KR101575012B1 - A temperature sensor using a reduced graphene oxide film - Google Patents

Abstract

The present invention relates to a manufacturing method of a temperature sensor using a reduced graphene thin film which is based on a two-dimensional structured graphene and a temperature sensor thereof, comprising: a step of forming an electrode pattern on the upper part of a substrate; a step of coating a reduced graphene thin film over the upper part of the electrode patterns; a step of depositing a composite protective film on the upper part of the reduced graphene thin film.

Description

TECHNICAL FIELD [0001] The present invention relates to a temperature sensor using a reduced graphene thin film,

The present invention relates to a method of manufacturing a temperature sensor using a reduced graphene thin film and a temperature sensor using the reduced graphene thin film, and more particularly, to a method of manufacturing a temperature sensor using a reduced graphene thin film based on graphene having a two- .

Graphite, which is one of the most well-known structures of carbon, is a structure in which plate-shaped two-dimensional graphene sheets are stacked with only carbon atoms sp2-hybridized and connected by hexagonal shape only. Recently, it has been known that graphene sheets are peeled off from a graphite sheet or an aqueous layer, and the properties of the sheets are investigated. As a result, it is known that they have very high conduction properties. The mobility of the graphene sheet known to date is known to have a high value of about 20,000 to 50,000 cm ² / Vs. Graphene has good thermal, electrical and mechanical properties and is expected to be applicable in as many areas as carbon nanotubes. In particular, the two-dimensional structure of graphene has distinctive physical properties, as well as a very unique advantage over other carbon isotopes in terms of electro-electronic applications. In other words, it is an advantage that a general top-down semiconductor process represented by printing, etching and the like can be introduced due to the two-dimensional structure to construct an electronic circuit. For such a large-scale application, it is most important to make a large-area graphene on a semiconductor substrate. As a typical method of producing graphene, a hot-phase chemical method is used, or a method in which graphene raw material is oxidized to obtain oxidized graphene and then reduced again. Especially in the latter case, the dispersion properties in the solution are favorable, so that various applications are expected.

The temperature sensor converts a temperature into an electric signal such as a voltage or a resistance change and displays the value as a numerical value so that the temperature can be known. The conductors and the semiconductor have characteristics of electrical resistance and conductivity This shows the opposite result.

That is, the resistance of the conductor increases when the temperature rises, and the resistance of the semiconductor decreases when the temperature rises.

On the other hand, in the case of a semiconductor, resistance is reduced when the temperature rises, and the electrons in the semiconductor inherent band can be easily transferred to the conduction band due to thermal energy when the temperature rises, thereby improving the conductivity.

Graphene is similar to semiconductors in that the resistance decreases when the temperature rises. Representative semiconductor device temperature sensors with similar semiconductor characteristics are NTC thermistors and are characterized by a resistance temperature coefficient

[Relation 1]

_{R (T) = R 0 (} 1 + αΔT) or = αΔT

In this case, R and R0 are the resistances when the temperatures are T and T0, respectively, and? Is the resistance temperature coefficient.

 Relation 1 is a general resistance thermometer, not an NTC thermistor. However, as mentioned above, the temperature coefficient of the NTC thermistor has a negative temperature coefficient, so it is continuously decreased. This resistance characteristic can be expressed as shown in Equation 2 below.

[Relation 2]

_{R = R 0 expB {(1} / T) - (1 / T 0)}

In this case, R and R0 are the resistance when the temperature is T and T0, respectively, and B is the temperature dependence of the thermistor as a constant according to the thermistor material.

Relation 2 is again a constant term, and can be expressed as the following equation. When the lnR value is taken, the graph slope of the linear NTC curve has a straight line shape as shown in FIG.

[Relation 3]

B = 1 / {(1 / T) - (1 / T 0)} * lnR / R 0

The temperature coefficient α for a change of 1 ° C is expressed as follows.

[Relation 4]

? = 1 / R * dR / dT

The NTC sensor material is a semiconductor obtained by sintering 2 to 3 types of oxides such as Ni, Co, Mn, Cu, and Titanium so as to have an appropriate resistivity and temperature coefficient.

The operating temperature of NTC sensor is -50 ~ 500 ℃. However, the tendency of unstable operation of electronic circuit increases within this temperature range. To reduce this, the thermistor and I.C circuit are combined and used as sensor.

