A Ga 3+ Preparation method of doped In2O3 MEMS formaldehyde sensor

Abstract

The present invention belongs to the field of gas sensors and specifically discloses a Ga 3+ The preparation method of the doped In2O3 MEMS formaldehyde sensor comprises the following steps: (S1) mixing a soluble indium salt, a soluble gallium salt, urea, a weak acid and a strong base salt with deionized water to form a uniform mixed solution; (S2) subjecting the mixed solution to a hydrothermal reaction at a temperature of 100-200°C for 2h-48h; (S3) subjecting the hydrothermal product to an annealing heat treatment in an air atmosphere to obtain Ga 3+ Doped In2O3 material. The present invention introduces Ga into the In2O3 material. 3+ Doping and controlling Ga 3+ The doping amount does not exceed 15%. After doping, the grain size is reduced and the crystal structure changes (from hexagonal phase indium oxide to dual-phase heterojunction indium oxide). When applied to MEMS formaldehyde sensors, based on the "small size" effect of doping and the synergistic effect of dual-phase heterojunction, the indium oxide MEMS formaldehyde sensing performance can be effectively improved.

Description

Technical Field

[0001] The present invention belongs to the field of gas sensors, and more specifically, relates to a Ga 3+ Preparation method of doped In2O3 MEMS formaldehyde sensor. Background Art

[0002] Formaldehyde, a common indoor gas pollutant, is widely present in interior decoration materials such as paint, new furniture, and coatings. It seriously affects people's health and can even cause cancer. Therefore, there is a need to develop fast, portable, and highly sensitive gas sensors for detection. Semiconductor gas sensors offer advantages such as ease of integration, portability, and simple operation. However, existing formaldehyde sensors mostly use pure-phase semiconductor materials and heterojunctions of different phases, while dual-phase heterojunctions of the same material are rarely used. This has, to a certain extent, hindered the development of formaldehyde detection.

[0003] Indium oxide (In2O3) is an important wide bandgap n-type semiconductor material with important applications in the field of formaldehyde gas sensors. Heterogeneous ion doping can create more oxygen defects, improve the catalytic activity of sensitive materials, form more adsorbed oxygen, and also form a size effect to improve gas sensing performance. Ga and In are in the same main group and have similar chemical properties, and Ga 3+ Radius less than In 3+ As a special heterojunction structure, the twin phase heterojunction can regulate the Fermi level position, increase the barrier height of semiconductor materials, adjust the mobility and carrier concentration of semiconductor materials, and improve the performance of gas sensors, with superior performance compared to pure phase.

[0004] Based on this, it is necessary to develop and design a Ga 3+ The doped double-phase In2O3 MEMS formaldehyde sensor has high sensitivity, high stability and good gas sensing properties to formaldehyde, which has important reference value in the field of manufacturing formaldehyde MEMS sensors. Summary of the Invention

[0005] In view of the above defects or improvement needs of the prior art, the purpose of the present invention is to provide a Ga 3+ Preparation method of doped In2O3 MEMS formaldehyde sensor, wherein Ga is introduced into In2O3 material 3+ Doping and controlling Ga 3+The doping amount does not exceed 15% (corresponding to the mass ratio of soluble gallium salt to soluble indium salt in the hydrothermal precursor not exceeding 0.15:1). After doping, the grain size is reduced and the crystal structure changes (from hexagonal indium oxide to dual-phase heterojunction indium oxide). When further applied to MEMS formaldehyde sensors, in particular, liquid surface self-assembly film formation and film scooping can be used to prepare sensitive material films. The obtained Ga 3+ The doped In2O3 thin film is a single-layer film with uniform thickness. This synergistic effect of the doping's "small size" and the bimorph heterojunction effectively improves the performance of indium oxide MEMS formaldehyde sensing. Furthermore, the excellent uniformity of the single-layer film optimizes the sensor's repeatability and stability. This method, which produces a highly sensitive and stable formaldehyde sensor, could provide a reference for the development of new, efficient formaldehyde MEMS sensors.

