KR102260165B1 - Nitrogen oxide gas detection sensor - Google Patents

Abstract

The nitrogen oxide gas detection sensor according to the present invention comprises: a double channel including a graphene layer and a metal oxide thin film positioned in contact with one surface of the graphene layer; a source electrode and a drain electrode spaced apart from each other on the metal oxide thin film of the double channel; a gate oxide film positioned in contact with the other surface of the double-channel graphene layer; and a gate electrode positioned on a gate oxide film region corresponding to a region spaced apart between the source electrode and the drain electrode.

Description

Nitrogen oxide gas detection sensor

The present invention relates to a nitrogen oxide gas detection sensor, and more particularly, to a nitrogen oxide gas detection sensor having excellent gas adsorption/desorption stability and improved sensitivity.

A conventional semiconductor gas sensor for detecting nitrogen oxide (NOx) gas is a gas sensor based on metal oxides such as _{zinc oxide (ZnO), tin oxide (SnO 2} ), indium oxide (In ₂ O ₃ ), and tungsten oxide (WO _{3 ).} has been used universally. Such a metal oxide-based gas sensor has advantages of excellent gas selectivity and easy manufacturing and operation, but has disadvantages in that it is difficult to detect low concentration gas and has low durability. In order to solve this problem, graphene-based gas sensors are being studied recently. Graphene has a linear band structure near the Fermi level, so the current can be easily changed by the transfer of a small amount of charge by the adsorbed gas. to be. However, due to such high chemical inertness, the selectivity of the detection gas is lowered, and the detection gas is selectively adsorbed only in the graphene defects region, and the current is recovered by the gas desorption. The disadvantage is that this does not proceed smoothly.

Therefore, there is a need to develop a gas sensor that has excellent sensitivity to a very small amount of nitrogen oxide gas and at the same time secures adsorption/desorption reaction stability of the detection gas.

An object of the present invention is to provide a nitrogen oxide gas detection sensor having excellent gas adsorption/desorption stability and improved sensitivity to nitrogen oxide gas.

A nitrogen oxide (NOx) gas detection sensor according to the present invention includes a double channel including a graphene layer and a metal oxide thin film positioned in contact with one surface of the graphene layer; a source electrode and a drain electrode spaced apart from each other on a double-channel metal oxide thin film; a gate oxide film positioned in contact with the other surface of the double-channel graphene layer; and a gate electrode positioned on a gate oxide film region corresponding to a region spaced apart between the source electrode and the drain electrode.

In the nitrogen oxide gas detection sensor according to an embodiment of the present invention, the gate voltage-drain current (V _gs - I _ds ) of the detection sensor may have a Dirac point.

In the nitrogen oxide gas detection sensor according to an embodiment of the present invention, the graphene layer may be a single-layer graphene.

In the nitrogen oxide gas detection sensor according to an embodiment of the present invention, the metal oxide of the metal oxide thin film is titanium (Ti), zinc (Zn), indium (In), tungsten (W), niobium (Nb), molyb It may be an oxide of one or more elements selected from denum (Mo), magnesium (Mg), tin (Sn), strontium (Sr), yttrium (Y), and gallium (Ga), or a composite oxide thereof.

In the nitrogen oxide gas detection sensor according to an embodiment of the present invention, the source electrode and the drain electrode may have an interdigitated structure.

The present invention includes a nitrogen oxide gas detection method using the aforementioned nitrogen oxide gas detection sensor.

The present invention includes a method for manufacturing the above-described nitrogen oxide gas detection sensor.

A nitrogen oxide gas detection sensor according to the present invention comprises: a) transferring a graphene layer on an insulating film; b) forming a metal oxide thin film on the transferred graphene layer using atomic layer deposition; and c) forming a source electrode and a drain electrode spaced apart from each other on the metal oxide thin film, and forming a gate electrode on the opposite surface of the insulating film on which the transferred graphene layer is located.

The nitrogen oxide gas detection sensor according to the present invention has a double-channel structure of a graphene layer and a metal oxide thin film, so it can detect a very small amount of nitrogen oxide gas and has excellent gas adsorption/desorption stability and sensitivity It has the effect of sensitively detecting trace amounts of nitrogen oxide gas.

1 is (a) the IV measurement result of the zinc oxide-graphene composite thin film according to the change in the thickness of the zinc oxide thin film analyzed at room temperature, (b) the oxidation according to the change in the thickness of the zinc oxide thin film analyzed at the operating temperature of 250 ° C. The IV measurement result of the zinc-graphene composite thin film and (c) the measurement result of the ohmic resistance value according to the change in the operating temperature and the thickness of the zinc oxide thin film,
_{2 shows (a)-(d) transmission characteristics (V DS} ) of a zinc oxide-graphene composite thin film-based nitrogen oxide (NOx) gas detection sensor having a zinc oxide thin film thickness of 5 nm, 30 nm, 50 nm and 100 nm, respectively; = 0.1V), (e) a diagram showing the change in the Fermi level according to the thickness of the zinc oxide thin film, and (f) the carrier concentration of graphene according to the thickness of the zinc oxide thin film at _{V G = 0 V (n} ) is the result of analyzing
3 is (a) a result of analyzing _{the transmission characteristics (V DS} = 10mV) of a NOx gas detection sensor based on a zinc oxide-graphene composite thin film before and after _{NO 2} gas injection at an operating temperature of 250 ° C. (b) NO _{2 It} is a diagram showing the change of the Fermi level due to charge compensation after gas injection,
4 is a result of analyzing the resistance change of Examples 2, 3, 5 and Comparative Example 1 after _{NO 2 gas injection,}
5 is a result of analyzing the reactivity to _{the NO 2} gas of Example 2, Example 3, Example 5 and Comparative Example 1.

