Classifications

• • H—ELECTRICITY
  • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
  • H05B—ELECTRIC HEATING; ELECTRIC LIGHT SOURCES NOT OTHERWISE PROVIDED FOR; CIRCUIT ARRANGEMENTS FOR ELECTRIC LIGHT SOURCES, IN GENERAL
  • H05B3/00—Ohmic-resistance heating
  • H05B3/10—Heating elements characterised by the composition or nature of the materials or by the arrangement of the conductor
• • 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
  • H01C17/20—Apparatus or processes specially adapted for manufacturing resistors adapted for coating resistive material on a base by pyrolytic processes
• • 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
  • H01C7/02—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 having positive temperature coefficient
  • H01C7/021—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 having positive temperature coefficient formed with two or more layers
• • H—ELECTRICITY
  • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
  • H05B—ELECTRIC HEATING; ELECTRIC LIGHT SOURCES NOT OTHERWISE PROVIDED FOR; CIRCUIT ARRANGEMENTS FOR ELECTRIC LIGHT SOURCES, IN GENERAL
  • H05B3/00—Ohmic-resistance heating
  • H05B3/20—Heating elements having extended surface area substantially in a two-dimensional [2D] plane, e.g. plate-heater
  • H05B3/22—Heating elements having extended surface area substantially in a two-dimensional [2D] plane, e.g. plate-heater non-flexible
  • H05B3/26—Heating elements having extended surface area substantially in a two-dimensional [2D] plane, e.g. plate-heater non-flexible heating conductor mounted on insulating base
  • H05B3/265—Heating elements having extended surface area substantially in a two-dimensional [2D] plane, e.g. plate-heater non-flexible heating conductor mounted on insulating base the insulating base being an inorganic material, e.g. ceramic

