JPS60115841A - Ion sensor - Google Patents

Abstract

PURPOSE:To decrease heating temp. and to obtain an excellent sensor by coating a mixture composed of metallic alkoxides and metallic acetylacetonate corresponding to the metallic compsn. for forming desired ion sensitive oxide glass on a base material for an ion sensor and subjecting the coating to a heating treatment. CONSTITUTION:A mixture composed of alkoxides acetylacetonate of respective metals so as to form the compsn. corresponding to the inorg. compd. Na2O, SiO2, Al2O3, B2O3, etc. to be used for production of an ion selective glass electrode is dissolved in methanol or the like and the soln. is coated on the insulating film (SiO2 film) 14 on the gate part 13 of, for example, a field effect type transistor element 1 thereby forming uniformly a liquid film. The element is then rested for about 20mis in air to have the moisture in air absorbed in the coating thereby hydrolyzing the metallic alkoxides and acetylacetonate. Such element 1 is subjected to a heating treatment for about 5min at about 450 deg.C in an electric furnace to form a uniform glass sensitive film 2. The transparent and uniform film 2 is thus efficiently formed at the lower temp. than in the case of using only the metallic alkoxide and the sensor having excellent linearity in responsiveness is obtd.

Description

DETAILED DESCRIPTION OF THE INVENTION (a) Field of Industrial Application 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) Prior art Conventionally, ion-sensitive glass membranes for ion sensors such as ion-selective glass electrodes, as typified by pH electrodes, have been produced by melting various raw materials at high temperatures (usually over 1400°C) and forming them into a certain shape. It is made with. 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 in terms of molding, and as a result, the resulting glass electrode also has a large internal resistance, which is 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 of 500°C or higher in the final process to convert the film into oxide glass, and field-effect transistors (FE
When fabricating an ion sensor that combines an electric element such as a field effect ion selective electrode (IS-FET) with a sensitive film formed on the gate of a T), there is a risk that the electric element may be adversely affected by the heating temperature. There was that. Therefore, it has been desired to lower the heat treatment temperature.

Furthermore, since the hydrolysis rate of alkaline earth metal alkoxides is extremely fast, ion-sensitive oxide glasses containing alkaline earth metals (e.g., pH glass membranes) can be uniformly It was difficult to produce transparent IIIJ.

Moreover, since alkaline earth metal alkoxides are hardly soluble in lower alcohols, which are good bath media for hydrolyzing other alkoxides, there is also the problem that it is difficult to obtain a uniform alkoxide raw material bath solution. Ta.

(C) Purpose This invention has been made in view of the above-mentioned conventional problems, and an object of the present invention is to provide an ion sensor equipped with an ion-sensitive glass film that can be formed under lower heat treatment temperature conditions. purpose. 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 easily and efficiently.

B) Structure 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 corresponding to the metal composition of the desired ion-sensitive oxide glass. An ion sensor is provided, which is formed by applying an 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.

The metal alkoxides used in this invention include various inorganic oxides (Na2O, SiO□, A1.203, B2O3
etc.) are used, specifically NaOCH3, Ca (oc 2H5) 2.5
i(OC2H5) 4, At(OC3H7)3, B(O
Examples include C2H5)3.

On the other hand, as the metal acetylacetonate used in this invention, unique metal acetylacetonates used in the field of chelate titration can be used, and specific examples thereof include calcium acetylacetonate, aluminum acetylacetonate, and titanium acetylacetonate. nate, 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 a sensitive glass is intended, a mixed solution corresponding to the composition of Si, Na and Ca may be used, and when a Na+sensitive glass is intended, a mixture of Si, Na and Ca may be used.

A mixed solution corresponding to the composition of Na, At and B may be used, and the same applies to other combinations. Such a metal alkoxide/metal acetylacetonate mixed solution lacks the 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 1-sensitivity glass in the above example, it is preferable 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.

It is preferable to use a volatile hydrophilic solvent as the solvent for the metal alkoxide/golden acetylacetonate mixed solution, and water may be contained in the solvent. As mentioned above, lower alcohols such as methanol and ethanol are suitable as the volatile hydrophilic solvent. In addition, it is desirable to heat the thread to the melting point of the metal alkoxide or metal acetylacetonate, which has the highest melting point when dissolved in the solvent, to make the solution as uniform as possible.

The above solution is first applied to the base material of the ion sensor. The thickness of the final glass film is usually 01 to 0.
．． The thickness is adjusted to 2 μm.

The metal alkoxide and metal acetylacetonate in the applied solution are gradually hydrolyzed by water absorbed through the solvent and/or contained water, respectively,
A uniform gel-like film is formed 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 includes an ion-selective glass electrode, a coated wire type ion-selective electrode, and an 15-F
Any form of ET may be used. 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, by coating the ion-sensitive surface of a prefabricated or commercially available glass electrode tube and providing an appropriate internal electrode and internal liquid, N.
A desired ion-selective electrode such as an a+ ion-selective electrode can be easily obtained. In addition, when producing a coachite wire type ion-selective electrode, an electronically conductive or ion-conductive material such as amalgam or solid electrolyte (e.g., transition metal...logenide or sulfide) is added to the lead wire of a metal such as gold or platinum. It can be easily obtained by coating a conductive substance layer and forming the ion-sensitive glass membrane on top of the coating.

