Metal oxide semiconductor (MOS) gas sensor with laminated structure and preparation method thereof

Abstract

The invention provides an MOS gas sensor with a laminated structure and a preparation method of the MOS gas sensor. The MOS gas sensor comprises a substrate, and a heater layer, a protective layer, a measuring electrode layer and a sensitive material layer which are arranged layer by layer along the thickness direction of the substrate, wherein the heater layer is fixedly arranged on one surface of the substrate; the protective layer is fixedly arranged on the heater layer and is used for wrapping all or part of the outer surface of the heater layer; the measuring electrode layer is fixedly arranged on the protective layer; the sensitive material layer is fixedly arranged on the measuring electrode layer and used for sensing target gas. The heater layer, the protective layer, the measuring electrode layer and the sensitive material layer of the MOS gas sensor are all located on the same side of the substrate of the sensor, the problem that the heater is likely to be unstable due to the fact that the heater is exposed in the environment for a long time is solved through the structure, the environment interference resistance is improved, and therefore the performance of the sensor is improved; in addition, according to the preparation method, the process steps are reduced, and the production cost is effectively reduced.

Description

Technical Field

[0001] The present invention relates to the technical field of gas sensors, and in particular to a MOS gas sensor with a stacked structure and a preparation method thereof. Background Art

[0002] A gas sensor is a device that converts the measured gas concentration into a corresponding electrical signal according to a certain rule. It is widely used in many fields such as industrial production, medical treatment, aerospace, and energy. Among them, MOS (Metal-Oxide Semiconductor Gas Sensor) gas sensors occupy an important position in the field of gas sensors due to their high response sensitivity, high reliability, low cost, and simple device structure. MOS gas sensors are sensors that detect gas by detecting the conductivity changes caused by the interaction between gas and the surface of metal oxide semiconductors. They are widely used in air quality monitoring, industrial environment monitoring, household gas leak detection, and other fields.

[0003] However, the sensitive characteristics of MOS gas sensors are easily affected by external factors such as ambient temperature, humidity, and interfering gases. In particular, the heating layer material is easily affected by the external environment due to long-term exposure to the environment, resulting in the instability of the heating layer material, which affects the response characteristics of the gas sensor.

[0004] Therefore, a new type of laminated structure is needed to prevent the heating layer material from being exposed to the environment, enhance the ability of the gas sensor to resist environmental interference, and thus effectively improve the performance of the gas sensor. Summary of the invention

[0005] In view of this, an embodiment of the present invention provides a MOS gas sensor with a stacked structure and a method for manufacturing the same, so as to eliminate or improve one or more defects existing in the prior art.

[0006] In a first aspect, the present invention provides a MOS gas sensor with a stacked structure, the MOS gas sensor comprising a substrate and a heater layer, a protective layer, a measuring electrode layer and a sensitive material layer arranged layer by layer along the thickness direction of the substrate;

[0007] Wherein, the heater layer is fixedly arranged on one surface of the substrate, and the heater layer comprises a heater and a heating electrode;

[0008] The protective layer is fixedly arranged on the heater layer, and is used to wrap all or part of the outer surface of the heater layer, and the protective layer is an insulating structure;

[0009] The measuring electrode layer is fixedly arranged on the protective layer, and the measuring electrode layer includes measuring electrodes arranged in a set shape;

[0010] The sensitive material layer is fixedly arranged on the measuring electrode layer and is used for sensing the target gas.

[0011] In some embodiments, the area of ​​the protection layer is larger than the area of ​​the heater layer, and the protection layer is configured to completely cover the surface and surrounding sides of the heater layer.

[0012] In some embodiments, the protective layer is made of glass glaze.

[0013] In some embodiments, the heater is made of Pt, Au, Ru or an alloy thereof.

[0014] In some embodiments, the sensitive material layer is made of SnO2.

[0015] In some embodiments, the substrate is made of Al2O3 ceramic sheet.

[0016] In some embodiments, the thickness of the heater layer is between 10-15 μm.

[0017] In some embodiments, the thickness of the protective layer is between 6-8 μm.

[0018] In some embodiments, the thickness of the sensing electrode layer is between 10-15 μm.

[0019] In some embodiments, the thickness of the sensitive material layer is between 50-60 μm.

