A gas sensor with adjustable response and measurement range and a method for manufacturing the same

Abstract

This invention belongs to the field of gas sensing technology and discloses a gas sensor with adjustable responsivity and measurement range, and its fabrication method. The sensor includes a bottom conductive film, an upper conductive film, and a ceramic tube with gold electrodes. The upper conductive film is deposited on the surface of the bottom conductive film. The materials of the bottom and upper conductive films are SnO2 or ITO, and the bottom and upper conductive films are made of different materials. The bottom conductive film is deposited on a pretreated Si wafer, and then the upper conductive film is deposited on the bottom conductive film, followed by annealing and heat treatment. Test results show that when SnO2 is the bottom layer and ITO is the top layer with partial coverage, it exhibits high sensitivity response to acetone gas in the concentration range of 10 ppb-1000 ppm. When ITO is fully covered, the response saturates at 300 ppm, which is suitable for low concentration detection. Conversely, when ITO is the bottom layer and SnO2 is the top layer, the fully covered structure has a wide response range, responding in the concentration range of 10 ppb-1000 ppm, while the half-covered structure is suitable for low concentration detection, and basically saturates at 300 ppm. This invention replaces traditional circuit adjustment with physical coverage area control, enabling dynamic range switching without complex signal processing, and significantly improving the applicability of the sensor in scenarios such as medical diagnosis and environmental monitoring.

Description

Technical Field

[0001] This invention belongs to the field of gas sensing technology, specifically relating to a gas sensor with adjustable response and measurement range and its preparation method. Background Technology

[0002] Gas sensors have received widespread attention in recent years as key components in environmental monitoring, industrial process control, public safety, and medical diagnostics. Among them, metal-oxide-semiconductor (MOS) gas sensors are widely used due to their simple structure, low cost, fast response, and high sensitivity to a variety of gases. The mainstream materials include tin oxide (SnO2), zinc oxide (ZnO), tungsten oxide (WO3), and indium tin oxide (ITO).

[0003] Acetone, as an important volatile organic compound (VOC), has a concentration level closely related to the human body's metabolic state. For example, the acetone concentration in the breath of diabetic patients can be as high as 1.8 ppm, far exceeding the 0.3–0.9 ppm range in healthy individuals. The difference in acetone concentration between healthy individuals and patients with diseases can span several orders of magnitude, and sensors with a single sensitivity design cannot simultaneously meet the needs of low-concentration screening and high-concentration early warning. Therefore, developing a gas sensor capable of detecting acetone with high sensitivity and a wide range is of great value in the field of medical diagnostics. However, existing single-material sensors generally suffer from the problem of not being able to simultaneously achieve high sensitivity and a wide dynamic range: high sensitivity often means a significant response in the low-concentration region, but it is prone to rapid saturation at medium to high concentrations; while doping and modification methods used to extend the range may sacrifice the ability to detect low-concentration gases.

[0004] Existing technologies for optimizing the structure of gas sensors largely rely on material modification or complex processes. However, these methods often struggle to balance cost, process compatibility, and performance improvement. For example, while doping with precious metals can enhance gas adsorption capacity, the high cost of precious metals and the complexity of the manufacturing process make them unsuitable for large-scale applications. Electronic nose systems combining multi-sensor arrays with pattern recognition algorithms can cover a wide concentration range, but their reliance on complex hardware integration and software processing increases system size and power consumption, significantly raising deployment costs and making them unsuitable for portable or low-cost applications. Most importantly, existing technologies cannot achieve active control of response characteristics through the sensor's structural design; that is, they cannot flexibly switch between high-sensitivity, low-range and wide-range, medium-sensitivity modes on a single device. Summary of the Invention

[0005] To overcome the problems in existing technologies, such as the inability to simultaneously achieve sensitivity and dynamic measurement range, reliance on external systems for performance adaptation, and lack of active control capabilities in structural design, the purpose of this invention is to provide a gas sensor with adjustable responsivity and measurement range, and its preparation method. This method can achieve dynamic adaptation of the response range and sensitivity to the target gas.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows: A gas sensor with adjustable responsivity and measurement range includes a bottom conductive film, an upper conductive film, and a ceramic tube with gold electrodes; the upper conductive film is deposited on the surface of the bottom conductive film, and the bottom and upper conductive films are made of SnO2 or ITO, with the bottom and upper conductive films being made of different materials.

[0007] Furthermore, the underlying conductive film completely covers the gold electrode.

[0008] Furthermore, the bottom conductive film is made of SnO2, and the top conductive film is made of ITO; or The bottom conductive film is made of ITO, and the top conductive film is made of SnO2.

[0009] A method for fabricating a gas sensor with adjustable responsivity and measurement range includes the following steps: depositing a bottom conductive film on a pretreated Si wafer using radio frequency magnetron sputtering, then depositing an upper conductive film on the bottom conductive film, then annealing, and finally heat treatment to obtain a gas sensor with adjustable responsivity and measurement range.

