Preparation method of pn junction film-based surface acoustic wave sensor for hydrogen sulfide detection
By preparing CuO-TiO2 composite sol on SAW sensors and forming pn junction films, the problem of insufficient sensitivity and response speed when detecting H2S gases is solved, and higher frequency response and selectivity are achieved, especially in high Faster response in humidity environments.
Patent Information
- Application Number
- CN202310870722.1
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2023-07-17
- Publication Date
- 2025-01-17
AI Technical Summary
Existing surface acoustic wave (SAW) sensors have insufficient sensitivity and response speed when detecting hydrogen sulfide (H2S) gases, especially in high humidity environments.
Using a SAW sensor based on a pn junction film, the CuO-TiO2 composite sol was prepared and coated on the SAW resonator by rotary coating. Combined with high-temperature annealing and crystallization, a pn junction film of p-type CuO and n-type TiO2 was formed, and the amplifier circuit was connected. and phase shift circuit to improve the frequency response capability of the sensor.
The frequency response speed and selectivity to H2S gas is significantly improved, especially in high humidity environments, which are faster than low humidity environments, and are much higher than those of pure CuO or pure TiO2 thin film sensors.
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Abstract
Description
Technical Field
[0001] The invention belongs to the technical field of electronic gas-sensitive devices and relates to a method for preparing a pn junction thin-film-based surface acoustic wave sensor for hydrogen sulfide detection. Background Art
[0002] The development of modern industry has greatly promoted the great progress of human society. But at the same time, its byproducts (such as toxic gases) have brought serious harm to the environment. Hydrogen sulfide (H2S) is a colorless gas with a pungent odor, which often appears in industries such as sewage treatment, food processing, petroleum refining, papermaking and waste treatment. The unique toxicological mechanism of H2S makes it a terrible killer in related industries. Therefore, it is often necessary to detect H2S leaks quickly and accurately.
[0003] Many gas sensors have been developed and used to monitor H2S in real time, and sensitive materials are a very important component of the sensor. Metal oxide semiconductor (MOS) is a commonly used sensitive material for H2S gas sensors, including p-type MOS (such as CuO) and n-type MOS (such as TiO2 and WO3). The literature reports that CuO nanoneedle arrays deposited on ceramic tubes by magnetron sputtering have good sensitivity, selectivity and repeatability to H2S (Sensors and Actuators B: Chemical, 326, 2021, 128993). The literature reports that nanocrystalline TiO2 films were deposited on silicon substrates with appropriate roughness and defects using pulsed laser deposition technology, which gives H2S sensors better response and lower detection limits (Applied Surface Science, 549, 2021, 149281).
[0004] In recent years, pn junction materials used as H2S gas sensitive materials have attracted increasing attention. It is well known that there is a depletion layer at the interface of the pn junction. The internal potential field of the depletion layer increases the barrier for electron transfer, which manifests as an ultra-high resistance of the pn junction. When the pn junction is in contact with H2S gas, the barrier is lowered due to the interaction between the pn junction and the H2S gas, resulting in a decrease in resistance. This change in pn junction resistance manifests as an extremely high response of the sensor. Literature reports that stacked Cu nanorods were prepared on obliquely and vertically assembled SnO2 ceramic nanorods using a simple spray method. x(x＝1,2) O: SnO2 nanocomposite film. Thinner Cu xThe O layer is dispersed on the thicker SnO2 nanorods, forming a large number of pn junctions on the surface of the composite film, so that the sensor has good H2S sensing performance (Sensors and Actuators B: Chemical, 273, 2018, 1054-1061). Literature reports that p-type CuO nanoparticles are modified on the surface of n-type MoO3 nanorods to form a one-dimensional pn junction. The sensor based on this pn junction material exhibits excellent H2S sensing performance, and its response is 53.3 times that of the original MoO3 nanorods (Sensors and Actuators B: Chemical, 171-172, 2012, 256-262).
