US3569801A - Thin film triodes and method of forming - Google Patents

Thin film triodes and method of forming Download PDF

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US3569801A
US3569801A US829322A US3569801DA US3569801A US 3569801 A US3569801 A US 3569801A US 829322 A US829322 A US 829322A US 3569801D A US3569801D A US 3569801DA US 3569801 A US3569801 A US 3569801A
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electrodes
thin film
laminar structure
insulating film
control electrode
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Ivar Giaever
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General Electric Co
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General Electric Co
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L21/00—Processes or apparatus adapted for the manufacture or treatment of semiconductor or solid state devices or of parts thereof
    • H01L21/02—Manufacture or treatment of semiconductor devices or of parts thereof
    • H01L21/04—Manufacture or treatment of semiconductor devices or of parts thereof the devices having potential barriers, e.g. a PN junction, depletion layer or carrier concentration layer
    • H01L21/18—Manufacture or treatment of semiconductor devices or of parts thereof the devices having potential barriers, e.g. a PN junction, depletion layer or carrier concentration layer the devices having semiconductor bodies comprising elements of Group IV of the Periodic Table or AIIIBV compounds with or without impurities, e.g. doping materials
    • H01L21/24—Alloying of impurity materials, e.g. doping materials, electrode materials, with a semiconductor body
    • H—ELECTRICITY
    • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10D—INORGANIC ELECTRIC SEMICONDUCTOR DEVICES
    • H10D99/00—Subject matter not provided for in other groups of this subclass

