CuO / si hetero pn junction hydrogen sensor and preparation method thereof

Abstract

This invention relates to the field of hydrogen sensor technology, and in particular to a CuO / Si heterojunction hydrogen sensor and its fabrication method. First, an N-type Si wafer is treated with a femtosecond pulsed laser to induce a pointed, cone-shaped nanostructure on its surface. This not only increases the specific surface area of ​​the sensor, but the periodically arranged nanostructure further enhances its adsorption performance for gas molecules. Then, a continuous, highly crystalline P-type CuO nanofilm is fabricated on the surface of the N-type Si wafer using magnetron sputtering. Finally, by selecting appropriate electrode materials, the CuO / Si heterojunction hydrogen sensor is fabricated. Compared to existing technologies, the fabrication process of this invention is environmentally friendly, easy to operate and control, and the resulting PN junction (CuO / Si) hydrogen sensor can operate at room temperature, exhibiting excellent sensing performance and high sensitivity, showing promising application prospects.

Description

Technical Field

[0001] This invention relates to the field of hydrogen sensor technology, and in particular to a CuO / Si heterojunction hydrogen sensor and its preparation method. Background Technology

[0002] In modern life, technological development and progress are inseparable from the use of various energy sources, and hydrogen energy, a new energy source, is being used more and more widely in today's energy market. Compared with traditional energy sources, hydrogen energy has many advantages. First, hydrogen energy is highly efficient, and its combustion products have less damage and pollution to the environment, and it is being used in various fields along with new energy sources such as solar energy and nuclear energy. Second, processes such as water electrolysis are relatively mature, and hydrogen production is simple and reliable, which can meet the needs of large-scale use.

[0003] However, hydrogen molecules are small, making them highly susceptible to leakage, whether intentional or accidental, during production, storage, transportation, and installation. Furthermore, hydrogen is transparent, odorless, and has a relatively low ignition point; when its concentration in the air is between 4% and 75%, it will explode upon contact with an open flame. Therefore, real-time hydrogen detection is necessary in many situations to ensure safety. Clearly, hydrogen detection and real-time alarm systems are of paramount importance.

[0004] Copper oxide (CuO) is a common gas-sensitive material. When it encounters reducing gases (such as hydrogen), the O2 adsorbed on its surface reacts. - CuO reacts with the reducing gas, releasing electrons and altering the carrier concentration within it, thus changing its resistance (current). If it is then exposed to air, its resistance returns to normal. Furthermore, CuO exhibits good stability, is non-toxic, inexpensive, and easy to prepare, making it widely used in gas sensing. However, CuO alone has low sensitivity, long response and recovery times, and extremely poor selectivity. It also readily reacts with VOCs, leading to significant errors. Therefore, in gas sensing, CuO is often combined with other materials to form composite materials.

[0005] Silicon (Si) is a widely used material in the semiconductor field. It exhibits good integration, high stability, non-toxicity, and mature manufacturing processes. Different types of Si semiconductors can be obtained by doping it with different elements, allowing it to form various junctions with other semiconductors. These junctions are widely used in gas sensing, electronic circuits, and other fields. The combination of N-type Si and P-type copper oxide to form a PN junction significantly improves its sensitivity to hydrogen gas, shortens response and recovery times, and, based on the inherent properties of Si, facilitates its integration into electronic devices, thus promoting integration.

[0006] When p-type CuO and n-type Si combine to form a heterojunction hydrogen sensor, they form a PN junction. When exposed to a reducing gas (such as hydrogen), a large amount of O... - When combined with reducing gas hydrogen, it forms water and releases a large number of free electrons, causing a change in its internal space charge region. Based on this principle, a PN junction type hydrogen sensor can be fabricated.

[0007] PN junction (CuO / Si) hydrogen sensors have excellent sensing performance, high sensitivity, low response and recovery constants, and Si-based sensors are easier to integrate, showing promising application prospects.