[0005] Resistive sensors for H2S detection based on pn junction materials have been reported in many literatures, but it is still unclear for surface acoustic wave (SAW) sensors. Since pn junction materials have a significant resistance response to H2S, and the frequency change of SAW sensors is closely related to the change of electrical properties of sensitive materials. Therefore, it can be predicted that the change of electrical properties of pn junction materials will lead to extremely high frequency response of SAW sensors. Summary of the invention
[0006] The purpose of the present invention is to propose a pn junction thin film based SAW sensor based on a pn junction sensitive material, based on the significant resistance response of a resistive sensor to H2S gas, combined with the relationship between the electrical properties of the sensitive material and the frequency change of the SAW sensor, so as to improve the sensing performance of the SAW sensor to H2S.
[0007] To achieve this goal, the following technical solutions are applied:
[0008] Prepare CuO-TiO2 composite sol, and apply it on the SAW resonator by spin coating, then anneal and crystallize at high temperature, and then connect it with the amplifier circuit and phase shift circuit to form a pn junction thin film based SAW sensor. The specific process is as follows:
[0009] 1. Preparation of CuO sol:
[0010] The copper compound is dissolved in a mixed solution of ethylene glycol methyl ether and deionized water (the volume ratio of ethylene glycol methyl ether to deionized water is 1:1, 2:1, 3:1 and 4:1), magnetically stirred evenly at room temperature, and then left to stand for 18-30 hours to obtain a CuO sol.
[0011] 2. Preparation of TiO2 sol:
[0012] The titanium compound is added to an anhydrous ethanol solution, and magnetic stirring is performed at room temperature to obtain a uniform solution. Subsequently, ammonia water is added under vigorous stirring, and the solution is allowed to stand for 18-30 hours to obtain a TiO2 sol.
[0013] 3. Preparation of CuO-TiO2 composite sol:
[0014] Take appropriate amounts of CuO sol and TiO2 sol, mix them, stir them evenly with magnetic force at room temperature, and then leave them for 18-30 hours to obtain CuO-TiO2 composite sol.
[0015] 4. Preparation of pn junction thin film based SAW sensor:
[0016] The SAW resonator was cleaned with acetone, anhydrous ethanol and deionized water, and the CuO-TiO2 composite sol was coated on the SAW resonator by spin coating. The solvent was evaporated in a drying oven and then placed in a muffle furnace for high-temperature annealing and crystallization. The resonator was then connected to the amplifier circuit and the phase shift circuit to form a pn junction thin film-based SAW sensor composite of p-type CuO and n-type TiO2.
[0017] Further, the copper compound in step 1 is one or more of Cu(NO3)2·3H2O, Cu(CH3COO)2·H2O, and CuCl2·2H2O; the titanium compound in step 2 is C 16 H 36 One or more of O4Ti and TiOSO4.
[0018] Furthermore, the concentration of CuO sol and TiO2 sol in step 1 and step 2 is 0.2-0.5 mol / L.
[0019] Furthermore, the molar ratio of Cu to Ti in the composite sol of step 3 is 0.2-5.
[0020] Furthermore, in step 4, the rotation speed of the spin coating method is 7000-9000 rpm, the duration is 20-30 s, and the cycle is repeated 3 times.
[0021] Furthermore, in step 4, the annealing temperature is 400-500° C. and the duration is 1-2 hours.
[0022] In summary, the beneficial effects of the present invention are as follows:
[0023] The p-type CuO and n-type TiO2 are compounded to form a pn junction film. Since the current response of the pn junction film to H2S gas is stronger than that of CuO film and TiO2 film, when the pn junction film is applied to the SAW sensor, the frequency response increases rapidly, much higher than that of pure CuO film and pure TiO2 film. In addition, the pn junction film-based SAW sensor has good gas selectivity and stability, and has a faster response speed in a high humidity environment than in a low humidity environment. BRIEF DESCRIPTION OF THE DRAWINGS
[0024] Figure 1XRD diffraction patterns of CuO, TiO2 and pn junction films, where CT0.5, CT1 and CT2 represent the molar ratios of Cu and Ti in the pn junction film of 0.5, 1 and 2 respectively.
[0025] Figure 2 The frequency response bar graph of SAW sensors based on CuO, TiO2 and pn junction films to 10ppm H2S gas.
[0026] Figure 3 (a) is the dynamic frequency response diagram of the pn junction thin film based SAW sensor to 10ppm NO2, NH3, H2, CO, HCl and H2S gases. Figure 3 (b) Stability test of pn junction thin film based SAW sensor to 1-100ppm H2S gas within 140 days. DETAILED DESCRIPTION
[0027] The present invention is further described below with reference to specific examples. It should be understood that the purpose of the examples is to further illustrate the content of the present invention, and they cannot be interpreted as limiting the protection scope of the present invention in any sense.
