Surface plasma enhanced echo wall tubular humidity sensor and preparation method thereof

Abstract

The invention discloses a surface plasma enhanced echo wall tubular humidity sensor and a preparation method thereof, and belongs to the technical field of humidity sensing. According to the invention, the Y2O3 / ZrO2 thin film and Au nanoparticles deposited on the Y2O3 / ZrO2 thin film are self-curled into a tubular structure through the internal stress of the Y2O3 / ZrO2 thin film, and the humidity-sensitive hydrogel is added on the curled Y2O3 / ZrO2 thin film. The humidity sensor is simple in structure and easy to manufacture. The structure of the tubular echo wall mode resonant cavity can be changed by water absorption or dehydration of the humidity-sensitive hydrogel when the humidity changes, so that the optical property of the tubular echo wall mode resonant cavity is changed, humidity detection is realized by utilizing wavelength change of a WGM mode, and meanwhile, the influence of a tube wall structure on optical resonance can be enhanced by surface plasmas generated by Au nano-particles, so that the humidity detection accuracy is improved. And the wavelength change amplitude of the WGM mode is increased when the humidity changes, so that the prepared sensor has extremely high detection sensitivity to the environment humidity.

Description

Technical Field

[0001] The present invention relates to a surface plasmon enhanced whispering gallery mode tubular humidity sensor and a preparation method thereof, belonging to the technical field of humidity sensing. Background Art

[0002] In an optical microcavity formed by a pipe structure, total reflection of light at the tube wall / medium interface enables light waves to propagate in its annular cross-section and interfere with themselves to form a stable standing wave. This optical mode is called the whispering gallery mode (WGM). In this optical resonance mode, only light waves of specific wavelengths can propagate in the tubular structure, and its wavelength is called the resonance wavelength (Opt. Express 2007, 15, 9139.). WGM microcavities have high quality factors, small mode volumes, and are easy to fabricate, attracting extensive attention (Nature 2003, 421, 925.).

[0003] In the prior art, tubular microcavities have been used to prepare humidity sensors. Specifically, reference can be made to the patent document with the publication number CN114894745A and the name of an optical fiber humidity sensor based on a whispering gallery microcavity. However, this humidity sensor requires the cooperation of a special-shaped optical fiber and a whispering gallery microcavity, with a complex structure and high fabrication difficulty. Summary of the Invention

[0004] In order to solve the above problems existing currently, the present invention provides a surface plasmon enhanced whispering gallery mode tubular humidity sensor and a preparation method thereof. The technical solution is as follows:

[0005] As an aspect of the present invention, a surface plasmon enhanced whispering gallery mode tubular humidity sensor is provided, including: a substrate layer, a first nanometer thin film layer, a second nanometer thin film layer, and a noble metal nanoparticle layer arranged in sequence from bottom to top. The first nanometer thin film layer and the second nanometer thin film layer release stress and curl from the same end, so that the first nanometer thin film layer, the second nanometer thin film layer, and the noble metal nanoparticle layer form a tubular microcavity. A humidity-sensitive hydrogel layer is covered on the outside of the first nanometer thin film layer.

[0006] Further, the humidity-sensitive hydrogel layer is prepared from acrylamide (AM), sulfobetaine (SBMA), and methacryloyloxyethyl trimethyl ammonium chloride (METAC).

[0007] Further, the first nanometer thin film layer is a Y 2 O 3 nanometer thin film, and the second nanometer thin film layer is a ZrO 2 nanometer thin film.

[0008] Further, Y 2 O 3The thickness of the nanometer thin film is 10 - 30 nm, ZrO 2 The thickness of the nanometer thin film is 40 - 120 nm, Y 2 O 3 The thickness ratio of the nanometer thin film and ZrO 2 The thickness ratio of the nanometer thin film is 3 - 5.

[0009] Furthermore, the noble metal nanoparticle layer is an Au nanoparticle layer.

