KR100958695B1 - High-performance sensor for detecting carbon dioxide and manufacturing method thereof - Google Patents

Abstract

The present invention relates to a high-performance sensor for detecting carbon dioxide and a method for manufacturing the same, wherein the carbon dioxide detecting sensor of the present invention including a reference electrode, a sensing electrode, and a Li-BWO-based electrolyte thin film between the two electrodes has a high ion conductivity. Due to the use of the BWO-based electrolyte thin film, it reduces the power consumption of the sensor, has excellent sensitivity and recovery time, and can be used as a high performance sensor because it can vary the arrangement of the current collector. .

Description

High-performance sensor for detecting carbon dioxide and its manufacturing method {HIGH-PERFORMANCE SENSOR FOR DETECTING CARBON DIOXIDE AND MANUFACTURING METHOD THEREOF}

The present invention relates to a high performance sensor for detecting carbon dioxide exhibiting excellent Li ion conducting properties and a method of manufacturing the same.

Carbon dioxide detection sensors generally have a wide variety of uses, including plant growth, microbial culture, exhaust gas analysis, and freezing storage. Currently, the type of carbon dioxide sensor that is mainly used is electrolyte type sensor that detects voltage or current generated between electrodes through electrochemical reaction (redox reaction) between electrodes according to carbon dioxide concentration and 4.24㎛ infrared wavelength. Optical sensors using the principle that carbon dioxide absorbs light, and gas thermal conductivity sensors using the temperature change of the heating element due to the difference in thermal conductivity of the gas.

1 is a schematic diagram showing a schematic structure of a prior art electrolyte type sensor, showing a carbon dioxide sensing sensor manufactured using a Li ₃ PO ₄ solid electrolyte of a bulk structure.

An electrolyte according to the related literature, such as L. Satyanarayana [solid state ionics 177 ( 2007), 3485-3490, Characteristics and performance of binary carbonate auxiliary phase CO 2 sensor baed on Li 3 PO 4 solid electrolyte] Li 3 PO 4 The carbon dioxide sensing sensor manufactured by the conventional solid-phase reaction method or the sintering method using Li ₂ TiO ₂ -TiO ₂ as a reference electrode, the thickness of the carbon dioxide sensor was not effectively reduced effectively, and was manufactured according to the follow-up studies of Arkbar. The sensor having a Li ₃ PO ₄ electrolyte added with 5 mol% of SiO ₂ exhibited a higher electromotive force (EMF) value at the same concentration of carbon dioxide than the sensor having an electrolyte of Li-PON.

Korean Patent Publication No. 2005-0005899 also discloses a thin film gas sensor having a bulk structure.

 FIG. 2 is a schematic diagram showing another manufacturing process of an electrolyte sensor of the prior art, wherein a carbon dioxide sensor manufactured according to a microelectromechanical system (MEMS) using a Na-Si-Co-N electrolyte thin film is shown. The manufacturing process is shown.

In this regard, Lee et al., Sensor and actuators B 102 (2004), 20-26, Thin film micro carbon dioxide sensor using MEMS process, use Na-Si-Co-N as an electrolyte and use a reference electrode. The thin film type CO2 sensor was manufactured by using micro precision mechanical process (MEMS).

The conventional carbon dioxide sensors described above may be divided into a bulk structure and a MEMS structure using a thin film process in terms of structure. From the point of view of the material, the sensing electrode may be divided into Li ₂ CO ₃ , SnO ₂ , LaOCl, La ₂ O _3, or a composite oxide thereof, and the reference electrode may be divided into a Li conductor or a non-reference electrode. The electrolyte may be divided into a Li-based electrolyte or a Na-based electrolyte.

When the same material is used, the carbon dioxide sensor of the MEMS structure using the thin film process may have superior power consumption characteristics and sensing characteristics than the carbon dioxide sensor of the bulk structure, and in particular, it may be advantageous in terms of production and characteristics management, and thus it is easy to be commercialized.

