Gas sensor and method for preparing the same

Abstract

The present application discloses a gas sensor and a preparation method thereof, belonging to the field of semiconductor technology. The gas sensor includes a substrate, a channel layer and a barrier layer, the source and the drain are both arranged on the side of the barrier layer away from the substrate, the first electrode and the second electrode are electrically connected to the source and the drain respectively, the gate is arranged between the source and the drain, and the third electrode and the fourth electrode are electrically connected to the gate respectively. The material of the gate includes a sensitive metal material, which can react with the detected gas, thereby affecting the concentration of the two-dimensional electron gas in the channel layer below the gate, so that the current between the source and the drain changes, thereby realizing gas detection. In addition, the gate voltage can be adjusted by the third electrode and the fourth electrode to reduce the on-current of the transistor, so that the current change caused by the reaction of the gas with the gate is more obvious, and the sensitivity of the device is improved. In addition, the gate can also be equivalent to a heating resistor to increase the reaction rate of the detected gas with the sensitive metal material and reduce power consumption.

Description

Technical Field

[0001] The present application belongs to the field of semiconductor technology, and in particular relates to a gas sensor and a method for preparing the same. Background Art

[0002] Gas sensors can be divided into electrochemical, semiconductor, catalytic combustion, and thermal conductivity types according to their working principles. Semiconductor devices are small in structure, easy to integrate, and low in cost, and have a large application market. However, current semiconductor gas sensors still have problems such as low sensitivity and long response time. In addition, semiconductor gas sensors usually require multi-layer wiring or heaters around the sensor to increase the temperature, resulting in high costs and high power consumption.

[0003] Based on this, how to improve the sensitivity of gas sensors and reduce power consumption has become a key research direction in this field. Summary of the invention

[0004] The present application provides a gas sensor and a preparation method thereof, aiming to improve the sensitivity and reduce the power consumption.

[0005] In a first aspect, the present application provides a gas sensor comprising at least one sensing unit. The sensing unit comprises a substrate, a channel layer and a barrier layer, wherein the channel layer is arranged on the substrate, and the barrier layer is arranged on the side of the channel layer away from the substrate. The sensing unit also comprises a source and a drain, wherein the source and the drain are both arranged on the side of the barrier layer away from the substrate. The sensing unit also comprises a first electrode and a second electrode, wherein the first electrode is arranged on the side of the source away from the substrate and is electrically connected to the source, and the second electrode is arranged on the side of the drain away from the substrate and is electrically connected to the drain. The sensing unit also comprises a gate, a third electrode and a fourth electrode, wherein the gate, the third electrode and the fourth electrode are all arranged on the side of the barrier layer away from the substrate, wherein the material of the gate comprises a sensitive metal material, the gate is arranged between the source and the drain, and the third electrode and the fourth electrode are electrically connected to the gate, respectively.

[0006] In some embodiments, the orthographic projections of the source and the drain on the substrate are both in the shape of interdigitated fingers, the source and the drain are cross-arranged, a groove is formed between the source and the drain, the gate is arranged in the groove, and extends along the groove.

[0007] In some embodiments, the orthographic projection of the trench on the substrate is in an S-shape, and the orthographic projection of the gate on the substrate is also in an S-shape.

[0008] In some embodiments, the orthographic projections of the third electrode and the fourth electrode on the substrate are both linear, and the linear shape includes at least two connected line segments, and the extension directions of the two line segments intersect.

[0009] In some embodiments, the third electrode and the fourth electrode are integrally provided, and the gate is located on a side of the third electrode and the fourth electrode away from the substrate.

[0010] In some embodiments, the material of the gate includes at least one of platinum, palladium, a platinum alloy, a palladium alloy, or zinc oxide.

[0011] In some embodiments, the orthographic projections of the first electrode and the second electrode on the substrate are both linear, and the linear shape includes at least two connected line segments, and the extension directions of the two line segments intersect.

