JPH0469337B2 - - Google Patents

Description

[Detailed Description of the Invention] (a) Industrial Application Field This invention relates to an ion sensor. More specifically, the present invention relates to an ion sensor that can selectively detect specific ions in a liquid and can be used for various analyzes and measurements.

(b) Conventional technology Conventionally, ion-sensitive glass membranes of ion sensors such as ion-selective glass electrodes, as typified by PH electrodes, have been used to heat various raw materials at high temperatures (usually over 1400°C).
It is manufactured by melting it and molding it into a certain shape. However, with this method, it is difficult to obtain a glass film with the intended composition because the composition tends to change due to evaporation of volatile components during high-temperature melting, and there are production difficulties due to the generation of bubbles in the glass.
Furthermore, there is a limit to the thickness of the glass film due to molding, so the resulting glass electrode also has a large internal resistance.
This was disadvantageous in terms of accurate electrochemical measurements.

For this reason, an ion sensor has been proposed in which an ion-sensitive glass film is formed by a solution method (hydrolysis and heat treatment) of a plurality of metal alkoxides corresponding to the metal composition of the desired ion-sensitive oxide glass.

However, in practice, such ion sensors still require heat treatment at temperatures above 500°C in the final process to convert the film into oxide glass, and a sensitive film is placed on the gate of a field-effect transistor (FET). The field-effect ion-selective electrode (IS-
When manufacturing ion sensors in combination with electric elements such as FETs, there was a risk that the electric elements could be adversely affected by the heating temperature. Therefore, it has been desired to lower the heat treatment temperature.

Furthermore, alkaline earth metal alkoxides in particular have a very fast hydrolysis rate, so if an ion-sensitive oxide glass containing an alkaline earth metal as a component (e.g. PH glass membrane) is intended, it will be uniform and transparent. It was difficult to fabricate a film with a similar shape. Moreover, since alkaline earth metal alkoxides are hardly soluble in lower alcohols, which are good solvents for hydrolyzing other alkoxides, there was also the problem that it was difficult to obtain a uniform alkoxide raw material solution.

(c) Purpose This invention has been made in view of the above conventional problems, and one purpose is to provide an ion sensor equipped with an ion-sensitive glass membrane that can be formed under lower heat treatment temperature conditions. do. moreover,
Another object of the present invention is to provide an ion sensor equipped with an ion-sensitive glass membrane that is transparent, uniform, and can be formed simply and efficiently.

(d) Configuration Thus, according to the present invention, an ion-sensitive glass film is formed on an ion sensor substrate, and the ion-sensitive glass film contains metal alkoxide/metal alkoxide corresponding to the metal composition of the desired ion-sensitive oxide glass. An ion sensor is provided, which is formed by applying a metal acetylacetonate mixed solution onto an ion sensor substrate and heat-treating it.

The most distinctive feature of this invention is that the ion-sensitive glass membrane is formed not from a plurality of metal alkoxide solutions corresponding to the metal composition thereof, but from a plurality of metal alkoxide/metal acetylacetonate mixed solutions. In other words, it is formed from an organic metal compound mixed solution in which at least one of the plurality of metal alkoxides as raw materials is replaced with the corresponding metal acetylacetonate.

As the metal alkoxide used in this invention,
Various inorganic oxides (Na ₂ O, SiO ₂ , A ₂ O ₃ ,
_{B2O3 ,} etc.) are used, specifically _NaOCH3 , Ca( _OC2H5 ) ₂ , _Si
(OC ₂ H ₅ ) ₄ , A(OC ₃ H ₇ ) ₃ , B(OC ₂ H ₅ ) ₃ and the like.

On the other hand, as the metal acetylacetonate used in this invention, various metal acetylacetonates used in the field of chelate titration can be used, and specific examples thereof include calcium acetylacetonate, aluminum acetylacetonate, and titanium acetylacetonate. , zinc acetylacetonate, iron acetylacetonate, potassium acetylacetonate, zirconium acetylacetonate, and the like.

The composition of the metal alkoxide/metal acetylacetonate mixed solution is determined depending on the metal composition of the desired ion-sensitive oxide glass. For example, when intending H ⁺ sensitive glass, Si, Na
It is sufficient to use the above-mentioned mixed solution corresponding to the composition of Si, Ca and Na ⁺ sensitive glass.
A mixed solution corresponding to the composition of Na, A, and B may be used, and the same applies to other combinations.
Such a metal alkoxide/metal acetylacetonate mixed solution has a characteristic that the conversion temperature to an oxide is lower than that of the corresponding metal alkoxide solution.

