US2158748A - Manufacture of electrical rectifiers - Google Patents

Manufacture of electrical rectifiers Download PDF

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Publication number
US2158748A
US2158748A US181993A US18199337A US2158748A US 2158748 A US2158748 A US 2158748A US 181993 A US181993 A US 181993A US 18199337 A US18199337 A US 18199337A US 2158748 A US2158748 A US 2158748A
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blank
coating
oxide
copper
blanks
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Expired - Lifetime
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US181993A
Inventor
Philip H Dowling
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Hitachi Rail STS USA Inc
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Union Switch and Signal Inc
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Priority to US181993A priority Critical patent/US2158748A/en
Priority to GB33566/38A priority patent/GB521455A/en
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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
    • H01L21/16—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 cuprous oxide or cuprous iodide
    • H01L21/161—Preparation of the foundation plate, preliminary treatment oxidation of the foundation plate, reduction treatment
    • H01L21/164—Oxidation and subsequent heat treatment of the foundation plate
    • 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
    • H01L21/02104—Forming layers
    • H01L21/02365—Forming inorganic semiconducting materials on a substrate
    • H01L21/02518—Deposited layers
    • H01L21/02521—Materials
    • H01L21/02565—Oxide semiconducting materials not being Group 12/16 materials, e.g. ternary compounds
    • 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
    • H01L21/02104—Forming layers
    • H01L21/02365—Forming inorganic semiconducting materials on a substrate
    • H01L21/02612—Formation types
    • H01L21/02614—Transformation of metal, e.g. oxidation, nitridation
    • 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
    • H01L21/16—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 cuprous oxide or cuprous iodide
    • H01L21/161—Preparation of the foundation plate, preliminary treatment oxidation of the foundation plate, reduction treatment

Definitions

  • the blanks are then transferred immediately to a second furnace which is maintained at a temperature in the neighborhood of 550 C., and are allowed to remain in this latter furnace only for a suflicient length of time to permit them to cool down to the temperature of the second furnace.
  • the oxidized blanks are then removed from the second furnace and are suddenly cooled or quenched as by plunging the blanks into cold Water or a current of cold air.
  • rectifiers manufactured by this process exhibit the characteristic that when a voltage is applied to them in the high resistance direction, the high or blocking resistance, as it is generally termed, will decrease at first relatively rapidly and then somewhat more slowly with time until it attains an apparently stable value which may be considerably less than the initial value.
  • the stable virtual value of the reverse current when an alternating voltage is applied to the rectifier, is increased due to this effect, and this effect accordingly in some instances determines the voltage for which the rectifier is capable of effecting satisfactory rectification in service.
  • This change in blocking resistance with time is ordinarily known as creep or reverse creep, and is usually temporary in character, the apparent resistance in the reverse direction gradually returning toward its original value when the voltage is removed.
  • the blanks after being cleaned are oxidized to an equal degree on both sides by heating them in an oxidizing atmosphere at the usual oxidizing temperature long enough to form an appreciable coating of cuprous oxide on the copper, a coating of one thousandth of an inch or more in thickness generally being sufficient.
  • This preliminary coating is then removed, preferably although not necessarily, by immersing the blanks in a dilute solution of nitric acid. A 25% solution by volume or less is satisfactory for this step in the process.
  • the blanks are immersed in the nitric acid solution for such alength of time that the cuprous oxide is completely removed, but that the copper is not appreciably acted on by the acid.
  • the blanks When the oxide has been properly removed in this manner, the blanks will be left with a highly polished surface which carries the microscopic traces of the outlines of the cuprous oxide crystals of the preliminary oxide coating. It is preferable not to disturb this polished surface, but merely to thoroughly remove all traces of acid and finely divided copper brought down by ,the action of the acid.
  • the water used to wash the blanks should be reasonably free from impurities, it being preferable to use distilled water for at least a final rinsing of the blanks.
  • the blanks After the blanks have been thoroughly washed, the blanks are then oxidized a second time by any process which would yield reasonably good rectifiers without the use of the above described preliminary oxidation of the blanks, one process which is suitable for this second oxidation being the process described hereinbefore at the beginning of the specification.
  • the steps for reducing creep consist in forming on both sides of a copper blank :1 thin coating of cuprous oxide, and then removing this coating prior to subjecting the blank to a subsequent oxidizing process.
  • the process 01' preparing a copper oxide rectifier element which consists in forming on both sides of a copper blank a coating of cuprous oxide, removing this coating by immersing the blank in a solution of 25% by volume of nitric acid, ,washing the blank to remove the acid and the finely divided copper formed by the acid treatment, and then reoxidizing the blank.
  • the process 01' preparing a copper oxide rectifier element which consists in forming on both sides of a copper blank a thin coating of cuprous oxide, immersing the blank in a dilute solution of nitric acid just long enough to remove this coating and leave the blank with a highly polished surface, washing the blank in water to remove all traces of acid and finely divided copper formed by the acid treatment, and then reoxidizing the blank.

