JP2001066276A - One-chip ion concentration-measuring device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To achieve a compact, high-performance concentration-measuring device that fully utilizes the features of an SOI(silicon on insulator) substrate by using the micromachining technique for forming a liquid channel and a comparison electrode functional part in the silicon substrate of the SOI substrate. SOLUTION: In a comparison electrode functional part 15 being provided in a silicon substrate 3 that is the substrate of an SOI substrate 2 and a lower substrate 11, a liquid well 17 of inner liquid 16 such as KCI solution is formed across both the substrates 3 and 11. Then, an inner electrode 18 that is made of Ag/AgCI is provided in the liquid well 17. The liquid channel 18 being connected to the liquid well 17 is formed at the junction of both the substrates 3 and 12, and a thick-diameter 19a is formed in the middle. A field-control micro pump 20 is provided at the thick-diameter 19a. Then, the upper end of the liquid channel 19 is connected to a pH sensor 7, thus forming a liquid channel part 21. Also, the comparison electrode functional part 15, the liquid channel 19, or the like is formed by the micromachining technique.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to a one-chip type ion concentration measuring device having an ion sensor section formed on an SOI substrate. Here, SOI means Silicon O
n Insulator, examples of such a substrate include an epitaxially grown SOI substrate and a commercially available bonded SOI substrate.

[0002]

2. Description of the Related Art An ion sensor section is formed on the SOI substrate.
As a one-chip type ion concentration measurement device, for example,
One-chip p disclosed in JP-A-9-203721
There is an H sensor. FIG. 6 shows the one-chip pH sensor.
This is a diagram schematically showing a main part, and in this figure, reference numeral 61 denotes a product.
A lithic SOI substrate, a silicon single crystal substrate 62;
The upper surface of the silicon substrate 62 is formed by epitaxial growth.
Al formed by_TwoO _ThreeThe thin film 63 and this Al_TwoO_Three
It is formed on the upper surface of the thin film 63 by epitaxial growth.
And a silicon layer 64. Then, the silicon layer 64
SiO 2_TwoSi through the film 65_ThreeN_FourFrom the membrane
Is formed on the silicon layer 64.
N⁺Sources 69 and drains are placed on layers 67 and 68, respectively.
The in 70 is formed, and the ISFET 71 is formed.

In order to measure the pH of a solution using the one-chip pH sensor, a cell 72 made of an appropriate material is formed on the upper surface of the pH sensor section 66, and the cell 72 is measured.
This is performed by housing the solution 73 therein and immersing the comparison electrode 74 in the solution 73.

In the above one-chip pH sensor, S
Since the ISFET 71 is formed on the OI substrate 61, it has excellent features such as good electrical insulation, high stability and high performance, and the pH of the solution 73 can be accurately measured.

[0005]

However, in the above-mentioned conventional one-chip pH sensor, a reference electrode 74 is prepared when the solution 73 is measured, and the reference electrode 74 is provided in the pH sensor section 66.
It is necessary to provide it on the
It cannot be said that the space on the OI substrate 61 side was effectively utilized.

[0006] The above-mentioned problem is also occurring in an apparatus for measuring an ion concentration other than pH.

The present invention has been made in consideration of the above-mentioned matters, and an object of the present invention is to provide a more compact and high-performance one-chip type ion concentration measuring apparatus which makes full use of the features of an SOI substrate. That is.

[0008]

According to the present invention, there is provided a one-chip type ion concentration measuring apparatus in which an ion sensor is formed on an SOI substrate.
The liquid flow path and the reference electrode function part are formed in the silicon substrate part of the OI substrate by using a micromachining technique (claim 1).

In the one-chip type ion concentration measuring apparatus having the above structure, the inside of the relatively thick silicon substrate portion of the SOI substrate can be effectively used, and the overall size can be reduced.

In the one-chip type ion concentration measuring apparatus, the reference electrode function section may include an internal liquid, a reference electrode internal electrode, and a liquid junction. May have an electric field control type micropump (claim 3). Furthermore, the ion sensor section may be formed by an ISFET or a chemical CCD (claim 4).

