KR20220090142A - Transistor heterojunction hydrogen sensor including metal-nanoparticles dual catalyst layer - Google Patents

Abstract

The present invention relates to a method for manufacturing a hydrogen sensor including a double catalyst layer and to a hydrogen sensor.
In detail, the method of manufacturing a hydrogen sensor of the present invention comprises the steps of forming a GaN layer on a substrate; forming an AlGaN barrier layer on the GaN layer; an ohmic layer forming step of disposing a source and a drain on the AlGaN barrier layer; and forming a sensing material layer, disposing a sensing material layer on the AlGaN barrier layer. Preferably, the step of forming the sensing material layer includes forming a first catalyst layer and forming a second catalyst layer on the first catalyst layer, and the second catalyst layer is formed by a spin coating method.

Description

Transistor heterojunction hydrogen sensor including metal-nanoparticles dual catalyst layer

The present invention relates to a heterojunction transistor hydrogen sensor comprising a metal-nanoparticle double catalyst layer.

Recently, hydrogen has been intensively studied as a clean renewable energy source to replace existing petroleum-based fuels. It is important to detect leaky hydrogen gas because hydrogen gas easily ignites and explodes. That is, there is a need to develop a hydrogen sensor with improved response characteristics capable of quickly and accurately detecting the hydrogen gas concentration.

In particular, since the hydrogen catalytic reaction environment required for sensing of hydrogen gas is performed at a higher temperature than a general environment, the hydrogen sensor must be able to operate stably even at a high temperature. Accordingly, a sensor based on gallium nitride (GaN) with a wide energy band gap is suitable.

Specifically, GaN has a lower intrinsic carrier concentration than silicon (Si) and gallium arsenide (GaAs) due to a wider energy band gap. This low intrinsic carrier concentration allows the semiconductor properties to be maintained at much higher temperatures than conventional semiconductor materials such as Si and GaAs and to have low leakage current properties. Therefore, GaN can work stably in a high-temperature environment where hydrogen-catalyzed reaction occurs than conventional semiconductor materials such as Si and GaAs.

Furthermore, when an AlGaN/GaN heterojunction transistor is used as a hydrogen sensor platform, the polarization-induced two-dimensional electron gas (2DEG) channel formed at the interface between AlGaN and GaN has high electron mobility and is thin. It has the advantage of being able to detect hydrogen with high sensitivity due to the AlGaN barrier layer. Accordingly, hydrogen can be detected with a transistor-type sensor device of an AlGaN/GaN high electron mobility transistor (HEMT) sensor device platform.

In particular, the sensor element detects hydrogen by a change in current caused by a change in surface potential when hydrogen as a target material is attached to the catalyst by disposing a catalyst, which is a sensing material, at the gate position of the transistor. Platinum (Pt), palladium (Pd) and oxide semiconductors (eg, ZnO, SnO2, TiO2) have been studied as suitable catalysts applicable to the hydrogen sensor. It has been reported that the solubility of hydrogen in palladium (Pd) is about three times higher than that in platinum (Pt), although the hydrogen diffusion coefficients are similar for the two materials.

On the other hand, in an oxide semiconductor, gas molecules are absorbed by oxygen vacancies. Because of the reduction mechanism by the oxygen attack point in the hydrogen gas sensing environment, it is difficult for a hydrogen sensor based on an oxide semiconductor to distinguish hydrogen from other gases.

Recently, it has been reported that sensing hydrogen gas with a double catalyst of a metal oxide semiconductor (eg, ZnO, SnO ₂ and TiO ₂ ) and noble metals (Pt, Pd and Au) improves sensor performance. In this regard, some research groups have published research results of improving the detection characteristics of hydrogen (H ₂ ) by adding ZnO nanorods to the Pd catalyst. In addition, research on improving the hydrogen sensing ability by depositing Ni, Pd and Pt on a TiO ₂ nanotube-based hydrogen sensor was also published.

In this way, by introducing the metal-nanoparticle double catalyst layer into the hydrogen sensor, the hydrogen sensing performance can be improved. However, a method for preparing a metal-nanoparticle double catalyst has been prepared by a complicated method at a high cost. Accordingly, in the present invention, a catalyst for a hydrogen sensor capable of preparing a metal-nanoparticle bonding layer in a simple manner is presented.

An object of the present invention is to provide a metal-nanoparticle double catalyst layer as a catalyst for a hydrogen sensor in a simple and inexpensive way.

