Method of manufacturing miniaturized components of chemical and

Details Method of manufacturing miniaturized components of chemical and Method of manufacturing miniaturized components of chemical and

1993-01-07

1995-02-28

Niebling, John

Chemistry: electrical and wave energy

Apparatus

Electrolytic

204403, 204414, 427534, 427289, 427290, 427307, G01N 2726

Patent

active

053934016

DESCRIPTION:

BRIEF SUMMARY
BACKGROUND OF THE INVENTION

The invention concerns a method of manufacturing supports for miniaturized components of sensors that detect chemicals and biologicals by means of ion-selective membranes. The invention also concerns a method that employs the aforesaid supports to manufacture chemical and biological detection components and vertical ion-selective field-effect transistors (VISFET's). Finally, the invention concerns the chemical and biological detection sensor components manufactured by the aforesaid methods.
The manufacture of very small versions of microsensors that operate on the principle of ion-selective electrodes (ISE's) without liquid interior electrolytes is known. Electrodes with liquid membranes can be employed for example in accordance with what is called the coated-wire principle (P. Bergveld, "Development and Application of Chemical Sensors in Liquids," p. 403, in Sensors and Sensory Systems for Advanced Robots, Berlin and Heidelberg, Springer, 1988). A fine silver wire is coated with what is called an ion-selective liquid membrane. Such an electrode is tiny enough to be inserted in the blood vessels. Coated-film electrodes are manufactured by a similar process. The simplest coated-film electrode is a substrate of plastic covered with a thin coat of silver or silver chloride over silver and then with the ion-selective liquid membrane. Coated-film electrodes of this type can also be manufactured on a silicon substrate instead of a plastic substrate.
The manufacture of ion-selective liquid membranes is also known in itself. Such membranes can consist for example of a polyvinyl-chloride matrix that includes both a softener and an ionophore, an electrically active substance that dictates the membrane's ion selectivity. The material is dissolved and poured, and the solvent evaporates, leaving a solidified membrane. Examples will be evident from the sales literature Selectophore Inonophores for Ion-Selective Electrodes, published by Fluka Feinchemikalien GmbH, Neu-Ulm.
There are drawbacks, however, to known miniaturized sensors that operate on the ISE principle. First, the membrane adheres very poorly to the wire or layer of silver. Again, a phenomenon called bleed leads to impoverishment of the ionophore in the membrane. Electrochemical properties are lost and the change in composition can even impair the biocompatibility of a membrane intended for medical applications.
The same problems occur when ion-selective liquid membranes are employed at the gates of ion-selective field-effect transistors (ISFET's). The literature cites attempts to solve the adhesion problem with nets of polyimide and anisotropically etched silicon lids with narrow openings (Gopel, Hesse, and Zemel, eds., Sensors, Weinheim, VCH, 1989, Vol. 1, Chap. 4, pp. 97-99). All that the nets do, however, is solve the adhesion problem. The silicon lid is very difficult to position properly in areas measuring less than 0.1 mm across.
Integrating an ion-selective sensor component into an integrated circuit leads to additional problems relating to encapsulation. The silicon chip is tiny enough to confine the active surface of the membrane to the immediate vicinity of the fine bond filaments that electrically connect the chips to the sensor-housing contacts.
The literature reports attempts to solve the problem by positioning the contacts on the rear of the transistor (cf. e.g. Ewald, van den Berg, and Grisel, "Technology for Backside Contacted pH-sensitive ISFETs Embedded in a p-Well Structure," Sensors and Actuators 1 (1990), 335-40).
One drawback to such an approach is that, since the side of the chip with the delicate semiconducting signal-electronics structures is separated from the fluid being analyzed only by a thin inactivating layer, even a very slight contamination of the semiconductor structures will render the sensing electronics unusable. The aforesaid encapsulating problem in particular will occur not only in conjunction with ion-selective sensor components with liquid membranes but with those with other types of mem

REFERENCES:
patent: 4645562 (1987-02-01), Liao et al.
patent: 4874499 (1989-10-01), Smith et al.
patent: 5111221 (1992-05-01), Fare et al.
patent: 5183549 (1993-02-01), Joseph et al.

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