JPS61155851A - Semiconductor ion sensor - Google Patents

Abstract

PURPOSE:To improve the durability of an ion sensor and to reduce the size thereof by coating a gate region of a field effect transistor having a needle-like structure with a hollow yarn-like film consisting of a hydrophobic high polymer contg. an ion sensitive material. CONSTITUTION:A lead wire 2 is connected to a source electrode and drain electrode 1 of the gate-insulated field effect transistor and is coated with a catheter 3. The gate region of the electrode 1 projecting from the catheter 3 is coated with the hollow yarn-like film 5 consisting of the hydrophobic high- polymer having the ion sensitive material. The resin 6 is sealed into the aperture at the top end thereof. Plastic PVC, silicon, etc. which are incorporated therein with the ion sensitive material, i.e., valinomycin, crown ether, etc. are used for the film 5. Such sensor is constituted to a single or multiple sensors. Since the hollow yarn-like film is used, the ion sensor is made water-proof and is obtd. with the simple stage.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a semiconductor ion sensor comprising a gate insulated field effect transistor having a gate sensitive region at its tip. In particular, the present invention relates to a highly water-resistant semiconductor ion sensor suitable for measuring ion activity in an electrolyte.

(Prior Art) Glass electrodes have conventionally been used to measure the ion activities of hydrogen ions, sodium ions, potassium ions, calcium ions, and the like. This electrode is suitable for medical, physiological fields,
Particularly when used to measure various ions in a living body, it is inserted into living tissue. Therefore, attempts have been made to miniaturize the above electrodes. However, it is known that the following problems occur when glass electrodes are miniaturized.

(1) Since the resistance value of the glass film is approximately 10MΩ,
A high input resistance amplifier is required.

(2) Since the glass film is thin, its mechanical strength is low.

(8) When measuring a specific chemical substance present in a minute part, the electrode area becomes small, so the resistance value of the glass film becomes high.

As a result, the measurement device becomes large and complicated, and the electrode itself is fragile and fragile, which poses practical problems, especially when used as an electrode for measuring specific chemical substances in a living body by inserting it into living tissue.

In order to overcome the drawbacks of such glass electrodes, the applicant of the present invention proposed a new ion sensor utilizing the electric field effect of a semiconductor in Japanese Patent Publication No. 57-43863.

This ion sensor uses an insulating film made of silicon oxide and silicon nitride or an insulating film made of silicon oxide, silicon nitride, and an ion-sensitive film as an electrode in place of the metal plate that constitutes the gate electrode of a conventional MOSFET, and has a needle-shaped electrode. It has a structure in which a gate insulating film is placed at the tip of the base, and the potential is measured by directly contacting this insulating film with the liquid to be measured.
on 5ensitlveField Effect
Transistor (I5FET). The ion sensor using the silicon oxide and silicon nitride insulating films as gate electrodes can selectively measure hydrogen ions. Further, the surface K1 of the above-mentioned two-layer structure. Furthermore, various ions can be selectively measured by coating with an ion-sensitive membrane that is selectively sensitive to specific chemical substances.

The measurement principle is based on the fact that electrical conduction in a conduction channel between a drain and a source depends on the potential at the interface between the gate insulating film and the liquid to be measured. Therefore, it is possible to achieve ultra-miniaturization while keeping the output impedance low, and to create multiple chemically sensitive layers on a single semiconductor substrate. Especially low output impedance.

Moreover, because of its small size, it is useful as a medical biomonitoring sensor that is used by inserting it into living tissue.

The ion-sensitive membrane that covers the gate surface of the 15FET can be a glass membrane, a poorly soluble salt membrane, a liquid membrane, etc., but a liquid membrane in which an ion exchange substance, neutral carrier, or chloride is dispersed in a polymeric medium can be used. is preferably used because it has a wide range of applications and is easy to manufacture. 15FET whose gate surface is coated with a liquid film containing such an ion-sensitive substance
is JP 55-13544, JP 54-13019.
No. 6, JP-A-54-130197, etc.