Another object of the present invention is to provide a double catalyst layer of a hydrogen sensor with improved sensing response when exposed to hydrogen.

Another object of the present invention is to provide a heterojunction transistor hydrogen sensor including a metal-nanoparticle double catalyst layer.

The present invention provides a method for manufacturing a hydrogen sensor including a double catalyst layer and a hydrogen sensor.

In detail, the method of manufacturing a hydrogen sensor of the present invention comprises the steps of forming a GaN layer on a substrate; forming an AlGaN barrier layer on the GaN layer; an ohmic layer forming step of disposing a source and a drain on the AlGaN barrier layer; and forming a sensing material layer, disposing a sensing material layer on the AlGaN barrier layer. Preferably, the step of forming the sensing material layer includes forming a first catalyst layer and forming a second catalyst layer on the first catalyst layer, and the second catalyst layer is formed by a spin coating method.

In an embodiment, the method further includes forming a first insulating film on the AlGaN barrier layer.

In an embodiment, the step of forming the ohmic layer further includes a rapid heat treatment at a predetermined temperature.

In an embodiment, the step of forming a pad includes disposing a metal pad electrode on the ohmic layer after the step of forming the sensing material layer.

In an embodiment, in the forming of the sensing material layer, the sensing material layer is disposed in a region between the source and the drain.

In an embodiment, the first catalyst layer includes Pd.

In an embodiment, the method further includes forming a second insulating layer between the region where the ohmic layer and the sensing material layer are disposed.

In an embodiment, the second catalyst layer is formed after the insulating film forming step, and the second catalyst layer includes ZnO nanoparticles.

In an embodiment, the second catalyst layer is formed by spin coating a predetermined solution in which the ZnO nanoparticles are dispersed.

In an embodiment, the predetermined solution is a cosolvent in which at least two or more solvents are mixed.

In an embodiment, the average diameter of the ZnO nanoparticles is characterized in that the range of 3 to 10 nm.

In an embodiment, after forming the second catalyst layer, a predetermined heat treatment is performed.

The present invention also relates to a hydrogen sensor, comprising: a GaN buffer layer and a GaN channel layer stacked on a substrate; an AlGaN barrier layer disposed on the GaN channel layer; an ohmic layer including a source and a drain disposed on the AlGaN barrier layer; and a sensing material layer disposed on the AlGaN barrier layer. Furthermore, the sensing material layer is characterized in that a first catalyst layer and a second catalyst layer are stacked.

In an embodiment, a first insulating layer is further disposed on the AlGaN barrier layer.

In an embodiment, a metal pad electrode is further disposed on the ohmic layer.

In an embodiment, the sensing material layer is disposed in a region between the source and the drain.

In an embodiment, the first catalyst layer includes Pd.

In an embodiment, the second catalyst layer includes ZnO nanoparticles.

In an embodiment, the average diameter of the ZnO nanoparticles is characterized in that the range of 3 to 10 nm.

In an embodiment, the thickness of the second catalyst layer is characterized in that the range of 10 to 100 nm.

In an embodiment, a second insulating layer is disposed between the region in which the ohmic layer and the sensing material layer are disposed.

According to the method for manufacturing a hydrogen sensor according to the present invention, the response characteristics of the hydrogen sensor can be improved by forming the first catalyst layer and the second catalyst layer in the sensing material layer forming step. Furthermore, the second catalyst layer has the effect of reducing manufacturing cost by spin-coating a predetermined solution in which ZnO nanoparticles are dispersed.

In addition, in the step of forming the second catalyst layer, the second catalyst layer is uniformly formed by forming the second catalyst layer based on a predetermined solution in which ZnO nanoparticles are homogeneously dispersed in a cosolvent in which at least two or more solvents are mixed. can do.

The hydrogen sensor according to the present invention may provide a hydrogen sensor with improved reactivity by improving hydrogen absorption by disposing a second catalyst layer on the first catalyst layer. In detail, the second catalyst layer includes ZnO nanoparticles, and the reaction surface area with hydrogen gas is increased to improve absorption of hydrogen molecules.