[0008] In existing technologies, there are methods for preparing PN junction (CuO / Si) hydrogen sensors, including chemical synthesis and annealing deposition. Chemical methods mainly include oxidation and electrochemical methods. Oxidation requires copper salts as the source of copper oxide and involves organic oxidation, which is environmentally harmful, and the process of forming copper oxide is complex. Electrochemical methods require using metallic copper as an electrode, depositing a CuO thin film via electrolysis, and finally combining it with N-type Si to form a PN junction hydrogen sensor. This method is complex, costly, and difficult to scale up. Annealing deposition requires first thermally coating a Cu layer of a certain thickness onto an N-type Si substrate, then annealing it at 300°C for 4 hours to oxidize it, resulting in a heterojunction structure. The CuO formed by this method is difficult to form a film with good continuity, and Si is easily oxidized under annealing conditions, causing uneven heterojunction formation and poor sensing performance.

[0009] In view of this, the present invention is proposed. Summary of the Invention

[0010] The purpose of this invention is to provide a CuO / Si heterojunction hydrogen sensor and its preparation method. Compared with the prior art, this preparation method is green and environmentally friendly, easy to operate and control, and the prepared PN junction type (CuO / Si) hydrogen sensor can work at room temperature and has excellent sensing performance.

[0011] In a first aspect, the present invention provides a method for preparing a CuO / Si heterojunction hydrogen sensor, comprising the following steps:

[0012] First, the surface of an N-type Si wafer in distilled or deionized water is treated with a femtosecond pulsed laser. Then, the Si wafer is placed in hydrofluoric acid to remove the surface oxide layer. Finally, a P-type CuO nanofilm is sputtered onto the surface of the N-type Si wafer using magnetron sputtering to prepare a CuO / Si heterojunction hydrogen sensor.

[0013] In the fabrication method of the CuO / Si heterojunction hydrogen sensor of this invention, firstly, an N-type Si wafer in distilled water is treated with a femtosecond pulsed laser to induce a spike-like micro / nano structure on the surface of the N-type Si wafer. Then, the Si wafer is placed in hydrofluoric acid to remove the surface oxide layer, making the Si bond more tightly with the subsequently sputtered CuO. Subsequently, a continuous and highly crystalline P-type CuO nanofilm is prepared on the surface of the N-type Si wafer using magnetron sputtering. Finally, by selecting appropriate electrode materials, the CuO / Si heterojunction hydrogen sensor is fabricated. This fabrication method is suitable for large-area fabrication and meets the requirements of mass production. Furthermore, the prepared CuO / Si heterojunction hydrogen sensor can operate at room temperature and exhibits excellent power consumption and compatibility.

[0014] In a preferred embodiment of this technical solution, when using femtosecond pulsed laser processing, the N-type Si wafer is placed in distilled or deionized water, and then the surface of the N-type Si wafer is micro- or nano-processed using a femtosecond pulsed laser. This induces the formation of a pointed, cone-shaped nanoarray structure on the surface of the N-type Si wafer, which not only increases the specific surface area of ​​the sensor, but also further enhances the sensor's adsorption performance for gas molecules due to the periodic and regular arrangement of the nanostructures, thus improving sensing efficiency. Furthermore, using distilled or deionized water as the medium avoids contamination of the sample surface compared to other organic solvent media.

[0015] This invention does not impose strict limitations on the conditions for femtosecond pulsed laser processing. Studies have shown that by controlling the processing power to be 4.5mW, the scanning speed to be 1.0mm / s, and the scanning interval to be 0.02mm during femtosecond pulsed laser processing, stable cone-shaped nanostructures can be rapidly induced on the surface of N-type Si wafers to achieve mass production. The center wavelength of the femtosecond pulsed laser is 800nm, and the repetition frequency is 1kHz.

[0016] This invention preferably uses a heavily doped N-type Si wafer with high resistivity as the sensor substrate to improve the sensor's sensing performance and meet electrode requirements. Specifically, the resistivity of the N-type Si wafer is 1-3 ΩΩcm.

[0017] As a preferred embodiment of this technical solution, before processing the N-type Si wafer using magnetron sputtering, a surface treatment is performed on the N-type Si wafer to ensure that CuO and Si can bond tightly. This treatment can increase the active sites on the surface of the N-type Si wafer and remove the SiO2 oxide layer remaining on the surface due to femtosecond pulsed laser processing. Preferably, during the surface treatment, the N-type Si wafer is placed in hydrofluoric acid with a concentration of 10-15% and kept for 4-6 minutes.

[0018] In order to obtain a P-type CuO nanofilm with good crystallinity during magnetron sputtering, the present invention first sputters copper oxide on a glass slide, determines the optimal sputtering parameters by measuring XRD, and then sputters a P-type CuO nanofilm on the surface of an N-type Si substrate using a Cu target under these parameters.