[0010] Furthermore, the conditions for depositing the underlying conductive film are as follows: sputtering power of 100W-300W, heating temperature of 200℃-400℃, working gas flow rate of 20-40sccm Ar, deposition pressure of 1Pa-3Pa, and deposition time of 10min.

[0011] Furthermore, the conditions for depositing the upper conductive film are as follows: sputtering power of 100W-300W, heating temperature of 200℃-400℃, working gas flow rate of 20-40sccm Ar, deposition pressure of 1Pa-3Pa, and deposition time of 7min.

[0012] Furthermore, the annealing conditions are: annealing temperature of 300℃-500℃ and annealing time of 20S-40S.

[0013] Furthermore, the heat treatment conditions are as follows: apply a heating voltage to the annealed sample, starting from 2-2.6V and gradually increasing to 5-5.3V, and heat at 5V until the voltage across the sample stabilizes.

[0014] Furthermore, the heating time is 30-70 minutes.

[0015] Furthermore, the Si wafer is cut into substrates of the required size using a laser scribing method, and then immersed in a mixed solution of sulfuric acid and hydrogen peroxide at 100~150 ℃ for 10~30 minutes, followed by ultrasonic cleaning with acetone and deionized water. The mixed solution of sulfuric acid and hydrogen peroxide is prepared by mixing 98% sulfuric acid and 20% hydrogen peroxide solution in a volume ratio of 3:1.

[0016] Compared with the prior art, the present invention has the following beneficial effects: (1) Simple process and low cost: The radio frequency magnetron sputtering method is adopted, the preparation process is standardized and easy to scale up, and it is highly compatible with existing semiconductor processes. Compared with the complex processes of traditional precious metal doping and heterostructure construction, this invention not only significantly reduces material costs, but also improves process consistency, making the sensor more suitable for low-cost, large-scale deployment scenarios.

[0017] (2) Flexible adaptation of sensitivity and dynamic range: By adjusting the coverage area of ​​the upper conductive film on the bottom conductive film, the sensor response characteristics can be actively adjusted and the measurement range can be dynamically adjusted, so that the same sensor can exhibit high sensitivity response or be suitable for low concentration detection in a wide concentration range of 10ppb-1000ppm without the need for complex circuit compensation or multi-sensor array, which significantly improves the adaptability of the sensor in different application scenarios.

[0018] (3) Structural design enhances stability and consistency: By combining two layers of thin film materials (such as SnO2 / ITO) and using annealing processes, the crystallinity and interfacial bonding strength of the thin film are optimized, ensuring that the sensor has high response consistency and long-term stability under standard testing conditions, and avoiding performance fluctuations caused by thin film defects. Compared with traditional technical solutions that rely on single materials, noble metal doping, or multi-sensor arrays, this invention significantly improves sensitivity stability, dynamic range adaptability, and environmental adaptability by controlling the material combination and coverage method of the two-layer conductive thin film, providing a low-cost, high-reliability gas sensing solution for medical diagnosis, industrial safety, and other scenarios.

[0019] Furthermore, this invention uses a ceramic tube substrate as the base, and sequentially deposits a bottom layer and an upper layer of conductive thin films on the substrate surface using a magnetron sputtering method. The bottom layer conductive thin film material is SnO2 or ITO, and the upper layer material is SnO2 or ITO. For example, when the bottom layer is SnO2 and the upper layer is ITO with partial coverage, the sensor exhibits a high sensitivity response to acetone gas in the concentration range of 10 ppb-1000 ppm; while when the bottom layer is ITO and the upper layer is SnO2 with partial coverage, the response tends to saturate at 300 ppm, which is suitable for low concentration detection. Attached Figure Description

[0020] Figure 1 This is a schematic diagram of the sensor structure described in this invention; wherein, (a) is a plan view and (b) is an exploded view; In the figure, 1-upper conductive film, 2-lower conductive film, 3-gold electrode, 4-heating wire, 5-ceramic tube; Figure 2 The gas response curve of the sensor in Comparative Example 1 is shown. Figure 3 The complete gas response curve of the sensor in Example 1; Figure 4 The response curve of the sensor in Example 1 at extremely low gas concentrations; Figure 5 The gas response curve of the sensor in Example 2; Figure 6 The complete gas response curve of the sensor in Example 3; Figure 7 The response curve of the sensor in Example 3 at extremely low gas concentrations; Figure 8 The image shows the gas response curve of the sensor in Example 4. Detailed Implementation

[0021] To facilitate understanding of the present invention, a more complete description will be given below with reference to the accompanying drawings. Preferred embodiments of the invention are shown in the drawings. However, the invention can be implemented in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided to provide a thorough and complete understanding of the disclosure of the invention.