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  • Engineering & Computer Science (AREA)
  • Physics & Mathematics (AREA)
  • Condensed Matter Physics & Semiconductors (AREA)
  • General Physics & Mathematics (AREA)
  • Manufacturing & Machinery (AREA)
  • Computer Hardware Design (AREA)
  • Microelectronics & Electronic Packaging (AREA)
  • Power Engineering (AREA)
  • Thermal Sciences (AREA)
  • Chemical Treatment Of Metals (AREA)
  • Manufacture Of Switches (AREA)

Description

Patented May 16, 1939 UNITED STATES PATENT OFFICE MANUFACTURE OF ELECTRICAL RECTIFIE Philip H. Dowling, Forest Hills, Pa., assignor to The Union Switch & Signal Company, Swissvale, Pa., a corporation of Pennsylvania No Drawing. Application December 27, 1937, Serial No. 181,993
13 Claims.
neighborhood of about 1000 C. This heating of the blanks causes a layer of red or cuprous oxide to be formed on the blanks, and is continued until the cuprous oxide layer is of the desired thickness, a heating period of from 8 to 13 minutes usually being sufficient to produce an oxide layer of the desired thickness. After a sufficient amount of oxide has been formed on the blanks, the blanks are then transferred immediately to a second furnace which is maintained at a temperature in the neighborhood of 550 C., and are allowed to remain in this latter furnace only for a suflicient length of time to permit them to cool down to the temperature of the second furnace. The oxidized blanks are then removed from the second furnace and are suddenly cooled or quenched as by plunging the blanks into cold Water or a current of cold air. This leaves the blanks with an inner coating of cuprous or red oxide of copper and a thin outer coating of black oxide of copper, the oxide coating on the face which is not in contact with the contiguous face of the adjacent blank being much heavier than the oxide coating on the opposite face. Each blank is next treated to remove the black oxide from both faces of the blank, and the red oxide from the face which has the thinnest oxide coating. One process which is particularly suitable for removing the excess oxide from the blanks is described and claimed in Letters Patent of the United States No. 2,094,642, granted to me on October 5, 1937. As a last step, the exposed face of the cuprous oxide remaining on the blanks is carbonized, as by rubbing into this face powdered petroleum coke.
It is well-known that rectifiers manufactured by this process, as well as by other well-known processes, exhibit the characteristic that when a voltage is applied to them in the high resistance direction, the high or blocking resistance, as it is generally termed, will decrease at first relatively rapidly and then somewhat more slowly with time until it attains an apparently stable value which may be considerably less than the initial value. The stable virtual value of the reverse current, when an alternating voltage is applied to the rectifier, is increased due to this effect, and this effect accordingly in some instances determines the voltage for which the rectifier is capable of effecting satisfactory rectification in service. This change in blocking resistance with time is ordinarily known as creep or reverse creep, and is usually temporary in character, the apparent resistance in the reverse direction gradually returning toward its original value when the voltage is removed.
The decrease in resistance constituting the reverse creep appears to be dependent upon the physical and chemical features of the metal from which the rectifier is manufactured. However,
, certain processes of manufacture will reduce this creep, and one object of my invention is to provide such a process.