However, in order to manufacture the electrolyte thin film using the thin film process has a disadvantage of a long process time or a long heat treatment time. Specifically, in the case of Li-PON electrolyte, a long process time of at least 6 to 7 hours is required, and in the case of Na-Si-Co-N electrolyte, a long heat treatment time of 7 to 10 hours is required to obtain a desired crystal phase. in need. This disadvantage causes a cost problem in the commercialization of the actual carbon dioxide sensor, especially in the carbon dioxide sensor using a Na-Si-Co-N electrolyte may cause a difference in sensor dynamics due to the crystal phase difference.

Therefore, the present inventors have studied diligently, the Li-BWO-based electrolyte recently developed as an electrolyte of a thin-film Li secondary battery is manufactured by a simple vacuum evaporation method, so the process time is very short as a few minutes, especially in the amorphous state excellent ion conduction characteristics With this in mind, it was found that a high-performance sensor can be manufactured by depositing Li-BWO-based electrolyte thin film on a large-area substrate in a short time by simple thermal evaporation method and manufacturing a carbon dioxide sensor using MEMS. The present invention has been completed.

[Document 1] Korean Patent Publication No. 2005-0005899 (LG Electronics Co., Ltd.) 2005.01.15

L. Satyanarayana et al., Solid state ionics 177 (2007), 3485-3490, Characteristics and performance of binary carbonate auxiliary phase CO ₂ sensor baed on Li ₃ PO ₄ solid electrolyte

Lee et al., Sensor and actuators B 102 (2004), 20-26, Thin film micro carbon dioxide sensor using MEMS process

It is therefore an object of the present invention to provide a solid Li electrolyte-containing high performance carbon dioxide sensing sensor exhibiting excellent Li ion conducting properties and a method of manufacturing the same.

In order to achieve the above object, the present invention provides a carbon dioxide sensing sensor comprising a reference electrode, a sensing electrode and a Li-B-W-O-based electrolyte thin film between the two electrodes.

The present invention also provides a method for manufacturing a carbon dioxide sensor using a microelectromechanical system (MEMS),

(1) depositing each of the reference electrode and the first current collector thin film on the substrate using sputtering or vacuum evaporation;

(2) depositing a Li-B-W-O-based electrolyte thin film on the thin film prepared in step (1) by using a vacuum evaporation method; And

(3) depositing each of the second current collector and the sensing electrode thin film on the electrolyte thin film prepared in step (2) by sputtering or vacuum evaporation;

It includes, it provides a method of manufacturing the carbon dioxide sensor.

The solid Li electrolyte-containing carbon dioxide sensing sensor according to the present invention reduces the power consumption of the sensor by thinning all electrodes using a very thin solid Li electrolyte, which is difficult to be achieved by a conventional bulk process or a thick film process. And it has a recovery force, can be varied in the arrangement of the current collector can be usefully used as a high performance sensor.

According to an embodiment of the present invention, a carbon dioxide sensor includes: (1) depositing each of a reference electrode and a first current collector thin film on a substrate using sputtering or vacuum evaporation; (2) depositing a Li-B-W-O-based electrolyte thin film on the thin film prepared in step (1) by using a vacuum evaporation method; And (3) depositing each of the second current collector and the sensing electrode thin film by using sputtering or vacuum evaporation on the electrolyte thin film prepared in step (2), wherein The steps are described in more detail as follows.

<Step (1)>

In step (1), each of the reference electrode and the first current collector thin film is deposited on the substrate using conventional sputtering or vacuum evaporation.

The substrate, the reference electrode, and the first current collector may be made of a material commonly used in constructing a carbon dioxide sensing sensor, and may have a thickness in a conventional range.

As the substrate, a silicon wafer having both surfaces polished can be used. Silicon is a relatively inexpensive material and is suitable for use as a substrate because of its very smooth surface and many devices that can process it.

As a suitable material for the reference electrode, a material having both diffusion and electron conduction of Li may be used. Specific examples thereof include LiCoO ₂ , V ₂ O ₅ , LiMnO ₂ , LiMn ₂ O _4, and composite oxides thereof. In the present invention, LiCoO ₂ is preferable.

As a material suitable for the first current collector, Ti, Pt, Au, a mixture thereof, and a Ti / Pt double thin film may be used.

