JPH0421815B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an ion sensor using a gate FET. Forming an ion-sensitive film on the gate insulating film of an insulated gate FFT creates a so-called ion-sensitive field effect transistor (after Ion Sensitive FET).
It is well known that it becomes an ISFET).
Its structure is shown in FIGS. 1a and 1b. Figure a is a cross-sectional view,
Figure b is a top view. In the figure, 101 is a P-type semiconductor substrate, 102 is a gate insulating film, 103 is a source, 104 is a drain, 105 is a field insulating film, 106 is an ion sensitive film, 107 is a source electrode, 108 is a drain electrode, 109 is a source and This is a contact hole for the drain. FIG. 2 is a conceptual diagram when such an ISFET is used. The ISFET is immersed in a solution 201, and a reference potential is applied to the solution by a battery 202 and a reference electrode 203. Further, the substrate 101 and the source 103 are normally set to the same potential. At this time, an electric double layer is formed on the surface of the ion-sensitive membrane,
The potential difference generated there changes depending on the ion concentration of the solution. In other words, on the surface of the ion-sensitive membrane,
This creates a battery whose electromotive force changes depending on the ion concentration. Therefore, changes in ion concentration can be read as changes in current ID between the source and drain. However, when actually performing measurements using the apparatus shown in Figure 2, in order to remove unnecessary current (noise current) flowing between the reference electrode, source, drain, and substrate, all parts other than the ion-sensitive membrane that are in contact with the solution ( (including wiring) must be covered with a thick insulating film. This film also serves to prevent parasitic MOST from occurring on the ISFET surface. In ISFETs using ordinary silicon bulk crystals, the surface of the substrate is inevitably exposed when the chip is separated, so after the chip is made, it is necessary to cover the entire surface with a thick insulating film, leaving only the ion-sensitive film and electrode terminals. However, it is not easy to produce a thick insulating film with high mechanical strength using a method suitable for mass production with a high yield. In order to eliminate these drawbacks, a silicon single crystal thin film is formed on a sapphire substrate .
Saphire, called SOS board), and ISFET
A method was proposed to make it. The structure of the ISFET in this case is shown in FIGS. 3a and 3b. Figure a shows a cross-sectional view, and figure b shows a top view. In FIGS. 3a and 3b, 301 is a sapphire substrate, and 302 is a silicon single crystal thin film. As is clear from the figure, since the ISFET is formed on a silicon thin film separated into islands, the silicon substrate is not exposed even when it is made into a chip. Therefore, in order to prevent the above-mentioned unnecessary current and parasitic MOST, it is sufficient to cover only the top surface of the ISFET.
Therefore, the manufacturing technology is also very simple and the yield is improved. However, 1. ISFET characteristics change due to heating during the formation of a thick insulating film and the impact of charged particles and X-rays. Additionally, when peripheral circuits such as ISFET amplifier circuits are incorporated on a chip, their characteristics change when the insulating film is formed. 2. Since the ISFET itself is immersed in a solution, the characteristics of the gate oxide film of the ISFET and the FETs that make up the peripheral circuit are affected by the ions to be measured (Na ⁺ , K ^+, etc.), making it impossible to obtain long-term stability. There are drawbacks such as, and solutions to these drawbacks have been awaited. An object of the present invention is to provide an ion sensor that improves these drawbacks.According to the present invention, a metal gate is provided on the gate insulating film of an insulating film gate field effect transistor, and an ion-sensitive film is provided on the extension wiring of the metal gate. The field effect transistor and the ion sensitive membrane portion are separated by an extended wiring portion, each formed as a separate chip, and electrically connected to each other by each extended wiring portion. A metal gate is provided on the gate insulating film of the ion sensor and the plurality of field effect transistors, one end of which is separated from the transistor by a metal wiring. This is an ion sensor in which different types of ion-sensitive membranes are formed on the ion-sensitive membranes collected in a small area, and the field-effect transistor and the ion-sensitive membrane portion are separated by a metal wiring portion, and each is formed as a separate chip. There is obtained an ion sensor characterized in that the respective wiring portions are connected via means for electrically connecting each other. The contents of the present invention will be specifically explained below using the drawings. Figures 4a, b, and c are examples of the ion sensor according to the present invention. Figure a is a top view of an ion sensor using an SOS substrate, and Figures 4b and c are A-A', B-
FIG. Figure b shows the FET part, c
The figure shows the sensitive membrane portions, which are separated or connected at 402. Separate connections can be made by taking lead wires from the FET side and the sensitive membrane and connecting them using a socket or the like. In the figure, 401 is a metal electrode formed on the gate insulating film of the FET and wired in a desired shape and at a desired position. A thin film of Al or polysilicon is used as the metal electrode. The ion sensitive film 106 is formed at the tip of these metal thin films. Since an ISFET with this structure can be used by immersing only the part with the sensitive film in a solution, there is no need to provide a thick insulating film on the ISFET itself or its peripheral circuitry, and the ISFET and its peripheral circuitry are
Not affected by negative effects such as Na ⁺ and K ⁺ . In this example, both the FET and the ion-sensitive part are formed on the sapphire substrate, but if such a structure is used, there is no difference in the ease of manufacturing the FTT even if bulk crystal is used, and the ion-sensitive film can also be easily fabricated. It may be formed not only on silicon or sapphire but also on any insulator. However, when using a silicon substrate, it is natural to form an insulating film on its surface and then form metal wiring and an ion-sensitive film thereon. FIG. 5 is an example of an application of the present invention. In this figure, 501 to 505 are for signal reading.
It is a FET. 507 is common source, 508~5
12 is a read terminal. Furthermore, the gate wiring of each FET is gathered into a small area 506 via a separation/connection portion 513, and different types of ion-sensitive films are provided for each. Arrays of such ion-sensitive membranes are made on a microscopic area on silicon or an insulating substrate such as sapphire, so by appropriately processing the shape of the silicon or sapphire, they can be directly implanted into a living body or used in a subject. It can be used even when there is only a very small amount of
A device with this configuration can simultaneously collect information about various ions at almost one point. Also
Manufacturing is easy because the FET section and the sensitive membrane can be made on separate chips, and if one breaks down, all you have to do is replace it. This has not been possible with conventional ISFETs that use large glass ion electrodes or have an ion-sensitive film formed directly on the gate insulating film of the FET. This was made possible for the first time by the structure of the present invention, in which the FET and the sensitive membrane are provided in separate locations, and they are separated and connected. Note that it is desirable that the wiring connecting the gate electrode and the ion sensitive part be electrically shielded. Note that Fig. 5 shows an example in which all FETs are sensitive to ions, but Fig. 6 shows an example in which all FETs are sensitive to ions, but in Fig. 6 they are not sensitive to ions as a means to obtain a reference signal.
This is an example in which a FET 602 is provided. 60 in the figure
1 has a material such as CDS that is not sensitive to ions provided on the metal wiring. 603 is FET6
This is the output terminal of 02. With this configuration, the absolute value of the ion concentration can be measured by taking the difference between the output of the ISFET having an ion-sensitive membrane and the output of the FET 603. It is also possible to obtain a reference signal by applying a voltage from the outside to the gate of the FET 602.
Also, in the examples of FIGS. 5 and 6, the reference electrode is not integrated with the ion-sensitive membrane. Therefore, it is necessary to place it in the liquid during measurement. Conventionally, an Ag-Agcl electrode has been used as a reference electrode. Such a reference electrode can be provided in the ion sensing section. FIG. 7 shows an example of the configuration of an ion sensor in which a reference electrode is provided in the ion sensing section. In the figure, 701 is a reference electrode, and 702 is its lead wire. In this configuration, the sensitive membrane, reference electrode, and FET for obtaining the standard output signal are all integrated in a small area, so the fifth
This configuration is useful for further downsizing the entire measurement system, reducing the amount of the object to be examined, and simplifying the measurement compared to the configuration examples shown in FIGS. Although the case where an electrical double layer is formed on the sensitive film by Na ⁺ , K ⁺ , H ⁺ , etc. has been described above, the gist of the present invention is not limited to these. A charge is formed, thereby
It goes without saying that this method can be applied to all reactions in which the FET current is controlled.

