CA1041220A - Field emitting device and method of making same - Google Patents
Field emitting device and method of making sameInfo
- Publication number
- CA1041220A CA1041220A CA233,569A CA233569A CA1041220A CA 1041220 A CA1041220 A CA 1041220A CA 233569 A CA233569 A CA 233569A CA 1041220 A CA1041220 A CA 1041220A
- Authority
- CA
- Canada
- Prior art keywords
- field emitting
- emitting element
- emitting device
- pointed tip
- field
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
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Classifications
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
- H01J29/00—Details of cathode-ray tubes or of electron-beam tubes of the types covered by group H01J31/00
- H01J29/46—Arrangements of electrodes and associated parts for generating or controlling the ray or beam, e.g. electron-optical arrangement
- H01J29/52—Arrangements for controlling intensity of ray or beam, e.g. for modulation
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
- H01J1/00—Details of electrodes, of magnetic control means, of screens, or of the mounting or spacing thereof, common to two or more basic types of discharge tubes or lamps
- H01J1/02—Main electrodes
- H01J1/30—Cold cathodes, e.g. field-emissive cathode
- H01J1/304—Field-emissive cathodes
- H01J1/3042—Field-emissive cathodes microengineered, e.g. Spindt-type
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
- H01J3/00—Details of electron-optical or ion-optical arrangements or of ion traps common to two or more basic types of discharge tubes or lamps
- H01J3/02—Electron guns
- H01J3/021—Electron guns using a field emission, photo emission, or secondary emission electron source
- H01J3/022—Electron guns using a field emission, photo emission, or secondary emission electron source with microengineered cathode, e.g. Spindt-type
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
- H01J63/00—Cathode-ray or electron-stream lamps
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
- H01J9/00—Apparatus or processes specially adapted for the manufacture, installation, removal, maintenance of electric discharge tubes, discharge lamps, or parts thereof; Recovery of material from discharge tubes or lamps
- H01J9/02—Manufacture of electrodes or electrode systems
- H01J9/022—Manufacture of electrodes or electrode systems of cold cathodes
- H01J9/025—Manufacture of electrodes or electrode systems of cold cathodes of field emission cathodes
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
- H01J2893/00—Discharge tubes and lamps
- H01J2893/0031—Tubes with material luminescing under electron bombardment
Landscapes
- Engineering & Computer Science (AREA)
- Manufacturing & Machinery (AREA)
- Cathode-Ray Tubes And Fluorescent Screens For Display (AREA)
- Cold Cathode And The Manufacture (AREA)
- Electrodes For Cathode-Ray Tubes (AREA)
- Electron Sources, Ion Sources (AREA)
Abstract
A FIELD EMITTING DEVICE AND METHOD OF MAKING SAME
Abstract of the Disclosure A field emitting device includes at least one pyramidal shaped field emitting element on a surface of an electrically conductive substrate. The element has a pointed tip on which only is disposed at least one needle-like projection. In one embodiment, an electron extracting electrode is mounted in parallel spaced relation to, and electrically insulated from, the substrate surface. The electron extracting electrode has at least one aperture therein, the aperture being positioned substantially coaxially with a corresponding pyramidal shaped field emitting element.
Abstract of the Disclosure A field emitting device includes at least one pyramidal shaped field emitting element on a surface of an electrically conductive substrate. The element has a pointed tip on which only is disposed at least one needle-like projection. In one embodiment, an electron extracting electrode is mounted in parallel spaced relation to, and electrically insulated from, the substrate surface. The electron extracting electrode has at least one aperture therein, the aperture being positioned substantially coaxially with a corresponding pyramidal shaped field emitting element.
Description
- _ R~A 68,018 O
1 This invention relates to field emitting devices, particularly non-thermionic field emitting devices, and methods of making the same.
Non-thermionic field emitting devices, wherein electron emission is stimulated by an electric potential applied near a pointed cathode, are well known. Prior art sharply pointed field emitting devices can be broadly categorized by the type of material used in fabrication.
One such category is based upon the use o semiconductor material, e.g., silicon or germanium, particularly for photodetectors; however, such use as large area cold cathode sources is severly limited. The physical properties and costs alone of the single crystal semiconductor materials limit the size of the arrays. Thus, in "Fabrication and Some Applications of Large-Area Silicon Field Fmission Arrays", Solid State Electronics, 1974, Vol. 17, pages 155-163, Thomas et al. consider large-area arrays to be on the order of only 10 cm2. In addition to ; being size limited, the current densities obtainable from semiconductor field emitters are less than those obtainable from metals.
