KR20220018870A - Ultra-low power gas sensor based on suspended nano structure and manufacturing method thereof - Google Patents

Abstract

According to an embodiment, an ultra-low power gas sensor based on a suspended nanostructure comprises: a substrate comprising: a substrate having a groove which is formed on the upper surface thereof to be recessed and has a predetermined opening; a first insulating layer disposed on the upper surface, and for covering a portion of the opening of the groove and not covering the remainder excluding the portion; a nanostructure disposed on the first insulating layer; a first conductor deposited on a portion, which is vertically opposite to the opening not covered by the first insulating layer, among a portion of the surface of the nanostructure, a portion of an upper surface of the first insulating layer, and the bottom surface of the groove; a second insulating layer deposited on a portion of the first conductor, a portion of the surface of the nanostructure in which the first conductor is not deposited, a portion of the first insulating layer, and the groove of the substrate; a second conductor formed on a portion of the surface of the second insulating layer deposited on the nanostructure; a first electrode contacting both sides of the first conductor and the second insulating layer deposited on the upper surface of the nanostructure; and a second electrode contacting a portion of the second insulating layer and both sides of the second conductor. The first conductor can be insulated from the second conductor.

Description

ULTRA-LOW POWER GAS SENSOR BASED ON SUSPENDED NANO STRUCTURE AND MANUFACTURING METHOD THEREOF

The present invention relates to an ultra-low power gas sensor based on a floating nanostructure and a method for manufacturing the same.

Recently, various types of gas sensors are being developed focusing on sensing materials and sensing methods. Among them, semiconductor metal oxide nanomaterials are attracting attention due to their advantages such as high sensitivity, miniaturization, and low price.

In addition, in the recent sensor market, the demand for Internet of Things (IoT)-based smart sensors is increasing, and the demand for miniaturization, low power consumption, sustainability, low cost and mass production potential required for continuous and organic monitoring and management is increasing. is increasing

Metal oxides (ZnO, SnO ₂ , In ₂ O ₃ , etc.) operate at high temperatures (250~600℃) and require high power consumption. It requires power consumption, which can be operated only for up to 5 hours with an AA battery (2000 mAh), and there is a problem in that the sustainability and reliability of the sensor element are deteriorated due to high heat loss to the outside.

In order to reduce the power consumption of these metal oxide-based gas sensors, research on miniaturization of heater and sensor systems and effective thermal efficiency improvement using floating nanostructures are continuing.

Korean Patent Publication No. 10-1027074 (Registered on March 29, 2011)

An object to be solved by the present invention is to provide an ultra-low power gas sensor based on an airborne nanostructure and a method for manufacturing the same.

In addition, it is possible to provide a gas sensor that is competitive in performance or price compared to the currently commercialized gas sensor through such an airborne nanostructure-based ultra-low power gas sensor and its manufacturing method. can be included in

However, the problems to be solved of the present invention are not limited to those mentioned above, and other problems to be solved that are not mentioned can be clearly understood by those of ordinary skill in the art to which the present invention belongs from the following description. will be.

A floating nanostructure-based ultra-low power gas sensor according to an embodiment includes: a substrate having a groove having a predetermined opening, which is formed in a concave shape on an upper surface; a first insulating layer disposed on the upper surface, the first insulating layer covering a portion of the opening of the groove and not covering the remaining portion except for the portion; a nanostructure disposed on the first insulating layer; a first conductor deposited on a portion of a surface of the nanostructure, a portion of an upper surface of the first insulating layer, and a portion of a bottom surface of the groove, which is vertically opposite to the opening not covered by the first insulating layer; a portion of the first conductor, a portion of the surface of the nanostructure on which the first conductor is not deposited, a portion of the first insulating layer, and a second insulating layer deposited in the groove of the substrate; a second conductor formed on a portion of the surface of the second insulating layer deposited on the nanostructure; a first electrode in contact with both sides of the first conductor and the second insulating layer deposited on the upper surface of the nanostructure; and a second electrode in contact with a portion of the second insulating layer and both sides of the second conductor, wherein the first conductor may be insulated from the second conductor.

In addition, the first conductor deposited on a portion of the surface of the nanostructure and the first conductor deposited on a portion of the upper surface of the first insulating layer are a portion perpendicular to the opening not covered by the first insulating layer It may be insulated from the first conductor deposited on the .

In addition, materials constituting the first insulating layer and the second insulating layer may be different from each other.

In addition, the first conductor, the first electrode, and the second electrode may include gold (Au).

In addition, the second conductor may include zinc oxide (ZnO).

In addition, an area of the remaining portion of the opening of the groove may be smaller than an area of a bottom surface of the groove.

In addition, a portion of the opening of the groove covered by the first insulating layer may be an edge of the opening of the groove.

In addition, the nanostructure may include a pillar portion disposed on the first insulating layer; and a nanowire supported by the pillar part and disposed to cross the opening of the groove.

In addition, the nanostructure may include two pillar portions, and both ends of the nanowire may be supported by each of the two pillar portions.

A method of manufacturing an airborne nanostructure-based ultra-low power gas sensor according to an embodiment includes: forming a recess having a predetermined opening on an upper surface of a substrate on which a first insulating layer is formed; forming a nanostructure on the first insulating layer; depositing a first conductor on a portion of the surface of the nanostructure, a portion of an upper surface of the first insulating layer, and a portion of a bottom surface of the groove, which is perpendicular to an opening not covered by the first insulating layer; depositing a part of the first conductor, a part of the surface of the nanostructure on which the first conductor is not deposited, a part of the first insulating layer, and a second insulating layer in the groove of the substrate; depositing a second conductor on a portion of the surface of the second insulating layer deposited on the nanostructure; forming a first electrode region in contact with both sides of the first conductor and the second insulating layer deposited on the upper surface of the nanostructure; and forming a second electrode region in contact with a portion of the second insulating layer and both sides of the second conductor, wherein the first conductor may be insulated from the second conductor.