[0012] In some embodiments, the material of the channel layer includes at least one of gallium nitride, gallium arsenide, or indium gallium arsenide, and the material of the barrier layer includes at least one of indium gallium nitride, aluminum gallium nitride, indium phosphide, aluminum gallium arsenide, or indium aluminum arsenide.

[0013] In some embodiments, the substrate includes a cavity, and the orthographic projection of the sensing unit on the substrate is located within the region where the cavity is located.

[0014] In a second aspect, the present application further provides a method for preparing a gas sensor, comprising the following steps S10 to S50:

[0015] Step S10: forming a channel layer on the substrate.

[0016] Step S20: forming a barrier layer on a side of the channel layer away from the substrate.

[0017] Step S30: forming a source and a drain on a side of the barrier layer away from the substrate.

[0018] Step S40: forming a first electrode and a second electrode, wherein the first electrode is located at a side of the source away from the substrate and electrically connected to the source, and the second electrode is located at a side of the drain away from the substrate and electrically connected to the drain.

[0019] Step S50: forming a gate, a third electrode and a fourth electrode, wherein the gate, the third electrode and the fourth electrode are all arranged on the side of the barrier layer away from the substrate, the material of the gate comprises a sensitive metal material, the gate is located between the source and the drain, and the third electrode and the fourth electrode are electrically connected to the gate respectively.

[0020] In an embodiment of the present application, the gas sensor includes at least one sensing unit. The sensing unit includes a stacked substrate, a channel layer and a barrier layer, and the barrier layer is arranged on the side of the channel layer away from the substrate. A two-dimensional electron gas is formed in the heterostructure formed by the channel layer and the barrier layer. The sensing unit also includes a source, a drain, a gate, a first electrode, a second electrode, a third electrode and a fourth electrode, and the source, the drain, the gate, the third electrode and the fourth electrode are all arranged on the side of the barrier layer away from the substrate, the gate is arranged between the source and the drain, the third electrode and the fourth electrode are electrically connected to the gate respectively, the first electrode is arranged on the side of the source away from the substrate, and is electrically connected to the source, and the second electrode is arranged on the side of the drain away from the substrate, and is electrically connected to the drain.

[0021] The material of the gate includes a sensitive metal material, which can react with the detected gas and thereby affect the concentration of the two-dimensional electron gas in the channel layer below the gate. When a voltage is applied to the gas sensor through the first electrode and the second electrode, the concentration of the two-dimensional electron gas will affect the current between the source and the drain, thereby reflecting the external gas conditions.

[0022] In addition, the third electrode and the fourth electrode are electrically connected to the gate, respectively. The third electrode and the fourth electrode can be connected to a suitable voltage source. Under the voltage division effect of the gate resistor, the third electrode resistor and the fourth electrode resistor, the voltage at the gate can be adjusted, thereby reducing the on-current of the transistor. When the gas reacts with the sensitive metal material to cause the current change between the source and the drain to be the same, the smaller the on-current of the transistor, the greater the current change percentage, that is, the more obvious the current change. Based on this, the sensitivity of the gas sensor can be improved.

[0023] In addition, the gate can also be equivalent to a heating resistor. When the third electrode and the fourth electrode are connected to a voltage source, the reaction rate of the detected gas and the sensitive metal material can be improved by heating the gate. The gate serving as a heater is beneficial to reducing costs, saving wiring design, and reducing power consumption.

[0024] Additional aspects and advantages of the present application will be given in part in the description below, and in part will become apparent from the description below, or will be learned through the practice of the present application. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] The above and / or additional aspects and advantages of the present application will become apparent and easily understood from the description of the embodiments in conjunction with the following drawings, in which:

[0026] Figure 1 A top view of a gas sensor provided in an embodiment of the present application;

[0027] Figure 2 for Figure 1 A cross-sectional view of the gas sensor along the section line AA';

[0028] Figure 3 for Figure 1 Equivalent circuit diagram of the gas sensor;

[0029] Figure 4 A flow chart of a method for preparing a gas sensor provided in an embodiment of the present application;

[0030] Figure 5~Figure 12 A diagram of the steps for preparing a gas sensor provided in an embodiment of the present application. DETAILED DESCRIPTION

[0031] The following will be combined with the accompanying drawings to clearly and completely describe the technical solutions in some embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments provided by the present application, all other embodiments obtained by ordinary technicians in this field belong to the scope of protection of the present application.