[0019] Studies have shown that, during the magnetron sputtering process of this invention, the sputtering power is controlled at 90W, the substrate temperature at room temperature, the sputtering time at 20min, and the substrate vacuum degree at 1.7×10⁻⁶. -3 With a target-substrate distance of 400 mm, argon as the working gas and oxygen as the reactant gas, and an argon-to-oxygen flow ratio of 20:5, the prepared P-type CuO nanofilm exhibited the highest crystallinity and best continuity.

[0020] As a preferred embodiment of this technical solution, before the femtosecond pulsed laser treats the surface of the N-type Si wafer, the N-type Si wafer is ultrasonically cleaned to remove impurities from the surface of the N-type Si wafer; preferably, during the ultrasonic cleaning, the N-type Si wafer is placed in deionized water and ultrasonically cleaned for 10-20 seconds, and then dried with nitrogen gas.

[0021] Finally, after sputtering a P-type CuO nanofilm onto the surface of an N-type Si wafer, an Ag electrode is coated onto the surface of the P-type CuO nanofilm and wired to obtain a CuO / Si heterojunction hydrogen sensor.

[0022] Regarding the electrode, the present invention preferably uses an Ag electrode. Compared with the Au electrode, which has a larger work function, the Ag electrode is inexpensive and suitable for large-scale industrial production. Compared with the Cu electrode, it avoids the mutual influence between the Cu electrode and P-type CuO.

[0023] Secondly, the CuO / Si heterojunction hydrogen sensor prepared by the above method should also fall within the scope of protection of this invention.

[0024] The CuO / Si heterojunction hydrogen sensor and its preparation method of the present invention have at least the following technical effects:

[0025] In the fabrication method of the CuO / Si heterojunction hydrogen sensor of this invention, firstly, the N-type Si wafer is treated with a femtosecond pulsed laser to induce a pointed conical nanostructure on the surface of the N-type Si wafer. This not only increases the specific surface area of ​​the sensor, but also further enhances the adsorption performance of gas molecules due to the periodic and regular arrangement of the nanostructure. Subsequently, to further improve the bonding effect between P-type CuO and N-type Si, the oxide layer on the surface of N-type Si is removed using the industrially common method of HF cleaning and etching of SiO. Then, a continuous and highly crystalline P-type CuO nanofilm is prepared on the surface of the N-type Si wafer using magnetron sputtering. Finally, by selecting appropriate electrode materials, an Ag-CuO-Ag ohmic contact is formed on the P-type CuO surface, and an Ag-Si-Ag ohmic contact is formed on the N-type Si surface, thus obtaining the CuO / Si heterojunction hydrogen sensor. The preparation process of this invention is simple and easy to understand, and easy to operate and control, enabling large-scale industrial production. Furthermore, the prepared PN junction (CuO / Si) hydrogen sensor can operate at room temperature, has excellent sensing performance and high sensitivity, and has good application prospects. Attached Figure Description

[0026] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0027] Figure 1 This is a flowchart illustrating the fabrication method of the CuO / Si heterojunction hydrogen sensor of the present invention.

[0028] Figure 2 This is a scanning electron microscope image of an N-type Si wafer after surface treatment by a femtosecond pulsed laser according to the present invention.

[0029] Figure 3 The IV characteristic curves of the CuO / Si heterojunction hydrogen sensor prepared in this invention are shown for air environment and 3% hydrogen concentration at room temperature.

[0030] Figure 4 The image shows the XRD pattern of the P-type CuO nanofilm obtained by magnetron sputtering in this invention.

[0031] Figure 5 The response sensitivity of the CuO / Si heterojunction hydrogen sensor prepared in this invention to different concentrations of hydrogen gas is shown.

[0032] Figure 6 The IV characteristic curve is shown for the sample prepared in Comparative Example 1 of this invention.

[0033] Figure 7 The image shows the XRD pattern of the nanofilm obtained by magnetron sputtering in Comparative Example 2 of this invention.

[0034] Figure 8 The image shows the XRD pattern of the nanofilm obtained by magnetron sputtering in Comparative Example 3 of this invention.

[0035] Figure 9 The image shows the XRD pattern of the nanofilm obtained by magnetron sputtering in Comparative Example 4 of this invention. Detailed Implementation

[0036] It should be noted that the following detailed descriptions are illustrative and intended to provide further explanation of this application. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains.