Hereinafter, a nitrogen oxide gas detection sensor of the present invention will be described in detail with reference to the accompanying drawings. The drawings introduced below are provided as examples so that the spirit of the present invention can be sufficiently conveyed to those skilled in the art. Accordingly, the present invention is not limited to the drawings presented below and may be embodied in other forms, and the drawings presented below may be exaggerated to clarify the spirit of the present invention. At this time, if there is no other definition in the technical terms and scientific terms used, it has the meaning commonly understood by those of ordinary skill in the technical field to which this invention belongs, and in the following description and accompanying drawings, Descriptions of known functions and configurations that may be unnecessarily obscure will be omitted. Also, the singular forms used in the specification and appended claims may also be intended to include the plural forms unless the context specifically dictates otherwise. In this specification and the appended claims, the units used without special mention are based on weight, and in one example, the unit of % or ratio means weight % or weight ratio.

A nitrogen oxide gas detection sensor (hereinafter, NOx sensor) according to the present invention includes a double channel including a graphene layer and a metal oxide thin film positioned in contact with one surface of the graphene layer; a source electrode and a drain electrode spaced apart from each other on a double-channel metal oxide thin film; a gate oxide film positioned in contact with the other surface of the double-channel graphene layer; and a gate electrode positioned on a gate oxide film region corresponding to a region spaced apart between the source electrode and the drain electrode. In this case, the nitrogen oxide gas (NOx gas) may include nitrogen monoxide (NO), nitrogen dioxide (NO ₂ ), nitrous oxide (N ₂ O), or a mixed gas thereof.

The NOx sensor according to the present invention has a double-channel structure of a graphene layer and a metal oxide thin film, and allows the metal oxide thin film to come into contact with NOx gas, thereby changing the charge concentration of the metal oxide thin film and the charge concentration of the metal oxide thin film due to NOx adsorption. NOx gas can be detected using the change in the electrical state of the graphene layer caused by

Accordingly, the NOx sensor according to the present invention has a double-channel structure of a graphene layer and a metal oxide thin film, and has excellent gas adsorption/desorption characteristics while being able to detect a very small amount of NOx gas (change) of NOx gas (change) in quasi-real time It has the advantage of being able to detect it.

In detail, adsorption and desorption of NOx gas occurs in the double-channel metal oxide thin film, and current movement occurs in the graphene layer, so the presence or absence of NOx gas or change in concentration can be detected extremely quickly and reliably in real time. , as the charge change of the metal oxide thin film caused by the NOx gas is amplified and detected as the current change of the graphene layer having a linear band, extremely sensitive detection of the NOx gas can be made.

As is known, when NOx gas is adsorbed to the metal oxide thin film, the charge concentration of the metal oxide thin film is changed. However, when the NOx gas is detected by directly measuring the change in the charge concentration of the metal oxide thin film, the difference in the charge concentration generated by the NOx gas is not very large, so there is a limit to the detection of the ppb level concentration.

However, the NOx sensor according to the present invention detects a change in the electrical properties of the graphene layer by the metal oxide thin film whose charge concentration is changed by NOx, not the change in the charge concentration of the metal oxide thin film itself, so that a very small amount of NOx gas is also reliably It has the advantage of being able to detect it. In detail, when the charge concentration of the metal oxide thin film is changed by the NOx gas, graphene positioned in contact with the metal oxide thin film is sensitive to even a slight change in the charge concentration of the metal oxide thin film due to the unique linear band structure of graphene. The current can be varied to have extremely good gas detection sensitivity. In addition, since the region substantially reacting with NOx (adsorption region) is a metal oxide rather than graphene, it may have excellent adsorption/desorption stability for NOx gas.

As described above, the NOx sensor according to the present invention has high gas sensitivity and gas adsorption/desorption stability at the same time, and has the advantage of being able to detect very precisely and sensitively a very small amount of NOx gas in real time.

In order for the NOx sensor to reliably and quantitatively detect NOx gas and at the same time improve the detection sensitivity for NOx gas, the NOx sensor detection current (I _ds (NOx)) according to the adsorption of NOx gas, drain from the source electrode in the presence of NOx gas the value of a current to the electrodes) value, and itself is large, the detected current (I _ds (NOx)) is to the glass, and the detected current according to the NOx concentration with a linear relationship to the NOx concentration as possible (I _ds (NOx)) Big change is good.