[0010] As another aspect of the present invention, there is provided a preparation method of a surface plasmon enhanced whispering gallery mode tubular humidity sensor for preparing the above - mentioned surface plasmon enhanced whispering gallery mode tubular humidity sensor, including:

[0011] Step (1) Prepare a substrate layer;

[0012] Step (2) Spin - coat a layer of photoresist on the cleaned substrate as a sacrificial layer;

[0013] Step (3) Divide the sacrificial layer into several regular patterns by photolithography;

[0014] Step (4) Deposit a certain thickness of yttrium oxide (Y 2 O 3 ) nanometer thin film layer and zirconium oxide (ZrO 2 ) nanometer thin film layer on the patterned sacrificial layer by a coating method at different rates and a certain tilt angle;

[0015] Step (5) Deposit a layer of Au film on the film deposited with Y 2 O 3 / ZrO 2 by a coating method;

[0016] Step (6) Place the substrate deposited with Y 2 O 3 / ZrO 2 nanometer thin film and Au film layer in an acetone solution to remove the sacrificial layer, release the Y 2 O 3 / ZrO 2 nanometer thin film, and the internal stress drives the Y 2 O 3 / ZrO 2 nanometer thin film to self - curl and make the Au film layer curl to form a tubular micro - cavity, obtaining a Y 2 O 3 / ZrO 2 curled micro - tube;

[0017] Step (7) For Y 2 O 3 / ZrO2 The coiled microtubes are subjected to critical point drying to avoid the collapse of the tubular structure;

[0018] Step (8) Anneal the Y microtubes deposited with the Au thin film layer under the protection of a nitrogen atmosphere to convert the Au thin film into Au nanoparticles, obtaining an Au nanoparticle layer. 2 O 3 / ZrO 2 The coiled microtubes are annealed under the protection of a nitrogen atmosphere to convert the Au thin film into Au nanoparticles, obtaining an Au nanoparticle layer.

[0019] Step (9) Immerse the Y microtubes deposited with the Au nanoparticle layer in a humidity-sensitive hydrogel solution and dry them in an oven to prepare a surface plasmon-enhanced whispering gallery mode tubular humidity sensor. 2 O 3 / ZrO 2 The coiled microtubes are annealed under the protection of a nitrogen atmosphere to convert the Au thin film into Au nanoparticles, obtaining an Au nanoparticle layer.

[0020] In step (3):

[0021] The regular patterns include circles, squares, long rectangles and other common regular figures.

[0022] In step (4):

[0023] The coating methods include electron beam evaporation, magnetron sputtering, atomic layer deposition, sol-gel, physical vapor deposition, chemical vapor deposition, and the preferred method is electron beam evaporation.

[0024] The different rates specifically refer to that the deposition rate of Y 2 O 3 is ZrO 2 is Y 2 O 3 and ZrO 2 The deposition rate ratio is 5 to 10 times.

[0025] The tilt angle is 10° to 60°, and the preferred tilt angle is 15° to 45°.

[0026] The Y 2 O 3 nanothin film has a thickness of 10 to 30 nm, the ZrO 2 nanothin film has a thickness of 40 to 120 nm, and the thickness ratio of Y 2 O 3 and ZrO 2 is 3 to 5.

[0027] In step (5):

[0028] The described coating method includes electron beam evaporation, magnetron sputtering, atomic layer deposition, sol-gel, physical vapor deposition, and chemical vapor deposition. The preferred method is electron beam evaporation.

[0029] The deposition rate of the Au film is The preferred rate is

[0030] The thickness of the Au film is 0.5 - 6 nm, and the preferred thickness is 1 - 4 nm.

[0031] In step (8):

[0032] The annealing temperature is 300 - 800 °C, and the annealing time is 10 - 50 minutes.

[0033] In step (9):

[0034] The humidity-sensitive hydrogel solution is prepared by mixing a mixed solution of acrylamide (AM), sulfobetaine (SBMA), and methacryloyloxyethyl trimethyl ammonium chloride (METAC) in a molar ratio of 2:3:3 with N,N'-methylenebisacrylamide (used as an initiator) and ammonium persulfate (used as a cross-linking agent) to form a mixed aqueous solution with a concentration fraction of 10%.