1A to 1G are cross-sectional views illustrating a method of manufacturing a hydrogen sensor according to the present invention.
2A is an XRD pattern of ZnO nanoparticles forming the second catalyst layer of the sensing material layer of the present invention, and FIGS. 2B and 2C are microscope images of ZnO nanoparticles forming the second catalyst layer.
3 is an image of a thin film containing ZnO nanoparticles prepared by spin-coating with a solution in which ZnO nanoparticles are dispersed in various solvents and various solutions. 3(h) is a diagram showing the average diameter and film thickness of ZnO nanoparticles according to the effect of the chloroform volume fraction in a chloroform/ethanol cosolvent.
4A to 4E are diagrams comparing current-voltage characteristics for each temperature of a heterojunction transistor hydrogen sensor having a sensing material layer of the present invention and a hydrogen sensor of a comparative example according to whether hydrogen is injected or not, and in FIG. 4f, bias dependence according to temperature Represents the response characteristics.
FIG. 5A is a diagram illustrating repeatability characteristics of a heterojunction transistor hydrogen sensor according to an embodiment of the present invention and a comparative example, and FIG. 5B is an enlarged view of FIG. 5A.

Hereinafter, the embodiments disclosed in the present specification will be described in detail with reference to the accompanying drawings, but the same or similar components are assigned the same reference numerals regardless of reference numerals, and overlapping descriptions thereof will be omitted. In addition, in the description of the embodiments disclosed in the present specification, if it is determined that detailed descriptions of related known technologies may obscure the gist of the embodiments disclosed in the present specification, the detailed description thereof will be omitted. In addition, it should be noted that the accompanying drawings are only for easy understanding of the embodiments disclosed in the present specification, and should not be construed as limiting the technical spirit disclosed herein by the accompanying drawings.

Terms including an ordinal number such as 1st, 2nd, etc. may be used to describe various elements, but the elements are not limited by the terms. The above terms are used only for the purpose of distinguishing one component from another. The singular expression includes the plural expression unless the context clearly dictates otherwise.

In the present application, terms such as “comprises” or “have” are intended to designate that a feature, number, step, operation, component, part, or combination thereof described in the specification exists, but one or more other features It should be understood that this does not preclude the existence or addition of numbers, steps, operations, components, parts, or combinations thereof.

It is also understood that when an element, such as a layer, region, or substrate, is referred to as being “on” another component, it may be directly present on the other element or intervening elements in between. There will be.

The present invention provides a heterojunction transistor hydrogen sensor based on an AlGaN/GaN HEMT sensor. Furthermore, a method for improving the hydrogen sensing performance of the sensor by introducing a metal-nanoparticle double catalyst layer into a hydrogen sensor is disclosed.

1A to 1G are cross-sectional views illustrating a method of manufacturing a hydrogen sensor 1000 according to the present invention.

Referring to Figure 1a, the hydrogen sensor is fabricated from an AlGaN/GaN heterojunction platform. A GaN layer 200 and an AlGaN barrier layer 300 are formed on the substrate 100 . In this case, the GaN layer 200 may include a GaN buffer layer and a GaN channel layer. A first insulating layer 400 may be stacked on the AlGaN barrier layer 300 . The first insulating layer 400 may have a structure in which a SiNx layer 420 is stacked on a GaN cap 410 according to an embodiment.

In addition, a source and a drain may be disposed on the AlGaN barrier layer 300 . Here, the source and the drain are not distinguished and may be defined as the ohmic layer 500 . The ohmic layer 500 may be formed of a metal. The ohmic layer 500 may be disposed after removing a partial region of the first insulating layer 400 and partially etching the AlGaN barrier layer 300 in the thickness direction.

The ohmic layer 500 may be in a form in which one or more metal layers are stacked. In addition, after forming the ohmic layer 500, rapid heat treatment may be performed at a predetermined temperature in order to achieve a low ohmic contact resistance.

Referring to FIG. 1B , the AlGaN barrier layer 300 and part of the GaN layer 200 of the outer shell of the ohmic layer 500 are etched to isolate the hydrogen sensor device.

Referring to FIG. 1C , the first catalyst layer 610 is formed in a region between the source and the drain forming the ohmic layer 500 . The first catalyst layer 610 may be disposed after partial etching in the thickness direction of the first insulating layer 400 and the AlGaN barrier layer 300 . The first catalyst layer 610 includes Pd. Preferably, the first catalyst layer 610 may be in the form of a film deposited with Pd.

Referring to FIG. 1D , a metal pad electrode 510 may be disposed on the ohmic layer 500 . The metal pad electrode 510 may be formed of a metal.