However, when manufacturing a 15-F'ET, it is easy to form the ion-sensitive glass film on the gate part of the FET* element, which is composed of a source part, 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 part insulating film, a gate part insulating film (usually SiO2
Although it was necessary to convert or coat the surface of the gate insulating film with silicon nitride (Si3N4) in advance, it is possible to form a coating directly on the gate insulating film without performing such treatment and still have good response. It has also been found that an ion sensor equipped with this method can be obtained, and is also favorable in terms of yield.

The specific structure of such l5-PET is shown in FIG. In the figure, (1) shows an FET element composed of a source part (11), a drain part (0), a gate part (T), and an SiO□ insulating film (14), and (2) shows a metal alkoxide/ This figure shows an ion-sensitive glass membrane coated from a metal acetylacetonate mixed solution. Especially the l5
In -F18T, the temperature during the production of the ion-sensitive glass film is lower than that of the conventional one, so the thermal influence on the FET element is reduced.

(E) Examples Example 1゜SiO: Na2O: CaO is 72:20:
A pHl5-FET was prepared with an H+ sensitive oxide glass composition having a composition ratio of 8 (mot%).

First, in 40d of methanol, tetraethoxysilay (
5i (QC2H5)4) was added in an amount of 0.012 mot, and sodium methoxy (NaOCH3) and calcium aceteracetonate (Ca (Cs H70□)2) were added.
) was added in an amount corresponding to the above molar ratio and stirred at 80° C. for 30 minutes to obtain a uniform metal alkoxide/metal acetylacetonate mixed bath liquid. This solution was added to a field effect transistor wire (0.5we x 6.5m x O,2m
= gate part insulating film (S
A uniform liquid film was formed by applying the solution onto a 10□ film) by a dipping method.

Next, the above element is left in the air for about 20 minutes to hydrolyze and gel the metal alkoxide and metal acetylacetonate by light, and then the element is placed in an electric furnace and heat treated at 450°C for 5 minutes. As a result, an ion sensor of the present invention as shown in FIG. 1 was obtained in which a transparent H+ sensitive glass film with a thickness of approximately 0.111 m was uniformly formed on the gate insulating film. The results of measuring the responsiveness are shown in Figure 2. As shown, the slope was 58 m/H and the linearity was excellent.

Example 2゜5iOaNaO:B2O3:At203 is 66:20
2.2: Na with a composition ratio of 3 m L 1 (mo1%)
Na I S F E with the intention of sensitive oxide glass composition
I made T.

Tetraethoxysilane, sodium methoxy, triethoxyboron (B(OC2H5)3) corresponding to the above molar ratio
) and aluminum acetylacetonate (At(c5
t-t7o2),,) was dissolved in methanol, and this was nuclided into FgT cords and hydrolyzed in the same manner as in Example 145
A Nal5-FET similar to that shown in FIG. 1 was obtained by heat treatment at 0° C. for about 10 minutes.

The responsiveness of this ion sensor to Na+ ions is
A solution of 10 to 10 mot/l of Na 1tit (2
When measured at 40°C), excellent linearity was obtained above 10 mol/l, with a slope of 5fi, 6rn/dec
This was close to Nernst's theoretical value.

On the other hand, triisopropoxyaluminum was used instead of the aluminum acetylacetonate (i.e.,
An ion sensor obtained in the same manner as above except that all metal alkoxides were made of corresponding metal alkoxides and the heat treatment temperature was 500°C had similar excellent linearity and a diameter of 58.2 m.
//deo was close to Nernst's theoretical value,
When the heat treatment temperature was lowered by 50°C and carried out at 450°C for 10 minutes, ■ vitrification was insufficient and the response slope was 44-7 m/a.
. .

It was found that the straightness and boxability were also inferior. That is, it has been found that heat treatment at about 450° C. is insufficient when only metal alkoxide is used.

(f) Effects As mentioned above, the ion sensor of the present invention can reduce the heat treatment temperature compared to conventional similar sensors, and is advantageous from an energy standpoint, especially in terms of FI.
) It is advantageous when an electric element such as a T 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 the drawing]

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. (11...FET element, (2)...
...Ion-sensitive glass membrane, Ol)...
Source part, (1no...Drain part, 03)
・・・・・・・・・Gate part, 041・・・・・・・・・
・Insulating film. Agent Patent Attorney Nogawa 46 Inu Department

Claims (3)

[Claims] (1) An ion-sensitive glass film is formed on an ion sensor substrate, and the ion-sensitive glass film is coated with a metal alkoxide/gold maple acetylacetonate mixed solution corresponding to the metal composition of the desired ion-sensitive oxide glass. An ion sensor characterized in that it is formed by applying it onto an ion sensor base material and subjecting it to heat treatment. (2) The 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) Metal acetylacetonate is alkaline earth gold M
7. The ion sensor according to claim 1 or 2, which is 7 cetyl acetonate.