KR102290337B1 - Manufacturing Method of Electrode for Gas Sensor and Gas Sensor - Google Patents

Abstract

providing a porous polymer membrane in the chamber; Plasma pretreatment of the surface of the porous polymer film as a plasma formed while introducing a processing gas into the chamber; and forming a metal thin film by physical vapor deposition on the plasma-pretreated porous polymer film.

Description

Manufacturing method of electrode for gas sensor and gas sensor

The present invention relates to a method for manufacturing an electrode for a gas sensor and a gas sensor, and more particularly, to a method for manufacturing an electrode for a gas sensor, which increases adhesion to a porous polymer film to ensure good bonding with a metal thin film, and a gas sensor manufactured using the same.

As the industrial society is advanced, production sites are diversified, and various types of gas are not only used but also generated at each industrial site, so safety management of gas accidents is emerging as a serious problem. In order to prevent gas-related safety accidents in advance, it is necessary to be able to detect small changes in gas concentration as well as to detect the presence of low-concentration gases in the case of toxic gases that can harm the human body when exposed to the human body in small amounts for a long time. there should be For gases that are closely related to environmental pollution and gas safety accidents at industrial sites, such as toxic gas and oxygen gas, an electrochemical gas sensor using redox reaction is most suitable and is already widely used. The structure generally has a gas inlet on one side so that external gas can be introduced, and the introduced gas is decomposed at the electrode through the porous polymer membrane to generate ions, and the generated ions move to the opposite electrode through the electrolyte. so that an electric current can be formed.

In the case of the conventional electrochemical gas sensor, when the electrode is formed on the porous polymer film, the electrode is formed on the porous polymer film by printing or by a sputtering method. When an electrode is formed by printing an electrode on a porous polymer membrane, there is a problem in that the porous polymer membrane is bent, deformed, and contracted due to thermal shock because a heat treatment process must be performed. In addition, if the sputtering method is performed, there is no such problem as there is no heat treatment process.

Laid-Open Patent Publication No. 10-2006-0080786

The present invention relates to a method for manufacturing an electrode for a gas sensor that improves adhesion of a porous polymer film to facilitate bonding with a metal thin film when manufacturing an electrode for a gas sensor, and a gas sensor manufactured using the same.

providing a porous polymer membrane in the chamber; Plasma pretreatment of the surface of the porous polymer film as a plasma formed while introducing a processing gas into the chamber; and forming a metal thin film by physical vapor deposition on the plasma-pretreated porous polymer film.

The plasma pretreatment process and the process of forming the metal thin film may be continuously performed in-situ.

The processing gas may include at least one of argon (Ar) or oxygen (O _{2 ).}

The process of forming the metal thin film may be performed by sputtering at room temperature.

The porous polymer membrane may be made of Teflon or polyethylene.

The metal thin film may include at least one of Au, Pt, Ag, and Pd.

The thickness of the metal thin film may be greater than 0 mm and less than or equal to 0.4 mm, and the size of pores occurring on the surface of the metal thin film may be greater than 0 μm and less than or equal to 0.3 μm.

a working electrode for electrochemically reacting the gas to be detected; a counter electrode corresponding to the working electrode; a reference electrode for controlling the potential of the working electrode; an electrolyte provided between the working electrode, the counter electrode, and the reference electrode; and a housing accommodating the working electrode, the counter electrode, the reference electrode, and the electrolyte, and having a gas passage hole through which the gas passes, wherein at least one of the working electrode, the counter electrode, and the reference electrode according to claim 1 . It can be manufactured by the method of manufacturing an electrode for a gas sensor of claim 7 .

The electrolyte may be in a solid or semi-solid state.

The present invention relates to a method for forming an electrode for a gas sensor and a gas sensor manufactured using the same for improving adhesion by plasma pre-treatment on the surface of a porous polymer film so that a metal thin film is well bonded.

When plasma pretreatment is performed on the surface of the porous polymer membrane, the surface energy is lowered by chemically breaking some of the bonds of the element elements on the surface. In addition, by physically roughening the surface, the bonding strength with other materials may be increased to improve adhesion.

