Etching a substrate: processes – Gas phase etching of substrate – Application of energy to the gaseous etchant or to the...
Patent
1995-03-27
1996-11-19
Tung, T.
Etching a substrate: processes
Gas phase etching of substrate
Application of energy to the gaseous etchant or to the...
204415, 205783, 216 72, 216 75, B23K 2600
Patent
active
055759300
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Field of the Invention
The electrochemical amperometric detection of redox gases such as oxygen is a well established technique, and the electrode used in such a technique is often referred to as a "Clark Electrode". In the case of an oxygen Clark Electrode, this detection is based on oxygen transport through a gas-permeable membrane to an enclosed electrolyte solution, and the subsequent reduction of oxygen dissolved in this solution, usually on a platinum or gold sensing electrode. The potential of this sensing electrode is held at negative potential compared to the potential of the electrolyte solution by use of a reference electrode, classically a silver/silver chloride electrode. A schematic diagram illustrating this conventional approach is shown in FIG. 1 of the accompanying drawings.
The response time of classical detection devices, where the sensing electrode, on which the electrochemical reaction takes place, is separated from the gas-permeable membrane by a thin (e.g. a submillimeter thick) layer of electrolyte solution, is more than 100 seconds. The response time is limited by the linear diffusion rate of the redox gas through the gas-permeable membrane and into the electrolyte solution as depicted in FIG. 1.
The present invention is based on the use of gas-permeable polymer films (for example films a few microns thick of e.g. polypropylene or polyester) metallized on one side (e.g. with gold or platinum). Such metallized films are commercially available and are currently used in the food packaging industry.
At the heart of the present invention is the use of a novel type of composite gas-permeable membrane which has been manufactured by demetallizing (e.g. by using UV excimer laser photoablation) areas of a metallized polymer film, to obtain a regular array of gas-permeable micropores each having a diameter or width of a few microns. The micropores can be in the form of microdiscs and/or microbands, since the shape of each area is of secondary importance.
2. Description of the Related Art
Our prior International application published as WO 9108474 discloses the use of photoablation for the creation of apertures in electrically insulating material when creating microelectrodes and EP-A-0494382 discloses the creation of an electrochemical cell in which photoablation is used to drill holes in an insulating substrate of the cell and to expose metallized areas on the substrate. EP-A-0494382 does disclose a gas-permeable membrane but not one subjected to subsequent thinning (e.g. by photoablation).
SUMMARY OF THE INVENTION
According to one aspect of the invention there is provided a method of manufacturing a gas-permeable membrane for an amperometric gas electrode from a polymer film metallized on one surface thereof which method comprises demetallizing areas of the metallized film to obtain a regular array of gas-permeable micropores having a diameter or width of a few microns.
The polymer film can be inherently gas-permeable when demetallized, but if made of non-permeable material can be made gas-permeable over the localised areas where demetallization is effected.
Conveniently, the regular array of micropores is obtained by excimer laser photoablation, preferably using a UV excimer laser. The metallized film is desirably of gold or platinum and the polymer film preferably is polypropylene or polyester.
Suitably each micropore comprises a porous plug replacing film material removed in the demetallizing process.
An amperometric gas electrode made by the method of the invention represents a further aspect of this invention as do disposable devices using such electrodes and incorporating enzymes or microbes for controlled biological testing methods.
BRIEF DESCRIPTION OF THE DRAWINGS
The invention will now be further described, by way of example, with reference to the accompanying drawings, in which:
FIG. 1 is a schematic view of a classical amperometric oxygen electrode,
FIG. 2 is a schematic view of a first embodiment of electrode in accordance with this inventi
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McAleer Jerome F.
Seddon Brian J.
Tietje-Girault Jordis
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