[0006] To achieve the above object, according to one aspect of the present invention, a Ga 3+ The method for preparing doped In2O3 material is characterized by comprising the following steps:

[0007] (S1) mixing a soluble indium salt, a soluble gallium salt, urea, a weak acid and strong base salt, and deionized water to form a uniform mixed solution; in the mixed solution, the mass fraction of the soluble indium salt is 0.1% to 5%, the mass ratio of the weak acid and strong base salt to the soluble indium salt is 0.05% to 2%:1, the mass ratio of urea to the soluble indium salt is 0.1% to 2%:1; and the mass ratio of the soluble gallium salt to the soluble indium salt does not exceed 0.15:1;

[0008] (S2) transferring the mixed solution obtained in step (S1) into a reaction vessel, and then performing a hydrothermal reaction at a temperature of 100-200° C. for 2 h to 48 h;

[0009] (S3) annealing the hydrothermal product obtained in step (S2) in an air atmosphere to obtain Ga 3+ Doped In2O3 material.

[0010] As a further preferred embodiment of the present invention, in the step (S1), the mass ratio of the soluble gallium salt to the soluble indium salt is 0.05:1, 0.10:1 or 0.15:1; preferably 0.10:1.

[0011] As a further preferred embodiment of the present invention, in the step (S1), the soluble indium salt is indium nitrate hydrate, and the weak acid and strong base salt is sodium citrate;

[0012] For the mixed solution, the concentrations of indium nitrate hydrate, sodium citrate and urea in the mixed solution correspond to the mixed solution obtained by adding 0.1000-0.5000 g of indium nitrate hydrate, 0.1000-0.5000 g of sodium citrate and 0.0500-0.5000 g of urea to every 40 mL of deionized water.

[0013] As a further preferred embodiment of the present invention, in the step (S1), the soluble indium salt is selected from indium chloride hydrate, indium nitrate hydrate, and indium acetate hydrate;

[0014] The soluble gallium salt is selected from gallium nitrate hydrate;

[0015] The weak acid and strong base salt is selected from sodium citrate, sodium acetate, and sodium carbonate;

[0016] The stirring is magnetic stirring at room temperature.

[0017] As a further preferred embodiment of the present invention, in the step (S2), the hydrothermal reaction is specifically carried out at 160° C. for 24 hours.

[0018] As a further preferred embodiment of the present invention, in the step (S3), the annealing heat treatment is specifically carried out in an air atmosphere at a heating rate of 3°C / min and an annealing temperature of 450°C for 2 hours.

[0019] According to another aspect of the present invention, the present invention provides the above-mentioned Ga 3+ Preparation method of doped In2O3 material and its application in formaldehyde gas detection.

[0020] According to another aspect of the present invention, the present invention provides a Ga-based 3+ The MEMS formaldehyde sensor doped with In2O3 material is characterized in that the sensor is based on the above-mentioned Ga 3+ Preparation method of doped In2O3 material to produce Ga 3+ Doped In2O3 material is used as a sensitive material to sense formaldehyde.

[0021] According to another aspect of the present invention, the present invention provides the above-mentioned Ga-based 3+ A method for preparing a MEMS formaldehyde sensor doped with In2O3 material is characterized by comprising the following steps:

[0022] (1) Using the above-mentioned Ga 3+ Preparation method of doped In2O3 material to produce Ga 3+ Doping In2O3 material to obtain Ga 3+ Doped In2O3 material is used as a sensitive material, and the sensitive material is stirred and mixed with dodecanethiol and ethanol to form a dispersion;

[0023] (2) self-assembling the dispersion into a film on the surface of deionized water;

[0024] (3) using a MEMS device to pick up the thin film obtained in step (2), and drying it naturally, thereby obtaining a MEMS device with a thin film attached;

[0025] (4) Aging the MEMS device with the film obtained in step (3) to obtain a Ga-based 3+ MEMS formaldehyde sensor doped with In2O3 material.