Another category of devices encompasses the use of sharply pointed metallic field emitters, such as that disclosed in United States Patent No. 3,755,704 issued 28 August 1973 to Spindt et al. These devices, which utilize individual needle-like protuberances deposited on an electrode, suffer from two major disadvantages. First, the deposition procedure used to form the protuberances limits the area over which uniform arrays can be formed.
z ~ /\ 6~,()18 1(~41'~
1 This procedure includes projecting ~ source of emitter material essentially normal to a given surface while directin~ a source of masking material at the same surface, but at a shallow grazing angle--a critical operation which does not lend itself to forming very large quantities of emitter elements over very large surfaces. Second, the fabrication process entails the use of thin film techniques which produce relati~ely delicate structures that are sensitive to strong electrical forces characteristic of ~ield emission. Also, the relative thinness of the insulators used in the prior art devices, ~ypically on the order of l micron, causes manufacturing Prohlems since a single pin hole in the insulation can ruin an entire field emitter array.
In accordance with the invention, a non-thermionic field emitting device comprises an electrically conductive substrate having at least one field emitting element on a surface thereof. The field emitting element has a ; pointed tip, with at least one needle-like projection disposed thereon, which projects away from the substrate.
In the drawings:
FIGURE l is an isometric view of one emhodiment of the novel field emitting device;
FIGURE 2 is a sectional view taken along line
1 This invention relates to field emitting devices, particularly non-thermionic field emitting devices, and methods of making the same.
Non-thermionic field emitting devices, wherein electron emission is stimulated by an electric potential applied near a pointed cathode, are well known. Prior art sharply pointed field emitting devices can be broadly categorized by the type of material used in fabrication.
One such category is based upon the use o semiconductor material, e.g., silicon or germanium, particularly for photodetectors; however, such use as large area cold cathode sources is severly limited. The physical properties and costs alone of the single crystal semiconductor materials limit the size of the arrays. Thus, in "Fabrication and Some Applications of Large-Area Silicon Field Fmission Arrays", Solid State Electronics, 1974, Vol. 17, pages 155-163, Thomas et al. consider large-area arrays to be on the order of only 10 cm2. In addition to ; being size limited, the current densities obtainable from semiconductor field emitters are less than those obtainable from metals.
Another category of devices encompasses the use of sharply pointed metallic field emitters, such as that disclosed in United States Patent No. 3,755,704 issued 28 August 1973 to Spindt et al. These devices, which utilize individual needle-like protuberances deposited on an electrode, suffer from two major disadvantages. First, the deposition procedure used to form the protuberances limits the area over which uniform arrays can be formed.
z ~ /\ 6~,()18 1(~41'~
1 This procedure includes projecting ~ source of emitter material essentially normal to a given surface while directin~ a source of masking material at the same surface, but at a shallow grazing angle--a critical operation which does not lend itself to forming very large quantities of emitter elements over very large surfaces. Second, the fabrication process entails the use of thin film techniques which produce relati~ely delicate structures that are sensitive to strong electrical forces characteristic of ~ield emission. Also, the relative thinness of the insulators used in the prior art devices, ~ypically on the order of l micron, causes manufacturing Prohlems since a single pin hole in the insulation can ruin an entire field emitter array.
In accordance with the invention, a non-thermionic field emitting device comprises an electrically conductive substrate having at least one field emitting element on a surface thereof. The field emitting element has a ; pointed tip, with at least one needle-like projection disposed thereon, which projects away from the substrate.
In the drawings:
FIGURE l is an isometric view of one emhodiment of the novel field emitting device;
FIGURE 2 is a sectional view taken along line
2-2 of FIGIlRE l;
FIGURES 3, 4, 5 and 6 are sectional views showing steps of a novel method of making the field emitting device of FIGURE l;
FIGURE 7 is a portion of an enlarged plan view of a sheet employed in the novel method;
--~ R~A 68,018 1~41'~0 1 FIGURES 8~ 9, 10, 11 and 12 are sectional views showing further steps of the novel method;
FIGURE 13 is a cross section of a novel display device incorporating the device of FIGURE l;
FIGURE 14 is an electrical schematic diagram of the device depicted in FIGURE 13;
FIGURES 15 and 16 are potential energy diagrams depicting the relative potential energies of electrons at d~fferent locations within the device depicted in FIGURE 13;
FI~ E 17 is another electrical schematic diagram of the device depicted in FIGURE 13; and FI~URE 18 is another potential energy diagram depicting the relative potential energies of electrons at diferent locations within the device shown in FIGURE 13.
Referrring initially to FIGURES 1 and 2, an embodiment of a non-thermionic field emitting device according to the present invention is generally designatèd as 10. The field emitting device 10 comprises a substrate .: .
