JP4157699B2 - pH sensor - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a pH sensor using an electrode having a film made of boron carbon nitrogen on the surface.
[0002]
[Prior art]
In recent years, efforts aimed at environmental conservation have been made in various fields. Electric vehicles are indispensable for sweeping air pollution caused by exhaust gas, and battery research and development has been actively conducted. In addition, development of treatment technology for waste and sewage discharged from manufacturing factories is strongly desired. These research and development largely depend on the electrochemical field, and the performance is limited by the material of the electrochemical reaction electrode. Gold, platinum, carbon, and the like are known as electrochemical electrode materials, but materials with a wider potential window are desired. In addition, sensing of electrolyte solutions and gases, and biosensors in the biological field are important.
[0003]
So far, ion-sensitive field effect transistors (ISFETs) in which an ion-sensitive film is formed on the gate portion of a MOSFET have been produced. The names of the sensor and the electrochemical device used here include all of the above-described battery, material synthesis, decomposition device, element having a substance detection function, and the like. Currently, it is important to improve the performance of sensors and electrochemical devices, and the development of new base materials suitable for this is desired.
[0004]
In order to solve this problem, it is considered that diamond is used for an electrochemical electrode in recent years, and research is being conducted. Conventionally, it has been found that it has a wider potential window compared to gold, platinum, and carbon used as electrodes, and it has been suggested that it may be applied as a biological material sensor. However, it is considered that the growth temperature is relatively high and it is not easy to form a film on a large-area substrate.
[0005]
[Problems to be solved by the invention]
In this situation, a diamond thin film that is rich in chemical stability and has excellent characteristics such as high thermal conductivity has attracted attention. However, at present, a large-area film formation technique by plasma CVD has not been established. is there. Therefore, a new material that is easy to synthesize and has other characteristics comparable to diamond, such as a potential window, is desired.
[0006]
The present invention has been made in view of the above situation, and an object thereof is to provide a pH sensor using an electrode having a boron carbon nitrogen-based thin film having a wide potential window comparable to diamond.
[0007]
[Means for Solving the Problems]
PH sensor of the present invention for solving the above problems is characterized by using an electrode that having a film made of boron carbon nitrogen on the surface.
[0009]
【Example】
The film forming method and film forming apparatus of the present invention will be described in detail below with reference to the drawings.
[0010]
(Example 1)
A first example in which an electrochemical electrode is fabricated using the film of the present invention and a potential window, which is one of important characteristics, is evaluated is shown below. A boron carbon nitrogen thin film is formed on a silicon substrate by plasma assisted chemical vapor deposition. Boron trichloride, nitrogen, and methane were used as source gases. High frequency (13.56 MHz) power was supplied to generate inductively coupled plasma of nitrogen. Boron trichloride and methane were decomposed and a boron carbon nitrogen thin film was deposited on the substrate. The substrate temperature was 650 ° C. Film formation is possible even at low temperatures up to 300 ° C. The film thickness was 50-100 nm. It was shown by transmission electron microscope and transmission electron beam diffraction that the obtained film was a polycrystalline thin film and contained a lot of amorphous components.
[0011]
The potential window as an electrochemical electrode was evaluated using a 0.5 molar sulfuric acid solution. Ag / AgCl was used for the reference electrode and platinum was used for the counter electrode. It has been found that a potential window of -1.5V to 2V can be obtained as shown in FIG. This is equivalent to the case of a diamoside thin film, and is used as an electrode material for an electrochemical device.
[0012]
In this embodiment, silicon is used as the substrate material, but other metals and semiconductor materials can also be used. Further, although nitrogen gas, boron chloride, and methane gas are used as the material gas in the plasma-assisted chemical vapor synthesis method of the present embodiment, ammonia gas can also be used as the nitrogen material. Further, diborane gas can be used instead of boron chloride. Further, as the carbon supply, ethane gas other than methane gas, hydrocarbon gas such as acetylene gas, and organic compounds of boron and nitrogen such as trimethylboron can be used. Regarding the synthesis method, not only the plasma-assisted chemical vapor synthesis method but also physical vapor phase synthesis methods such as other sputtering methods can be used.
[0013]
(Example 2)
The second embodiment of the present invention relates to the production of a sensor and is shown in FIG. A boron carbon nitrogen film is synthesized using the same film forming method as in the first embodiment. The boron carbon nitrogen thin film 2 is formed on the quartz substrate 1 by plasma assisted chemical vapor deposition.
[0014]
Boron trichloride, nitrogen, and methane were used as source gases. High frequency (13.56 Mhz) power was supplied to generate inductively coupled plasma of nitrogen. Boron trichloride and methane were decomposed and a boron carbon nitrogen thin film was deposited on the substrate. The substrate temperature was 650 ° C.
[0015]
The film thickness was 100 nm. The boron carbon nitrogen thin film 2 is exposed in the form of stripes 3 and nickel is deposited on both sides thereof to form electrodes. These two electrodes are used as the source electrode 5 and the drain electrode 4 . Since it is necessary to bring the solution into contact only with the portion of the boron carbon nitrogen thin film 2 exposed in the stripe 3 shape, the electrode portion is covered with the resin 6.
[0016]
