JPH0387644A - Ion sensor and sensor plate - Google Patents

Abstract

PURPOSE:To obtain the sensor which has high measurement accuracy and is usable without calibrating the output value corresponding to an ion concn. by forming the silver chloride particles of silver chloride layers essentially consisting of the silver chloride to <=1mum grain size. CONSTITUTION:Silver layers 2a, 2b are respectively formed by electroplating on copper electrodes 1a, 1b and the silver chloride layers 3a, 3b are formed on the surfaces of the silver layers 2a, 2b. The silver chloride particles of the silver layers 2a, 2b are formed to <=1mum grain size. The silver chloride layer 3a is coated with an ion sensitive film 4 essentially consisting of a vinyl chloride/vinyl acetate copolymer. A dam body 5 is formed of the insulator of an epoxy resin so as to enclose the electrode formed with this ion sensitive film 4 and the silver chloride layer 3b. The sensor plate which is laminated with the silver layers 2a, 2b and the silver chloride layers 3a, 3b respectively on the copper electrodes 1a, 1b, is provided with the ion sensitive film 4 on the silver chloride layer 3a and uses the silver chloride layer 3b as a reference electrode for sepn. is obtd. in such a manner. Since the silver chloride particles are densely packed at a high density, the fluctuation of the potential generated between the silver chloride layers and the ion sensitive film is lessened.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an ion sensor that does not require output calibration and reduces variations in output characteristics, and a sensor plate for its components.

[Conventional technology]

An ion sensor is used to measure the concentration of ions in a sample liquid, and is a so-called ion-sensitive field-effect transistor in which an ion-sensitive film is formed on the gate electrode of a field-effect transistor (FET) formed in a semiconductor. Transistor (
ISFET). This 15FET utilizes the fact that when an ion-sensitive membrane is brought into contact with a sample liquid, the conductivity near the semiconductor surface changes in response to changes in the electric field generated at the interface between the ion-sensitive membrane and the solution, and this is controlled by an external circuit. It is designed to be detectable.

In this 15FET, a separate gate electrode is provided not on the semiconductor substrate on which the FET is formed, but on another insulating substrate, an ion-sensitive membrane is provided on this, and a separate comparison electrode is provided facing each other to make it an independent component. A so-called separated gate type 15FET is also known, which is used by connecting the FET to an FET.

The ion sensing part of such a separated gate type I5FET ion sensor is made of a so-called printed wiring board, which is made by bonding a 35 μm-thick copper foil onto an insulating substrate, such as a glass epoxy resin substrate, using a photolithographic method, etc. A copper conductive pattern of a predetermined shape is etched by etching, and then electrolytically plated using a commercially available thick silver plating bath, etc., a silver layer is formed on the surface to a thickness of several μs 1 to 20 μs, and then a silver layer is etched using hydrochloric acid. A silver chloride layer having a thickness of several micrometers is formed on the surface of the silver layer by immersing it in a solution or a sodium chloride solution and performing an electrochemical conversion treatment. Next, after forming an embankment using an insulating resin, such as an epoxy resin, to surround the electrode, which has a laminated structure of a silver layer and a silver chloride layer on the surface layer, an embankment containing a macrocyclic compound called an ionophore, an ion exchange resin, etc. It forms an ion-sensitive membrane, and this structure was proposed in a previous application.

[Problem to be solved by the invention]

However, even if conventional ion sensors are manufactured in the same way under the same conditions, there will be differences in output corresponding to the same ion concentration, and even though the ion concentration is constant,
Constant output is often not obtained. Therefore, each ion sensor is used after being calibrated.

In the calibration method, after connecting the ion sensor to the output circuit device, two different predetermined solutions are prepared, the ion sensor is immersed in one of the ion concentration solutions, and the output is read. If the value differs from a predetermined standard value, the circuit constants of the output circuit device are adjusted to match the standard output value. Next, the ion sensor is immersed in a solution with another ion concentration, and the circuit constants are adjusted in the same manner as above so that the output value matches the standard value corresponding to that ion concentration. After that, immerse the ion sensor in one of the above ion concentration solutions again, and if the output value differs from the corresponding standard value, adjust the circuit constants again in the same way as above, and repeat this for the other ion concentrations. Repeat the calibration until the output value for the ion concentration becomes the standard value.

This kind of proofreading work involves many steps and is cumbersome.
Furthermore, it was labor-intensive and difficult to use as an ion sensor.