[0020] In some embodiments, the heaters of the heater layer are arranged in an S-shaped circuitous manner, and two heating electrodes are provided, which are respectively located on both sides of the heater in the length direction and close to the same length side of the heater layer.

[0021] In some embodiments, the protection layer is configured to cover at least a region of the heater and leave a window at a position corresponding to the heating electrode, so that the region of the heating electrode is exposed to the surface of the MOS gas sensor.

[0022] In some embodiments, the size of the measuring electrode layer is configured to be fully covered by the area of ​​the heater, the measuring electrodes are arranged in a zigzag shape, and have at least one electrode connection point, the electrode connection point is located on one side of the measuring electrode in the width direction and close to a length side of the measuring electrode layer, and the electrode connection point of the measuring electrode and the heating electrode are respectively located on both sides of the width direction of the MOS gas sensor;

[0023] The size of the sensitive material layer is configured to be completely covered by the area of ​​the measuring electrode.

[0024] In a second aspect, the present invention further provides a preparation method for preparing the MOS gas sensor with the above-mentioned laminated structure, the method comprising the following steps:

[0025] preparing the heater layer on a surface of a substrate by a first process;

[0026] After the heater layer is prepared, the protective layer is prepared on the heater layer by a second process, so that the protective layer wraps all or part of the outer surface of the heater layer;

[0027] After the protective layer is prepared, the measuring electrode layer is prepared on the protective layer by a third process;

[0028] After the measuring electrode layer is prepared, the sensitive material layer is prepared on the measuring electrode layer by a fourth process.

[0029] In some embodiments, the first process, the second process, the third process or the fourth process comprises any one of screen printing, photolithography, sputtering deposition, spray coating, chemical vapor deposition or physical vapor deposition.

[0030] In some embodiments, the substrate is an Al2O3 ceramic sheet, and the step of preparing the heater layer on a surface of the substrate by a first process includes: preparing the heater layer on the Al2O3 ceramic sheet by screen printing, leveling for 10-15 minutes after printing, drying at 80°C for 10-15 minutes after leveling, and sintering at 850°C for 10 minutes after drying;

[0031] The step of preparing the protective layer on the heater layer by a second process comprises: preparing the protective layer on the heater layer by screen printing, leveling for 10-15 minutes after printing, drying at 80° C. for 10-15 minutes after leveling, and sintering at 600° C. for 10 minutes after drying;

[0032] The step of preparing the measuring electrode layer on the protective layer by the third process comprises: preparing the measuring electrode layer on the protective layer by screen printing, leveling for 10-15 minutes after printing, drying at 80° C. for 10-15 minutes after leveling, and sintering at 850° C. for 10 minutes after drying;

[0033] The step of preparing the sensitive material layer on the measuring electrode layer by the fourth process includes: preparing the sensitive material layer on the measuring electrode layer by screen printing, leveling for 10-15 minutes after printing, drying at 80°C for 10-15 minutes after leveling, and sintering at 500°C for 120 minutes after drying.

[0034] According to the technical solutions described in the MOS gas sensor with a laminated structure and the preparation method thereof in the embodiments of the present invention, the beneficial effects that can be obtained include at least: the heater layer, protective layer, measuring electrode layer and sensitive material layer of the MOS gas sensor are all located on the same side of the substrate of the sensor, and this structure avoids the problem of heater instability that may be caused by long-term exposure of the heater to the environment, improves the ability to resist environmental interference, and is beneficial to improving the performance of the sensor; in addition, the heater in this laminated structure can not only provide the working temperature for the sensitive material, but also has conductivity, which also reduces the process steps and effectively reduces the production cost.

[0035] Additional advantages, purposes, and features of the present invention will be described in part in the following description, and will become apparent to those skilled in the art after studying the following, or may be learned from the practice of the present invention. The purposes and other advantages of the present invention may be achieved and obtained by the structures specifically indicated in the specification and the accompanying drawings.

[0036] Those skilled in the art will appreciate that the objectives and advantages that can be achieved with the present invention are not limited to the above specific description, and the above and other objectives that can be achieved by the present invention will be more clearly understood from the following detailed description. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] The drawings described herein are used to provide a further understanding of the present invention, constitute a part of this application, and do not constitute a limitation of the present invention. The components in the drawings are not drawn to scale, but are only for illustrating the principles of the present invention. In order to facilitate the illustration and description of some parts of the present invention, the corresponding parts in the drawings may be enlarged, that is, they may become larger relative to other components in the exemplary device actually manufactured according to the present invention. In the drawings:

[0038] Figure 1 FIG. 4 is a schematic structural diagram of a MOS gas sensor with a stacked structure in one embodiment of the present invention.

