US3862422A - Method of operation of photoconductive varistor - Google Patents

Method of operation of photoconductive varistor Download PDF

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Publication number
US3862422A
US3862422A US319346A US31934672A US3862422A US 3862422 A US3862422 A US 3862422A US 319346 A US319346 A US 319346A US 31934672 A US31934672 A US 31934672A US 3862422 A US3862422 A US 3862422A
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United States
Prior art keywords
electrodes
varistor
photoconductive
pair
dark current
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Expired - Lifetime
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US319346A
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English (en)
Inventor
Herbert R Philipp
Lionel M Levinson
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General Electric Co
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General Electric Co
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Application filed by General Electric Co filed Critical General Electric Co
Priority to US319346A priority Critical patent/US3862422A/en
Priority to NL7316788A priority patent/NL7316788A/xx
Priority to DE2363437A priority patent/DE2363437A1/de
Priority to SE7317307A priority patent/SE388711B/xx
Priority to JP48143685A priority patent/JPS4997265A/ja
Priority to GB5980673A priority patent/GB1457748A/en
Priority to FR7346760A priority patent/FR2212619A1/fr
Application granted granted Critical
Publication of US3862422A publication Critical patent/US3862422A/en
Anticipated expiration legal-status Critical
Expired - Lifetime legal-status Critical Current

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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01C—RESISTORS
    • H01C7/00—Non-adjustable resistors formed as one or more layers or coatings; Non-adjustable resistors made from powdered conducting material or powdered semi-conducting material with or without insulating material
    • H01C7/10—Non-adjustable resistors formed as one or more layers or coatings; Non-adjustable resistors made from powdered conducting material or powdered semi-conducting material with or without insulating material voltage responsive, i.e. varistors

