Laser modified ZnO-based gas sensor and preparation method thereof

Abstract

The invention relates to a laser modified ZnO-based gas sensor and a preparation method thereof. The ZnO-based gas sensor comprises an electrode substrate and a ZnO film arranged on the electrode substrate; the ZnO thin film is prepared through a magnetron sputtering method, annealing and laser etching treatment are sequentially carried out, and a regular net structure is formed on the surface of the ZnO thin film after laser etching. The preparation method comprises the following steps: preparing a ZnO film on the surface of an electrode substrate through magnetron sputtering; carrying out annealing treatment on the electrode substrate attached with the ZnO thin film; carrying out laser etching treatment on the surface of the annealed ZnO thin film to form a regular net-shaped structure; and assembling the electrode substrate attached with the laser modified ZnO film to finally obtain the ZnO-based gas sensor. Compared with the prior art, the surface of the ZnO film is modified through laser etching, and the assembled ZnO-based gas sensor has excellent sensitivity, selectivity, cycling stability and moisture resistance.

Description

Technical Field

[0001] The invention belongs to the technical field of gas sensors, and in particular relates to a laser-modified ZnO-based gas sensor and a preparation method thereof. Background Art

[0002] Metal oxide semiconductor (MOS) gas sensors based on electrical signals have excellent characteristics such as low power consumption, high sensitivity, low power consumption and easy integration. They are widely used in many fields such as industrial production, agricultural environment monitoring, air quality assessment and medical diagnosis.

[0003] As the core of gas sensors, the performance of gas-sensitive materials directly determines the detection accuracy of gas sensors. At present, the preparation methods of gas-sensitive materials mainly include hydrothermal method, electrospinning method, sol-gel method, atomic force deposition method and magnetron sputtering method. Among them, magnetron sputtering method has become an ideal choice for large-scale preparation of gas-sensitive films due to its simple process operation, safe preparation process, low cost and good reproducibility. However, MOS gas-sensitive films prepared by magnetron sputtering are usually dense and uniform, lacking complex micro-nano structures, which to a certain extent limits the adsorption of target gas molecules in the environment on the surface of gas-sensitive materials, thereby adversely affecting the sensitivity and response speed of the sensor.

[0004] Therefore, it is necessary to perform surface treatment on the MOS gas-sensitive film to improve the adsorption effect and response speed of the target gas molecules on the surface of the gas-sensitive material. Summary of the invention

[0005] The purpose of the present invention is to provide a laser-modified ZnO-based gas sensor and a preparation method thereof in order to overcome the defects of the prior art.

[0006] The purpose of the present invention can be achieved by the following technical solutions:

[0007] The present invention provides a laser-modified ZnO-based gas sensor, comprising an electrode substrate and a gas-sensitive portion arranged on the electrode substrate, wherein the gas-sensitive portion is a ZnO film; the ZnO film is prepared by a magnetron sputtering method, and is sequentially annealed and laser-etched;

[0008] Among them, a regular network structure is formed on the surface of the ZnO film after laser etching.

[0009] Furthermore, the electrode substrate includes a gold electrode, a platinum wire, an alumina substrate and a heating electrode in sequence from top to bottom.

[0010] The present invention also provides a method for preparing a laser-modified ZnO-based gas sensor, comprising the following steps:

[0011] S1: Preparation of ZnO thin film on the surface of electrode substrate by magnetron sputtering;

[0012] S2: annealing the electrode substrate with the ZnO film attached thereto;

[0013] S3: performing laser etching on the surface of the annealed ZnO film, and finally forming a regular network structure on the surface of the ZnO film;

[0014] S4: subsequently assembling the electrode substrate with the laser-modified ZnO thin film attached thereto, and finally obtaining the ZnO-based gas sensor.

[0015] Furthermore, in step S1, the sputtering power of the magnetron sputtering is 80-120 W, preferably 30 sccm, and the sputtering time is 20-40 min, preferably 30 min.

[0016] Furthermore, in step S1, the magnetron sputtering is performed in an inert gas atmosphere, and the flow rate of the inert gas is 25-35 sccm, preferably 30 sccm.

[0017] Furthermore, in step S1, the magnetron sputtering uses a ZnO target material with a purity greater than 99.99%.

[0018] Furthermore, in step S2, the annealing temperature is 360-450°C, preferably 400°C; the annealing time is 180-300 min, preferably 240 min.

[0019] Furthermore, in step S3, the scanning path of the laser etching is a unidirectional line-by-line scanning in the X and Y directions, and there are several intersection points on the scanning path.