[0039] Figure 2 Schematic diagram of the structure of the heater layer in one embodiment of the present invention.

[0040] Figure 3 FIG. 4 is a schematic diagram of the structure of a protective layer in an embodiment of the present invention.

[0041] Figure 4 FIG. 4 is a schematic diagram of the structure of a measuring electrode layer in an embodiment of the present invention.

[0042] Figure 5 FIG. 4 is a schematic structural diagram of a sensitive material layer in an embodiment of the present invention.

[0043] Figure 6 It is a flowchart of a preparation method in one embodiment of the present invention.

[0044] Figure 7 This is a photo of a MOS gas sensor in one embodiment of the present invention.

[0045] Figure 8 The graph is a gas-sensitive response graph of a methane sensor prepared according to the preparation method in an embodiment of the present invention.

[0046] Reference numerals:

[0047] 1. Substrate; 2. Heater layer; 21. Heater; 22. Heating electrode; 3. Protective layer; 4. Measuring electrode layer; 41. Measuring electrode; 42. Electrode connection point; 5. Sensitive material layer. DETAILED DESCRIPTION

[0048] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the embodiments and the accompanying drawings. Here, the illustrative embodiments of the present invention and their descriptions are used to explain the present invention, but are not intended to limit the present invention.

[0049] It should also be noted that, in order to avoid obscuring the present invention due to unnecessary details, only structures and / or processing steps closely related to the solutions according to the present invention are shown in the accompanying drawings, while other details that are not closely related to the present invention are omitted.

[0050] It should be emphasized that the term “include / comprises” when used herein refers to the presence of features, elements, steps or components, but does not exclude the presence or addition of one or more other features, elements, steps or components.

[0051] It should also be noted that, unless otherwise specified, the term “connection” herein may refer not only to a direct connection but also to an indirect connection with an intermediate.

[0052] Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. In the accompanying drawings, the same reference numerals represent the same or similar components, or the same or similar steps.

[0053] The resistance type gas sensor in the prior art can be divided into direct heating type and indirect heating type according to the heating method. Among them, the indirect heating type resistance type gas sensor can be further divided into tubular indirect heating type and planar indirect heating type. The MOS gas sensor with a planar indirect heating structure consists of five parts: a heating electrode, a heater, a protective layer, a measuring electrode and a sensitive material layer. Generally speaking, the heating electrode is located on the front of the sensor, while the measuring electrode is located on the back. During the use of the MOS gas sensor with this structure, since the heating layer material is exposed to the environment for a long time, it will be affected by the environment, and the heating layer material will degrade and become unstable, thereby affecting the sensitivity and stability of the sensor; secondly, the MOS gas sensor with this structure often needs to print a layer of ruthenium-based resistor paste on the heating electrode to form a closed loop.

[0054] In the present invention, the heater, protective layer, measuring electrode and sensitive material layer are all located on the same side of the sensor. This structure avoids the problem of heater instability caused by long-term exposure of the heater to the environment, improves the ability to resist environmental interference, and is beneficial to improving the performance of the sensor. In addition, the heater in this laminated structure can not only provide working temperature for the sensitive material, but also has conductivity, thereby reducing process steps and effectively reducing production costs.

[0055] In a first aspect, the present invention provides a MOS gas sensor with a stacked structure, such as Figure 1 As shown, the MOS gas sensor includes a substrate 1 and a heater layer 2, a protective layer 3, a measuring electrode layer 4 and a sensitive material layer 5 arranged layer by layer along the thickness direction of the substrate 1. The substrate 1 is the basis of all components of the device, carrying other layers, and can be made of insulating or heat-conductive materials (such as ceramics, silicon wafers, etc.).

[0056] The heater layer 2 is fixedly arranged on one surface of the substrate 1, and the heater layer 2 includes a heater 21 and a heating electrode 22. The heater 21 is used to provide a high temperature environment required for the sensor to work, to ensure that the sensitive material layer 5 (such as a metal oxide semiconductor material) reaches its working temperature, and to improve the conductivity. The presence of the heater layer 2 can make the metal oxide material sufficiently active so as to react to the gas molecules. The heating electrode 22 can drive the heater 21 by a heating current, thereby maintaining the working temperature of the sensor. The heating electrode 22 can be composed of a resistive material (such as platinum or a metal oxide).