[0032] Unless the context requires otherwise, throughout the specification and claims, the term "comprising" is to be construed in an open, inclusive sense, ie, meaning "including, but not limited to."

[0033] In the following, the terms "first" and "second" are used for descriptive purposes only and are not to be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of the features. In the description of the embodiments of the present application, unless otherwise specified, "plurality" means two or more.

[0034] When describing some embodiments, the term "connection" and its derivative expressions may be used. The term "connection" should be understood in a broad sense. For example, "connection" can be a fixed connection, a detachable connection, or an integral connection; it can be directly connected or indirectly connected through an intermediate medium. For example, when describing some embodiments, the term "connection" may be used to indicate that two or more components are in direct physical or electrical contact with each other.

[0035] Additionally, the use of “based on” is meant to be open and inclusive, as a process, step, calculation, or other action “based on” one or more stated conditions or values ​​may, in practice, be based on additional conditions or values ​​beyond those stated.

[0036] It will be understood that when a layer or an element is referred to as being on another layer or substrate, it can be directly on the other layer or substrate, or intervening layers may be present between the layer or element and the other layer or substrate.

[0037] Exemplary embodiments are described herein with reference to cross-sectional views that are idealized exemplary drawings. In the drawings, the thickness of layers and the area of ​​regions are exaggerated for clarity. Therefore, variations in shape relative to the drawings due to, for example, manufacturing techniques and / or tolerances are conceivable. Therefore, the exemplary embodiments should not be interpreted as being limited to the shapes of the regions shown herein, but include deviations in shape due to, for example, manufacturing. Therefore, the regions shown in the drawings are schematic in nature, and their shapes are not intended to illustrate the actual shape of regions of the device, and are not intended to limit the scope of the exemplary embodiments.

[0038] Examples of the embodiments are shown in the accompanying drawings, wherein the same or similar reference numerals throughout represent the same or similar elements or elements having the same or similar functions. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain the present application, and cannot be understood as limiting the present application.

[0039] At present, semiconductor gas sensors have a wide range of applications, but they still have problems such as low sensitivity and long response time. In addition, semiconductor gas sensors usually require multi-layer wiring or heaters to be placed around the sensor to increase the temperature, resulting in high costs and high power consumption.

[0040] To solve at least one of the above problems, in a first aspect, an embodiment of the present application provides a gas sensor, such as Figure 1~Figure 3 As shown, Figure 1 A top view of a gas sensor provided in an embodiment of the present application, Figure 2 for Figure 1 The cross-sectional view of the gas sensor along the section line AA', Figure 3 for Figure 1 Equivalent circuit diagram of the gas sensor.

[0041] The gas sensor 10 includes at least one sensing unit 100. The sensing unit 100 includes a substrate 11, a channel layer 12 and a barrier layer 13, wherein the channel layer 12 is disposed on the substrate 11, and the barrier layer 13 is disposed on a side of the channel layer 12 away from the substrate 11. The sensing unit 100 also includes a source S and a drain D, wherein the source S and the drain D are both disposed on a side of the barrier layer 13 away from the substrate 11. The sensing unit 100 also includes a first electrode 21 and a second electrode 22, wherein the first electrode 21 is disposed on a side of the source S away from the substrate 11 and is electrically connected to the source S, and the second electrode 22 is disposed on a side of the drain D away from the substrate 11 and is electrically connected to the drain D. The sensing unit 100 also includes a gate G, a third electrode 23 and a fourth electrode 24. The gate G, the third electrode 23 and the fourth electrode 24 are all arranged on the side of the barrier layer 13 away from the substrate 11. The material of the gate G includes a sensitive metal material. The gate G is arranged between the source S and the drain D. The third electrode 23 and the fourth electrode 24 are electrically connected to the gate G respectively.

