GB2136451A - Depositing porous films by evaporating material on to a surface - Google Patents

Depositing porous films by evaporating material on to a surface Download PDF

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Publication number
GB2136451A
GB2136451A GB08404775A GB8404775A GB2136451A GB 2136451 A GB2136451 A GB 2136451A GB 08404775 A GB08404775 A GB 08404775A GB 8404775 A GB8404775 A GB 8404775A GB 2136451 A GB2136451 A GB 2136451A
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United Kingdom
Prior art keywords
mesh
film
porous
deposited
depositing
Prior art date
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Granted
Application number
GB08404775A
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GB8404775D0 (en
GB2136451B (en
Inventor
Gerald Herbert Swallow
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
General Electric Co PLC
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General Electric Co PLC
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Priority claimed from GB838306718A external-priority patent/GB8306718D0/en
Application filed by General Electric Co PLC filed Critical General Electric Co PLC
Priority to GB08404775A priority Critical patent/GB2136451B/en
Publication of GB8404775D0 publication Critical patent/GB8404775D0/en
Publication of GB2136451A publication Critical patent/GB2136451A/en
Application granted granted Critical
Publication of GB2136451B publication Critical patent/GB2136451B/en
Expired legal-status Critical Current

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    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C14/00—Coating by vacuum evaporation, by sputtering or by ion implantation of the coating forming material
    • C23C14/04—Coating on selected surface areas, e.g. using masks
    • C23C14/042—Coating on selected surface areas, e.g. using masks using masks
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N27/00—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means
    • G01N27/02—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating impedance
    • G01N27/22—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating impedance by investigating capacitance
    • G01N27/226—Construction of measuring vessels; Electrodes therefor

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  • Chemical & Material Sciences (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Electrochemistry (AREA)
  • Physics & Mathematics (AREA)
  • Health & Medical Sciences (AREA)
  • Life Sciences & Earth Sciences (AREA)
  • Analytical Chemistry (AREA)
  • Biochemistry (AREA)
  • General Health & Medical Sciences (AREA)
  • General Physics & Mathematics (AREA)
  • Immunology (AREA)
  • Pathology (AREA)
  • Engineering & Computer Science (AREA)
  • Materials Engineering (AREA)
  • Mechanical Engineering (AREA)
  • Metallurgy (AREA)
  • Organic Chemistry (AREA)
  • Physical Vapour Deposition (AREA)

Abstract

The material, e.g. gold, is evaporated onto the surface through a mesh. The film may be at least one of the water vapour porous electrodes provided on opposite faces of a slab of hygroscopic dielectric material to form a capacitor humidity sensor.