12 o an electrically conductive material, such as copper, 2!C having a matrix array of field emitting elements 14 on one surface thereof. Each field emitting element 14 comprises ;~ a conically or a pyramidally shaped field emitter 16, with - at least one needle-like projection or "tiplet" 18 located on the tip thereof. The field emitter 16 and the tiplets 18 are composed of a material having good field emission characteristics 9 such as copper. A layer of insulating material 20, such as glass, is bonded to the surface of the substrate having the field emitting elements 14 thereon.
The insulating layer 20 has an array of apertures 21
FIGURES 3, 4, 5 and 6 are sectional views showing steps of a novel method of making the field emitting device of FIGURE l;
FIGURE 7 is a portion of an enlarged plan view of a sheet employed in the novel method;
--~ R~A 68,018 1~41'~0 1 FIGURES 8~ 9, 10, 11 and 12 are sectional views showing further steps of the novel method;
FIGURE 13 is a cross section of a novel display device incorporating the device of FIGURE l;
FIGURE 14 is an electrical schematic diagram of the device depicted in FIGURE 13;
FIGURES 15 and 16 are potential energy diagrams depicting the relative potential energies of electrons at d~fferent locations within the device depicted in FIGURE 13;
FI~ E 17 is another electrical schematic diagram of the device depicted in FIGURE 13; and FI~URE 18 is another potential energy diagram depicting the relative potential energies of electrons at diferent locations within the device shown in FIGURE 13.
Referrring initially to FIGURES 1 and 2, an embodiment of a non-thermionic field emitting device according to the present invention is generally designatèd as 10. The field emitting device 10 comprises a substrate .: .
12 o an electrically conductive material, such as copper, 2!C having a matrix array of field emitting elements 14 on one surface thereof. Each field emitting element 14 comprises ;~ a conically or a pyramidally shaped field emitter 16, with - at least one needle-like projection or "tiplet" 18 located on the tip thereof. The field emitter 16 and the tiplets 18 are composed of a material having good field emission characteristics 9 such as copper. A layer of insulating material 20, such as glass, is bonded to the surface of the substrate having the field emitting elements 14 thereon.
The insulating layer 20 has an array of apertures 21
3 therethrou~h which are positioned such that the layer covers
-4-R~A 68,018 J4~20 l the surface of the suhstrate while leaving the field emitting elements 14 exposed through the apertures 21.
An electron extracting elec~rode 22, of an electrically conductive material such as a beryllium copper alloy, is bonded to the insula~ing layer 2n. The electron extracting electrode 22 has a plurality o apertures 24 therein, the number of aPertures corresponding to the number of field emitting elements 14 in the matrix array. The apertures 24 are positioned such that each aperture is aligned substantially coaxially with a correspondin~ field emitting element 14.
To obtain the desired emission of electrons from the field emitting elements 14, the positive terminal of a voltage source 26 is connected to the electron extracting elèctrode 22 and the negati~e terminal is connected to the array of field emitting elements 14 through the substrate 12. Electrons, which are emitted from the tiplets 18 under the influence of the applied voltage, pass through the apertures 24 toward a suitable anode electrode, such as a phosphor coated screen ~not shown).
In accordance with the invention, the device 10 c~ould comprise a single field emitting element 14 having an electron extracting electrode 22 with a single aperture therein, to generate a single stream of electrons, instead of the shown large array of field emitting elements and electron extracting elactrodes generating a large number of individually addressable electron streams.
To make the field emitting device 10, one surface of a substrate 12 of an electrically conductive material, such as copper, is made substantially clean, flat and free . ,:
RCA 68,018 l from blemish. Then, as shown in FIGUR~ 3, a layer 28 of photosensitive etch-resistant, i.e., ~hotoresist, material is applied to the prepared surface and exposed to a light source through a transparency having an array of black dots. The unexposes area of the photoresist layer 28 is nex~ washed away, leaving an array of holes 30. The surface of the substrate is then under etched through the holes 30, leaving an array o interconnected hemispherical valleys 32 shown in FIGURB 4. It is to be noted that, l although the previous steps use a negative photoresist material an~ transparency, they cou:ld be equally well carried out using a positive photoresist material and transparency.
Next, referring to FIGURE 5, the photoresist layer 28 is stripped off, leaving an array of mesa-like ~ structures 34. The copper substrate 12 is then oxidized, ;~ by any well-known method such as heating in airJ ~forming a layer of copper oxide 36 havin~ a thickness of ~pproximately 2 mils. As shown in FIGURE 6, the valleys 32 àre then partially filled with a layer 38 of an electrically insulating ma~erial, such as glass. Onemethod of filling the valleys with glass is to place a sheet of glass approximately 3 mils thick across the tops o~ the mesa-like structures 34 in a ~acuum oven. A vacuum is drawn, and the glass is heated until it hecomes semi-molten and settles down into the valleys 32, leaving only a thin layer of glass 40 covering the tops of the mesa-like structures 34. The vacuum substantially eliminates any air which may be trapped between the glass layer and the valleys 32.