[0042] In the embodiment of the present application, a two-dimensional electron gas is formed in the heterostructure formed by the channel layer 12 and the barrier layer 13, and the material of the gate G includes a sensitive metal material, which can react with the gas to be detected, thereby affecting the concentration of the two-dimensional electron gas in the channel layer 12 below the gate G. When a voltage is applied to the gas sensor 10 through the first electrode 21 and the second electrode 22, the concentration of the two-dimensional electron gas in the channel layer 12 will affect the current between the source S and the drain D, thereby reflecting the external gas situation. Depending on the type of gas to be detected, such as hydrogen, carbon monoxide, etc., the type of sensitive metal material is also different.

[0043] In addition, the third electrode 23 and the fourth electrode 24 are electrically connected to the gate G, respectively. Figure 3 As shown, the third electrode 23 and the fourth electrode 24 can be connected to a suitable voltage source V0, and the gate resistor R g Under the voltage division effect of the third electrode resistor R1 and the fourth electrode resistor R2, the voltage at the gate G can be adjusted, that is, V G =V0*[(R1+R g1 ) / R], where R=R1+R g1 +R g2+ R2, R g= R g1 +R g2 Then, the first electrode 21 and the second electrode 22 are connected to a suitable stable excitation source, that is, to maintain V D -V S Finally, adjust V G -V S The size of can make the gate G have a suitable voltage. D -V S” represents the potential difference between the drain D and the source S, “V G -V S ” represents the potential difference between the gate G and the source S.

[0044] Take the midpoint of the gate G as an example. At this time, R g1 =R g2 , when the third electrode resistor R1 and the fourth electrode resistor R2 are equal in size, the voltage of the gate G is V G =V0 / 2. Usually, the voltage source V0 has a value range of -10V~0V. Correspondingly, the voltage of the gate G has a value range of -5V~0V, which can reduce the on-current of the transistor to a suitable value range.

[0045] The change in current between the source and drain caused by the reaction between the gas and the sensitive metal material is denoted as I0, and the on-current of the transistor is denoted as I. The smaller the on-current I is, the greater the current change percentage I0 / I is, that is, the more obvious the current change is, the higher the sensitivity of the gas sensor 10 is.

[0046] In other words, by adjusting the voltage of the gate G through the third electrode 23 and the fourth electrode 24 , the on-current of the transistor can be reduced, thereby improving the sensitivity of the gas sensor 10 .

[0047] In addition, the gate resistor R g It can also be equivalent to a heating resistor. When the third electrode 23 and the fourth electrode 24 are connected to the voltage source V0, the gate G can act as a heater to increase the reaction rate of the detected gas and the sensitive metal material. That is, in the embodiment of the present application, the gate G can also act as a heater, and there is no need to set up a separate heater, which is beneficial to reducing costs, saving wiring design, and reducing power consumption.

[0048] In some embodiments, Figure 1 and Figure 2 As shown, the orthographic projections of the source S and the drain D on the substrate 11 are both in the shape of interdigitated fingers. The source S and the drain D are arranged crosswise, a trench T1 is formed between the source S and the drain D, and the gate G is arranged in the trench T1 and extends along the trench T1.

[0049] For example, in some embodiments, Figure 1 and Figure 2 As shown, the orthographic projection shape of the trench T1 on the substrate 11 is S-shaped, and the orthographic projection shape of the gate G on the substrate 11 is also S-shaped.

[0050] The above-mentioned morphology structure is conducive to increasing the width of the gate G and reducing the on-resistance. In addition, it can also increase the area of ​​the gate G, which is conducive to the reaction between the detected gas and the sensitive metal material, thereby improving the sensitivity of the gas sensor 10.

