US3673539A - Electrical resistance element with a semiconductor overlay - Google Patents

Electrical resistance element with a semiconductor overlay Download PDF

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Publication number
US3673539A
US3673539A US36047A US3673539DA US3673539A US 3673539 A US3673539 A US 3673539A US 36047 A US36047 A US 36047A US 3673539D A US3673539D A US 3673539DA US 3673539 A US3673539 A US 3673539A
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United States
Prior art keywords
overlay
resistance
germanium
potentiometer
track
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Expired - Lifetime
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US36047A
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English (en)
Inventor
Robert M Healy
Robert Marshall
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Bunker Ramo Corp
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Bunker Ramo Corp
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01C—RESISTORS
    • H01C17/00—Apparatus or processes specially adapted for manufacturing resistors
    • H01C17/28—Apparatus or processes specially adapted for manufacturing resistors adapted for applying terminals
    • H01C17/288—Apparatus or processes specially adapted for manufacturing resistors adapted for applying terminals by thin film techniques
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01C—RESISTORS
    • H01C10/00—Adjustable resistors
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01C—RESISTORS
    • H01C10/00—Adjustable resistors
    • H01C10/30—Adjustable resistors the contact sliding along resistive element
    • H01C10/308—Adjustable resistors the contact sliding along resistive element consisting of a thin film
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01C—RESISTORS
    • H01C17/00—Apparatus or processes specially adapted for manufacturing resistors
    • H01C17/06—Apparatus or processes specially adapted for manufacturing resistors adapted for coating resistive material on a base
    • H01C17/075—Apparatus or processes specially adapted for manufacturing resistors adapted for coating resistive material on a base by thin-film techniques
    • H01C17/08—Apparatus or processes specially adapted for manufacturing resistors adapted for coating resistive material on a base by thin-film techniques by vapour deposition