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  • FIG. 1 A first figure.
  • This invention relates to thin film tunneling devices and to the method of their fabrication.
  • the invention relates to thin film devices wherein tunneling current flow between the edges of two closely positioned electrodes is controlled by an electrical signal applied to a relatively small band gap material, e.g. a semiconductor, disposed in electrical contact with the edges of the tunneling electrodes.
  • a relatively small band gap material e.g. a semiconductor
  • l-ligh mobility tunneling devices in accordance with this invention can be fabricated by vacuum deposition of the semiconductive layer along an exposed edge of the tunneling electrodes with the close proximity of the electrodes effectively producing a single crystalline electrical characteristic in the deposited polycrystalline or amorphous semiconductive layer.
  • Thin film devices utilizing quantum-mechanical tunneling of elementary charge carriers heretofore have been characterized by a laminar metal-insulator-metal structure wherein tunneling current flows through the insulator spacing the metal electrodes.
  • Tunneling structures of the heretofore mentioned type also have been formed atop single crystalline semiconductive substrates to permit electrical signals applied between the metallic electrodes to appear in amplified form at an output terminal bonded to the substrate. In these devices however a large percentage of tunneling current flow is diverted to the control electrode situated atop the semiconductive substrate and high mobility is achieved only with single crystal-line semiconductive substrates.
  • Another thin film amplifying device utilizes two electrodes deposited on a single crystalline semiconductive substrate which substrate provides a barrier to current flow between electrodes.
  • a thin oxide film serves to space apart and insulate the two slightly overlapping electrodes and, upon application of a suitable potential between the electrodes, the barrier to current flow in the substrate breaks down at the edge of one electrode to emit electrons into the substrate for collection by an electrically biased collector contact to the substrate.
  • Collector current flow in the amplifying device is by conventional Schottky emission with current control being achieved by constriction of the flow channel at the edges of the electrode atop the substrate. Although some tunneling current may flow between the overlapping portions of the juxtaposed emitter and base electrodes, this tunneling current flow is subject to the deficiencies heretofore described for the metal-oxide-metal-semiconductive substrate laminar structure.
  • conventional thin film field effect transistors heretofore have been characterized by a semiconductive layer deposited atop spaced apart metallic source and drain electrodes on an insulating substrate.
  • the portion of the semiconductive layer between the source and drain electrodes is sequentially overlayed with an insulator and gate electrode to permit control of current fiow between the source and drain electrodes by a potential applied to the gate electrode.
  • the spacing between the source and drain electrodes however generally is in the order of microns and current transport of into the semiconductive layer is achieved by Schottky emission.
  • the semiconductive layer must be grown epitaxially to offer a single single crystalline orientation for current flow.
  • a thin film laminar device characterized by first and second metallic film electrodes spaced apart by an insulating film of a material having a band gap sufficiently large to substantially negate electron fiow between electrodes.
  • An insulating layer having a work function sufficiently small relative to the electrodes to carry essentially all current flow between electrodes bypasses the insulating film while the thin dimension of the large band gap insulating film, e.g. 50-500A; permits current flow in the bypassing insulating layer to be achieved by quantum-mechanical tunneling upon application of a suitable potential to the spaced apart electrodes.
  • a control electrode having a large work function relative to the insulating layer is electrically bonded to the insulating layer and means are provided for controlling the tunneling current flow through the insulating layer by the application of a suitable electrical signal to the control electrode to alter the flow channel between the tunneling electrodes.
  • the insulating layer interconnecting the electrodes acts as a single crystalline structure to charge carrier flow between-electrodes notwithstanding an amorphous or polycrystalline structure in the insulating layer.
  • the insulatinglayer can be formed by conventional vapor deposition of a semiconductor atop an exposed edge of the laminar structure in counterdistinction to conventional solid state devices requiring epitaxial growth of the semiconductive layer for high charge carrier mobility.
  • FIG. 1 is a flow chart depicting in block diagram form the method of this invention
  • FIG. 2 is a pictorial illustration of 'thefabrication of a thin film tunneling device in accordance with this invention.
  • FIG. 3 is an isometric view of an alternate tunneling device constructed in accordance with this invention.
  • FIGS. 1 and 2 The method of forming a tunneling device in accordance with this invention is illustrated in FIGS. 1 and 2 and initially comprises the vacuum deposition of metallic electrode 10 upon an insulating substrate 12 previously prepared in conventional fashion for deposition by being washed in detergent. rinsed with de-ionized water and dried.
  • electrode 10 is a metal having a small work function relative to a subsequently to be deposited semiconductive layer (as will be more fully explained hereinafter) and suitably may be a metal such as indium, tin or aluminum'deposited to a thickness of. for example, 1,000A.
  • any conventional technique for forming electrode l0 can be employed.
  • vacuum deposition of the chosen metal at a pressure between l X 10-to l X 10- torr generally is suitable.
  • insulating film l4 and-a counterelectrode 16 are sequentially vacuum deposited thereon to form laminar structure 18.
  • lnsulating film l4 desirably is of a material having a large band gap to negate current flow between electrodes 10 and l6 through the insulating film.
  • suitable insulating films for this purpose are high purity aluminum oxide, silicon monoxide or silicon dioxide with vacuum evaporation of spectroscopic grade pellets of the chosen insulator at pressures of approximately l X l0- torr generally being suitable for deposition of the insulating film atop electrode 10.
  • the chosen insulating film is deposited to a thickness in excess of 50A.