In addition, the first conductor deposited on a portion of the surface of the nanostructure and the first conductor deposited on a portion of the upper surface of the first insulating layer are a portion perpendicular to the opening not covered by the first insulating layer It may be insulated from the first conductor deposited on the .

In addition, materials constituting the first insulating layer and the second insulating layer may be different from each other.

In addition, the first conductor, the first electrode, and the second electrode may include gold (Au).

In addition, the second conductor may include zinc oxide (ZnO).

In addition, the area of the portion of the opening of the groove not covered by the first insulating layer is, It may be narrower than the width of the bottom surface of the groove.

In addition, a portion of the opening of the groove covered by the first insulating layer may be an edge of the opening of the groove.

In addition, the forming of the nanostructure may include: forming a pillar portion on the first insulating layer; and forming a nanowire supported by the pillar part and crossing the opening of the groove.

In addition, the forming of the nanostructure may include forming the two pillar portions on the first insulating layer, and both ends of the nanowire may be supported by each of the two pillar portions.

In the floating nanostructure-based ultra-low power gas sensor according to an embodiment, the first conductor deposited on a portion of the surface of the nanostructure and the first conductor deposited on a portion of the upper surface of the first insulating layer are the upper surface of the substrate Since the first conductors deposited on the bottom surface of the grooves having a predetermined opening, which are concave and formed in the , are electrically insulated from each other, the first conductors deposited on the nanostructure can be used as a heater.

In addition, in the floating nanostructure-based ultra-low power gas sensor according to an embodiment, a portion of the first conductor, a portion of the surface of the nanostructure on which the first conductor is not deposited, a portion of the first insulating layer, and a groove of the substrate A second insulating layer is deposited on the nanostructure, and a second conductor deposited on a portion of the surface of the second insulating layer deposited on the nanostructure can be used as a gas sensor.

In addition, the ultra-low power gas sensor based on a floating nanostructure according to an embodiment can be operated with ultra-low power because it can utilize a heater using a floating nanostructure that is different from the conventional substrate-attached or micro-sized heater. It is possible, and it can be used in various applications through the development of a floating nanostructure coated with a second conductor (a metal oxide nanowire is used in the present invention).

In addition, the heater of the ultra-low-power gas sensor based on the floating nano-structure according to an embodiment can be applied to various sensors (gas sensor, bio-sensor, temperature sensor, flow sensor, etc.) that can be applied to IoT that requires ultra-small and low-power operation. It can be used as a possible sensor platform.

1 is a cross-sectional view of a gas sensor based on a floating nanostructure according to an embodiment.
2 is a three-dimensional view of a gas sensor based on a floating nanostructure according to an embodiment.
3 is a block diagram of a method for manufacturing a gas sensor based on floating nanostructures according to an embodiment.
4 and 5 are process diagrams illustrating a method of manufacturing a gas sensor based on a floating nanostructure according to an embodiment.
6 is a scanning electron microscope photograph for explaining iso-etching a substrate according to an embodiment.
7 is a view showing a cross-sectional view of a nanowire in an airborne nanostructure-based gas sensor according to an embodiment.
8 is a scanning electron microscope photograph for explaining a cross-sectional view of a nanowire in a gas sensor based on a floating nanostructure according to an embodiment.
9 is a view showing the results of performing an experiment to confirm the performance of the air-floating nanostructure-based gas sensor according to an embodiment.
10 is a graph comparing the performance when using the airborne nanostructure-based gas sensor according to an embodiment and the performance when using the conventional substrate-type external heat source.

Advantages and features of the present invention and methods of achieving them will become apparent with reference to the embodiments described below in detail in conjunction with the accompanying drawings. However, the present invention is not limited to the embodiments disclosed below, but may be implemented in various different forms, and only these embodiments allow the disclosure of the present invention to be complete, and common knowledge in the art to which the present invention pertains It is provided to fully inform those who have the scope of the invention, and the present invention is only defined by the scope of the claims.

In describing the embodiments of the present invention, if it is determined that a detailed description of a well-known function or configuration may unnecessarily obscure the gist of the present invention, the detailed description thereof will be omitted. In addition, the terms to be described later are terms defined in consideration of functions in an embodiment of the present invention, which may vary according to intentions or customs of users and operators. Therefore, the definition should be made based on the content throughout this specification.

1 is a cross-sectional view of a gas sensor 100 based on floating nanostructures according to an embodiment, and FIG. 2 is a three-dimensional view of a gas sensor 100 based on floating nanostructures according to an embodiment.

1 and 2 , a gas sensor 100 based on a floating nanostructure according to an embodiment includes a substrate 110 , a first insulating layer 120 , a nanostructure 130 , and a first conductor ( 140), the second insulating layer 150, the second conductor 160, the first electrode 170, and the second electrode 180 may include, but is not limited thereto.

The substrate 110 may include a groove 115 having a predetermined opening 110 - 1 formed in a concave shape on the upper surface.

The substrate 110 may serve as a support for physically supporting the nanostructures 130 (including pillars and nanowires), which will be described later. Furthermore, a first insulating layer (or insulating film) 120 to be described later may be provided on at least the surface of the substrate 110 so as not to affect the current or voltage detected through the nanostructure 130 to be described later. . For example, the substrate 110 may be an insulating substrate capable of isotropic etching, such as a sapphire or quartz substrate.

