Process for producing a surface gate of an integrated electro-ch

Details Process for producing a surface gate of an integrated electro-ch Process for producing a surface gate of an integrated electro-ch

1993-05-06

1994-09-27

Quach, T. N.

Fishing, trapping, and vermin destroying

437 1, 437 59, 204416, 204418, H01L 21335, G01N 27414

Patent

active

053507010

DESCRIPTION:

BRIEF SUMMARY
FIELD OF THE INVENTION

The present invention relates to an integrated chemical sensor, comprising a field-effect transistor in which the metal gate is replaced by a selective membrane of the ionic species to be dosed and placed in contact with the solution to be analyzed.
Such sensors result from the evolution or development of the properties of the field-effect transistors comprising, in a semi-conducting substrate, two doped zones, called source and drain, and, in a layer of a dielectric material covering the semi-conductor and the doped zones, a central zone covered by a gate whose variable electrical supply makes it possible to modulate the passage of the current between the source and the drain.


DESCRIPTION OF THE RELATED ART

In publication IEEE TRANS, BIOMED. Eng. BME, 17 (1970) 70, P. BERGVELD proposed eliminating the gate and placing the surface of the dielectric material directly in contact with an electrolytic solution containing H.sup.+ and OH.sup.- ions and in which a polarization electrode is immersed. For a given polarization, a drain current is obtained, representative of the concentration of the electrolytic solution. Any modification of concentration modulates the drain current. The transistor then functions as an integrated chemical sensor.
In order to broaden the domain of application limited to the medium containing H ions, it has been proposed to interpose an iono-sensitive surface gate between the electrolytic solution and the surface of the dielectric material. Such a surface gate may comprise an organic or inorganic membrane, connected by gluing, by supply or by chemical deposit in vacuo. Such a method makes it possible to produce a surface gate specific to a product and thus capable of analysis of the latter in a specific medium.
Such a development has brought a certain advantage with respect to broadening of the range of application, but is not entirely satisfactory, due to ageing of the added organic or inorganic membrane, which lacks reliability over time.
In order to overcome this problem, it has been proposed, particularly in Application FR-2 600 212 (86-08989), to make a directly integrated sensitive surface gate with the objective of eliminating the presence of the added membrane. According to this technique, the surface gate is subjected directly to a treatment of hydroxidation, then to a treatment of impregnation with a solution of silane, followed by condensation of the silane.
This technique is satisfactory but may be considered as being of limited application, due to the necessity of having available, for the phase of impregnation, a silane in solution incorporating the group specific to the sensitivity to be given to the surface gate being treated.
Furthermore, it has been determined that such a technique does not allow maximum performance to be obtained, particularly for certain specific sensitivities, such as those to alkaline-earth species and, more particularly, to the calcium ion.
Now, such sensors are a subject of real need in numerous applications requiring electrochemical analysis, including big-medical analysis, water hardness testing, agronomy (analysis of nutritive solutions), and the environment (analysis of fresh- and sea-water).


SUMMARY OF THE INVENTION

The object of the present invention is to solve the above problem by proposing a novel process for making, on an electrochemical sensor, a selective surface gate particularly sensitive to alkaline-earth species, and more particularly, to the calcium ion, and wherein the operational characteristics of the sensors are reliable over time and allow a thorough miniaturization of sensors comprising a selective surface gate.
The invention comprises a process for making a surface gate of an integrated electrochemical sensor comprising a field-effect transistor having two doped zones, wherein the doped zones are a source and a drain, and having a surface on which a surface gate is to be formed, wherein the process comprises the steps of: subjecting the surface to a treatment of hydroxylation in order to obta

REFERENCES:
patent: 4514263 (1985-04-01), Janata
patent: 5011589 (1991-04-01), Amemiya et al.
patent: 5077229 (1991-12-01), Forlani
Shindengen, Patent Abstracts of Japan, 6, No. 195, Oct. 5, 1982; JA 57-104852.
Aktik et al., J. Appl. Phys., 51 (9), Sep. 1980, pp. 5055-5057.

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