JP2002250712A - Ion sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an ion sensor in which the size can be reduced while prolonging the lifetime. SOLUTION: The ion sensor comprises a silicon substrate 1 having an ISFET 10 responsive to a specified ion formed on the major surface side, a liquid communicating part 38 formed at a thin part 1b which is formed by opening a recess 1a in the rear surface of the silicon substrate 1 and provided with a large number of fine pores 38a for touching an electrolyte 31 filling the recess 1a to a measuring solution on the major surface side of the silicon substrate 1, a support 15 boded to the silicon substrate 1 to choke the recess 1a, and a reference electrode 34 of silver - silver chloride touching the electrolyte 31. A liquid storing part 17 communicating with the recess 1a opening to the rear surface of the silicon substrate 1 and storing the electrolyte 31 is provided in the support 15 and the liquid storing section 17 made across the recess 1a and the support 15 is filled with the electrolyte 31.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an ion sensor.

[0002]

2. Description of the Related Art Conventionally, an ion sensor having a glass electrode system 20 and a reference electrode system 30 as shown in FIG. 5 and an ion-sensitive field-effect transistor (Ion Sensitive Field Transistor) as shown in FIG. Effect Transisto
r: ISFET) 10 and a reference electrode system 30 are known.

[0005] A glass electrode system 20 shown in FIG. 5 includes a glass film 21 for generating a potential corresponding to a specific ion activity in a measurement solution A, an internal solution (for example, a saturated potassium chloride solution or an electrolytic solution such as a gel) 22. And an internal electrode 24 (for example, a silver-silver chloride electrode) inserted into the support tube 23 and in contact with the internal liquid 22. The electrode system is generally called a glass electrode. . FIG.
The reference electrode system 30 is provided with a support tube 32 filled with an internal solution (for example, a saturated potassium chloride solution or an electrolytic solution such as a gel) 31, and a fine hole for bringing the internal solution 31 into contact with the measurement solution A. This is an electrode system including a liquid junction member (for example, porous ceramics) 33 and a reference electrode (for example, a silver-silver chloride electrode) 34 inserted into the support tube 32.

On the other hand, the ISFET 10 in FIG.
N on the main surface side of the silicon substrate 1 ⁺Dray consisting of layers
Region 2 and n⁺The source region 3 consisting of layers is separated
Formed on the portion between the two regions 2 and 3_TwoConsisting of membrane
An ion-sensitive film (for example, Si) through the gate oxide film 5_Three
N_Four6) are formed. Also, the drain region
2, a drain electrode 7 is formed on the source region 3.
Has a source electrode 8 formed on each of the electrodes 7 and 8.
A protective film 40 is formed. In addition, the silicon substrate 1
Field acid on the inactive region of ISFET 10
An oxide film 9 is formed. The reference electrode in FIG.
The configuration of the system 30 is the same as that of the reference electrode system 30 in FIG.
You.

When the ISFET 10 shown in FIG. 6 is immersed in a measurement solution (aqueous solution) A containing specific ions (H ^{+ in} the example of FIG. 7), as shown in FIG. , Si ₃ N ₄ film) The surface potential is generated by the interaction between the surface of the silicon substrate 6 and the specific ions in the measurement solution A, and a portion between the drain region 2 and the source region 3 on the main surface side of the silicon substrate 1 is formed. Since the size of the channel 4 to be formed changes, the drain current Id flowing between the drain electrode 7 and the source electrode 8 changes according to the size of the specific ion.

In the ion sensor having the structure shown in FIG. 6, the output voltage Vrs between the reference electrode system 30 and the source electrode 8 of the ISFET 10 is kept constant, and the drain voltage Vd applied between the drain electrode 7 and the source electrode 8 is reduced. By measuring the drain current Id at a constant value, the ion concentration of a specific ion can be known.

[0007]

The above-mentioned ISFET 10
Has the advantage that it can be downsized and can respond at high speed as compared with the glass electrode 20. However, in the ion sensor of FIG. 6, the reference electrode system 30 is relatively larger than the ISFET 10, There was a problem that the sensor could not be sufficiently reduced in size as a whole.