More specifically, the substrate 110 may be in the form of a wafer or a film, and in terms of physical properties, the substrate may be a rigid substrate or a flexible substrate. Crystallographically, the substrate may be a single crystal, a polycrystalline body, an amorphous body, or a mixed phase in which a crystalline phase and an amorphous phase are mixed. When the substrate is a laminated substrate in which two or more layers are laminated, each layer may be independently of a single crystal, polycrystalline, amorphous, or mixed phase.

Physically, the substrate 110 may be an inorganic substrate including a semiconductor. The substrate 110 may include a group 4 semiconductor including silicon (Si), germanium (Ge), or silicon germanium (SiGe); Group III-V semiconductors including gallium arsenide (GaAs), indium phosphorus (InP), or gallium phosphorus (GaP); Group 2-6 semiconductors including cadmium sulfide (CdS) or zinc telluride (ZnTe); Group 4-6 semiconductor including lead sulfide (PbS); Alternatively, there may be a laminated substrate in which two or more materials selected from these are laminated to form each layer. In this case, as described above, the first insulating layer 120 to be described later may be provided on the surface of the substrate 110 .

The first insulating layer 120 is disposed on the upper surface of the substrate 110 , and covers only a portion 110 - 2 of the openings 110 - 1 of the groove 115 of the substrate 110 , and The remaining portions 110 - 3 excluding some may not be covered.

Here, the remaining portion 110 - 3 not covered by the first insulating layer 120 may be narrower than the width of the bottom surface 110 - 4 of the groove 115 of the substrate 110 , and the first insulating layer 120 . A portion 110 - 2 of the opening 110 - 1 of the groove 115 of the substrate 110 covered by the layer 120 may be an edge of the opening 110 - 1 , but is not limited thereto.

The nanostructure 130 may be disposed on the first insulating layer 120 , and may include a plurality of pillar portions 130-1 and 130-2 and the nanowire 130-3, and the nanostructure ( 130) may be composed of carbon (C, Carbon).

The plurality of pillar portions 130-1 and 130-2 may include a first pillar portion 130-1 and a second pillar portion 130-2, and the plurality of pillar portions 130-1 and 130- 2) may each have at least two slope surfaces (or inclined surfaces).

The nanowire 130-3 is supported by each of the plurality of pillar portions 130-1 and 130-2, and may be disposed to cross the opening 110-1 of the groove 115 of the substrate 110. Both ends of the nanowire 130 - 3 may be supported by each of the plurality of pillars 130 - 1 and 130 - 2 .

Meanwhile, as an example, the width of the nanowire 130 - 3 may be 300 nm and the thickness may be 400 nm.

The first conductor 140 includes a portion 140 - 1 and 140 - 2 of the surface of the nanostructure 130 , a portion 140 - 4 of the upper surface of the first insulating layer 120 , and a groove of the substrate 110 . Among the bottom surfaces 110 - 4 of 115 , the first insulating layer 120 may be deposited on a portion 140 - 3 perpendicular to the opening 110 - 1 not covered.

Here, as for the first conductors 140-1 and 140-2 deposited on a portion of the surface of the nanostructure 130, the first conductor 140-1 is deposited on the upper portion of the nanostructure 130, and a plurality of A first conductor 140 - 2 may be deposited on a slope in a direction from each of the pillars 130 - 1 and 130 - 2 toward the opening 110 - 1 of the substrate 110 .

In addition, the first conductor 140 - 4 deposited on a portion of the upper surface of the first insulating layer 120 is disposed between the first and second pillars 130 - 1 and 130 - 2 of the nanowire. A first conductor 140 - 4 may be deposited on a portion perpendicularly opposed to 130 - 3 .

Meanwhile, the first conductors 140-1 and 140-2 deposited on a portion of the surface of the nanostructure 130 and the first conductor 140-4 deposited on a portion of the upper surface of the first insulating layer 120 ) is a first conductor 140-3 deposited on a portion of the bottom surface of the groove 115 of the substrate 110 that is vertically opposite to the opening 110-1 not covered by the first insulating layer 120. and may be insulated from each other.

The first conductors 140-1, 140-2, 140-3, and 140-4 may include gold (Au) as a conductive material, but is not limited thereto.

On the other hand, the gas sensor 100 based on the floating nanostructure according to an embodiment may be used as a heater (or nano heater) by using the first conductor 140 - 1 deposited on the upper surface of the nanostructure 130 . .

The second insulating layer 150 is a portion of the first conductors 140-1, 140-2, 140-3, and 140-4, and the first conductors 140-1, 140-2, 140-3, 140 -4) may be deposited on a portion of the surface of the nanostructure on which the deposition is not performed, a portion of the first insulating layer 120 , and the groove 115 of the substrate 110 .

Here, the second insulating layer 150 deposited on a portion of the first conductors 140-1, 140-2, 140-3, and 140-4 is the first conductor (150) deposited on the upper surface of the nanostructure 130. 140-1), the surface of the first conductor 140-2 deposited on a part of the surface of the nanostructure 130, and the first insulating layer 120 among the bottom surface of the groove 115 of the substrate 110 The first conductor ( 140-4) may be deposited on the surface.

In this case, the first insulating layer 120 and the second insulating layer 150 according to an example may be formed by atomic layer deposition, sputtering, plasma enhanced chemical vapor deposition, or the like. It may be formed through a commonly used method, such as a vapor deposition method. In the case of the first insulating layer 120, it may be formed using thermal oxidation. In one non-limiting example, the first insulating layer 120 and the second insulating layer 150 may include silicon oxide, hafnium oxide, aluminum oxide, zirconium oxide, barium-titanium composite oxide, yttrium oxide, tungsten oxide, and tantalum oxide. , zinc oxide, titanium oxide, tin oxide, barium-zirconium composite oxide, silicon nitride, silicon oxynitride, zirconium silicate, hafnium silicate, hafnium oxide, a mixture thereof or a composite thereof or the like.