Referring to FIG. 1E , a second insulating layer 700 may be deposited on the entire surface of the hydrogen sensor of FIG. 1D for surface passivation of the hydrogen sensor.

Referring to FIG. 1F , a portion of the second insulating layer 700 may be etched to expose the first catalyst layer 610 and the ohmic layer 500 . Accordingly, the second insulating layer 700 may be disposed between the ohmic layer 500 and the first catalyst layer 610 .

Referring to FIG. 1G , the sensing material layer 600 may be formed by disposing the second catalyst layer 620 on the first catalyst layer 610 . The second catalyst layer 620 may include ZnO nanoparticles. In detail, the second catalyst layer 620 may be formed by spin coating with a predetermined solution in which ZnO nanoparticles are dispersed. In this case, it is appropriate that the average diameter of the ZnO nanoparticles is less than 10 nm. When the average diameter of the ZnO nanoparticles is 10 nm or more, voids between the nanoparticles are large, and the effect of increasing the surface area according to the stacking of the nanoparticles is low.

Furthermore, the predetermined solution in which the ZnO nanoparticles are dispersed may be a co-solvent in which at least two or more solvents are mixed. In addition, the thickness of the second catalyst layer 620 may be in the range of 10 to 100 nm. When the thickness of the second catalyst layer 620 is less than 10 nm, the degree of improvement is weak because the amount of hydrogen absorbed from ZnO is small. ), the distance reached through diffusion is long, so the effect of improvement is not high.

In addition, the hydrogen sensor 1000 of the present invention disclosed by forming the second catalyst layer 620 by spin coating and then further hardening the ZnO nanoparticles by a predetermined heat treatment can be manufactured.

A predetermined solution in which ZnO nanoparticles are dispersed based on the above-described cosolvent makes it possible to form a uniform second catalyst layer 620 . The uniformity of the second catalyst layer 620 including ZnO nanoparticles is greatly affected by the solvent. For example, when a pure solvent such as chloroform, butanol, or ethanol is used, the uniformity of the second catalyst layer 620 including ZnO nanoparticles is deteriorated. An experiment on the spin coating solution for forming the second catalyst layer 620 will be described later.

On the other hand, the conventional method for preparing a metal-nanoparticle double catalyst has been prepared by a high-cost and complicated method, but in the present invention, a metal-nanoparticle double catalyst (Pd) is a simple method of spin-coating a predetermined solution in which ZnO nanoparticles are dispersed. /ZnO NP) has the effect of reducing the manufacturing cost.

In the hydrogen sensor 1000 , a GaN layer 200 and an AlGaN barrier layer 300 are disposed on a substrate 100 , and in detail, the GaN layer 200 may include a GaN buffer layer and a GaN channel layer. A first insulating layer 400 may be further stacked on the AlGaN barrier layer 300 , and the first insulating layer 400 may have a structure in which a SiNx layer 420 is stacked on a GaN cap 410 according to an embodiment.

An ohmic layer 500 is disposed on the AlGaN barrier layer 300 , and the ohmic layer 500 may be divided into a source and a drain. A metal pad electrode 510 formed of a metal may be disposed on the ohmic layer 500 . Further, the AlGaN barrier layer 300 and the GaN layer 200 outside the ohmic layer 500 are partially etched to isolate the hydrogen sensor element.

Meanwhile, the sensing material layer 600 is disposed in a region between the source and drain forming the ohmic layer 500 . The sensing material layer 600 may be formed of a first catalyst layer 610 and a second catalyst layer 620 , and a second catalyst layer 620 is stacked on the first catalyst layer 610 . The hydrogen sensor 1000 of the present invention may be formed by disposing the second insulating layer 700 between the sensing material layer 600 and the ohmic layer 500 .

To describe the sensing material layer 600 , the first catalyst layer 610 may include Pd, and preferably, the first catalyst layer 610 may be in the form of a Pd-deposited film. The thickness of the first catalyst layer 610 may be in the range of 10 to 50 nm. The second catalyst layer 620 may be formed of ZnO nanoparticles, and have an average diameter in the range of 3 to 10 nm. Furthermore, the thickness of the second catalyst layer 620 is formed in the range of 10 to 100 nm.