[0022] Furthermore, elements in this invention are referred to as being "fixed to" or "set on" another element, which may be directly on the other element or may also include an intervening element. When an element is considered to be "connected" to another element, it may be directly connected to the other element or may also include an intervening element. The terms "vertical," "horizontal," "left," "right," and similar expressions used herein are for illustrative purposes only and do not represent the only possible implementation.

[0023] See Figure 1In (a) and (b), a gas sensor with adjustable responsivity and measurement range according to the present invention includes a base, a ceramic tube 5, a bottom conductive film 2, and an upper conductive film 1. The ceramic tube 5 serves as a substrate. Both the bottom conductive film 2 and the upper conductive film 1 are SnO2 or ITO, and the materials of the bottom conductive film 2 and the upper conductive film 1 are different. The upper conductive film 1 is deposited on the surface of the bottom conductive film 2 in a fully or partially covered manner. The ceramic tube 5 has a gold electrode 3. The ceramic tube 5 is manufactured by Zhengzhou Weisheng Electronic Technology Co., Ltd., and a heating wire 4 is disposed inside the ceramic tube 5.

[0024] The method for fabricating a gas sensor with adjustable responsivity and measurement range of the present invention achieves switchability of responsivity and measurement range through active control of the double-layer conductive film structure and coverage area, and achieves dynamic adaptation of the response range and sensitivity to the target gas by actively controlling the coverage of the upper conductive film. Specifically, the method includes the following steps: S1. Substrate pretreatment: A Si wafer of appropriate size is cut as the substrate. After removing surface contaminants by chemical solution, ultrasonic cleaning with deionized water, and drying the surface with high-purity nitrogen, the substrate pretreatment is completed, and the substrate is obtained for subsequent material performance characterization.

[0025] In step S1, the wafer is cut into substrates of the required size using laser scribing technology; the substrates are then immersed in a "311" solution (a mixture of 98% sulfuric acid solution and 20% hydrogen peroxide solution at a volume ratio of 3:1) at 100-150 °C for 10-30 minutes, and then ultrasonically cleaned with acetone and deionized water for 10-20 minutes respectively to obtain the substrates.

[0026] S2. Conductive Thin Film Deposition: A thin film is deposited on the ceramic tube 5 using an RF magnetron sputtering system. By controlling the sputtering power (100W-300W), heating temperature (200℃-400℃), and working gas flow rate (20-40 sccm Ar), and after pre-sputtering cleaning at a certain pressure (3.5Pa-6.5Pa), the deposition pressure is adjusted to (1Pa-3Pa) for thin film growth, resulting in a uniform conductive thin film deposited on the surface of the ceramic tube. During film deposition, it is necessary to ensure that the underlying conductive thin film 2 completely covers the gold electrode 3.

[0027] In step S2, if it is a double-layer conductive film, the bottom conductive film is sputtered first. If it is SnO2, it is sputtered for 10 minutes in an argon atmosphere. Then the sample is taken out, and its surface is partially covered for sputtering of the top conductive film. The material is ITO, and it is sputtered for 7 minutes in an argon atmosphere to obtain a semi-covered structure.

[0028] If the upper conductive film is a full cover, then there is no need to cover it, and the upper conductive film material can be sputtered directly.

[0029] The same applies when ITO is the underlying conductive thin film material.

[0030] S3. Rapid annealing: The ceramic tube with the deposited conductive thin film prepared in step S2 is placed in a rapid annealing furnace for annealing. The annealing temperature is controlled at 300℃-500℃ and the annealing time is 20s-40s. This improves the crystallization quality of the thin film, ensures good interface contact, and significantly enhances the stability of the sensor.

[0031] S4. Device Fabrication: The sample from step S3 is soldered onto the substrate and heated. The sample is placed in the test circuit, and a heating voltage is applied, starting from approximately 2-2.6V and gradually increasing to approximately 5-5.3V. Heating is then maintained at the highest voltage for a period of time, typically 30-70 minutes, until the voltage across the sample stabilizes. This yields a gas sensor with adjustable responsivity and measurement range. After a period of settling, testing can begin.

[0032] The tests were conducted using the WS-30A gas-sensitive element tester manufactured by Zhengzhou Weisheng Electronic Technology Co., Ltd. This instrument is equipped with an 18-liter sealed acrylic glass test chamber, a precision evaporation stage, a gas circulation fan, and a high-precision electrical signal acquisition system. The test environment was set to a constant temperature of 25±1℃ and humidity of 45% RH. The test circuit voltage was fixed at 5V, and the heating wire voltage was 4.28V, corresponding to an operating temperature of 280℃ (the heating voltage was adjusted if temperature testing was required). The test circuit is shown in the figure below.