(Problem to be solved by the invention) However, the 15FET whose gate surface is coated with a liquid film suffers from decreased sensitivity and drift during use, making it impossible to measure ion activity stably over a long period of time. There was a problem. In particular, when a plurality of IBFETs are integrated and the gate region of each IBFET is coated with a liquid film containing a different ion-sensitive substance, the characteristics (especially ion sensitivity) of the individual IBFETs vary widely and are unstable. In addition, there is a problem that the service life is extremely short due to imperfections such as water resistance. This is thought to be due to the adoption of a dip coating method for coating the gate region with the ion-sensitive film, which is difficult to control for uniform film thickness and is prone to peeling and pinholes.

As a result of further study, the present invention was arrived at.

That is, the present invention provides a gate region of a gate insulated field effect transistor having a needle-like structure having a gate sensitive region at its tip, and one end surface of which is a hollow fiber-like homogeneous membrane made of a hydrophobic polymer containing an ion-sensitive substance. A semiconductor ion sensor characterized by being coated.

(Function) In the present invention, since the 15FET is ultra-small, the ion-sensitive film is coated with an ion-sensitive material as a coating method for the ion-sensitive film, which was conventionally thought to have no choice but to adopt a side dip coating method. The gate region is coated with a hollow fiber-like membrane made of a hydrophobic polymer containing . The reason why the ionic activity can be measured stably over a long period of time due to such characteristics is presumed as follows.

■ Because the ion-sensitive membrane is pre-formed into a hollow shape, the membrane thickness can be kept constant.

- Since the gate region of the 15FET is inserted and fixed into the hollow part of the hollow fiber, there is no peeling of the membrane.

■ Hollow fiber membranes without pinholes or cracks can be obtained because they are formed into hollow fibers in advance.

For the above reasons, it is presumed that a practical ion sensor with excellent water resistance can be provided.

Such features are extremely useful for fabricating a multi-sensor in which multiple 15FETs are integrated.

(Example 5A) Next, an example of the semiconductor ion sensor of the present invention will be described with reference to the drawings. Figure 1 (&), Φ) shows l5F used in the present invention.
I; shows a plan view and a sectional view of T1.

In this figure, a silicon (St) substrate 11 has an elongated p
The substrate 11 is formed from a --shaped silicon single crystal, and includes an elongated parallel n-type drain diffusion region 12 and a source diffusion region 13 extending in the longitudinal direction on the central surface of the substrate 11 .

The surface region of the substrate 11 located between these two diffusion regions forms a gate region 16.

There is an n shadow region 12.1 in the surface of the substrate 11 excluding the gate portion.
A two-way channel stopper region 17 is formed over the substrate 110 to prevent conduction channels from forming on the surface of the substrate 110 between the n-type source and drain diffusion regions 12, 13, except for the gate region 16. Further, the rear end portion 18 of the source diffusion region 12 is electrically connected to a source electrode 20 made of A4 and a substrate electrode through an n+ contact region 19. Further, the rear end portion 21 of the drain diffusion region 13
is electrically connected to a drain electrode 23 made of AI through an n+ contact region 22.

On the surface of the silicon substrate 11, from the stepped portion 24 in FIG.
Silicon oxide (50%
loz) film 27 and silicon nitride (SisN4) film 28
The coating has a two-layer structure.

Such a 15FET has a width of 0.4 mm, a length of 5 mm, and a thickness of 0.1 mm.
5+u+. The 15FET whose gate region is covered with a silicon oxide film and a silicon nitride film is selectively sensitive to hydrogen ions and is used as a sensor.

The l5FET 1 shown in FIG. 1 is housed in a catheter 3 after connecting lead wires 2 to the source and drain electrodes as shown in FIG. It is fixed within the catheter by an electrically insulating resin 4 sealed within the catheter.