According to one process which I have found to be useful for reducing reverse creep, the blanks after being cleaned are oxidized to an equal degree on both sides by heating them in an oxidizing atmosphere at the usual oxidizing temperature long enough to form an appreciable coating of cuprous oxide on the copper, a coating of one thousandth of an inch or more in thickness generally being sufficient. This preliminary coating is then removed, preferably although not necessarily, by immersing the blanks in a dilute solution of nitric acid. A 25% solution by volume or less is satisfactory for this step in the process. The blanks are immersed in the nitric acid solution for such alength of time that the cuprous oxide is completely removed, but that the copper is not appreciably acted on by the acid. When the oxide has been properly removed in this manner, the blanks will be left with a highly polished surface which carries the microscopic traces of the outlines of the cuprous oxide crystals of the preliminary oxide coating. It is preferable not to disturb this polished surface, but merely to thoroughly remove all traces of acid and finely divided copper brought down by ,the action of the acid. The water used to wash the blanks should be reasonably free from impurities, it being preferable to use distilled water for at least a final rinsing of the blanks. After the blanks have been thoroughly washed, the blanks are then oxidized a second time by any process which would yield reasonably good rectifiers without the use of the above described preliminary oxidation of the blanks, one process which is suitable for this second oxidation being the process described hereinbefore at the beginning of the specification.
It should be pointed out that it is important that the preliminary oxidation of the blanks should form a uniform oxide coating on both sides of the blanks since otherwise, when the preliminary oxide coating is removed preparatory to the second oxidation, the copper blanks will no longer be of uniform thickness and will not be fiat. Another method which I have found to be satisfactory to reduce creep is to increase the length of time the blanks are maintained in the oxidizing furnace in the hitherto generally employed process outlined at the beginning of the specification. For example, rectifier blanks which are oxidized for approximately 20 minutes, instead of the usual time of from 8 to 13 minutes, at a temperature in the neighborhood of 1000 C. in an oxidizing atmosphere, prior to transferring them to the second or annealing furnace, show a marked improvement in so far as creep is concerned, over blanks which are oxidized in the usual way. This last mentioned process is subject to the disadvantage that the increased oxidation time increases the thickness of the oxide coating, and thereby increases the resistance of the rectifier in the low resistance direction. However, in cases where the stability of the resistance of the blanks in the high resistance direction is of more importance than the value of the resistance in the low resistance direction, this latter process is of material benefit.
Although I have herein shown and described only two processes of manufacture of electrical rectifiers embodying my invention, it is understood that various changes and modifications may be made therein within the scope of the appended claims without departing from the spirit and scope of my invention.
Having thus described my invention, what I claim is:
1. In the process preparing rectifier elements, the steps for reducing creep which consist in forming on both sides of a copper blank :1 thin coating of cuprous oxide, and then removing this coating prior to subjecting the blank to a subsequent oxidizing process.
2. The process of preparing a copper oxide rectifier element which consists in forming an oxide coating on both sides of a copper blank, removing this coating, and then forming a second oxide coating on the blank.
3. The process of preparing a copper oxide rectifier element which consists in forming a relatively thin oxide coating on both sides of a copper blank, removing this coating by the action of nitric acid, and then forming a second oxide coating on the blank.
4. The process of preparing a copper oxide rectifier element which consists in forming a relatively thin oxide coating on both sides of a copper blank, immersing the blank in a dilute solution of nitric acid long enough to completely remove this coating but not long enough to appreciably act on the copper, and then forming a. second oxide coating on the blank.
5. The process at preparing a copper oxide rectifier element which consists in forming on both sides of a copper blank a cuprous oxide coating having a thickness of approximately one thousandth of an inch, removing this coating, and then reoxidizing the blank. I