[0037] It should be noted that the terminology used herein is for the purpose of describing particular implementations only and is not intended to limit the exemplary implementations according to this application. As used herein, the singular form includes the plural form unless the context clearly indicates otherwise. Furthermore, it should be understood that when the terms "comprising" and / or "including" are used in this description, they indicate the presence of features, steps, operations, devices, components, and / or combinations thereof.

[0038] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0039] Example 1

[0040] 1. Ultrasonic cleaning of Si wafers

[0041] An N-type Si wafer (10mm×10mm×0.5mm) with a resistivity of 1-3 ΩΩcm was placed in deionized water and sonicated for 15 seconds, then dried with nitrogen gas.

[0042] 2. Femtosecond pulsed laser processing

[0043] An N-type Si wafer is placed in a container, distilled water is poured into the container, and the N-type Si wafer is placed on a three-dimensional motorized translation stage of a femtosecond laser micro / nano processing platform. The laser is guided above the translation stage and focused onto the surface of the N-type Si wafer. The movement parameters of the three-dimensional motorized translation stage are set and processing begins.

[0044] Femtosecond pulsed laser processing parameters: processing power of 4.5mW, scanning speed of 1mm / s, scanning interval of 0.02mm, and processing area size of 10mm×10mm.

[0045] 3. Magnetron sputtering treatment

[0046] The sample was surface treated in hydrofluoric acid with a concentration of approximately 13.3% for 5 minutes; after treatment, a P-type CuO nanofilm was sputtered using a Cu target.

[0047] Magnetron sputtering parameters:

[0048] The power was 90W, the heating temperature was room temperature, the sputtering time was 20 minutes, and the substrate vacuum level was 1.7 × 10⁻⁶. -3 Pa, the flow rate ratio of argon to oxygen is 20:5.

[0049] 4. Electrode coating

[0050] An Ag electrode was coated on the surface of a P-type CuO nanofilm to obtain a CuO / Si heterojunction hydrogen sensor.

[0051] Compare with Example 1

[0052] A standard Si wafer was selected for femtosecond pulsed laser processing.

[0053] Everything else is basically the same as in Example 1.

[0054] Compare with Example 2

[0055] After changing the sputtering parameters, the sputtered sample was subjected to XRD measurement.

[0056] The sputtering parameters for magnetron sputtering are:

[0057] The power was 80W, the heating temperature was room temperature, the sputtering time was 30 minutes, and the substrate vacuum level was 1.7 × 10⁻⁶. -3 Pa, the flow rate ratio of argon to oxygen is 32:4.

[0058] Compare with Example 3

[0059] After changing the sputtering parameters, the sputtered sample was subjected to XRD measurement.

[0060] The sputtering parameters for magnetron sputtering are:

[0061] The power was 90W, the heating temperature was room temperature, the sputtering time was 10 minutes, and the substrate vacuum was 1.7 × 10⁻⁶. -3 Pa, the flow rate ratio of argon to oxygen is 32:4.

[0062] Compare with Example 4

[0063] After changing the sputtering parameters, the sputtered sample was subjected to XRD measurement.

[0064] The sputtering parameters for magnetron sputtering are:

[0065] The power was 75W, the heating temperature was room temperature, the sputtering time was 30 minutes, and the substrate vacuum level was 1.7 × 10⁻⁶. -3 Pa, the flow rate ratio of argon to oxygen is 32:4.

[0066] Depend on Figure 2 It is known that when an N-type Si wafer is placed in deionized water and then treated with a femtosecond pulsed laser, a periodically arranged cone-shaped nanostructure can be induced on the surface of the N-type Si wafer.

[0067] Depend on Figure 3 It can be seen that the CuO / Si heterojunction hydrogen sensor prepared in Example 1 of this invention exhibits excellent heterojunction characteristics. Specifically, before the voltage reaches 2V, the current is almost zero, and the reverse current is small, exhibiting reverse current cutoff characteristics. After the voltage reaches 2V, the current rises rapidly, exhibiting forward current conduction characteristics. Furthermore, the current change is significantly different when the hydrogen concentration in the environment is 3%. Compared to Control Example 1 (… Figure 6 Using ordinary Si wafers for femtosecond pulsed laser processing, it is impossible to obtain a PN junction type hydrogen sensor.