[0011]

Embodiments of the present invention will be described with reference to the drawings. First, FIG. 1 shows a one-chip type pH as a one-chip type ion concentration measuring apparatus of the present invention.
In this figure, a sensor 1 is schematically shown. In this figure, reference numeral 2 denotes a monolithic SOI substrate, a silicon single crystal substrate (thickness, for example, 0.5 mm) 3 as a silicon substrate portion, and epitaxial growth on the upper surface of the silicon substrate 3. and Al ₂ O ₃ thin film 4 formed by the Al ₂ O ₃ thin film 4
And a silicon layer 5 formed by epitaxial growth on the upper surface of the substrate. Then, on the upper surface of the silicon layer 5,
A pH sensor portion 7 made of a Si ₃ N ₄ film is formed via an SiO ₂ film 6, and an ISFET comprising a source 8, a drain 9 and a gate 10 is formed on the silicon layer 5.
A section (an example of an ion sensor section) 11 is formed.

In FIG. 1, reference numeral 12 denotes a lower substrate which is bonded to the lower surface of the silicon single crystal substrate 3 by anodic bonding or the like, and is made of a silicon substrate having a thickness similar to that of the silicon substrate 2. Reference numeral 13 denotes a case provided so as to cover the periphery of the upper surface of the SOI substrate 2, the lower substrate 12, and the pH sensor unit 7, and is made of an appropriate resin. The upper portion 13a of the case 13 forms a cell facing the pH sensor section 7 and is formed so as to be able to store a solution 14 as a sample.

Reference numeral 15 denotes a comparison electrode function unit provided in the silicon substrate 3 and the lower substrate 11, which are substrate portions of the SOI substrate 2, and a liquid reservoir 1 for an internal solution 16 such as a KCl solution.
7 is formed over both substrates 3 and 11. In the liquid reservoir 17, an internal electrode 18 made of Ag / AgCl is provided.

Numeral 18 denotes a liquid flow path connected to the liquid reservoir 17, which is formed at a joint portion between the two substrates 3, 12.
A large diameter portion 19a is formed in the middle thereof, and an electric field control type micropump 20 is provided in the large diameter portion 19a. The liquid flow path 19 is bent upward substantially at a right angle at the large-diameter portion 19a, and the upper end thereof is connected to the pH sensor section 7.
To form a liquid junction 21.

The reference electrode function section 15 and the liquid flow path 19 are formed by using a micromachining technique.

In the one-chip type pH sensor 1 having the above-described structure, by storing the solution 14 in the cell 13a, the pH of the solution 14 can be measured similarly to the conventional one-chip type pH sensor. The one-chip type pH sensor 1 is provided in the substrate portion 3 of the SOI substrate 2 having the pH sensor portion 7 formed on the upper surface and in the lower substrate 12 of the one-chip type pH sensor 1. Device. It is also suitable for pH measurement when the amount of the solution 14 is small.

FIG. 2 shows the one-chip type p shown in FIG.
This embodiment shows a modification of the H sensor. In this embodiment, the SOI substrate 2 and the lower substrate 12 except for the pH sensor section 7 are entirely covered with a solution-resistant resin 22. 1A can be suitably used for pH measurement when the solution 14 is in a large amount or when the solution 14 is flowing.

One-chip pH shown in FIGS. 1 and 2
In the sensor, the solution 14 is located outside the one-chip type pH sensor 1 or 1A. Instead, a so-called flow in which the solution 14 flows through a flow path formed inside the one-chip type pH sensor is described. You may comprise a through type.
Hereinafter, this will be described with reference to FIGS.

First, the one-chip type pH shown in FIG.
In the sensor 1B, the solution 14 is placed inside the SOI substrate 2.
Are formed. And one chip type p
In the H sensor 1B, the comparison electrode function unit 15
It is formed over the substrate 2 and the lower substrate 12. In FIG. 3A, reference numeral 24 denotes a pH sensitive portion made of Al ₂ O ₃ , 25 denotes a Si single crystal thin film, and 26 denotes a liquid junction.

