FET type sensor and a method for driving the same

Claim 2

In a field effect transistor-type sensor including an insulated gate field effect transistor device incorporated with a sensitive means for exhibiting a variation in its dielectric constant due to a physical or chemical interaction with the quantity to be detected, said sensitive means being located between the gate insulating film and the gate electrode of said field effect transistor device; the improvement comprising: an auxiliary electrode located between said gate insulating film and said sensitive means; and a resistance means connected to said auxiliary electrode and through which a DC bias voltage for stabilizing the operating point of said field effect transistor device is applied to said auxiliary electrode.

Claim 3

A field effect transistor-type sensor according to claim 1 wherein said sensitive means is a moisture sensitive means, the electrostatic capacity of which varies with the absorption and the desorption of water vapor or moisture.

Claim 4

A field effect transistor-type sensor according to claim 3, wherein said moisture sensitive means is at least one selected from the group consisting of a cellulose derivative film, a vinyl derivative film, an organic or an inorganic solid electrolyte film and a metal oxide film.

Claim 7

A field effect transistor-type sensor according to claim 1 wherein said sensitive means is a layer of dielectric material.

Claim 8

A field effect transistor type sensor according to claim 5 wherein said resistance means is connected between said gate electrode and said auxiliary electrode.

Claim 9

A field effect transistor-type sensor according to claim 6 wherein said resistance means is a fixed resistor.

Claim 10

A field effect transistor-type sensor according to claim 6 wherein the resistance value of said resistance means is substantially greater than the AC inmedance of said sensitive means at a frequency f; and further comprising means for applying a DC voltage having an AC voltage of said freguency f superposed thereon to said gate electrode; and means for detecting the amplitude of the AC component of the drain current of said field effect transistor device as a measure of the variation of the electrosatic capacity of said sensitive means.

Claim 11

A field effect transistor-type sensor comprising in combination: a semiconductor body having spaced source and drain regions formed therein adjacent one surface to define a channel region therebetween; an insulating layer covering said surface and having openings above said source and drain regions; source and drain electrodes contacting said source and drain regions, respectively, via the respective said openings; an auxiliary electrode disposed on said insulating layer over said channel region; a sensitive insulating film, which exhibits a variation in its dielectric constant due to a physical or chemical interaction with a quantity to be detected, disposed on said auxiliary electrode; a gate electrode disposed on the outer surface of said sensitive insulating film; means for applying a DC voltage having an AC voltage superimposed thereon to said gate electrode; a resistance connected between said auxiliary electrode and said gate electrode, said resistance having a value, which is substantially greater than the AC impedance of said sensitive insulating film at the frequency of said AC voltage; and means for detecting the amplitude f of the AC component of the drain current of said field effect transistor.

Claim 12

A field effect transistor-type sensor comprising in combination: a semiconductor body having spaced source and drain regions formed therein adjacent one surface to define a channel region therebetween; an insulating layer covering said surface and having openings above said source and drain regions; source and drain electrodes contacting said source and drain regions, respectively, via the respective said openings; an auxiliary electrode disposed on said insulating layer over said channel region; a sensitive insulating film, which exhibits a variation in its dielectric constant due to a physical or chemical interaction with a quantity to be detected, disposed on said auxiliary electrode; a gate electrode disposed on the outer surface of said sensitive insulating film; means for applying a DC voltage having an AC voltage superimposed thereon to said gate electrode; a resistance connected between said auxiliary electrode and said gate electrode, said resistance having a value, which is substantially greater than the AC impedance of said sensitive insulating film at the frequency of said AC voltage; and means for detecting the amplitude f of the AC component of the drain current of said field effect transistor.

Claim 13

A field effect transistor as defined in claim 9 wherein said resistance is a fixed resistor.