In the present invention, the surface of the silicon wafer polished on both sides is oxidized, and then the oxidized wafer surface is etched in a desired pattern (eg, reactive ion etching (RIE) or KOH etching), and then sputtering or Vacuum evaporation can be used to deposit the reference electrode thin film on the patterned surface. Thereafter, a photoresist (PR) may be coated on the reference electrode, and the first current collector may be deposited on the photoreceptor layer by sputtering or vacuum evaporation.

The order of deposition of the reference electrode and the current collector thin film may be any first, and the reference electrode is preferably larger than the area of the current collector. The reference electrode layer and the first current collector layer can then be formed on the substrate in a desired pattern by lifting off the formed photoconductor layer.

<Step (2)>

In step (2), a Li-B-W-O-based electrolyte thin film is deposited on the first current collector thin film prepared in step (1) by using a conventional vacuum evaporation method.

The Li-B-W-O-based electrolyte thin film may be deposited to a thickness of 0.2 to 50 ㎛, it may be made of a material represented by the following formula (1):

Li _x -B _y -W _z -O _δ

Where

x is from 0.5 to 1.2,

y is 0.5 to 1.2,

z is from 0.6 to 1.5,

δ is 0.5 to 1.5.

<Step (3)>

In step (3), the second current collector and the sensing electrode thin film are deposited on the electrolyte thin film prepared in the above step (2) using conventional sputtering or vacuum evaporation, respectively.

The second current collector and the sensing electrode may be made of a material commonly used in constructing a carbon dioxide sensing sensor, and may have a thickness in a conventional range.

As a material suitable for the second current collector, the same material as that used for the first current collector can be used.

Li ₂ CO ₃ , SnO ₂ , LaOCl, La ₂ O ₃ and composite oxides thereof may be used as a suitable material for the sensing electrode, and Li ₂ CO ₃ is preferable in the present invention.

In the present invention, the second current collector may be deposited on the electrolyte thin film prepared in the step (2) by sputtering or vacuum evaporation, wherein the deposition is optionally performed at a desired position using a mask as necessary. can do. Thereafter, the sensing electrode thin film may be deposited by sputtering or vacuum evaporation.

The order of deposition of the sensing electrode and the second current collector may be any first, and the sensing electrode is preferably larger than the area of the current collector.

Finally, the carbon dioxide sensing sensor of the present invention can be manufactured by performing etching on the back side of the substrate based on a conventional micro precision mechanical process (MEMS).

A schematic diagram of a carbon dioxide detecting sensor manufacturing process according to one embodiment of the present invention is shown in FIG. 3B.

The carbon dioxide sensor can be manufactured in the order of reference electrode / electrolyte thin film / sensing electrode or vice versa. Since the electrolyte can react with moisture over time, the thin film placed on the electrolyte to prevent degradation of the electrolyte in the air. It is preferable to adjust the area of the film to be larger than the area of the electrolyte thin film.

The high performance sensor for detecting carbon dioxide according to the present invention may exhibit a detection area of 100 to 10,000 ppm, preferably 500 to 5,000 ppm at an operating temperature of 25 to 500 ° C.

Hereinafter, the present invention will be described in detail by the following examples. However, the following examples are merely to illustrate the invention, but the content of the present invention is not limited to the following examples.

Example 1 Fabrication of Reference Electrode and First Current Collector

On a conventional double-side polished silicon wafer, a 3 × 3 mm ² area LiCoO ₂ reference electrode was deposited to a thickness of 200 nm using RF magnetron sputtering, followed by heat treatment at a temperature of 700 ° C. for 30 minutes. The RF power was 150 W, the deposition time was 30 minutes, and the target used was 4 inches. Subsequently, after the photoconductor layer was coated on the reference electrode, the photoconductor layer formed by sputtering was separated and removed. Ti / Pt double thin films were deposited in order of thickness of 20 nm and 200 nm, respectively, with an area of 1.5 × 1.5 mm ² by DC magnetron sputtering to form a first current collector layer. At this time, the DC power was 150 W (400 V, 0.37-0.38 A), and the deposition times were 5 minutes and 10 minutes for the Ti / Pt double thin films, respectively.

Example 2. Preparation of Electrolyte Thin Film

On the first current collector manufactured in Example 1, a Li-BWO-based electrolyte thin film having an area of 4 x 4 mm ² and a thickness of 1 μm for 10 minutes by using a vacuum evaporation method (in this case, Li _x -B _y -W x is 1, y is 1.1, z is 1, and δ is 1.1 at _z- O _δ ).