In addition, the NTC thermistor temperature sensor has a disadvantage in that an IC guarantee circuit must be combined and the measured graph is converted into a linear graph again.

A related prior art is Korean Patent No. 0481929 (registered on March 30, 2005, temperature sensor using a thermistor thin film and its manufacturing method).

의 관계식을 고온에서 가지는 환원 그래핀 박막을 이용한 온도 센서 제조방법 및 온도 센서를 제공하기 위한 것이다.The present invention is based on a graphene material

And a temperature sensor using the reduced graphene thin film having a relational expression at a high temperature.

The technical objects to be achieved by the present invention are not limited to the above-mentioned technical problems.

According to another aspect of the present invention, there is provided a method of manufacturing a temperature sensor using a reduced graphene thin film, the method comprising: forming an electrode pattern on a substrate; Coating the electrode pattern with a reducing graphene thin film; And depositing a composite protective film on the reduced graphene thin film.

Specifically, the reduced graphene thin film is a reduced graphene composite film or a reduced graphene self-assembled film.

The reducing graphene composite membrane may further include a step of dissolving the reducing polymer in an aqueous solution to form a polymer solution; Mixing the polymer solution with ethanol or isopropanol to form a mixed solution; Mixing the mixed solution and the oxidized graphene solution under a predetermined condition, and dispersing the mixture by ultrasonic treatment for a predetermined period of time.

Also, the reducing polymer is a polymer having an alcohol group.

Further, the polymer solution is further mixed with an organic solvent or a surfactant.

The mixing conditions of the oxidized graphene solution and the mixed solution are mixed in a volume ratio of 1: 0.1 to 1: 3.

The reduced graphene composite film coating may be one of spin coating, inkjet printing, spray coating, and dispenser methods.

The reduced graphene self-assembled film coating may be performed by transferring the reduced graphene self-assembled film to a substrate having the electrode pattern formed thereon by a reduced graphene intermediate solution, Thereby forming an assembled film.

The reduced graphene self-assembling film may further include a step of preparing a reduced graphene intermediate solution by adding a reducing agent to the oxidized graphene; Placing the liquid absorbing cloth and the substrate on the heating means in order; Applying the reducing graphene intermediate solution to the substrate when the temperature of the substrate reaches a predetermined temperature by heating with the heating means; Blocking the air flow of the substrate coated with the reduced graphene intermediate solution and forming a reduced graphene self-assembled film while reducing graphene is formed on the reduced graphene intermediate solution; And drying the water under the reducing graphene self-assembling membrane.

Further, the method may further include a heat treatment step after coating the reduced graphene thin film.

Further, the heat treatment temperature is a temperature higher than the use temperature of the temperature sensor.

The composite passivation layer may be formed of one selected from the group consisting of polystyrene (PS), polystyylene (PE), polystyrene-polyethylene mixed layer (PES), nitrogen fill protective layer, oxide SiO ₂ thin layer, do.

According to another aspect of the present invention, there is provided a temperature sensor using a reduced graphene thin film manufactured by the method of manufacturing a temperature sensor using the reduced graphene thin film of the present invention.

The temperature sensor is characterized in that a change in resistance value with respect to a temperature change has a linear relationship.

INDUSTRIAL APPLICABILITY As described above, the present invention can obtain a more precise and stable linear graph without changing the measured graph value, and has the effect of reducing the cost of the sensing material and facilitating the interface.

의 관계식을 가지게 되어 종래의 NTC 센서와 달리 로그 계상회로 또는 소자, 고온 동작을 보정하는 보상회로가 필요치 않으며,

의 관계와 매우 일치하여 정밀한 온도 측정이 가능하다는 효과가 있다. In addition,

A logarithmic phase circuit or element and a compensation circuit for correcting the high temperature operation are not required unlike the conventional NTC sensor,

So that accurate temperature measurement is possible.

Therefore, as an automatic control sensor, it is coated thinly on a region where the heat should be read, and the resistance according to the change of temperature can be measured and utilized as a temperature sensor.