[0035] In the present invention, by combining a tubular microcavity with a humidity-sensitive hydrogel, the absorption or dehydration of the hydrogel caused by humidity changes will change the structure of the whispering gallery mode resonator of the tubular microcavity, thereby changing its optical properties. The humidity is detected by using the wavelength change of the WGM mode. In addition, noble metal nanoparticles are used to modify the whispering gallery mode tubular resonator. At the interface of the nanoparticles, collective oscillations of surface electrons will occur, localizing the electromagnetic field around the particles, causing field enhancement. This local surface plasmon resonance effect can effectively enhance the influence of the resonator tube wall structure on optical resonance.

[0036] Therefore, through the preparation of the whispering gallery mode of the tubular microcavity and the surface plasmon enhancement method, the humidity sensor prepared by combining a humidity-sensitive hydrogel can change the tubular structure under different humidity environments, realizing highly sensitive humidity detection, and can be used for integrated and miniaturized humidity sensor devices. The preparation method of this sensor is compatible with the current industrial semiconductor manufacturing process, and has significant application value and prospects.

[0037] The present invention has the following advantages:

[0038] (1) The humidity sensor proposed by the present invention has the advantage of anti-electromagnetic interference compared with traditional capacitive and resistive humidity sensors, and can operate safely in an environment with a high electric field.

[0039] (2) The humidity sensing using the whispering gallery mode tubular resonator proposed by the present invention is smaller in volume and higher in integration compared with the existing planar humidity sensors, and is convenient for compatibility with modern semiconductor integrated devices.

[0040] (3) The whispering gallery mode tubular resonator modified by Au nanoparticles proposed by the present invention optimizes the resonance performance of the resonator and increases the structural sensitivity of the resonator. On this basis, a hydrogel layer is added to the surface of the resonator, so that the structure of the tubular whispering gallery mode resonator changes under different humidity conditions, and then the humidity is detected by using the change of the WGM mode wavelength. Compared with the previous whispering gallery mode humidity sensors, the humidity detection sensitivity to the environment is higher.

[0041] (4) The surface plasmon enhanced whispering gallery tubular humidity sensor provided by the present invention does not need to rely on special-shaped optical fibers to cooperate with the whispering gallery microcavity, has a simple structure, and low preparation difficulty. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the following will briefly introduce the drawings required for the description of the embodiments. Obviously, the following drawings are only some embodiments of the present invention. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative efforts.

[0043] Figure 1 Schematic diagram of the hierarchical structure of the nano-film before releasing and curling provided by the present invention;

[0044] Figure 2 Schematic diagram of the structure of the surface plasmon enhanced whispering gallery tubular humidity sensor provided by the present invention;

[0045] Figure 3 For the Y provided by the present invention 2 O 3 / ZrO 2 Optical microscope photograph of the coiled microtube;

[0046] Figure 4 SEM image of the surface plasmon enhanced whispering gallery tubular humidity sensor provided by the present invention;

[0047] Figure 5 Simulation diagram of the humidity response test results of the surface plasmon enhanced whispering gallery tubular humidity sensor provided by the present invention;

[0048] Figure 6 Simulation diagram of the resonance wavelength corresponding to the resonance mode with azimuthal mode number 144 under different humidities provided by the present invention;

[0049] Reference numerals in the figure: 1 is the substrate layer, 2 is the sacrificial layer, 3 is the first nanometer thin film layer, 4 is the second nanometer thin film layer, 5 is the noble metal thin film layer, 6 is the humidity-sensitive hydrogel layer, and 7 is the noble metal nanoparticle layer. Detailed implementation manners

[0050] To make the objectives, technical solutions, and advantages of the present invention clearer, the following will further describe the embodiments of the present invention in detail with reference to the accompanying drawings.