[0020] Furthermore, in step S3, the interval of the etching path is 20-30 μm, preferably 25 μm; the laser etching rate is 2000-3000 mm / s, preferably 2500 mm / s.

[0021] Furthermore, in step S3, the laser etching uses a picosecond pulse laser, and the laser output power is 0.1-0.25W.

[0022] Compared with the prior art, the present invention has the following beneficial effects:

[0023] (1) The present invention prepares a ZnO film on a planar electrode substrate by magnetron sputtering, and modifies the surface of the ZnO film by laser etching. The ZnO-based gas sensor obtained after assembly improves the adsorption effect and response speed of target gas molecules on the surface of the gas-sensitive material, and has excellent sensitivity, selectivity, cycle stability and moisture resistance.

[0024] (2) The present invention forms a regular grid structure on the surface of the ZnO film through laser etching. The grid structure includes several intersection points of etching paths, which can increase the contact area between gas molecules and the ZnO film and effectively promote the adsorption-desorption of gas molecules on the surface of the ZnO film.

[0025] (3) The present invention effectively controls the oxygen vacancy concentration on the surface of the ZnO film by changing the laser etching power, thereby improving the gas-sensing performance of the sensor to various gases.

[0026] (4) The gas sensor of the present invention has good gas-sensing properties for a variety of gases, and has better selectivity for ethanol, and can detect ethanol under high relative humidity.

[0027] (5) The preparation method of the ZnO-based gas sensor proposed in the present invention is easy to operate and has strong reproducibility, which greatly simplifies the preparation process of the gas sensor and is suitable for large-scale mass production. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 The present invention is a flow chart of the preparation method of the ZnO-based gas sensor.

[0029] Figure 2 It is a schematic structural diagram of the ZnO-based gas sensor of the present invention.

[0030] Figure 3 This is a surface SEM (Scanning electron microscope) image of a ZnO film prepared as a comparative example of the present invention.

[0031] Figure 4 This is the surface SEM image of the LE-ZnO film prepared in Example 2 of the present invention.

[0032] Figure 5 These are the test results of surface oxygen vacancy concentration of the films prepared in the comparative example and Examples 1-4 of the present invention.

[0033] Figure 6 The selectivity test graphs of the sensors prepared in the comparative example and embodiments 1-4 of the present invention to 100 ppm ammonia, xylene, methanol, acetone and ethanol.

[0034] Figure 7 This is a test graph of the response-recovery time of the sensor prepared in the comparative example and Example 2 of the present invention to 100 ppm ethanol at 320°C.

[0035] Figure 8 This is the 100-cycle response curve of the sensor prepared in Example 2 of the present invention to 100 ppm ethanol.

[0036] Fig. 9 The gas sensor prepared in Example 2 of the present invention responds to 5-500 ppm ethanol at an operating temperature of 320°C.

[0037] Fig.10 This is the cyclic response curve of the sensor prepared in the comparative example of the present invention to 100 ppm ethanol in an environment with a relative humidity of 50%-90%.

[0038] Fig.11 This is the cyclic response curve of the sensor prepared in Example 2 of the present invention to 100 ppm ethanol in an environment with a relative humidity of 50%-90%.

[0039] Description of the markings in the figure:

[0040] 1-ZnO film, 2-gold electrode sheet, 3-heating electrode, 4-alumina ceramic substrate, 5-platinum wire, 6-hexagonal base. DETAILED DESCRIPTION

[0041] The present invention is described in detail below in conjunction with the accompanying drawings and specific embodiments. This embodiment is implemented based on the technical solution of the present invention, and provides a detailed implementation method and specific operation process, but the protection scope of the present invention is not limited to the following embodiments.

[0042] Unless otherwise specified, the reagents, methods, instruments and equipment used in the present invention are conventional reagents, methods, instruments and equipment in the art. Unless otherwise specified, the reagents and materials used in the following examples are commercially available.

[0043] Among them, the electrode substrate was purchased from Suzhou Myms Sensing Technology Co., Ltd., which includes a gold electrode, a platinum wire, an alumina substrate and a heating electrode from top to bottom. The sensitive film and the gold electrode sheet are arranged on the ceramic substrate, and the heating electrode is arranged under the ceramic substrate.

[0044] Embodiment 1:

[0045] This embodiment provides a laser-modified ZnO-based gas sensor, such as Figure 1 As shown, the specific preparation method is as follows:

[0046] (1) Clean the surface of the planar electrode substrate with anhydrous ethanol to remove particle impurities on the surface of the planar electrode substrate, and place it in a drying oven to dry after cleaning.