Meanwhile, materials constituting the first insulating layer 120 and the second insulating layer 150 may be different from each other, but the present invention is not limited thereto.

The second conductor 160 may be deposited on a portion of the surface of the second insulating layer 150 deposited on the nanostructure 130 .

On the other hand, the second conductor 160 is a surface of the second insulating layer 150 deposited on the surface of the first conductor 140-4 deposited on a portion of the upper surface of the first insulating layer 120 and the It may also be deposited on the surface of the second insulating layer 150 deposited on the first insulating layer 120 .

As an example, the second conductor 160 may include zinc oxide (ZnO) as a conductive material or a metal oxide sensor material.

For example, the second conductor 160 is grown on the seed layer 163 and the seed layer 163 deposited on the surface of the second insulating layer 150 deposited on the nanowire 130-3. Nanowires 165 may be included.

Meanwhile, in the gas sensor 100 based on the floating nanostructure according to an embodiment, the second conductor 160 is deposited on a part of the surface of the second insulating layer 150 deposited on the nanostructure 130 . can be used as a gas sensor.

Furthermore, the second conductor 160 may be insulated from the first conductors 140 - 1 , 140 - 2 , 140 - 3 and 140 - 4 from each other due to the second insulating layer 150 .

The first electrode 170 is a region for power connection of the first conductor 140 - 1 deposited on the upper surface of the nanostructure 130 , and the first conductor 140 - 1 deposited on the upper surface of the nanostructure 130 . ) and the second insulating layer 150 , respectively.

That is, when power is connected to the first electrode 170 , current flows through the first conductor 140-1 deposited on the upper surface of the nanostructure 130 , and the first conductor 140-1 is used as a heater. can

In this case, a DC voltage source may be connected to the first electrode, but this is only an example and is not limited thereto.

The second electrode 180 is a region for power connection of the second conductor 160 , and may be in contact with a portion of the second insulating layer 150 and both sides of the second conductor 160 , as an example. , the second electrode 180 may also be in contact with a predetermined region on both sides of the second conductor 160 .

That is, when power is connected to the second electrode 180, current flows through the second conductor 160 deposited on a portion of the surface of the second insulating layer 150 deposited on the nanostructure 130, The second conductor 160 may be used as a gas sensor.

In this case, a DC voltage source and an ammeter for measuring a change in resistance of a sensing material (eg, zinc oxide (ZnO)) of the second conductor 160 may be connected to the second electrode 180 , but this is only one example. Examples are not limited thereto.

As an example, the first electrode 170 and the second electrode 180 may include gold (Au) as a conductive material or a metal oxide sensor material, but is not limited thereto.

Meanwhile, in the floating nanostructure-based gas sensor 100 according to an embodiment, when a voltage is applied by connecting a power source to the first electrode 170 , Joule heating occurs and the second conductor 160 can be heated, and since it supplies the activation energy required for gas reaction, it is not necessary to use high power consumption as in the conventional substrate-type external heat source, and the gas is heated for a long time with low power (eg, 1.8 mW). It has a perceptible effect.

3 is a block diagram of a method for manufacturing a gas sensor 100 based on a floating nanostructure according to an embodiment. In addition, this process may be performed by a person or a manufacturing device.

Referring to FIG. 3 , first, a groove 115 having a predetermined opening 110 - 1 may be concavely formed on the upper surface of the substrate 110 on which the first insulating layer 120 is formed (step S100 ). ).

Thereafter, the nanostructure 130 may be formed on the first insulating layer 120 (step S200 ).

Thereafter, among a part of the surface of the nanostructure 130 , a part of the upper surface of the first insulating layer 120 , and the bottom surface of the groove 115 of the substrate 100 , the openings not covered by the first insulating layer 120 ( 110-1), the first conductors 140-1, 140-2, 140-3, and 140-4 may be deposited on a portion perpendicularly opposed to the portion (step S300).

Thereafter, a portion of the first conductors 140-1, 140-2, 140-3, and 140-4, and the first conductors 140-1, 140-2, 140-3, and 140-4 are deposited. A second insulating layer 150 may be deposited on a part of the surface of the nanostructure 130 that is not present, a part of the first insulating layer 120 , and the groove 115 of the substrate 110 (step S400 ).

Thereafter, the second conductor 160 may be deposited on a portion of the surface of the second insulating layer 150 deposited on the nanostructure 130 (step S500 ).

Thereafter, the first electrode region 170 in contact with both sides of the first conductor 140 - 1 and the second insulating layer 150 deposited on the upper surface of the nanostructure 130 may be formed (step S600 ).

On the other hand, after performing step S400 and before performing step S500, a partial region of the second insulating layer 150 deposited on a portion of the first conductor 140-1 deposited on the nanostructure 130 is removed. It may be etched, and in this case, the etched region may be an upper end of the pillar portions 130 - 1 and 130 - 2 of the nanostructure 130 . In addition, although the first electrode region 170 may be formed in the etched region in step S600, the present invention is not limited thereto.

Thereafter, a second electrode region 180 in contact with a portion of the second insulating layer 150 and both sides of the second conductor 160 may be formed (step S700 ).

In this case, the first conductors 140-1, 140-2, 140-3, and 140-4 may be insulated from the second conductor 160 and deposited on a portion of the surface of the nanostructure 130. The first conductors 140 - 1 and 140 - 2 and the first conductor 140 - 4 deposited on a portion of the upper surface of the first insulating layer 120 are the bottom of the groove 115 of the substrate 100 . The surface of the first insulating layer 120 may be insulated from each other from the conductor 140-3 deposited on a portion perpendicularly opposite to the opening 110-1 not covered by the first insulating layer 120, but is not limited thereto.