  • insulating film 14 to inhibit tunneling current flow through insulating film 14; during operation while the maximum thickness of the insulating film should be below 500A. to permit tunneling of charge carriers through a subsequently to be deposited relatively smaller band gap material, e.g. a semiconductor, electrically bypassing the insulating film.
  • band gap material e.g. a semiconductor
  • Counter electrode 16 normally is a low work function metal identical to the metal employed to deposit electrode 10, e.g. indium, tin, aluminum, etc. and suitably is deposited to a thickness of approximately 1,000A. Any electrode thickness however can be employed, if desired, provided the electrode is electrically continuous and of sufficient thickness to carry the s desired tunneling current flow therethrough.
  • laminar structure 18 After formation of laminar structure 18, at least a portion of one edge of the structure is mechanically removed, e.g. cut away with a knife edge, to expose each layer forming the laminar structure whereupon a layer 20 of, for example, cadmium sulfide is deposited to a thickness of approximately 2 mils atop the exposed edge of the laminar structure.
  • a layer 20 of, for example, cadmium sulfide is deposited to a thickness of approximately 2 mils atop the exposed edge of the laminar structure.
  • layer 20 can be any nonmetal characterized by a small work function with metal electrodes 10 and 16 relative to the work function between the metal electrodes and insulating film 14 and thus would include high conductivity insulators, such as the semiconductors cadmium sulfide, lead sulfide, germanium, silicon, etc., as well as more conventional insulators such as zinc oxide or lead oxide doped to a resistivity between 10- and l ohm-cm.
  • layer 20 may be characterized by a work function of approximately one-half ev. relative to the electrodes to maximize current flow between electrodes in layer 20.
  • the'work function between layer 14 and metallic electrodes 10 and 16 should be at least approximately twice the work function between the metallic electrodes and layer 20 to assure at least 70 percent of the current flow between electrodes passes between the edges of the electrodes by way of layer 20.
  • insulating film l4 spacing the electrodes preferably is of a thickness between 50A. and 200A. although insulator film thicknesses as high as 500A. may be employed with semiconductor materials such as cadmium sulfide and lead sulfide having a free carrier charge concentration of 10"carriers/cm; a high mobility is observed by tunneling current flowing through layer 20 notwithstanding an amorphous or polycrystalline structure in the layer.
  • semiconductor materials such as cadmium sulfide and lead sulfide having a free carrier charge concentration of 10"carriers/cm; a high mobility is observed by tunneling current flowing through layer 20 notwithstanding an amorphous or polycrystalline structure in the layer.
  • layer 20 can be conveniently formed by evaporation of cadmium sulfide in a vacuum of approximately I X 10-to l X lO-torr.
  • the evaporating crucible (not shown) desirably is placed to the side of the laminar structure adjacent the removed edge rather than directly below the laminar structure.
  • a straight line drawn between the center of laminar structure 18 and the center of the crucible evaporating layer 20 forms an angle between 60 and 12 with the planes of electrodes 10 and 16.
  • control electrode 22 is deposited atop the face of layer 20 remote from laminar structure 18' to regulate the tunneling cur-rent flow through layer 20.
  • control electrode 22 is a metal, e.g. platinum, gold, etc., having a relatively high work function with layer 20 to inhibit electron flow from the control electrode into the juxtaposed semiconductor layer.
  • the control electrode source is located in the vacuum deposition chamber at a location closely adjacent, or identical to, the location of layer 20 source and evaporation is suitably conducted at a pressure of X -torr.
  • leads 24, 26 and 28 are electrically bonded to electrodes l0, l6 and 22, respectively, by suitable techniques, e.g. soldering or thermal compression bonding, to permit the application of biasing voltages to the structure.
  • a voltage source 30 of approximately 0.1 volt is connected between electrode 10 and counter electrode 16 to produce a tunneling current fiow 32 from the edges of the electrodes through layer 20 with current flow through insulating layer 14 being inhibited by the wide band gap of the insulating layer.
  • a variable control voltage source 34 of approximately 1.0 0.1 volts is applied between control electrode 22 and electrode 10, equipotential lines of force 36 extend into layer 20 to constrict or enhance the tunneling current flow therethrough in proportion to the magnitude and polarity of the applied control voltage.
  • FIG. 3 An alternate tunneling thin film structure 38 in accordance with this invention is depicted in FIG. 3 and generally comprises a laminar structure having the control electrode 40 centrally disposed between tunneling electrodes 42 and 44.
  • Structure 38 is similar to laminar structure 18 of FIG. 1 except for the positioning of control electrode 40 and is characterized by two metallic tunneling electrodes 42 and 44 having a low work function, e.g. one-half ev. relative to a semiconductive layer 46 of, for example, cadmium sulfide disposed in electrical contact with'each layer of the laminar structure along an exposed edge thereof.
  • Control electrode 40 is of a material, eg platinum or gold, having a large, e.g. l.5 ev.
  • electrodes 42 and 44 may be any thickness, e.g. approximately 1,000A; while the maximum total dimension of control electrode 40 and insulating films 48 and 50 must be less than the total dimension permitting tunneling current to flow between electrode 42 and 44 through semiconductor layer 46.
  • control electrode 40 ideally is approximately 200A. thick with insulating layers 48 and 50 each being approximately 10OA. in thickness.
  • the width W of the electrodes should be minimized, e.g. to approximately l0 microns, thereby reducing the capacitance between electrodes 42 and 44 and increasing the switching speed of the tunneling structure.
  • Structure 38 can be fabricated by the sequential vapor deposition of electrode 42, insulating film 48, control electrode 40, insulating film 50 and electrode 44 from crucibles positioned directly below the insulating substrate 52 accepting the deposition of the layers thereon.