The gate region is coated with a hollow fiber membrane 5 shown in the diagram containing an ion-sensitive substance.

Examples of the ion-sensitive substance to be contained in the hollow fiber membrane include palinomycin, crown ether, nonactin, and sodium chloride for potassium senna.
/row ether, didecyl phosphate calcium salt, P-octylphenyl phosphate calcium salt for calcium sensors, and dimethyl distearyl ammonium salt for anion measurement. Examples of polymers containing the above-mentioned ion-sensitive substances include hydrophobic polymers such as polyvinyl chloride, silicone, polyurethane polycarbonate, polypropylene, and polyethylene that have been plasticized with dioctyl adipic acid, dioctyl phenylphosphonic acid, tricresyl phosphoric acid, etc. , polystyrene, etc. are used.

To make such a hollow fiber membrane, if the ion-sensitive material can withstand the molding conditions, molding may be used,
If this is not possible, apply a solution containing a sensitive substance and a polymer using a rod with an outer diameter approximately equal to that of senna.
It can also be obtained by removing the core after drying. The obtained hollow fiber membrane is cut into a required length. At this time, No. 1 (b)
), the opening at the tip of the hollow fiber membrane may be sealed in advance with resin 6. The polymer to be sealed at this time does not necessarily have to be the same material as the hollow fiber membrane, as long as it has good adhesion to the hollow fiber membrane. In addition, when producing by molding, a molded product as shown in Fig. 1 (b) may be directly produced. If the wall thickness of the hollow fiber is too thin, the strength will be weak, and the thickness of the hollow fiber will be too thin. Since it is difficult to cover K, 108 or more is preferable. There is no particular limit to the thickness, but it is preferable to make the outer diameter of the hollow fiber membrane approximately equal to the outer diameter of the catheter in order to smooth the surface of the final product.The sensitive membrane forming such a hollow fiber membrane is hydrophobic. It must be a homogeneous membrane. A homogeneous membrane here means that there are no pores in the membrane, and for example, a homogeneous membrane includes a PvC matrix in which a plasticizer is concentrated, such as plasticized vinyl chloride. Moreover, colloidal silica, glass fiber, etc. may be mixed as a reinforcing material for the membrane.

The hollow fiber membrane thus prepared is placed over the exposed portion of the catheter of the 15FET device as shown in FIG.

At this time, if the hollow fiber membrane is directly placed over the gate area of 15FET1, a thin layer of air will remain and the response of Senna will become unstable. Therefore, adhesive liquid 7 is applied around the gate area or inside the catheter, and It is important to prevent gaps from forming between the region and the hollow fiber membrane.

As the adhesive liquid 7, a solution of a sensitive film, a solvent of a sensitive film, or a conductive adhesive can be used.

If a hollow fiber membrane with an unsealed tip as shown in Figure 4(a) is used, the liquid to be measured will enter through the opening at the tip as shown in Figure 4. It is necessary to seal the opening with a membrane solution).

Finally, as shown in FIG. 5, the entire tip of the sensor is dip-coated with a sensitive film solution 8 to fill in the pinholes and smooth the entire surface, thereby obtaining a semiconductor ion sensor.

6 and 7 are examples of multiple senna using the senna of the present invention.

It has the same structure as the 15FET shown in Figure 1, and the same number is written in the same place and the explanation is omitted, but this Senna has a common drain and three gates 16(a), 16Φ)%1
6 (0), and are arranged at appropriate intervals in the vertical direction. The shaded area in the figure other than the gate is surface K.
A P+ layer (channel stopper) is created to separate each gate. The spacing between these gates can be made as small as desired, but if it is made too small, it becomes difficult to bring the boundary of the sensitive film exactly between the gates, so the spacing is preferably 0.5 to 3 mm. At the other end of the 15FET, an electrode is arranged to connect a lead wire for output. In the case of Fig. 8, the drain/electrode mother common to each l5FIT, the substrate electrode 29 and each l5FE
T source electrodes 20 (a), 20 (b), 20 (C
)' are provided. The multiplex sensor shown in Figure 8 has a length of 12u1, a width of 0.5wt, and a length of 150μ.
The smaller the size of the 0 senna, the better from the viewpoint of use, but if the atn is small, the element may break during processing, so the length is usually 5 to 20 m.