[0026] Through the above technical solutions conceived by the present invention, compared with the prior art, the present invention introduces Ga into the In2O3 material. 3+ Doping, Ga was first discovered 3+ Phase transition after doping with In2O3, i.e., Ga 3+ Doping causes the transition from pure cubic indium oxide to cubic / hexagonal indium oxide (i.e., dual-phase indium oxide with both cubic and hexagonal phases), resulting in a heterojunction, increasing the barrier height and improving gas sensing performance. On the other hand, doping regulates the carrier concentration and mobility of the sensitive material, increasing the resistivity and thus improving the baseline resistance (R a ), according to the sensitivity definition R a / R g , thereby improving gas-sensing performance. The Ga ion-doped indium oxide used in the present invention is a dual-phase heterojunction material based on indium oxide. In addition, the sensitive layer of the formaldehyde sensor of the present invention can be a self-assembled monolayer film. The thickness of the sensitive layer can be controlled by controlling the thickness of the self-assembled film, providing a basis for studying the relationship between the thickness of the sensitive layer and gas-sensing performance.

[0027] Taking the following embodiment of this application as an example, by controlling Ga 3+ Doping In2O3 with a doping amount of 0%, 5%, 10%, and 15% to prepare a series of Ga 3+ Doping In2O3 sensitive materials, after testing, it is known that after the sensitive material is doped, not only the grain size is reduced (small-sized grain materials help improve gas-sensitive performance, corresponding to the "small size" effect), but also the crystal structure is optimized (from hexagonal phase indium oxide to dual-phase heterojunction indium oxide), forming a dual-phase heterojunction, including hexagonal phase and cubic phase, the carrier concentration and mobility of the material are also adjusted accordingly. The results of the examples below show that when Ga 3+ The MEMS sensor's formaldehyde sensing performance is optimal when the doping level is 10% Ga (corresponding to a 0.10:1 mass ratio of soluble gallium salt to soluble indium salt in the hydrothermal precursor). Furthermore, the sensor's sensitive film can be preferably formed via self-assembly technology, resulting in a single, uniformly thick film.

[0028] The Ga obtained by the present invention 3+ Doped In2O3 materials are particularly suitable for use in formaldehyde gas sensors (especially formaldehyde MEMS sensors). Corresponding formaldehyde gas tests show that Ga 3+ The MEMS sensor doped with In2O3 has excellent sensitivity and high stability, which is attributed to the synergistic effect of the doping "small size" effect and the twin phase heterojunction to improve the formaldehyde gas sensing performance, and the highly uniform self-assembled sensitive monolayer film can further optimize the repeatability and stability of the device. 3+ Doped In2O3 MEMS sensors have important application value in formaldehyde gas detection.

[0029] In summary, the present invention is through Ga 3+ Doping with In2O3 causes a phase transition in indium oxide, providing a strategy for preparing high-performance phase-change materials. Furthermore, the method for preparing a high-performance MEMS formaldehyde sensor has far-reaching application prospects in formaldehyde gas detection and provides insights for the development and preparation of other high-performance gas sensors. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 The X-ray diffraction diagram of indium oxide doped with 0% Ga, 5% Ga, 10% Ga and 15% Ga describes the phase of indium oxide before and after Ga doping, wherein 0% Ga doped indium oxide is indium oxide not doped with Ga (the same below). Figure 1 It can be seen that 0% Ga-doped indium oxide is h-In2O3 (ie, hexagonal In2O3).

[0031] Figure 2 The Raman spectra of indium oxide doped with 0% Ga, 5% Ga, 10% Ga, and 15% Ga describe the phases of indium oxide before and after Ga doping. Figure 1 The results support each other.

[0032] Figure 3 This is a scanning electron microscope image of 10% Ga indium oxide; Figure 3 (a), (b), and (c) correspond to surface SEM images at different magnifications. Figure 3 (d) corresponds to the cross-sectional SEM image of the single-layer film; Figure 3 It can be shown that the prepared doped indium oxide has good monodispersity and uniform size, and the film thickness is uniform.