[0033] The heating power supply V operates through a gas-sensitive element. h Test circuit power supply V C The voltage V across the load resistor R1 connected in series with the gas-sensitive element is measured. out This is used to reflect the characteristics of the gas-sensitive element. The main test steps are as follows: 1) First, place the welded sensor into the tester and let it stand in the air for 10-15 minutes to heat until the output voltage is stable.

[0034] 2) Then close the lid and introduce a gas of a specific concentration into the sealed test system, or place a liquid of a specific concentration into the gas chamber to evaporate. Observe the readings; if a reaction occurs, maintain this state for 60 seconds.

[0035] 3) After the reaction is complete, open the test chamber and wait until the reading returns to the initial value before stopping the test and recording the data. Purge the test cover for 10 minutes to remove residual gas, then begin the next set of tests.

[0036] 4) Once a certain type of gas has been tested, stop testing for one day and start the next test 24 hours later to prevent the sensor performance from deteriorating due to prolonged operation.

[0037] The following are specific examples.

[0038] Example 1 S1. Substrate Pretreatment: A 2-inch double-sided polished Si wafer was selected and cut into 3 cm × 1 cm substrate wafers using a laser dicing machine. The substrate was immersed in a 110 ℃ "311" solution for 30 minutes, followed by ultrasonic cleaning in acetone and deionized water for 15 minutes each to thoroughly remove surface organic matter and particulate contaminants. After cleaning, the substrate surface was dried with high-purity nitrogen gas, completing the substrate pretreatment.

[0039] S2. Conductive Thin Film Deposition: An RF magnetron sputtering system was used to deposit a SnO2 thin film as the underlying conductive film on a ceramic tube. Ceramic tubes with gold electrodes 3 were sequentially placed in a tray, and the substrate was placed on top. The sputtering power was set to 200 W, and the heating temperature to 300 °C. High-purity argon (25 sccm) was used as the working gas, and the SnO2 target was ignited at a pressure of 4.5 Pa. Pre-sputtering was performed for 5 minutes to clean the target surface and stabilize the plasma. The chamber working pressure was then stabilized to 1.5 Pa, and deposition continued for 5 minutes to form a uniform and dense SnO2 thin film. The sample was then removed, and half of the ceramic tube surface was covered before ITO film sputtering. The substrate was treated similarly, with the coverage area carefully controlled during the covering process, which could be calibrated under a light microscope. The sputtering power was set to 200 W, the heating temperature to 300 ℃, and the argon concentration to 25 sccm. The gas was ignited at a pressure of 3.8 Pa and pre-sputtered for 3 minutes. Then the pressure was stabilized to 2 Pa and sputtered for 4 minutes to form the upper conductive film.

[0040] S3. Rapid annealing: Place the ceramic tube prepared in step S2 into a rapid annealing furnace for annealing at a controlled temperature of 400℃ for 30 seconds, followed by holding at that temperature for 1 minute. Remove the tube when it has cooled to room temperature.

[0041] S4. Device Fabrication: The sample from step S3 is soldered onto the substrate and then heated. The sample is placed in the test circuit, and a heating voltage is applied, slowly increasing from 2.6V to 5.3V. Once the voltage across its terminals stabilizes, it is heated at 5.3V for 1 hour to ensure complete resistance stabilization, meaning the voltage remains constant when no gas test is performed. This yields a gas sensor with adjustable responsivity and measurement range. After allowing the gas sensor to cool for 12 hours, gas response testing can be performed.

[0042] Example 2 S1. Same as Example 1; S2. Conductive Thin Film Deposition: An RF magnetron sputtering system was used to deposit a SnO2 thin film as the underlayer on a ceramic tube. The ceramic tubes were sequentially placed in a tray, and the substrate was placed on top. The sputtering power was set to 200 W, and the heating temperature to 300 °C. High-purity argon (25 sccm) was used as the working gas, and the SnO2 target was ignited at a pressure of 4.5 Pa. Pre-sputtering was performed for 5 minutes to clean the target surface and stabilize the plasma. The chamber pressure was then stabilized to 1.5 Pa, and deposition continued for 5 minutes to form a uniform and dense SnO2 thin film. The sample was then removed, and an ITO thin film was sputtered onto the surface of the ceramic tube. The substrate underwent the same treatment, and when shielding, the area covered was controlled to be as small as possible, which could be calibrated under a light microscope. The sputtering power was set to 200 W, the heating temperature to 300 °C, and the argon concentration to 25 sccm. Ignition was performed at a pressure of 3.8 Pa, and pre-sputtering was performed for 3 minutes. The pressure was then stabilized to 2 Pa, and sputtering continued for 4 minutes.

[0043] S3. Same as Example 1; S4. Same as Example 1.