Accordingly, in the NOx sensor having a dual channel of a graphene layer and a metal oxide thin film, a source electrode-metal oxide thin film channel- a first current movement path of the drain electrode; a second current path of the source electrode-the metal oxide thin film under the source-graphene-the metal oxide thin film under the drain-drain electrode; and a third current moving path through which current flows through both the first current moving path and the second current moving path; it is preferable that the current flows through the middle, second or third current moving path, in particular, the current flows through the second current moving path it's good

In the NOx sensor according to an embodiment, the gate voltage-drain current (V _gs - I _ds ) of the NOx sensor may have a Dirac point. The gate voltage-drain current (V _gs - I _ds ) of the NOx sensor is a Dirac voltage formed as an ambipolar characteristic appears, the source-drain current (I _ds ) of the NOx sensor is the second current movement path or It directly indicates that it is generated by the third current movement path. When the current flows by the second current moving path or the third current moving path, the detection current A is 10 ^-2 order to 10 ^-5 order level, for example, 10 ^-3 order (order). ) to 10 ^-4 order (order) level, specifically 1x10 ^-4 to 9x10 ^-3 may have a large value, and further, when a current flows by the second current flow path, a larger current value (10 ^{− 3} orders or more).

Experimentally, the bipolar characteristic may mean that the voltage-current graph, which is the value of the drain current (Ids) according to the gate voltage (V _{gs ) at a constant drain voltage (V ds ), has a concave shape, and the Dirac point (or} Dirac voltage) may mean a voltage value at the lowest point (a point at which the slope of the voltage-current graph changes from positive to negative) in the concave voltage-current graph.

Specifically, in the NOx sensor, the double-channel metal oxide thin film has a thickness of 100 nm or less, and the current (detection current) moves through both the graphene layer and the metal oxide thin film by the metal oxide thin film having a thickness of 100 nm or less ( a third current movement path). Advantageously, the thickness of the metal oxide thin film may be 70 nm or less, more advantageously 60 nm or less, even more advantageously 50 nm or less. As the thickness of the metal oxide thin film becomes thinner, the amount of current that moves through the graphene in the third current movement path may increase, and when a metal oxide thin film of 70 nm or less, more advantageously 60 nm or less, is provided, substantially most of the current is transferred to graphene It can flow through the layers. In this case, the metal oxide thin film has a thickness capable of forming a uniform and stable film, for example, a thickness of 2 nm or more, and a more practical example, a thickness of 5 nm or more so as to stably prevent direct adsorption of NOx gas to the graphene layer. However, it is not necessarily limited thereto.

When a current flows through the graphene layer (second current flow path), a large current (I _ds ) may occur at the same NOx concentration, and the high current value (I _ds ) and the linear band structure of graphene Sensitive current changes enable reliable detection of ppb-level NOx gases. In addition, when a current flows through the graphene layer (second current flow path), the linearity of the current increase according to the voltage increase (or decrease) is excellent due to the bipolar characteristic in the gate voltage-drain current of the NOx sensor, making it more quantitative It has the advantage of being able to accurately detect NOx. In addition, even a small charge change in the metal oxide thin film causes a very large change in current in the graphene layer, thereby greatly improving the detection sensitivity.

In one embodiment, the NOx sensor may have a Dirac voltage controlled according to the thickness of the metal oxide thin film. That is, in the NOx sensor according to an embodiment of the present invention, current movement occurs by the graphene layer even though the source electrode and the drain electrode are in contact with the metal oxide thin film (a channel is formed in the graphene layer, the second current movement path or the third current movement path), thereby having a Dirac voltage indicated by the intrinsic properties of graphene, and controlling the Dirac voltage of the double channel by the thickness of the metal oxide thin film.

Specifically, the NOx sensor has a double channel composed of a graphene layer and a metal oxide thin film, and as the metal oxide thin film is stacked in contact with one surface of the graphene layer to form an interface with the graphene layer, the graphene layer and the The metal oxide thin film may be in an electrically bonded state. Accordingly, depending on the relative height between the Fermi energy level of the metal oxide thin film and the Fermi level (or Dirac level) of graphene, charge transfer may occur from the metal oxide thin film to graphene or from graphene to the metal oxide thin film. In addition, such charge transfer direction and charge transfer degree may correspond to the dopant type (p-type dopant or n-type dopant) and doping degree doped in the graphene layer.

In one embodiment, as the thickness of the metal oxide thin film increases, defects such as oxygen vacancy in the metal oxide thin film (NOx unreacted state) increase, the Fermi level of the metal oxide thin film decreases, moves from graphene to the metal oxide thin film, and the graphene layer may have an n-type doped effect. Accordingly, as the thickness of the metal oxide thin film increases, the graphene layer may have an effect of being more heavily doped with an n-type dopant.

Due to the n-type doping effect, the Dirac voltage of the double channel may vary depending on the thickness of the metal oxide thin film, and in one embodiment, as the thickness of the metal oxide thin film increases, the Dirac voltage moves in a more negative direction. can

In one embodiment, by controlling the thickness of the metal oxide thin film to 2 to 100 nm, specifically 5 to 100 nm, more specifically 20 to 80 nm, more specifically 30 to 70 nm level, even more specifically 40 to 60 nm, 0V It is possible to control the Dirac voltage (Dirac point) nearby, and most of the detection current flows substantially through the second current movement path, and it can have a gate voltage-drain current characteristic having a polarity with excellent linearity, and a drain voltage (source). in contrast drain voltage) level of 0.1V may have a 10 ^-3 order (order) to ^10-4 extremely large amount of current (I _ds, a of the order (order)).