R~A 68,018 ,.~
~ '2 ~
1 llsing stan~ard pho~o etching techniques, a pattern of holes 42, as shown in FIGURE 7, is etche~ into a sheet 44 of conductive material, such as a beryllium copper alloy. The pattern is such that, when the copper alloy sheet 44 is placed on the etched surface of the copper substrate 12, the holes 42 will be ali~ned with and surround the mesa-like structures 34. After the glass has settled into the valleys 3Z, it is slowly cooled to substan*ially room temperature. The copper alloy sheet 44 is then positioned on the etched sùrface o the copper substrate 12, so that the mesa-li~e structures 34 protrude through the holes 42 while the remainder o~ the co~ner alloy sheet 44 is mounted on the glass insulating material 38 (see FI~URE 8). The resulting structure is heated to bond `~
~he copper alloy to the ~lass insulating material 38, and ; then removed from the oven and allowed to cool to substantially room temperature. Next, the thin layer o glass 40 which co~ers the mesa-like structures 34 is removed to expose the copper oxide 36. The copper oxide is then etched away to form pyramidally shaped field~emitters `16, as shown in FIGURE 9. These emitters 16 typically have artip diameter on the order of approximately 5 mic~ons.
Next, a porous layer 46 o a material which does not form an appreciable oxide layer, such as chromium, gold or rhodium, is deposited on the~ tips of the field emitters 16, as shown in FIGURE 10. Preferably, layer 46 is deposited by electroplatin~ chromium on the tips of the ~ield emitters using known porous plating techniques, as described for example by A.H. Sully in "Chromium", Butterworthsg London (1954), Chapter 5. The chromium layer 46 has pores or :
RG~ 68,018 ~ ~ 1 2'~0 l cracks 47 therethrough which are typically 1 micron apart.
The field emitters 16, with the porous layer 46 deposited on the tips thereof, are then heated in air to oxidize those surfaces of the field emitters which are exposed beneath the pores or cracks 47. The oxidation forms sharp points of copper oxide-covered copper beneath the solid ~ortions of the porous layer 46, as indicated ~y the dotted line 48 in PIGURE 11. After cooling to approximately room temperature, the oxide is chemically stripped from the tips of the field emitters 16, causing the porous layer 46 to fall of and leave an array of exposed tiplets 18 as shown in FIGURE 12.
To describe the operation of the novel device 10, reference is made to PIGURES 13 through 18. FIGURE 13 shows a single electron beam display ~evice generally deslgnated as 49, which includes a non-thermionic ield emitting device 10 having a single field emitting element 14 and an electron extracting electrode 22 with a single aperture 24 therein. Also included in the display device 49 is an electron target, here a phosphor coated display screen, 50 and a screen electrode 52 having a mesh-like structure formed by a multiplicity of finely spaced apertures 54. The components of the display device 49 are joined together to form an airtight cavity 55 which is evacuated to provide a vacuum environment between the field emitting element 14 and the display screen 50.
FIGURE 14 is a schematic representation of the single emitter display device 49 connected for basic operation. The positive terminal of a voltage source 26 is ~ 2~ RCA 68,018 1 connected to the electron extracting electrode 22, and the negative terminal thereof is connected to ground. Voltage source 26 is on the order of 100 volts dc. The positive terminal of a first bias voltage source 56 is connected to a switch 58, and the negative terminal thereof is con-nected to ground. The negative terminal of a second bias voltage source 60 is connected to the switch 58, and the positive terminal thereof is connected to ground. First and second bias voltage sources 56 and 60, respectively, are typically 5 volts dc each. The positive terminal of a high voltage source 62 is connected to the phosphor coated screen 50, and the negative terminal thereof is connected to ground. High voltage source 62 is on the order of 20,000 ;~
volts dc.
15FIGU~ES 15 and 16 are potential energy diagrams depicting the relative potential energies of electrons at different locations within the device 49 when the voltages applied to the electron extracting electrode 22 and the phosphor coated screen 50 are 100 volts and 20,000 volts, respectively. Point 64 represents the potential energy ` o~ electrons at the tiplets 18, point 66 is the potential energy of electrons at the electron extracting electrode 22, point 68 is the potential energy of electrons at the screen electrode 52, and point 70 is the potential energy of electrons at the phosphor coated screen 50. FIGURE 15 corresponds to position a of switch 58 in FIGURE 14, wherein the voltage on the field emitting element 14 is +5 volts and the voltage on the screen electrode 52 is -5 volts.
