US3803443A

US3803443A - Charged particle beam scanning device with electrostatic control

Info

Publication number: US3803443A
Application number: US00281925A
Authority: US
Inventors: W Hant
Original assignee: Northrop Grumman Corp
Current assignee: Northrop Grumman Corp; Northrop Grumman Systems Corp
Priority date: 1970-11-16
Filing date: 1972-08-18
Publication date: 1974-04-09
Anticipated expiration: 1991-04-09

Abstract

A plurality of control plates are sandwiched between a cathode and a target to control the flow of charged particles such as electrons and ions therebetween. Each control plate has a plurality of apertures formed therein which are effectively aligned with corresponding apertures on all the other control plates, such aligned apertures forming beam channels. The control plates further have paired conductive electrodes thereon arranged in predetermined coded finger patterns. Voltages are selectively applied to the control plate electrodes by means of switching circuitry to electrostatically focus the charged particles through the apertures associated with certain selected electrodes while simultaneously aborting the passage of charged particles through the apertures associated with the remaining electrodes. In this manner, by selective switching control of the control plates, a beam or plurality of beams can be directed to a selected portion or portions of the target at a time.

Description

Hant

CHARGED PARTICLE BEAM SCANNING DEVICE WITH ELECTROSTATIC 3,708,713 1/1973 McCann 315/12 Primary ExaminerBenjamin R. Padgett CONTROL [75] Inventor: William Hant, Los Angeles, Calif. Assistant Exammer p' Nelson [73] Assignee: Northrop Corporation, Los Angeles, 57] ABSTRACT Calif. A plurality of control plates are sandwiched between a [22] 1972 cathode and a target to control the flow of charged [21] Appl. No.: 281,925 particles such as electrons and ions therebetween'. Each control plate has a plurality of apertures formed Related Apphcauon Data therein which are effectively aligned with correspond- Cmfifluafiomimpa" of 895379. 16, ing apertures on all the other control plates, such 1970' abandmedaligned apertures forming beam channels. The control plates further have paired conductive electrodes [52] US. Cl 315/11, 315/12, 313/68, thereon arranged in predetermined coded finger pap 313/82 BF terns. Voltages are selectively applied to the control [5 [Ill- CI- plate electrodes means of Switching circuitry to [58] new of Search 315/11 13 313/68 electrostatically focus the charged particles through 313/82 95 the apertures associated with certain selected electrodes while simultaneously aborting the passage of [56] References C'ted charged particles through the apertures associated UNITED STATES PATENTS with the remaining electrodes. In this manner, by se- 3,182,221 5/1965 Poor, Jr. 315 12 x lective switching control of the control plate a beam 3,408,532 lO/I968 Hultberg et al 3l5/l2 or plurality of beams can be directed to a selected 3,612,944 10/1971 Requa et a1 1 315/12 portion or portions of the target at a time, 3.678330 7/1972 Landrum 315/12 X 3,683.230 8/1972 Bingham et al. 313/68 R 11 Claims, 3 Drawing Figures -73 .1. will 1- a2 a5 a4 85 a 86 8| Ill |m ADDRESSING 75 "I vs 77 78 79 LOGK;

a0 CONTROL 250 SIGNAL SOURCE,

CHARGED PARTICLE BEAM SCANNING DEVICE WITH ELECTROSTATIC CONTROL This application is a continuation in part of my application, Ser. No. 89,879 filed Nov. 16, 1970, and now abandoned.

This invention relates to a charged particle beam scanning device and more particularly to such a device utilizing electrostatic control which is capable of response to a digital control signal.

In US. Pat. No. 3,408,532, issued Oct. 29, 1968, to

Northrop Corporation, the assignee of the present application, an electron beam scanning device is described which utilizes flat dynode control plates sandwiched between a flat cathode and a flat target plate. In the device of US. Pat. No. 3,408,532, the dynode control plates have binary coded finger pattern electrodes which encompass apertured portions of the control plates, the apertures being aligned with each other to form electron beam channels between the cathode and target. In the device of this patent the dynode control plates perform both control and electron multiplication functions. As pointed out in this patent, this type of scanning device has distinct advantages over cathode ray tube scanning devices of the prior art, in view of its compact configuration, high linearity, and its capability of response to randomly addressed digital control signals.