Therefore, a reference electrode system 30 having the configuration shown in FIG. 8 has been proposed. The reference electrode system 30 of FIG.
The thin portion 35b is formed by opening the recess 1a on the back surface.
Are provided, and a flat plate-like support member 36 is joined to the back surface of the silicon substrate 35 so as to close the opening surface of the recess 1a, and the inner surface of the recess 1a and the support member 3 are provided.
6 is filled with an electrolyte 31 and a reference electrode 3 comprising a silver-silver chloride electrode (silver / silver chloride electrode).
4 is inserted, and a liquid junction 38 made of porous silicon for bringing the electrolytic solution 31 into contact with the measuring solution is formed into a thin portion 35.
b.

In each of the reference electrode systems 30, the electrolytic solution 31 gradually elutes into the measurement solution. In the reference electrode system 30 having the structure shown in FIG. Is filled in the recess 1a opened in the back surface of the reference electrode system 30 shown in FIG.
However, the amount of the electrolytic solution 31 was extremely small as compared with that of the above, and the life was short. If the life of the reference electrode system 30 is short, the replacement frequency of the reference electrode system 30 increases, and the cost increases.

[0010] The present invention has been made in view of the above circumstances, and an object of the present invention is to provide an ion sensor that can be reduced in size and lengthened in life.

[0011]

According to a first aspect of the present invention, there is provided a semiconductor substrate in which an ion-sensitive film sensitive to a specific ion is formed so as to be exposed on a main surface side. A small hole is formed in the thin portion formed by opening the recess on the back surface of the semiconductor substrate to allow the electrolyte filled in the recess and the measurement solution on the main surface side of the semiconductor substrate to come into contact with each other. A liquid junction, a support joined to the semiconductor substrate so as to close the recess, and a reference electrode in contact with the electrolytic solution. A liquid reservoir is provided on the support. According to this configuration, since the ion-sensitive film and the liquid junction are provided on the main surface side of one semiconductor substrate, the size of the entire ion sensor can be reduced, and the area of the ion sensor can be reduced with a smaller area as compared with the related art. Since it is possible to measure the concentration of a specific ion in the measurement solution, it is possible to measure the measurement solution in a narrower space. In addition, a liquid reservoir portion communicating with the concave portion opened on the back surface of the semiconductor substrate and storing the electrolytic solution is provided on a support joined to the semiconductor substrate so as to close the concave portion on the rear surface of the semiconductor substrate. Therefore, the amount of the electrolytic solution in contact with the reference electrode can be increased without using a separate member, and the life can be extended.

According to a second aspect of the present invention, in the first aspect of the present invention, the ion-sensitive film is formed on the main surface side of the thin portion of the semiconductor substrate. The area of the semiconductor substrate can be reduced as compared with the case where the semiconductor substrate is formed on the main surface side of a portion other than the thin portion, and further downsizing can be achieved.

According to a third aspect of the present invention, in the second aspect of the present invention, the liquid junction has a large number of the small holes formed over the entire thin portion, and the semiconductor substrate has the liquid junction formed therein. A MOSFET is formed on a main surface side of a portion other than the region, and a gate electrode of the MOSFET is extended so as to overlap the liquid junction, and the ion-sensitive film is provided on the main surface side of the thin portion. Are formed so as to cover the ion-sensitive film and the gate electrode, since a large number of through holes communicating with the respective small holes of the liquid junction are formed, the surface area of the ion-sensitive film is relatively large. Therefore, as compared with the case where the surface area of the ion-sensitive membrane is small, the positioning of the ion-sensitive membrane with respect to the measurement solution is facilitated and the usability is improved.

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS (Embodiment 1)
As shown in FIG. 1, the ion sensor
If H ⁺) Is formed on the main surface side
P-type silicon substrate 1 serving as a semiconductor substrate, and silicon
Formed on the back surface of the substrate 1 by opening a recess 1a.
Electrolyte formed in the thinned portion 1b filled in the recess 1a
(Eg, saturated potassium chloride solution) 31 and silicon
Many for contacting the measurement solution on the main surface side of the substrate 1
Junction 38 provided with fine small holes 38a, and recess 1
a (eg, a support joined to the silicon substrate 1 so as to cover
For example, plastic molded article) 15 and electrolytic solution 31
With a reference electrode 34 consisting of a silver-silver chloride electrode in contact
I have. In this case, the support 15 supports the silicon substrate 1
A rectangular parallelepiped shape with a storage recess 16 for storage opened at the front
The inner bottom surface of the storage recess 16a and the p-type
The back surface of the recon board 1 is joined (adhered). Ma
The ISFET 10 and the liquid junction 38 are
It is formed spaced apart on the main surface side. Also,
The small hole 38a of the liquid junction 38 is formed to penetrate the front and back.
Have been.