The width of the exposed stripe 3 of the boron carbon nitrogen thin film 2 was set to 100 μm. ○ Attach to the container 8 containing the solution through the ring 7. The gate electrode 9 is placed in the solution 10 and connected to the source electrode 5 . A bias 11 is applied to the drain electrode 4 . Check the applied voltage and the relationship between the current flowing between the source electrode 5 and the drain electrode 4 on the drain electrode 4. This current-voltage characteristic is measured for solutions 10 having different pHs. When the pH of the solution was increased, a current change between the source electrode 5 and the drain electrode 4 was detected, and it was confirmed that the solution operated as a pH sensor.
[0017]
In this embodiment, quartz is used as the substrate material, but other insulator materials can also be used. Also. Although nitrogen gas, boron chloride, and methane gas are used as material gases in the plasma-assisted chemical vapor synthesis method of the present embodiment, ammonia gas can also be used as the nitrogen material.
[0018]
Further, diborane gas can be used instead of boron chloride. Further, as the carbon supply, ethane gas other than methane gas, hydrocarbon gas such as acetylene gas, and organic compounds of boron and nitrogen such as trimethylboron can be used. Regarding the synthesis method, not only the plasma-assisted chemical vapor synthesis method but also physical vapor phase synthesis methods such as other sputtering methods can be used. Although nickel was used as the electrode material, the present invention is not limited to this, and various metals can be used.
[0019]
The sample shown in FIG. 2 is used not only as a pH sensor but also as a biological material sensor.
[0020]
(Example 3)
The third embodiment of the present invention relates to the fabrication of a sensor comprising a boron carbon nitrogen film and a silicon MOSFET, and is shown in FIG. Using the same film forming method as in the first embodiment, a boron carbon nitrogen film is synthesized by a plasma assisted chemical vapor deposition method. A MOSFET structure in which a source 22 and a drain 23 region are formed in silicon 21, metal electrodes 22a and 23a are attached thereon, and a SiO ₂ film is formed as a gate insulating film 24 between the source-drain electrodes 22a and 23a. A sample is used as a substrate. The thickness of the SiO ₂ film that is the gate insulating film 24 is made thinner than that used in a normal silicon MOSFET. The boron carbon nitrogen thin film 25 of the present invention is formed on the SiO ₂ film as the gate insulating film 24. Boron trichloride, nitrogen, and methane were used as source gases. High frequency (13.56 MHz) power was supplied to generate inductively coupled plasma of nitrogen. Boron trichloride and methane were decomposed, and a boron carbon nitrogen thin film 25 was deposited on the substrate. Board temperature was 400 ° C.. The film thickness was 10 nm. The prepared sample is attached to the container 26 in which the solution is placed. The gate electrode 27 is placed in the solution 28 and connected to the source electrode 22a. A bias 29 is applied to the drain electrode 23a. The relationship between the voltage applied to the drain electrode 23a and the current flowing between the source electrode 22a and the drain electrode 23a is examined. This current-voltage characteristic is measured for solutions 28 having different pHs. When the pH of the solution was increased, a current change between the source electrode 22a and the drain electrode 23a was detected, and it was confirmed that the solution operated as a pH sensor.
[0021]
The sample shown in FIG. 3 is used not only as a pH sensor but also as a biological material sensor.
[0022]
【The invention's effect】
The electrode, electrochemical device, and sensor of the present invention can use a boron carbon nitrogen film as a base material to improve performance and create new functions. The boron carbon nitrogen film used in the present invention is a material having a wider potential window than gold, platinum, and carbon conventionally used as electrode materials, and enables a redox reaction of substances that have been difficult so far, and is a new substance It can also be applied to sensing. In addition, large area synthesis is easy and synthesis is possible even at low temperatures. For this reason, it is possible to provide an indispensable pH sensor in the fields related to environmental conservation and biological material research, and it is considered that further research on environmental conservation and biological material will be promoted by realizing a pH sensor having a new function in the future.
[Brief description of the drawings]
FIG. 1 is a current-potential curve of a boron carbon nitrogen film electrode according to the present invention. FIG. 2 is a schematic sectional view of a sensor using a boron carbon nitrogen film according to a second embodiment of the present invention. Cross-sectional schematic diagram of sensor using boron carbon nitrogen film according to the embodiment [Explanation of symbols]
1 ... quartz substrate 2 · boron carbon nitrogen film 3 ... stripe portion 4 ... drain electrode 5 ... source electrode 6 ... resin 7 ... O-ring 8 · container 9 · gate electrode 10 .. The solution 11 ·· Bias 21 ·· Silicon 22 ·· Source 22a · · Source electrode 23 · · Drain 23a · · Drain electrode 24 · · Gate insulating film 25 · · Boron carbon nitrogen thin film 26 · · Container 27 · · Gate electrode 28 · ·solution

Claims (5)

PH sensor, characterized by using an electrode that having a film made of boron carbon nitrogen on the surface. The pH sensor according to claim 1, wherein the film is a polycrystalline thin film and contains a lot of amorphous components. PH sensor according to claim 1 or 2, characterized in that it has the film on the gate insulating film of the MOSFET. A source electrode and a drain electrode are formed on the film,
The source electrode and the drain electrode are exposed to a portion in contact with the solution, covered with a resin, and attached to a container for containing the solution through an O-ring,
A gate electrode is placed in the solution and connected to the source electrode;
The pH sensor according to any one of claims 1 to 3 , wherein a bias is applied to the drain electrode. Source and drain regions are formed in silicon, a source-drain electrode is attached as a metal electrode on the source region and the drain region, and a SiO ₂ film is formed as a gate insulating film between the source-drain electrodes. ,
The pH sensor according to claim 4 , wherein a gate electrode is placed in a solution, connected to the source electrode, and a bias is applied to the drain electrode.

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