Example 3 Fabrication of Sense Electrode and Second Current Collector

On the thin film prepared in Example 2, a Ti / Pt double thin film was formed using DC magnetron sputtering to a thickness of 20 nm and 200 nm, respectively, to form a second current collector layer with an area of 1.5 x 1.5 mm ² . At this time, a second current collector layer was selectively formed on the desired pattern using a mask. Deposition conditions were the same as those of the first current collector of Example 1 above. Subsequently, a Li ₂ CO ₃ sensing electrode having an area of 5 x 5 mm ² was deposited to a thickness of 300 nm by using RF magnetron sputtering, and then heat-treated for 30 minutes at a temperature of 650 ° C. It was the same as the reference electrode of Example 1 except that it was minutes.

Example  4. MEMS  Manufacture of structures

A backside etching process on the opposite side of the silicon wafer that exactly matches the position of the sensing electrode is performed on the basis of micro-mechanical processes (MEMS) to produce a membrane whose final area is equal to or less than 50% of the reference electrode area. It was. For reference, a photograph taken by FESEM (Field Emission Scanning Electron Microscopy) of depositing an electrode and a Li-BWO-based solid Li electrolyte thin film on a silicon substrate is shown in FIG. 3A, and a current collector and Li deposited on a stepped silicon substrate. A photograph taken of the BWO-based electrolyte thin film by FESEM is shown in FIG. 4.

Figure 1 shows a schematic diagram of a carbon dioxide sensing sensor prepared using a Li ₃ PO ₄ solid Li electrolyte of the bulk structure of the prior art.

Figure 2 shows a schematic diagram of a carbon dioxide sensing sensor manufacturing process manufactured by a micro precision mechanical process (MEMS) using another conventional Na-Si-Co-N electrolyte thin film.

FIG. 3A illustrates a photograph taken by FESEM (Field Emission Scanning Electron Microscopy) when the electrode and the Li-B-W-O-based solid Li electrolyte thin film are deposited on a silicon substrate.

Figure 3b shows a schematic diagram of a carbon dioxide sensor manufacturing process according to an embodiment of the present invention.

Figure 4 shows a photograph taken with the current collector and the Li-B-W-O-based electrolyte thin film deposited on the stepped Si substrate in FESEM.

Claims (8)

A reference electrode, a sensing electrode, and a Li-B-W-O-based electrolyte thin film between the two electrodes, Carbon dioxide detecting sensor, characterized in that the Li-B-W-O-based electrolyte thin film made of a material represented by the following formula (1): [Formula 1] Li _x -B _y -W _z -O _δ Where x is from 0.5 to 1.2, y is 0.5 to 1.2, z is from 0.6 to 1.5, δ is 0.5 to 1.5. delete The method of claim 1, The Li-B-W-O-based electrolyte thin film, characterized in that having a thickness of 0.2 to 50 ㎛, carbon dioxide detection sensor. The method of claim 1, And the reference electrode is made of a material selected from the group consisting of LiCoO ₂ , V ₂ O ₅ , LiMnO ₂ , LiMn ₂ O _4, and composite oxides thereof. The method of claim 1, And the sensing electrode is made of a material selected from the group consisting of Li ₂ CO ₃ , SnO ₂ , LaOCl, La ₂ O _3, and composite oxides thereof. In the method of manufacturing a carbon dioxide sensor using a microelectromechanical system (MEMS), (1) depositing each of the reference electrode and the first current collector thin film on the substrate using sputtering or vacuum evaporation; (2) depositing a Li-B-W-O-based electrolyte thin film on the thin film prepared in step (1) by using a vacuum evaporation method; And (3) depositing each of the second current collector and the sensing electrode thin film on the electrolyte thin film prepared in step (2) by sputtering or vacuum evaporation; Including, the manufacturing method of the carbon dioxide sensor. The method of claim 6, And the reference electrode and the sensing electrode thin film have an area larger than that of the first and second current collector thin films. The method of claim 6, And a thin film deposited on the electrolyte thin film has a larger area than the electrolyte thin film.

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