Definitions

  • a resistance element incorporating this improvement has a much lower temperature coefficient of resistance.
  • a germanium overlay may be provided by evacuating the space about the resistive element to a pressure of about 2x10 torr, supplying the gennanium material in granular particles ranging in fineness between 180-320 mesh by vibration and gravity in a steady and even flow thereof to the evacuated space at a point with respect to which the resistor track is exposed, and then evaporating the gennanium at the point by electrical resistance heating to vaporization temperature at about 1,850" C.
  • a resistance element so made When used in a potentiometer with a movable contact, a resistance element so made exhibits superior wear stability, and good contact resistance variation characteristics.
  • This invention relates generally to electrical resistance devices,.and more particularly to a resistive element therefor having a semi-conductive overlay, and a method of fabricating the same.
  • the element is particularly applicable in variable resistors, such as trimmers, which are useful in affording desired adjustments of electrical circuitry.
  • adjustment of electrical resistance is accomplished in variable resistor units by movement of a wiper contact along a resistor track.
  • the resistor track be a thin film deposit of material yielding uniform electrical properties.
  • a nickel-chromium-iron alloy has been commonly used for such a deposit, but the alloy is subject to oxidation which gives rise to objectionable wear and noise, in the operation of the variable resistor unit.
  • a partial solution has been afi'orded in the past by coating the resistor track with a thin film overlay of a noble metal such as platinum, rhodium, or palladium, as disclosed in U.S. Pat. No. 3,353,134 issued Nov. 14, 1967 to V. D. Elarde.
  • the noble metal overlays have been limited in application for a variety of reasons.
  • the deposition process by thermal evaporation from a tungsten filament is wasteful of material, and gives poor thickness uniformity, as demonstrated by wide divergencies in the properties of various resistive elements deposited in the same batch.
  • the resistivity of the noble metals is usually much lower than that of the resistor track on which they are deposited.
  • the thickness of the noble metal overlays must be extremely thin, to limit shunting of the resistor track, i.e. reduction of the terminal-to-terminal resistance value by addition of the overlay. For this reason, thickness has been necessarily limited to less than 100 Angstrom units, at which thickness the resistivity of the noble metal overlay is likely to be between 8,000 and 13,000 ohms per square.
  • a new and improved resistive element is required.
  • a thin film overlay of a semi-conductive material covers the resistor track of a variable resistance element.
  • the semi-conductive material may be germanium, silicon, indium antimonide, titanium oxide or ferric oxide.
  • the semi-conductive material is supplied in granular particles ranging in fineness between 180-320 mesh from a vibratory feeder-hopper down a vertical feed pipe, in an even and steady flow to the boat, which is electrically heated to the vaporization temperature of the semi-conductive material. Evaporation of the semi-conductive material occurs as the particles contact the boat.
  • the thickness of semi-conductive material may be deduced from measurements of the electrical resistance of the deposit upon a standard glass element having terminals and leads to the exterior of the deposition apparatus. After the desired thickness has been reached, the resistive elements are cooled to about 155 C., at which point the vacuum deposition apparatus is vented to the atmosphere and the resistive elements, which then have a semi-conductive overlay in accordance with the present invention, may be removed.
  • CMV contact resistance variation
  • MIL-R-22097 prescribes conditions for test. Under these conditions it is found that the noise figure for trimmers with germanium overlay is about one-tenth that of trimmers with no overlay. The figure for those with silicon overlay is'about two-thirds that of trimmers with germanium overlay.
  • wear Another property, briefly referred to as wear, is the percentage change in end-to-end resistance, between an initial measurement and one made after 200 cycles of rotation of the movable contact.
  • the change observed in trimmers with either germanium or silicon overlay is less than half that found in those with no overlay.
  • Temperature coefficient is also of interest, and here comparison must be made between trimmers utilizing a noble metal overlay, as taught in U.S. Pat. No. 3,353,134, and those utilizing the present invention.
  • addition of a noble metal overlay tends to give the composite resistance a strong positive temperature coefficient of resistance. For some applications this may be desirable, but the semi-conductive overlays have a definite advantage where low values of temperature coefficient are desired.
  • the overlay material has a low, even negative, temperature coefficient of resistance which aids in offsetting the normally positive coefficient of the basic resistor track.