[0033] Figure 4 This is a transmission electron microscope image of 10% Ga indium oxide; Figure 4 (a), (b), and (c) correspond to TEM images at different magnifications; Figure 4 The scale bars in the lower left corner of (a), (b), and (c) correspond to 200nm, 100nm, and 20nm respectively; Figure 4 This shows that the prepared doped indium oxide has good monodispersity and uniform size, and is loose and porous.

[0034] Figure 5 The dynamic characteristics of formaldehyde gas were tested on indium oxide doped with 0% Ga, 5% Ga, 10% Ga, and 15% Ga at 180°C. The figure shows that the 10% Ga-doped indium oxide sensor has excellent sensitivity, and the sensitivity is improved after doping.

[0035] Figure 6 The repeatability of 0% Ga, 5% Ga, 10% Ga, and 15% Ga-doped indium oxide was tested five times for 200 ppm formaldehyde gas at 180°C. The figure shows that the Ga-doped indium oxide sensor has excellent repeatability.

[0036] Figure 7 These are the physical picture and electron microscope picture of the formaldehyde gas sensor obtained in Example 1.

[0037] in addition, Figure 1 、 Figure 2 The h-In2O3 that appears in the graph represents hexagonal In2O3, and the c-In2O3 represents cubic In2O3. DETAILED DESCRIPTION

[0038] In order to make the objectives, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely for the purpose of explaining the present invention and are not intended to limit the present invention. In addition, the technical features involved in the various embodiments of the present invention described below may be combined with each other as long as they do not conflict with each other.

[0039] In general, Ga 3+ The preparation method of the doped In2O3 MEMS formaldehyde sensor can include the following steps: 3+ Preparation of doped In2O3 materials) and preparation of formaldehyde sensors. Taking indium nitrate hydrate as the indium source, sodium citrate as the weak acid and strong base salt, and gallium nitrate hydrate as the gallium source as an example, the preparation of sensitive materials can be carried out as follows:

[0040] S10: 0.1000-0.5000 g of In(NO3)3.4.5H2O, 0.1000-0.5000 g of sodium citrate, and 0.0500-0.5000 g of urea were sequentially added to 40 ml of deionized water to prepare a mixed solution, and magnetically stirred at room temperature for 2 hours;

[0041] S20: 0%, 5%, 10%, and 15% Ga(NO3)3.xH2O relative to the mass of In(NO3)3.4.5H2O were added to the above solution, respectively, and magnetically stirred for 2 hours to form a uniform mixed solution; wherein 0%, 5%, 10%, and 15% refer to the mass ratio of Ga(NO3)3.xH2O to In(NO3)3.4.5H2O;

[0042] S30: The stirred solution was transferred to a 50 ml autoclave and subjected to a hydrothermal synthesis reaction at 160° C. for 24 hours;

[0043] S40: washing, centrifuging and drying the product after the above reaction to obtain a precursor powder sample;

[0044] S50: annealing the powder in air atmosphere at 450° C. at a heating rate of 3° C. / min for 2 hours.

[0045] The preparation of the formaldehyde sensor can be carried out by self-assembly of the liquid surface into a film and then scooping the film. For example, the preparation can be carried out according to the following steps:

[0046] S1: The prepared sensitive material is stirred and mixed with dodecanethiol and ethanol to form a dispersion;

[0047] S2: self-assembling the above dispersion into a film on the surface of deionized water;

[0048] S3: Using a MEMS device to pick up the above-mentioned film and letting it dry naturally;

[0049] S4: Aging the MEMS device with the thin film on a 1.2V aging table for 48 hours.