Description

SPECIFICATION Method of depositing porous films This invention relates to methods of depositing porous films.
In order for a deposited film of material to be porous it is necessary for the film to be thin. At the same time, the film will normally be required to be of sufficient thickness to constitute a substantially continuous film, for example, so as to provide an equipotential surface where, as is frequently the case, the film consists of electrically conductive material and constitutes an electrode of a device e.g a capacitor.
It is an object of the present invention to provide a method of depositing a porous film which facilitates the meeting of these two conflicting requirements.
According to the present invention a method of depositing a porous film of material onto a surface comprises evaporating the material onto the surface through a mesh.
The method has the advantage that a high degree of control may be exerted since the porosity can be controlled not only by controlling the quantity of deposited material, but also by choice of the mesh size and distance between the mesh and the surface.
One particular application of the invention is in the construction of humidity sensors of the kind comprising a capacitor comprising a slab of hygroscopic dielectric material provided with electrodes on its opposite faces at least one of which is porous to water vapour.
In such a device the porous electrode suitably consists of gold because of its chemical stability.
One method in accordance with the invention will now be described by way of example.
The method is used to form a porous gold electrode of a capacitor humidity sensor of the kind mentioned above.
The deposition is carried out in a conventional vacuum evaporator of the kind used widely in the manufacture of semi conductor and thin film circuits.
The gold to be deposited is placed in the furnace in a boat and the surface on which the gold is to be deposited is disposed horizontally, face down, about 1 2 centimetres above the boat.
The surface will normally be masked to restrict deposition to selected areas of the surface by a reticle plate or by a mask provided on the surface by known photolithographic techniques.
Between the boat and the surface, spaced 2 millimetres from the surface, there is disposed a stainless steel wire mesh of size 1 25 meshes to the centimetre, the mesh being held in a suitable frame.
Deposition of the film is effected by vapourising the gold by boiling, deposition of a satisfactory electrically conductive film, porous to water vapour, typically taking about half a minute.
The deposited film is found to be of smoothly varying thickness with the maximum thickness at points corresponding to the centres of the holes in the mesh and minimum thickness along lines corresponding to the centres of the wires of the mesh. The porosity of the film is ensured by the thinner areas, but at the same time the thinner areas are of restricted area and connected by relatively thick areas so that the film exhibits overall good electrical conductivity.
It will be appreciated that the porosity and electrical conductivity of the film may be controlled by choice of the mesh size and spacing of the mesh from the surface. Thus, in generai, the difference in thickness of the thinner and thicker areas may be increased by reducing the spacing or increasing the mesh size. However for the best results a mesh of size not less than 50 meshes to the centimetre is used and the spacing between the mesh and the surface is not more than 3 millimetres. It will be understood that the choice of a suitable size for the area of the source of material to be deposited will depend on the area of the surface on which material is to be deposited.However, it is pointed out that in general the source should have a sufficiently large area to avoid parts of the surface on which material is to be deposited being totally screened from the source by the wires of the mesh so that virtually no material is deposited on such parts.
1. A method of depositing a porous film of material onto a surface comprising evaporating the material onto the surface through a mesh.
2. A method according to Claim 1 wherein said surface is disposed substantially horizontally, face down, above a source of said material, said mesh being positioned between the surface and the source substantially parallel to and adjacent said surface.
3. A method according to Claim 1 or Claim 2 wherein said material is an electrically conductive material.
4. A method according to Claim 3 wherein said material is gold.
5. A method according to any one of the preceding claims wherein said mesh is a metal mesh.
6. A method according to Claim 5 wherein said mesh is a stainless steel mesh.
7. A method according to any preceding claim wherein the mesh has not less than 50 meshes to the centimetre.
8. A method according to any preceding claim wherein the mesh is spaced from the surface by a distance not greater than 3 millimetres.
9. A method of depositing a porous film onto a surface substantially as hereinbefore described by way of example.
10. A porous film produced by a method according to any one of the preceding claims.
**WARNING** end of DESC field may overlap start of CLMS **.

Claims (11)

**WARNING** start of CLMS field may overlap end of DESC **. SPECIFICATION Method of depositing porous films This invention relates to methods of depositing porous films. In order for a deposited film of material to be porous it is necessary for the film to be thin. At the same time, the film will normally be required to be of sufficient thickness to constitute a substantially continuous film, for example, so as to provide an equipotential surface where, as is frequently the case, the film consists of electrically conductive material and constitutes an electrode of a device e.g a capacitor. It is an object of the present invention to provide a method of depositing a porous film which facilitates the meeting of these two conflicting requirements. According to the present invention a method of depositing a porous film of material onto a surface comprises evaporating the material onto the surface through a mesh. The method has the advantage that a high degree of control may be exerted since the porosity can be controlled not only by controlling the quantity of deposited material, but also by choice of the mesh size and distance between the mesh and the surface. One particular application of the invention is in the construction of humidity sensors of the kind comprising a capacitor comprising a slab of hygroscopic dielectric material provided with electrodes on its opposite faces at least one of which is porous to water vapour. In such a device the porous electrode suitably consists of gold because of its chemical stability. One method in accordance with the invention will now be described by way of example. The method is used to form a porous gold electrode of a capacitor humidity sensor of the kind mentioned above. The deposition is carried out in a conventional vacuum evaporator of the kind used widely in the manufacture of semi conductor and thin film circuits. The gold to be deposited is placed in the furnace in a boat and the surface on which the gold is to be deposited is disposed horizontally, face down, about 1 2 centimetres above the boat. The surface will normally be masked to restrict deposition to selected areas of the surface by a reticle plate or by a mask provided on the surface by known photolithographic techniques. Between the boat and the surface, spaced 2 millimetres from the surface, there is disposed a stainless steel wire mesh of size 1 25 meshes to the centimetre, the mesh being held in a suitable frame. Deposition of the film is effected by vapourising the gold by boiling, deposition of a satisfactory electrically conductive film, porous to water vapour, typically taking about half a minute. The deposited film is found to be of smoothly varying thickness with the maximum thickness at points corresponding to the centres of the holes in the mesh and minimum thickness along lines corresponding to the centres of the wires of the mesh. The porosity of the film is ensured by the thinner areas, but at the same time the thinner areas are of restricted area and connected by relatively thick areas so that the film exhibits overall good electrical conductivity. It will be appreciated that the porosity and electrical conductivity of the film may be controlled by choice of the mesh size and spacing of the mesh from the surface. Thus, in generai, the difference in thickness of the thinner and thicker areas may be increased by reducing the spacing or increasing the mesh size. However for the best results a mesh of size not less than 50 meshes to the centimetre is used and the spacing between the mesh and the surface is not more than 3 millimetres. It will be understood that the choice of a suitable size for the area of the source of material to be deposited will depend on the area of the surface on which material is to be deposited.However, it is pointed out that in general the source should have a sufficiently large area to avoid parts of the surface on which material is to be deposited being totally screened from the source by the wires of the mesh so that virtually no material is deposited on such parts. CLAIMS
1. A method of depositing a porous film of material onto a surface comprising evaporating the material onto the surface through a mesh.
2. A method according to Claim 1 wherein said surface is disposed substantially horizontally, face down, above a source of said material, said mesh being positioned between the surface and the source substantially parallel to and adjacent said surface.
3. A method according to Claim 1 or Claim 2 wherein said material is an electrically conductive material.
4. A method according to Claim 3 wherein said material is gold.
5. A method according to any one of the preceding claims wherein said mesh is a metal mesh.
6. A method according to Claim 5 wherein said mesh is a stainless steel mesh.
7. A method according to any preceding claim wherein the mesh has not less than 50 meshes to the centimetre.
8. A method according to any preceding claim wherein the mesh is spaced from the surface by a distance not greater than 3 millimetres.
9. A method of depositing a porous film onto a surface substantially as hereinbefore described by way of example.
10. A porous film produced by a method according to any one of the preceding claims.
11. A humidity sensor comprising a slab of hygroscopic dielectric material provided with electrodes on its opposite faces at least one of which comprises a porous film of material deposited by a method according to any one of Claims 1 to 9.
GB08404775A 1983-03-11 1984-02-23 Depositing porous films by evaporating material on to a surface Expired GB2136451B (en)