[0044] Example 3 S1. Same as Example 1; S2. An ITO thin film was deposited on a ceramic tube as the underlayer using an RF magnetron sputtering system. The ceramic tubes were sequentially placed in a tray, and the substrate was placed on top. The sputtering power was set to 200 W, and the heating temperature to 300 °C. High-purity argon (25 sccm) was used as the working gas, and the ITO target was ignited at a pressure of 3.8 Pa. Pre-sputtering was performed for 3 minutes to clean the target surface and stabilize the plasma. The chamber pressure was then stabilized to 2 Pa, and deposition continued for 4 minutes, resulting in a uniform and dense ITO thin film. The sample was then removed, and half of the ceramic tube surface was covered before sputtering a SnO2 thin film. The substrate underwent the same treatment. When covering the substrate, the area covered was controlled to be as small as possible, and calibration could be performed under an optical microscope. The sputtering power was set to 200 W, the heating temperature to 300 °C, and the argon concentration to 25 sccm. Ignition was performed at a pressure of 4.5 Pa, and pre-sputtering was performed for 5 minutes. The pressure was then stabilized to 1.5 Pa, and sputtering continued for another 5 minutes.

[0045] S3. Same as Example 1; S4. Same as Example 1.

[0046] Example 4 S1. Same as Example 3; S2. After ITO sputtering, the sample is not shielded; subsequent sputtering operations (i.e., SnO2 film sputtering) are performed directly. The specific process is as follows: An ITO film is deposited on a ceramic tube as the substrate using an RF magnetron sputtering system. The ceramic tubes are placed sequentially in a tray, and the substrate is placed on top. The sputtering power is set to 200 W, and the heating temperature to 300 °C. High-purity argon (25 sccm) is used as the working gas, and the ITO target is ignited at a pressure of 3.8 Pa for 3 minutes to clean the target surface and stabilize the plasma. The chamber working pressure is then stabilized to 2 Pa, and deposition continues for 4 minutes to achieve a uniform and dense ITO film. The sample is then removed, and SnO2 film sputtering is performed. The sputtering power is set to 200 W, the heating temperature to 300 °C, and the argon concentration to 25 sccm. Ignition is performed at a pressure of 4.5 Pa, and pre-sputtering is carried out for 5 minutes. The pressure is then stabilized to 1.5 Pa, and sputtering continues for another 5 minutes.

[0047] S3. Same as Example 3; S4. Same as Example 3.

[0048] In Example 4, the sputtering parameters are the same as in Example 3. The difference is that after ITO sputtering, the sample is not shielded, and subsequent sputtering operations, i.e., sputtering of SnO2 thin film, are performed directly.

[0049] Example 5 S1. Substrate Pretreatment: A 2-inch double-sided polished Si wafer was selected and cut into 3 cm × 1 cm substrate wafers using a laser dicing machine. The substrate was immersed in a 150 ℃ "311" solution for 10 minutes, followed by ultrasonic cleaning in acetone and deionized water for 20 minutes each to thoroughly remove surface organic matter and particulate contaminants. After cleaning, the substrate surface was dried with high-purity nitrogen gas, completing the substrate pretreatment.

[0050] S2. Conductive Thin Film Deposition: An RF magnetron sputtering system was used to deposit a SnO2 thin film as the underlying conductive film on a ceramic tube. Ceramic tubes with gold electrodes 3 were sequentially placed in a tray, and the substrate was placed on top. The sputtering power was set to 100 W, and the heating temperature to 300 °C. High-purity argon (20 sccm) was used as the working gas, and the SnO2 target was ignited at a pressure of 6.5 Pa. Pre-sputtering was performed for 5 minutes to clean the target surface and stabilize the plasma. The chamber working pressure was then stabilized to 1.0 Pa, and deposition continued for 5 minutes to form a uniform and dense SnO2 thin film. The sample was then removed, and half of the ceramic tube surface was covered before ITO film sputtering. The substrate underwent the same treatment. When covering the ceramic tube, the area covered was controlled as much as possible, and calibration could be performed under a light microscope. The sputtering power was set to 100 W, the heating temperature to 300 ℃, and the argon concentration to 20 sccm. The gas was ignited at a pressure of 3.8 Pa and pre-sputtered for 3 minutes. Then the pressure was stabilized to 2 Pa and sputtered for 4 minutes to form the upper conductive film.

[0051] S3. Rapid annealing: Place the ceramic tube prepared in step S2 into a rapid annealing furnace for annealing at 300℃ for 40 seconds, followed by holding at that temperature for 1 minute. Remove it after cooling to room temperature.

[0052] S4. Device Fabrication: The sample from step S3 is soldered onto the substrate and heated. The sample is placed in the test circuit, and a heating voltage is applied, slowly increasing from 2.0V to 5.3V. Once the voltage across its terminals stabilizes, it is heated at 5.3V for 30 minutes to ensure complete resistance stabilization, meaning the voltage across its terminals remains constant when no gas testing is performed. This yields a gas sensor with adjustable responsivity and measurement range.