[0047] (2) The planar electrode substrate obtained in step (1) was pasted on a ceramic sheet and fixed on the base of the chamber of a JCP200 high vacuum magnetron sputtering coating machine. A ZnO target (purity 99.99%) was used. When the vacuum degree reached 8.0×10 -4High-purity argon gas was introduced at 30 sccm at 1.5 Pa, the chamber pressure was 1.5 Pa, the sputtering power was 100 W, and the sputtering time was 30 min.

[0048] (3) The planar electrode substrate with the ZnO film attached thereto obtained in step (2) is placed in a crucible, and the crucible is placed in the furnace chamber of a SX2-1.5-12C integrated muffle furnace, and the annealing temperature is set to 400° C., the annealing time is set to 240 min, and the annealing atmosphere is air.

[0049] (4) The planar electrode substrate with ZnO thin film obtained in step (3) is placed on the movable workbench of a picosecond pulse laser system. The scanning path is unidirectional line-by-line scanning in the X and Y directions. The etching area is 9 mm × 9 mm. The laser output power is 0.1 W. The laser etching rate is 2500 mm / s. The etching path interval is 25 μm.

[0050] (5) The planar electrode substrate with the laser-modified ZnO film (hereinafter referred to as LE-ZnO film) obtained in step (4) is welded to a hexagonal base to obtain a gas sensor with LE-ZnO film as a sensitive material. The schematic diagram of the finally obtained ZnO-based gas sensor is shown in FIG. Figure 2 shown.

[0051] Embodiment 2:

[0052] This embodiment provides a laser-modified ZnO-based gas sensor, and the preparation method is basically the same as that of Embodiment 1, except that in step (4) of this embodiment, the laser output power is 0.15W.

[0053] Embodiment 3:

[0054] This embodiment provides a laser-modified ZnO-based gas sensor, and the preparation method is basically the same as that of Embodiment 1, except that in step (4) of this embodiment, the laser output power is 0.2W.

[0055] Embodiment 4:

[0056] This embodiment provides a laser-modified ZnO-based gas sensor, and the preparation method is basically the same as that of Embodiment 1, except that in step (4) of this embodiment, the laser output power is 0.25W.

[0057] Comparative Example 1:

[0058] This comparative example is a ZnO-based gas sensor that has not been subjected to laser modification treatment. The specific preparation method is as follows:

[0059] (1) Clean the surface of the planar electrode substrate with anhydrous ethanol to remove particle impurities on the surface of the planar electrode substrate, and place it in a drying oven to dry after cleaning.

[0060] (2) The planar electrode substrate obtained in step (1) was pasted on a ceramic sheet and fixed on the base of the chamber of a JCP200 high vacuum magnetron sputtering coating machine. A ZnO target (purity 99.99%) was used. When the vacuum degree reached 8.0×10 -4 High-purity argon gas was introduced at 30 sccm at 1.5 Pa, the chamber pressure was 1.5 Pa, the sputtering power was 100 W, and the sputtering time was 30 min.

[0061] (3) The planar electrode substrate with the ZnO film attached thereto obtained in step (2) is placed in a crucible, and the crucible is placed in the furnace chamber of a SX2-1.5-12C integrated muffle furnace, and the annealing temperature is set to 400° C., the annealing time is set to 240 min, and the annealing atmosphere is air.

[0062] (4) The planar electrode substrate with the ZnO thin film attached thereto obtained in step (3) is welded to a hexagonal base to obtain a gas sensor with the ZnO thin film as the sensitive material.

[0063] The present invention performs the following tests on Examples 1-4 and Comparative Example 1:

[0064] (1) Morphology characterization: The surfaces of the LE-ZnO thin film of Example 2 and the ZnO thin film of the comparative example were characterized using a scanning electron microscope (SEM).

[0065] (2) Characterization of surface oxygen vacancy concentration: The oxygen vacancy concentration of the LE-ZnO thin films prepared in Examples 1-4 and the ZnO thin film prepared in the comparative example was characterized by X-ray photoelectron spectroscopy (XPS).

[0066] (3) Ethanol response test: The performance test of the gas sensor is completed using the CGS-8 intelligent gas-sensitive analysis system (Beijing Elite Technology Co., Ltd.). Use a micro-syringe to inject ethanol liquid into the evaporating dish inside the test box and heat it to make it evaporate quickly. Under the action of the built-in fan, the ethanol gas quickly diffuses throughout the test box and fully reacts with the gas-sensitive material. The sensitivity of the tested sensor can be calculated using the formula Ra / Rg, where Ra is the resistance of the sensor in the air and Rg is the resistance of the sensor in the target gas. Repeating the above operation can complete the cyclic response test of the sensor. The response recovery time of the gas sensor is defined as the time required for the resistance change to reach 90% after the gas is introduced and exhausted.