[0050] The following are specific embodiments:

[0051] Example 1

[0052] 0.2500g of In(NO3)3.4.5H2O, 0.3500g of sodium citrate, and 0.075g of urea were added sequentially to 40ml of deionized water to form a mixed solution, which was then magnetically stirred at room temperature for 2 hours. To this solution, 0, 0.0125g, 0.0250g, and 0.0375g of Ga(NO3)3.xH2O were added, respectively, with the mixtures being designated as 0% Ga, 5% Ga, 10% Ga, and 15% Ga, and magnetically stirred for 2 hours to form a homogeneous mixed solution. The stirred solution was transferred to a 50ml autoclave and subjected to a hydrothermal synthesis reaction at 160°C for 24 hours. The reaction product was washed, centrifuged, and dried to obtain a precursor powder sample. The powder was then annealed at 450°C for 2 hours in an air atmosphere at a heating rate of 3°C / min to obtain the sensitive material.

[0053] The prepared sensitive material can be mixed with dodecanethiol and ethanol to form a dispersion with reference to the existing technical manufacturing process (such as Chinese patent applications 202211018680.0 and 202211018681.5). The dispersion is self-assembled into a film on the surface of deionized water. The above-mentioned film is fished out using a MEMS device and dried naturally, and the MEMS device with the film attached is aged on a 1.2V aging table for 48 hours. Gas-sensitive test operation: The formaldehyde gas sensing test of the above-prepared device is carried out at the optimal heating temperature of 180°C using the static gas distribution method.

[0054] Example 2

[0055] 0.100g of In(NO3)3.4.5H2O, 0.1000g of sodium citrate, and 0.0050g of urea were added sequentially to 40ml of deionized water to form a mixed solution, which was then magnetically stirred at room temperature for 2 hours. To this solution, 0, 0.0050g, 0.0100g, and 0.0150g of Ga(NO3)3.xH2O were added (represented as 0% Ga, 5% Ga, 10% Ga, and 15% Ga, respectively), and magnetically stirred for 2 hours to form a homogeneous mixed solution. The stirred solution was transferred to a 50ml autoclave and subjected to a hydrothermal synthesis reaction at 160°C for 24 hours. The reaction product was washed, centrifuged, and dried to obtain a precursor powder sample. This powder was then annealed at 450°C for 2 hours in an air atmosphere at a heating rate of 3°C / min to obtain the sensitive material.

[0056] The prepared sensitive material was mixed with dodecanethiol and ethanol to form a dispersion. The dispersion was then self-assembled into a film on the surface of deionized water. The film was removed using a MEMS device and allowed to air dry. The MEMS device with the film attached was then aged for 48 hours on a 1.2V aging table. Gas sensing testing was performed using the static gas distribution method at an optimal heating temperature of 180°C for formaldehyde gas sensing.

[0057] Example 3

[0058] 0.5000g of In(NO3)3.4.5H2O, 0.5000g of sodium citrate, and 0.1000g of urea were added sequentially to 40ml of deionized water to form a mixed solution, which was then magnetically stirred at room temperature for 2 hours. To this solution, 0, 0.0250g, 0.0500g, and 0.0750g of Ga(NO3)3.xH2O were added (denoted as 0% Ga, 5% Ga, 10% Ga, and 15% Ga, respectively), and magnetically stirred for 2 hours to form a homogeneous mixed solution. The stirred solution was transferred to a 50ml autoclave and subjected to a hydrothermal synthesis reaction at 160°C for 24 hours. The reaction product was washed, centrifuged, and dried to obtain a precursor powder sample. The powder was then annealed at 450°C for 2 hours in an air atmosphere at a heating rate of 3°C / min to obtain the sensitive material.

[0059] The prepared sensitive material was mixed with dodecanethiol and ethanol to form a dispersion. The dispersion was then self-assembled into a film on the surface of deionized water. The film was removed using a MEMS device and allowed to air dry. The MEMS device with the film attached was then aged for 48 hours on a 1.2V aging table. Gas sensing testing was performed using the static gas distribution method at an optimal heating temperature of 180°C for formaldehyde gas sensing.