Priority Applications (1)

Application Number Priority Date Filing Date Title
GB08404775A GB2136451B (en) 1983-03-11 1984-02-23 Depositing porous films by evaporating material on to a surface

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
GB838306718A GB8306718D0 (en) 1983-03-11 1983-03-11 Depositing porous films
GB08404775A GB2136451B (en) 1983-03-11 1984-02-23 Depositing porous films by evaporating material on to a surface

Publications (3)

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GB8404775D0 GB8404775D0 (en) 1984-03-28
GB2136451A true GB2136451A (en) 1984-09-19
GB2136451B GB2136451B (en) 1986-06-25

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Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0465973A1 (en) * 1990-07-02 1992-01-15 Xerox Corporation Plywood effect suppression in photosensitive imaging members
FR2750494A1 (en) * 1996-07-01 1998-01-02 S P S I Soc High sensitivity capacitive humidity sensor

Citations (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB1051251A (en) *
GB570200A (en) * 1941-12-23 1945-06-27 Cinema Television Ltd Improvements in or relating to methods of coating surfaces by evaporation
GB654708A (en) * 1948-07-03 1951-06-27 Emi Ltd Improvements relating to the production of etched glass surfaces
GB712105A (en) * 1951-05-04 1954-07-21 Nat Res Dev Improvements in or relating to deposition of films and coatings
GB1006076A (en) * 1961-04-25 1965-09-29 Emi Ltd Improvements in or relating to methods of forming a pattern of conducting material ona substantially insulating support
GB1418644A (en) * 1971-12-03 1975-12-24 Bosch Gmbh Robert Metal coating

Patent Citations (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB1051251A (en) *
GB570200A (en) * 1941-12-23 1945-06-27 Cinema Television Ltd Improvements in or relating to methods of coating surfaces by evaporation
GB654708A (en) * 1948-07-03 1951-06-27 Emi Ltd Improvements relating to the production of etched glass surfaces
GB712105A (en) * 1951-05-04 1954-07-21 Nat Res Dev Improvements in or relating to deposition of films and coatings
GB1006076A (en) * 1961-04-25 1965-09-29 Emi Ltd Improvements in or relating to methods of forming a pattern of conducting material ona substantially insulating support
GB1418644A (en) * 1971-12-03 1975-12-24 Bosch Gmbh Robert Metal coating

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0465973A1 (en) * 1990-07-02 1992-01-15 Xerox Corporation Plywood effect suppression in photosensitive imaging members
FR2750494A1 (en) * 1996-07-01 1998-01-02 S P S I Soc High sensitivity capacitive humidity sensor

Also Published As

Publication number Publication date
GB8404775D0 (en) 1984-03-28
GB2136451B (en) 1986-06-25

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