The recess 1a is formed by anisotropically etching the back side of the silicon substrate 1. The liquid junction 38a may be made of porous silicon formed by making a part of the thin part 1b made of silicon porous, or may be made of a thin part 1b made of a part of the silicon substrate 1. The small holes 38a may be formed by anisotropic etching. Further, although the support 15 is a molded product made of plastic, a molded product made of metal may be subjected to an appropriate insulation treatment.

In the ISFET 10, a drain region 2 and a source region 3 are formed on the main surface side of the silicon substrate 1 with a space therebetween, and a gate oxide film 5 made of a SiO ₂ film is interposed between the two regions 2 and 3. For example, a Si ₃ N ₄ film or Ta ₂ O ₅
The ion-sensitive film 6 is formed. The pad 7a connected to the drain region 2 is electrically connected to the drain wiring 12 provided on the front surface of the support 15 via a bonding wire W, and the pad 8a connected to the source region 3 is supported. It is electrically connected to the source wiring 13 disposed on the front surface of the body 15 via a bonding wire W.

The ISFET 10 according to the present embodiment
Is for measuring the concentration of hydrogen ions (H ⁺ ) as the concentration of a specific ion. The ion-sensitive film 6 is formed of a Si ₃ N ₄ film or a Ta ₂ O ₅ film. Is not limited to a Si ₃ N ₄ film or a Ta ₂ O ₅ film,
When specific ions other than hydrogen ions are used as measurement ions, the ion-sensitive film 6 may be formed of a material that is sensitive to desired specific ions.

When the ISFET 10 having the configuration shown in FIG. 1 is immersed in a measurement solution (aqueous solution) containing hydrogen ions (H ⁺ ), an interface potential is generated due to the interaction between the surface of the ion-sensitive membrane 6 and the ions in the measurement solution. And hydrogen ion concentration (pH)
The size of a channel (not shown) formed in a portion between the drain region 2 and the source region 3 on the main surface side of the silicon substrate 1 changes according to the size of the hydrogen ion concentration (pH). The drain current Id flowing between the drain electrode 7 and the source electrode 8 changes according to the magnitude of the current.

Therefore, the reference electrode 34 and the ISFET 1
0, the output voltage Vrs between the source electrode 8 and the source electrode 8 is constant,
Further, the pH can be known by measuring the drain current Id when the drain voltage Vd applied between the drain electrode 7 and the source electrode 8 is constant.

Incidentally, the ion sensor of this embodiment is
The support body 15 is provided with a liquid reservoir 17 that communicates with a recess 1 a opened on the back surface of the silicon substrate 1 and stores the electrolytic solution 31. Therefore, in the ion sensor of the present embodiment,
Recess 1a opened on the back surface of silicon substrate 1 and support 1
The electrolyte solution 31 is filled over the liquid reservoir 17 provided in the fuel cell 5. Here, the liquid reservoir 17 provided on the support 15 is formed so as to extend to one side (the right side in FIG. 1B) of the support 15, and the electrolytic solution is provided on the one side of the support 15. An injection port 19 for filling the liquid 31 is opened. The inlet 19 of the support 15 is closed by the cap 18, and the above-described reference electrode 34 is inserted through the cap 18.

Hereinafter, a method of manufacturing the ion sensor according to the present embodiment will be briefly described.

First, a thin portion 1b is formed by opening a recess 1a on the back surface of the silicon substrate 1 by anisotropic etching, and then the ISFET 1 is formed on the main surface side of the silicon substrate 1.
0 is formed by, for example, a process according to a general MOSFET manufacturing process. Next, by forming a large number of small holes 38a in the thin portion 1b of the silicon substrate 1, the liquid junction 3 is formed.
8 is formed. Then, the ISFET 10 and the liquid junction 3
The silicon substrate 1 on which 8 has been formed is adhered to the support 15,
The bonding wires W, W are bonded as described above, and then the electrolyte solution 31 is filled from the injection port 19, the injection port 19 is closed with the cap 18, and finally, the reference electrode 34 is inserted through the cap 18.

However, in the ion sensor of the present embodiment, since the ion-sensitive film 6 and the liquid junction 38 are provided on the main surface side of one silicon substrate 1, the overall size of the ion sensor is reduced. Since it is possible to measure the concentration of a specific ion in the measurement solution with a smaller area than in the conventional case, it is possible to measure the measurement solution in a narrower space. Further, the liquid reservoir 17 communicating with the concave portion 1a opened on the back surface of the silicon substrate 1 and storing the electrolytic solution 31 is joined to the silicon substrate 1 so as to close the concave portion 1a on the rear surface of the silicon substrate 1. Since the support member 15 is provided on the support 15, the amount of the electrolytic solution 31 in contact with the reference electrode 34 can be increased without using a separate member, and the life can be extended. Note that the semiconductor substrate is not limited to a p-type silicon substrate.