[0053] Example 6 S1. Substrate Pretreatment: A 2-inch double-sided polished Si wafer was selected and cut into 3 cm × 1 cm substrate wafers using a laser dicing machine. The substrate was immersed in a 130 ℃ "311" solution for 20 minutes, followed by ultrasonic cleaning in acetone and deionized water for 15 minutes each to thoroughly remove surface organic matter and particulate contaminants. After cleaning, the substrate surface was dried with high-purity nitrogen gas, completing the substrate pretreatment.

[0054] S2. Conductive Thin Film Deposition: An RF magnetron sputtering system was used to deposit a SnO2 thin film as the underlying conductive film on a ceramic tube. Ceramic tubes with gold electrodes 3 were sequentially placed in a tray, and the substrate was placed on top. The sputtering power was set to 300 W, and the heating temperature to 200 °C. High-purity argon (40 sccm) was used as the working gas, and the SnO2 target was ignited at a pressure of 5.0 Pa. Pre-sputtering was performed for 5 minutes to clean the target surface and stabilize the plasma. The chamber working pressure was then stabilized to 3.0 Pa, and deposition continued for 5 minutes to form a uniform and dense SnO2 thin film. The sample was then removed, and half of the ceramic tube surface was covered before ITO film sputtering. The substrate underwent the same treatment. When covering the ceramic tube, the area covered was controlled as much as possible, and calibration could be performed under an optical microscope. The sputtering power was set to 300 W, the heating temperature to 200 ℃, and the argon concentration to 40 sccm. The gas was ignited at a pressure of 3.8 Pa and pre-sputtered for 3 minutes. Then the pressure was stabilized to 2 Pa and sputtered for 4 minutes to form the upper conductive film.

[0055] S3. Rapid annealing: Place the ceramic tube prepared in step S2 into a rapid annealing furnace for annealing at a controlled temperature of 500℃ for 30 seconds, followed by holding at that temperature for 1 minute. Remove the tube when it has cooled to room temperature.

[0056] S4. Device Fabrication: The sample from step S3 is soldered onto the substrate and heated. The sample is placed in the test circuit, and a heating voltage is applied, slowly increasing from 2.3V to 5.1V. Once the voltage across its terminals stabilizes, it is then heated at 5.1V for 70 minutes to ensure complete resistance stabilization, meaning the voltage across its terminals remains constant when no gas testing is performed. This yields a gas sensor with adjustable responsivity and measurement range.

[0057] Example 7 S1. Substrate Pretreatment: A 2-inch double-sided polished Si wafer was selected and cut into 3 cm × 1 cm substrate wafers using a laser dicing machine. The substrate was immersed in a 100 ℃ "311" solution for 30 minutes, followed by ultrasonic cleaning in acetone and deionized water for 10 minutes each to thoroughly remove surface organic matter and particulate contaminants. After cleaning, the substrate surface was dried with high-purity nitrogen gas, completing the substrate pretreatment.

[0058] S2. Conductive Thin Film Deposition: An RF magnetron sputtering system was used to deposit a SnO2 thin film as the underlying conductive film on a ceramic tube. Ceramic tubes with gold electrodes 3 were sequentially placed in a tray, and the substrate was placed on top. The sputtering power was set to 200 W, and the heating temperature to 400 °C. High-purity argon (30 sccm) was used as the working gas, and the SnO2 target was ignited at a pressure of 3.5 Pa. Pre-sputtering was performed for 5 minutes to clean the target surface and stabilize the plasma. The chamber working pressure was then stabilized to 1.5 Pa, and deposition continued for 5 minutes to form a uniform and dense SnO2 thin film. The sample was then removed, and half of the ceramic tube surface was covered before ITO film sputtering. The substrate underwent the same treatment. When covering the ceramic tube, the area covered was controlled as much as possible, and calibration could be performed under a light microscope. The sputtering power was set to 200 W, the heating temperature to 400 ℃, and the argon concentration to 30 sccm. The gas was ignited at a pressure of 3.8 Pa and pre-sputtered for 3 minutes. Then the pressure was stabilized to 2 Pa and sputtered for 4 minutes to form the upper conductive film.

[0059] S3. Rapid annealing: Place the ceramic tube prepared in step S2 into a rapid annealing furnace for annealing at a controlled temperature of 400℃ for 20 seconds, followed by holding at that temperature for 1 minute. Remove the tube when it has cooled to room temperature.

[0060] S4. Device Fabrication: The sample from step S3 is soldered onto the substrate and heated. The sample is placed in the test circuit, and a heating voltage is applied, slowly increasing from 2.5V to 5.0V. Once the voltage across its terminals stabilizes, it is heated at 5.0V for 50 minutes to ensure complete resistance stabilization, meaning the voltage across its terminals remains constant when no gas testing is performed. This yields a gas sensor with adjustable responsivity and measurement range.