[0057] The protective layer 3 is fixedly arranged on the heater layer 2, and is used to wrap all or part of the outer surface of the heater layer 2, and the protective layer 3 is an insulating structure. The protective layer 3 serves as external protection for the heater layer 2, and also plays an insulating role to prevent current leakage or short circuit, and ensure the stability of the heater layer 2. The protective layer 3 can be made of high-temperature resistant ceramics or other insulating materials (such as alumina, silicate, etc.). The protective layer 3 not only provides electrical isolation, but also reduces the impact of the external environment on the performance of the sensor.

[0058] The measuring electrode layer 4 is fixedly arranged on the protective layer 3, and the measuring electrode layer 4 includes measuring electrodes 41 arranged in a set shape. The main function of the measuring electrode 41 is to monitor the conductivity change during the gas detection process by contacting the sensitive material layer 5. The measuring electrode 41 can be composed of a plurality of electrodes, and the shape and arrangement of the electrodes have an important influence on the sensitivity and response speed of the sensor. The set shape arrangement means that these electrodes will be arranged according to a certain rule to achieve a uniform electric field distribution, thereby improving the accuracy of gas detection.

[0059] The sensitive material layer 5 is fixedly arranged on the measuring electrode layer 4 and is used to sense the target gas. The sensitive material layer 5 is the core part of the sensor and can be made of metal oxide materials (such as tin oxide SnO2, zinc oxide ZnO, etc.). These metal oxide materials have the ability to selectively respond to different gases. When the target gas contacts the sensitive material, the gas reacts with the surface of the metal oxide, thereby changing its conductivity. The sensitive material layer 5 can quickly respond to changes in the gas.

[0060] In the above embodiment, the heating electrode 22 ensures that the metal oxide material is at a suitable working temperature through the heating system, while the measuring electrode 41 is responsible for sensing the change in material conductivity, and then monitoring the change in gas concentration. The heating electrode 22 and the measuring electrode 41 can also work together in the operation of the sensor to form a complete gas detection circuit, thereby realizing an efficient gas sensing function. The heating electrode 22 is connected to a stable power supply, and the measuring electrode 41 is in contact with the sensitive material layer 5 to form a conductivity measurement loop. A small voltage (such as a DC voltage) is applied to measure the conductivity change caused by the reaction of the target gas with the sensitive material layer 5 through the conductivity of the measuring electrode 41. During operation, the conductivity of the sensor will change with the concentration of the target gas, thereby affecting the current between the electrodes, and the target gas concentration is inferred by these current changes.

[0061] In the above embodiment, the heater layer 2, protective layer 3, measuring electrode layer 4 and sensitive material layer 5 of the MOS gas sensor are all located on the same side of the substrate 1 of the sensor. This structure avoids the problem that the heater 21 may be unstable due to long-term exposure to the environment, improves the ability to resist environmental interference, and is beneficial to improving the performance of the sensor; in addition, the heater 21 in this laminated structure can not only provide the working temperature for the sensitive material, but also has conductivity, thereby reducing the process steps and effectively reducing the production cost.

[0062] In some embodiments, the function of the heater 21 is mainly to provide working temperature for the sensitive material and improve the conductivity, so the material of the heater 21 will directly affect the performance of the MOS gas sensor. Optionally, the material of the heater 21 is Pt, Au, Ru or alloy. The material of the heater layer 2 has high electrical conductivity, good high temperature resistance and chemical stability. Platinum (Pt) has excellent high temperature resistance and chemical stability, and can work stably for a long time in a high temperature environment without being easily oxidized; gold (Au) as a precious metal has good conductivity and chemical stability; ruthenium (Ru) is a very hard and high temperature resistant metal with good oxidation resistance, and is usually used in applications requiring extremely high temperature stability. Alloy refers to an alloy synthesized from metals such as platinum, ruthenium or gold. The alloy material can adjust its conductivity, high temperature resistance and other physical properties as needed to meet specific application requirements. In addition to platinum, gold, ruthenium and alloys, the protective layer 3 can also consider metals such as molybdenum (Mo), tungsten (W) or chromium (Cr) or their alloys.