Since the potential energy of electrons at the screen electrode 52 (point 68) is higher than the potential energy of electrons at the field emitting element 14 (point 64), RCA f)8,018 ~ 4 ~
l electrons which have heen extracted from the field emitting element will face a potential energy barrier and not be able to transit the screen electrode toward the phosphor coated screen 50.
When the switch 58 of FIGURE 14 is placed in position b, the voltages on the field emittin~ element 14 and the screen electrode 52 are reversed, produclng the electron potential energy diagram of FI~URE 16. Since the potential energy of electrons at the field emitting element 14 ~point 64) is now higher than the potential energy of electrons at the screen electrode 52 (point 68) the potential energy barrier is eliminated and electrons which have been extracted from the field emitting element will pass through the screen electrode and strike the phosphor coated screen 50 to produce light.
;
In FIGUR~ 17, C represents the capacitance between the screen electrode 52 and the field emitting element 14. A pulse-type si~nal having a positive voltage with respect to the field emitting element is applied to the screen electrode, causing the capacitance C to cha~ge up to an appropriate voltage. After the capacitance chargin~, the potential energy of electrons at the scre~en electrode, indicated by point 68 ~a) in FIGIJRF. 18, is less than that at the field emitting element 14, indicated by point 64 and reference line 74 in the same figure. When a signal of, e.g.j 100 volts dc is applied to the electron - extracting electrode 22, some of the electrons emanating from the field emitting element 14 will transit the screen electrode 52 and strike the phosphor coated screen 50, while others will strike the screen electrode and R~A 68,018 ~ 2 ~
1 cause the voltage stored on the canacitance C to be reduced. As more electrons strike the screen electrode, the voltage on the capacitance C will be reduced further, until the potential energy of electrons at the screen electrode (point 68(b)) becomes substantially eaual to that at the field emitting element 14 and further passa~e of electrons through the screen electrode is prohibited.
Hence, the quantity of electrons striking the Phosphor coated screen 50 can be regulated by varying the voltage Of the applied signal.
Major advantages of the novel device of the invention, over prior art devices, include the improved structural stength and heat transfer characteristics afforded by the combination of a slender tiplet on a relatively large pyramidal or conical base. Another advantage lies in the enhanced reliability afforded by a plurality of tiplets,as opposed to the prior art single point, at each emission site. The failure of one of a plurality of tiplets will not appreciably degrade the performance of a particular site as would the failure of a single pointed tip in a prior art device. Still another disadvantate accrues from the method which permits the fabrication of large (on the order of 106) quantities of uniform emission sites over a large area (on the order 2S of lOft.2). Additional uniformity of si~e-to-site emission is obtained by the use of a screen electrode as disclosed herein.
The device of the present invention, when embodied as an array of field emitting e~ements, can be used in applications requiring a large area cathode having a . -~1~ -.. . .
' RCA 68,018 Canada 1~4:1Z~O
1 plurality of electron sources, such as disclosed in United States Patents No. 3,176,184, issued 30 March 1965 to Mopkins; No. 3,539,719, issued 10 November 1970 to Requa, et al.; and No. 3,708,713, issued 2 January 1973 to McCann. In addition, the display device disclosed herein can be used as a programmable device, by selectively generating one or more streams of electrons and controlling the quantity of electrons which impinge upon the phosphor coated screen. The selective generation of electron streams may be accomplished, for example, by utilizing strips of field emitting elements disposed in a matrix relationship with screen electrode strips. Generation of an electron stream can be effected by causing the proper differential valtage to be applied between any desired lS field emitting element and the intersecting screen electrode strip. Modulation of the quantity of electrons striking the phosphor coated screen can be accomplished, for example, by selectively applying a signal voltage to the intersecting screen electrode strip, to charge the associated screen electrode emitting element capacitance to control the passage of electrons.
.
' :
An electron extracting elec~rode 22, of an electrically conductive material such as a beryllium copper alloy, is bonded to the insula~ing layer 2n. The electron extracting electrode 22 has a plurality o apertures 24 therein, the number of aPertures corresponding to the number of field emitting elements 14 in the matrix array. The apertures 24 are positioned such that each aperture is aligned substantially coaxially with a correspondin~ field emitting element 14.
To obtain the desired emission of electrons from the field emitting elements 14, the positive terminal of a voltage source 26 is connected to the electron extracting elèctrode 22 and the negati~e terminal is connected to the array of field emitting elements 14 through the substrate 12. Electrons, which are emitted from the tiplets 18 under the influence of the applied voltage, pass through the apertures 24 toward a suitable anode electrode, such as a phosphor coated screen ~not shown).
