Method for preparing a gas sensitive sensor device based on three-dimensional hollow nanostructures

Abstract

The application provides a method for preparing a three-dimensional hollow nanostructure-based gas sensor, which comprises the following steps: (1) performing surface cleaning treatment on a substrate; (2) forming an etching resist layer on the substrate by using an electron beam etching resist; (3) performing pattern exposure, development and fixation on the etching resist layer to form an etching resist layer with a cavity structure; (4) performing thin film deposition on the etching resist layer with the cavity structure formed in step (3) to form a dielectric layer on the side wall and bottom wall of the cavity structure and the upper surface of the etching resist layer; (5) removing the dielectric layer on the upper surface of the etching resist layer and then removing the etching resist layer to obtain a hollow tube structure with an open upper end formed by the dielectric layer; (6) performing thin film deposition on the surface of the tube structure and the exposed surface of the substrate to form a two-dimensional electron gas structure; and (7) forming an active material sensitive to a gas to be detected on the two-dimensional electron gas structure. The sensor prepared by the method has high sensitivity and recovery speed.

Description

Technical Field

[0001] This invention belongs to the field of gas sensors. Specifically, this invention relates to a method for fabricating gas-sensitive sensor devices based on three-dimensional hollow nanostructures. Background Technology

[0002] Gas sensors are mainly used for the detection of a specific gas. They are devices that convert gas concentration information into parameters using physical or chemical principles and output corresponding electrical signals.

[0003] Two-dimensional electron gas (2D electron gas) is a fundamental model in two-dimensional systems, describing how electrons in a crystal are confined in one direction but move freely within a two-dimensional space defined by the other two directions. Currently, 2D electron gas has wide applications in the field of gas sensors.

[0004] Currently, gas sensors with two-dimensional electron gas prepared using traditional methods typically have planar structures for their two-dimensional electron gas, resulting in limited sensitivity or recovery speed. For example, Akhil Ranjan et al. prepared a planar two-dimensional electron gas composed of AlGaN / GaN (Akhil Ranjan, et.al., AlGaN / GaN HEMT-based high-sensitive NO2 gas sensors, 2019, Jpn. J. Appl. Phys., 58, SCCD23.), whose sensitivity to NO2 was only 5.5% at 300℃; another example is Sung Min Kim et al. (Kim, SM, et.al., High-Performance, Transparent Thin Film Hydrogen Gas Sensor Using 2D Electron Gas at Interface of Oxide Thin Film Heterostructure Grown by Atomic Layer Deposition, Adv. Funct. Mater., 2019, 29, 1807760.) who prepared a planar two-dimensional electron gas of Al2O3 / TiO2, whose H2 sensor had a particularly long recovery time of up to 245 seconds.

[0005] Therefore, there is an urgent need to develop a gas sensor with high sensitivity and fast recovery speed. Summary of the Invention

[0006] The purpose of this invention is to provide a method for fabricating a gas-sensitive sensor based on a three-dimensional hollow nanostructure. The sensor fabricated using this method exhibits high sensitivity and fast recovery speed.

[0007] The above-mentioned objective of the present invention is achieved through the following technical solution.

[0008] This invention provides a method for fabricating a gas-sensitive sensor based on a three-dimensional hollow nanostructure, comprising the following steps:

[0009] (1) Perform surface cleaning treatment on the substrate;

[0010] (2) A resist layer is formed on the substrate using an electron beam resist;

[0011] (3) The resist layer is patterned, developed and fixed using an electron beam exposure system to form a resist layer with a cavity structure;

[0012] (4) A thin film is deposited on the resist layer with cavity structure formed in step (3) using an atomic layer deposition system to form a dielectric layer on the peripheral and bottom walls of the cavity structure and on the upper surface of the resist layer surrounding the cavity structure; wherein the thickness of the formed dielectric layer is less than half of the minimum dimension of the cross-section of the cavity structure and less than the thickness of the resist layer (i.e., the height of the cavity structure).

[0013] (5) After removing the medium layer on the upper surface of the resist layer, remove the resist layer to obtain a tube structure with an open upper end and hollow structure composed of the medium layer.

[0014] (6) Thin film deposition is performed on the surface of the tube structure and the exposed substrate surface using an atomic layer deposition system to form a two-dimensional electron gas structure;

[0015] (7) An active material sensitive to the gas to be measured is formed on the two-dimensional electronic gas structure to obtain a gas-sensitive sensor device.