[0063] In some embodiments, the area of ​​the protective layer 3 is larger than the area of ​​the heater layer 2, and the protective layer 3 is configured to completely cover the surface and surrounding sides of the heater layer 2. Ensure that the heater layer 2 is not damaged by external substances during operation. For example, some gas sensors may be exposed to water vapor, dust, polluted gases, etc. during use, which may corrode the material of the heater layer 2 or affect the heating performance. By providing a covering layer, the protective layer 3 effectively prevents damage from these external factors.

[0064] In addition, the design of the protective layer 3 also helps stabilize the thermal conductivity of the sensor. The heater 21 needs to maintain a constant temperature, and the protective layer 3 can effectively reduce heat loss, ensure that the temperature of the heater layer 2 remains within a suitable working range, and avoid temperature fluctuations caused by heat leakage.

[0065] The protective layer 3 can also protect the heater layer 2 from physical damage. Since the heater layer 2 can be made of certain fragile materials, the protective layer 3 provides a physical barrier to prevent damage to the heater layer 2 caused by external mechanical impact or extrusion. For example, during the assembly, transportation or daily use of the sensor, the protective layer 3 can effectively absorb or disperse external forces to reduce direct impact on the heater 21. The protective layer 3 can also enhance the adaptability of the sensor to the environment, especially in harsh environments, such as high humidity, high temperature or environments with complex gas composition. The protective layer 3 can effectively extend the service life of the heater layer 2 and ensure the long-term and stable operation of the gas sensor. The coverage of the protective layer 3 is not only physical protection, but also prevents external gases, dust or other contaminants from directly contacting the heater layer 2. Especially in precision gas sensors, the entry of contaminants may change the performance of the sensor or cause the sensor to fail.

[0066] In some embodiments, the function of the protective layer 3 is mainly to isolate the heater 21 from the measuring electrode 41, protect the heater 21, prevent static electricity and contact with air. Optionally, the material of the protective layer 3 is glass glaze, the glaze is cadmium-free and lead-free, low-fired, surface glossy, and has excellent acid resistance. Glass glaze has good high temperature resistance and can remain stable at high temperatures of hundreds of degrees Celsius; the surface of glass glaze is very smooth and has strong chemical stability. It can resist corrosion from most chemical substances and can effectively protect the heater layer 2 from gas and moisture in the environment; glass glaze can form a solid protective layer 3 to prevent the external environment (such as dust, dirt, etc.) from directly contacting the sensitive layer or heater 21, avoiding mechanical damage; glass glaze usually has good adhesion and can firmly adhere to the surface of the heater 21 or other substrate 1 materials to ensure stability during long-term use. The main function of the protective layer 3 is to prevent external substances or gases from interfering with the sensitive material layer 5 and the heater 21, and it also has the characteristics of high temperature resistance and chemical corrosion resistance. In addition to glass glaze, silicate ceramics (SilicateCeramics), silicon dioxide (SiO2) coating, silicon nitride (Si3N4) and aluminum oxide (Al2O3) coating are also used.

[0067] In some embodiments, the sensitive material is the core of the MOS gas sensor. The components, crystal structure, morphology, porosity, specific surface area, etc. of the sensitive material directly affect the sensitivity, selectivity, response recovery and other properties of the gas sensor. Metal semiconductor oxides can be selected as sensitive materials to construct sensitive elements. When the sensitive material is at the working temperature, its surface will adsorb oxygen in the air to form adsorbed oxygen ions. When it comes into contact with the target gas, the adsorbed oxygen ions on the surface of the sensitive material will react with the target gas, thereby causing the resistance value of the gas sensor to change.

[0068] Optionally, the material of the sensitive material layer 5 is SnO2. SnO2 has semiconductor properties, and its conductivity changes with the concentration of gases in the environment. When a target gas (such as carbon monoxide, ammonia, methane, etc.) contacts the surface of SnO2, the gas molecules react with SnO2, causing its conductivity to change. SnO2 has high sensitivity to a variety of gases, especially strong reaction ability to oxidizing gases at room temperature. Tin oxide is a relatively cheap and easy to prepare material, and its sensitive performance can be optimized by adjusting the synthesis conditions (such as doping with different elements). SnO2 can still maintain good stability at higher temperatures and is suitable for working at high temperatures. In addition to SnO2, the sensitive material layer 5 can also be made of materials such as titanium oxide (TiO2), zinc oxide (ZnO), tin molybdenum oxide (SnMoO4), metal oxides (such as CuO, Fe2O3) or conductive polymers.