In accordance with the invention, the device 10 c~ould comprise a single field emitting element 14 having an electron extracting electrode 22 with a single aperture therein, to generate a single stream of electrons, instead of the shown large array of field emitting elements and electron extracting elactrodes generating a large number of individually addressable electron streams.
To make the field emitting device 10, one surface of a substrate 12 of an electrically conductive material, such as copper, is made substantially clean, flat and free . ,:
RCA 68,018 l from blemish. Then, as shown in FIGUR~ 3, a layer 28 of photosensitive etch-resistant, i.e., ~hotoresist, material is applied to the prepared surface and exposed to a light source through a transparency having an array of black dots. The unexposes area of the photoresist layer 28 is nex~ washed away, leaving an array of holes 30. The surface of the substrate is then under etched through the holes 30, leaving an array o interconnected hemispherical valleys 32 shown in FIGURB 4. It is to be noted that, l although the previous steps use a negative photoresist material an~ transparency, they cou:ld be equally well carried out using a positive photoresist material and transparency.
Next, referring to FIGURE 5, the photoresist layer 28 is stripped off, leaving an array of mesa-like ~ structures 34. The copper substrate 12 is then oxidized, ;~ by any well-known method such as heating in airJ ~forming a layer of copper oxide 36 havin~ a thickness of ~pproximately 2 mils. As shown in FIGURE 6, the valleys 32 àre then partially filled with a layer 38 of an electrically insulating ma~erial, such as glass. Onemethod of filling the valleys with glass is to place a sheet of glass approximately 3 mils thick across the tops o~ the mesa-like structures 34 in a ~acuum oven. A vacuum is drawn, and the glass is heated until it hecomes semi-molten and settles down into the valleys 32, leaving only a thin layer of glass 40 covering the tops of the mesa-like structures 34. The vacuum substantially eliminates any air which may be trapped between the glass layer and the valleys 32.
R~A 68,018 ,.~
~ '2 ~
1 llsing stan~ard pho~o etching techniques, a pattern of holes 42, as shown in FIGURE 7, is etche~ into a sheet 44 of conductive material, such as a beryllium copper alloy. The pattern is such that, when the copper alloy sheet 44 is placed on the etched surface of the copper substrate 12, the holes 42 will be ali~ned with and surround the mesa-like structures 34. After the glass has settled into the valleys 3Z, it is slowly cooled to substan*ially room temperature. The copper alloy sheet 44 is then positioned on the etched sùrface o the copper substrate 12, so that the mesa-li~e structures 34 protrude through the holes 42 while the remainder o~ the co~ner alloy sheet 44 is mounted on the glass insulating material 38 (see FI~URE 8). The resulting structure is heated to bond `~
~he copper alloy to the ~lass insulating material 38, and ; then removed from the oven and allowed to cool to substantially room temperature. Next, the thin layer o glass 40 which co~ers the mesa-like structures 34 is removed to expose the copper oxide 36. The copper oxide is then etched away to form pyramidally shaped field~emitters `16, as shown in FIGURE 9. These emitters 16 typically have artip diameter on the order of approximately 5 mic~ons.
Next, a porous layer 46 o a material which does not form an appreciable oxide layer, such as chromium, gold or rhodium, is deposited on the~ tips of the field emitters 16, as shown in FIGURE 10. Preferably, layer 46 is deposited by electroplatin~ chromium on the tips of the ~ield emitters using known porous plating techniques, as described for example by A.H. Sully in "Chromium", Butterworthsg London (1954), Chapter 5. The chromium layer 46 has pores or :
RG~ 68,018 ~ ~ 1 2'~0 l cracks 47 therethrough which are typically 1 micron apart.
The field emitters 16, with the porous layer 46 deposited on the tips thereof, are then heated in air to oxidize those surfaces of the field emitters which are exposed beneath the pores or cracks 47. The oxidation forms sharp points of copper oxide-covered copper beneath the solid ~ortions of the porous layer 46, as indicated ~y the dotted line 48 in PIGURE 11. After cooling to approximately room temperature, the oxide is chemically stripped from the tips of the field emitters 16, causing the porous layer 46 to fall of and leave an array of exposed tiplets 18 as shown in FIGURE 12.
To describe the operation of the novel device 10, reference is made to PIGURES 13 through 18. FIGURE 13 shows a single electron beam display ~evice generally deslgnated as 49, which includes a non-thermionic ield emitting device 10 having a single field emitting element 14 and an electron extracting electrode 22 with a single aperture 24 therein. Also included in the display device 49 is an electron target, here a phosphor coated display screen, 50 and a screen electrode 52 having a mesh-like structure formed by a multiplicity of finely spaced apertures 54. The components of the display device 49 are joined together to form an airtight cavity 55 which is evacuated to provide a vacuum environment between the field emitting element 14 and the display screen 50.