[0016] The inventors of this application unexpectedly discovered that by forming the two-dimensional electron gas structure of this invention on the surface of a three-dimensional hollow structure, a gas sensor with ultra-high sensitivity and recovery speed can be obtained. In this invention, a three-dimensional hollow dielectric nanotube structure is used as the "skeleton" of the gas sensor. Without being bound by theory, this is likely because the three-dimensional high-depth-to-weight ratio (i.e., the ratio of height to thickness) of the tube structure has a larger specific surface area, which can increase the contact area between the gas and the device and accelerate the response speed, thus improving the sensitivity and recovery speed of the gas sensor.

[0017] It should be noted that in step (4), the thickness of the dielectric layer needs to be less than half the minimum dimension of the cross-section of the cavity structure and less than the thickness of the resist layer (the thickness of the resist layer is the height of the cavity structure, which is also the height of the tube structure) in order to form a hollow tube structure, rather than a solid tube structure. This is because if the thickness of the dielectric layer is greater than or equal to half the minimum dimension of the cross-section of the cavity structure or greater than or equal to the thickness of the resist layer, the formed dielectric layer will fill the cavity structure.

[0018] Furthermore, traditional micro / nano fabrication processes struggle to fabricate tube structures with high aspect ratios. The inventors of this application unexpectedly discovered that atomic layer assembly processes can stably and easily prepare such ultra-high aspect ratio tube structures.

[0019] In addition, the inventors of this application unexpectedly discovered that combining a high-depth-ratio three-dimensional structure with an ultra-thin two-dimensional electron gas significantly improves the performance of the gas sensor.

[0020] Preferably, in the method described in this invention, the substrate is selected from one or more of silicon wafers, quartz, polydimethylsiloxane (PDMS), and polyimide (PI).

[0021] Preferably, in the method described in this invention, the cleaning process in step (1) is carried out by a method including the following steps: ultrasonic cleaning is performed sequentially using acetone, isopropanol and deionized water, and then the mixture is dried with a nitrogen gun.

[0022] Preferably, in the method described in this invention, the electron beam resist is selected from one or more of PMMA, ZEP520 and AR-N7520.

[0023] Preferably, in the method described in this invention, the thickness of the resist layer is 100-1000 nm.

[0024] Preferably, in the method described in this invention, the size of the pattern exposed in step (3) is 50nm-5000nm. In a specific embodiment of this invention, an electron beam exposure system is used for pattern exposure in step 3), and the width of the exposed pattern is generally between 50nm and 5000nm, and its height is equal to the height of the electron beam resist layer.

[0025] Preferably, in the method of the present invention, when the electron beam resist is PMMA, the developing solution used for developing contains MIBK and IPA in a volume ratio of 1:3; when the electron beam resist is ZEP520, the developing solution used for developing is butyl acetate; when the electron beam resist is AR-N 7520, the developing solution used for developing is methyl ammonium hydroxide (TMAH).

[0026] Preferably, in the method described in this invention, the fixing solution used in step (3) is isopropanol (IPA).

[0027] Preferably, in the method described in this invention, the temperature used in the atomic layer deposition system does not exceed the glass transition temperature of the resist.

[0028] Preferably, in the method described in this invention, the temperature used by the atomic layer deposition system is 80-120°C.

[0029] Preferably, in the method described in this invention, the deposition material for the thin film deposition in step (4) is one or more of titanium oxide, aluminum oxide and hafnium oxide.

[0030] Preferably, in the method described in this invention, the thickness of the dielectric layer formed in step (4) is 8-50 nm. The thinnest dielectric layer can be 8 nm thick and 650 nm high, exhibiting an extremely high depth-to-depth ratio of 81:1.

[0031] Preferably, in the method described in this invention, the dielectric layer on the upper surface of the resist layer in step (5) is removed by an inductively coupled plasma etching system.

[0032] Preferably, in the method described in this invention, the flow rate of Cl2 used in the inductively coupled plasma etching system during the etching process is 10-30 sccm, the flow rate of BCl3 is 5-10 sccm, the power of the RF source is 5-30W, the power of the ICP source is 300-800W, and the gas pressure is 4-30 mTorr.

[0033] Preferably, in the method of the present invention, the removal of the resist layer in step (5) is performed by oxygen plasma or ozone removal.

[0034] Preferably, in the method described in this invention, the ratio of the height to the thickness of the tube structure in step (5) is (1-100):1.

