Film or coating deposition and powder formation

Details Film or coating deposition and powder formation Film or coating deposition and powder formation

1998-06-15

2001-12-18

Parker, Fred J. (Department: 1762)

Coating processes

Direct application of electrical, magnetic, wave, or...

Electrostatic charge, field, or force utilized

C427S483000, C427S485000, C427S598000, C427S314000

Reexamination Certificate

active

06331330

ABSTRACT:

FIELD OF THE INVENTION
This invention relates to film or coating deposition and powder formation.
Ceramic, polymer and other films, coatings and powders are used in, for example, structural and functional electronic applications.
BACKGROUND
As background, the distinction between a film and a coating is very loosely defined and is not important to the operation or description of the present invention. In one definition, a film would be considered as a layer under about 10 &mgr;m thick, and a coating would be of greater thickness. In the present description, however, the terms are generally used interchangeably.
The following are examples of previously proposed techniques for generating such films, coatings and powders: physical vapour deposition (PVD) (a generic term given to a variety of sputtering techniques such as radio frequency (RF) sputtering, reactive magnetron sputtering and ion beam sputtering); flame spray deposition (FSD); the so-called sol-gel process; electrostatic spray pyrolysis (ESP); and chemical vapour deposition (CVD). Two particular examples are disclosed in EP-A-0 103 505 and Applied Physics Letters, Vol. 67, No. 22, November 1995, pp 3337-3339.
However, none of these techniques has been found to provide good control of the stoichiometry, morphology, microstructure and properties of multicomponent oxide films and a relatively high growth rate and deposited area of a deposited film. Also, the CVD and PVD techniques tend to need expensive equipment and highly skilled technicians for effective operation.
SUMMARY OF THE INVENTION
This invention provides a method of depositing a material onto a substrate, the method comprising the steps of:
feeding a material solution comprising one or more precursor compounds, a solvent and a pH-modifying catalyst to an outlet to provide a stream of droplets of the material solution;
generating an electric field to electrostatically attract the droplets from the outlet towards the substrate; and
providing an increase in temperature between the outlet and the substrate.
Further respective aspects of the invention (to which the various preferred features are equally applicable) are defined in the appended claims.
Embodiments of this method, which will be referred to hereinafter as electrostatic spray assisted vapour deposition (ESAVD), enable the fabrication of both thin and thick films. The technique combines the advantages of CVD and electrostatic spray deposition whilst alleviating the problems associated therewith. In comparison to other film deposition techniques, ESAVD has a high deposition rate and efficiency, and allows easy control of the stoichiometry and microstructure of the deposits. In addition, it is a simple, cheap, and low-temperature synthesis method suitable for the fabrication of a variety of different films. The method also allows the deposition of a film on large surface area substrates.
The use of the pH-modifying catalyst (which can be acid or alkali) can provide a clearer solution with increased electrical conductivity, and so can give finer droplets and thus a better coating quality.
The method can be performed so that the substrate and other pieces of apparatus are open to the surrounding ambient atmosphere, the other ambient gaseous reactants refer to any other gaseous reactants (such as oxygen, for example) that may be present in the atmosphere. In another embodiment, the method may performed within the confines of a container and said other ambient gaseous reactants may be supplied to said container, thereby to enable the deposition of a particular film.
Both simple and multicomponent ceramic oxide films have been fabricated using the above mentioned method. In one embodiment, the film may be a ceramic film such as PZT (Lead Zirconate Titanate) or a doped film such as YSZ (Yttria Stabilised Zirconia). Other films may include PbTiO
3
, BaTiO
3
, La(Sr)MnO
3
, NiO-YSZ, SnO
2
-In
2
O
3
and other Indium-Tin Oxide films. The film may also be a structural and/or functional film such as an electroceramic film.
Preferably, the droplets are charged to a voltage within the approximate range 5-30 kilovolts with respect to the substrate.
In one embodiment, the temperature increases gradually to a temperature in the approximate range 100 to 650 degrees celsius (the temperature used may depend on the type of coating). Varying the processing parameters enables the production of dense porous and/or thin/thick films all of which have good adhesion to the substrate.
Preferably, the film has a thickness between a nanometer and approximately 100 micrometers, or much thicker.
In any of the above embodiments, the catalyst may be an acid such as ethanoic acid or hydrochloric acid. In this case, the required pH may be between 2 and 5.
Alternatively, the catalyst may be an alkali such as NH
3
. In this case, the required pH may be between 9 and 12.
The invention can be particularly useful for producing polymer coatings, in which case it is preferred that the electric field is maintained during at least part of the time during which the substrate cools down after coating has been performed. This can urge the polymer into a desirable polar structure.


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patent: 5298277 (1994-03-01), Hirose
patent: 5344676 (1994-09-01), Kim et al.
patent: 43 32 890 A1 (1994-03-01), None
patent: 0 103 505 A1 (1984-03-01), None
patent: 0 252 755 (1988-01-01), None
patent: 0 252 755 A1 (1988-01-01), None
Ryu et al., “Fabrication of ZnO thin films using charged liquid cluster beam technique”, Applied Physics Letters, vol., 67, No. 22, pp. 3337-3339, Nov. 27, 1995.
Salata et al., “Fabrication of CdS nanoparticles embedded in a polymer film by gas-aerosol reactive electrostatic deposition technique”, Thin Solid Films, vol. 251, No. 1, pp. 1-3, Oct. 15, 1994.
Viguie et al., “Chemical Vapor Deposition at Low Temperatures”, Journal of the Electrochemical Society, vol. 122, No. 4, pp. 585-588, Apr. 1, 1975.
Blandenet et al., “Thin Layers Deposited by the Pyrosol Process”, Thin Solid Films, vol. 77, pp. 81-90, 1981.

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