Definitions

  • the electrical resistance between the electrodes is a non-linear function of the electrical potential applied between the electrodes and is additionally a function of the intensity of illumination of the interelectrode gap.
  • the photoconductor sensitivity is further a function of the voltage across the electrodes.
  • This invention relates to photoconductors. More particularly, this invention relates to the discovery and embodiments thereof of a photoeonductor effect in polycrystalline varistors comprising sintered bodies of a first metal oxide as a major constituent including additionally an admixture of other metal oxides and/or halides.
  • V is the voltage applied across the material
  • C is a constant which is a function of the physical dimensions of the body, its composition, and the parameters of the process employed to form the body, and
  • a is a constant for a given range of current and is a measure of the non-linearity of the resistance characteristic of the body.
  • varistor materials are silicon carbide. Silicon carbide and other non-metallic I varistor materials are characterized by having an alpha exponent of less than six. Recently, a family of polycrystalline metallic oxide varistor materials have been produced which exhibit an alpha exponent in excess of 10. These new varistor materials comprise a sintered body of zinc oxide crystal grains, including additionally an intergranular layer of other metal oxides and/or halides, as, for example, beryllium oxide, bismuth oxide, bismuth fluoride, or cobalt fluoride, and are described, for example, in U.S. Pat. No. 3,682,841, issued to Matsuoka et al., on Aug. 8, 1972 and U.S. Pat. No. 3,687,871, issued to Masuyama et al., on Aug. 29, 1972.
  • Photoconductivity of zinc oxide itself is known in the art. Photoconductivity of pure polycrystalline and monocrystalline zinc oxide was experimentally measured and reported by Harrison in 93 Phys. Rev. No. 1 at page 52 in 1954. Furthermore, photoconductivity of zinc oxide and other Group II-Group VI compounds, as for another example, cadmium sulfide, is a theoretically predictable phenomenon.
  • the photoconductivity of zinc oxide does not contribute photoconductivity to zinc oxide based polycrystalline varistors because the zinc oxide grains are relatively highlyconductive and so any radiation induced changejin resistivity of the zinc oxide grains which may occur is not observable-because of the high resistance of theintergranular material comprising oxides and/or halides ofother metals. Accordingly, any photoconductivity to be found in these polycrystalline varistors must result from photoconductivity ofthe intergranular material. Heretofore, such photoconductivity has not been observed despite experimental efforts to obtain the effect.
  • the electrodes have a gap therebetween which provides for the conduction of electrical currents from one electrode to another through a portion of the varistor material and provides for illumination of the current-carrying portion ofthe I varistor material.
  • Thepotential applied across the electrodes is selected to provide the desired photoconductor sensitivity and photocurrent magnitude.
  • FIG. 1 is a plan view of a photoconductive varistor which may be used in practicing this invention.
  • FIG. 2 is a plan view'of a modification of the photoconductive varistor of FIG. I having four electrodes disposed on a face thereof, and being adapted for use in a photodetector circuit including a dark current bucking circuit in accordance with this invention.
  • FIG. 3 is a plan view of a modification of the photoconductive varistor of FIG. 1 having coaxially configured electrodes.
  • FIG. 4 is an elevation view of a photoconductive varistor in accordance with one embodiment of this invention wherein the photoconductive varistor of FIG. 1 is provided with electrodes on both major faces thereof, whereby one pair of electrodes is shielded from energy incident on the other pair of electrodes by rial having a surface on which are disposed first and second electrodes 11 and 12. Electrodes I1 and 12 have respectively substantially parallel facing edges 13 and 14 which cooperatively define a gap 15 between electrodes 11 and 12 on the surface of polycrystalline varistor l0.
  • Varistor 10 is shown in the drawing as having a circular shaped surface and represents a disk or plinth of polycrystalline varistor material.
  • the disk or plinth shape is a convenient one to manufacture, but this invention is not so limited and other shapes, as for example, a rectangular prism shape may be employed if desired for design reasons.
  • Polycrystalline varistor disk 10 is fabricated by pressing and sintering a mixture comprising zinc oxide as a major constituent and other metal oxides and/or halides as minor constituents.
  • the varistor disk is comprised by weight of principally zinc oxide with bismuth oxide and antimony oxide as secondary constituents and smaller amounts of each of other metal oxides. This embodiment exhibited a varistor alpha exponent of 40.
  • Electrodes l1 and 12 are applied to a face of polycrystalline varistor disk 10 in a convenient manner known in the art and may, for example, be applied as silver paint or as evaporated or sputtered metals such as Aluminum, Zinc, or Platinum.
  • the spacing between parallel facing edges 13 and 14 of the electrodes is selected to determine the varistor voltage of the device.
  • the varistor voltage is accordingly a function of the width of gap 15.
  • Gap 15 also provides for illumination of the current-carrying portion of varistor disk 10.
  • B is a positive function of the intensity and frequency of electromagnetic energy illuminating gap 15, and of the electrical potential across gap 15; the other parameters being identified above.
  • the magnitude of the photocurrent generated in a photoconductive polycrystalline varistor in accordance with this invention is a function of the electrical potential between the electrodes.
  • the photosensitivity of the photoconductive varistor is also a function of the potential across the gap. Sensitivity is inversely proportional to the potential; that is, at lower voltages the ratio of dark current plus photocurrent to dark current is greater than it is at higher voltages.
  • the following table illustrates the relationship between the electrical potential across gap 15 on the one hand and photocurrent magnitude and photoconductor sensitivity on the other hand.
  • the photoconductive varistor of this invention is extremely sensitive at low operating voltages. For example, in the range 0.5 to 5 volts, the ratio of photocurrent plus dark current to dark current is on the order of 6,000. On the other hand, in this low voltage range, the photocurrent magnitude is quite small. In accordance with this invention, therefore, operation of the photoconductive varistor at low voltages is useful in applications such as precision radiation intensity measurements in which the highest sensitivity is required and in which high gain, low noise, amplifiers may be conveniently incorporated in the utilization apparatus which receives the output ofthe photoconductive varistor.
  • the table also indicates that at high applied voltages a relatively large photocurrent magnitude is obtained.
  • the sensitivity of the photoconductive varistor is greatly decreased.
  • the table indicates that at 128 volts across gap 15 the ratio of photocurrent plus dark current to dark current is two.
  • One milliampere of photocurrent is
  • operation of a photoconductive polycrystalline varistor at high voltages is useful in applications in which direct utilization of the photocurrent output of a photodetector is desired, as, for example, to operate a small motor, for automatic shutter adjustment, for example.
  • varistor disk has two pairs of electrodes disposed on a face thereof. Electrodes 11a and 12a comprise the photoconductor electrodes and operate as described above with reference to electrodes 11 and 12 of FIG. 1. Electrodes 11b and 12b are the reference electrodes. The portion of gap 15 comprising the varistor conductive path between electrodes 11b and 12b is covered with a shield member not shown for preventing radiation from impinging thereon. Accordingly, dark current plus photocurrent flows between electrodes 11a and 12a and dark current only flows between electrodes 11b and 12b. Because of the nature of the varistor material, cross currents, as, for example, between electrodes 11b and 12a, or 1111 and 12 b, will not flow.
  • This method has the advantage over the constant current source bucking method of being usable, for a given photoconductive varistor'device, at any operating voltage without need for changing components of a bucking current source.
  • This method has the advantage over the prior art chopping method of providing a DC. output signal at a higher power level for utilization.
  • FIG. 3 illustrates an alternative embodiment of the photoconductive polycrystalline varistor of this invention having coaxially disposed electrodes and comprises varistor disk 10 having circular electrode 120 and annular electrode llc disposed thereon and defining annular gap 15 therebetween.
  • the compensation method described with reference to FIG. 2 may be employed with a modification of electrode arrangement and consequent further simplification.-
  • a second pair of electrodes in the same pattern as those shown is disposed on the opposite, unseen, face of varistor disk 10, as illustrated in FIG. 4.
  • One such set of electrodes 11 and 12 as shown in FIG. 4 functions as the photoconductor electrode pair and the other 21 understood that within the scope of the appended and 22 as shown in FIG. 4 serves to provide the referclaims the invention may be practiced otherwise than is specifically described.