(Embodiment 2) The basic configuration of an ion sensor of this embodiment is substantially the same as that of Embodiment 1. As shown in FIG. 2, a drain electrode 7 and a source electrode 8 are formed on the back side of the silicon substrate 1 as shown in FIG. The feature is that the electrode 34 is provided. Note that the same components as those in the first embodiment are denoted by the same reference numerals, and description thereof will be omitted.

In the present embodiment, the recess 1c reaching the drain region 2 and the source region 3 described in the first embodiment is opened on the back surface of the silicon substrate 1, and extends over the inner surface of the recess 1c and the back surface of the silicon substrate 1. An insulating film 41 is formed, and the drain electrode 7 and the source electrode 8 are connected to the drain region 2 and the source region 3 via contact holes provided in the insulating film 41, respectively. Here, the drain electrode 7 and the source electrode 8 extend to the back surface of the silicon substrate 1 and are connected to the drain wiring 12 and the source wiring 13 formed integrally with the support 15. The ion-sensitive film 6 is formed on the main surface side of the thin portion 1d formed by opening the recess 1c.

The reference electrode 34 is formed along the inner surface of the recess 1 a described in the first embodiment, extends to the back surface of the silicon substrate 1, and is provided integrally with the support 15 for the silver-silver chloride electrode wiring. 14. An insulating film (not shown) is formed between the reference electrode 34 and the inner surface of the recess 1a.

In this embodiment, the electrodes 7, 8, and 34 and the wiring 1 are arranged on the bottom side of the storage recess 16 of the support 15.
Can make connections between 2, 13, and 14,
Water resistance is improved.

(Embodiment 3) The basic configuration of the ion sensor of this embodiment is substantially the same as that of Embodiment 1, and as shown in FIG.
It is characterized in that 0 is formed. Where IS
A pad 7a connected to the drain region 2 of the FET 10,
The pad 8a connected to the source region 3 is provided at a portion other than the thin portion 1b, and the drain region 2 and the source region 3 extend outside the thin portion 1b. Note that the same components as those in the first embodiment are denoted by the same reference numerals, and description thereof will be omitted. Also, 9 in FIG. 3A indicates a field oxide film.

In this embodiment, the ISFET 1
0 is formed on the main surface side of the thin portion 1b of the silicon substrate 1, so that the ISFET 10 is formed on the main surface side of a portion other than the thin portion 1b of the silicon substrate 1 as in the first embodiment. Thus, the area of the silicon substrate 1 can be reduced (in short, the area of the chip can be reduced), and the size can be further reduced.

(Embodiment 4) The basic configuration of the ion sensor of this embodiment is substantially the same as that of Embodiment 1, and as shown in FIG. 4, a gate is used instead of the ion-sensitive film 6 of the ISFET 10 described in Embodiment 1. By providing the electrode 56, the MOSFET 50 is formed on the main surface side of the silicon substrate 1,
It is characterized in that the gate electrode 56 of the SFET 50 is extended to a position overlapping the liquid junction 38, and the ion-sensitive film 6 is formed so as to cover the gate electrode 56 on the main surface side of the thin portion 1b. Here, the ion-sensitive film 6 and the gate electrode 56 are formed with a large number of through-holes 6a and 56a communicating with the small holes 38a of the liquid junction 38, respectively. Note that the same components as those in the first embodiment are denoted by the same reference numerals, and description thereof will be omitted. Also, reference numeral 9 in FIG. 4 denotes a field oxide film.

However, in the ion sensor according to the present embodiment, the surface area of the ion-sensitive membrane 6 can be made relatively large as compared with each of the above-described embodiments. 6 becomes easy, and the usability is improved.