The sensing material layer 600 including the first catalyst layer 610 and the second catalyst layer 620 is a metal-nanoparticle double catalyst, and the hydrogen sensing performance can be improved by introducing it to the hydrogen sensor. In particular, since the second catalyst layer 620 is formed of nanoparticles, a reaction surface area with hydrogen, which is a sensing gas, is increased. Accordingly, the present invention can provide the hydrogen sensor 1000 having improved reactivity by improving the absorption of hydrogen molecules. Furthermore, the reactivity improved by the second catalyst layer 620 can improve the performance of the hydrogen sensor 1000 by changing the surface potential of the hydrogen sensor 1000 element to amplify the channel current change at the AlGaN/GaN interface. there is

Hereinafter, embodiments and experimental examples of the present invention will be described.

2A is an XRD pattern of ZnO nanoparticles forming the second catalyst layer of the sensing material layer of the present invention, and FIGS. 2B and 2C are microscope images of ZnO nanoparticles forming the second catalyst layer. As described above, the hydrogen sensor of the present invention forms the second catalyst layer with a predetermined solution containing ZnO nanoparticles. Accordingly, an embodiment of synthesizing ZnO nanoparticles will be described.

Synthesis of ZnO nanoparticles

ZnO nanoparticles are prepared by hydrolyzing a precursor material containing Zn, and impurities in the reaction can be removed by centrifugation. In order to perform spin coating with the prepared ZnO nanoparticles, they can be dispersed in a predetermined solvent using an ultrasonicator.

As an example, ZnO nanoparticles were synthesized by hydrolyzing Zn(CH ₃ COO) ₂ ·2H ₂ O(Sigma-Aldrich) with KOH (Samchun, 95%) in methanol (Sigma-Aldrich, 99.9%). Specifically, a Zn(CH ₃ COO) ₂ ·2H ₂ O solution (13.4 mM in 125 ml methanol) and a KOH solution (23 mM in 65 ml methanol) were stirred, and the reaction time was 2 hours.

ZnO nanoparticles were formed by the reaction of the mixed solution, and the ZnO nanoparticles were separated by centrifugation (4000 rpm, for 20 min, Lagogene, 124BR). Centrifugation, decanting the supernatant, and dispersing the ZnO nanoparticles in methanol were repeated three or more times to remove any impurities present on the surface of the ZnO nanoparticles.

Referring to Fig. 2a, the crystal structure of ZnO nanoparticles was characterized by X-ray diffraction (XRD, D/MAX-2200, Rigaku, X-ray beam source of Cu Kα). The crystal structure of the synthesized ZnO nanoparticles (PDF # 36-1451) was characterized by powder XRD. Peaks at 31.8°, 34.5°, 47.5°, 56.6°, 62.9° and 68° corresponding to (100), (002), (101), (102), (110), (103) and (100) It was confirmed that crystalline ZnO showing

2b and 2c, the morphology and crystal structure of ZnO NPs were characterized by high-resolution transmission electron microscopy (HRTEM, Tecnai G2F30). ZnO synthesized in the shape of ZnO nanoparticles observed by HRTEM showed lattice spacing of 0.26 nm and 0.25 nm, indicating that the crystals correspond to the (002) and (101) planes, respectively. In addition, the average diameter of ZnO nanoparticles is in the range of 3 to 10 nm.

On the other hand, in order to prepare the second catalyst layer uniformly formed of ZnO nanoparticles, it is essential to uniformly disperse the ZnO nanoparticles in a solution phase. Accordingly, the dispersion degree of ZnO nanoparticles in various solvents was confirmed, and an appropriate solvent was selected.

Different solvents (chloroform, butanol, ethanol and co-existence of chloroform/ethanol with various mixing ratios) were tested to achieve a uniform ZnO nanoparticle coating. This is shown in FIG. 3 .

Figure 3 (a) is a dispersion of various ZnO nanoparticles, the higher the transparency, the better the dispersed solution. The solvents are explained from left to right: butanol, ethanol, ethanol/chloroform (3:1), ethanol/chloroform (2:1), ethanol/chloroform (1:1), ethanol/chloroform (1:2), ethanol/chloroform ( 1:3), chloroform. At this time, the ratio of the mixed solvent is mixed in a volume ratio.

3 (b) to (g) are images of thin films prepared by spin-coating a dispersion of ZnO nanoparticles using each solvent. (b) chloroform; (c) butanol; (d) chloroform/ethanol (1:3, v:v); (e) chloroform/ethanol (1:1, v:v); and (g) ZnO nanoparticles SEM image of a thin film prepared based on a solvent with chloroform/ethanol (3:1, v:v). (g) ZnO nanoparticles as a solvent with chloroform/ethanol (3:1, v:v) formed the most uniform thin film without aggregation.

