JPS6216677Y2 - - Google Patents

Description

[Detailed description of the invention] The present invention is an ion sensor device using an insulated gate field effect transistor (hereinafter abbreviated as FET sensor), which eliminates alternating current induced disturbances and allows accurate ion concentration measurement at all times. The present invention relates to a sensor device.

Traditionally, this type of ion sensor device uses
For example, a structure shown in FIG. 1 is known as an FET sensor. In the figure, reference numeral 1 denotes a P-type silicon substrate, on which an N-type drain 2 and a sensor source 3 are formed. 4, 5, and 6 are the common drain layer 2, the sensor source 3, and each electrode portion of the silicon substrate 1;
Reference numeral 7 denotes a sensor gate portion, a cross section of which is shown in FIG.

As is clear from FIG. 2, the gate section 7 has a two-layer structure of a silicon oxide layer 8 and a silicon oxide layer 9 formed on the silicon substrate 1, and the sensor gate section 7 has, for example, an ion ion layer. A sensitive layer 10 is coated.

As shown in the circuit of FIG. 3, the ion sensor device consisting of the FET sensor and the liquid junction type comparison electrode configured as described above is connected to the test liquid 12 in the container 11 together with the comparison electrode 13 for keeping the potential of the electrolytic solution 12 constant. Immersed. A positive potential of a voltage source Vd is connected to the drain electrode 2 of the FET sensor, and a constant current circuit 14 is connected to the source electrode 3 to operate as a source follower circuit. With this circuit configuration, the conductivity is changed on the semiconductor surface under the gate insulating film by the interface potential between the gate insulating film and the electrolyte, and the change in the interface potential at this time is extracted as the source potential change Vs. this
Since Vs has a linear relationship with the logarithm of the ion concentration,
By measuring this Vs, the ion concentration can be measured.

However, when measuring the ion concentration in a solution using the circuit described above, the value of the source potential changes due to AC induction disturbances, such as indoor AC wiring or AC leaking through the floor entering the sensor circuit via the ground wire. It may be difficult to measure the ion concentration. Particularly high impedance, e.g. 100KΩ
When the above-mentioned small liquid junction type reference electrode is used or when the drain current is 30 μA or less, the above-mentioned alternating current induction disturbance is large and measurement is difficult in practice. For small FET sensors, this means that alternating current induction disturbances are large, and measurements are especially difficult for ultra-small FET sensors that are inserted into living organisms to measure ion concentrations in living organisms, and sometimes It may even become impossible to measure.

In order to improve the S/N ratio of the signal by removing the AC induced disturbances mentioned above, the present inventors connected the sensor circuit that comes into contact with the living body with other circuits using an isolation amplifier, and We discovered that by shielding the body and connecting it to a guard electrode, external signals, mainly alternating current, flowing through the living body would not flow to the sensor circuit, allowing accurate measurements to be taken at all times.After further study, we discovered that the guard electrode By integrally providing the ion sensor near the sensor gate, it has become possible to provide an ion sensor device that has the characteristics of an FET sensor and is free from alternating current disturbances during measurement.

Next, the ion sensor of the present invention will be explained with reference to the drawings. FIG. 4 shows the FET sensor shown in FIG. 1 in which a guard electrode 15 is integrally provided. The guard electrode 15 only needs to maintain electrical continuity with the gate 7 of the FET sensor, and its mounting position and shape can be arbitrarily selected. However, in order to achieve the characteristics of an FET sensor that is small enough to be inserted into the body, the guard electrode must also be small. Therefore, it is preferable that the guard electrode be placed as close as possible to the gate of the FET sensor and that its shape be small. Practically speaking, it is desirable that the distance between the gate and the guard electrode be 1 mm or less. Further, the shape of the guard electrode may be any shape, but in the case of the elongated FET sensor shown in FIG. 4, it is preferable to make it elongated along the shape of the sensor. The guard electrode can be made of conductive metals such as copper, aluminum, and gold; however, highly corrosion-resistant noble metals such as gold, platinum, and silver are particularly recommended for FET sensors that are inserted into living organisms. preferable. These metals can be provided on the surface of the FET sensor by known means such as vapor deposition or printing. Especially when using vapor deposition means, FETs such as Ta ₂ O ₅ and Si ₃ N ₄ are used to improve the adhesion between the metal and the FET sensor.
By providing an adhesive layer such as a chromium layer that has good adhesion to Si ₃ N ₄ and high adhesion to metal on the substrate surface, and depositing metal on the adhesive layer, the metal layer can be easily removed during measurement. Peeling can be prevented. Further, plating these metals on the metals provided by vapor deposition or the like is also a preferable method since a thick guard electrode that is less likely to be corroded by the liquid can be obtained.

The thickness of the above-mentioned metal layer is normally preferably several thousand amps or more in order to function as a guard electrode and to prevent peeling during use.

After attaching lead wires to each electrode and guard electrode of the FET sensor obtained in this way, it was embedded in a catheter to protect the bonding part and the lead wires, and measurements were taken in the living body using a liquid junction type reference electrode.
This can be done using the circuit shown in the figure.

As described above, the ion sensor device of the present invention is extremely compact by integrating the guard electrode and the FET sensor, and also uses methods such as bypassing only the AC component via the guard line of the isolation amplifier. This is extremely useful in practice as it prevents failures and allows accurate measurements to be taken at all times.

[Brief explanation of the drawing]

Figure 1 is a plan view of the FET sensor, Figure 2 is a cross-sectional view of the gate, Figure 3 is a measurement circuit using the FET sensor, and Figure 4 is a guard electrode integrated with the FET sensor. FIG. 5 is a circuit diagram using the FET sensor integrated with the guard electrode shown in FIG. 4. 2...Drain, 3...Source, 7...Gate, 15...Guard electrode.

Claims (1)

[Scope of utility model registration request] An ion sensor device comprising an insulated gate field effect transistor having a sensor gate that generates an interfacial potential according to the ion activity in an electrolyte, and a liquid junction type reference electrode, the sensor gate of the insulated gate field effect transistor An ion sensor device characterized by integrally providing a guard electrode close to the ion sensor for removing AC induced interference.