[0035] Preferably, in the method of the present invention, the thin film deposition on the tube structure surface and the exposed substrate surface using an atomic layer deposition system in step (6) is performed by a method including the following steps: sequentially growing a titanium oxide thin film and an aluminum oxide thin film on the tube structure surface and the exposed substrate surface using an atomic layer deposition system to obtain a two-dimensional electron gas structure composed of a titanium oxide thin film and an aluminum oxide thin film.

[0036] Preferably, in the method described in this invention, the thickness of the titanium oxide thin film in the two-dimensional electron gas structure is 5-20 nm.

[0037] Preferably, in the method described in this invention, the thickness of the alumina film in the two-dimensional electron gas structure is 2-10 nm.

[0038] In one specific embodiment of the present invention, the method of the present invention includes the following steps:

[0039] 1) Perform surface cleaning treatment on the substrate;

[0040] 2) First, coat the substrate with a layer of electron beam resist;

[0041] 3) The pattern is exposed using an electron beam exposure system, then developed using a developer, and finally fixed using a fixer, thus creating a resist pore structure with an extremely high depth-to-depth ratio on the resist.

[0042] 4) Deposition of a dielectric thin film using an atomic layer deposition system, wherein the dielectric thin film may be TiO2, Al2O3, or HfO2, etc.

[0043] 5) The dielectric film on top is removed using an inductively coupled plasma etching system, and the remaining electron beam resist is removed to obtain a dielectric nanotube structure array with an extremely high depth-to-depth ratio.

[0044] 6) TiO2 and Al2O3 films are deposited sequentially using an atomic layer deposition system to obtain a two-dimensional electron gas structure composed of TiO2 and Al2O3.

[0045] 7) Finally, active materials, such as Pd, SnO2 or WO3, are grown on the obtained ultrathin three-dimensional hollow nanostructure using electron beam deposition equipment to obtain gas sensors that are sensitive to different gases.

[0046] In a specific embodiment of the present invention, the electron beam resist used can be positive resist PMMA or ZEP520 electron beam resist, or negative resist AR-N 7520 electron beam resist.

[0047] In a specific embodiment of the present invention, in step (6), an atomic layer deposition system is used again to deposit an ultrathin TiO2 material on the sample, typically with a thickness of 5-20 nm. This ensures that all surfaces of the sample obtained in step (6), including the substrate surface and the inner and outer surfaces of the TiO2 nanotube structure, are coated with a continuous TiO2 film. In step (6), an ultrathin Al2O3 material is also deposited on the sample using an atomic layer deposition system, typically with a thickness of 2-10 nm. This ensures that a continuous Al2O3 film is deposited on the TiO2 film deposited in step (6), thereby forming a continuous TiO2 / Al2O3 two-dimensional electron gas. Furthermore, the Al2O3 film needs to be very thin to allow free electrons to pass through it.

[0048] In a specific embodiment of the present invention, in step (7), an appropriate active material is deposited using an electron beam deposition apparatus according to the gas to be detected, with a thickness typically of 2-10 nm. It is necessary to ensure that the active material does not form a continuous thin film, so that the conductivity of the gas sensor is determined by the two-dimensional electron gas structure, rather than by the active material. For example, to prepare an H2 sensor, Pd metal particles are grown; to prepare a Cl2 sensor, SnO2 particles are grown; and to prepare an NH3 sensor, WO3 particles are grown.

[0049] The present invention has the following beneficial effects:

[0050] The sensor prepared by the method of the present invention has ultra-high sensitivity and recovery speed. Attached Figure Description

[0051] The embodiments of the present invention will now be described in detail with reference to the accompanying drawings, wherein:

[0052] Figure 1 These are schematic diagrams and scanning electron microscope images of the three-dimensional sensor prepared in Embodiment 1 of the present invention.

[0053] Figure 2 These are physical images of the planar sensor and the three-dimensional sensor prepared in Comparative Example 1 and Example 1 of the present invention; wherein the left image is a physical image of the planar sensor prepared in Comparative Example 1, and the right image is a physical image of the three-dimensional sensor prepared in Example 1.

[0054] Figure 3 This is a comparison chart of the sensitivity of the planar sensor and the three-dimensional sensor prepared in Comparative Example 1 and Example 1 of the present invention.

[0055] Figure 4 This is a SEM image of the hollow nanostructure with ultrathin wall thickness prepared in Example 3 of the present invention.