As described above, since the Dirac point of the NOx sensor is controlled by the thickness of the metal oxide thin film, when the thickness uniformity of the metal oxide thin film is poor, it is difficult to show a clean bipolar characteristic, and the voltage-current linearity at the gate voltage before and after the Dirac point. This may be damaged. Accordingly, the metal oxide thin film preferably has an RMS surface roughness of 4 nm or less, preferably 3 nm or less, and substantially has a thickness uniformity of 1 to 3 nm.

One in the embodiments, the metal oxide thin film may be a polycrystalline thin film, the metal oxide crystals in diameter may include a nano-grain 10 ⁰ nanometer order (nm order) to 10 ¹ nanometer order (nm order) . Due to the structural instability of these nano-grains and grain boundaries, it has the advantage that NOx gas can be adsorbed and desorbed smoothly.

In one embodiment, the metal oxide may be an n-type semiconductor. The n-type semiconductor metal oxides are titanium (Ti), zinc (Zn), indium (In), tungsten (W), niobium (Nb), molybdenum (Mo), magnesium (Mg), tin (Sn), strontium (Sr), an oxide of at least one element selected from yttrium (Y) and gallium (Ga), or a composite oxide thereof, but is not necessarily limited thereto. However, in terms of more stable adsorption and desorption of NOx gas, the intrinsic n-type metal oxide is preferably zinc oxide.

The graphene of the graphene layer may be a multi-layer graphene such as monolayer graphene, double-layer graphene, or triple-layer graphene, but in terms of stable and reproducible bipolar properties It is advantageous to be single-layer graphene.

In one embodiment, the surface of the metal oxide thin film exposed between the source electrode and the drain electrode spaced apart from each other may be a reaction region in which adsorption of NOx gas occurs. In terms of maximizing the NOx gas adsorption area, the source electrode and the drain electrode may have an interdigitated structure, but is not limited thereto, and may have any electrode structure known to maximize the reaction area in the sensor field. When the source electrode and the drain electrode have an interdigitated structure, the distance between the electrodes is at the level of 100 to 500 μm, the width of the electrode is at the level of 50 to 150 μm, and the length of the finger bar is at the level of 2,700 to 3,500, specifically, The spacing between the electrodes may be at the level of 50 to 600 μm, the width of the electrodes at the level of 70 to 130 μm, the interlocking length at the level of 2,900 to 3,300 μm, more specifically, the spacing between the electrodes may be at the level of 100 to 500 μm, and , The width of the electrode may be 80 to 120 μm, and the interlocking length may be 3,000 to 3,200 μm, but is not limited thereto.

The gate electrode may be positioned on a region of the gate insulating layer corresponding to a spaced region between the source electrode and the drain electrode spaced apart from each other. That is, the gate electrode may be formed so as to apply a vertical electric field (an electric field in the thickness direction of the dual channel) to at least a double channel located in a region spaced apart between the source electrode and the drain electrode. When the source electrode and the drain electrode have an interlocking structure, the gate electrode may have a shape corresponding to the shape of the spaced region between the source electrode and the drain electrode, but is not limited thereto.

The gate insulating layer may be a layer of an insulating material, and may be, for example, an oxide, nitride or oxynitride of a non-metal or post-transition metal, but is not limited thereto.

Optionally, a semiconductor layer may be positioned between the gate insulating layer and the gate electrode, and the doped semiconductor layer serves as a support for supporting the dual channel and transfers the voltage applied to the gate electrode to the double channel through the gate insulating layer ( conductor) and stably suppressing leakage current toward the gate. The semiconductor of the semiconductor layer may be a group 4 material such as silicon or germanium, but is not limited thereto, and a p-type dopant containing a group 3 element such as boron and gallium or an n containing a group 5 element such as phosphorus Of course, it may be in a state doped with a -type dopant. Accordingly, the semiconductor layer may be 1 to 10 mΩcm, preferably 1 to 8 mΩcm, more preferably, 1 to 5 mΩcm, but is not necessarily limited thereto.

The electrode material of the source electrode, the drain electrode, or the gate electrode may be any metal, and may include, but is not limited to, copper, aluminum, nickel, titanium, silver, gold, platinum, palladium, and the like.

The present invention includes a NOx gas detection method using the above-described NOx sensor.

In detail, the NOx gas detection method includes a reference setting step of measuring _{the drain current I ds} (ref) of the NOx sensor before introduction of the detection target gas containing NOx gas; A detection step of introducing a detection target gas containing NOx gas into the surface-exposed metal oxide thin film region between the source electrode and the drain electrode of the NOx sensor _{and measuring the drain current I ds} (NOx); may include, NOx gas may be detected based on a drain current value changed (increased) before and after introduction of the detection target gas. In this case, it goes without saying that the NOx gas may be detected with a changed resistance value using a resistance calculated based on the current instead of a changed current value before and after the introduction of the detection target gas.