By depositing the electrode on the porous polymer film with improved adhesion in the above method by physical vapor deposition, the electrode is not separated, thereby increasing the effect of the gas sensor.

1 is a flowchart illustrating a method of forming an electrode for a gas sensor according to an embodiment of the present invention.
Figure 2 is a graph showing the surface energy of the plasma pre-treated porous polymer membrane according to an embodiment of the present invention.
3 is a view of the surface of the plasma pre-treated porous polymer membrane according to an embodiment of the present invention observed by SEM.
Figure 4 is a graph of the measurement result of the plasma pre-treated electrode resistance according to an embodiment of the present invention.
5 is a cross-sectional view of a gas sensor coupling according to an embodiment of the present invention.

Hereinafter, embodiments of the present invention will be described in more detail with reference to the accompanying drawings. However, the present invention is not limited to the embodiments disclosed below, but will be implemented in various different forms, and only these embodiments allow the disclosure of the present invention to be complete, and the scope of the invention to those of ordinary skill in the art will be completely It is provided to inform you. In the description, the same reference numerals are assigned to the same components, and the sizes of the drawings may be partially exaggerated in order to accurately describe the embodiments of the present invention, and the same reference numerals refer to the same elements in the drawings.

The gas sensor conducts electrolysis while maintaining the interface between the electrode and the electrolyte solution at a constant potential, and the detection gas passing through the porous polymer membrane reacts with the working electrode to change the set potential, thereby selectively proceeding oxidation and reduction reactions to quantitatively It is a sensor that detects

1 is a flowchart illustrating a method of forming an electrode for a gas sensor according to an embodiment of the present invention.

Referring to FIG. 1 , the method for forming an electrode for a gas sensor according to an embodiment of the present invention includes the steps of providing a porous polymer film 200 in a chamber (S100); Plasma pretreatment of the surface of the porous polymer film 200 as a plasma formed while introducing a processing gas into the chamber (S200); and forming a metal thin film on the plasma pretreated porous polymer film 200 by physical vapor deposition (S300).

First, a process of providing the porous polymer film 200 in the chamber is performed (S100). The chamber provides an internal space and can be maintained in a vacuum state, a support is provided at the lower end to place a desired object, and an electrode is provided at the upper end. The porous polymer membrane 200 is a porous membrane having excellent permeability as a gas permeable membrane of the gas sensor.

Next, plasma pretreatment is performed on the porous polymer film 200 (S200). The plasma is a state in which electrons are separated from atoms or molecules in a gaseous state and contains electrons and ions, and has high electrical conductivity. Therefore, when the gas containing impurities passes through the discharge electrode, the electrons generated in the discharge electrode are attached to the impurity particles and the particles become negatively charged. The negatively charged particles move to the positively charged collector electrode by electrostatic attraction and attach As a result, impurities of the porous polymer film 200 may be removed.

In addition, as the plasma moves to the electrode provided under the support and collides with it, the chemical bond of the porous polymer film 200 is broken, increasing the surface energy to improve adhesion, and as a physical effect, the surface area of the porous polymer film 200 is roughened by increasing the surface area Adhesion with other materials may also have the effect of increasing.

2 is a graph showing the surface energy of Teflon according to the processing gas (or discharge gas) according to the plasma pretreatment process according to an embodiment of the present invention. Figure 2 (a) shows the binding energy of Teflon without plasma treatment. Figure 2(b) shows the binding energy of Teflon treated with argon (Ar) plasma in the process gas. Figure 2(c) shows the binding energy of Teflon treated with _{oxygen (O 2 ) plasma in the process gas.} FIG. 4(d) shows the binding energy of Teflon treated with argon (Ar) and oxygen (O _{2 ) plasma in the process gas.}