[0051] Example 1:

[0052] An embodiment of the present invention provides a surface plasmon enhanced whispering gallery mode tubular humidity sensor, as Figure 2 shown, including: a substrate layer, a first nanometer thin film layer, a second nanometer thin film layer, and a noble metal nanoparticle layer arranged in sequence from bottom to top. The first nanometer thin film layer and the second nanometer thin film layer release stress and curl from the same end to form a tubular microcavity for the first nanometer thin film layer, the second nanometer thin film layer, and the noble metal nanoparticle layer. A humidity-sensitive hydrogel layer is covered on the outer side of the first nanometer thin film layer.

[0053] Specifically, in the embodiment of the present invention, the humidity-sensitive hydrogel layer is PAM-co-PSMBM-co-PMETAC prepared by using acrylamide (AM), sulfobetaine (SBMA), and methacryloyloxyethyl trimethyl ammonium chloride (METAC). The first nanometer thin film layer is a Y 2 O 3 nanometer thin film, and the second nanometer thin film layer is a ZrO 2 nanometer thin film. The thickness of the Y 2 O 3 nanometer thin film is 10 - 30 nm, the thickness of the ZrO 2 nanometer thin film is 40 - 120 nm, and the thickness ratio of the Y 2 O 3 nanometer thin film to the ZrO 2 nanometer thin film is 3 - 5. The noble metal nanoparticle layer is an Au nanoparticle layer.

[0054] The surface plasmon enhanced whispering gallery mode tubular humidity sensor provided by the embodiment of the present invention combines a tubular microcavity with a humidity-sensitive hydrogel. Since the water absorption or dehydration of the hydrogel caused by humidity changes will change the structure of the whispering gallery mode resonant cavity of the tubular microcavity, thereby changing its optical properties, the humidity is detected by using the wavelength change of the WGM mode. The device also uses noble metal nanoparticles to modify the whispering gallery mode resonant cavity, and utilizes the structure sensitivity of the surface plasmon enhanced resonant cavity to increase the wavelength change amplitude of the WGM mode when the humidity changes. The surface plasmon enhanced whispering gallery mode tubular humidity sensor not only has a simple structure and is easy to fabricate, but also its sensitivity has been greatly improved.

[0055] Example 2:

[0056] An embodiment of the present invention provides a preparation method of a surface plasmon enhanced whispering gallery mode tubular humidity sensor, as Figure 1 and Figure 2 shown, including:

[0057] (1) Coating a layer of photoresist as a sacrificial layer on a cut and cleaned substrate by spin coating;

[0058] (2) Dividing the photoresist layer into 5×5 circular patterns with a diameter of 300 microns by photolithography;

[0059] (3) Depositing a yttrium oxide (Y with a deposition rate of 2 O 3 ) nanometer thin film with a thickness of 15 nm and a deposition rate of and an inclination angle of 30°, and depositing a zirconia (ZrO 2 ) nanometer thin film with a thickness of 45 nm and an inclination angle of 30°;

[0060] (4) Depositing a 3 nm Au thin film on the Y 2 O 3 / ZrO 2 nanometer thin film by electron beam evaporation at a speed of ;

[0061] (5) Placing the substrate deposited with Y 2 O 3 / ZrO 2 nanometer thin film and Au thin film in an acetone solution to remove the photoresist sacrificial layer and release the Y 2 O 3 / ZrO 2 nanometer thin film. The internal stress drives the nanometer thin film to achieve self - curling. The optical microscope photograph of the self - curled Y 2 O 3 / ZrO 2 curled microtube is as Figure 3 shown;

[0062] (6) Performing critical point drying on the self - curled tubular structure to avoid the collapse of the tubular structure;

[0063] (7) Annealing the Y 2 O 3 / ZrO 2 microtube deposited with Au thin film at 400 °C under nitrogen atmosphere protection for 30 minutes to convert the Au thin film into Au nanoparticles.

[0064] (8) The Y2 O 3 / ZrO 2 The microtubes were immersed in the prepared humidity-sensitive hydrogel solution (10 μL of N,N′-methylenebisacrylamide and 10 μL of ammonium persulfate were added to 1 mL of the AM / SBMA / METAC mixed solution) for 45 minutes, and then dried in an oven at 60 °C for 5 hours to prepare a surface plasmon-enhanced whispering gallery mode tubular humidity sensor. The SEM image of the device is shown as Figure 4 shown.