[0069] In some embodiments, the substrate 1 is made of Al2O3 ceramic sheet. Al2O3 has excellent electrical insulation properties, which makes it very suitable for use as the substrate 1 of the heater 21 and sensitive material in the gas sensor, avoiding current leakage or unnecessary interference. Aluminum oxide ceramics can withstand extremely high temperatures and can work stably in high temperature environments above 1000°C; Al2O3 has high hardness and compressive strength, which can effectively prevent mechanical damage and protect sensitive materials and the heater layer 2 from external pressure. Al2O3 has good stability in most chemical environments and is not easily affected by gas components or corrosive substances. In addition to Al2O3, the substrate 1 can also be made of silicon (Si), aluminum nitride (AlN), aluminum silicate (Al2SiO5) or ceramic composites.

[0070] In some embodiments, the thickness of the heater layer 2 is between 10-15 μm. The heater layer 2 is made of a material with good electrical conductivity and high temperature resistance, and its main function is to heat the sensitive material layer 5 by electric current so that it reaches the required working temperature. The thickness of the heater layer 2 directly affects the heating speed and energy efficiency. The thickness range of the heater layer 2 in the embodiment of the present invention can balance the heating efficiency and thermal stability, ensuring the reliability of the sensor in fast response and long-term use.

[0071] In some embodiments, the thickness of the protective layer 3 is between 6 and 8 μm. The thickness range of the protective layer 3 in the embodiments of the present invention is sufficient to provide necessary protection while not excessively increasing the thickness of the protective layer 3 to affect the gas sensing response or increase the power consumption of the heater 21 .

[0072] In some embodiments, the thickness of the measuring electrode layer 4 is between 10-15 μm. The main function of the measuring electrode layer 4 is to be electrically connected to the sensitive material layer 5 to detect the change of the electrical signal caused by the gas reaction. The thickness of the electrode layer is closely related to the conductivity, stability and response speed of the sensor. The thickness range of the measuring electrode layer 4 in the embodiment of the present invention can provide good conductivity and sufficient mechanical strength without affecting the rapid response of the sensor.

[0073] In some embodiments, the thickness of the sensitive material layer 5 is between 50-60 μm. The sensitive material layer 5 is the most critical part of the gas sensor, responsible for reacting with gas molecules and causing changes in electrical signals. Its thickness directly affects the sensitivity, response speed and operating temperature of the sensor. The thickness range of 50-60 μm balances the sensitivity and response speed, so that the sensor can provide appropriate response under various gas concentrations without excessive delay.

[0074] In some embodiments, Figure 2 As shown, the heater 21 of the heater layer 2 is arranged in an S-shaped circuitous arrangement, and two heating electrodes 22 are provided, which are respectively located on both sides of the heater 21 in the length direction and close to the same length side of the heater layer 2. The S-shaped layout enables the heater 21 to generate heat evenly in a larger area, avoiding the problem of local overheating or uneven heating that may occur in traditional linear heaters 21. Through the circuitous arrangement, more heating locations can be achieved in the same area, increasing thermal efficiency and ensuring that the sensitive material layer 5 quickly reaches the operating temperature. The S-shaped heater 21 layout helps to reduce heat accumulation in a certain local area, thereby improving the long-term stability of the sensor.

[0075] In some embodiments, Figure 3 As shown, the protective layer 3 is configured to at least cover the area of ​​the heater 21, thereby protecting the heater 21 from direct damage by external pollutants, moisture, dust, etc. Figure 3 As shown, the protective layer 3 is in a "convex" shape. A window is left in the protective layer 3 at a position corresponding to the heating electrode 22, so that the area of ​​the heating electrode 22 is exposed to the surface of the MOS gas sensor, so as to electrically connect the heating electrode 22.