3 (h) is a diagram showing the average diameter and film thickness of ZnO nanoparticles according to the effect of the chloroform volume fraction in the chloroform/ethanol cosolvent. Here, the average diameter and film thickness of ZnO nanoparticles showed a minimum in 75% of chloroform, and from this, dispersion of ZnO nanoparticles in a cosolvent with chloroform/ethanol (3:1, v:v) and the thin film were the most homogeneous. was confirmed. Therefore, in order to form the second catalyst layer, the spin coating solution containing ZnO nanoparticles was optimized to be 3:1 per volume of chloroform/ethanol.

In Examples and Experimental Examples of the present invention, a dispersion of ZnO nanoparticles was prepared and used as a spin coating solution as follows based on the description of FIG. 3 described above.

Preparation of Dispersion of ZnO Nanoparticles

The prepared ZnO nanoparticles were finally dispersed in chloroform/ethanol (3:1, v:v) for 2 hours using an ultrasonicator. Finally, a solution of ZnO nanoparticles having a concentration of 15 mg/ml was obtained.

Preparation of a hydrogen sensor including a double catalyst layer

Example

The hydrogen sensor was fabricated on an AlGaN/GaN heterojunction platform. An AlGaN/GaN heterojunction epitaxial layer was grown on a 1 mm thick Si(111) substrate. A 4.2 μm GaN buffer layer, a 420 nm GaN channel layer, a 23 nm Al _0.24 Ga _0.76 N barrier layer, a 3.5 nm GaN cap layer, and a 10 nm in-situ SiNx passivation layer are sequentially stacked on the substrate. At this time, the concentration of 2-DEG formed in AlGaN/GaN was 9 × 10 ¹² cm ^-2 and the mobility was 1,470 cm ² /Vs.

After solvent cleaning the device in which the GaN buffer layer or the in-situ SiNx passivation layer is prepared on the substrate, the region where the ohmic layer is to be formed is defined using photolithography, and the in-situ SiNx passivation is performed using a CF ₄ based inductively coupled plasma etching method. The layer and the GaN cap were etched, and the lower AlGaN barrier layer was etched to the middle by a Cl ₂ /BCl ₂ based reactive ion etching method.

Then, after forming an ohmic layer by depositing Ti/Al/Ni/Au (= 200/1200/250/500 Å) metal, rapid heat treatment is performed at 800° C. for 30 seconds in an N ₂ atmosphere to improve contact resistance. did

The region where the sensing material layer was formed was defined as the region between the ohmic layers, and the same etching was performed to form the ohmic layer. Specifically, the thickness of the AlGaN barrier layer under the sensing material layer is 10 nm. The sensing material layer was defined to have an area of 24 × 100 μm ² , and a Pd film as a first catalyst layer was deposited to a thickness of 30 nm in this area.

A Ti/Au (= 20/250 nm) metal layer was deposited on the previously formed ohmic layer to form a pad electrode, and for surface passivation, a 100 nm SiNx film was deposited by PECVD at a temperature of 190°C to form a second insulating layer. did The second insulating layer deposited on the region where the ohmic layer and the sensing material layer were formed was removed by a CF ₄ based inductively coupled plasma etching method.

A solution in which ZnO nanoparticles were dispersed in a cosolvent of chloroform/ethanol (3:1, v:v) was spin-coated at 3000 rpm for 30 seconds to form a second catalyst layer with a thickness of 20 nm. Additionally, heat treatment was performed at 120° C. for 1 hour to harden the second catalyst layer.

comparative example

Meanwhile, in order to compare the performance of the hydrogen sensor including the double catalyst layer of the present invention, the hydrogen sensor of the comparative example was also prepared in the same manner as in the previous example, but a hydrogen sensor having a single Pd catalyst excluding the second catalyst layer was prepared.

Experimental Example 1: Sensor Characteristics Evaluation

Sensor characterization was performed at various temperatures from 25 °C to 250 °C in a gas chamber, and 4% hydrogen gas was used for the reaction test. 4A to 4E show current-voltage characteristics for each temperature of a heterojunction transistor hydrogen sensor having a sensing material layer of the present invention and a hydrogen sensor of a comparative example according to the presence or absence of hydrogen injection.