[Brief explanation of drawings]

Figures 1a and 1b are a cross-sectional view and a top view of a conventional ISFET using a bulk crystal. Figure 2 shows how to use it, Figure 3 a and b show how to use the SOS board.
FIG. 2 is a cross-sectional view and a top view of a conventional example of an ISFET. Fourth
Figures a, b, and c show a top view and a sectional view of an ion sensor according to the present invention, and Figures 5 to 7 are diagrams for explaining application examples of the present invention. In the figure, 101 is a silicon substrate, 102, 1
03 and 104 are the source, drain and gate insulating films of the ISFET, respectively. 105 is a field oxide film, 106 is an ion sensitive film, 107,1
08 are source and drain electrodes, respectively. 2
01 is a solution to be measured, 202 is a battery, 203 is a reference electrode, 301 is a sapphire substrate, 302 is a silicon thin film, 401 is a metal thin film, 402 is a separation and connection part, 501 to 505 are ISFETs, 506 is a sensitive membrane integration part, 507 is a source common terminal, 508 to 5
12 is a read terminal, 513 is a separation coupling part, 60
1 is a metal electrode, 602 is an FET, 603 is a read terminal, 701 is a reference electrode, and 702 is a terminal for applying voltage.

Claims (1)

[Scope of Claims] 1. An ion sensor comprising a metal gate provided on a gate insulating film of an insulating film gate field effect transistor, and an ion sensitive film formed on an extended wiring of the metal gate, wherein the field effect transistor and the ion sensitive film An ion sensor characterized in that the parts are separated by an extended wiring part, each formed as a separate chip, and connected to each other via means for electrically coupling each other at each extended wiring part. 2. A metal gate is provided on the gate insulating film of a plurality of field effect transistors, and one end of the gates is gathered in a micro area separated from the transistor by a metal wiring, and different types of ion-sensitive films are formed on them. an ion sensor comprising: the field effect transistor and the sensitive membrane portion separated by a metal wiring portion, each formed on a separate chip; and means for electrically coupling the respective wiring portions to each other; An ion sensor characterized in that the ion sensor is coupled via a.