FIGURE 14 is a schematic representation of the single emitter display device 49 connected for basic operation. The positive terminal of a voltage source 26 is ~ 2~ RCA 68,018 1 connected to the electron extracting electrode 22, and the negative terminal thereof is connected to ground. Voltage source 26 is on the order of 100 volts dc. The positive terminal of a first bias voltage source 56 is connected to a switch 58, and the negative terminal thereof is con-nected to ground. The negative terminal of a second bias voltage source 60 is connected to the switch 58, and the positive terminal thereof is connected to ground. First and second bias voltage sources 56 and 60, respectively, are typically 5 volts dc each. The positive terminal of a high voltage source 62 is connected to the phosphor coated screen 50, and the negative terminal thereof is connected to ground. High voltage source 62 is on the order of 20,000 ;~
volts dc.
15FIGU~ES 15 and 16 are potential energy diagrams depicting the relative potential energies of electrons at different locations within the device 49 when the voltages applied to the electron extracting electrode 22 and the phosphor coated screen 50 are 100 volts and 20,000 volts, respectively. Point 64 represents the potential energy ` o~ electrons at the tiplets 18, point 66 is the potential energy of electrons at the electron extracting electrode 22, point 68 is the potential energy of electrons at the screen electrode 52, and point 70 is the potential energy of electrons at the phosphor coated screen 50. FIGURE 15 corresponds to position a of switch 58 in FIGURE 14, wherein the voltage on the field emitting element 14 is +5 volts and the voltage on the screen electrode 52 is -5 volts.
Since the potential energy of electrons at the screen electrode 52 (point 68) is higher than the potential energy of electrons at the field emitting element 14 (point 64), RCA f)8,018 ~ 4 ~
l electrons which have heen extracted from the field emitting element will face a potential energy barrier and not be able to transit the screen electrode toward the phosphor coated screen 50.
When the switch 58 of FIGURE 14 is placed in position b, the voltages on the field emittin~ element 14 and the screen electrode 52 are reversed, produclng the electron potential energy diagram of FI~URE 16. Since the potential energy of electrons at the field emitting element 14 ~point 64) is now higher than the potential energy of electrons at the screen electrode 52 (point 68) the potential energy barrier is eliminated and electrons which have been extracted from the field emitting element will pass through the screen electrode and strike the phosphor coated screen 50 to produce light.
;
In FIGUR~ 17, C represents the capacitance between the screen electrode 52 and the field emitting element 14. A pulse-type si~nal having a positive voltage with respect to the field emitting element is applied to the screen electrode, causing the capacitance C to cha~ge up to an appropriate voltage. After the capacitance chargin~, the potential energy of electrons at the scre~en electrode, indicated by point 68 ~a) in FIGIJRF. 18, is less than that at the field emitting element 14, indicated by point 64 and reference line 74 in the same figure. When a signal of, e.g.j 100 volts dc is applied to the electron - extracting electrode 22, some of the electrons emanating from the field emitting element 14 will transit the screen electrode 52 and strike the phosphor coated screen 50, while others will strike the screen electrode and R~A 68,018 ~ 2 ~
1 cause the voltage stored on the canacitance C to be reduced. As more electrons strike the screen electrode, the voltage on the capacitance C will be reduced further, until the potential energy of electrons at the screen electrode (point 68(b)) becomes substantially eaual to that at the field emitting element 14 and further passa~e of electrons through the screen electrode is prohibited.
Hence, the quantity of electrons striking the Phosphor coated screen 50 can be regulated by varying the voltage Of the applied signal.
Major advantages of the novel device of the invention, over prior art devices, include the improved structural stength and heat transfer characteristics afforded by the combination of a slender tiplet on a relatively large pyramidal or conical base. Another advantage lies in the enhanced reliability afforded by a plurality of tiplets,as opposed to the prior art single point, at each emission site. The failure of one of a plurality of tiplets will not appreciably degrade the performance of a particular site as would the failure of a single pointed tip in a prior art device. Still another disadvantate accrues from the method which permits the fabrication of large (on the order of 106) quantities of uniform emission sites over a large area (on the order 2S of lOft.2). Additional uniformity of si~e-to-site emission is obtained by the use of a screen electrode as disclosed herein.
The device of the present invention, when embodied as an array of field emitting e~ements, can be used in applications requiring a large area cathode having a . -~1~ -.. . .