[0051] In some embodiments, Figure 1 and Figure 2 As shown, the third electrode 23 and the fourth electrode 24 are integrally provided, and the gate G is located on a side of the third electrode 23 and the fourth electrode 24 away from the substrate 11 .

[0052] Based on this, the contact area between the gate G and the detected gas can be maximized, which can not only ensure the reliability of the electrical connection between the third electrode 23 and the fourth electrode 24 and the gate G respectively, but also make full use of the gate G, which is beneficial to improving the sensitivity of the gas sensor 10.

[0053] In some embodiments, the material of the gate G includes at least one of platinum, palladium, platinum alloy, palladium alloy or zinc oxide. The above materials can react with hydrogen to affect the concentration of the two-dimensional electron gas in the channel layer 12, and the detection of hydrogen gas can be achieved by calibrating the change in the current between the first electrode 21 and the second electrode 22.

[0054] In some embodiments, the material of the channel layer 12 includes at least one of gallium nitride, gallium arsenide, or indium gallium arsenide, and the material of the barrier layer 13 includes at least one of indium gallium nitride, aluminum gallium nitride, indium phosphide, aluminum gallium arsenide, or indium aluminum arsenide.

[0055] The above materials have high electron mobility and good semiconductor properties, and can improve the sensitivity of the gas sensor 10 compared with traditional semiconductor gas sensors.

[0056] In some embodiments, Figure 1 As shown, the substrate 11 includes a cavity K0, and the orthographic projection of the sensor unit 100 on the substrate 11 is located within the region where the cavity K0 is located.

[0057] The setting of the cavity K0 enables the sensing unit 100 to form a suspended island structure, thereby reducing the rate of heat loss through solid conduction, which is conducive to keeping the temperature rise caused by the heating of the gate G in the suspended island structure as much as possible, and improving the reaction rate between the sensitive metal material and the detected gas. Based on this, full utilization of heat can be achieved, which is conducive to reducing power consumption.

[0058] In some embodiments, Figure 1 As shown, the orthographic projections of the third electrode 23 and the fourth electrode 24 on the substrate 11 are both linear, and the linear shape includes at least two connected line segments, and the extension directions of the two line segments intersect.

[0059] Exemplarily, in combination with the setting of the cavity K0, it can be understood that the sensing unit 100 forming the suspended island structure is connected to the main body through the cantilever beam, and the cantilever beam plays a supporting role for the suspended island structure. In addition, the third electrode 23 and the fourth electrode 24 are respectively designed for routing on the surface of the cantilever beam away from the substrate 11, and pads are respectively formed on the main body.

[0060] The positive projections of the third electrode 23 and the fourth electrode 24 on the substrate 11 are both linear, and the linear shape includes at least two connected line segments, and the extension directions of the two line segments intersect. It can be understood that the third electrode 23 and the fourth electrode 24 and their corresponding cantilever beams have a curved design. This curved design is conducive to stress release, which can avoid damage caused by stress in the process preparation process and improve the yield rate. The curved design is also conducive to resisting external resonance or impact and improving reliability.

[0061] In some embodiments, Figure 1 As shown, the orthographic projections of the first electrode 21 and the second electrode 22 on the substrate 11 are both linear, and the linear shape includes at least two connected line segments, and the extension directions of the two line segments intersect.

[0062] Similar to the above principle, the curved design of the first electrode 21 and the second electrode 22 and their corresponding cantilever beams is conducive to stress release, improving the yield rate, and resisting external resonance or impact, thereby improving reliability.

[0063] In a second aspect, the present application also provides a method for preparing a gas sensor, such as Figure 4 As shown, Figure 4 A flow chart of a method for preparing a gas sensor provided in an embodiment of the present application, Figure 5~Figure 12 A diagram of the steps for preparing a gas sensor provided in an embodiment of the present application.

[0064] The preparation method comprises the following steps S10 to S50:

[0065] Step S10: Figure 5 As shown, a channel layer 12 is formed on a substrate 11 .