[0065] The spectral detection results of the prepared surface plasmon-enhanced whispering gallery mode tubular humidity sensor at different environmental humidities are shown as Figure 5 shown, Figure 6 which is the calibration curve of environmental humidity versus resonant wavelength change. Therefore, the device has a high sensitivity of 1.25 kΩ per 1% concentration. The high sensitivity to environmental humidity benefits from the enhanced optical detection by the coiled tubular whispering gallery type structure and the surface plasmon enhancing the structural sensitivity of the WGM mode wavelength to the tubular resonator.

[0066] Example 3:

[0067] A surface plasmon-enhanced whispering gallery tubular humidity sensor was prepared according to the method of Example 2, except that the pattern formed by the photoresist through the photolithography process in step (2) was a square with a side length of 300 μm.

[0068] When the photoresist was spin-coated on the silicon substrate and then lithographed through the photolithography process, the designed exposure pattern was a 5×5 arrangement of squares with a side length of 300 μm, and the pattern spacing was 300 μm. Then, Y 2 O 3 / ZrO 2 nanofilm deposition, release of the coil, and other subsequent steps were carried out in the same manner as in Example 2. The coiled regions were different when the Y 2 O 3 / ZrO 2 nanofilm with different shapes was released and coiled. For the microtubes formed by the circular pattern, the thickness in the middle part was greater than that at the edge, while for the microtubes of the square pattern, the thickness of the film at the edge and in the middle part was the same, which would affect the resonant performance of light during humidity detection.

[0069] Example 4:

[0070] A surface plasmon-enhanced whispering gallery tubular humidity sensor was prepared according to the method of Example 2, except that in step (3), the deposition method of the Y 2 O 3 / ZrO 2 film and in step (4), the deposition method of the Au film was magnetron sputtering.

[0071] Y2 O 3 / ZrO 2 The O / ZrO nanometer thin film and the Au thin film are deposited by magnetron sputtering. The sputtering power is 200 W. The thicknesses of the thin films are the same as those in Example 2, which are 15 nm, 45 nm, and 3 nm respectively. The deposition rate and the tilt angle are also the same as those in Example 2 for the electron beam.

[0072] Example 5:

[0073] Prepare the surface plasmon enhanced whispering gallery mode tubular humidity sensor according to the method of Example 2, except that in step (3), the thicknesses of the Y 2 O 3 and ZrO 2 nanometer thin films are 20 nm and 80 nm respectively.

[0074] In step (3), the electron beam evaporation method is adopted. Similarly, deposit the Y nanometer thin film with a thickness of 20 nm at a deposition rate of 2 O 3 and a tilt angle of 30°. Deposit the ZrO thin film with a thickness of 80 nm at a deposition rate of 2 and a tilt angle of 30°. The thickness ratio of the two additional nanometer thin films helps to achieve faster curling during the release process.

[0075] Example 6:

[0076] Prepare the surface plasmon enhanced whispering gallery mode tubular humidity sensor according to the method of Example 2, except that in step (4), the deposition thickness of the Au thin film is 0.5 nm.

[0077] Compared with Example 2, the reduced thickness of the Au thin film will reduce the density of the Au nanoparticles after annealing, resulting in a weakened surface plasmon enhancement effect and poor device resonance performance during humidity detection.

[0078] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A surface plasmon enhanced whispering gallery tubular humidity sensor, characterized in that: include: The substrate layer, the first nanofilm layer, the second nanofilm layer and the noble metal nanoparticle layer are arranged in sequence from bottom to top. The first nanofilm layer and the second nanofilm layer release stress and curl themselves from the same end to form a tubular microcavity. The outer side of the first nanofilm layer is covered with a humidity-sensitive hydrogel layer.