When the hydrogen sensor was exposed to hydrogen, the output current level increased. The output current level is associated with a decrease in the surface potential of the material sensing layer due to the Pd-H chemical reaction. As the temperature increases, both the sensing current and the quiescent current level decrease, which is associated with a decrease in electron mobility due to scattering with increasing temperature.

Looking at the hydrogen sensors of Examples and Comparative Examples, it was observed that the standby current level slightly changed at all temperatures. However, it was observed that the increase in the current level of the embodiment was larger as a result of the hydrogen sensor having a double catalyst layer, which is the embodiment, when exposed to hydrogen, the sensing response to hydrogen was further improved.

Reactivity is defined as follows.

Here, I _gas is an output current level measured by hydrogen injection, and I _air is a standby current level in a state in which hydrogen is not injected. 4F shows the bias-dependent response characteristic according to temperature. Both the hydrogen sensors of Examples and Comparative Examples increased the reaction rate as the temperature increased. The maximum reactivity was observed at 200 °C. At 250°C, the reactivity slightly decreased, because the electron mobility had a more dominant influence than the effect of lowering the activation of the reaction. That is, the reactivity and electron mobility according to the temperature have a conflicting relationship with each other.

Referring to FIG. 4f , the hydrogen sensor including the double catalyst layer of the example exhibited significantly higher response characteristics than the Pd single catalyst of the comparative example regardless of the bias voltage or temperature. Hereinafter, the mechanism of the hydrogen sensor will be described.

When the double catalyst layer (ZnO-NPs/Pd) of the present invention is exposed to hydrogen gas, hydrogen molecules are ionized and captured at the oxygen vacancies of the second catalyst layer (ZnO nanoparticles). The second catalyst layer, which is formed of ZnO nanoparticles and has an increased surface area, can absorb hydrogen gas more effectively.

Then, the hydrogen ions captured in the second catalyst layer (ZnO nanoparticles) are dissolved in the lower Pd layer. This process is made easier than when the hydrogen molecules of the comparative example are directly dissolved in Pd. In the case of the Pd single catalyst of the comparative example, some hydrogen ions are not completely dissolved in Pd and are discharged as hydrogen gas again. However, the sensing material layer formed of the double catalyst layer of the embodiment increases the amount of hydrogen dissolved in the Pd layer by repeating the ionization process by reabsorbing hydrogen gas.

Thereafter, the chemical reaction of hydrogen diffusion in the first catalyst layer (Pd layer) of the embodiment induces a dipole effect and changes the surface potential of the AlGaN/GaN heterojunction. As the hydrogen absorption increases, the surface potential decreases, which increases the 2DEG concentration of AlGaN/GaN, resulting in an increase in the current level. The reaction of the hydrogen sensor is reversible, and the initial state can be restored when the hydrogen supply is terminated.

Experimental Example 2: Repeatability Measurement

For the repeatability test of hydrogen sensitivity, the temperature was set at 200 °C. In detail, the process of injecting 4% hydrogen gas for 10 seconds and holding for 50 seconds was repeated. The bias voltage was set to 3V.

5A is a diagram illustrating repeatability characteristics of a heterojunction transistor hydrogen sensor according to an embodiment of the present invention and a comparative example, and FIG. 5B is an enlarged view of FIG. 5A.

As shown in FIGS. 5A and 5B , the hydrogen sensors of the Example and Comparative Example recovered to the initial current level when hydrogen injection was stopped, and exhibited stable and excellent repeatability characteristics. Among the repeatability characteristics of the hydrogen sensor, the response time was defined as the time for the saturation current to reach the 90% level, and the recovery time was defined as the time for the saturation current to return to the 10% level.

The hydrogen sensor of Comparative Example had both response and recovery times of 1 second, but the hydrogen sensor of Example had response and recovery times of 2 seconds and 1.5 seconds, respectively. This is due to the trapping and detrapping processes at oxygen vacancys present in the ZnO nanoparticles of the hydrogen sensor of the embodiment having a double catalyst layer.