At this time, when the detection target gas itself, or a detection target gas is generated, transported or discharged environment with a temperature of the high T ₁ more places (places where detection is performed by using a NOx sensor), the ambient temperature, the NOx sensor also in T ₁ Of course, it may be in a state heated to a temperature.

In the reference setting step and the detection step, the NOx sensor may be in a state in which a gate voltage is applied through the gate electrode. In this case, the gate voltage may be a voltage corresponding to a linear increase region in which the drain current linearly increases according to the increase or decrease of the gate voltage in the gate voltage-drain current (V _gs - I _{ds ) graph of the NOx sensor.} Specifically, the linear increase region is a unit voltage in each of the first region positioned on the positive voltage side and the second region positioned on the negative voltage side based on the Dirac point in the gate voltage-drain current (V _gs - I _{ds ) graph.} It may mean a region in which the slope (α) of the current, which is a change in the drain current value according to the change, is maintained within ±10%.

The present invention includes a method for manufacturing the above-described NOx sensor.

The manufacturing method of the NOx sensor according to the present invention comprises: a) transferring the graphene layer on the insulating film; b) forming a metal oxide thin film on the transferred graphene layer using atomic layer deposition; and c) forming a source electrode and a drain electrode spaced apart from each other on the metal oxide thin film, and forming a gate electrode on the opposite surface of the insulating film on which the transferred graphene layer is located.

In this case, the insulating film in step a) may be the above-described gate insulating film, and the insulating film may be formed on a semiconductor layer (including a substrate). The transfer of the graphene layer may be performed by any method known to be used for transferring the graphene layer to a desired position. For example, after forming a polymer layer to cover the graphene grown on the catalyst metal film, removing the catalyst metal film to prepare a graphene-polymer layer composite film, and then placing the graphene on the insulating film to be transferred, and then placing the polymer layer may be carried out by removing the catalytic metal film or the polymer layer may be carried out using an etchant that selectively melts and removes the material, but the present invention is not limited by the spherical graphene layer transfer method.

In order to form a double channel, step b) of forming a metal oxide thin film on the transferred graphene layer may be performed. At this time, as described above, the Dirac point of the NOx sensor is changed by the thickness of the metal oxide thin film, NOx gas is adsorbed to the metal oxide thin film, and a charge change in the metal oxide thin film occurs, and between the metal oxide thin film and the graphene layer Due to the electrical interaction, the current (I _ds ) flowing through the graphene layer is changed to detect NOx gas, so that a thin and uniform metal oxide thin film should be formed.

Accordingly, step b) may be performed by atomic layer deposition, and through this, a metal oxide thin film having a very precisely designed thickness and having an extremely low RMS surface roughness can be manufactured. In addition, when a metal oxide thin film is formed by using atomic layer deposition, metal oxide nanograins may be formed due to defect regions such as graphene's inherent carbon structure and wrinkles.

The fabrication of the metal oxide thin film using atomic layer deposition (ALD) may be performed by sequentially alternately contacting the transferred graphene layer with a first precursor gas that is a metal precursor and a second precursor gas containing oxygen.

In this case, the second precursor gas containing oxygen may include, but is not limited to, _{H 2} O, H ₂ O ₂ , O ₂ , O _{3 or a mixture thereof.} The first precursor gas is a metal source in a conventional chemical vapor deposition (CVD) or ALD process, specifically, titanium (Ti), zinc (Zn), indium (In), tungsten (W), niobium (Nb), Any organic metal compound used as a source of molybdenum (Mo), magnesium (Mg), tin (Sn), strontium (Sr), yttrium (Y) or gallium (Ga) can be used. Using zinc as an example, the first precursor gas may be diethylzinc, etc., but the present invention is not limited by the specific type of the precursor gas used as the source of the metal element.

The temperature (the temperature of graphene) during the atomic layer deposition in step b) may be any temperature at which the metal oxide is smoothly formed by the precursor gas (the first precursor gas and the second precursor gas). As an example, the temperature at which the atomic layer deposition is performed in step b) may be 100 to 200° C., but may be appropriately changed depending on the material of the spherical precursor gas used.

More specifically, step b) comprises i) steps i) through iv) steps of i) supply of a first precursor gas, ii) purging with an inert gas, iii) supply of a second precursor gas, and iv) purging with an inert gas. As one cycle, it may include repeating the cycle. In this case, it goes without saying that the thickness of the metal oxide thin film is controlled by the number of repetitions of the cycle.

A material may be deposited as a single atomic layer by supply of a precursor gas (a first precursor gas or a second precursor gas), and unreacted precursor gas (and by-products) may be removed during purging with an inert gas.

In step i), the supply amount of the first precursor gas, the contact time of the first precursor gas and graphene, the purging time in the purging steps (ii, iv) and iii), the supply amount of the second precursor gas, the second precursor gas The contact time between the graphene and the graphene may be any condition commonly used in the atomic layer deposition method.

The electrodes (gate, drain, and source electrodes) of step c) may be performed by depositing a metal using a mask having a designed pattern (pattern corresponding to the shape of the electrode). In this case, the deposition of the metal may be performed using physical vapor deposition or chemical vapor deposition, and specifically, thermal evaporation may be performed, but the present invention provides a specific deposition method Of course, it cannot be limited by .