In particular, when the composition of the corresponding ion-sensitive oxide glass contains an alkaline earth metal, it is best to combine the corresponding alkaline earth metal acetylacetonate with a metal alkoxide corresponding to other metals. preferable. That is, it is preferable not to use the alkaline earth metal alkoxide used in combination with the conventional alkoxide solution method, but to use alkaline earth metal acetylacetonate instead. More specifically, in the case of the H ⁺ -sensitive glass in the above example, it is preferred to combine lower alkoxysilane, lower sodium alkoxy and calcium acetylacetonate. In such a combination, in addition to the effect of reducing the processing temperature, since no alkaline earth metal alkoxide is used, there is no extreme difference in the rate of hydrolysis, and as a result, a desirable transparent and uniform ion-sensitive glass film can be efficiently formed. can be done. Furthermore, lower alcohols that are easy to handle as organic solvents can be used.

As the solvent for the metal alkoxide/metal acetylacetonate mixed solution, it is preferable to use a volatile hydrophilic solvent, and this solvent may contain water. As mentioned above, lower alcohols such as methanol and ethanol are suitable as the volatile hydrophilic solvent. When dissolving in a solvent, it is desirable to heat the solution to about the melting point of the metal alkoxide or metal acetylacetonate having the highest melting point to make the solution as uniform as possible.

The above solution is first applied to the base material of the ion sensor. This thickness is usually adjusted to such an extent that the final glass film has a thickness of 0.1 to 0.2 μm.

The metal alkoxide and metal acetylacetonate in the applied solution are absorbed through the solvent and gradually hydrolyzed by the water and/or the water content, forming a uniform gel-like film as the solvent evaporates. . By heating the gel-like membrane thus obtained, the hydrolyzate of the gel-like membrane is dehydrated and condensed to form an oxide glass, thereby obtaining the ion-sensitive glass membrane of the present invention. The heating temperature at this time is usually less than 500°C, which is sufficient, and the heating temperature is several tens of degrees lower than when a solution containing only metal alkoxide is used.

The ion sensor of the present invention may be in the form of an ion-selective glass electrode, a coated wire type ion-selective electrode, or an IS-FET.
When producing an ion-selective glass electrode, an electrode tube with a carrier, such as glass, whose tip can be coated with an ion-sensitive glass membrane is used as the ion sensor substrate, and the surface of this substrate is coated with the glass membrane as described above. It is appropriate to apply a coating of Usually, a desired ion-selective electrode such as a Na ⁺ ion-selective electrode can be easily obtained by coating the ion-sensitive surface of a glass electrode tube prepared in advance or commercially available, and providing an internal electrode or internal liquid as appropriate. I can do it. In addition, when producing a coated wire type ion-selective electrode, an electronically conductive or ionically conductive material such as amalgam or a solid electrolyte (for example, a transition metal halide or sulfide) is used for the lead wire of a metal such as gold or platinum. This can be easily obtained by coating a layer of material and forming the ion-sensitive glass membrane on top of the layer.

In addition, when fabricating IS-FET, the source part,
The ion-sensitive glass film can be easily formed by coating the gate part of the FET element, which is composed of a drain part and a gate part. Conventionally, when coating an ion-sensitive glass film on the gate part of such a FET element, that is, on the gate insulating film, the surface of the gate insulating film (usually a SiO ₂ film) was previously coated with silicon nitrogen (Si ₃ N ₄ ). Although conversion or coating was required, an ion sensor with good response can be obtained even if the coating is directly formed on the gate insulating film without such treatment.
Moreover, it was also found that it is preferable in terms of yield.
The specific configuration of such an IS-FET is shown in Figure 1. In the figure, 1 is a source part 11, a drain part 1
2 shows an FET element composed of a gate part 13 and a SiO ₂ insulating film 14, and 2 shows an ion-sensitive glass film coated with a metal alkoxide/metal acetylacetonate mixed solution. In particular, in IS-FETs like this, the temperature during fabrication of the ion-sensitive glass membrane is lower than that of conventional ones.
Thermal influence on the FET element is reduced.

(E) Examples Example 1 PH was applied with the intention of creating an H ⁺ sensitive oxide glass composition with a composition ratio of SiO ₂ :Na ₂ O:CaO of 72:20:8 (mo%).
An IS-FET was fabricated.