Definitions

• the invention relates to a thin-film heating element, consisting of a temperature-stable, electrically insulating substrate with a thin, electrically conductive, mutually compensating foreign atoms, each consisting of at least one acceptor-forming element and at least one donor-forming element doped metal oxide layer, which is provided with connection electrodes .
• An acceptor is a local defect in a semiconductor that can pick up an electron or equivalent to give up a defect electron.
• the associated electronic energy level is in the forbidden band, whereby the exact position together with the cross-section for electrons determines the effect of the acceptor.
• the host lattice atom is replaced by an atom that has one valence electron less than the host lattice atom.
• a donor is an impurity in a semiconductor that can donate an electron located at it.
• the associated electronic energy level is in the forbidden band, the exact position and the cross-section for electrons and defect electrons determining the effect of the donor.
• a host lattice atom is replaced by an atom that has one valence electron more than the host lattice atom.
• electrically conductive, thin metal oxide layers on a temperature-stable, electrically insulating substrate serve as resistance heaters in devices to be heated, for example heated glass panes (eg car windows) or warming plates or similar devices can be used, these thin layers being usable as heaters in a temperature range up to 500 ° C.
• glass or ceramic substrates are coated in a pyrolytic process from solutions which, for example, the chlorides, bromides, iodides, sulfates, nitrates, oxalates or acetates of tin, indium, cadmium, tin and antimony, tin and indium or tin and cadmium with or contain no dopant additives such as tin, iron, copper or chrome.
• the layers formed by pyrolytic deposition themselves then consist of the corresponding metal oxide (s).
• thin-film heating elements that reach surface temperatures higher than 500 ° C.
• US Pat. No. 2,564,709 discloses thin, electrically conductive indium oxide layers which are doped with each other in pairs to compensate for foreign atoms composed of at least one acceptor and at least one donor-forming element in an amount of up to 10 atom%, however, the amounts of the acceptor and donor-forming elements each differ by more than 10%.
• This known layer material has proven to be insufficiently stable at higher surface temperatures.
• the invention has for its object to provide a thin-film heating element that is stable up to temperatures of over 600 ° C and high enough to operate it on mains voltage.
• the metal oxide layer is doped with amounts of the mutually compensating foreign atoms which differ by no more than 10% in an amount of up to 10 atom% each.
• the invention is based on the knowledge that with thin, electrically conductive metal oxide layers on appropriately temperature-stable substrates, surface temperatures of 1000 ° C. at power densities of more than 10 W / cm2, corresponding to current densities of more than 1000 A / cm2 with a low positive temperature coefficient of electrical resistance ⁇ ⁇ 3.10 ⁇ 4 K ⁇ 1 can be achieved if the metal oxide layers are doped with both relatively high and approximately equal amounts of mutually compensating foreign atoms each consisting of at least one element forming an acceptor and at least one element forming a donor.
• the relatively high doping leads to reduced electron mobility and thus to relatively high resistance values.
• the low positive temperature coefficient of the electrical resistance and its temperature stability of the layers according to the invention are attributed to the pairwise compensation of the elements forming the acceptors and donors.
• SnO2 layers are used as metal oxide layers on hard glass, quartz glass or glass ceramic substrates for the construction of the heating element.
• the metal oxide layers are not to be considered independently of the substrate, in particular the thermal stability, the thermal expansion coefficient of the substrate material and also a possible diffusion of foreign substances from the substrate into the metal oxide layer.
• quartz glasses and glass ceramics with their extremely low expansion coefficients ( ⁇ 0/1000 ⁇ 0.5 or 0.1.10 ⁇ 6 K sich1) are suitable for a coating with doped SnO2 or In2O3 layers ( ⁇ ⁇ 4.10 ⁇ 6 K ⁇ 1) have proven to be equally suitable substrates, such as hard glasses with an expansion coefficient ⁇ ⁇ 3 to 4.10 ⁇ 6 K ⁇ 1.
• a SnO2 layer is doped with indium, boron and / or aluminum as the acceptor-forming element (s) and with antimony and / or fluorine as the donor-forming element (s).
• the metal oxide layer is doped with at least one element which forms an acceptor and a donor in an amount of 3 to 5 atom% each.
• the advantages achieved with the invention consist in particular in the fact that heating elements are created which can be switched on and off suddenly, which, due to their low heat capacity, have already reached their final temperature after a relatively short period ( ⁇ 4 to 5 min), and which have been switched off cool down the power supply just as quickly.
• Another advantage is that the metal oxide layers according to the invention are optically clear, free from streaks, streak-free and crack-free and have a high degree of transparency. These properties of the metal oxide layers according to the invention have a particularly advantageous effect if transparent substrates are used; For example, a bread roaster can be equipped with transparent heating disks, with which the browning of the toast can be easily checked visually.
• the heating elements according to the invention retain unchanged properties in air for several 1000 operating hours and switching cycles. This also applies to large-area heating elements of more than 1dm2. Another advantage is that the sheet resistance of the layers according to the invention can be selected so that they can be operated directly from the mains voltage after electrodes, for example metal layer electrodes, have been attached.
• Layers according to the invention were produced by spray pyrolysis from a solution.
• 9.6 g of SbCl3 and 9.3 g of InCl3 were dissolved as dopants in a solution of 100 ml of SnCl4 in 500 ml of butyl acetate.
• This dopant addition corresponds to a doping of 4.5 atom% Sb and 4.5 atom% In.
• SnO2 layers with a density of free charge carriers of N ⁇ 6.1020 / cm3 were by spraying the above solution as a fine aerosol on about 500 ° C hot substrates with a dimension of 15 ⁇ 15 cm2 from a hard sprayed on glass as it is commercially available under the trademarks Pyrex or Tempax.
• the layers had a layer thickness of 0.1 ⁇ m and, after an annealing process (forming process) in air at a temperature of 600 ° C. over a period of 1 h, a sheet resistance of 160 ⁇ .
• the metal oxide layers produced in the context of the invention have surface resistances of between approximately 20 and 500 ⁇ with layer thicknesses in the range from 0.05 to 0.5 ⁇ m.
• substrates with a dimension of 15 ⁇ 15 cm2 were further coated from glass ceramic with SnO2 layers with a thickness of 0.3 ⁇ m. These layers also had a stable sheet resistance of ⁇ 60 ⁇ after a formation process at a temperature of ⁇ 600 ° C for a period of ⁇ 1 h.
• Metal-layer electrodes were also attached to the substrates coated in this way, and electrically heated hot plates were built from these heating elements, which were operated at a mains voltage of 220 V with a power of 800 W and a surface temperature of 600 C.
• the electrical resistance of the layers was unchanged after a 200 switch-on and switch-off cycle. This heating element was still operational even with an output of 1.1 kW.
• Quartz glass tubes can e.g. use as a heat exchanger in instantaneous water heaters, in coffee machines or generally as a heat exchanger in professional applications.
• While continuous operation of the heating elements up to a recrystallization temperature of around 700 ° C is possible on glass ceramic substrates, operating temperatures of 1000 ° C can be achieved on quartz glass tubes, quartz glass rods or quartz glass plates. For example, a 1 dm2 quartz glass plate with an area resistance of R 37 ⁇ was operated at this temperature for a period of 1000 h.
• Heating elements with plate-shaped substrates can be used as heating disks for toasters, heating or hot plates, hot plates, table ovens, irons, as underfloor heating in heatable thermos jugs or similar devices.
• Heating elements with tubular substrates can be used as heat exchangers for instantaneous heaters, coffee machines, dishwashers, washing machines, tumble dryers, room air heaters, hair dryers or similar devices.
• Heating elements with rod-shaped or tubular substrates can be used, for example, as infrared radiators or radiation ovens.

Landscapes

• Engineering & Computer Science (AREA)
• Microelectronics & Electronic Packaging (AREA)
• Ceramic Engineering (AREA)
• Manufacturing & Machinery (AREA)
• Chemical & Material Sciences (AREA)
• Physics & Mathematics (AREA)
• Electromagnetism (AREA)
• Resistance Heating (AREA)
• Surface Heating Bodies (AREA)

Applications Claiming Priority (2)

Publications (3)

Family

ID=6321510

Family Applications (1)

Country Status (4)

Cited By (8)

Families Citing this family (37)

Family Cites Families (6)

• 1987
  • 1987-02-21 DE DE19873705639 patent/DE3705639A1/de not_active Withdrawn
• 1988
  • 1988-02-16 EP EP88200279A patent/EP0280362B1/fr not_active Expired - Lifetime
  • 1988-02-16 DE DE3889359T patent/DE3889359D1/de not_active Expired - Fee Related
  • 1988-02-18 JP JP63034117A patent/JP2616947B2/ja not_active Expired - Lifetime
  • 1988-02-22 US US07/158,522 patent/US4889974A/en not_active Expired - Fee Related

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