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  • Engineering & Computer Science (AREA)
  • Microelectronics & Electronic Packaging (AREA)
  • Physics & Mathematics (AREA)
  • Electromagnetism (AREA)
  • Thermistors And Varistors (AREA)
  • Light Receiving Elements (AREA)
  • Photometry And Measurement Of Optical Pulse Characteristics (AREA)
  • Adjustable Resistors (AREA)
US319346A 1972-12-29 1972-12-29 Method of operation of photoconductive varistor Expired - Lifetime US3862422A (en)

Priority Applications (7)

Application Number Priority Date Filing Date Title
US319346A US3862422A (en) 1972-12-29 1972-12-29 Method of operation of photoconductive varistor
NL7316788A NL7316788A (xx) 1972-12-29 1973-12-07
DE2363437A DE2363437A1 (de) 1972-12-29 1973-12-20 Verfahren zum betrieb von fotoleitenden varistoren
SE7317307A SE388711B (sv) 1972-12-29 1973-12-20 Sett att driva en fotoledande varistor
JP48143685A JPS4997265A (xx) 1972-12-29 1973-12-24
GB5980673A GB1457748A (en) 1972-12-29 1973-12-27 Method of operation of a varistor
FR7346760A FR2212619A1 (xx) 1972-12-29 1973-12-28

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
US319346A US3862422A (en) 1972-12-29 1972-12-29 Method of operation of photoconductive varistor

Publications (1)

Publication Number Publication Date
US3862422A true US3862422A (en) 1975-01-21

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US319346A Expired - Lifetime US3862422A (en) 1972-12-29 1972-12-29 Method of operation of photoconductive varistor

Country Status (7)

Country Link
US (1) US3862422A (xx)
JP (1) JPS4997265A (xx)
DE (1) DE2363437A1 (xx)
FR (1) FR2212619A1 (xx)
GB (1) GB1457748A (xx)
NL (1) NL7316788A (xx)
SE (1) SE388711B (xx)

Cited By (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4001586A (en) * 1975-05-09 1977-01-04 Plessey Incorporated Thick film sensor and infrared detector
US20070128822A1 (en) * 2005-10-19 2007-06-07 Littlefuse, Inc. Varistor and production method
US20100189882A1 (en) * 2006-09-19 2010-07-29 Littelfuse Ireland Development Company Limited Manufacture of varistors with a passivation layer
CN107037087A (zh) * 2017-05-08 2017-08-11 中国电建集团中南勘测设计研究院有限公司 一种测量水流掺气浓度的传感器及测量方法

Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3202820A (en) * 1963-01-28 1965-08-24 Barnes Eng Co Infrared detector mounting structure
US3453432A (en) * 1966-06-23 1969-07-01 Barnes Eng Co Pyroelectric radiation detector providing compensation for environmental temperature changes
US3478210A (en) * 1967-08-23 1969-11-11 Gen Electric Extended range infrared moisture gage standards
US3610931A (en) * 1969-02-11 1971-10-05 Martin G Woolfson Thermistor circuit for detecting infrared radiation

Patent Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3202820A (en) * 1963-01-28 1965-08-24 Barnes Eng Co Infrared detector mounting structure
US3453432A (en) * 1966-06-23 1969-07-01 Barnes Eng Co Pyroelectric radiation detector providing compensation for environmental temperature changes
US3478210A (en) * 1967-08-23 1969-11-11 Gen Electric Extended range infrared moisture gage standards
US3610931A (en) * 1969-02-11 1971-10-05 Martin G Woolfson Thermistor circuit for detecting infrared radiation

Cited By (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4001586A (en) * 1975-05-09 1977-01-04 Plessey Incorporated Thick film sensor and infrared detector
US20070128822A1 (en) * 2005-10-19 2007-06-07 Littlefuse, Inc. Varistor and production method
US20100189882A1 (en) * 2006-09-19 2010-07-29 Littelfuse Ireland Development Company Limited Manufacture of varistors with a passivation layer
CN107037087A (zh) * 2017-05-08 2017-08-11 中国电建集团中南勘测设计研究院有限公司 一种测量水流掺气浓度的传感器及测量方法

Also Published As

Publication number Publication date
GB1457748A (en) 1976-12-08
DE2363437A1 (de) 1974-07-04
NL7316788A (xx) 1974-07-02
FR2212619A1 (xx) 1974-07-26
SE388711B (sv) 1976-10-11
JPS4997265A (xx) 1974-09-13

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