[0068] Combination Figure 4 and Figure 7-9 It is known that the present invention can obtain a P-type CuO nanofilm with higher crystallinity under specific magnetron sputtering parameters, which, when combined with an N-type Si wafer, can form a CuO / Si heterojunction hydrogen sensor. However, when using the magnetron sputtering parameters in Comparative Examples 2-4, the obtained nanofilm may be a mixture of copper oxide and cuprous oxide. Figure 7 It may also be a mixture of CuO and Cu. Figure 8 It is also possible to obtain a non-crystallized substance. Figure 9 This does not meet our actual needs, and it is difficult to form a high-quality heterojunction when combined with an N-type Si wafer.

[0069] Meanwhile, the present invention also analyzed the response sensitivity of the CuO / Si heterojunction hydrogen sensor prepared in Example 1 of the present invention under different hydrogen concentrations. The sensitivity values ​​are given by S = (I a -I b )×100% / I a I received a I represents the sample surface current in the absence of hydrogen gas. b This refers to the sample surface current measured in a hydrogen atmosphere. The voltage V used for all sensitivity measurement parameters is 4V. Figure 5 It can be seen that the CuO / Si heterojunction hydrogen sensor prepared in Example 1 of the present invention has high sensitivity when the hydrogen concentration is 0-3%.

[0070] In summary, the PN junction (CuO / Si) hydrogen sensor prepared by this invention can operate at room temperature without the need for high-temperature heating before sensing, which can effectively reduce energy consumption. Furthermore, it has excellent sensing performance and high sensitivity, which can meet sensing requirements and has good application prospects.

[0071] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for preparing a CuO / Si hetero-PN junction hydrogen sensor, characterized in that, Includes the following steps: First, the surface of an N-type Si wafer with a resistivity of 1-3 Ω•cm is treated using a femtosecond pulsed laser to induce a spike-shaped micro / nano structure on the surface of the N-type Si wafer. The surface oxide layer of the N-type Si wafer is removed by placing it in hydrofluoric acid. Then, using magnetron sputtering, a P-type CuO nanofilm was sputtered on the surface of an N-type Si wafer under an argon to oxygen flow ratio of 20:5 to prepare a CuO / Si heterojunction hydrogen sensor. During the femtosecond pulsed laser processing, the processing power is controlled at 4.5mW, the scanning speed is 1.0mm / s, the scanning interval is 0.02mm, and the center wavelength of the femtosecond pulsed laser is 800nm ​​with a repetition frequency of 1kHz. The magnetron sputtering process is performed at a processing power of 90 W, a substrate temperature of room temperature, a sputtering time of 20 min, a substrate vacuum degree of 1.7×10 -3 Pa, a distance between the target and the substrate of 400 mm, an argon gas as a working gas, and an oxygen gas as a reaction gas.

2. The production method according to claim 1, characterized by, When using femtosecond pulsed laser processing, an N-type Si wafer is placed in a dielectric, and the surface of the N-type Si wafer is micro- or nano-processed using a femtosecond pulsed laser. The medium is distilled water or deionized water.

3. The preparation method according to claim 1, characterized in that, Before processing the N-type Si wafer using magnetron sputtering, the N-type Si wafer undergoes surface treatment; During the surface treatment, the N-type Si wafer is placed in hydrofluoric acid with a concentration of 10-15% and kept for 4-6 minutes.

4. The method of claim 1, wherein, During the magnetron sputtering process, a Cu target is used to sputter a P-type CuO nanofilm onto the surface of an N-type Si substrate.

5. The preparation method according to claim 1, characterized in that, Before the N-type Si wafer is treated with femtosecond pulsed laser, the N-type Si wafer is ultrasonically cleaned. During the ultrasonic cleaning process, the N-type Si wafer is placed in deionized water and ultrasonicated for 10-20 seconds, and then dried with nitrogen gas.

6. The method of claim 1, wherein, After sputtering a P-type CuO nanofilm onto the surface of an N-type Si wafer, an Ag electrode is coated onto the surface of the P-type CuO nanofilm to obtain a CuO / Si heterojunction hydrogen sensor.

7. A CuO / Si hetero-PN junction hydrogen sensor, characterized in that, It is prepared by the preparation method according to any one of claims 1-6.

Images