[0066] For example, in order to reduce lattice mismatch and dislocation density, a buffer layer 14 is provided between the substrate 11 and the channel layer 12 in some embodiments. The buffer layer 14 can improve the performance and reliability of the device.

[0067] Exemplarily, the material of the buffer layer 14 includes AlN, and the material of the channel layer 12 includes GaN.

[0068] Step S20: Figure 6 As shown, a barrier layer 13 is formed on a side of the channel layer 12 away from the substrate 11 .

[0069] Exemplarily, the material of the barrier layer 13 includes AlGaN. In some embodiments, a whole layer of AlGaN may be formed first, and then etched using an inductively coupled plasma etching process to form a desired size and morphology.

[0070] Step S30: Figure 7 As shown, a source S and a drain D are formed on a side of the barrier layer 13 away from the substrate 11 .

[0071] For example, in some embodiments, the orthographic projections of the source S and the drain D on the substrate 11 are both in the shape of interdigitated fingers, and the source S and the drain D are arranged crosswise.

[0072] Then, for protection and isolation, after forming the source S and drain D, as shown in Figure 8 As shown, a first passivation layer 15 is formed, and the first passivation layer 15 exposes a portion of the source electrode S and a portion of the drain electrode D. The first passivation layer 15 also exposes a portion of the barrier layer 13 to form a trench T1 between the source electrode S and the drain electrode D.

[0073] Step S40: Fig. 9 As shown, a first electrode 21 and a second electrode 22 are formed. The first electrode 21 is located on a side of the source S away from the substrate 11 and is electrically connected to the source S. The second electrode 22 is located on a side of the drain D away from the substrate 11 and is electrically connected to the drain D.

[0074] Step S50: Figure 9~Figure 11 As shown, a gate G, a third electrode 23 and a fourth electrode 24 are formed. The gate G, the third electrode 23 and the fourth electrode 24 are all arranged on the side of the barrier layer 13 away from the substrate 11. The material of the gate G includes a sensitive metal material. The gate G is located between the source S and the drain D. The third electrode 23 and the fourth electrode 24 are electrically connected to the gate G respectively.

[0075] For example, in some embodiments, Fig. 9 As shown, the first electrode 21, the second electrode 22, the third electrode 23 and the fourth electrode 24 can be formed in the same process, and their wiring design can refer to Figure 1 The third electrode 23 and the fourth electrode 24 are only partially located in the trench T1, so as to facilitate the subsequent electrical connection with the gate G.

[0076] Then, if Fig.10 As shown, a second passivation layer 16 is formed, and the second passivation layer 16 exposes the trench T1 and exposes a portion of the third electrode 23 and a portion of the fourth electrode 24 .

[0077] Afterwards, if Fig.11As shown, a gate G is formed in the trench T1, and the thickness ranges from 4 nm to 300 nm. The material of the gate G includes a sensitive metal material. Depending on the type of the detected gas, the sensitive metal material is different. For example, when the gas sensor 10 is used to detect hydrogen, the material of the gate G includes at least one of platinum, palladium, platinum alloy, palladium alloy or zinc oxide.

[0078] Finally, in some embodiments, to reduce power consumption, such as Fig.12 As shown, an inductively coupled plasma etching process is used to etch and remove a portion of the channel layer 12 , and a top etching process is used to remove a portion of the substrate 11 to form a cavity K0 , so that the sensor unit 100 forms a suspended island structure.

[0079] So far, we can form Figure 1 A gas sensor 10 is shown.

[0080] The preparation method has a relatively simple preparation process, and the prepared gas sensor 10 detects gas based on the fact that the reaction between the gas and the gate G affects the concentration of the two-dimensional electron gas in the channel layer 12, and has a high sensitivity. In addition, by adjusting the voltage of the gate G through the third electrode 23 and the fourth electrode 24, the on-current of the transistor can be reduced, so that the percentage of current change caused by the change in the concentration of the two-dimensional electron gas is more obvious, further improving the sensitivity.