1 is a graph showing resistance versus conductor and semiconductor temperature.
2 is a view showing a state in which electrons move to a conduction band when a semiconductor temperature rises.
3 is a graph showing a resistance graph according to an NTC thermistor temperature.
4 is a flowchart illustrating a method of manufacturing a temperature sensor using a reduced graphene thin film according to an embodiment of the present invention.
5 is a flowchart illustrating a method of forming a reduced graphene composite film in a method of manufacturing a temperature sensor using a reduced graphene thin film according to an embodiment of the present invention.
6 is a flowchart illustrating a method of forming a reduced graphene self-assembled film in a method of manufacturing a temperature sensor using a reduced graphene thin film according to an embodiment of the present invention.
7 is a graph showing a temperature-resistance relationship graph of a reduced graphene composite film and a reduced graphene self-assembled film of a temperature sensor using a reduced graphene thin film according to an embodiment of the present invention.
8 is a graph showing a temperature-resistance relationship regression graph of a temperature sensor using a reduced graphene thin film according to an embodiment of the present invention.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. In the drawings, the same components are denoted by the same reference symbols whenever possible. In the following description, well-known functions or constructions are not described in detail since they would obscure the invention in unnecessary detail.

FIG. 4 is a flowchart illustrating a method of manufacturing a temperature sensor using a reduced graphene thin film according to an embodiment of the present invention. The method of manufacturing a temperature sensor using a reduced graphene thin film is as follows.

First, an electrode pattern is formed on the substrate (S100). In this case, since the line width or the number of lines in the electrode pattern is deviated from the gist of the present invention, the structure of the device can be a form that can measure the resistance, so that the shape of the pattern is not limited. Further, The temperature measurement error range can be reduced.

Second, an electrode pattern is coated with a reduced graphene composite film or a reduced graphene self-assembled film (S200).

The reduced graphene composite membrane can be prepared as shown in FIG. 5, and the reduced graphene composite membrane is first melted in an aqueous solution to form a polymer solution (S211). At this time, the reducing polymer is preferably a polymer having an alcohol group.

For example, the polymer having an alcohol group includes polyvinyl alcohol (PVA), polyvinyl nitrate (PVN), polyvinyl acetate (PVAc), and polyvinyl acetal, and since the alcohol group plays a reducing role, Graphene can be reduced.

Then, the polymer solution is mixed with ethanol or isopropanol to form a mixed solution (S212). At this time, the reason why ethanol or isopropanol is mixed in the polymer solution is to improve the coating property, and it is preferable that the volume ratio of the polymer solution: ethanol or isopropanol is 1: 0.1 to 1: 2.

 Here, there is a problem in that too much ethanol or isopropanol is added to form a precipitate when mixed with graphene grains in the future, or the life of the mixed solution is shortened. When ethanol or isopropanol is added at a ratio of less than 0.1 to the polymer solution, Which can lead to surface defects due to bubbles.

In addition, an organic solvent or surfactant may be further added to the polymer solution to improve coating properties. At this time, the organic solvent or the surfactant is preferably mixed at less than 0.1 wt% with respect to the polymer solution.

Then, the mixed solution and the oxidized graphene solution are mixed under a predetermined condition and dispersed by ultrasonic treatment for a predetermined period of time (S213). At this time, the volume ratio of the mixed liquid and the oxidized graphene solution is 1: 0.1 to 1: 3, mixed according to the coating method and the final application point of the solution, and then dispersed by ultrasonic treatment for 10 minutes.

Here, the graphene oxide solution is formed by adding graphite and sodium nitrate salt to a concentrated sulfuric acid solution. In this case, the first solution is formed by adding 2 to 4 g of graphite and 1 to 2 g of sodium nitrate to 50 to 150 ml of concentrated sulfuric acid, and the concentrated sulfuric acid is concentrated aqueous solution of sulfuric acid at a concentration of 90 to 99 %to be.

Next, the temperature of the first solution is adjusted to 0 캜, and potassium permanganate in a powder state is mixed. At this time, it is preferable to mix 3 to 12 g of potassium permanganate as an example.

Here, to adjust the temperature of the first solution to 0 ° C, the container containing the first solution may be immersed in a bowl containing ice water to adjust the temperature.

Next, the first solution to which potassium permanganate is added is raised to a predetermined temperature. At this time, the preset temperature in the embodiment is 35 ° C, but the temperature can be adjusted within the range of 20 ° C to 80 ° C depending on the type of graphite.