FIG. 3B is a modification of the one-chip type pH sensor 1B shown in FIG. 3A. In FIG. 3B, the comparison electrode function part 15 is formed only on the SOI substrate 2 side. I have.

FIGS. 4 and 5 show a one-chip type pH sensor 1C incorporating a chemical CCD. FIG. 4 is a perspective view showing the appearance of the one-chip type pH sensor 1C. In FIG. 5, reference numeral 27 denotes a flow path through which the solution 14 flows, and a silicon substrate 30 on which a chemical CCD 28 and a CCD charge transfer section 29 are formed as shown in FIG.
Is formed within. FIG. 5A shows a chemical CCD2.
8 shows a measuring unit, in which 31 is a pH-sensitive unit which is sensitive to pH as a chemical phenomenon, and 32 to 34 are electrodes. FIG. 5B schematically shows an example of the configuration of the CCD charge transfer section 29. In this figure, 35 is a vertical scanning circuit, 36 is a horizontal scanning circuit, and 3 is a horizontal scanning circuit.
Reference numerals 7 and 38 denote switching elements that are turned on and off by the scanning circuits 35 and 36, 39 denotes a switching gate voltage power supply, and 40 denotes a resistor for extracting a current as a voltage to an output terminal 41.

The one-chip type pH sensor 1B having the above configuration,
In 1C, since the solution 14 to be measured is not exposed to the outside during the measurement, it is possible to perform more accurate measurement without foreign substances entering the solution.

Although the one-chip type ion concentration measuring apparatus in the above embodiment measures the pH of a solution, the present invention is not limited to this. By forming an ion sensor portion that is sensitive to ions other than (pH), various ion concentrations can be measured.

[0024]

As described above, according to the one-chip type ion concentration measuring apparatus of the present invention, a liquid flow path and a comparative electrode function section are formed in a silicon substrate section of an SOI substrate by using micromachining technology. As a result, the features of the SOI substrate such as good electrical insulation can be fully utilized, and it can operate stably and have high performance.
It is smaller and more compact.

[Brief description of the drawings]

FIG. 1 is a longitudinal sectional view schematically showing an example of a one-chip type pH sensor as a one-chip type ion concentration measuring device of the present invention.

FIG. 2 is a longitudinal sectional view schematically showing a modification of the one-chip type pH sensor.

FIGS. 3A and 3B are longitudinal sectional views each showing an example of a one-chip type pH sensor in which a solution flow path is formed.

FIG. 4 is a diagram showing an external shape of a one-chip type pH sensor incorporating a chemical CCD.

FIG. 5A is a longitudinal sectional view schematically showing a configuration of a measuring unit in the one-chip type pH sensor, and FIG.
FIG. 3 is a diagram schematically illustrating an example of a configuration of a charge transfer unit 29.

FIG. 6 is a diagram for explaining a conventional technique.

[Explanation of symbols]

2 SOI substrate, 3 silicon substrate, 11, 31 ion sensor, 15 reference electrode function, 16 internal liquid,
18 internal electrode for comparison electrode 19 liquid channel 21, 21
A, 26: liquid junction, 28: chemical CCD.

Claims (4)

[Claims] 1. A one-chip type ion concentration measuring apparatus in which an ion sensor section is formed on an SOI substrate.
A one-chip type ion concentration measurement device, wherein a liquid flow path and a reference electrode function part are formed in a silicon substrate part of a substrate by using micromachining technology. 2. The one-chip type ion concentration measuring apparatus according to claim 1, wherein the reference electrode function section comprises an internal liquid, a reference electrode internal electrode, and a liquid junction. 3. The one-chip type ion concentration measuring apparatus according to claim 2, wherein the liquid junction comprises an electric field control type micropump. 4. The one-chip type ion concentration measuring apparatus according to claim 1, wherein the ion sensor section comprises an ISFET or a chemical CCD.