[0076] In some embodiments, the size of the measuring electrode layer 4 is configured to be fully covered by the area of ​​the heater 21. When the heater 21 is working, the measuring electrode 41 needs to be able to accurately sense the temperature of the heating area; by covering the area of ​​the heater 21, the measuring electrode 41 can collect data more comprehensively to ensure measurement accuracy. Figure 4As shown, the measuring electrode 41 is arranged in a zigzag shape and has at least one electrode connection point 42. The electrode connection point 42 is located on one side of the measuring electrode 41 in the width direction and close to a length side of the measuring electrode layer 4. The electrode connection point 42 of the measuring electrode 41 and the heating electrode 22 are respectively located on both sides of the width direction of the MOS gas sensor. By reasonably configuring the arrangement and connection points of the electrodes, the sensitivity of the sensor can be improved, so that the measuring electrode 41 can detect changes in gas concentration more accurately. The measuring electrode layer 4 of this embodiment can improve the sensitivity, stability and response speed of the sensor, while reducing the interference between electrodes and the influence of thermal effects on sensor performance.

[0077] In the above embodiment, the measuring electrode 41 and the heating electrode 22 are arranged opposite to each other, that is, they are respectively located on both sides of the sensor width direction. Such a design facilitates the connection between the measuring electrode 41 and the external circuit, ensuring the smooth conduction of the current. By arranging the heating electrode 22 and the measuring electrode 41 on both sides of the width direction, the electrical interference between them can be effectively avoided, ensuring the accuracy of the measuring electrode 41. This layout method helps to reduce the overall size of the sensor, while improving the degree of coordination between components, thereby reducing power consumption and optimizing response time.

[0078] The function of the measuring electrode 41 in the embodiment of the present invention is to directly sense the resistance and current changes of the sensitive material and to achieve rapid and accurate detection. Therefore, the uniformity and consistency of the measuring electrode 41 will be directly related to whether the resistance or current changes of the sensitive material can be quickly detected. In addition, the measuring electrode 41 has excellent wire bonding characteristics, which can ensure good signal transmission performance, thereby improving the performance of the MOS gas sensor.

[0079] In some embodiments, the size of the sensitive material layer 5 is configured to be fully covered by the area of ​​the measuring electrode 41. The full coverage mentioned here means that the length and width of the measuring electrode 41 are not less than the length and width of the sensitive material layer 5, and the measuring electrode 41 can contact the entire surface of the sensitive material layer 5, which can ensure that the measuring electrode 41 can more accurately capture the signal changes from the sensitive material, thereby improving the accuracy and sensitivity of the sensor. By completely covering the sensitive material layer 5, the reaction of the measuring electrode 41 will be more uniform, and the electrical signal changes can be quickly captured by the measuring electrode 41 and transmitted to the circuit, thereby improving the response speed of the sensor.

[0080] In a second aspect, the present invention also provides a preparation method, such as Figure 6 As shown, the method for preparing the MOS gas sensor with the above-mentioned stacked structure comprises the following steps:

[0081] S10: The heater layer 2 is prepared on a surface of the substrate 1 by a first process; the heater layer 2 is a key component in the MOS gas sensor for controlling the sensor temperature. The heater layer 2 can be made of a resistive material (such as a metal oxide or a metal alloy) and can generate heat by heating with an electric current. According to different technical requirements, the first process may include thin film deposition techniques such as physical vapor deposition (PVD), chemical vapor deposition (CVD) or sputtering, which can form a uniform and functional heater layer 2 on the surface of the substrate 1.

[0082] S20: After the preparation of the heater layer 2 is completed, the protective layer 3 is prepared on the heater layer 2 by a second process, so that the protective layer 3 wraps all or part of the outer surface of the heater layer 2. The protective layer 3 can be made of an insulating material (such as silicon dioxide, silicon nitride or a polymer), and its main function is to protect the heater layer 2 from being corroded by the external environment (such as moisture, chemicals, etc.), while preventing the heater layer 2 from direct contact with the sensitive material layer 5. The protective layer 3 can also help the heater layer 2 remain stable during operation and avoid changes in the heating effect caused by changes in the external environment. The second process may include thin film deposition, spin coating, chemical sputtering or other processes that can accurately control the thickness and quality to ensure that the protective layer 3 is evenly and reliably covered on the heater layer 2.

[0083] S30: After the protective layer 3 is prepared, the measuring electrode layer 4 is prepared on the protective layer 3 by a third process. The measuring electrode layer 4 is an important component of the sensor, which is used to sense the electrical signal generated by the gas reaction and transmit the signal to the external electronic system. The third process can adopt microelectronic processes such as evaporation, sputtering, photolithography, etc. to ensure that the size and shape of the electrode layer meet the requirements, and at the same time ensure good contact between it and the protective layer 3 and the sensitive material layer 5.