6. The process of preparing a copper oxide rectifier element which consists in forming a relatively thin cuprous oxide coating on both sides of a copper blank, chemically treating the blank to remove this coating, and .then reoxidizing the blank. 1
7. The process 01' preparing a copper oxide rectifier element which consists in forming on both sides of a copper blank a coating of cuprous oxide, removing this coating by immersing the blank in a solution of 25% by volume of nitric acid, ,washing the blank to remove the acid and the finely divided copper formed by the acid treatment, and then reoxidizing the blank.
8. The process of preparing a copper oxide rectifler element which consists in forming on both sides or a copper blank a thin coating of cuprous oxide, immersing the blank in a dilute solution of nitric acid just long enough to remove this coating and leave the blank with a highly polished surface, and then reoxidizing the blank.
9. The process 01' preparing a copper oxide rectifier element which consists in forming on both sides of a copper blank a thin coating of cuprous oxide, immersing the blank in a dilute solution of nitric acid just long enough to remove this coating and leave the blank with a highly polished surface, washing the blank in water to remove all traces of acid and finely divided copper formed by the acid treatment, and then reoxidizing the blank.
10. The process of preparing a rectifier element which consists in heating a copper blank in an oxidizing atmosphere at a temperature 01' approximately 1000 C. to form a coating of cuprous oxide on both sides of the blank, chemically treating the blank to remove all traces of the oxide coating, and then reheating the blank in an oxidizing atmosphere at a temperature oi approximately 1000 C. to form a coating of cuprous oxide on the blank.
11. The process of preparing a rectifier element which consists in heating a copper blank in an oxidizing atmosphere at a temperature of approximately 1000 C. to form a coating of cuprous oxide on both sides of the blank, removing all traces of the oxide coating by subjecting the oxidized blank to the action of aweak solution of nitric acid, reheating the blank in an oxidizing atmosphere at a temperature of 1000 C. to form a coating of cuprous oxide on the blank, cooling the oxidized blank to a temperature of approximately 550 C., and then quenching said blank.
12. The process of preparing a rectifier element which consists in heating a copper blank in an oxidizing atmosphere at a temperature of approximately 1000 C. for a predetermined period of time to form a coating of cuprous oxide on both sides of the blank, chemically treating the blank to remove the oxide, reheating the blank in an oxidizing atmosphere at a temperature oiapproximately 1000 C. for a predetermined period of time to form a coating of cuprous oxide on the blank, cooling the blank to a temperature of approximately 550 C., and then quenching said blank to cool it.
13. The process of preparing a rectifier element which consists in heating a copper blank in an oxidizing atmosphere at a temperature of approximately 1000 C. to form a coating of cuprous oxide on both sides of the blank, removing all traces oi the oxide coating by subiecting the oxidized blank to the action of a weak solution of nitric acid, washing the blank to remove all traces of the nitric acid and any finely divided copper deposited on the blank by the action of the acid, reheating the blank in an oxidizing atmosphere at a temperature of 1000 C. to form a coating of cuprous oxide on the blank, cooling the oxidized blank to a tempera ture of approximately 550 C., and then quenching said blank.
PHILIP H. DOWLING.
US181993A 1937-12-27 1937-12-27 Manufacture of electrical rectifiers Expired - Lifetime US2158748A (en)

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Application Number Priority Date Filing Date Title
US181993A US2158748A (en) 1937-12-27 1937-12-27 Manufacture of electrical rectifiers
GB33566/38A GB521455A (en) 1937-12-27 1938-11-18 Improvements relating to the manufacture of electric dry-contact rectifiers

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US181993A US2158748A (en) 1937-12-27 1937-12-27 Manufacture of electrical rectifiers

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