  • the edge of the structure then is mechanically removed, e.g. by a knife edge or by removal of a second substrate (not shown) masking a portion of substrate 52, to expose each of the laminar layers and a semiconductive material, such as cadmium sulfide, is evaporated from a crucible positioned aside the exposed edge of the laminar structure to assure good electrical contact between deposited semiconductive layer 46 and each of the films forming structure 38.
  • a semiconductive material such as cadmium sulfide
  • vapor deposited cadmium sulfide characteristically possesses a polycrystalline structure
  • other materials such as germanium having an amorphous structure when deposited upon an unheated substrate also can be employed in forming tunneling structures in accordance with this invention with the close proximity of electrodes 42 and 44 resulting from the thin film laminar configuration of structure 38 producing a high mobility in charge carrier flow through semiconductive layer 46 notwithstanding the polycrystalline or amorphous nature of the layer.
  • the insulating films separating the electrodes also can be formed by oxidation of an electrode surface when the electrode is of a metal, e.g. aluminum, which is readily oxidizable.
  • tunneling device 38 is similar to that shown in FIG. 1 with an applied voltage of 0.1 to 1 volt from source 54 connected between electrodes 42 and 44 producing a tunneling current fiow 56 through amorphous or polycrystalline semiconductive layer 46.
  • a time varying control voltage source 58 of 0.1 to 1 volt then is applied between control electrode 40 and electrode 44 to form equipotential lines of force 60 within the semiconductive layer regulating the flow of tunneling current therein with current flow from the control electrode into the semiconductive layer being inhibited by the large work function between the control electrode and the semiconductive layer.
  • a thin film device comprising first and second electrodes, an insulating film disposed between said electrodes, said insulating film having a band gap sufficiently large to substantially inhibit current flow between said electrodes through said insulating film, an insulating layer bypassing said insulating film and interconnecting said first and second electrodes, said insulating layer having a work function sufficiently small relative to the electrodes to carry essentially all current flow between said electrodes, the flow channel between said electrodes in said insulating layer being sufficiently small to permit current fiow due to quantum-mechanical tunneling in response to a suitable potential applied between electrodes, means for applying said suitable potential between said electrodes, a control electrode electrically bonded to said insulating layer and means for applying an electrical signal to said control electrode to modulate the flow of tunneling current between said first and second electrodes.
  • a thin film device wherein said first and second electrodes and said insulating film form a laminar structure, at least one edge of said structure being exposed along a plane angularly disposed relative to the planes of said electrodes to bare the component layers of said laminar structure, and said insulating layer is deposited atop said exposed edge to interconnect said first and second electrodes.
  • a thin film device according to claim 2 wherein said insulating layer has an amorphous structure.
  • a thin film device wherein said insulating film is between 50 and 500A. in thickness, and said control electrode is a material having a large work function relative to said insulating layer to substantially negate current flow therebetween, said control electrode being disposed along the face of said insulating layer remote from said exposed edge of said laminar structure.
  • a thin film device wherein said first and second electrodes are low work function metals selected from the group consisting of indium, tin, and aluminum, said insulating film is an oxide of a metal selected from the group consisting of aluminum and silicon, said insulating layer is a semiconductor selected from the group consisting of cadmium sulfide, lead sulfide, germanium and silicon and said control electrode is a metal selected from the group consisting of gold and platinum.
  • control electrode is disposed intermediate said laminar structure at a location insulated from said first and second electrodes by said insulating film, said control electrode having a work function with said insulating layer substantially in excess of the work function between said insulating layer and said first and second electrodes.
  • a thin film device wherein said electrodes are metals selected from the group consisting-of indium; tin and aluminum, said insulating film is an oxide of a metal selected from the group consisting of aluminum and silicon, said insulating layer is a semiconductor selected from the group consisting of cadmium sulfide, lead sulfide, germanium, and silicon and said control electrode is a metal selected from the group consisting of gold and platinum.
  • a thin film device comprising first and second metallic electrodes spaced apart by a 50 to 500A. thick insulating film, said insulating film having a band gap sufficiently large to substantially inhibit charge flow between said electrodes, a polycrystalline semiconductive material bypassing said insulating film and interconnecting said electrodes, means for applying an electrical potential across said electrodes to produce a quantum-mechanical tunneling current flow between said electrodes through said polycrystalline semiconductive material, and means for applying a control signal to said polycrystalline material to regulate the flow of tunneling current therethrough.
  • a thin film device wherein the work function between said electrodes and said polycrystalline material is at least 1.5 ev. smallerthan the work function between said electrodes and said insulating film.
  • a thin film device wherein said insulating film is aluminum oxide in a thickness between 50 and 300A. and said polycrystalline material is a sulfide of a metal selected from the group consisting of cadmium and lead.
  • a method of forming a thin film device comprising vacuum depositing a metallic electrode upon a dielectric substrate, forming a 50-50OA. thick insulating film atop said metallic electrode, vacuum depositing a metallic counter electrode atop said insulating film to form a metal-insulator-metal laminar structure, exposing at least one edge of said laminar structure along a plane angularly disposed relative to the planes of said electrodes, vacuum depositing a layer of semiconductive material atop said exposed edge, said semiconductive material having a small work function relative to the electrodes of said laminar structure to permit quantummechanical tunneling of charge carriers between said electrodes through said semiconductive material and depositing a metal electrode atop said semiconductive layer.