Since the degree of oxidation of the preset temperature is greatly changed at a temperature near room temperature, the degree of oxidation can be controlled by setting the temperature.

A uniform sample could be obtained by setting the temperature at about 30 DEG C in the summer and about 20 DEG C in the winter and setting it at 35 DEG in the embodiment of the present invention.

Next, the degree of oxidation is controlled by keeping the temperature at the predetermined temperature for 30 to 90 minutes, and distilled water is added. At this time, as an example, 100 to 300 ml of distilled water is added.

Next, aqueous hydrogen peroxide is added to form the manganese halide salt to reduce the unreacted KMnO ₄ (potassium permanganate).

Finally, the oxidized graphene synthesized in manganese sulfide is extracted. At this time, the method of extracting the graphene oxide includes repeating centrifugal beating and washing the solution containing graphite oxide and graphene a plurality of times so that the pH of a clear solution separated by using distilled water becomes 7, After drying the graphene powder in a vacuum oven for 10 to 14 hours, 2 g of the oxidized graphene was dispersed in 200 to 400 ml of distilled water, and the distilled water containing the oxidized graphene was dispersed by using ultrasonic equipment for 30 minutes to 2 hours And extracted.

The coating method of the reduced graphene composite film is preferably any one of a spin coating method, an ink jet printing method, a spray coating method, and a dispenser method.

At this time, spin coating is a coating method in which a solution or a liquid substance of a substance to be coated is dropped onto a substrate and rotated at a high speed to spread thinly.

The reducing graphene self-assembling membrane can be produced as shown in FIG. 6, and the reducing graphene self-assembling membrane is prepared by adding graphene oxide into distilled water and reacting with a reducing agent (S221). Thus, the reaction rate and the aggregation phenomenon can be controlled by introducing the graphene oxide into the distilled water and adding the reducing agent. Conversely, if a reducing agent is added to the graphene oxide and distilled water is added, the reaction rate may vary and coagulation may occur.

More preferably, graphene oxide of 0.02 wt% is added to 30 ml of distilled water, and 9 to 21 ml of a reducing agent hydrazine having a concentration of 6% is added, followed by reaction for 15 minutes.

The weight ratio of the reducing agent to the oxidized graphene is in the range of 15: 1 to 35: 1. The reducing agent is a hydrazine or hydrazine derivative. The hydrazine derivative may be mono-methyl-hydrazine or di- methyl-hydrazine. Here, hydrazine is a reducing agent that is relatively free of residues after the reaction compared to other reducing agents, and does not aggregate within the self-assembly reaction time.

If the weight of the reducing agent is less than 15 times the weight of the oxidized graphene, a self-assembled film is not formed. If the weight of the reducing agent exceeds 35 times the weight of the oxidized graphene, The phenomenon occurs.

The hydrazine concentration is preferably 6% to 20%, and if it exceeds 20%, aggregation occurs.

Here, water is used as a solvent for adjusting the concentration of hydrazine.

The liquid absorbing cloth and the substrate are placed on the heating means in this order (S222). At this time, the heating means may be a means for raising the temperature of the substrate such as a hot plate.

Further, the liquid absorbing cloth is preferably 0.5 to 1.5 cm in thickness, and the liquid absorbing cloth absorbs the evaporated moisture.

When the temperature of the substrate reaches a preset temperature by heating with the heating means, the reduced graphene intermediate solution is applied to the substrate (S223). At this time, the predetermined temperature of the substrate is preferably 30 to 40 DEG C, and when the predetermined temperature of the substrate is 30 to 40 DEG C, the temperature of the liquid absorbing cloth is about 50 to 60 DEG C. [

0.06 to 0.15 ml / cm < ² > of the reducing graphene intermediate solution is applied to the substrate.

The amount of the reducing graphene intermediate solution to be filled in order to coat the entire substrate according to the temperature may be varied. Therefore, in the embodiment of the present invention, when the temperature of the substrate is 30 to 40 ° C, the reducing graphene intermediate solution is 0.06 to 0.15 ml / cm < ² >

The reduced graphene intermediate solution is cut off from the air flow of the coated substrate, and reduced graphene is formed on the reduced graphene intermediate solution to form a reduced graphene self-assembled film (S224).