Referring to FIG. 2 , the process gas may further include at least one _{of argon (Ar) and oxygen (O 2 ).} In addition, Figure 2 shows the measured values of F 1s XPS (X-ray Photoelectron Spectroscopy) of Teflon, and the XPS is an X-ray photoelectron spectroscopy method through photons of constant energy to the surface and interface elements, chemical bonding states, and energy levels. It is a surface analysis method to find out etc. Teflon, an embodiment of the present invention, is PTFE (C ₂ F ₄ ) and _{has a structure in which several CF 2} are connected, and has low surface energy and is stable, so the adhesion with other materials is not good. Therefore, when plasma pretreatment is performed on the Teflon, it is possible to increase the surface energy by breaking a part of _{the CF 2 bond, thereby improving adhesion with other materials.}

Referring to FIG. 2(a) showing the measured values of F 1s XPS of Teflon, when plasma treatment is not applied to Teflon, it can be seen that only the peak _{of CF 2 is detected in the binding energy around 690 eV.} However, referring to Figs. 2(b), (c), and (d), depending on the processing gas, a C-CF ₂ peak without F was detected together with a bonding energy of 687 eV, so that the bond between C and F was broken through plasma treatment. can be found. in addition, looking at the peak of the C-CF ₂ argon (Ar), oxygen (O _2), argon (Ar) + oxygen (O ₂₎ in order peak is seen argon (Ar) to be more nopjin in the that, It can be seen that the surface energy is increased in the order of oxygen (O ₂ ), argon (Ar) + oxygen (O _{2 ), so that the adhesion is further improved.}

3 is a diagram illustrating the surface of Teflon according to the processing gas during plasma pretreatment according to an embodiment of the present invention observed by SEM. Figure 3 (a) is the surface of Teflon not treated with plasma, Figure 3 (b) is argon (Ar) plasma, 3 (c) is oxygen (O ₂ ) plasma, 3 (d) is argon (Ar) + This is an SEM observation of the surface of Teflon treated with oxygen (O _{2 ) plasma.}

Referring to FIG. 3, it can be seen that the surface of the Teflon that is not subjected to the plasma treatment of FIG. 3(a) is clean and uniform. Therefore, it is judged that the adhesive force is low because the surface area is relatively small and the contact area with other materials is small. Figure 3 (b) is a picture of the surface of Teflon treated with argon (Ar) plasma, and it can be seen that the surface is slightly rougher than that of Teflon without plasma treatment. 3(c) and 3(d) show that _{the surface of Teflon treated with oxygen (O 2} ) plasma, argon (Ar) + oxygen (O ₂ ) plasma was very rough, and in particular, in the case of _{oxygen (O 2 ) plasma.} You can see that there is an air void. As such, the roughness of the surface is generated so that the porous polymer film can better support the metal thin film. However, as in the case of the oxygen (O ₂ ) plasma, if too large air pores are formed, the metal thin film formed thereon is not well supported and the adhesive strength is also reduced.

Next, a process of forming a metal thin film by physical vapor deposition on the plasma-pretreated porous polymer film 200 is performed (S300). The physical vapor deposition method may be, for example, sputtering, electron beam deposition, thermal deposition, laser molecular beam deposition, pulsed laser deposition, or the like. An embodiment of the present invention may be a method of depositing a metal thin film on the plasma-pretreated porous polymer film 200 by a sputtering method. In particular, in sputtering, when ionized atoms are accelerated by an electric field and collide with a source material, atoms or molecules of the thin film material are ejected by the collision. There is an advantage in that the emitted atoms are deposited on the surface of a desired material to form a thin metal film.

As described above, when the electrode is deposited on the non-plasma-treated porous polymer film 200, the adhesion is not good, so when the gas sensor is operated, the electrode is separated, causing a malfunction or a side effect that the desired performance is not obtained.

In order to overcome this problem, in the present invention, plasma pretreatment was performed on the surface of the porous polymer film 200 to improve adhesion with other materials. Thus, the electrode manufactured by depositing a metal thin film on the plasma-pretreated porous polymer film 200 through sputtering according to an embodiment of the present invention can operate in a gas sensor more stably than the conventional electrode.