[0028] Comparative Example 1
[0029] Weigh 1.4496g of copper nitrate trihydrate (Cu(NO3)2·3H2O), dissolve it in a mixed solution of 20mL ethylene glycol methyl ether and deionized water (16mL ethylene glycol methyl ether, 4mL deionized water), stir it magnetically at room temperature for 10min, and then place it for 24h to obtain a CuO sol with a concentration of 0.3mol / L. The CuO sol is coated on the SAW resonator at a speed of 9000rpm for 30s, and the cycle is repeated 3 times. Then the solvent is evaporated in a drying oven at 300℃ and annealed at 450℃ in a muffle furnace for 2h; the resonator is connected to the amplifier circuit and the phase shift circuit to form a CuO-based SAW sensor.
[0030] Comparative Example 2
[0031] Weigh 2.0674 g of tetrabutyl titanate (C 16 H 36 O4Ti) was dissolved in 20mL of anhydrous ethanol solution, and magnetically stirred for 30min at room temperature. Then, 0.25mL of ammonia water (25-28wt%) was added under high-speed stirring, and the mixture was placed for 24h to obtain a TiO2 sol with a concentration of 0.3mol / L. The TiO2 sol was coated on a SAW resonator at a speed of 9000rpm for 30s, and the cycle was repeated 3 times. Then, the solvent was evaporated in a drying oven at 300℃, and annealed at 450℃ in a muffle furnace for 2h. The resonator was connected to an amplifier circuit and a phase shift circuit to form a TiO2-based SAW sensor.
[0032] Embodiment 1
[0033] Step 1: Weigh 1.4496 g of copper nitrate trihydrate (Cu(NO3)2·3H2O), dissolve it in a mixed solution of 20 mL of ethylene glycol methyl ether and deionized water (16 mL of ethylene glycol methyl ether, 4 mL of deionized water), stir it magnetically at room temperature for 10 min, and then leave it for 24 h to obtain a CuO sol with a concentration of 0.3 mol / L. Weigh 2.0674 g of tetrabutyl titanate (C 16 H 36 O4Ti) was dissolved in 20mL of anhydrous ethanol solution and magnetically stirred at room temperature for 30min. Then, 0.25mL of ammonia water (25-28wt%) was dropped into the solution under high-speed stirring and allowed to stand for 24h to obtain a TiO2 sol with a concentration of 0.3mol / L.
[0034] Step 2: Take the same volume of CuO sol and TiO2 sol and mix them, stir them magnetically for 30 minutes at room temperature, and place them for 24 hours to obtain a CuO-TiO2 composite sol with a molar ratio of Cu to Ti of 1:1, which is recorded as CT1 composite sol. The SAW resonator is cleaned with acetone, anhydrous ethanol and deionized water, and the CT1 composite sol is coated on the SAW resonator by spin coating, and the coating is performed 3 times, each time at a speed of 9000 rpm and a duration of 30 seconds.
[0035] Step 3: Place the SAW resonator coated with the CT1 composite sol in step 2 in a drying oven at 300°C for 10 minutes to dry the solvent, then anneal and crystallize at 450°C in a muffle furnace for 2 hours, and then connect the SAW resonator to the corresponding amplification circuit and phase shift circuit to form a CT1 thin film-based SAW sensor.
[0036] The frequency response and response time of the CT1 thin film based SAW sensor to 10ppm H2S in a 20%-90% humidity environment are shown in the following table.
[0037]
[0038] Embodiment 2
[0039] Step 1: Weigh 1.4496 g of copper nitrate trihydrate (Cu(NO3)2·3H2O), dissolve it in a mixed solution of 20 mL of ethylene glycol methyl ether and deionized water (16 mL of ethylene glycol methyl ether, 4 mL of deionized water), stir it magnetically at room temperature for 10 min, and then leave it for 24 h to obtain a CuO sol with a concentration of 0.3 mol / L. Weigh 2.0674 g of tetrabutyl titanate (C 16 H 36O4Ti) was dissolved in 20mL of anhydrous ethanol solution and magnetically stirred at room temperature for 30min. Then, 0.25mL of ammonia water (25-28wt%) was dropped into the solution under high-speed stirring and allowed to stand for 24h to obtain a TiO2 sol with a concentration of 0.3mol / L.
