Measuring and testing – Gas analysis – Detector detail
Patent
1996-05-03
1998-03-10
Brock, Michael
Measuring and testing
Gas analysis
Detector detail
338224, 4273722, G01N 2712
Patent
active
057263477
DESCRIPTION:
BRIEF SUMMARY
The present invention is directed to a method for manufacturing an element formed by semiconductor(s) to be used for detecting a gas produced by combustion, according to which at least two substances of different composition, of which at least one is a semiconductor in a powder state, are dispersed in the state of powders insoluble in a solvent to obtain a heterogeneous suspension wherein the granular state of the semiconductor substance is maintained. The heterogenous suspension is applied on an insulating substrate having a specific resistivity value of at least 10.sup.12 .OMEGA. cm, said solvent being eliminated after application of the suspension.
Such a method is known from the U.S. Pat. No. 4,381,922. According to the known method, a mixture of semiconductor powders composed of metallophthalocyanines which are organic semiconductors is prepared. These powders are poured into an organic solvent in order to modify their initial phthalocyanine structure. In order to form the element formed by semiconductor(s), the suspension thus obtained is applied on an insolating substrate provided with the necessary electrical contacts.
Such elements formed by semiconductors are used in combustion gas detectors, such as for example fire detectors or exhaust gas detectors. According to the particular choice of the type of semiconductor or of the organic semiconductor substance used, they can be rendered particularly qualified for a well determined application.
A drawback of the known semiconductors is that they present a molecular crystalline structure and that the intermolecular bonds are assured by van der Waals forces. In these circumstances, with time and even at ambient temperature, bonds can be established between the constitutive powder particles of the semiconductor powder used. This results in a natural and progressive sintering of the preparations. Over time, this phenomenon leads to a quite rapid decrease in the semiconductor's specific surface which implies a limited life span of the detectors provided with such an element formed by semiconductor(s). Indeed, the powder is dissolved in the organic solvent in order to enable the initial phthalocyanine molecular structure to be modified and to obtain a homogeneous suspension. The organic character of the deposited powders thus leads to a sintering of the phthalocyanine powder particles which provokes a decrease of the specific surface at relatively short-term. The sintering phenomenon provokes, at ambient temperature, a sticking of powders which highly reduces the sensibility to the gaseous agents of the element formed by semiconductor(s).
The object of the invention is to realise a method for manufacturing an element composed of semiconductor(s) destined to a detector for gas produced by combustion having a longer life span while not limiting its applications.
To this end, a method for manufacturing an element composed of semiconductor(s) according to the invention is characterised in that the powders are not submitted to sintering and in that at least one semiconductor substance is a mineral semiconductor. The powders no longer being submitted to sintering neither during the manufacturing of the semiconductor nor in time, a substantially greater specific surface is obtained. The nature and the structure of the semiconductor barely change any more. Since different substances are used, the sintering process caused by time appears only feebly, what sensibly lengthens the life span of the semiconductor thus realised. Moreover, the mineral or organic semiconductors are generally in the state of powders deposited without sintering, what renders them totally suitable for the method according to the invention and enables a detection at ambient temperature. In thus avoiding the emergence of a sintering process, the sensibility of the captors no longer sensibly evolves over time.
A first preferred embodiment of a method according to the invention is characterised in that a mineral semiconductor of one of the n or p types is used which leads to n-p-n or p-n-p junctio
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