At this time, the air flow of the substrate is blocked by the chamber or the cover, and the chamber or the cover has a shape in which the water evaporated at the upper part does not fall off onto the substrate so that moisture to be evaporated does not fall on the substrate, It can be in the form of a cone.

Here, the reason why the air flow is blocked is that the generated film is floating in a liquid phase, and therefore, the entire film moves due to slight vibration or air flow, and cracks may be generated.

At this time, the reaction time varies depending on the amount of the reduced graphene solution, but it is dried for 50 to 90 minutes while maintaining the same temperature of the substrate.

Thus, even if a reducing agent is added according to a reducing agent, the reaction time to be reduced is considerably long at room temperature, so that the solution containing the reducing agent has stability against precipitation for more than one day. When the solution is dropped on the substrate during this period, The reduction reaction is promoted, and a part of it precipitates as reduced graphene.

Precipitated reduced graphenes float on the surface of the solution because of the lack of solubility, and as the reaction progresses, the reduced graphenes start to self-assemble on the surface of the solution, resulting in a self-assembled form of the entire area.

The water under the reducing graphene self-assembling membrane is dried (S225).

There are two methods for coating the reduced graphene self-assembled film formed on the substrate as described above.

One is a method of forming a reduced graphene self-assembled film with a reducing graphene intermediate solution and then transferring to a substrate having an electrode pattern formed thereon. The other is a method of directly forming a reducing graphene self- And the remaining part is removed.

Here, when the reduction graphene self-assembled film is removed, it can be removed by an adhesive force like a tape.

It is preferable to perform additional heat treatment after coating the reduced graphene thin film in the same manner as described above. At this time, the heat treatment temperature is higher than the use temperature of the temperature sensor. The approximate temperature range is 120 deg. C to 600 deg. C, but is not limited thereto.

For example, if the temperature of the temperature sensor is 500 degrees or less, heat treatment is performed in vacuum to 550 degrees. It is preferable to heat-treat in a vacuum or nitrogen atmosphere because it burns when exposed to air.

A method of coating the reduced graphene composite film of the present invention by spin coating will be described. When spin coating is performed on the patterned electrode and heat treatment is performed at 120 to 600 ° C for 30 minutes to 1 hour, the polymer having vinyl groups Degradation occurs and part of the polymer is converted into polyacetylene unit. The reaction between the heat and the polymer and the graphene oxide in the process reduces the oxidized graphene to form a composite film of polyacetylene-reduced graphene.

At this time, the conductivity is much better than the known conductivity of graphene.

Finally, a composite protective film is deposited on the reduced graphene thin film (S300). At this time, the composite passivation layer is formed to prevent the upper part of the reduced film from being in contact with external moisture or oxygen.

At this time, it is preferable to use any one of a polystyrene (PS), a polystyrene (PE), a polystyrene-polyethylene mixed film (PES), a nitrogen filled protective film, an oxide SiO ₂ thin film and a lead glass protective film.

Here, the mixed film of polystyrene, polyethylene, and polystyrene-polyethylene is suitable for a temperature sensor used in an environment of 200 ° C or lower, and the nitrogen-filled protective film, the oxide SiO ₂ thin film, and the lead glass protective film are suitable for a temperature sensor used in a high temperature environment.

This is a composite protective film for a suitable environment and does not limit the kind of the composite protective film depending on the environment.

Lead glass protection film is a protective film made by melting lead glass at 300 ℃ or higher.

The temperature sensor using the reduced graphene thin film manufactured by the above method preferably has a linear relationship between changes in resistance value with respect to temperature change, more preferably a relationship between temperature and resistance is a linear equation, It has an inverse proportion to this temperature.

의 관계와 매우 일치하여 정밀한 온도 측정이 가능하다는 효과가 있다. 이는 도 7 및 도 8을 통해 알 수 있다. The temperature sensor using the reduced graphene thin film

So that accurate temperature measurement is possible. This can be seen from FIG. 7 and FIG.

7 is a graph showing a temperature-resistance relationship of a graphene composite film and a self-assembled reduced graphene composite film. The permeability of the 4-layer spin-coating film is 65%, and the permeability of the b.5-layer spin-coating film is 55%. The 6-layer coating had a transmittance of 48%, d. The 8-layer coating film shows a transmittance of 38%.