[0040] Step 2: According to the molar ratio of Cu:Ti=0.5, weigh the CuO sol and TiO2 sol, mix them, stir them magnetically for 30 minutes at room temperature, and place them for 24 hours. The obtained composite sol is recorded as CT0.5 composite sol. The SAW resonator is cleaned with acetone, anhydrous ethanol and deionized water, and the CT0.5 composite sol is coated on the SAW resonator by spin coating method, and the coating is carried out 3 times, each time at a speed of 9000rpm and a duration of 30s.
[0041] Step 3: Place the SAW resonator coated with the CT0.5 composite sol in a drying oven at 300°C for 10 minutes to dry the solvent, then anneal and crystallize at 450°C in a muffle furnace for 2 hours, and then connect the SAW resonator to the corresponding amplification circuit and phase shift circuit to form a CT0.5 thin film-based SAW sensor.
[0042] Embodiment 3
[0043] Step 1: Weigh 1.4496 g of copper nitrate trihydrate (Cu(NO3)2·3H2O), dissolve it in a mixed solution of 20 mL of ethylene glycol methyl ether and deionized water (16 mL of ethylene glycol methyl ether, 4 mL of deionized water), stir it magnetically at room temperature for 10 min, and then leave it for 24 h to obtain a CuO sol with a concentration of 0.3 mol / L. Weigh 2.0674 g of tetrabutyl titanate (C 16 H 36 O4Ti) was dissolved in 20mL of anhydrous ethanol solution and magnetically stirred at room temperature for 30min. Then, 0.25mL of ammonia water (25-28wt%) was dropped into the solution under high-speed stirring and allowed to stand for 24h to obtain a TiO2 sol with a concentration of 0.3mol / L.
[0044] Step 2: According to the molar ratio of Cu:Ti=2, weigh the CuO sol and TiO2 sol, mix them, stir them magnetically for 30 minutes at room temperature, and place them for 24 hours. The obtained composite sol is recorded as CT2 composite sol. The SAW resonator is cleaned with acetone, anhydrous ethanol and deionized water, and the CT2 composite sol is coated on the SAW resonator by spin coating method. The coating is carried out 3 times, each time at a speed of 9000rpm and a duration of 30s.
[0045] Step 3: Place the SAW resonator coated with the CT2 composite sol in a drying oven at 300°C for 10 minutes to dry the solvent, then anneal and crystallize at 450°C in a muffle furnace for 2 hours, and then connect the SAW resonator to the corresponding amplification circuit and phase shift circuit to form a CT2 thin film-based SAW sensor.
[0046] The above embodiments are only used to explain the present invention, and the description is relatively specific and detailed, but it cannot be understood as limiting the scope of protection of the present application. It should be pointed out that for ordinary technicians in this field, any modifications and changes made to the present invention without departing from the technical solution concept of the present application belong to the scope of protection of the present application.
Claims
1. A method for preparing a pn junction thin film-based surface acoustic wave sensor for hydrogen sulfide detection, characterized in that: The method has the following preparation steps: (1) preparing a CuO sol using a copper compound as a copper source and preparing a TiO2 sol using a titanium compound as a titanium source, and compounding the obtained CuO sol and TiO2 sol to obtain a CuO-TiO2 composite sol; (2) The composite sol is coated on a surface acoustic wave resonator, annealed and crystallized at high temperature in a muffle furnace, and then connected to a circuit to obtain a pn junction thin film-based surface acoustic wave sensor.
2. The method for preparing a pn junction thin film based surface acoustic wave sensor according to claim 1, characterized in that: The molar ratio of Cu to Ti in the composite sol of step (1) is 0.2-5.
3. The method for preparing a pn junction thin film based surface acoustic wave sensor according to claim 1, characterized in that: In step (2), the annealing temperature is 400-500 °C and the duration is 1-2 h.
4. A pn junction thin film-based surface acoustic wave sensor as prepared as claimed in claim 1 has excellent frequency response to hydrogen sulfide at room temperature, good selectivity and stability, and responds faster in a high humidity environment than in a low humidity environment.