[0067] (4) Gas selectivity test: The selectivity test of the gas sensor is completed by measuring the sensitivity of the sensor to ethanol and reference gases (ammonia, xylene, methanol and acetone).

[0068] (5) Moisture resistance test: The moisture resistance test of the gas sensor is completed by changing the relative humidity (RH) in the sealed box. The relative humidity in the sealed box is changed by a humidifier and a dehumidifier, and is detected in real time by a hygrometer. When the relative humidity in the test box reaches the target value, humidification is stopped and ethanol liquid is injected. After the test time is reached, the ethanol gas is discharged.

[0069] Figure 3 This is a surface SEM image of the ZnO film in the comparative example. It can be seen from the image that the surface of the ZnO film is relatively smooth, uniform and dense, without obvious undulations and defects. Figure 4 This is a surface SEM image of the LE-ZnO film described in Example 2. As can be seen from the figure, a regular grid structure is formed on the surface of the film after laser etching. This structure significantly increases the roughness of the film surface and effectively expands the contact area between the sensitive material and the gas molecules. In addition, the presence of the grid structure can also promote the flow of gas on the surface of the film, accelerate the adsorption and desorption process of the gas, and thus improve the response-recovery time of the sensor.

[0070] Figure 5 The O1s spectra of the ZnO film prepared in the comparative example and the LE-ZnO film prepared in Examples 1-4. The O1s spectra can be decomposed into two main peaks, namely, lattice oxygen (O L ) and oxygen vacancies (O V ). Among them, oxygen vacancies can serve as additional sites for gas molecule adsorption, thereby improving the gas-sensing performance of the sensor. From the XPS characterization results, it can be seen that the oxygen vacancies (O V ) concentration is 55.6%, which is significantly higher than other examples (Example 1: 47.8%; Example 3: 51.2%; Example 4: 49.6%; Comparative Example: 30.9%) and the comparative example. This shows that the oxygen vacancy concentration on the surface of the ZnO film can be effectively regulated by controlling the power of laser etching.

[0071] Figure 6 The selectivity test results of the sensors prepared by the comparative example and Examples 1-4 of the present invention for 100ppm ammonia, xylene, methanol, acetone and ethanol at a working temperature of 320°C. It can be seen that the sensitivity of the LE-ZnO sensor prepared by Example 2 to ethanol is 13.6, which is higher than the comparative example and other examples (Comparative example: 6.5; Example 1: 10.4; Example 3: 12.1; Example 4: 11.9). In addition, Examples 1-4 have different degrees of response improvement to the gases involved in the selectivity test, which shows that the gas sensor preparation scheme provided by the present invention is a universal method for improving gas sensitivity performance.

[0072] Figure 7This is the response recovery curve of the LE-ZnO sensor prepared in Example 2 of the present invention to 100 ppm ethanol at 320°C, and the inset is the response recovery curve of the ZnO sensor prepared in the comparative example to 100 ppm ethanol at 320°C. It can be seen from the figure that the response-recovery time of the LE-ZnO sensor is much lower than that of the ZnO sensor, indicating that laser etching helps to improve the response-recovery rate of the sensor.

[0073] Figure 8 This is the 100-cycle response recovery curve of the LE-ZnO sensor prepared in Example 2 of the present invention to 100 ppm ethanol at an operating temperature of 320°C. It can be seen that the sensitivity of the LE-ZnO sensor prepared in Example 2 has no obvious fluctuation within 100 cycles, which indicates that the LE-ZnO sensor has excellent cycle stability.

[0074] Fig. 9 This is the dynamic response curve of the LE-ZnO sensor prepared in Example 2 of the present invention to 5-500ppm ethanol. It can be seen from the figure that the sensitivity of the LE-ZnO sensor gradually increases with the increase of concentration. When the ethanol concentration exceeds 300ppm, although the sensitivity increases slowly, it still shows an obvious improvement trend, indicating that the LE-ZnO sensor prepared in Example 2 has a wider detection range and a lower detection limit.