  • one of the objects of this invention is to provide a novel resistive element for a variable resistor.
  • Another object of this invention is to provide an overlay which is practical for use on resistor tracks of relatively high resistance values, and of medium resistance values in miniaturized elements.
  • Still another object is to provide an overlay of semiconductive material for a resistor track in an adjustable resistance device.
  • FIG. I is a perspective view having a partially broken away section, showing a resistive element according to the present invention, and illustrating its application in a potentiometer.
  • FIGS. 2a through 2d are plan views showing the various steps in depositing of thin film material on a resistive element.
  • FIG 3 is a schematic perspective view illustrating a vacuum deposition apparatus for fabrication of resistive elements in accordance with the present invention.
  • FIG. 4 is a schematic block diagram setting forth the steps in fabricating the semi-conductive overlay of the present invention.
  • FIG. 1 a potentiometer 10 which may be substantially the same as that shown in FIG. 3 of U.S. Pat. No. 3,353,134.
  • the potentiometer embodies a resistive element 12 formed on a substrate 20 of flat disc configuration as shown, providing a support surface 21.
  • a central opening 22 and a peripheral notch 23 are provided in substrate 20 for mating receiption within a casing (not shown) such as that disclosed in U.S. Pat. No. 3,353,134.
  • the substrate 20 may be fabricated in blank form out of a variety of available insulating materials, such as are afforded by insulating plastics, for example the phenolic and epoxy resins. However, a ceramic such as steatite, alumina, beryllia, glass, quartz and the like are found to be preferable materials for the substrate 20. Borosilicate glass and other high temperature insulating glass are highly satisfactory.
  • the support surface 21 preferably is smooth and regular for bonding of various films of materials thereon, as described hereafter.
  • a film track 30 of electrically resistive material is bonded on the surface 21 about the periphery of substrate 20, as shown.
  • the material of track 30 may be any of the commonly used resistor materials.
  • a relatively thin film of nickeI-chromium-iron alloy may be provided, having a range of resistance of 500 ohms to 20,000 ohms with a film thickness of 2,000 to I Angstrom units.
  • cermet materials may be utilized to provide a relatively thick film resistance element for the track 30, having a thickness appreciably above 2,000 Angstrom units.
  • a relatively wide range of resistance values say from 10 ohms to 10 meg ohms, may be provided in different versions of variable resistor units.
  • the track 30 may be bonded on to the surface 21 by the usual techniques presently common in the art.
  • Terminal means are provided by the deposit of metallic terminal pads 40, 42 at opposite ends of the track 30, bordering the peripheral notch 23.
  • pads 40, 42 are a good electrical conductor such as nickel, silver, etc., having a good electrical contact with the track 30.
  • a wiper or slider contact a portion of which is shown at 60, is connected by a lead 28 to the potentiometer intermediate terminal 29.
  • An overlay film 50 of semi-conductive material coats the track 30 as illustrated.
  • the semi-conductive material of overlay 50 is selected from a group consisting of germanium, silicon, indium antimonide, titanium oxide and ferric oxide. The preferred materials are germanium and silicon.
  • the thickness of the overlay 50 is not critical, as was the case in the noble metal overlays of the prior art, since the resistivity of the semiconductive material is considerably higher than that of the resistor track 30. Preferably, thickness of the overlay 50 is between 100 and 4,000 Angstrom units.
  • FIGS. 2a through 2d illustrate the fabrication of a resistive element in accordance with the present invention.
  • a blank substrate 20 is shown in FIG. 2a.
  • the terminal pads 40, 42 are first deposited thereon as illustrated in FIG. 2b.
  • resistor track 30 is provided on the surface 21 as illustrated in FIG. C.
  • the semi-conductor overlay 50 is provided over the resistor track 30 to provide a resistive element in accordance with the present invention.
  • a flash evaporation apparatus for the fabrication of resistive elements in accordance with the present invention is indicated generally by the numeral 80 in FIG. 3.
  • the vacuum deposition apparatus 80 consists of a solid base 81 and bell jar 82 enclosing a space which may be evacuated by the vacuum pump 83.
  • the apparatus 80 may be vented to the atmosphere through a vent 84.
  • Support rods 85 are provided to position various elements within the bell jar 82.
  • a mask array dome 90 is supported on the support rod 85 a distance above the base 81 and provides a parabolic or spherical support orientation for the removable trays 91 with respect to a point within the bell jar 82.
  • Depressions 92 in the trays 91 are shaped for reception of the substrate blanks 20 shown in FIG. 2a.
  • the depressions 92 include openings (not shown) therethrough corresponding to the resistor track 30 of each resistive element 10. It is understood that preferably the shape of the depressions 92 accounts for the peripheral notch 23, so that the resistor tracks 30 may be properly oriented with respect to the openings (not shown) in depressions 92.