[0032]

According to the first aspect of the present invention, there is provided a semiconductor substrate in which an ion-sensitive film sensitive to specific ions is formed on the main surface side, and a recess is formed on the back surface of the semiconductor substrate. A liquid junction provided with a small hole for contacting the electrolyte solution formed in the formed thin portion and filling the recess with the measurement solution on the main surface side of the semiconductor substrate, and closing the recess; A support electrode joined to the semiconductor substrate and a reference electrode in contact with the electrolytic solution, and a liquid reservoir communicating with the recess and storing the electrolytic solution is provided on the support member. Since the ion-sensitive film and the liquid junction are provided on the main surface side of one semiconductor substrate, it is possible to reduce the size of the entire ion sensor, and to reduce the area of the measurement solution with a smaller area than before. It is possible to measure the concentration of specific ions Since that, there is an effect that the measurement of the measurement solution enables in a narrower space. In addition, a liquid reservoir portion communicating with the concave portion opened on the back surface of the semiconductor substrate and storing the electrolytic solution is provided on a support joined to the semiconductor substrate so as to close the concave portion on the rear surface of the semiconductor substrate. So
There is an effect that the amount of the electrolytic solution in contact with the reference electrode can be increased without using a separate member, and the life can be extended.

According to a second aspect of the present invention, in the first aspect of the present invention, the ion-sensitive film is formed on the main surface side of the thin portion of the semiconductor substrate. The area of the semiconductor substrate can be reduced as compared with the case where the semiconductor substrate is formed on the main surface side of a portion other than the thin portion, and there is an effect that the size can be further reduced.

According to a third aspect of the present invention, in the second aspect of the invention, the liquid junction has a large number of the small holes formed over the entire thin portion, and the semiconductor substrate has the liquid junction formed therein. A MOSFET is formed on a main surface side of a portion other than the region, and a gate electrode of the MOSFET is extended so as to overlap the liquid junction, and the ion-sensitive film is provided on the main surface side of the thin portion. Are formed so as to cover the ion-sensitive film and the gate electrode, since a large number of through holes communicating with the respective small holes of the liquid junction are formed, the surface area of the ion-sensitive film is relatively large. Therefore, compared to the case where the surface area of the ion-sensitive membrane is small, the positioning of the ion-sensitive membrane with respect to the measurement solution is facilitated, and the usability is improved. .

[Brief description of the drawings]

FIG. 1 shows a first embodiment, in which (a) is a schematic plan view,
(B) is a schematic sectional view.

FIG. 2 shows a second embodiment, in which (a) is a schematic plan view,
(B) is a schematic sectional view, (c) is a schematic side sectional view.

3A and 3B show a third embodiment, in which FIG. 3A is a schematic cross-sectional view with a part cut away, and FIG. 3B is a schematic plan view with a part cut off.

4A and 4B show a fourth embodiment, in which FIG. 4A is a schematic cross-sectional view with a part broken, FIG. 4B is a schematic plan view with a part broken, and FIG. 4C is an enlarged view of a main part of FIG.

FIG. 5 is a schematic configuration diagram of an ion sensor showing a conventional example.

FIG. 6 is a schematic configuration diagram of an ion sensor showing another conventional example.

FIG. 7 is a diagram illustrating the principle of the above.

FIG. 8 is a sectional view of a main part of another conventional example.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Silicon substrate 1a Depression 1b Thin part 2 Drain region 3 Source region 5 Gate oxide film 6 Ion sensitive film 15 Support 16 Storage recess 17 Liquid reservoir 31 Electrolyte 34 Reference electrode 38 Liquid junction 38a Small hole

Claims (3)

[Claims] 1. A semiconductor substrate formed in such a manner that an ion-sensitive film sensitive to specific ions is exposed on the main surface side, and a thin-walled portion formed by opening a recess in the back surface of the semiconductor substrate. A liquid junction provided with a small hole for contacting the electrolytic solution filled in the recess and the measurement solution on the main surface side of the semiconductor substrate, and the semiconductor substrate so as to close the recess An ion sensor, comprising: a joined support; and a reference electrode in contact with the electrolyte, wherein the support is provided with a liquid reservoir communicating with the recess and storing the electrolyte. 2. The ion sensor according to claim 1, wherein the ion-sensitive film is formed on a main surface side of the thin portion of the semiconductor substrate. 3. The liquid junction, wherein a large number of the small holes are formed throughout the thin portion, and the semiconductor substrate is provided with a MOS on a main surface side of a portion other than a region where the liquid junction is formed.
The FET is formed, and the gate electrode of the MOSFET is extended so as to overlap the liquid junction. The ion-sensitive film is formed so as to cover the gate electrode on the main surface side of the thin portion, and 3. The ion sensor according to claim 2, wherein the sensitive film and the gate electrode are formed with a large number of through holes communicating with the small holes of the liquid junction.