' RCA 68,018 Canada 1~4:1Z~O
1 plurality of electron sources, such as disclosed in United States Patents No. 3,176,184, issued 30 March 1965 to Mopkins; No. 3,539,719, issued 10 November 1970 to Requa, et al.; and No. 3,708,713, issued 2 January 1973 to McCann. In addition, the display device disclosed herein can be used as a programmable device, by selectively generating one or more streams of electrons and controlling the quantity of electrons which impinge upon the phosphor coated screen. The selective generation of electron streams may be accomplished, for example, by utilizing strips of field emitting elements disposed in a matrix relationship with screen electrode strips. Generation of an electron stream can be effected by causing the proper differential valtage to be applied between any desired lS field emitting element and the intersecting screen electrode strip. Modulation of the quantity of electrons striking the phosphor coated screen can be accomplished, for example, by selectively applying a signal voltage to the intersecting screen electrode strip, to charge the associated screen electrode emitting element capacitance to control the passage of electrons.
.
' :
Claims (5)
1. A non-thermionic field emitting device com-prising an electrically conductive substrate and at least one field emitting element on a surface of said substrate, said field emitting element having a pointed tip projecting away from said substrate, wherein said element has at least one needle-like projection disposed on said tip only, said projection and tip each being of a material having good field emission characteristics.
2. A field emitting device according to claim 1, wherein said field emitting element has a substantially pyramidal shape.
3. A method of making a field emitting device, comprising forming one or more mesa-like structures on a surface of an electrically conductive substrate; coating said surface with an electrically insulating layer; apply-ing an electrically conductive layer having one or more apertures therein on said insulating layer, each of said apertures positioned substantially coaxially with a corres-ponding one of said mesa like structures; forming a pointed tip on each mesa-like structure; and forming at least one needle-like projection on said pointed tip only.
4. A method according to claim 3, wherein said pointed tip is formed by oxidizing the surface of its corresponding mesa-like structure to a predetermined depth and then selectively etching away the oxide.
5. A method according to one of claims 3 or 4, wherein said needle-like projection is formed by depositing a porous layer of an oxidation resistant material on the surface of said pointed tip, oxidizing said surface of said pointed tip to a predetermined depth through the pores of said porous layer, and then etching away the oxide layer.
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US502669A US3921022A (en) | 1974-09-03 | 1974-09-03 | Field emitting device and method of making same |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1041220A true CA1041220A (en) | 1978-10-24 |
Family
ID=23998842
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA233,569A Expired CA1041220A (en) | 1974-09-03 | 1975-08-15 | Field emitting device and method of making same |
Country Status (11)
| Country | Link |
|---|---|
| US (1) | US3921022A (en) |
| JP (1) | JPS5152274A (en) |
| AU (1) | AU497692B2 (en) |
| CA (1) | CA1041220A (en) |
| DE (1) | DE2539234A1 (en) |
| ES (2) | ES440515A1 (en) |
| FR (1) | FR2331145A1 (en) |
| GB (1) | GB1498232A (en) |
| IT (1) | IT1042214B (en) |
| NL (1) | NL7510328A (en) |
| ZA (1) | ZA755552B (en) |
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-
1974
- 1974-09-03 US US502669A patent/US3921022A/en not_active Expired - Lifetime
-
1975
- 1975-08-14 AU AU83973/75A patent/AU497692B2/en not_active Expired
- 1975-08-15 CA CA233,569A patent/CA1041220A/en not_active Expired
- 1975-08-27 ES ES440515A patent/ES440515A1/en not_active Expired
- 1975-08-29 ZA ZA755552A patent/ZA755552B/en unknown
- 1975-09-01 IT IT26789/75A patent/IT1042214B/en active
- 1975-09-02 FR FR7526851A patent/FR2331145A1/en not_active Withdrawn
- 1975-09-02 NL NL7510328A patent/NL7510328A/en not_active Application Discontinuation
- 1975-09-02 JP JP10685375A patent/JPS5152274A/en active Pending
- 1975-09-03 GB GB36331/75A patent/GB1498232A/en not_active Expired
- 1975-09-03 DE DE19752539234 patent/DE2539234A1/en not_active Withdrawn
-
1976
- 1976-01-09 ES ES444173A patent/ES444173A1/en not_active Expired
Also Published As
| Publication number | Publication date |
|---|---|
| NL7510328A (en) | 1976-03-05 |
| ES444173A1 (en) | 1977-06-16 |
| FR2331145A1 (en) | 1977-06-03 |
| IT1042214B (en) | 1980-01-30 |
| DE2539234A1 (en) | 1976-03-11 |
| US3921022A (en) | 1975-11-18 |
| JPS5152274A (en) | 1976-05-08 |
| AU497692B2 (en) | 1978-12-21 |
| AU8397375A (en) | 1977-02-17 |
| ES440515A1 (en) | 1977-03-01 |
| ZA755552B (en) | 1977-03-30 |
| GB1498232A (en) | 1978-01-18 |
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