2 is a diagram showing an orthogonal view of the components of the first embodiment positioned in an alignment fixture prior to bonding;

Figure 3 is a diagram showing a longitudinal section of an example electron-gun structure according to the second embodiment of the invention, suitable for use in, and forming part of the outer envelope of, a cathode-ray tube; Figure 4 Is a perspective diagram of a cathode-ray tube deflection-electrode structure according to the third embodiment of the invention, suitable for use in combination with the

electron-gun structure of the second embodiment.

There is shown in Figure 1 an integrated electron-tube structure according to the first embodiment comprising a set of metal electrode plates 1, the number and dimensions of which are selected according to the particular electronic design requirements, separated by tubular ceramic spacers 2 of length also determined by the design requirements. For convenience of alignment, the metal plates and spacers are preferably all of the same outside diameter, although the ceramic spacers may be made slightly smaller to allow for tolerances in the diameter of standard ceramic tubuing. The mating surfaces of the plates and spacers are ground flat and smooth and assembled in proper alignment in a jig which permits an axial load to be applied uniformly in I ine with the areas to be bonded as indicated by the arrows 3 during subsequent heating to effect the bonds. It has been found satisfactory to apply only sufficient axial load to achieve intimate contact of the mating surfaces. In Figure 2 is shown a simple method of aligning the metal plates 1 and spacers 2 of the first embodiment by means of an accurately-ground 'V'-block 4. Whilst they are resting in the 'V'-block, the elements 1 and 2 may be clamped axial ly and the clamped assembly then removed from the 'V'-block before being heated to the bonding temperature. This alignment method may be adapted to suit other embodiments of the invention by adding appropriate features to the 'V'-block. The simple structure of Figure 1 is limited in its application as part of the outer envelope of a vacuum tube because of the low breakdown- oltage of closely-spaced electrodes in air.

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In Figure 3 is shown an integrated electron-tube structure according to the second embodiment, comprising part of a cathode-ray tube electron gun in which planar and cylindrical electrodes are combined with ceramic insulators in such manner as to substantially reduce external potential gradients and in which: a metal ring 5 provides attachment means for a conventional thermionic planar cathode and heater assembly, which may be sealed to the said ring by brazing, and further provides connection to a control electrode comprising a metal deposition 6 on a ceramic insulator 7; a first accelerating electrode comprises a metal disc 8 bonded to the insulator 7 and a cylindrical insulator 9 and further comprises on the major portion of the inner surface of the insulator 9 a cylindrical metal deposition 10 which electrically contacts the disc 8; a focus electrode comprises a metal disc 11 bonded to the ceramic tube 9; a second accelerating electrode comprises a metal deposition 13 on the major portion of the Inner surface of a ceramic tube 12 which is bonded to the disc 11 and to a mounting plate 15, the latter providing means, for example threaded holes 16, for attachment of further electrode structures, for example the deflecti structure of the third embodiment; sealed feed-through connections 14 may be provided as required for connection to deflection electrodes where these are Incorporated as when the second and third embodiments are combined, and may be attached by known brazing or reaction-bonding techniques;

reaction-bonds 17, 19 and 22 are formed between solid metal an metal-coated ceramic surfaces, whilst reaction-bonds 18, 20 and 21 are formed under the same conditions of temperature and pressure between solid metal and bare ceramic surfaces. In Figure 4 is shown a deflection-electrode structure accordin to the third embodiment, which is adapted for use in a precision cathode-ray tube in combination with an electron-gun structure in accordance with the second embodiment, and which comprises: two pairs of deflection electrodes 24 and 28 being metal layers deposited on the inner surfaces of ceramic-bar substrates 23 and 27 respectively; metal electrode-plates 25, 26 and 29, reaction-bonded to metallized end faces of the said ceramic bars, the said end faces being interconnected by further metallization of the said ceramic bars, but usually insulated from the said deflection electrodes; means for attaching the deflection-electrode structure to an electron-gun structure, for example screw holes 30.

It wi I I be apparent to those ski I led in the art that a wide range of electron-tube devices and structures may be fabricated in like manner to the fore-going embodiments by a combination of any number of appropriately designed elements. In particular, in other non-illustrated embodiments of the present invention the functions of amplification, oscillation, frequency conversion, rectification, modulation, signal sampling and conversion, scan conversion, commutation, multiplexing, information display, helical slow-wave structure, cavity resonator, waveguide, electric or magnetic field coupling, directional coupling, capacitor, inductor, resistor,

electron-bombarded semiconductor tube, thermionic cathode tube, cold cathode tube, gas-filled tube, photon detection, electron multiplication, filtering, light generation, light amplification, X-ray generation, electron or ion-beam generation, focussing or deflection may be realised individually or in combination.

Furthermore, the ceramic material may be varied, for example to employ partially-stabilised zirconia (PSZ); the metal electrode material may be varied, for example, to employ gold, nickel or a particular al loy of copper; the metal electrode material may be plated with another metal to achieve reaction-bonding compatibility or with any substance to achieve particular electrode properties; and the ceramic material may be metallized In any desired pattern to achieve complex or multiple electrode configurations.

I have found the advantages of the illustrated embodiments of this invention to be: that each is able to provide accurate and stable control of an electron beam and to have little sensitivity to the effects of shock vibration and extreme temperature variations; that each may be fabricated by a rapid, reliable and accurate assembly method at low cost; that a first alternative precision lens structure is provided which may be employed in an evacuated enclosure; that a second alternative precision lens structure is provided which may comprise part of an integrated electron tube including the outer wall of the evacuated enclosure and has provision for the embodiment of a readil available thermionic heater-cathode assembly, a deflection structure

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and a final anode structure (not illustrated) which may incorporate a semiconductor integrated-circuit target; that an integrated precision deflection structure is provided which may be adapted for use with simple deflection plates, meander-line deflection plates or helical deflection components by interchanging only the metallized ceramic elements.