(Example 1) NOx gas detection sensor including gate insulating layer/graphene layer/ZnO layer

Step 1: Fabrication of a channel layer having a gate insulating layer/graphene layer/ZnO layer

First, a 25 μm thick Cu foil is placed inside a thermal chemical vapor deposition (TCVD) reactor, and then 100 sccm of H ₂ is injected and heated to 1050° C., and when the temperature in the reactor is stabilized, 2 sccm of CH ₄ was injected and reacted for 25 minutes to synthesize graphene on Cu foil. Thereafter, poly(methyl methacrylate) (PMMA) was spin-coated on the graphene synthesized on the Cu foil, and then the Cu foil was removed by etching, and the remaining etching solution was washed with deionized water. PMMA-coated graphene was transferred onto a SiO ₂ /highly-doped Si substrate (SiO ₂ thickness = 300 nm, resistance < 0.005 Ωcm), respectively, and then PMMA was removed using acetone. In this case, the SiO ₂ /highly-doped Si substrate used was used as a gate insulator and a gate electrode, and the thickness of the substrate was 300 nm.

After placing the graphene-transferred SiO ₂ /Si substrate in an atomic layer deposition (ALD) chamber, a working pressure in the chamber was fixed to 3.0 Torr using a throttle valve. and ZnO was deposited on _{the graphene-transferred SiO 2} /Si substrate using diethyl zinc (DEZ) and H ₂ O as zinc (Zn) and oxygen (O) sources, respectively, at 150°C. Atomic layer deposition was repeated 28 times to fabricate a gate insulating layer/graphene layer/ZnO layer having a ZnO thickness of 5 nm. At this time, the one-time process of atomic layer deposition includes the steps of opening the throttle valve and injecting vaporized DEZ for 0.4 seconds; purging for 10 seconds using Ar gas of 300 sccm; opening the throttle valve and injecting _{vaporized H 2 O for 1 second;} and purging for 10 seconds using Ar gas of 300 sccm; was performed sequentially.

Step 2: Fabrication of NOx gas detection sensor having gate insulating layer/graphene layer/ZnO layer

After masking using a metal shadow mask on the ZnO layer of the channel layer prepared in the above step, an Al electrode is deposited through a thermal evaporator, and the source electrode and the source electrode are interdigitated. A drain electrode was formed. At this time, the number of interlocking regions of the deposited Al electrode is 6, the thickness is 80 nm, the spacing between the electrodes is 300 μm, the height is 400 um, the width is 3100 um, and the total sensing area is 7.44 mm ² to be.

(Example 2) NOx gas detection sensor including gate insulating layer/graphene layer/ZnO layer

The atomic layer deposition process is repeated 84 times in step 1 of Example 1, except that a ZnO layer having a thickness of 15 nm is manufactured, which is the same as the manufacturing method of Example 1.

(Example 3) NOx gas detection sensor including gate insulating layer/graphene layer/ZnO layer

The atomic layer deposition process was repeated 164 times in step 1 of Example 1, except that a ZnO layer having a thickness of 30 nm was manufactured, and the manufacturing method was the same as in Example 1.

(Example 4) NOx gas detection sensor including gate insulating layer/graphene layer/ZnO layer

The manufacturing method of Example 1 is the same as that of Example 1, except that the atomic layer deposition process is repeated 278 in step 1 of Example 1 to deposit and manufacture a ZnO layer having a thickness of 50 nm.

(Example 5) NOx gas detection sensor including gate insulating layer/graphene layer/ZnO layer

The atomic layer deposition process is repeated 550 times in step 1 of Example 1, except that a ZnO layer having a thickness of 100 nm is manufactured, which is the same as the manufacturing method of Example 1.

(Comparative Example 1) NOx gas detection sensor including gate insulating layer/graphene layer

A sensor was manufactured in the same manner as in Example 1, except that in step 1 of Example 1, the process of depositing ZnO on graphene was not performed, and a source electrode and a drain electrode having a structure directly interlocked with each other were formed on graphene. did.

(Experimental Example 1) Electrical Characteristics Analysis of Zinc Oxide-Graphene Composite Thin Film

The IV characteristics of the zinc oxide-graphene composite thin film were measured using semiconductor characterization equipment (Keithley, 4200 scs model) was used to measure the current value in the region of -1 V to 1 V. The resistance of the zinc oxide-graphene composite thin film was analyzed by calculating the current value measured at 1 V in the measured IV linear graph.

(Experimental Example 2) Characteristic evaluation of NOx gas detection sensor

_{The electrical conductivity characteristics of the NOx gas detection sensor were measured by flowing an inert gas (N 2} ) gas of 100 sccm using the vacuum probe station used in Experimental Example 1 to maintain a constant pressure, and applying a constant voltage of 0.1 V to time was measured using the measured current value, and the electrical conductivity characteristics of the NOx gas detection sensor were analyzed by converting the change in the current value measured at 0.1 V into resistance. In addition, the gas response of _{the NOx gas detection sensor was measured by injecting a reactive gas (20 ppm NO 2} gas) at a flow rate of 100 sccm at 250° C. for 10 minutes and measuring the resistance change of the NOx gas detection sensor, and the measured resistance It was calculated by the following equation using the rate of change of .