[0061] Comparative Example 1 S1. Same as Example 1; S2. Single-layer deposition was performed during the coating process. An RF magnetron sputtering system was used to deposit a single-layer ITO film as a conductive film on a ceramic tube. The ceramic tubes were sequentially placed in a tray, and the substrate was placed on top. The sputtering power was set to 200 W, and the heating temperature to 300 °C. High-purity argon (25 sccm) was used as the working gas, and the ITO target was ignited at a pressure of 3.8 Pa. Pre-sputtering was performed for 3 minutes to clean the target surface and stabilize the plasma. Subsequently, the chamber working pressure was stabilized to 2 Pa, and deposition continued for 4 minutes, resulting in a uniform and dense ITO film.

[0062] S3. Same as Example 1; S4. Same as Example 1.

[0063] The devices prepared in the examples and comparative examples were subjected to the following experiments: The response test was conducted on a dedicated gas testing platform (Zhengzhou Weisheng Electronic Technology Co., Ltd.). Acetone liquid of the required concentration was introduced and heated to evaporate. After the sensor reading stabilized, the sealed space was opened to release the gas. This process was repeated multiple times to obtain the sensor's response curve.

[0064] This invention explores the impact of film coverage on device performance by comparing the responses of single-layer and double-layer thin films, as well as different coverage conditions of double-layer conductive films. The responses show that, regardless of the structure, the double-layer conductive film's response to acetone gas is stronger than that of the single-layer structure, indicating that the double-layer structure can effectively enhance the device's response to gases.

[0065] Figure 3 and Figure 4 This paper presents a bilayer thin-film structure with SnO2 as the bottom layer and ITO as the top layer, where the top ITO layer is partially covered. In this configuration, ITO only covers half of the SnO2 surface, allowing gas molecules to directly contact the SnO2 in the uncovered area while also indirectly diffusing through the covered ITO layer. This structure significantly increases the effective contact area between the gas and SnO2, resulting in a strong response across a wide concentration range of 10 ppb–1000 ppm. The response intensity continuously increases with increasing concentration, without significant saturation. At 1000 ppm, the response can reach as high as 50, compared to ITO's 4.1 response, representing an improvement of over 1000%. Even at an extremely low concentration of 10 ppb, a response of 1.3 is observed.

[0066] Figure 5 This demonstrates a double-layer thin-film structure with SnO2 as the bottom layer and ITO as the top layer, where the top ITO layer forms a fully covered sensor. In this configuration, the ITO film completely covers the SnO2 surface, forming a continuous conductive layer. Gas molecules must diffuse through the ITO layer to the SnO2 sensitive layer. Due to the high oxygen permeability of ITO, the fully covered structure allows gas molecules to uniformly permeate to the bottom SnO2 layer. However, due to the shielding effect of the top ITO layer, the contact area between the gas and SnO2 is limited, causing the sensor's response to acetone gas to tend to saturate at 300 ppm, with the response approaching 7, compared to the ITO layer in Comparative Example 2. Figure 2 The response rate is 3.5 times that of the standard, with an increase of 100%, and the increase is slow at higher concentrations. This characteristic indicates that the full-coverage structure is more suitable for detection in the low to medium concentration range, and can be used as a detection alarm at high concentrations.

[0067] Figure 6 and Figure 7This study demonstrates a bilayer thin-film structure with ITO as the bottom layer and SnO2 as the top layer, where the top SnO2 layer forms a semi-covered sensor. In acetone gas adsorption tests, the sample's response increased with increasing concentration, but the trend was clearly limited. At extremely low concentrations, there was a relatively weak signal, approximately 1.1 at 100 ppb. The signal became noticeable from 1 ppm, but the response growth slowed significantly at around 100 ppm. At 300 ppm, the response value was only slightly higher than 100 ppm and almost stopped increasing, approximately 4.3, exhibiting a clear response saturation phenomenon. At 1000 ppm, the response was not significantly different from that at 300 ppm. The overall response curve flattened in the high-concentration region, with a narrow dynamic range, indicating that the sensor in this structure was approaching its detection limit. Compared to the ITO monolayer structure, the overall response improvement was relatively small, making it suitable for detection at low to medium concentrations. At high concentrations, it could be used as a detection alarm.

[0068] Figure 8 This study demonstrates a bilayer thin-film structure with ITO as the bottom layer and SnO2 as the top layer, where the top SnO2 layer provides full coverage of the sensor. In contrast, this sample exhibits a continuously enhancing response across the entire test concentration range without any stagnation. At a high concentration of 1000 ppm, the response value continues to rise steadily without any signs of saturation, reaching a response of 10, an improvement of over 100% compared to a single ITO layer. A clear response is also maintained at low concentrations, with a response of 1.6 at 10 ppb, making it suitable for low-concentration environments and also applicable for wide-range detection.