The width is preferably 0.3 to 1.0 mm and the thickness is preferably 100 to 300 μm.

Although the above-mentioned 15FET was fabricated on a silicon wafer, it is also possible to fabricate it on an insulating substrate such as sapphire.

As shown in FIG. 6 (IL), this senna is embedded into the catheter 3 by bonding the lead wire 2 to the electrode, fixing it to the support 9, and leaving the gate portion. multiple ISF
The gap between gT1 and the inner wall of the catheter is filled with insulating resin 4 to prevent the bonding part from shorting due to the measurement liquid.

The thus processed senna is covered with a hollow fiber membrane 5 (C) containing an ion-sensitive substance at the rootmost gate portion 1 (i (c)) as shown in FIG. 6).

The method for covering the hollow fiber membrane is the same as that for the single senna shown in FIG. 1, but the opening at the tip does not need to be sealed because it is covered with another hollow fiber membrane.

Next, a hollow fiber membrane 5(6) containing an ion-sensitive substance different from that of the hollow fiber membrane 5(C) is coated on the second gate portion 16(b) as shown in FIG. 6(C). At this time, it is necessary to adhere the boundary between the two hollow fiber membranes 16(b) and 16(e) with an adhesive to prevent the measurement liquid from entering through the boundary. Although the outer diameters of the hollow fiber membranes may be different, it is preferable that they have the same outer diameter because the shape will be smooth. Next, the third gate region 16 (IL) is covered with a hollow fiber membrane containing an ion-sensitive membrane different from the above-mentioned two ion-sensitive substances, and the tip is glued with adhesive 6 as shown in FIG. 6 (ψ).
By sealing the ions with the ions, it is possible to obtain a multiple ion sensor that is sensitive to three types of ions. At this time, the combination of the three hollow fiber membranes is arbitrary, but since the hydrophobic ion-sensitive membrane and the hydrophilic enzyme-immobilized membrane do not have good adhesion, it is not recommended to mix them in one senna. Undesirable.

The multisensor fabricated in this way is elongated and has excellent water resistance, so it is suitable for being inserted into a blood vessel catheter or tissue using an indwelling needle to monitor blood or body fluids.

Moreover, a plurality of ion sensors of the present invention can be arranged side by side. Figure 7 is an example of a horizontal multiplex sensor.
FETs are formed side by side on a single silicon wafer. At this time, the bonding portions are arranged integrally, but the gate sensitive portions are manufactured separately. The 15FET constituting the multiplex sensor has the same structure as the 15FET shown in FIG. 1, so the same number is written in the same place and the explanation will be omitted. Each of these l5FE
Multiple senna can be made by covering T with hollow fiber membranes* (a), (b), and (e). This senna is mainly suitable as a flow-through cell type senna, and by bringing the gate portion of this senna into direct contact with a measuring liquid, it is possible to measure the concentration of a chemical substance in an extremely small amount of a sample. Another advantage of this Senna is that, unlike the multiple sensor shown in Figure 8, in which the gate parts are lined up vertically, each ISF'ET gate part is independent, so the hydrophilic sensitive film and the hydrophobic sensitive film It is possible to use a mixture of membranes, and any combination of enzyme sensors and ion sensors, ion sensors and...sensors, etc. is possible.

The present invention will be specifically explained below using Examples.

Example 1 and Comparative Example 1 A 5FET having Si 3N4 as a sensitive film shown in FIG. 1 was used with an inner diameter of 0. A sensor shown in FIG. 2 was fabricated by being embedded in a nylon 11 catheter of sm, outer diameter □, and 6 tm. Separately, a hollow fiber membrane was prepared by coating a stainless steel wire with an outer diameter of 0.3 mm with a solution having the composition shown below.