In more detail, a method for manufacturing the airborne nanostructure-based gas sensor 100 according to an embodiment will be described with reference to FIGS. 4 and 5 . 4 and 5 are process diagrams illustrating a method of manufacturing the nanostructure-based gas sensor 100 according to an embodiment. In addition, this process may be performed by a person or a manufacturing device.

First, referring to FIG. 4 , 1) a substrate 110 is prepared, and 2) the substrate 110 is oxidized to form the first insulating layer 120 .

In this case, the substrate 110 may be a silicon wafer, and the first insulating layer 120 may be a silicon oxide film (SiO ₂ ).

Thereafter, 3) coating (eg, spin coating) a first photoresist on the first insulating layer 120, 4), 5) UV exposure using a first photomask Accordingly, the first photoresist in the predetermined central region may be removed.

Here, the first photoresist may be a negative photoresist.

6) Buffered oxide etchant (BOE) etching is performed to remove the first insulating layer located in a predetermined central region, 7) removing the first photoresist coated in the region except for the predetermined central region, and at least one or more The substrate 110 may be etched using a gas.

That is, through steps 6) and 7), the first insulating layer 120 (silicon oxide film (SiO2)) and the substrate 110 (silicon (Si)) may be iso-etched, respectively. In step 7), if the etching rate of the substrate 110 is relatively faster than the etching rate of the first insulating layer 120, the substrate etching is performed to the lower portion of the first insulating layer 120 at the edge of the opening 110-1. can

More specifically, referring to FIG. 6 , in step 7), the first insulating layer 120, SiO ₂ ) The substrate 110, Si is isotropically etched to the lower end, and the isotropically etched substrate 110, silicon ( It can be seen that the side surface of Si)) is curved.

At this time, the gas used to etch the substrate 110 in step 7) is sulfur hexafluoride (SF ₆ ) and octafluorocyclobutane (C ₄ F ₈ ) may be, but is not limited thereto.

Referring back to FIG. 4 , 8) a second photoresist may be coated (eg, SU-8 negative photoresist may be spin coated). In this case, as for the second photoresist, the second photoresist may be coated up to the etched portion of the substrate 110 .

On the other hand, the second photoresist used in step 8) is SU-8 photoresist, which is the same negative photoresist as the first photoresist, but can be used only to create a polymer structure that is modified of carbon through thermal decomposition, that is, a nano structure. have.

Then, 9) UV exposure is performed using the second photomask (cross-linking of the polymer from the upper end of the photoresist to the substrate can be performed), and 10) UV exposure is performed using the third photomask. Accordingly, two pillar portions (which may be photoresist pillar portions) disposed on the first insulating layer 120 and a wire (which may be a photoresist wire) supporting the two pillar portions may be generated (at this time, the substrate exposure energy can be adjusted so that cross-linking does not occur until Nanostructure 130 including carbon electrodes and carbon wire may be formed by performing a process of converting carbon to carbon.

In more detail, since a volume reduction of up to 90% occurs in the process of performing the thermal decomposition in step 12), the photoresist wire having a micrometer diameter is carbonized and the nanostructure 130 having a nanometer diameter ( or carbon nanowires), wherein the nanostructure 130 has a diameter of several tens of nm to several hundreds of nm, a length of several to several hundred μm, and an interval between the substrate and the wire may be 1 to several tens of μm, e.g. For example, the nanostructure 130 may have a diameter of 250 to 400 nm and a length of 130 to 170 μm.

In this case, the thermal decomposition may be performed at a preset temperature in a vacuum state or in an inert gas environment, and the electrical conductivity of carbon of the nanostructure 130 may be adjusted according to the thermal decomposition temperature. For example, when the thermal decomposition temperature is kept low, the nanostructure 130 may have a very low electrical conductivity compared to the metal compared to the metal, and the nanostructure 130 may have graphite at the same level as the insulator according to the thermal decomposition temperature. Even higher conductivity can be adjusted.

In this case, the nanostructure 130 may be composed of carbon, and includes two carbon pillars and carbon nanowires supporting the two carbon pillars, and in this case, the carbon nanowires may be formed in a suspended form.

The nanostructure 130 may be formed as a conductor or an insulator, and when the nanostructure 130 is formed as a nonconductor, if a conductor is deposited on the nanostructure 130, the conductor may act as a nanoelectrode body. .

Thereafter, 13) a third photoresistor may be coated (eg, spin coating), and 14) the carbon nanowire 130-3 of the nanostructure 130 is applied to the portion using a fourth photomask. 15) The third photoresist of the carbon nanowire 130-3 of the nanostructure 130 may be removed by performing UV exposure.

Here, the third photoresist may be a negative photoresist.

After removing the third photoresist of the portion of the carbon nanowire 130 - 3 of the nanostructure 130 , 16) a portion of the surface of the nanostructure 130 and the first insulation are performed using E-beam evaporation A first conductor 140 - 3 may be deposited on a portion of the top surface of the layer 120 and a bottom surface of the etched portion of the substrate 110 , and 17 ) the remaining third photoresistor may be removed.

For example, the first conductors 140-1, 140-2, 140-3, and 140-4 may include gold (Au), but is not limited thereto, and the conductor includes a material having high electrical conductivity. can do. In addition, a method of depositing the first conductors 140-1, 140-2, 140-3, and 140-4 is not limited to electron beam deposition, and a method of depositing a conductor such as thermal evaporation or sputtering may be used. .

Referring to FIG. 5 , 18) the second insulating layer 150 is formed with a portion of the first conductors 140-1, 140-2, 140-3, and 140-4, and the first conductors 140-1 and 140 -2, 140-3, and 140-4 may be deposited on a portion of the surface of the nanostructure 130 on which the deposition is not performed, a portion of the first insulating layer 120 and the groove 115 of the substrate 110 . . Here, the second insulating layer 150 may be hafnium oxide (HfO ₂ ).