[0081] In addition, the cavity K0 formed by etching can also reduce the conduction loss of heat in the solid, which is conducive to retaining more of the temperature rise caused by the heating of the gate G in the suspended island structure, thereby increasing the reaction rate between the detected gas and the sensitive metal material of the gate G, thereby improving sensitivity and reducing power consumption.

[0082] The above is only a specific implementation of the present application, but the protection scope of the present application is not limited thereto. Any changes or substitutions that a person skilled in the art can think of within the technical scope disclosed in the present application should be included in the protection scope of the present application. Therefore, the protection scope of the present application should be based on the protection scope of the claims.

Claims

1. A gas sensor, characterized in that: comprising at least one sensing unit; The sensing unit comprises: substrate; A channel layer is disposed on the substrate; A barrier layer, disposed on a side of the channel layer away from the substrate; A source electrode and a drain electrode are both arranged on a side of the barrier layer away from the substrate, the orthographic projections of the source electrode and the drain electrode on the substrate are both in the shape of interdigitated fingers, the source electrode and the drain electrode are arranged crosswise, and a groove is formed between the source electrode and the drain electrode; a first electrode and a second electrode, wherein the first electrode is disposed on a side of the source electrode away from the substrate and electrically connected to the source electrode; and the second electrode is disposed on a side of the drain electrode away from the substrate and electrically connected to the drain electrode; The gate, the third electrode and the fourth electrode are all arranged on a side of the barrier layer away from the substrate, the material of the gate comprises at least one of platinum, palladium, a platinum alloy, a palladium alloy or zinc oxide, and the gate is arranged in the groove and extends along the groove; The third electrode and the fourth electrode are electrically connected to the gate, respectively, and are used to adjust the voltage of the gate to reduce the on-current of the transistor, wherein the gate is also used as a heating resistor to increase the reaction rate of the detected gas with the gate.

2. The gas sensor according to claim 1, characterized in that The orthographic projection of the groove on the substrate is in an S shape, and the orthographic projection of the gate on the substrate is also in an S shape.

3. The gas sensor according to claim 1, characterized in that: The orthographic projections of the third electrode and the fourth electrode on the substrate are both linear, and the linear shape includes at least two connected line segments, and the extension directions of the two line segments intersect.

4. The gas sensor according to claim 1, characterized in that: The third electrode and the fourth electrode are integrally arranged, and the gate is located on a side of the third electrode and the fourth electrode away from the substrate.

5. The gas sensor according to claim 1, characterized in that: The orthographic projections of the first electrode and the second electrode on the substrate are both linear, and the linear shape includes at least two connected line segments, and the extension directions of the two line segments intersect.

6. The gas sensor according to claim 1, characterized in that The material of the channel layer includes at least one of gallium nitride, gallium arsenide or indium gallium arsenide, and the material of the barrier layer includes at least one of indium gallium nitride, aluminum gallium nitride, indium phosphide, aluminum gallium arsenide or indium aluminum arsenide.

7. The gas sensor according to claim 1, characterized in that: The substrate includes a cavity, and the orthographic projection of the sensing unit on the substrate is located within the region where the cavity is located.

8. A method for preparing a gas sensor, for preparing the gas sensor as claimed in claim 1, characterized in that: include: forming a channel layer on a substrate; forming a barrier layer on a side of the channel layer away from the substrate; forming a source electrode and a drain electrode on a side of the barrier layer away from the substrate; forming a first electrode and a second electrode, wherein the first electrode is located at a side of the source electrode away from the substrate and electrically connected to the source electrode; and the second electrode is located at a side of the drain electrode away from the substrate and electrically connected to the drain electrode; A gate, a third electrode and a fourth electrode are formed. The gate, the third electrode and the fourth electrode are all arranged on a side of the barrier layer away from the substrate. The material of the gate includes a sensitive metal material. The gate is located between the source and the drain. The third electrode and the fourth electrode are electrically connected to the gate, respectively.

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