The device of this invention is an improvement over the device described in the aforementioned patent, which provides several advantages thereover. First, while the combination of electron multiplication functions and control functions in the same control plate, thus providing dual utilization of such plates, enables the minimization of the number of such plates required for any particular application requirement, such dual utilization necessitates a design compromise between optimum design for the electron multiplication and the control functions. Thus, to obtain electron multiplication it is necessary to place successively higher voltages on the control plate-dynode members as we proceed from the cathode to the target. This imposes demands on the power supply as well as presenting voltage insulation problems between the electrodes, particularly when considering the close spacing involved in a compact configuration of the type to be desired. Further, in the implementation of the dynodes, resistive coatings are utilized in the holes between the electrodes on the opposite surfaces of each dynode-control plate, which provides a continuous strip current with its resultant power dissipation. Further, an undesirable distortion in the target display in the form of a dark line effect is directly attributable to the resistive coatings in the channels and the transverse capacitive coupling between cut-off and conducting channels. Finally, it has been found to be somewhat costly to fabricate control plates which also have secondary emissive properties.

The device of this invention provides an improvement for certain applications over the'electron beam scanning device of the aforementioned patent. It is to be noted, however, that in view of the fact that in the device of the present invention additional plates may be required for electron multiplication, especially where high electron currents are required, the device of the aforementioned patent combining the dynode and control functions in the same plates may have advantages in certain situations.

In the device of the present invention, the control functions are handled in separate control plates which achieve no electron multiplication. The beam is channeled through the control plates by electrostatic focusing from control plate to control plate, the focusing voltages applied between successive plates being relatively low and not increasing appreciably for successive pairs of plates. Cut-off is achieved with a cut-off potential which is close to the potential of the electron source so that all of the potentials necessary for the control functions are relatively low. Further, there is no resistive coating between electrodes on opposite sides of the control plates, and hence no dissipative strip current to contend with, or the dark line effect encountered in the prior art device mentioned above. For applications where moderately high beam currents are required, separate electron multiplier units may be provided, but these units can be designed solely for optimum beam multiplication and need not be designed for beam control functions, thus facilitating their design for the single intended purpose. It is to be noted that the device of this invention can be utilized to control not only electrons but other charged particles such as positive or negative ions.

It is therefore the principal object of this invention to provide an electron beam scanner of compact flat proportions which can be electrostatically controlled in response to relatively low voltage digital control signals, has excellent cut-off characteristics and in which power dissipation is minimized.

Other objects of this invention will become apparent as the description proceeds in connection with the accompanying drawings, of which:

FIG. 1 is a schematic drawing of one embodiment of the device of the invention,

FIG. 2 is a cross-sectional view illustrating the construction of the embodiment of FIG. 1, and

FIG. 3 is a cross-sectional view showing details of the structure of the electron beam channels of the embodiment of FIGS. 1 and 2.

Briefly described, the device of the invention comprises an area charged particle source,'such as an electron source, and a flat plate target, between which are sandwiched a plurality of control plates for controlling the flow of electrons between the electron source and the target. Each of the control plates has a plurality of apertures formed therein, corresponding apertures of successive plates being aligned with each other to form electron beam channels between the electron source and the target. Each of the control plates further has a pair of electrodes on each of the opposite broad surfaces thereof, such electrodes being arranged in a predetermined binary coded finger pattern which varies from control plate to control plate. Switching control circuit means which operates in response to addressing logic is connected to each of the paired electrodes of the control plates, selected electrodes receiving a voltage such as to focus electrons passing through the apertures thereof, while the remaining electrodes are simultaneously receiving a potential such as to abort the passage of electrons through the apertures associated therewith. In this manner, the electron beam can selectively be addressed to any scanning element or elements of the target in response to digital control signals. The device may also include an electron beam multiplier interposed in the electron path to multiply the electron beam as well as a modulation control plate for effecting a modulation of the intensity of the beam.