After depositing each electrode on Teflon treated with the processing gas (argon (Ar), oxygen (O ₂ ), argon (Ar) + oxygen (O _{2 )) plasma according to an embodiment of the present invention, adhesive force through scotch tape} Evaluation was carried out. The scotch tape evaluation method is a method of evaluating whether the electrode deposited on the porous polymer film 200 is left on the polymer film 200 by attaching and detaching the electrode with a scotch tape.

It was found that the electrode deposited on Teflon, which was not subjected to plasma treatment, had poor adhesion between the electrode and the polymer film 200 because many electrodes were attached to the scotch tape. Next, when the adhesion strength was evaluated by the scotch tape method on the electrode deposited on the surface-treated porous polymer film 200 using argon (Ar) plasma, it was confirmed that the electrode did not come out on the scotch tape, and between the polymer film 200 and the electrode. It was confirmed that the adhesion was improved because of the good adhesion. Finally, when the adhesion strength of the electrode deposited on Teflon treated with oxygen (O ₂ ) and argon (Ar) + oxygen (O ₂ ) plasma was tested by the Scotch method, Scotch as when treated with argon (Ar) plasma The electrode did not come off the tape. However, it was confirmed that the color of the electrode was discolored whether it was oxidized under the influence of oxygen (O _{2 ).} However, this is only an example and is not limited thereto.

4 is a graph of electrode resistance measurement results according to a process gas during plasma pretreatment according to an embodiment of the present invention.

Referring to FIG. 4 , in the case of an electrode deposited on Teflon that has not been treated with plasma, resistance was not measured. Next, in the case of an electrode deposited on Teflon treated with argon (Ar) plasma, the lowest electrode resistance value was obtained. The electrode deposited on Teflon treated with oxygen (O ₂ ) and argon (Ar)+oxygen (O ₂ ) plasma showed a higher resistance value than the electrode deposited on Teflon treated with argon (Ar) plasma. This is expected due to the oxidation effect according to the color change of the electrode in the evaluation of adhesion by scotch tape. In addition, _{the electrode deposited on Teflon treated with oxygen (O 2} ) plasma showed the highest resistance value, which is judged to be due to the influence of pores identified in the microstructure with reference to FIG. 3(c).

2, 3, 4, according to an embodiment of the present invention, if comprehensively judged by the adhesion evaluation by the scotch tape, argon (Ar) + oxygen (O ₂ ) plasma-treated porous polymer membrane according to FIG. (200) had the highest surface energy and the roughness of the surface was good according to FIG. 3, but in FIG. 4, the resistance was relatively high and there was a disappointment that the electrode was oxidized and discolored when the adhesive force was evaluated by the scotch tape, so oxygen (O ₂ ) The adhesion of plasma, argon (Ar) + oxygen (O ₂ ) plasma was excellent, but in addition, the electrode deposited on the porous polymer film 200 treated with argon (Ar) plasma did not have a discoloration problem, had good adhesion, and had relatively low resistance. As it is small, it can be considered as the most suitable treatment gas.

Meanwhile, the plasma pretreatment process and the process of forming the metal thin film may be continuously performed in-situ. If it does not proceed in-situ, the porous polymer film 200 is plasma-treated in the chamber in a vacuum state, then the vacuum is released again, and then the chamber is created in a vacuum state again to proceed with the process of forming a metal thin film. Efficiency decreases as unnecessary time and effort are put into it. Therefore, the chamber that performs the plasma pretreatment process and the process of forming the metal thin film is formed as a chamber having a single space or a chamber in which two or more spaces are formed and connected between the spaces, so that the two processes can be performed in the same space. there is.

The process of forming the metal thin film may be performed by sputtering at room temperature.

In the prior art, an electrode is formed by printing a solution containing metal particles on a porous polymer membrane. After drying the applied solution, heat treatment and firing are essential. At this time, during the heat treatment (sintering) process, the porous polymer film with low thermal stability was bent or contracted while heat was applied, so that the metal thin film could not be deposited correctly.

Therefore, in order to overcome this, the present invention chemically and physically modifies the surface of the porous polymer film 200 by treating plasma to increase adhesion. As the electrode is deposited on the porous polymer film 200 with increased adhesion, bonding occurs well, and it is possible to prevent the electrode from being separated during operation of the gas sensor, thereby reducing efficiency.