Gas reactivity = ΔR/R ₀ x 100 (here, ΔR (rate of change of resistance) = R-R0, R ₀ = initial resistance)

Before evaluating the characteristics of the NOx gas detection sensor, the electrical characteristics of the zinc oxide-graphene composite thin film were checked in a gas measurement environment, and the results are shown in FIG. 1 .

1 (a) and (b) are the I-V measurement results of the zinc oxide-graphene composite thin film according to the change in the thickness of the zinc oxide thin film analyzed at room temperature and 250° C., respectively. As shown, it can be seen that the current value of the zinc oxide-graphene composite thin film decreases as the thickness of the zinc oxide increases or the temperature increases. It can be inferred that the resistance of the fin composite thin film increases.

Figure 1 (c) is a result of measuring the ohmic resistance (ohmic resistance) value according to the change in the operating temperature and the thickness of the zinc oxide thin film. As shown, as the temperature or the thickness of the zinc oxide thin film increases, the resistance of the zinc oxide-graphene composite thin film increases. In general, as the temperature increases, the resistance of the semiconductor-type zinc oxide thin film decreases, and in the graphene thin film, the resistance increases as phonons in the graphene are activated and scattered. It can be seen that the resistance characteristic of the pin follows.

Therefore, through the results of FIG. 1, it can be confirmed that the main conduction path of electrons and charges of the zinc oxide-graphene composite thin film is graphene, not zinc oxide.

The electrical interaction between graphene and zinc oxide was investigated by analyzing the change in electrical conductivity according to the change in the thickness of the zinc oxide thin film in the zinc oxide-graphene composite structure, and the results are shown in FIG. 2 .

2(a)-(d) are NOx gases each having a thickness of a zinc oxide thin film of 5 nm (Example 1), 30 nm (Example 3), 50 nm (Example 4) and 100 nm (Example 5), respectively. This is the result of analyzing the transmission characteristics (V _{DS = 0.1V) of the detection sensor.} As shown, the Dirac point is observed at low current, and the Dirac voltage is >150 V for Example 1 (ZnO 5 nm) and 73 V for Example 3 (ZnO 30 nm), respectively. , -26 V for Example 4 (ZnO 50 nm) and 73 V for Example 5 (ZnO 100 nm), showing ambipolar characteristics regardless of the thickness of the zinc oxide thin film. On the other hand, in the case of the Dirac voltage of Example 1 (ZnO 5 nm), it can be seen that it is located on the high positive (+) gate voltage side outside the measurement range, which means that the graphene is doped with p-type. In addition, it can be seen that as the thickness of ZnO increases, the Dirac voltage shifts to a negative (-) gate voltage, which means doping with n-type graphene. In particular, in the case of Example 5 (ZnO 100 nm), it can be confirmed that the unipolar characteristic is changed from the bipolar characteristic to the unipolar characteristic, which is a characteristic of the n-type semiconductor with reduced hole conduction.

FIG. 2E shows the change of the Fermi level according to the thickness of the zinc oxide thin film, and it can be seen that the Fermi level of the zinc oxide decreases as the thickness of the zinc oxide thin film increases. 2(f) is a result of analyzing the carrier concentration (n) of graphene according to the thickness of the zinc oxide thin film at _{V G = 0 V. Overall, as the thickness of the zinc oxide thin film increases, the hole concentration of graphene} decreases and the electron concentration increases. As a result, as the thickness of the zinc oxide thin film increases, the density of oxygen vacancies inside the thin film increases, and the Fermi level of zinc oxide increases from this, resulting in electrons moving from zinc oxide to graphene. Accordingly, it can be seen that the n-type doping phenomenon of graphene appears.

In order to confirm the gas sensing characteristics of the NOx gas detection sensor, when NO ₂ gas is adsorbed, a change in the electrical interaction between zinc oxide and graphene was investigated, and the results are shown in FIG. 3 .

3 (a) shows the transfer characteristics (V) of a zinc oxide-graphene composite thin film-based NOx gas detection sensor before and after _{NO 2} gas injection at an operating temperature of 250° C. of Example 3 (ZnO thickness: 30 nm) _DS = 10 mV), and FIG. 3 (b) is a diagram showing the change in the Fermi level due to charge compensation after _{NO 2 gas injection.} As shown, the _{Dirac voltages before and after NO 2} gas injection are 47 V and 53 V, respectively, and it can be seen that the voltage of the NOx gas sensor increases after the _{NO 2 gas injection, which means that the NO 2} gas is adsorbed to the gas sensor. It means that graphene is doped with p-type. These results can be described in more detail through FIG. 3(b). As shown, in general, when NO ₂ gas is adsorbed on the surface of zinc oxide, electrons from zinc _{oxide move to NO 2} gas molecules, the Fermi level of zinc oxide goes down, and electrons of graphene move to zinc oxide. It can be seen that additional p-type doping of graphene occurs.

