Miniature, Directed, Electron-beam Source

Abstract

A miniature, directed, electron-beam source, consisting of a conventional field emission source with an associated first anode plate, and several deposited layers of alumina and molybdenum for focusing and deflecting the electron beam, the deposited layers having a column etched through them to the field emission source.

Description

BACKGROUND OF THE INVENTION

THis invention relates to the electron beam art, and more particularly, to miniature electron beam sources which utilize deposited structure to focus and deflect the electron beam. In the prior art, electron beam sources have structure for focusing and deflecting the beam so that the beam may be controlled in intensity and direction according to the wishes of the operator. This structure is always a component type, that is, individual, distinct components are used to focus and deflect the eimtted electrons into a directed beam. Typical of the prior art are the U.S. Pats. to Newbury, No. 3,491,236, and to Kimura, No. 3,474,245, which disclose electron beam sources and structures to focus and deflect the emitted electrons into a useable electron beam. The structure which performs these functions consists of separate, physically distinct components.

Typical of a focusing structure is a layer or a grid network of metal, with an aperture or opening in that piece of metal. This opening acts like a lens for the electrons eminating from the source and is utilized to establish a directed beam. The emitted electrons which travel in the desired direction of the beam pass through the opening; the remaining electrons are caught by the metal sheet. Often there will be an electrical potential associated with the focusing structure to further focus and direct the beam through the opening and down the optical system. The deflection of the electron beam after it has passed through the focusing structure is usually and typically accomplished by four plate-like structures which surround the beam. By applying differing potentials to these plates, the beam may be deflected to varying degrees in any direction.

This type of structure for focusing and deflecting the emitted electrons into a directed electron beam has been very successful. However, the principle problem with this type of structure in focusing and deflecting electrons is the apparent physical limit (on the order of an inch) to which these components may be successfully miniaturized. Presently, there is a need for extremely small electron beam sources which have the capability of focusing and deflecting so that the beam may be controlled by an operator. Particularly in the area of computers, and in electron-beam-accessed computer memories, there is a need for large arrays of miniaturized electron beam sources to accurately access state-of-the-art miniaturized storage devices. At the present time, a larger single beam source is utilized with a variety of lenses to access the memories. Miniaturization of the electron beam source, however, is required for full utilization of presently miniaturized memory storage. Up to the present, the miniaturization of an electron beam source and its associated focusing and deflecting structure has been limited by the component type of structure. The present invention makes possible the fabrication of electron beam sources having focusing and deflecting capabilities of extremely small size, on the order of 25 microns in height, and 5 microns in diameter.

SUMMARY OF THE INVENTION

One object of this invention is to provide a miniaturized electron beam source with focusing and deflecting capabilities.

Another object of this invention is to provide an electron beam source having focusing and deflecting capabilities wherein a field emission source is utilized.

A further object of the present invention is to provide a miniaturized electron beam source having deflecting and focusing capabilities wherein the structure to accomplish the focusing and deflecting of the electrons is fabricated by material deposition techniques.

With these and other objects in view, this invention relates to an electron beam source having structure capable of focusing and deflecting the emitted electrons. More specifically, the invention relates to a miniaturized electron beam source having an electron source, with structure necessary to focus and deflect the emitted electrons deposited in proximity to the electron beam source. In the preferred embodiment, the electron source is a field emission electron source and its associated first anode plate. Alternating layers of alumina and molybdenum are then deposited to give the focusing capability to the structure. Another layer of alumina is deposited and a column is subsequently etched through the alumina close to the field emission source. Alumina is further deposited to form the necessary structure for deflecting the electron beam. The column is then further etched to reveal the field emission source.

DESCRIPTION OF DRAWINGS

FIG. 1 is a cross-sectional view of the miniature electron beam source;

FIG. 2 is a figurative, typical electrical connection of the miniature electron beam source, and

FIGS. 3 through 7 illustrates successive steps in making the miniature electron beam source.