First, 0.012 mo of tetraethoxysilane (Si(OC ₂ H ₅ ) ₄ ) was added to 40 ml of methanol, and sodium methoxy (NaOCH ₃ ) and calcium acetylacetonate (Ca(C ₅ H ₇ O ₂ ) ₂ ) were added. An amount corresponding to the above molar ratio was added and stirred at 80°C for 30 minutes to obtain a uniform metal alkoxide/metal acetylacetonate mixed solution. This solution is applied using the dip method onto the gate insulating film (SiO ₂ film) of a field effect transistor element (0.5 mm x 6.5 mm x 0.2 mm: gate surface area approximately 0.06 mm ² ) to form a uniform liquid film. I let it happen.

Next, the above element was left in the air for about 20 minutes to sufficiently hydrolyze the metal alkoxide and metal acetylacetonate to gel, and then the element was placed in an electric furnace and heat treated at 450°C for 5 minutes. An ion sensor of the present invention as shown in FIG. 1 was obtained in which a transparent H ⁺ sensitive glass film having a thickness of about 0.1 μm was uniformly formed on a gate insulating film.

Figure 2 shows the results of measuring the responsiveness of this ion sensor to H ⁺ at 26°C. Thus, the slope was 58 ^mV /PH and the linearity was excellent.

Example 2 SiO ₂ :Na ₂ O:B ₂ O ₃ :A ₂ O ₃ is 66:20:3:
A Na ⁺ IS-FET was fabricated with the intention of having a Na ⁺ sensitive oxide glass composition with a composition ratio of 11 (mo%).

Tetraethoxysilane corresponding to the above molar ratio,
Methoxysodium, triethoxyboron (B
(OC ₂ H ₅ ) ₃ ) and aluminum acetylacetonate (A(C ₅ H ₇ O ₂ ) ₂ ) were dissolved in methanol,
This was coated on an FET element in the same manner as in Example 1, hydrolyzed, and heat treated at 450° C. for about 10 minutes to obtain a Na ⁺ IS-FET similar to that shown in FIG. 1.

When the responsiveness of this ion sensor to Na ⁺ ions was measured in a solution (24.0°C) with a Na ⁺ activity of 10 ^-4 to ¹⁰⁰ mo/, excellent linearity was obtained above 10 ^-3 mo/. , the slope was 56.6 m ^V /dec, which was close to Nernst's theoretical value.

On the other hand, an ion sensor obtained in the same manner as above except that triisopropoxyaluminum was used instead of aluminum acetylacetonate (that is, all the corresponding metal alkoxides were used) and the heat treatment temperature was 500°C was obtained in the same manner. The linearity was excellent and the slope was 58.2 m ^V /dec, close to Nernst's theoretical value, but when the heat treatment temperature was lowered by 50°C and carried out at 450°C for 10 minutes, the vitrification was insufficient and the response was poor. The slope was 44.7 m ^V /dec, and the linearity was also found to be poor. In other words, it has been found that heat treatment at about 450°C is insufficient when only metal alkoxide is used.

(f) Effects As stated above, the ion sensor of the present invention can reduce the heat treatment temperature compared to similar conventional sensors, and is advantageous from an energy standpoint, especially when using electric current such as FET elements. This is advantageous when the element is used as a base material. Furthermore, ion sensors that use alkaline earth metal acetylacetonate as one component can easily and efficiently produce transparent and uniform ion-sensitive glass membranes compared to those that use alkaline earth metal alkoxides as one component. This is advantageous in manufacturing.

[Brief explanation of drawings]

FIG. 1 is a configuration explanatory diagram including a cross section showing a specific example of the ion sensor of the present invention, and FIG. 2 is a graph illustrating the responsiveness of the ion sensor of the present invention. 1... FET element, 2... ion-sensitive glass membrane,
11...source section, 12...drain section, 13...
...Gate portion, 14...Insulating film.

Claims (1)

[Claims] 1. A metal alkoxide/metal acetylacetonate mixed solution corresponding to the metal composition of the desired ion-sensitive oxide glass film is applied onto the ion sensor substrate, and an ion-sensitive oxide glass film is formed by heat treatment. A method for manufacturing an ion sensor, characterized by forming an ion sensor. 2. The method of manufacturing an ion sensor according to claim 1, wherein the ion sensor substrate is a field effect transistor element, and an ion-sensitive glass film is formed on the gate portion of the ion sensor substrate. 3. The method for producing an ion sensor according to claim 1 or 2, wherein the metal acetylacetonate is an alkaline earth metal acetylacetonate.