[0069] Other sensors in this invention include a base, a ceramic tube substrate, a bottom conductive film, and an upper conductive film. Both the bottom and upper conductive films are made of SnO2 or ITO, and the upper conductive film is deposited on the surface of the bottom conductive film in a fully or partially covered manner. The preparation method includes: sequentially depositing the bottom and upper conductive films on the surface of the ceramic tube by magnetron sputtering, adjusting the coverage area of ​​the upper conductive film, annealing, and then welding it to the base. The tube is then placed in a sealed space for testing, using acetone as the gas. Tests show that when SnO2 is the bottom layer and ITO is the upper layer with partial coverage, it exhibits high sensitivity to acetone gas in the concentration range of 10 ppb-1000 ppm. When ITO is fully covered, the response saturates at 300 ppm, suitable for low-concentration detection. Conversely, when ITO is the bottom layer and SnO2 is the upper layer, the fully covered structure has a wide response range, responding in the concentration range of 10 ppb-1000 ppm, while the partially covered structure is suitable for low-concentration detection, essentially saturating at 300 ppm. This invention replaces traditional circuit adjustment with physical coverage area control, achieving dynamic range switching without complex signal processing, significantly improving the sensor's applicability in medical diagnostics, environmental monitoring, and other scenarios. By adjusting the vertical position and coverage structure of the two materials, this invention can control the device's response and measurement range, showing promising application prospects in various fields.

[0070] The above description is only of the preferred embodiment of the present invention and should not be construed as limiting the scope of the claims. The present invention is not limited to the above embodiments, and variations in its specific structure are permitted. All variations made within the scope of the independent claims of the present invention are also within the scope of protection of the present invention.

[0071] Unless otherwise defined, 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 invention pertains. The terminology used in this specification is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

Claims

1. A gas sensor with adjustable responsivity and measurement range, characterized in that, It includes a bottom conductive film (2), an upper conductive film (1) and a ceramic tube (5) with a gold electrode (3); the upper conductive film (1) is deposited on the surface of the bottom conductive film (2), and the materials of the bottom conductive film (2) and the upper conductive film (1) are SnO2 or ITO, and the materials of the bottom conductive film (2) and the upper conductive film (1) are different.

2. The gas sensor with adjustable response and measurement range according to claim 1, characterized in that, The bottom conductive film (2) completely covers the gold electrode (3).

3. The gas sensor with adjustable response and measurement range according to claim 1, characterized in that, The bottom conductive film (2) is made of SnO2, and the top conductive film (1) is made of ITO; or The bottom conductive film (2) is made of ITO, and the top conductive film (1) is made of SnO2.

4. A method for fabricating a gas sensor with adjustable responsivity and measurement range, characterized in that, Includes the following steps: A bottom conductive film (2) is deposited on the pretreated Si wafer by radio frequency magnetron sputtering, and then an upper conductive film (1) is deposited on the bottom conductive film (2). After annealing, the gas sensor with adjustable responsivity and measurement range is obtained.

5. The method for preparing a gas sensor with adjustable response and measurement range according to claim 4, characterized in that, The conditions for depositing the bottom conductive film (2) are: sputtering power of 100W-300W, heating temperature of 200℃-400℃, working gas flow rate of 20-40sccm Ar, deposition pressure of 1Pa-3Pa, and deposition time of 10min.

6. The method for preparing a gas sensor with adjustable response and measurement range according to claim 4, characterized in that, The conditions for depositing the upper conductive film (1) are: sputtering power of 100W-300W, heating temperature of 200℃-400℃, working gas flow rate of 20-40sccm Ar, deposition pressure of 1Pa-3Pa, and deposition time of 7min.

7. The method for preparing a gas sensor with adjustable response and measurement range according to claim 4, characterized in that, The annealing conditions are: annealing temperature of 300℃-500℃ and annealing time of 20S-40S.

8. The method for preparing a gas sensor with adjustable response and measurement range according to claim 4, characterized in that, The heat treatment conditions are as follows: apply a heating voltage to the annealed sample, starting from 2-2.6V and gradually increasing to 5-5.3V, and heat at 5V until the voltage across the sample stabilizes.

9. The method for preparing a gas sensor with adjustable response and measurement range according to claim 8, characterized in that, The heating time is 30-70 minutes.

10. The method for preparing a gas sensor with adjustable responsivity and measurement range according to claim 4, characterized in that, The Si wafer is cut into substrates of the required size using a laser scribing method. Then, it is soaked in a mixed solution of sulfuric acid and hydrogen peroxide at 100-150 °C for 10-30 minutes, followed by ultrasonic cleaning with acetone and deionized water. The mixed solution of sulfuric acid and hydrogen peroxide is prepared by mixing 98% sulfuric acid and 20% hydrogen peroxide solution in a volume ratio of 3:1.

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