In addition, when sputtering is carried out, atoms or molecules of the thin film material are ejected and have high energy, so that a metal thin film can be formed even at room temperature. It is also possible to prevent process delay due to temperature change. In addition, by proceeding at room temperature, the porous polymer film does not undergo a firing process and there is no thermal shock, so it does not warp or shrink, and it becomes possible to form a uniform and thin metal thin film on the porous polymer film.

The porous polymer membrane 200 may be made of Teflon or polyethylene. The gas permeable membrane used in the gas sensor must have excellent gas permeability. Among them, the gas sensor electrode may be manufactured using the porous polymer film 200 made of Teflon or polyethylene having good performance.

The metal thin film may include at least one of Au, Pt, Ag, and Pd. If a metal thin film is formed using a metal with high reactivity as a metal used for an electrode, the metal thin film is oxidized leaving electrical conductivity and the gas sensor There will be a problem that the lifespan of the Therefore, the gas sensor can be used for a long time only when the electrode is manufactured using a stable metal that is stable and not oxidized due to its low reactivity.

The thickness of the metal thin film may be greater than 0 mm and less than or equal to 0.4 mm, and the size of pores occurring on the surface of the metal thin film may be greater than 0 μm and less than or equal to 0.3 μm. When the thickness of the metal thin film becomes the numerical thickness, adhesion to the porous polymer film is improved and the metal thin film can be uniformly deposited. If the thickness of the metal thin film exceeds 0.4 mm, not only the adhesive force is reduced, but also the performance of the gas sensor may be deteriorated because the electrical signal is not uniform because it is not uniformly deposited.

In addition, when the size of the pores on the surface of the metal thin film becomes larger than 0.3 μm, with reference to FIGS. 3 ( c ) and 4 , pores are formed in the porous polymer film 200 surface-treated with oxygen (O2) plasma, and the resistance of the electrode It can be seen that this is increased, and as described above, the support of the metal thin film cannot be performed smoothly. In addition, if pores are formed in the electrode itself, a side effect of not being able to measure a minute current may occur due to increased resistance.

Hereinafter, a gas sensor according to another embodiment of the present invention will be described in more detail, and details overlapping with those described above with respect to a method for manufacturing an electrode for a gas sensor according to an embodiment of the present invention will be omitted.

5 is a cross-sectional view of a gas sensor coupling according to an embodiment of the present invention.

Referring to FIG. 5 , a working electrode 300 for electrochemically reacting a detection target gas; a counter electrode 310 corresponding to the working electrode 300; a reference electrode 310 for controlling the potential of the working electrode; an electrolyte 400 provided between the working electrode 300 , the counter electrode 310 and the reference electrode 310 ; and a housing 100 accommodating the working electrode 300 , the counter electrode 310 , the reference electrode 310 and the electrolyte 400 , and having a gas passage hole 110 through which the gas passes, At least one of the working electrode 300 , the counter electrode 310 , and the reference electrode 310 may be manufactured by the method of manufacturing an electrode for a gas sensor.

The working electrode is a gas electrode that detects gas and causes an electrochemical reaction of the gas to be detected. The counter electrode 310 corresponds to the working electrode. Three electrodes of the reference electrode 310 for controlling the potential of the working electrode are provided, and an electrolytic cell containing an electrolyte 400 that can be contacted with them, a circuit for setting the potential of each electrode, and the like are connected.

As a material of the three electrodes, a noble metal catalyst such as platinum (Pt), gold (Au), or palladium (Pd) is applied to the porous polymer film 200 manufactured by the method for manufacturing an electrode for a gas sensor.

As the electrolyte 400, an acidic aqueous solution such as sulfuric acid or phosphoric acid was used.