Referring now to FlGS. 2 and 3, cross-sectional views illustrating the structure of one embodiment of the device of the invention are shown. It is to be noted that for illustrative purposes, an 8 X 8 display is shown, but that in most practical implementations, a much greater number of channels would be utilized to provide a much higher definition display. A vacuum tight casing is formed by means of side frame member 11, ceramic plate 12, and glass front viewing plate 14. The casing so formed is evacuated so as to provide a vacuum environment for the components contained therein.

Cathode 16, which as shown in FIG. 1 is in the form of a flat plate, is supported along opposite edges thereof on bar members 18, the top surface 16a of this plate having a radioactive coating thereon such as of tritium foil to provide an area source of electrons. It is to be noted that other area electron sources, such as those of the thermionic type as described, for example, in copending application, Ser. No. 83,909 filed Oct. 26, 1970 and assigned to Northrop Corporation, could be utilized. Mounted directly opposite cathode 16 is e1ectron lens plate 20, which is formed from a flat dielectric substrate 20a having overall

metallic coatings

20b and 20c deposited on the opposite broad surfaces thereof and conductive coatings 20a on the walls of the apertures between the surfaces, coatings 20d electrically interconnecting

coatings

20b and 200. Electron lens plate 20 is separated from cathode 16 by means of insulator bars 23.

Next in the stack are control plates -30, which are insulatively separated from each other by means of insulator plates 33 which may be of a ceramic material. Plate 25 is separated from lens plate 20 by means of insulator spacer bars 35. As can best be seen in FIG. 2, the control plates are formed of a dielectric substrate 40 which may be of a material such as ceramic or glass, having

similar electrodes

43 and 44 of a highly conductive material such as gold or copper deposited on the opposite surfaces thereof. The electrodes are arranged in predetermined finger patterns, as illustrated in FIG. 1, with the

opposite electrodes

43 and 44 of each control plate having the same finger patterns arranged opposite each other in mirror image relationship.

Electrodes

43 and 44 are electrically interconnected by means of coatings 46 which are deposited on the walls of the apertures extending between the opposite sides of the plates.

Mounted above control plate and separated therefrom by an insulator plate 33 is modulator plate 50. Modulator plate 50 is similar in general construction to the control plates in that it includes

electrodes

50a and 50b of a highly conductive material such as gold or copper on the opposite surfaces thereof, which are interconnected by conductive portions 50c deposited on the walls of the apertures of the plates, the conductive layers 50a-50c being deposited on dielectric substrate 50d. Modulator plate 50, however, differs from the control plates in that the

electrodes

50a and 50b are not arranged in a finger pattern but are rather deposited over the entire surface areas of the plate. Also, in the modulator plate, as can be noted in the drawing, the length of the apertures is substantially greater than that of the control plate, the choice of length to diameter ratio being designed to provide less abrupt cut-off characteristics to facilitate the handling of a modulation signal.

All of the various plates just described have a plurality of apertures 60 formed therein, corresponding apertures of successive plates being aligned with each other to form electron beam channels between cathode 16 and phosphor target 14.

It is to be noted that electron lens plate 20 and modulator plate 50 are not essential for the basic operation of the device, and an electron beam can be addressed to the target from the cathode in response to digital control signals without these particular plates. However, each one affords a special function which may be needed for a particular application requirement. Thus, the modulator plate 50 enables the intensity modulation of the beam where this may be called for, while the electron lens plate provides for increased input current which will contribute to higher intensity of the display.