[0056] Figure 5This is a schematic diagram of the ultrathin-walled solid nanostructure prepared in Comparative Example 2 of the present invention, and a sensitivity comparison diagram of sensors composed of hollow and solid nanostructures. Detailed Implementation

[0057] The present invention will be further described in detail below with reference to specific embodiments. The embodiments given are only for illustrating the present invention and are not intended to limit the scope of the present invention.

[0058] Example 1

[0059] In this embodiment, an H2 gas sensor was prepared using the fabrication method of the gas sensor device based on an ultrathin-walled three-dimensional hollow nanostructure provided by the present invention.

[0060] (1) Sonicate the quartz sheet for 5 minutes each in acetone, isopropanol and deionized water, and then dry it with a nitrogen gun.

[0061] (2) Coat the quartz plate after cleaning in step (1) with an 800 nm thick layer of PMMA electron beam resist.

[0062] (3) An electron beam exposure system was used to expose a hexagonal pattern, which consists of three rectangles spaced 60 degrees apart, with a width of 100 nm and a length of 600 nm. Then, a solution of MIBK:IPA = 1:3 was used for development for 1 min, followed by fixing with IPA solution for 30 s. Thus, a cavity resist structure was obtained in the resist.

[0063] (4) A TiO2 thin film was deposited using ALD at a temperature of 90°C and a thickness of 40 nm.

[0064] (5) The top TiO2 film was etched using an inductively coupled plasma etching system. The conditions were: Cl2 flow rate of 10 sccm, BCl3 flow rate of 5 sccm, RF power of 20W, ICP power of 500W, and gas pressure of 10 mTorr.

[0065] (6) Using reactive ion etching equipment, the remaining electron beam resist was removed by oxygen plasma. The conditions used were O2 flow rate of 100 sccm, RF power of 100 W, and gas pressure of 100 mTorr. In this way, a TiO2 nanotube structure array with a height-to-thickness ratio of 20:1 was obtained, which was used as the "skeleton" of the gas sensor.

[0066] (7) Atomic layer deposition was used to deposit 10 nm of TiO2 and 3 nm of Al2O3 in sequence, and finally electron beam evaporation was used to deposit 2 nm of metal Pd.

[0067] This embodiment successfully prepared as follows: Figure 1The H2 gas sensor device shown is based on an ultrathin-walled, three-dimensional hollow nanostructure.

[0068] like Figure 2 As shown, both the planar gas sensor device prepared in Comparative Example 1 and the three-dimensional gas sensor device prepared in Example 1 have high transparency, which is beneficial for the preparation of transparent components.

[0069] like Figure 3 As shown, the three-dimensional H2 sensor prepared in Example 1 has higher sensitivity and shorter recovery time than the planar H2 sensor prepared in Comparative Example 1. In particular, at a low concentration of 5 ppm, the sensitivity of the three-dimensional sensor is 31 times that of the planar sensor.

[0070] Example 2

[0071] This embodiment uses the fabrication method of gas-sensitive sensor based on ultrathin wall thickness three-dimensional hollow nanostructure provided by the present invention to prepare an NH3 gas sensor.

[0072] (1) Sonicate the PI flexible substrate for 5 minutes each in acetone, isopropanol and deionized water, and then dry it with a nitrogen gun.

[0073] (2) Coat an 800nm ​​thick layer of PMMA electron beam resist on the PI flexible substrate after cleaning in step (1).

[0074] (3) A square pattern with a side length of 150 nm was exposed using an electron beam exposure system; then, a solution of MIBK:IPA = 1:3 was used for development for 1 min, followed by fixing with IPA solution for 30 s. Thus, a cavity resist structure was obtained in the resist.

[0075] (4) An Al2O3 thin film was deposited using ALD at a temperature of 100°C and a thickness of 30 nm.

[0076] (5) The top Al2O3 film was etched using an inductively coupled plasma etching system. The conditions were: Cl2 flow rate of 10 sccm, BCl3 flow rate of 5 sccm, RF power of 20W, ICP power of 500W, and gas pressure of 10 mTorr.

[0077] (6) Using a reactive ion etching apparatus, the remaining electron beam resist was removed using oxygen plasma. The conditions used were an O2 flow rate of 100 sccm, an RF power of 100 W, and a gas pressure of 100 mTorr. In this way, an Al2O3 nanotube structure array with a height-to-thickness ratio of 27:1 was obtained.

[0078] (7) Atomic layer deposition was used to deposit 10 nm of TiO2 and 3 nm of Al2O3 in sequence, and finally electron beam evaporation was used to deposit 2 nm of WO3 material.