PREFERRED EMBODIMENT

The preferred embodiment describes the novel miniature electron beam source which consists of a field emission source, an electrostatic lens, and four deflection plates. Referring to FIG. 1, the field emission source is a cone of molybdenum 21, less than 3 microns in diameter at its base and less than 1 micron high. First and second anodes 14 and 17 are constructed of 1/4-micron thick molybdenum layers, separated from a base 12 and each other by 1-micron-thick layers 13 and 16 of alumina. These anodes with the proper choice of voltages focus the electrons which have been emitted from the field emission source. This beam is then deflected by four molybdenum plates, each plate being approximately 20 microns long. The height of this optical system is thus less than 25 microns, while its diameter is less than 5 microns.

FIG. 2 shows a figurative representation of the miniature electron beam source and shows electrical connections that are made within the electron beam source to achieve focusing and deflecting of the emitted electrons.

A detailed description of the preferred embodiment, showing the novel features of the invention, is best achieved by describing a method of manufacturing or making the electron beam source broadly described structurally above. Referring to FIG. 3, the process for making the invention begins with an optically smooth sapphire substrate 11. Referring again to FIG. 3, the first layer 12 of molybdenum is evaporated, using common evaporation techniques, on the sapphire substrate. This layer 12 of molybdenum is evaporated to a thickness of 1/4 micron. On top of this layer of molybdenum, a 1-micron-thick layer 13 of alumina is next evaporated. Another layer 14 of molybdenum is evaporated on the layer 13 of alumina, this second layer of molybdenum also being 1/4 micron in thickness. On top of this second layer 14 of molybdenum, a second layer 16 of alumina is evaporated, this layer also being 1 micron thick. On top of this second layer 16 of alumina, a third 1/4-micron-thick layer 17 of molybdenum is evaporated. Thus, on a typical, sapphire substrate of 5 microns diameter, alternate layers of molybdenum and alumina are evaporated, resulting in three layers of molybdenum and two layers of alumina, the molybdenum being deposited in layers of 1/4-micron thickness and the alumina being deposited in layers of one micron thickness. Additional layers of alumina and molybdenum may be evaporated to give further focusing properties.

Referring to FIG. 4, an opening is made in the structure down to the base layer 12 of molybdenum. Typically, the structure shown in FIG. 3 is coated with a standard photoresist, on which, after appropriate masking, exposure and development would leave an unprotected area about four microns in diameter. The molybdenum layers 17 and 14 and the alumina layers 16 and 13 are etched through, using standard etching solutions such as orthophosphoric acid or a solution of H.sub.2 SO.sub.4 +HNO.sub.3 and well-known techniques, to the first layer 12 of molybdenum. The resulting structure shown in FIG. 4 is then baked at a high temperature (usually 1,000.degree. Centigrade) to make the alumina layers 16 and 13 inert, and thus immune from further etching.

Referring now to FIG. 5, alumina is deposited at an angle of less than 15.degree. above the horizontal line 18 while the substrate structure is rotated. The deposition is continued until the opening in the deposited alumina is equal to the desired diameter of the base of the field emission source to be subsequently deposited. Thus, a layer 19 of alumina is laid down on top of the layer 17 of molybdenum until the opening is equal to the desired diameter of the field emission source. Molybdenum is then deposited in a direction normal to the surface of the structure as shown in FIG. 5 simultaneous with the continuing angle deposition of alumina. This simultaneous deposition of molybdenum and alumina continues until the opening in the alumina layer is closed by the deposition of the alumina. As can be seen from FIG. 5, the shape of the field emission sourc 21 (the deposited molybdenum) can be controlled by the deposition rates of the alumina and molybdenum. This simultaneous deposition technique for making a field emission source is not new and is fully explained by Mr. C. A. Spindt in an article in the Journal of Applied Physics, Vol. 39, No. 7, Pages 3,504 and 3,505, entitled "Thin Film Field Emission Cathode," dated June, 1968.

The deposition of the field emission source, which will provide the electrons, has been described, as has the structure necessary to focus the emitted electrons. The only remaining structure to be described is the deflection plates which deflect the emitted electrons.

Referring to FIG. 6, alumina is again deposited on top of the structure to a height of 20 microns. The total height of the deposited alumina above the layer 17 of molybdenum should be at least 20 microns to achieve a sufficient degree of deflection. This alumina layer, designated by the numeral 25, is then masked, and an opening through the alumina etched to within 1 micron of the opening 22, as shown in FIG. 6. This triangle-shaped opening, which occurs as a result of the deposition technique used to form the field emission source, is generally about one micron above the last layer of molybdenum 17.