That is, by depositing the second insulating layer 150 through step 18), electrical insulation is provided to the entire first conductor 140-1 and the nanostructure 130 deposited on the upper surface of the nanostructure 130 used as a heater. can make it happen

Thereafter, 19) a fourth photoresist may be coated (eg, spin coated). 20), 21) As UV exposure is performed using the fifth photomask, the fourth photoresist in a predetermined area may be removed.

Here, the fourth photoresist may be a negative photoresist.

Thereafter, 22) the second insulating layer 150 (HfO ₂ ) in the region from which the fourth photoresist is removed is etched, and 23) after the process of step 22) is performed, the remaining fourth photoresist may be removed.

More specifically, step 22) is a partial region of the second insulating layer 150 deposited on a part of the first conductor 140-1 deposited on the nanostructure 130 (the region from which the fourth photoresist is removed). ) may be etched, and in this case, the etched region may be the upper end of the pillar portions 130-1 and 130-2 of both ends of the nanowire 130-3 of the nanostructure 130 .

24) Coating (eg, spin coating) a fifth photoresist (positive photoresist), 25), 26) UV exposure using a sixth photomask, and thus a predetermined central area of the fifth photoresist can be removed.

On the other hand, the fifth photoresist used in step 24) may be a positive photoresist, not a negative photoresist like the first to fourth photoresists. At this time, the energy may be controlled so that the photoresist is not denatured to the substrate.

Thereafter, 27) a seed layer 163 of a second conductor including zinc oxide (ZnO) as a conductive material or metal oxide sensor material is deposited, and after the process of steps 28 and 27) is performed, the remaining fifth photoresist can be removed.

In this case, when depositing the seed layer of the second conductor 160 , the seed layer of the second conductor 160 is a brittle material, and unless deposition is made on the surface of the substrate 110 , easily can come off Therefore, when UV exposure is performed, precise control of separate UV exposure energy is not required.

At this time, when the air-floating nanostructure-based gas sensor 100 is used as a heater using the first conductor 140-1 deposited on the upper surface of the nanostructure 130, the temperature distribution of the heater may be non-uniform, Here, the temperature of the central region of the first conductor 140-1 is the highest, and the temperature decreases toward both ends of the first conductor. This is because the air floating nano structure-based gas sensor 100 uses the first conductor 140 - 1 deposited on the air floating nano structure as a heater, so that heat loss to the substrate and the carbon pillar is small. In this case, as the size of the first conductor 140-1 is smaller, the temperature difference between the center and both ends of the first conductor 140-1 may be larger.

On the other hand, the reactivity of the second conductor to the gas varies depending on the temperature. Therefore, in the floating nanostructure-based gas sensor 100, the second conductor must be coated on a relatively uniform temperature portion to show reproducible and reliable sensing results, so the seed layer 163 of the second conductor ) to be deposited in a predetermined central region (or may be a predetermined central region in the nanowire 130-3) in the second insulating layer 150 deposited on the surface of the first conductor 140-1 region. can

As an example, the second conductor 160 is selectively placed on a portion (within a temperature difference of 10 degrees) having a uniform heating temperature in the second insulating layer 150 deposited on the surface of the region of the first conductor 140-1. For coating, deposition (or coating) on the surface of the second insulating layer 150 corresponding to a predetermined portion (eg, 60 μm) in the entire nanowire 130-3 length (eg, 135 μm) can do.

Then, 29) in a sealed container (autoclave) in which constant pressure and temperature are maintained, nanomaterials (an example, nanowires) constituting the second conductor on the upper surface of the second conductor seed layer deposited in step 27) are sequenced (水熱) method can be grown.

7 and 8, the second conductor 160, ZnO grown by the hydrothermal method through step 29) is a metal oxide seed layer 163 and a metal oxide nanowire 165 formed on the surface of the metal oxide seed layer. ), and the metal oxide nanowires can grow radially on the surface of the metal oxide seed layer.

Accordingly, the thickness of the second conductor 160 (ZnO) may be greater than the thickness of the second insulating layer 150 . Furthermore, looking at the cross section of the floating nanostructure-based gas sensor 100 , the nanowire 130-3 of the nanostructure 130 is coated with a first conductor 140-1, and the first conductor The second insulating layer 150, HfO ₂ is coated on the sieve 140-1, and the second conductor 160, ZnO is deposited in the central region of the second insulating layer 150, HfO ₂ . can be checked

After 30) coating (eg, spin coating) the sixth photoresist, 31), and 32) UV exposure using the seventh photomask, the sixth photoresist in a predetermined area can be removed.

Here, the sixth photoresist may be a negative photoresist.

33) A region in contact with both sides of the first conductor 140-1 and the second insulating layer 150 deposited on the upper surface of the nanostructure 130 using E-beam evaporation, and the second insulation A material having high electrical conductivity may be deposited as a first electrode region and a second electrode region in a region in contact with a portion of the layer 150 and both sides of the second conductor 160 . As an example, the material having high electrical conductivity may include gold (Au), but is not limited thereto.

For example, the deposition method in step 33) is not limited to electron beam deposition, and a method of depositing a conductor such as thermal evaporation or sputtering may be used.

Thereafter, after the process of step 34) 33) is performed, the remaining sixth photoresist may be removed.

9 is a view showing the results of performing an experiment to confirm the performance of the air-floating nanostructure-based gas sensor according to an embodiment.

Referring to FIG. 9 , when a voltage is applied to the region of the first conductor 140-1 deposited on the upper surface of the nanostructure 130 usable as a heater, the region of the first conductor 140-1 is heated, and thus Accordingly, the resistance of the material of the second conductor 160 may decrease.