"Mw-4000 This hollow fiber was coated on the gate region of 15FET to fabricate the ion sensor shown in FIG. 5. At this time, the hollow fiber membrane and 15
Adhesion of FET, sealing of hollow fiber tip opening.

A sensitive membrane solution having the above composition was used for all final coatings. Table 1 shows the characteristics of the senna thus prepared and the senna (comparative example 1) prepared by repeatedly dip-coating the sensor shown in FIG. 2 with a sensitive membrane solution having the above composition five times. From Table 1, it is clear that the sensitivity and other characteristics of the Examples and Comparative Examples are almost the same, but the Examples are superior in yield and water resistance.

Table 1 Example 2 A multiple FIT device shown in FIG. 8 having three gates spaced apart by 1.2 IIJ was fabricated. This element has an inner diameter of 0, 5
A nylon 11 catheter with an outer diameter of 1.05 m was embedded using epoxy resin and a 0.3 Msφ stainless steel wire as a support as shown in Figure 6(a).

Separately, a THF cyclohexanone solution of polyvinyl chloride-sensitive material with the following composition was prepared, and each
G injection needles were coated repeatedly until the outer diameter was 0.9 HJIK, and after drying, the injection needles were pulled out to obtain hollow fiber membranes sensitive to ca", K", and organic cations, respectively.

Hollow fiber membrane (a) Hollow fiber membrane φ) Hollow fiber membrane ((ri, -1・5d cyclohexanone 1d cyclohexanone 1.5d *MW=4000 This is sequentially applied to each gate part of 15FET as shown in FIG. The solution used in the above hollow fiber fabrication was used to bond each hollow fiber membrane and 15FET, and 5% PvC and 5% dioctyl adipic acid were dissolved to bond each hollow fiber and seal the tips. A cyclohexanone solution was used.This senna can be inserted into an indwelling needle with an inner diameter of 1.2 m, and both senna have the same response characteristics and sensitivity as senna prepared by coating the gate part of a single ion sensor with the above solution. Furthermore, even after being immersed in water at 37° C. for one month, no peeling of the sensitive film or decrease in sensitivity was observed.

Example 3 An element shown in FIG. 7 was fabricated, in which four 15FETs shown in FIG. 1 were laid down and connected into one piece at the bebonding part.

By covering each of these three 15FETs with the three types of hollow fiber membranes used in Example 2, and after bonding, the bonding parts were embedded in an insulating resin.
We were able to produce senna that is sensitive to four ions: Ca'' and organic cations. All of these senna withstood two weeks of continuous measurement in water at 37°C.

(Effects) As described above, the ion sensor of the present invention is a single ion sensor with good water resistance and a simple process.

A multiple ion sensor can be obtained with good yield, making it an extremely useful senna in practice.

[Brief explanation of drawings]

Figures 1(a) and φ) are a plan view and a cross-sectional view of the 15FET used in the present invention, and Figures 2 to 5 illustrate the ion-sensor process in each step to explain the manufacturing method of the Ω ion sensor of the present invention. 6 (IL) to 6 (ψ are cross-sectional views of the multiple senna at each step to explain the manufacturing method of the vertical multiple senna of the present invention. )
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Claims (1)

[Scope of Claims] 1. A gate insulated field effect transistor having a needle-like structure having a gate sensitive region at its tip, the gate region and one end surface of which are hollow fibers made of a hydrophobic polymer containing an ion sensitive substance; A semiconductor ion sensor characterized by being coated with a homogeneous film. 2. A plurality of the gate insulated field effect transistors are provided, and each gate sensitive region and one end surface thereof are covered with a hollow fiber-like homogeneous membrane made of a hydrophobic polymer containing a different ion sensitive substance. The semiconductor ion sensor according to claim 1, characterized in that the semiconductor ion sensor has a selective characteristic for ions.