Referring now to FIG. 7, molybdenum is deposited from a single stationary source in order to form the deflection plates of the electron beam source. To insure proper adhesion between the alumina and the molybdenum, the surface of the alumina, prior to deposition, must be very clean. The angle at which the molybdenum is deposited onto the alumina depends upon the configuration of the column which has been etched previously in the alumina and the desired column diameter 23 which will be present at the conclusion of the deposition. Molybdenum is deposited until the desired surface configuration of the deposited plate 24 relative to the alumina is achieved, as shown in FIG. 7. The structure is then rotated 90.degree. and the above process is repeated. The deposition of alumina following the above explained process continues until four deflection plates, covering approximately 80 percent of the column surface area, are deposited on the alumina within the column. Because of the low deflection voltages involved (on the order of 50 volts), slight physical distortions along the length of the deposited plates will have little effect on the beam, and can thus be tolerated.

Acid is then used to etch through the remaining alumina shown in FIG. 6 to open the column to reveal the field emission source. Electrons emitted from the field emission source thus are focused by the two molybdenum focusing anodes, pass into the column within the deposited alumina, are deflected by the deflecting plates, and then pass out the upper end of the structure in a concentrated beam. Thus, by using standard, well-known deposition techniques, an electron beam source can be fabricated, to include a field emission source, focusing anodes, and deflection plates, resulting in a miniature electron beam source that is capable of good resolution and sensitivity, while being relatively inexpensive. Furthermore, the nature of the sapphire substrate allows these miniature beam sources to be made in large arrays. The crystal nature of the sapphire substrate is such that the substrate has either a random or regular array of open micron-size cavities. Each cavity might then contain a single field emission source, made in the manner explained above. By making use of the majority of the cavities in the substrate, a large array of electron beam sources may be packed into a relatively small area.

It is to be understood that the above described embodiment of the invention is merely illustrative of the principles thereof and that numerous modifications and embodiments of the invention may be derived within the spirit and scope thereof, and that the applicant is not limited to merely his preferred embodiment.

Claims

What is claimed is:

1. A miniature, directed electron beam source comprising:

an electrically conductive base;

a point source of electrons deposited on said base;

means for focusing said electrons, said focusing means including at least a first electrically insulative layer and at least a first anode, said at least first insulative layer being deposited on said base and said at least first anode being deposited on said insulative layer said focusing means being apertured to expose said electron source; and

means for deflecting said electrons, said deflecting means including an apertured electrically insulative layer and at least four deflecting plates, said insulative layer being deposited on said focusing means and to a depth of at least 20 microns, and said deflecting plates being deposited on said insulative layer abutting said aperture within said deflecting means each of said deflecting plates having a dimension along said aperture substantially equal to said depth.

2. An electron beam source in accordance with claim 1, wherein said focusing means includes first and second anodes, each anode having an aperture therein, said anodes being separated by a material which is inert with respect to said anodes.

3. An electron beam source in accordance with claim 2, wherein said source of electrons is a field emission source of electrons.

4. An electron beam source in accordance with claim 3, wherein said field emission source comprises:

a sapphire substrate;

a cathode layer of molybdenum deposited on said substrate;

a cathode cone of molybdenum deposited on said cathode layer; and

a first layer of alumina, deposited on said cathode layer, and having an aperture therein, and said first anode layer of molybdenum deposited on said first layer of alumina, said first anode layer having an aperture therein.

5. An electron beam source in accordance with claim 4, wherein said focusing means includes said first anode layer of molybdenum, said first anode deposited on said first layer of alumina, and having an aperture therein;

a second layer of alumina, deposited on said first anode and having an aperture therein; and

a second layer of molybdenum, deposited on said second layer of alumina and having an aperture therein.

6. An electron beam source in accordance with claim 5, wherein said deflecting means includes a third layer of alumina deposited on said second anode layer, said third layer of alumina having an aperture therein; and

four deflection plates, said deflection plates being deposited within said aperture of said third layer of alumina, said deflection plates being deposited at substantially equal angles to each other, and impinging only on said third layer of alumina.

7. An electron beam source in accordance with claim 6, wherein said third layer of alumina is at least 20 microns at its thickest point, and wherein said aperture in said first and second anode and said first, second and third alumina layers is not more than 4 microns in cross section.