7 and 8, it can be seen that the resistance decreases as the temperature increases. As it can be seen that the linear slope according to the number of layers of the coating film decreases as the thickness increases, , It can be seen that the range of change in the resistance value is large when the coating number is thin.

As described above, the present invention can obtain a more precise and stable straight line graph without converting the measured graph value, and has the effect of reducing the cost of the sensing material and facilitating the interface.

의 관계식을 가지게 되어 종래의 NTC 센서와 달리 로그 계상회로 또는 소자, 고온 동작을 보정하는 보상회로가 필요치 않으며,

의 관계와 매우 일치하여 정밀한 온도 측정이 가능하다는 효과가 있다. In addition,

A logarithmic phase circuit or element and a compensation circuit for correcting the high temperature operation are not required unlike the conventional NTC sensor,

So that accurate temperature measurement is possible.

Therefore, as an automatic control sensor, it is coated thinly on a region where the heat should be read, and the resistance according to the change of temperature can be measured and utilized as a temperature sensor.

The method of manufacturing the temperature sensor using the reduced graphene thin film and the temperature sensor using the reduced graphene thin film are not limited to the configuration and the operation method of the embodiments described above. The above embodiments may be configured so that all or some of the embodiments may be selectively combined to make various modifications.

Claims (14)

A method of manufacturing a temperature sensor,
Forming an electrode pattern on the substrate;
Coating the electrode pattern with a reducing graphene thin film; And
Depositing a composite protective film on the reducing graphene thin film,
The reduced graphene thin film is a reduced graphene composite film or a reduced graphene self-assembled film,
The reducing graphene self-assembled film coating may be a method of transferring a reducing graphene self-assembled film to a substrate having the electrode pattern formed thereon by a reducing graphene intermediate solution, or a method of directly transferring a reduced graphene self- Wherein the method comprises the steps of: preparing a reduced graphene thin film;
delete The method according to claim 1,
The reducing graphene composite membrane may be formed by dissolving a reducing polymer in an aqueous solution to form a polymer solution;
Mixing the polymer solution with ethanol or isopropanol to form a mixed solution; And
Mixing the mixed solution and the oxidized graphene solution under a predetermined condition, and ultrasonically dispersing the mixture for a predetermined period of time to disperse the mixed solution and the oxidized graphene solution.
The method of claim 3,
Wherein the reducing polymer is a polymer having an alcohol group.
The method of claim 3,
Wherein the polymer solution is further mixed with an organic solvent or a surfactant.
The method of claim 3,
Wherein the mixing conditions of the oxidized graphene solution and the mixed solution are mixed in a volume ratio of 1: 0.1 to 1: 3.
The method according to claim 1,
Wherein the reduced graphene composite film coating is one of spin coating, inkjet printing, spray coating, and dispenser methods.
delete The method according to claim 1,
Wherein the reduced graphene self-assembling film comprises: preparing a reduced graphene intermediate solution by adding a reducing agent to the oxidized graphene;
Placing the liquid absorbing cloth and the substrate on the heating means in order;
Applying the reducing graphene intermediate solution to the substrate when the temperature of the substrate reaches a predetermined temperature by heating with the heating means;
Blocking the air flow of the substrate coated with the reduced graphene intermediate solution and forming a reduced graphene self-assembled film while reducing graphene is formed on the reduced graphene intermediate solution; And
And drying the water under the reduced graphene self-assembled film. The method of manufacturing a temperature sensor using the reduced graphene thin film according to claim 1,
The method according to claim 1,
Wherein the reducing graphene thin film is coated with a reducing graphene thin film, followed by a heat treatment step.
[Claim 10]
Wherein the heat treatment temperature is higher than a temperature of use of the temperature sensor.
The method according to claim 1,
Wherein the composite protective film is made of one selected from the group consisting of polystyrene (PS), polystyylene (PE), polystyrene-polyethylene mixed film (PES), nitrogen fill protective film, oxide SiO ₂ thin film, A method of manufacturing a temperature sensor using a graphene thin film.
A temperature sensor using a reduced graphene thin film, which is manufactured by any one of claims 1, 3 to 7, and 9 to 12.
14. The method of claim 13,
Wherein the temperature sensor has a linear relationship with a change in resistance value with respect to a temperature change.

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