As described above, although the response and recovery time of the hydrogen sensor of the embodiment is longer than that of the comparative example, this is not at a level that predominantly affects the detection of hydrogen, and the embodiment also responds faster than the conventional sensor, similar to the comparative example. have speed

That is, the hydrogen reaction rate of the embodiment is not a major disadvantage when considering the application environment of the hydrogen sensor, but rather the effect of increasing the surface area with the second catalyst layer and improving the hydrogen detection performance is an improvement over the comparative example or the conventional hydrogen sensor . Therefore, the hydrogen sensor including the double catalyst layer of the present invention is a low-cost process of forming the second catalyst layer by spin coating, and has the advantage of improved performance.

The hydrogen sensor described above is not limited to the configuration and method of the above-described embodiments, but should be considered as an example. The above embodiments may be configured by selectively combining all or part of each embodiment so that various modifications can be made. The scope of the present invention should be determined by a reasonable interpretation of the appended claims, and all modifications within the equivalent scope of the present invention are included in the scope of the present invention.

This study was supported by Korea Electric Power Corporation's 2018 Energy Hub University Cluster Project (task number: R18XA02).

Claims (21)

forming a GaN layer on the substrate;
forming an AlGaN barrier layer on the GaN layer;
an ohmic layer forming step of disposing a source and a drain on the AlGaN barrier layer; and
a sensing material layer forming step of disposing a sensing material layer on the AlGaN barrier layer;
The sensing material layer forming step includes forming a first catalyst layer and
A method of manufacturing a hydrogen sensor including a double catalyst layer, characterized in that it comprises the step of forming a second catalyst layer on the first catalyst layer. According to claim 1,
The method of manufacturing a hydrogen sensor further comprising the step of forming a first insulating film on the AlGaN barrier layer. The method of claim 1,
Method of manufacturing a hydrogen sensor further comprising a rapid heat treatment at a predetermined temperature in the ohmic layer forming step. According to claim 1,
A method of manufacturing a hydrogen sensor including a pad forming step of disposing a metal pad electrode on the ohmic layer after the sensing material layer forming step According to claim 1,
In the sensing material layer forming step, the sensing material layer is
A method of manufacturing a hydrogen sensor disposed in a region between the source and the drain. According to claim 1,
The first catalyst layer is a method of manufacturing a hydrogen sensor comprising Pd. According to claim 1,
The method of manufacturing a small number sensor further comprising the step of forming a second insulating film between the region where the ohmic layer and the sensing material layer are disposed. 8. The method of claim 7,
forming the second catalyst layer after the insulating film forming step;
The second catalyst layer is a method of manufacturing a hydrogen sensor comprising ZnO nanoparticles. 9. The method of claim 8,
The second catalyst layer is a method of manufacturing a hydrogen sensor in which a predetermined solution in which the ZnO nanoparticles are dispersed is formed by spin coating. 10. The method of claim 9,
The predetermined solution is a method of manufacturing a hydrogen sensor in which at least two or more solvents are mixed. 10. The method of claim 9,
The average diameter of the ZnO nanoparticles is a method of manufacturing a hydrogen sensor in the range of 3 to 10 nm. 9. The method of claim 8,
A method of manufacturing a hydrogen sensor for performing a predetermined heat treatment after forming the second catalyst layer. a GaN buffer layer and a GaN channel layer stacked on a substrate;
an AlGaN barrier layer disposed on the GaN channel layer;
an ohmic layer including a source and a drain disposed on the AlGaN barrier layer; and
a sensing material layer disposed on the AlGaN barrier layer;
The sensing material layer is a hydrogen sensor comprising a double catalyst layer, characterized in that it comprises a first catalyst layer and a second catalyst layer is laminated. 14. The method of claim 13,
A hydrogen sensor further comprising a first insulating layer disposed on the AlGaN barrier layer. 14. The method of claim 13,
A hydrogen sensor in which a metal pad electrode is further disposed on the ohmic layer. 14. The method of claim 13,
The sensing material layer is disposed in a region between the source and the drain. 14. The method of claim 13,
The first catalyst layer is a hydrogen sensor comprising Pd. 14. The method of claim 13,
The second catalyst layer is a hydrogen sensor comprising ZnO nanoparticles. 19. The method of claim 18,
The average diameter of the ZnO nanoparticles is in the range of 3 to 10 nm hydrogen sensor. 19. The method of claim 18,
The thickness of the second catalyst layer is in the range of 10 to 100 nm hydrogen sensor. 14. The method of claim 13,
A hydrogen sensor in which a second insulating layer is disposed between the region in which the ohmic layer and the sensing material layer are disposed.

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