[0079] This example successfully fabricated a flexible NH3 gas sensor based on an ultrathin-walled three-dimensional hollow nanostructure.

[0080] Example 3

[0081] This embodiment uses the fabrication method of gas-sensitive sensor based on ultrathin wall thickness three-dimensional hollow nanostructure provided by the present invention to prepare a Cl2 gas sensor.

[0082] (1) Sonicate the silicon substrate for 5 minutes each in acetone, isopropanol and deionized water, and then dry it with a nitrogen gun.

[0083] (2) A 650nm thick PMMA electron beam resist is coated on the silicon substrate after cleaning in step (1).

[0084] (3) A circular pattern with a diameter of 150 nm was exposed using an electron beam exposure system. Then, the pattern was developed for 1 min using a MIBK:IPA = 1:3 solution, and fixed with IPA solution for 30 s. Thus, a cavity resist structure was obtained in the resist.

[0085] (4) A TiO2 thin film was deposited using ALD at a temperature of 90°C and a thickness of 8 nm.

[0086] (5) The top TiO2 film was etched using an inductively coupled plasma etching system. The conditions were: Cl2 flow rate of 10 sccm, BCl3 flow rate of 5 sccm, RF power of 20W, ICP power of 500W, and gas pressure of 10 mTorr.

[0087] (6) Using a reactive ion etching apparatus, the remaining electron beam resist was removed using oxygen plasma. The conditions used were an O2 flow rate of 100 sccm, an RF power of 100 W, and a gas pressure of 100 mTorr. In this way, a TiO2 nanotube structure array with a height-to-thickness ratio of 81:1 was obtained.

[0088] (7) Use atomic layer deposition to deposit 10 nm TiO2 and 3 nm Al2O3 in sequence, and finally use electron beam evaporation to deposit 2 nm of metal SnO2.

[0089] This embodiment successfully prepared as follows: Figure 4 The Cl2 gas sensor device shown is based on an ultrathin-walled, three-dimensional hollow nanostructure. Figure 4The device structure is shown to be even transparent, and the depth-to-depth ratio of the skeleton structure is as high as 81:1, which greatly increases the specific surface area and helps to improve the performance of the gas sensor.

[0090] Comparative Example 1

[0091] Fabrication of a planar H2 sensor

[0092] (1) Sonicate the quartz sheet for 5 minutes each in acetone, isopropanol and deionized water, and then dry it with a nitrogen gun.

[0093] (2) Atomic layer deposition was used to deposit 10 nm of TiO2 and 3 nm of Al2O3 in sequence, and finally electron beam evaporation was used to deposit 2 nm of metal Pd.

[0094] Comparative Example 2

[0095] This comparative example uses the fabrication method of the gas sensor device based on the ultrathin wall thickness three-dimensional solid nanostructure provided by the present invention to prepare an H2 gas sensor.

[0096] (1) Sonicate the quartz sheet for 5 minutes each in acetone, isopropanol and deionized water, and then dry it with a nitrogen gun.

[0097] (2) Coat the quartz plate after cleaning in step (1) with an 800 nm thick layer of PMMA electron beam resist.

[0098] (3) An electron beam exposure system was used to expose a hexagonal pattern, which consists of three rectangles spaced 60 degrees apart, with a width of 100 nm and a length of 600 nm. Then, a solution of MIBK:IPA = 1:3 was used for development for 1 min, followed by fixing with IPA solution for 30 s. Thus, a cavity resist structure was obtained in the resist.

[0099] (4) ALD is used to deposit TiO2 thin film at a deposition temperature of 90℃ and a film thickness of 60nm. This will fill the hexagonal pattern and form a solid hexagonal structure.

[0100] (5) The top TiO2 film was etched using an inductively coupled plasma etching system. The conditions were: Cl2 flow rate of 10 sccm, BCl3 flow rate of 5 sccm, RF power of 20W, ICP power of 500W, and gas pressure of 10 mTorr.

[0101] (6) Using reactive ion etching equipment, the remaining electron beam resist was removed by oxygen plasma. The conditions used were O2 flow rate of 100 sccm, RF power of 100 W, and gas pressure of 100 mTorr. In this way, a TiO2 nanostructure array with a height-to-thickness ratio of 8:1 was obtained, which was used as the "skeleton" of the gas sensor.

[0102] (7) Atomic layer deposition was used to deposit 10 nm of TiO2 and 3 nm of Al2O3 in sequence, and finally electron beam evaporation was used to deposit 2 nm of metal Pd.