  • a heater dome 95 is spaced above the mask array dome on the support rods 85, as shown.
  • Heater elements 96 are provided on the underside of the heater dome above each removable tray 91.
  • a power source 97 is connected .by leads 98, 99 to each heater element 96, and in this manner, provides energy to heat the resistor trays 91 facing the inside of the heater dome 95. It is understood that the heater element 96, power source 97, and leads 98, 99 shown in FIG. 3 are merely simplified schematic versions, and far more sophisticated means may be visualized by those skilled in the art.
  • a vibratory feeder-hopper 100 extends from a support rod outwardly over theheater dome 95.
  • the vibratory feederhopper may be of the well known type energized by electrical solenoids or motors to shake with regular vibrations.
  • a vertical feed pipe 102 having a funnel 103 at the top end extends through openings at the center of the mask array dome 90 and heater domer 95.
  • the funnel 103 engages within the opening through heater dome 95 to support the feed pipe 102 in a ver-. tical disposition, as shown.
  • the funnel 103 and pipe 102 extends freely through opening 104 in the mask array dome 90.
  • the funnel in 103 is positioned directly beneath the vibratory feeder-hopper 100.
  • a boat of a highly heat resistant material such as tantalum or molybdenum is provided at a central point with respect to the trays 91 in the mask array dome 90.
  • the boat is positioned at a point which is the focus of the parabolic or spherical support orientation of the trays 9I.
  • Resistive heaters 106, 107 are connected by power lines 108, 109 to a source of power 110, and serve to heat the boat 105.
  • a bracket extends from a support rod 85 as a mounting for a glass plate 116.
  • Spaced electrodes 119 are provided on the glass plate 116 and leads 117, 118 extend therefrom outside the bell jar to a meter 120 for readings of resistance across the glass plate 116 between electrodes 119.
  • the arrangement outlined is commonly referred to as a glass monitor," and its use is described at a later point in this specification.
  • the steps in the process of depositing the semi-conductive overlay 50 on a resistor track 30 are now described with reference to the apparatus shown in FIG. 3 and the block diagram shown in FIG. 4.
  • the individual resistor elements 10, each having a resistor track 30 such as that shown in FIG. 2c, are arrayed in the movable trays 91 by placing them in the depressions 92 with their surfaces 21 face downward. Only the tracks 30 are exposed through openings in the depressions 92, the remainder of surfaces 21 being masked therein.
  • the trays are placed in the mask array dome 90 with the resistor tracks 30 exposed to a focus point at the tantalum boat 105.
  • the space within the bell jar 82 is evacuated by the vacuum pump 83 to a pressure of about 2X 10' torr.
  • a supply of semiconductive material such as germanium, is provided in the vibratory feeder-hopper 100 in a granular form having particle fineness ranging between 180-320 mesh. Vibration and gravity provide an even flow of material. Particles of the semiconductive material flow from the feeder-hopper 100 and down the feed pipe 102 to drop on to the tantalum boat 105.
  • the heaters 106, 107 are energized through power lines 108, 109 by the source of power 110.
  • the tantalum boat 105 is heated to a temperature of about l,850 C.
  • a coating of the semi-conductive material will be deposited upon the plate 116, and with increasing thickness of the deposit, the resistance between the electrodes 119, as observed on the resistance measuring instrument 120, will decrease.
  • the glass monitor thus provides a means of determining the end point of the process, i.e., the point at which the desired thickness has been deposited on the tracks 30.
  • thickness of the overlay on the tracks is between 100 and 4,000 Angstrom units.
  • a typical deposit of germanium would be one having a room temperature resistivity of 500 megohms per square. At 300 C. this would be approximately 190,000 ohms per square. Such a deposit can be obtained in about 2% minutes.
  • the vibratory feederhopper 100, heat elements 96, 97 and heaters 106, 107 are turned off and the array is allowed to cool to about 155 C. Then the bell jar 82 may be vented to the atmosphere by opening vent 84. The individual resistive elements may be removed from the apparatus 80 and will have a semi-conductive overlay in accordance with the present invention.
  • a potentiometer comprising:
  • a resistance element which includes an insulating substrate providing a support surface
  • an overlay film of homogenous non-particulate semi-conductive material coating said track said material being selected from a group of semi-conductive materials such as germanium, silicon, indium antimonide, titanium oxide, ferric oxide or the like, and
  • said electrically resistive material is an alloy consisting essentially of 20 to 65 percent nickel, 15 to 75 percent chromium and the remainder iron, said track having a thickness of between and 4,000 Angstrom units.