Referring now to FIG. 1, the device of the invention is schematically illustrated. Each of control plates 25-30 has a pair of electrodes 25a,

25b

30a, 30b, on each of the opposite surfaces thereof. Thus, the electrodes on the opposite surfaces which are not shown are mirror images of the electrodes which are shown in the Figure. The electrodes are of a highly conductive material such as gold or copper, and each electrode 25a-30a is electrically insulated from its paired electrode 25b-30b respectively. As already explained in connection with FIGS. 2 and 3, the electrodes on opposite surfaces are electrically interconnected with each other by means of conductive coatings which may be of the same material as the electrodes on the walls of the apertures extending therebetween.

Binary digital control signals are fed from control signal source to addressing logic 71 which provides an appropriate control signal to each of switching circuits 75-80. Switching circuits 75-80 may be electronic switching circuits such as flipflops, capable of alternatively connecting the voltages fed thereto to either one or the other of the paired electrodes of the particular control plate associated therewith in response to the addressing logic. Voltages are applied to switching circuits 75-80 for use in controlling the electrodes from power sources 83-88 respectively. A beam accelerating voltage is applied between cathode l6 and target 14 from voltage source 73. Switching circuits 75-80 receive first voltages V -V from power sources 83-88 respectively, which are positive voltage with respect to ground, and a second voltage, V which is a negative voltage with respect to ground.

The switching circuits in response to addressing logic 71 alternatively connect V i-V as the case may be, to one of the paired electrodes of each control plate, and V, to the other paired electrode. For illustrative purposes, all of the electrodes receiving the voltage V are shown stippled, while those receiving V -V, are shown without stippling. Under such conditions a beam of electrons as indicated by line 89 will pass through only a single channel formed by the plate apertures, the flow of electrons being blocked through all other channels by virtue of the effect of a cut-off voltage V,, appearing somewhere in each of these other channels.

Thus, by selective switching control of plates 25-30, the electron beam can be controlled so that it excites a single elemental portion of target 14 at a time in the same general manner as described in connection with the aforementioned U.S. Pat. No. 3,408,532. In this instance, however, the control is effected by virtue of the electrostatic focusing, achieved by means of the electron lenses formed between electrode portions of successive plates having the potentials V -V applied thereto. The channels associated with the electrodes having the voltage V applied thereto are cut off, the electrons being repelled in these channels and drawn off by the electrodes.

Lens plate 20, which is utilized to increase the current, is generally similar in construction to control plates 25-30 and has overall

conductive coatings

20b and 20c on the opposite sides thereof, these coatings being electrically connected to each other by conductive coatings 20d in the aperture walls (see FIG. 3). Voltage V, is applied to the conductive coatings 20b-20d. Modulation plate 50 may be used to intensity modulate the signal in response to a modulation signal source 90. Modulation plate 50 is generally similar in construction to control plates 25-30, having similar electrodes on each of the opposite broad surfaces thereof, with conductive coatings on the walls of aperture 60 electrically interconnecting said surfaces. Modulation plate 50, however, is generally designed with a substantially greater thickness so that it has longer apertures than the control plates so as to provide less abrupt cut-off characteristics to suitably accommodate modulation signals having a reasonable dynamic range.

It is to be noted that while the device of the invention has been described in connection with the control of an electron beam, it can be utilized to equal advantage in the control of beams formed from other types of charged particles such as positive or negative ions.

Referring now additionally to FIG. 2, the various voltages and dimensional parameters utilized in the device of the invention will now be considered. In considering the spacing g, between control plates, it is to be noted that with a larger spacing the voltage required for cut-off decreases, as well as the possibility of voltage breakdown between conducting and cut-off plates. Greater spacing, however, increases the possibility of electrons being intercepted on the cylindrical hole surfaces of the dielectric spacers and the length over which the electron beams must be focused. Insulator plates 33 have greater aperture diameters than the control plates and thus have the walls of their apertures set back from the electron channels, formed by the control plate apertures. This avoids a build up of electron charge on the walls of the insulator plate apertures which would impair electron flow through the channels. While there is considerable latitude in choosing parameters, a particular design which provides satisfactory operation, has g and 6 equal to 6.5 mils, and a equal to 17 mils. With this design, V =20v; V 25v; V =83v; V =l4v; V =59v; V =4Ov; V =lOOv; V =16Ov and V,,=l0,000v.