[0103] This embodiment successfully prepared as follows: Figure 5 The H2 gas sensor device shown is based on an ultrathin-walled three-dimensional solid nanostructure. Furthermore, its sensitivity curve shows that the H2 sensor based on a three-dimensional hollow nanostructure (Example 1 of the present invention) has higher sensitivity compared to the H2 sensor based on a three-dimensional solid nanostructure.

Claims

1. A method for fabricating a gas-sensitive sensor based on a three-dimensional hollow nanostructure, comprising the following steps: (1) Perform surface cleaning treatment on the substrate; (2) An electron beam resist layer is formed on the substrate; (3) The resist layer is patterned, developed and fixed using an electron beam exposure system to form a resist layer with a cavity structure; (4) A thin film is deposited on the resist layer with cavity structure formed in step (3) using an atomic layer deposition system to form a dielectric layer on the peripheral and bottom walls of the cavity structure and on the upper surface of the resist layer surrounding the cavity structure; wherein the thickness of the formed dielectric layer is less than half of the minimum dimension of the cross-section of the cavity structure and less than the thickness of the resist layer. (5) After removing the dielectric layer on the upper surface of the resist layer, remove the resist layer to obtain a hollow tube structure with an open upper end formed by the dielectric layer. (6) Thin film deposition is performed on the surface of the tube structure and the exposed substrate surface using an atomic layer deposition system to form a two-dimensional electron gas structure; (7) An active material sensitive to the gas to be measured is formed on the two-dimensional electronic gas structure to obtain a gas-sensitive sensor device; The thin film deposition in step (6) using an atomic layer deposition system on the tube structure surface and the exposed substrate surface is performed by a method comprising the following steps: sequentially growing a titanium oxide thin film and an aluminum oxide thin film on the tube structure surface and the exposed substrate surface using an atomic layer deposition system to obtain a two-dimensional electron gas structure composed of a titanium oxide thin film and an aluminum oxide thin film.

2. The method according to claim 1, wherein, The substrate is selected from one or more of silicon wafers, quartz, polydimethylsiloxane, and polyimide.

3. The method according to claim 1, wherein, The cleaning process in step (1) is carried out by a method including the following steps: ultrasonic cleaning is performed sequentially with acetone, isopropanol and deionized water, and then dried with a nitrogen gun.

4. The method according to claim 1, wherein, The electron beam resist is selected from one or more of PMMA, ZEP520 and AR-N 7520.

5. The method according to claim 1, wherein, The thickness of the resist layer is 100-1000 nm.

6. The method according to claim 1, wherein, The size of the exposure pattern used in step (3) is 50nm-5000nm.

7. The method according to claim 4, wherein, When the electron beam resist is PMMA, the developing solution used in the developing process contains MIBK and IPA in a volume ratio of 1:

3. When the electron beam resist is ZEP520, the developing solution used for developing is butyl acetate; When the electron beam resist is AR-N 7520, the developing solution used is methyl ammonium hydroxide.

8. The method according to claim 1, wherein, The fixing solution used in step (3) is isopropanol.

9. The method according to claim 1, wherein, The temperature used in the atomic layer deposition system does not exceed the glass transition temperature of the resist.

10. The method according to claim 1, wherein, The atomic layer deposition system is used at temperatures of 80-120°C.

11. The method according to claim 1, wherein, The deposition material for the thin film deposition in step (4) is one or more of titanium oxide, aluminum oxide and hafnium oxide.

12. The method according to claim 1, wherein, The thickness of the dielectric layer formed in step (4) is 8-50 nm.

13. The method according to claim 1, wherein, The dielectric layer on the upper surface of the resist layer in step (5) is removed by an inductively coupled plasma etching system.

14. The method according to claim 13, wherein, The inductively coupled plasma etching system uses Cl2 with a flow rate of 10-30 sccm, BCl3 with a flow rate of 5-10 sccm, RF source power of 5-30W, ICP source power of 300-800W, and gas pressure of 4-30mTorr during the etching process.

15. The method according to claim 1, wherein, The removal of the resist layer in step (5) is achieved by oxygen plasma or ozone removal.

16. The method according to claim 1, wherein, The ratio of the height to the thickness of the tube structure in step (5) is (1-100):

1.

17. The method according to claim 1, wherein, In a two-dimensional electron gas structure, the thickness of the titanium oxide thin film is 5-20 nm.

18. The method according to claim 1, wherein, In a two-dimensional electron gas structure, the thickness of the alumina film is 2-10 nm.

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