Therefore, an ion sensor and its A sensor plate made of split parts was proposed in a previous application. According to this, the minimum variation in output for a sample liquid with a constant ion concentration is 0.8 m with a standard deviation.
This results in a measurement error of only about 3%, which is a considerable improvement over the standard deviation of 3.0 mV or more when the surface roughness is greater than 200 nm. However, when attempting to further improve measurement accuracy, it has not been possible to meet this demand, and improvements have been sought.

An object of the present invention is to provide an ion sensor that can be used without calibrating the output value corresponding to ion concentration.

Another object of the present invention is to improve measurement accuracy by further reducing variations in output values corresponding to ion concentrations.

[Means to solve the problem]

In order to solve the above-mentioned problems, the present invention provides an ion sensor in which a field-effect semiconductor can detect a sensitive value of a sample liquid using an electrode coated with an ion-sensitive membrane. An ion characterized in that the electrode has a laminated structure consisting of an upper layer mainly composed of silver chloride and a lower layer mainly composed of silver, and the particle size of the particles constituting the upper layer is smaller than 1 μm. It provides a sensor.

In addition, a separate gate electrode and a separate reference electrode, which are used in connection with the gate electrode of the field effect semiconductor, are provided on an insulating substrate separate from the field effect semiconductor substrate, and an ion-sensitive electrode is provided on the separate gate electrode. The separation gate electrode coated with the ion-sensitive membrane has a laminated structure consisting of an upper layer containing silver chloride as a main component and a lower layer containing silver as a main component, and the upper layer comprises The present invention provides a sensor plate characterized in that the particle diameter of the particles is smaller than 1 μm.

[Effect]

When the silver chloride particles in the silver chloride layer containing silver chloride as the main component are made to have a particle size of 1 μm or less, the silver chloride particles are densely and densely packed, and the potential generated between the silver chloride layer and the ion-sensitive membrane is reduced. Variations in the output of the ion sensor can be reduced.

〔Example〕

Next, examples of the present invention! @1 The explanation will be based on Figures (a) and (b).

The copper foil adhered to the paper polyester substrate 1 was buttered by a photographic method, polished with a 2 μm diamond slurry, and polished to a mirror surface [surface measured with a stylus film thickness meter (Tencor thin film surface profiler Alpha Step 200). Copper electrodes 1a and 1b having a predetermined shape were formed.

Next, using a cyan Yoroku strike mesh bath with the composition shown in Table 1 and a constant current power supply, a platinum-plated titanium mesh was used as an anode and the cathode current density was 0.5 A/dm. The substrate was immersed in the bath for a second, taken out, and washed with water.

Then, it was immersed in a cyan-based electrolytic silver plating solution having the composition shown in Table 1 while maintaining the temperature at 50°C, and electroplated for 15 minutes at a cathode current density of 1.2 A/dm using the silver edge as an anode.
Silver layers 2a, 2 of 15μ- thickness are provided on the copper electrodes 1a, lb, respectively.
It was a form of b.

Thereafter, in 0.1 normal (N) hydrochloric acid (HCI), the potential was swept for 5 cycles from 150 mV to 350 mV using the substrate as a working electrode, a platinum electrode as a counter electrode, and a silver or silver chloride electrode as a reference electrode. A fine grain silver chloride layer is preliminarily formed. Thereafter, the above substrate was used as an anode and the platinum-plated titanium mesh was used as a cathode in 0.1N hydrochloric acid, and the anode current density was 0.
Electrolytic treatment was performed at 23A/d- for 2 minutes and 40 seconds to form silver layers 2a and 2.
Silver chloride layers 3a and 3b were formed on the surface of b. The particle diameter of the silver chloride particles in this silver chloride layer was found to be 0.1 to 0.2 μm in diameter when observed using a scanning electron microscope. The surface roughness of this silver chloride layer was 200 nm as measured by the stylus thickness meter.

The silver chloride layer 3a is coated with an ion-sensitive membrane 4 mainly composed of a vinyl chloride-vinyl acetate copolymer, and an epoxy resin is applied so as to surround the electrode formed with this ion-sensitive membrane and the silver chloride electrode 3b. The embankment body 5 was formed of a resin insulator.

In this way, the copper electrodes 1a and 1b have silver layers 2a and 1b, respectively.
A sensor plate is completed in which the silver chloride layer 3a is provided with an ion-sensitive membrane 4, and the silver chloride layer 3b is used as a separation reference electrode.

In this way, 80 sensor plates were created.

These sensor plates use an electrode provided with an ion-sensitive membrane as a separation gate, which is connected to the gate electrode of an FET (not shown), and on the other hand, connects the FET to an output circuit device using the potential indicated by the separation comparison electrode as a reference value. However, by dropping the test liquid onto the inner side of the embankment body, the concentration of ions contained therein can be measured as an output value of the ion sensor.