Optimum focusing voltages are best determined experimentally for each design. It would appear from a theoretical point of view that the electron beams could best be focused by means of periodic electrostatic fields, as described, for example, by P. K. Tien in the Journal of Applied Physics, Volume 25, No. 10 (Oct.,

1954 However, in practice, often this does not appear to be the case. This may be due to the fact that each electron channel is a separate lens structure which has different aperture parameters and thus different optimum focusing potentials. With the application of common focusing potentials to a plurality of channels as in the present case, the overall best results are thus achieved with voltages that appear to be difficult to predict theoretically and can best be determined experimentally. It has been noted, that in most designs, the focusing potentials between at least one successive pair of control plates increases in value while that between another successive pair decreases in value. It also is to be noted that in the illustrative example, the potentials between successive pairs of plates successively increase and decrease except in the case of the two plates closest to the target, both of which increase.

The cut-off voltage, V should be chosen so as to bring the voltage at the center of the channels formed by the apertures to slightly below cathode potential. In view of the fact that this potential is applied to the sides of the apertures, it therefore must be slightly negative in order to make for such a potential at the centers of the channels.

It should be apparent that the device of the invention can be implemented with a plurality of beams to provide a plurality of simultaneous displays by eliminating one or more of the control plates shown in FIG. 1. In such event, the modulator plate would be designed to have several sections, one for each beam.

Thus, it can be seen that with the device of this invention, by virtue of electrostatic control the electron beam can selectively be focused through a single channel of the scanner at a time, the beam being aborted in all other channels in response to a digital control signal. The control voltages needed for such electrostatic control are relatively low as compared with similar devices of the prior art. Further, highly effective channel cut-off can be achieved with a cut-off potential near ground.

I claim:

1. In a charged particle beam scanning device,

an area source of charged particles,

an area target,

a plurality of control plates sandwiched between said source and said target for controlling the flow of charged particles therebetween, each of said control plates having a plurality of apertures formed therein, corresponding apertures of said control plates being aligned to form charged particle beam channels between the source and the target, said control plates further each having electrodes on each of the opposite broad surfaces thereof, the electrodes on one of each of said broad surfaces being a mirror image of the electrodes on the opposite surface thereof, the electrodes on each of said surfaces being electrically insulated from each other, and conductive means in said apertures for interconnecting oppositely positioned corresponding mirror image electrodes,

means for providing potentials to at least one of the electrodes of each of the electrodes of said control control plates respectively to focus said charged particles through selected control plate apertures, and

means for providing a cut-off potential to the remaining electrodes of the control plates,

whereby a beam of charged particles is focused by said focusing potentials through the channels formed by said selected apertures.

2. The device of claim 1 wherein said control plates comprise a dielectric substrate, said electrodes being deposited on said substrate.

3. The device of claim 1 wherein said electrodes are arranged in a binary coded finger pattern.

4. The device of claim 2 and further including dielectric separator plates interposed between said control plates, said separator plates having apertures formed therein corresponding to the apertures of said control plates, the apertures of said separator plates being wider than those of said control plates such that the walls of said separator plate apertures are set back from the channels formed by the control plates so as to avoid build-up of charge thereon.

5. The device of claim 3 and further including a modulator plate interposed between the control plates and the target and means for applying a modulation signal to said modulator plate.

6. The device of claim 1 wherein said means for providing potentials to focus the charged particles comprises means for providing accelerating potentials with respect to said area source to said one of the control plate electrodes of successive pairs of control plates to cause the passage of said charged particles through the selected control plate apertures, the accelerating potentials decreasing in value between at least one successive pair of control plates and increasing in value between at least another successive pair of control plates.