2. The surface plasmon enhanced whispering gallery tubular humidity sensor according to claim 1, characterized in that: The humidity-sensitive hydrogel layer is prepared by using acrylamide, sulfobetaine and methacryloyloxyethyltrimethylammonium chloride.

3. The surface plasmon enhanced whispering gallery tubular humidity sensor according to claim 1, characterized in that: The first nano-film layer is a Y2O3 nano-film, and the second nano-film layer is a ZrO2 nano-film.

4. The surface plasmon enhanced whispering gallery tubular humidity sensor according to claim 3, characterized in that: The thickness of the Y2O3 nanofilm is 10-30nm, the thickness of the ZrO2 nanofilm is 40-120nm, and the thickness ratio of the Y2O3 nanofilm to the ZrO2 nanofilm is 3-5.

5. The surface plasmon enhanced whispering gallery tubular humidity sensor according to claim 1, characterized in that: The noble metal nanoparticle layer is an Au nanoparticle layer.

6. A method for preparing a surface plasmon enhanced whispering gallery tubular humidity sensor, for preparing the surface plasmon enhanced whispering gallery tubular humidity sensor according to any one of claims 1 to 5, characterized in that: include: Step 1, preparing a substrate layer; Step 2, preparing a sacrificial layer: coating a layer of photoresist as a sacrificial layer on the cleaned substrate by spin coating, and patterning the sacrificial layer; Step 3, depositing a stress layer: depositing a first nano-thin film layer and a second nano-thin film layer of a preset thickness on the patterned sacrificial layer in sequence at different rates and preset tilt angles by a coating method; Step 4, depositing a noble metal thin film layer: depositing a layer of noble metal thin film layer on the second nano-thin film layer by a coating method; Step 5, self-curling of the film: placing the substrate on which the first nanofilm layer, the second nanofilm layer and the noble metal film layer are deposited in an acetone solution, thereby removing the sacrificial layer, releasing the first nanofilm layer and the second nanofilm layer, and causing the internal stress to drive the first nanofilm layer and the second nanofilm layer to self-curl, and causing the noble metal film layer to curl, thereby forming a tubular microcavity and obtaining a microtube; Step 6, drying: performing critical point drying on the self-curled tubular microcavity; Step 7, preparing a noble metal nanoparticle layer: annealing the microtubes on which the noble metal thin film layer is deposited under a nitrogen atmosphere to convert the noble metal thin film into noble metal nanoparticles, thereby obtaining a noble metal nanoparticle layer; Step eight, adding a humidity-sensitive hydrogel layer: immersing the microtubes deposited with the noble metal nanoparticle layer in a humidity-sensitive hydrogel solution, and drying in an oven to prepare a surface plasmon-enhanced whispering gallery tubular humidity sensor.

7. The method according to claim 6, characterized in that The preparation method of the humidity-sensitive hydrogel solution comprises: acrylamide, sulfobetaine and methacryloyloxyethyltrimethylammonium chloride are prepared into a mixed solution in a molar ratio of 2:3:3; The mixed solution is mixed with N,N′-methylenebisacrylamide and ammonium persulfate to form a humidity-sensitive hydrogel solution with a concentration fraction of 10%.

8. The method according to claim 7, characterized in that The step three comprises: The patterned sacrificial layer is coated with a film Depositing a Y2O3 nanofilm at a deposition rate of and an inclination angle of 10° to 60° to obtain a first nanofilm layer; Then, a coating method is used on the first nano-thin film layer to The ZrO2 nanofilm is deposited at a deposition rate and an inclination angle of 10° to 60° to obtain a second nanofilm layer, wherein the ratio of the deposition rates of the Y2O3 nanofilm and the ZrO2 nanofilm is 5 to 10 times, and the preferred inclination angle is 15° to 45°.

9. The method according to claim 8, characterized in that The fourth step is: coating the second nano-film layer with a coating method. A layer of Au thin film is deposited at a deposition rate of 10. The method according to claim 9, characterized in that The Au thin film layer has a thickness of 0.5 to 6 nm, preferably 1 to 4 nm.

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