Accordingly, applying a voltage to the region of the first conductor 140-1 deposited on the upper surface of the nanostructure 130 usable as a heater through the calculated resistance change degree data of the second conductor material according to the external temperature. Accordingly, the heating temperature value of the second conductor 160 may be predicted.

In more detail, in the floating nanostructure-based gas sensor 100 , the resistance of the second conductor 160 according to the voltage applied to the first conductor 140-1 deposited on the nanostructure 130 . It can be seen that the value is changed and the average temperature of the first conductor 140 - 1 deposited on the nanostructure 130 is increased.

10 is a graph comparing the performance when using the airborne nanostructure-based gas sensor 100 according to an embodiment and the performance when using a conventional substrate-type external heat source.

When a voltage is applied to the first conductor to heat the second conductor, the second conductor reacts with the gas to change the resistance of the second conductor. When the resistance of the second conductor in pure air not containing the gas to be detected is R _a , and the resistance of the second conductor when exposed to the gas to be detected is R _g , the second conductor is exposed to the gas to be detected. When the resistance of the conductor increases, the reactivity of the gas sensor can be expressed as R _g /R _a .

Referring to FIG. 10 , the graph line regarding the reactivity of the gas sensor according to the nitrogen dioxide gas concentration when the airborne nanostructure-based gas sensor 100 is used is a red line, and when a conventional substrate-type external heat source is used The graph line for the performance of is shown in blue.

At this time, there is no significant difference between the performance when the airborne nanostructure-based gas sensor 100 is used and the performance when the conventional substrate-type external heat source is used, whereas the airborne nanostructure-based gas sensor When 100 is used, power consumption is 1.8 mW, but when using a conventional substrate-type external heat source, power consumption is, for example, 50 W ~ 70 W, so it shows a big difference in power consumption. can be checked

Therefore, it can be confirmed that the power consumption of the airborne nanostructure-based gas sensor 100 according to an embodiment is much less than when using a conventional substrate-type external heat source. In addition, it can be seen that the temperature of the second conductor was uniformly heated when the reactivity when the entire sensor structure was heated with a substrate-type external heat source and the reactivity when heated with an air-floating nanostructure-based heater were similar. .

On the other hand, the floating nano-structure-based gas sensor 100 according to an embodiment. Using the phenomenon that an extreme volume reduction (90%) occurs in the process of volatilization of most organic substances except for carbon (C) through pyrolysis of the polymer, a micro-scale polymer structure is fabricated and pyrolyzed to produce a micro-scale polymer structure and perform special etching or fine alignment It is a technology that can easily produce nanoscale floating nanostructures without an alignment process. It does not require expensive equipment, technology, or materials, and it is characterized by a low production cost because it can be processed in a large area.

At this time, the temperature of the second conductor 160 (zinc oxide, ZnO) can be immediately heated to 600°C at a low power of 4.5 mW, and NO comparable to that when using a conventional substrate-type external heat source (250°C). ₂ Gas detection performance (minimum measured concentration of 100 ppb) can be achieved with extremely low power consumption of 1.8 mW.

Furthermore, in the airborne nanostructure-based gas sensor 100 according to an embodiment, as a groove having a predetermined opening is formed in the upper surface of the substrate, a groove having a predetermined opening is formed. ) process, the first conductors 140 - 1 , 140 - 2 , 140 - 3 , and 140 - 4 and the second conductor 160 may be selectively deposited on the nanostructure 130 .

In addition, the airborne nanostructure-based gas sensor 100 according to an embodiment can easily deposit (or coat) a material such as gold having good ductility, which is difficult to perform a nanopatterning process, on the nanostructure 130 .

As described above, in the ultra-low power gas sensor based on the floating nanostructure according to an embodiment, the first conductor deposited on a portion of the surface of the nanostructure and the first conductor deposited on a portion of the upper surface of the insulating layer are Since the first conductors deposited on the bottom surface of the groove having a predetermined opening, which are concave in the upper surface of the substrate, are electrically insulated from each other, the first conductor deposited on the nanostructure can be used as a heater.

In addition, in the floating nanostructure-based ultra-low power gas sensor according to an embodiment, a portion of the first conductor, a portion of the surface of the nanostructure on which the first conductor is not deposited, a portion of the first insulating layer, and a groove of the substrate A second insulating layer is deposited on the nanostructure, and a second conductor deposited on a portion of the surface of the second insulating layer deposited on the nanostructure can be used as a gas sensor.

In addition, the ultra-low power gas sensor based on a floating nanostructure according to an embodiment can be operated with ultra-low power because it can utilize a heater using a floating nanostructure that is different from the conventional substrate-attached or micro-sized heater. It is possible, and it can be used in various applications through the development of a floating nanostructure coated with a second conductor (a metal oxide nanowire is used in the present invention).

In addition, the ultra-low-power heater based on the floating nanostructure according to an embodiment is a sensor platform that can be applied to various sensors (gas sensor, biosensor, temperature sensor, flow sensor, etc.) that can be applied to IoT that requires ultra-small and low-power operation can be used as

Further, each block or each step may represent a module, segment, or portion of code that includes one or more executable instructions for executing the specified logical function(s). It should also be noted that in some alternative embodiments it is also possible for the functions recited in blocks or steps to occur out of order. For example, it is possible that two blocks or steps shown one after another may in fact be performed substantially simultaneously, or that the blocks or steps may sometimes be performed in the reverse order according to the corresponding function.