This ion sensor has potassium ion concentrations of 1mM and 3mM.
, 10+nM, and 305M solutions were dropped, and the respective outputs were measured to confirm that the output values had a linear relationship with the logarithm of the ion concentration. After that, connect the sensor plate to FET
The 79 sensor plates were connected in the same manner as above, and the same measurements were performed on the ion sensors using these sensor plates. Among these output values, the output values when a solution with a potassium ion concentration of 1 axis H was used as the sample liquid were extracted, statistically processed, and their standard deviations were determined, and are shown in Table 2. In addition, a copy of the electron micrograph is shown in Figure 2 (a), and this photo is submitted as the reference photo (a).

In the above Example 1, the silver strike plating is omitted,
The cathode current density was 0.42 A/d rd by immersing it in a cyan electrolytic plating solution with the composition shown in Table 1 at room temperature and using the chain line as the anode.
Electrolytic plating was performed for 20 minutes to form a silver layer with a thickness of approximately 15 μm, and the silver chloride layer was formed by omitting the preliminary formation of a fine-grain silver chloride layer, which was then observed using a scanning microscope. Sensor plates of 80 IIl were prepared in the same manner except that the particle diameter of the silver chloride particles was changed to 1 to 2 μm, and ion sensors were prepared using each of these plates. Measurements were made in the same manner, and the standard deviation of the output values was determined, and the results are shown in Table 2. In addition, a copy of the electron micrograph is shown in Figure 2 (a) and submitted as a reference photo (b).

Table 1 (Plating bath composition) Unit 2 g/Example 2 A silver chloride layer was formed in the same manner as in Example 1 except that the preliminary formation of the 11-layer chloride layer of fine particles was omitted, and then a scanning type 80 sensor plates were created in the same manner except that the particle size of the silver chloride particles observed with an electron microscope was changed to 0.2 to 0.5 μm, and each of these was used to create an ion sensor, and each was carried out. Measurement was carried out in the same manner as in Example 1, the standard deviation of the output value was determined, and the results are shown in Table 2.
Shown below.

In addition, a copy of the electron micrograph is shown in Figure 2 (c), and the photograph is submitted as a reference photograph (c).

Table 2 [Effects of the Invention] According to the present invention, the electrode provided with the ion-sensitive membrane has a laminated structure consisting of a lower layer (11 layers) mainly composed of silver and an upper layer mainly composed of silver chloride. The particle size of the layer particles is 1μ
Since the particles in the upper layer are densely and densely packed, the variation in the potential generated at the interface between the electrode and the ion-sensitive membrane is reduced, and as a result, the variation in the output potential of the ion sensor is reduced. decreases. Therefore, it is possible to provide an ion sensor that can be used without calibration at a predetermined ion concentration, which is extremely convenient for use.

[Brief explanation of drawings]

Fig. 1 (A) is a plan view of a sensor plate according to an embodiment of the present invention, Fig. 1 (B) is a sectional view taken along ■-■, and Fig. 2 (A) (
C) is a diagram showing the structure of the silver chloride layer of the separated gate electrode of the sensor plate prepared according to the embodiment of the present invention, and FIG.
B) is a diagram showing the structure of the Ti chloride layer of the separated gate electrode of the sensor plate before the improvement. In the figure, 1 is a substrate, 2a and 2b are silver layers, 3a and 3b are Ta chloride layers, 4 is an ion-sensitive membrane, and 5 is a bank body. August 31, 1st year Figure 1 (B) Figure (A) (B)

Claims (2)

[Claims] (1) In an ion sensor that uses an electrode covered with an ion-sensitive membrane to enable detection of the sensitive value of a sample liquid using a field-effect semiconductor, the electrode coated with the ion-sensitive membrane has silver chloride as its main component. An ion sensor characterized in that it has a laminated structure consisting of an upper layer and a lower layer containing silver as a main component, and the particles constituting the upper layer have a particle size smaller than 1 μm. (2) A separate gate electrode to be connected to the gate electrode of the field-effect semiconductor and a separate comparison electrode are provided on an insulating substrate separate from the field-effect semiconductor substrate, and ions are ionized to the separated gate electrode. A separated gate electrode coated with a sensitive membrane is formed into a laminated structure consisting of an upper layer mainly composed of silver chloride and a lower layer mainly composed of silver, and the upper layer is composed of A sensor plate characterized in that the particle diameter of the particles is smaller than 1 μm.