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US829322A 1969-06-02 1969-06-02 Thin film triodes and method of forming Expired - Lifetime US3569801A (en)

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DE (1) DE2026723A1 (en, 2012)
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Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4286275A (en) * 1980-02-04 1981-08-25 International Business Machines Corporation Semiconductor device
US4466008A (en) * 1980-10-30 1984-08-14 Heinz Beneking Field effect transistor

Citations (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2208455A (en) * 1938-11-15 1940-07-16 Gen Electric Dry plate electrode system having a control electrode
US2648805A (en) * 1949-05-30 1953-08-11 Siemens Ag Controllable electric resistance device
US3116427A (en) * 1960-07-05 1963-12-31 Gen Electric Electron tunnel emission device utilizing an insulator between two conductors eitheror both of which may be superconductive
US3121177A (en) * 1962-01-23 1964-02-11 Robert H Davis Active thin-film devices controlling current by modulation of a quantum mechanical potential barrier
US3250967A (en) * 1961-12-22 1966-05-10 Rca Corp Solid state triode
US3400456A (en) * 1965-08-30 1968-09-10 Western Electric Co Methods of manufacturing thin film components

Family Cites Families (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3254276A (en) * 1961-11-29 1966-05-31 Philco Corp Solid-state translating device with barrier-layers formed by thin metal and semiconductor material
US3267389A (en) * 1963-04-10 1966-08-16 Burroughs Corp Quantum mechanical tunnel injection amplifying apparatus

Patent Citations (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2208455A (en) * 1938-11-15 1940-07-16 Gen Electric Dry plate electrode system having a control electrode
US2648805A (en) * 1949-05-30 1953-08-11 Siemens Ag Controllable electric resistance device
US3116427A (en) * 1960-07-05 1963-12-31 Gen Electric Electron tunnel emission device utilizing an insulator between two conductors eitheror both of which may be superconductive
US3250967A (en) * 1961-12-22 1966-05-10 Rca Corp Solid state triode
US3121177A (en) * 1962-01-23 1964-02-11 Robert H Davis Active thin-film devices controlling current by modulation of a quantum mechanical potential barrier
US3400456A (en) * 1965-08-30 1968-09-10 Western Electric Co Methods of manufacturing thin film components

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4286275A (en) * 1980-02-04 1981-08-25 International Business Machines Corporation Semiconductor device
US4466008A (en) * 1980-10-30 1984-08-14 Heinz Beneking Field effect transistor

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GB1308562A (en) 1973-02-21
FR2045802A1 (en, 2012) 1971-03-05
FR2045802B1 (en, 2012) 1973-10-19
DE2026723A1 (en, 2012) 1970-12-10

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