The above description is merely illustrative of the technical idea of the present invention, and various modifications and variations will be possible without departing from the essential quality of the present invention by those skilled in the art to which the present invention pertains. Therefore, the embodiments disclosed in the present invention are not intended to limit the technical spirit of the present invention, but to explain, and the scope of the technical spirit of the present invention is not limited by these embodiments. The protection scope of the present invention should be interpreted by the following claims, and all technical ideas within the scope equivalent thereto should be interpreted as being included in the scope of the present invention.

100: gas sensor based on floating nano structure
110: substrate
120: first insulating layer
130: nano structure
140: first conductor
150: second insulating layer
160: second conductor
170: first electrode
180: second electrode

Claims (18)

A substrate comprising: a substrate having a groove having a predetermined opening formed in the upper surface of the concave;
a first insulating layer disposed on the upper surface, the first insulating layer covering a portion of the opening of the groove and not covering the remaining portion except for the portion;
a nanostructure disposed on the first insulating layer;
a first conductor deposited on a portion of the surface of the nanostructure, a portion of an upper surface of the first insulating layer, and a portion of the bottom surface of the groove, which is vertically opposite to the opening not covered by the first insulating layer;
a portion of the first conductor, a portion of the surface of the nanostructure on which the first conductor is not deposited, a portion of the first insulating layer, and a second insulating layer deposited in the groove of the substrate;
a second conductor formed on a portion of the surface of the second insulating layer deposited on the nanostructure;
a first electrode in contact with both sides of the first conductor and the second insulating layer deposited on the upper surface of the nanostructure; and
a second electrode in contact with a portion of the second insulating layer and both sides of the second conductor,
The first conductor is insulated from the second conductor
Ultra-low-power gas sensor based on floating nanostructures. The method of claim 1,
The first conductor deposited on a portion of the surface of the nanostructure and the first conductor deposited on a portion of the upper surface of the first insulating layer are deposited on a portion perpendicular to the opening not covered by the first insulating layer insulated from each other with the first conductor
Ultra-low-power gas sensor based on floating nanostructures. The method of claim 1,
Materials constituting the first insulating layer and the second insulating layer are different from each other
Ultra-low-power gas sensor based on floating nanostructures. The method of claim 1,
The first conductor, the first electrode, and the second electrode,
containing gold (Au),
Ultra-low-power gas sensor based on floating nanostructures. The method of claim 1,
The second conductor is
containing zinc oxide (ZnO),
Ultra-low-power gas sensor based on floating nanostructures. The method of claim 1,
The width of the remaining part of the opening of the groove is,
narrower than the width of the bottom surface of the groove
Ultra-low-power gas sensor based on floating nanostructures. The method of claim 1,
Some of the openings of the grooves covered by the first insulating layer are
the edge of the opening of the groove
Ultra-low-power gas sensor based on floating nanostructures. The method of claim 1,
The nanostructure is
a pillar portion disposed on the first insulating layer; and
and a nanowire supported by the pillar part and disposed to cross the opening of the groove
Ultra-low-power gas sensor based on floating nanostructures. 9. The method of claim 8,
The nanostructure includes two pillars,
Both ends of the nanowire,
supported by each of the two pillars
Ultra-low-power gas sensor based on floating nanostructures. forming a groove having a predetermined opening on the upper surface of the substrate on which the first insulating layer is formed;
forming a nanostructure on the first insulating layer;
depositing a first conductor on a portion of the surface of the nanostructure, a portion of an upper surface of the first insulating layer, and a portion of a bottom surface of the groove, which is perpendicular to the opening not covered by the first insulating layer;
depositing a second insulating layer on a part of the first conductor, a part of the surface of the nanostructure on which the first conductor is not deposited, a part of the first insulating layer, and a groove of the substrate;
depositing a second conductor on a portion of the surface of the second insulating layer deposited on the nanostructure;
forming a first electrode region in contact with both sides of the first conductor and the second insulating layer deposited on the upper surface of the nanostructure; and
Forming a second electrode region in contact with a portion of the second insulating layer and each of both sides of the second conductor,
The first conductor is insulated from the second conductor
A method for manufacturing an ultra-low-power gas sensor based on floating nanostructures. 11. The method of claim 10,
The first conductor deposited on a portion of the surface of the nanostructure and the first conductor deposited on a portion of the upper surface of the first insulating layer are deposited on a portion perpendicular to the opening not covered by the first insulating layer insulated from each other with the first conductor
A method for manufacturing an ultra-low-power gas sensor based on floating nanostructures. 11. The method of claim 10,
The materials constituting the first insulating layer and the second insulating layer are different from each other.
A method for manufacturing an ultra-low-power gas sensor based on floating nanostructures. 11. The method of claim 10,
The first conductor, the first electrode, and the second electrode,
containing gold (Au),
A method for manufacturing an ultra-low-power gas sensor based on floating nanostructures. 11. The method of claim 10,
The second conductor is
containing zinc oxide (ZnO),
A method for manufacturing an ultra-low-power gas sensor based on floating nanostructures. 11. The method of claim 10,
An area of the opening of the groove not covered by the first insulating layer is,
narrower than the width of the bottom surface of the groove
A method for manufacturing an ultra-low-power gas sensor based on floating nanostructures. 11. The method of claim 10,
Some of the openings of the grooves covered by the first insulating layer are
the edge of the opening of the groove
A method for manufacturing an ultra-low-power gas sensor based on floating nanostructures. 11. The method of claim 10,
The step of forming the nanostructure,
forming a pillar portion on the first insulating layer; and
It is supported by the pillar part and comprises the step of forming a nanowire to cross the opening of the groove
A method for manufacturing an ultra-low-power gas sensor based on floating nanostructures. 18. The method of claim 17,
The step of forming the nanostructure,
Forming the two pillar parts on the first insulating layer,
Both ends of the nanowire,
supported by each of the two pillars
A method for manufacturing an ultra-low-power gas sensor based on floating nanostructures.

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