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  • Engineering & Computer Science (AREA)
  • Microelectronics & Electronic Packaging (AREA)
  • Manufacturing & Machinery (AREA)
  • Physical Vapour Deposition (AREA)
  • Apparatuses And Processes For Manufacturing Resistors (AREA)
US36047A 1970-05-11 1970-05-11 Electrical resistance element with a semiconductor overlay Expired - Lifetime US3673539A (en)

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US3604770A 1970-05-11 1970-05-11

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US3673539A true US3673539A (en) 1972-06-27

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US (1) US3673539A (de)
CA (1) CA938687A (de)
CH (1) CH525542A (de)
DE (1) DE2116785A1 (de)
FR (1) FR2088468B3 (de)
GB (1) GB1343843A (de)
IL (1) IL36479A (de)
NL (1) NL7104640A (de)

Cited By (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO1982003723A1 (en) * 1981-04-10 1982-10-28 Roth Johann Electric contact,particularly for printed circuits of small electric appliances
US4651123A (en) * 1984-08-06 1987-03-17 International Hydraulic Systems, Inc Linear potentiometer
US4746896A (en) * 1986-05-08 1988-05-24 North American Philips Corp. Layered film resistor with high resistance and high stability
EP0241874A3 (de) * 1986-04-11 1989-05-24 AT&T Corp. Gegenstand mit Temperatursensor
US4845839A (en) * 1988-10-31 1989-07-11 Hamilton Standard Controls, Inc. Method of making a resistive element
US5554965A (en) * 1994-11-02 1996-09-10 The Erie Ceramic Arts Company Lubricated variable resistance control having resistive pads on conductive path
US20040130432A1 (en) * 2002-08-12 2004-07-08 Alps Electric Co., Ltd. Variable-resistance element

Families Citing this family (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4371861A (en) * 1980-12-11 1983-02-01 Honeywell Inc. Ni-fe thin-film temperature sensor
FR2547946B1 (fr) * 1983-06-22 1986-01-24 Nitto Electric Ind Co Element de resistance variable a curseur

Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2799756A (en) * 1953-07-29 1957-07-16 Gen Electric Precision potentiometer
US3240625A (en) * 1962-01-10 1966-03-15 Air Reduction Semiconductor film resistor
US3353134A (en) * 1964-08-17 1967-11-14 Amphenol Corp Resistive element and variable resistor
US3368919A (en) * 1964-07-29 1968-02-13 Sylvania Electric Prod Composite protective coat for thin film devices

Patent Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2799756A (en) * 1953-07-29 1957-07-16 Gen Electric Precision potentiometer
US3240625A (en) * 1962-01-10 1966-03-15 Air Reduction Semiconductor film resistor
US3368919A (en) * 1964-07-29 1968-02-13 Sylvania Electric Prod Composite protective coat for thin film devices
US3353134A (en) * 1964-08-17 1967-11-14 Amphenol Corp Resistive element and variable resistor

Cited By (9)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO1982003723A1 (en) * 1981-04-10 1982-10-28 Roth Johann Electric contact,particularly for printed circuits of small electric appliances
US4511076A (en) * 1981-04-10 1985-04-16 Braun Aktiengesellschaft Method of soldering circuit boards with solder-repellent contacts
US4651123A (en) * 1984-08-06 1987-03-17 International Hydraulic Systems, Inc Linear potentiometer
EP0241874A3 (de) * 1986-04-11 1989-05-24 AT&T Corp. Gegenstand mit Temperatursensor
US4746896A (en) * 1986-05-08 1988-05-24 North American Philips Corp. Layered film resistor with high resistance and high stability
US4845839A (en) * 1988-10-31 1989-07-11 Hamilton Standard Controls, Inc. Method of making a resistive element
US5554965A (en) * 1994-11-02 1996-09-10 The Erie Ceramic Arts Company Lubricated variable resistance control having resistive pads on conductive path
US20040130432A1 (en) * 2002-08-12 2004-07-08 Alps Electric Co., Ltd. Variable-resistance element
US6891465B2 (en) * 2002-08-12 2005-05-10 Alps Electric Co., Ltd Variable-resistance element

Also Published As

Publication number Publication date
DE2116785A1 (de) 1971-12-02
IL36479A (en) 1973-06-29
GB1343843A (en) 1974-01-16
IL36479A0 (en) 1971-05-26
FR2088468A3 (de) 1972-01-07
FR2088468B3 (de) 1974-02-15
NL7104640A (de) 1971-11-15
CH525542A (de) 1972-07-15
CA938687A (en) 1973-12-18

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