[0075] Fig.10 The response recovery curve of the ZnO-based sensor prepared in comparative example 1 of the present invention to 100 ppm ethanol at a relative humidity of 45%-90%. Obviously, with the increase of relative humidity, the response of the ZnO sensor shows obvious attenuation (45%-90%, 6.8-1.7), and when the humidity rises to 90%, ZnO has completely lost its monitoring ability, which indicates that the ZnO-based sensor prepared in the comparative example does not have moisture resistance.

[0076] Fig.11 The response recovery curve of the LE-ZnO sensor prepared in Example 2 of the present invention to 100ppm ethanol at a relative humidity of 45%-90%. It can be seen that with the increase of humidity, the sensitivity of the LE-ZnO sensor also decays to a certain extent. When the relative humidity rises from 45% to 90%, the sensitivity of the LE-ZnO sensor to 100ppm ethanol decays from 13.6 to 7.01. Compared with the ZnO sensor of Comparative Example 1, the moisture resistance of the LE-ZnO sensor is significantly improved, which shows that laser etching can improve the moisture resistance of the sensor.

[0077] In summary, the present invention prepares a surface laser-modified ZnO film on a planar electrode substrate by combining magnetron sputtering and laser etching, and finally conveniently and quickly prepares a gas sensor with excellent gas-sensitive performance. The ZnO-based sensor prepared by the present invention has excellent gas-sensitive selectivity, outstanding stability and ideal moisture resistance for ethanol. The unique microstructure of the film surface and the increase in oxygen vacancy concentration effectively improve the sensitivity, selectivity, moisture resistance and cycle stability of the sensor of the present invention. In addition, the preparation method of the present invention is simple and reliable, has strong reproducibility, and is suitable for large-scale production.

[0078] The above description of the embodiments is to facilitate the understanding and use of the invention by those skilled in the art. It is obvious that those skilled in the art can easily make various modifications to these embodiments and apply the general principles described herein to other embodiments without creative work. Therefore, the present invention is not limited to the above embodiments, and improvements and modifications made by those skilled in the art based on the disclosure of the present invention without departing from the scope of the present invention should be within the scope of protection of the present invention.

Claims

1. A laser-modified ZnO-based gas sensor, comprising an electrode substrate and a gas-sensitive portion disposed on the electrode substrate, characterized in that: The gas sensing part is a ZnO film; the ZnO film is prepared by magnetron sputtering, and is annealed and laser etched in sequence; Among them, a regular network structure is formed on the surface of the ZnO film after laser etching.

2. A laser-modified ZnO-based gas sensor according to claim 1, characterized in that: The electrode substrate comprises a gold electrode, a platinum wire, an alumina substrate and a heating electrode in sequence from top to bottom.

3. A method for preparing a laser-modified ZnO-based gas sensor according to claim 1 or 2, characterized in that: The following steps are involved: S1: preparing ZnO thin film on the surface of electrode substrate by magnetron sputtering; S2: annealing the electrode substrate with the ZnO film attached thereto; S3: performing laser etching on the surface of the annealed ZnO film, and finally forming a regular network structure on the surface of the ZnO film; S4: subsequently assembling the electrode substrate with the laser-modified ZnO thin film attached thereto, and finally obtaining the ZnO-based gas sensor.

4. The method for preparing a laser-modified ZnO-based gas sensor according to claim 3, characterized in that: In step S1, the sputtering power of the magnetron sputtering is 80-120 W, and the sputtering time is 20-40 min.

5. The method for preparing a laser-modified ZnO-based gas sensor according to claim 3, characterized in that: In step S1, the magnetron sputtering is performed in an inert gas atmosphere, and the flow rate of the inert gas is 25-35 sccm.

6. The method for preparing a laser-modified ZnO-based gas sensor according to claim 3, characterized in that: In step S1, the magnetron sputtering uses a ZnO target material with a purity greater than 99.99%.

7. The method for preparing a laser-modified ZnO-based gas sensor according to claim 3, characterized in that: In step S2, the annealing temperature is 360-450°C, and the annealing time is 180-300 minutes.

8. The method for preparing a laser-modified ZnO-based gas sensor according to claim 3, characterized in that: In step S3, the scanning path of the laser etching is a unidirectional line-by-line scanning in the X and Y directions, and there are several intersection points on the scanning path.

9. The method for preparing a laser-modified ZnO-based gas sensor according to claim 3, characterized in that: In step S3, the interval of the etching path is 20-30 μm, and the laser etching rate is 2000-3000 mm / s.

10. The method for preparing a laser-modified ZnO-based gas sensor according to claim 3, characterized in that: In step S3, the laser etching uses a picosecond pulse laser with a laser output power of 0.1-0.25W.

Images