[0060] The Ga obtained in Example 1 above 3+ The phase characterization of the doped indium oxide sample was carried out using XRD and Raman characterization techniques. The results are shown in the figure. Figure 1 and Figure 2 shown by Figure 1 and Figure 2 It can be seen that pure phase h-In2O3, 5% Ga 3+ 、10%Ga 3+ 、15%Ga 3+ After doping, a dual-phase c / h-In2O3 is obtained.

[0061] The Ga obtained in Example 1 above 3+ The microstructure of the doped indium oxide sample was characterized by SEM and TEM. Figure 3 and Figure 4 shown by Figure 3 (a), (b), and (c) show that 10% Ga 3+ The film is dense and uniform, with consistent thickness and uniform material size. Figure 3 From (d) in the figure, we can see that 10%Ga 3+ The film is a single layer film with uniform thickness; Figure 4 It can be seen that 10% Ga 3+The material size is uniform, the particle size is 300-400nm, and it has a rich pore structure, belonging to a mesoporous structure.

[0062] The Ga obtained in Example 1 above 3+ The formaldehyde sensing performance of the doped indium oxide device was tested, and the results were as follows Figure 5 and Figure 6 As shown in the figure, 10% Ga 3+ It has the best gas-sensing performance, which is more than doubled compared with the formaldehyde gas-sensing performance before doping. a / R g ) is increased from 50 to 110, optimizing the sensitivity and having good dynamic response, repeatability and stability.

[0063] The Ga obtained in Example 1 above 3+ The doped indium oxide device was tested under microscope, and the results were as follows Figure 7 shown by Figure 7 It can be seen that the sensitive material is in close contact with the micro-heating plate, and the sensitive film is a single-layer film.

[0064] It will be easily understood by those skilled in the art that the above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A Ga 3+ The preparation method of doping In2O3 material to change the crystal structure of In2O3 material is characterized in that: The following steps are involved: (S1) 0.2500 g of In(NO3)3·4.5H2O, 0.3500 g of sodium citrate, and 0.075 g of urea were sequentially added to 40 ml of deionized water and magnetically stirred; then, 0.0125 g, 0.0250 g, or 0.0375 g of Ga(NO3)3·xH2O was added thereto and magnetically stirred to form a uniform mixed solution; Alternatively: (S1) 0.100 g of In(NO3)3·4.5H2O, 0.1000 g of sodium citrate, and 0.0050 g of urea were sequentially added to 40 ml of deionized water and magnetically stirred; then, 0.0050 g, 0.0100 g, and 0.0150 g of Ga(NO3)3·xH2O were added thereto and magnetically stirred to form a uniform mixed solution; Alternatively: (S1) 0.5000 g of In(NO3)3·4.5H2O, 0.5000 g of sodium citrate, and 0.1000 g of urea were sequentially added to 40 ml of deionized water and magnetically stirred; then, 0.0250 g, 0.0500 g, and 0.0750 g of Ga(NO3)3·xH2O were added thereto and magnetically stirred to form a uniform mixed solution; (S2) transferring the mixed solution obtained in step (S1) into a reactor, and then performing a hydrothermal reaction at a temperature of 100-200° C. for 2 h to 48 h; (S3) annealing the hydrothermal product obtained in step (S2) in an air atmosphere at 450° C. for 2 hours to obtain Ga 3+ Doped In2O3 materials; compared to the Ga-free In2O3 obtained without using soluble gallium salts 3+ Doped pure hexagonal indium oxide, the Ga 3+ The doped In2O3 material contains both hexagonal In2O3 and cubic In2O3.

2. Ga as claimed in claim 1 3+ The preparation method of doping In2O3 material to change the crystal structure of In2O3 material is characterized in that: In the step (S2), the hydrothermal reaction is specifically carried out at 160° C. for 24 hours.

3. Ga as claimed in claim 1 3+ The preparation method of doping In2O3 material to change the crystal structure of In2O3 material is characterized in that: In the step (S3), the annealing heat treatment is performed at a heating rate of 3°C / min.

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