4 is an example of Example 2 (ZnO thickness: 15 nm), Example 3 (ZnO thickness: 30 nm), Example 4 (ZnO thickness: 50 nm), Example 5 (ZnO thickness: 100 nm) after _{NO 2 gas injection} ) and the result of analyzing the resistance change of Comparative Example 1. As shown, it can be seen that the NOx gas sensor based on the zinc oxide-graphene composite thin film exhibits excellent gas sensing properties in all examples, and it can be observed that the resistance characteristics change according to the thickness of the zinc oxide thin film. . Specifically, Examples 2, 3 and 4, in which the zinc oxide thin film had a thickness of less than 100 nm, showed excellent NO ₂ gas sensing characteristics, and _{it was confirmed that the resistance decreased when the NO 2} gas was adsorbed, and the zinc oxide thin film Example 5 having a thickness of 100 nm shows excellent NO ₂ gas sensing properties, and it can be seen that the resistance increases when _{NO 2 gas is adsorbed.} This result is because, as mentioned above, in the case of a gas sensor with a zinc oxide thin film thickness of less than 100 nm, the main conduction path of electric charge is the graphene layer, and in the case of a gas sensor with a zinc oxide thin film thickness of 100 nm, yes This is because, as the pin exhibits the behavior of an n-type semiconductor, electrons move from graphene to zinc oxide, so that current flows through graphene and zinc oxide at the same time, showing the behavior of a general gas sensor. On the other hand, it can be seen that the examples of the zinc oxide-graphene composite thin film-based NOx gas sensor show excellent recovery characteristics (adsorption and desorption characteristics) regardless of the zinc oxide thickness compared to Comparative Example 1, which is a graphene-based NOx gas sensor. can Specifically, it can be seen that by using the dual channel of the zinc oxide layer and the graphene layer, the zinc oxide layer is used as the main gas sensing channel and the graphene layer is used separately as the main charge transfer channel, thereby showing excellent recovery characteristics.

5 shows Example 2 (thickness of ZnO: 15 nm), Example 3 (thickness of ZnO: 30 nm), Example 4 (thickness of ZnO: 50 nm), Example 5 (thickness of ZnO: 100 nm) and Comparative Example 1 It is the result of analyzing the reactivity to _{NO 2 gas.} As shown, the gas reactivity of Examples 2, 3, 4 and 5 were 12.4%, 18.8%, 19.7%, and 17.5%, respectively, about 30 than the gas sensitivity of Comparative Example 1 of 0.7%. It can be seen that the results are doubled. Therefore, it can be seen that the zinc oxide-graphene composite thin film-based NOx gas sensor has significantly improved gas sensitivity than the graphene-based NOx gas sensor. In particular, as described above, in Examples 1 to 4, since substantially all current flows through the graphene layer, even a small charge change in the zinc oxide thin film causes a very large current change in the graphene layer, resulting in a ppb level of It is considered that NOx gas can be detected.

As described above, the present invention has been described with specific details and limited examples and drawings, but these are only provided to help a more general understanding of the present invention, and the present invention is not limited to the above embodiments, and the present invention is not limited to the above embodiments. Various modifications and variations are possible from these descriptions by those of ordinary skill in the art.

Therefore, the spirit of the present invention should not be limited to the described embodiments, and not only the claims to be described later, but also all those with equivalent or equivalent modifications to the claims will be said to belong to the scope of the spirit of the present invention. .

Claims (7)

a double channel including a graphene layer and a metal oxide thin film positioned in contact with one surface of the graphene layer;
a source electrode and a drain electrode spaced apart from each other on the metal oxide thin film of the double channel;
a gate oxide film positioned in contact with the other surface of the double-channel graphene layer; and
a gate electrode positioned on a gate oxide film region corresponding to a region spaced apart between the source electrode and the drain electrode;
A nitrogen oxide (NOx) gas detection sensor comprising a. The method of claim 1,
The gate voltage of the detection sensor-drain current (V _gs - I _ds ) is a nitrogen oxide gas detection sensor having a Dirac point. The method of claim 1,
The graphene layer is a single-layer graphene nitrogen oxide gas detection sensor. The method of claim 1,
The metal oxide of the metal oxide thin film is titanium (Ti), zinc (Zn), indium (In), tungsten (W), niobium (Nb), molybdenum (Mo), magnesium (Mg), tin (Sn), A nitrogen oxide gas detection sensor that is an oxide of one or more elements selected from strontium (Sr), yttrium (Y), and gallium (Ga) or a complex oxide thereof. The method of claim 1,
The source electrode and the drain electrode are interdigitated (interdigitated) structure of the nitrogen oxide gas detection sensor. A nitrogen oxide gas detection method using the nitrogen oxide gas detection sensor according to any one of claims 1 to 5. a) transferring the graphene layer on the insulating film;
b) forming a metal oxide thin film on the transferred graphene layer using atomic layer deposition; and
c) forming a source electrode and a drain electrode spaced apart from each other on the metal oxide thin film, and forming a gate electrode on the opposite surface of the insulating film on which the transferred graphene layer is located;
A method of manufacturing a nitrogen oxide gas detection sensor comprising a.

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