7. In a charged particle beam scanning device,

an area source of charged particles,

an area target,

a plurality of control plates sandwiched between said source and said target for controlling the flow of charged particles therebetween, each of said control plates having a plurality of apertures formed therein, corresponding apertures of said control plates being aligned to form charged particle beam channels between the source and the target, said control plates further each having a plurality of electrodes on at least one of the broad surfaces thereof, the electrodes on each of said surfaces being electrically insulated from each other,

means for providing focusing potentials to at least one of the electrodes of successive pairs of control plates respectively to focus said charged particles through selected control plate apertures, and

means for providing a cut-off potential to the remaining selected electrodes of the control plates,

8. The device of claim 7 wherein said electrodes are arranged in a binary coded finger pattern.

9. The device of claim 7 wherein said control plates comprise a dielectric substrate, said electrodes being deposited on said substrate.

10. The device of claim 7 and further including dielectric separation plates interposed between said control plates, said separator plates having apertures therein corresponding to the control plate apertures, the apertures of said separator plates being wider than those of said control plates such that the walls of said separator plate apertures are set back from the channels formed by the control plates so as to avoid build up of charge thereon.

1 l. The device of claim 7 wherein the means for providing focusing potentials comprises means for providing accelerating potentials with respect to the area source to said one of the control plate electrodes of successive pairs of control plates to cause the passage of said charged particles through the selected control plate apertures, the accelerating potentials decreasing in value between at least one successive pair of control plates and increasing in value between at least another successive pair of control plates.

Claims

1. In a charged particle beam scanning device, an area source of charged particles, an area target, a plurality of control plates sandwiched between said source and said target for controlling the flow of charged particles therebetween, each of said control plates having a plurality of apertures formed therein, corresponding apertures of said control plates being aligned to form charged particle beam channels between the source and the target, said control plates further each having electrodes on each of the opposite broad surfaces thereof, the electrodes on one of each of said broad surfaces being a mirror image of the electrodes on the opposite surface thereof, the electrodes on each of said surfaces being electrically insulated from each other, and conductive means in said apertures for interconnecting oppositely positioned corresponding mirror image electrodes, means for providing potentials to at least one of the electrodes of each of the electrodes of said control control plates respectively to focus said charged particles through selected control plate apertures, and means for providing a cut-off potential to the remaining electrodes of the control plates, whereby a beam of charged particles is focused by said focusing potentials through the channels formed by said selected apertures.

6. The device of claim 1 wherein said means for providing potentials to focus the charged particles comprises means for providing accelerating potentials with respect to said area source to said one of the control plate electrodes Pg,16 of successive pairs of control plates to cause the passage of said charged particles through the selected control plate apertures, the accelerating potentials decreasing in value between at least one successive pair of control plates and increasing in value between at least another successive pair of control plates.

7. In a charged particle beam scanning device, an area source of charged particles, an area target, a plurality of control plates sandwiched between said source and said target for controlling the flow of charged particles therebetween, each of said control plates having a plurality of apertures formed therein, corresponding apertures of said control plates being aligned to form charged particle beam channels between the source and the target, said control plates further each having a plurality of electrodes on at least one of the broad surfaces thereof, the electrodes on each of said surfaces being electrically insulated from each other, means for providing focusing potentials to at least one of the electrodes of successive pairs of control plates respectively to focus said charged particles through selected control plate apertures, and means for providing a cut-off potential to the remaining selected electrodes of the control plates, whereby a beam of charged particles is focused by said focusing potentials through the channels formed by said selected apertures.

11. The device of claim 7 wherein the means for providing focusing potentials comprises means for providing accelerating potentials with respect to the area source to said one of the control plate electrodes of successive pairs of control plates to cause the passage of said charged particles through the selected control plate apertures, the accelerating potentials decreasing in value between at least one successive pair of control plates and increasing in value between at least another successive pair of control plates.