In the gas sensor, the porous polymer film 200 is in contact with the housing 100 in which the gas passage hole 110 is drilled, and the electrolyte 400 is provided on the surface of the working electrode 300 deposited on the porous polymer film 200 . . The counter electrode 310 and the reference electrode 310 have a branch shape and are superimposed on the same side in a zigzag form, and are deposited on the porous polymer film 200 facing the working electrode 300 , and the porous polymer film 200 is a housing. 100. Meanwhile, at least one of the porous polymer membrane 200, the working electrode 300, the counter electrode 310, and the reference electrode 310 was manufactured by the method for manufacturing an electrode for a gas sensor. However, this is only an example and is not limited thereto.

The housing 100 includes a gas passage hole 110 on one surface and accommodates the working electrode 300, the counter electrode 310, the reference electrode 310, and the electrolyte 400 to form a gas sensor stably. A metal terminal is included so that the working electrode 300, the counter electrode 310, and the reference electrode 310 can be electrically connected to the inside of the housing 100, so it is generated through the electrochemical reaction of the detected gas. It allows current to pass through.

In addition, the potentiostatic electrolytic gas sensor controls the potential of the working electrode with respect to changes in the surrounding environment and keeps it constant, thereby generating a current corresponding to the change of the surrounding environment between the working electrode 300 and the counter electrode 310 . make it And by using the fact that the potential of the working electrode does not change and the oxidation-reduction potential differs depending on the gas type, it is possible to selectively detect the gas depending on the set potential of the circuit. Moreover, by changing the catalyst used for the gas electrode, high selectivity can be provided with respect to the target gas.

The electrolyte 400 may be in a solid or semi-solid state. Conventionally, there is a problem in mobility because the liquid electrolyte 400 is heavy and liquid. Therefore, by forming the electrolyte 400 as a solid or semi-solid, it is possible to obtain the advantage of convenience of movement, and since it is a solid rather than a liquid, it will be possible to further reduce the weight.

As such, although specific embodiments have been described in the description of the present invention, various modifications are possible without departing from the scope of the present invention. Therefore, the scope of the present invention should not be limited to the described embodiments, but should be defined by the claims to be described below as well as the claims and equivalents.

S100: Providing porous polymer film S200: Plasma pretreatment
S300: metal thin film formation
100: housing 110: gas passage hole
200: porous polymer membrane 300: working electrode 310: counter electrode / reference electrode 400: electrolyte

Claims (9)

providing a porous polymer membrane having carbon bonds in the chamber;
Plasma pretreatment of the surface of the porous polymer film as a plasma formed while introducing a processing gas into the chamber; and
and forming a metal thin film by physical vapor deposition on the plasma pretreated porous polymer film,
The process gas includes argon (Ar) and oxygen (O ₂ ),
The plasma pretreatment process and the process of forming the metal thin film are continuously performed in-situ,
The porous polymer membrane has a bond between C and F,
In the process of plasma pretreatment, at least some of the bonds of C and F of the porous polymer film are broken,
The thickness of the metal thin film exceeds 0 mm and is less than or equal to 0.4 mm,
The size of the pores generated on the surface of the metal thin film due to the pores of the plasma pre-treated porous polymer membrane exceeds 0㎛ and is 0.3㎛ or less for a gas sensor electrode manufacturing method.
delete delete The method of claim 1,
The process of forming the metal thin film is a method of manufacturing an electrode for a gas sensor that is performed by sputtering at room temperature.
The method of claim 1,
The porous polymer membrane is a method of manufacturing an electrode for a gas sensor made of Teflon or polyethylene.
The method of claim 1,
The metal thin film is a gas sensor electrode manufacturing method comprising at least one of Au, Pt, Ag and Pd.
delete a working electrode for electrochemically reacting the gas to be detected;
a counter electrode corresponding to the working electrode;
a reference electrode for controlling the potential of the working electrode;
an electrolyte provided between the working electrode, the counter electrode, and the reference electrode; and
and a housing for accommodating the working electrode, the counter electrode, the reference electrode and the electrolyte, and having a gas passage hole through which the gas passes,
At least one of the working electrode, the counter electrode, and the reference electrode is a gas sensor manufactured by the method for manufacturing an electrode for a gas sensor according to claim 1, and any one of claims 4 to 6.
9. The method of claim 8,
The electrolyte is a gas sensor in a solid or semi-solid state.

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