Elsevier

Sensors and Actuators

Volume 4, 1983, Pages 291-298
Sensors and Actuators

The extended gate chemically sensitive field effect transistor as multi-species microprobe

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Abstract

This paper describes a multi-species microprobe structure for potentiometric measurements and the appropriate patterning techniques of the chemically-sensitive membranes.

The structures consists of an integrated coaxial cable whose signal line is connected to a high input impedance electrometer with the shield boot-strapped in order to reduce capacitive charging effects. The electrometer is an on-chip source follower, designed for minimum input capacitance. The coaxial line, which is an extension of the gate of the transistor, is fabricated with a triple poly-silicon NMOS process. The whole structure is compatible with current IC technology and allows integration of on-chip signal conditioning circuitry. Units of four element probes, each covered with a different membrane, have been fabricated.

One important issue in multi-sensor fabrication is the deposition and patterning technique of the membranes. A scheme has been developed which allows successive patterning of both vacuum-deposited inorganics and spin coated polymers and gels. This technique has been successfully applied for a multi-species electrode of IRO2(H+),AgCl(Cl-) LaF3(F-) and Ag.

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Based on a Paper presented at Solid-State Transducers 83, Delft, The Netherlands, May 31 - June 3, 1983.

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