[0084] S40: After the measuring electrode layer 4 is prepared, the sensitive material layer 5 is prepared on the measuring electrode layer 4 by the fourth process. The sensitive material layer 5 is the core part of the MOS gas sensor, which is responsible for sensing the presence and concentration changes of the gas. Sensitive materials may include metal oxides (such as SnO2, WO3, TiO2, etc.), which will undergo physical or chemical reactions when contacted by gas molecules, causing their electrical properties (such as conductivity) to change, thereby affecting the electrode signal. The fourth process may use techniques such as solution coating, sputtering deposition, and chemical vapor deposition (CVD) of sensitive materials.

[0085] In the above embodiment, the method forms a structured gas sensor by stacking different functional layers layer by layer. The process and materials of each layer are carefully designed to ensure the working performance of the gas sensor. Through multiple fine process steps, it is ensured that the thickness and quality of each layer can be strictly controlled, thereby improving the overall performance of the sensor, especially in terms of the sensitivity and response speed of gas detection. The introduction of the protective layer 3 effectively improves the stability of the gas sensor and extends its service life, while reducing the negative impact of the external environment on the heater and sensitive materials. According to application requirements, each step in the process can be optimized and adjusted according to specific needs, such as changing the power of the heater, selecting different protective materials or sensitive materials, to meet the detection needs of different types of gases.

[0086] The preparation method uses a series of precise process steps to prepare a MOS gas sensor having a heater layer 2, a protective layer 3, a measuring electrode layer 4 and a sensitive material layer 5 layer by layer. This method can ensure the performance and reliability of each functional layer of the sensor, thereby optimizing the overall working effect of the gas sensor, and is widely applicable to various gas monitoring and environmental protection fields.

[0087] In some embodiments, the first process, the second process, the third process or the fourth process comprises any one of screen printing, photolithography, sputtering deposition, spray coating, chemical vapor deposition or physical vapor deposition.

[0088] Screen printing is to print conductive ink or slurry onto a substrate through a screen to form a thick film structure. This process is suitable for the preparation of large-area, thicker electrodes or heater layers 2. This process is simple to operate, suitable for large-scale production, and low cost. The photolithography process is to coat the photosensitive material on the substrate through photolithography technology, and form the desired pattern through ultraviolet light irradiation and development. It is suitable for high-precision microstructure pattern production. Photolithography can be used to make tiny structures of measuring electrode layers, especially in applications where precise control of size and shape is required. Sputtering deposition is to spray liquid or slurry onto the surface of the substrate through a spray to form a uniform coating. Spraying is suitable for large-area, thicker coating deposition. Spraying can be used to prepare protective layers or certain thicker sensitive material layers, especially in situations where a large area is required and uniformity requirements are not high. Chemical vapor deposition (CVD) is to deposit a thin film on the surface of the substrate through a chemical reaction. The gaseous precursor reacts with the substrate surface to generate the desired solid material. It is suitable for the deposition of oxides, nitrides, metals, etc. CVD can be used to deposit the protective layer 3 and the sensitive material layer 5, especially for applications requiring high-quality thin films, such as the silicon nitride protective layer 3 or the metal oxide sensitive material layer 5. Physical vapor deposition (PVD) is a process that converts a source material into a gaseous state and deposits it onto a substrate through a physical process (such as evaporation and sputtering). It is suitable for the preparation of metal or metal oxide layers. The process can control the thickness and composition of the film layer, and the deposited material has good adhesion and stability.

[0089] The choice of different processes depends on the design requirements of the sensor, such as the thickness, uniformity, material properties and manufacturing cost of the film layer. For example, if high-resolution and precise electrode patterns are required, photolithography can be selected; if a large-area, uniform electrode or heater layer 2 is required, screen printing or spraying may be more suitable; if a high-quality sensitive material layer 5 or protective layer 3 is required, CVD or sputtering deposition may be a better choice. In practical applications, these processes can be combined according to different layer structures. For example, screen printing can be used to prepare the heater layer 2, sputtering deposition can be used to prepare the electrode layer, and CVD can be used to prepare the protective layer 3 or sensitive material layer 5.

[0090] In some embodiments, the substrate 1 is an Al2O3 ceramic sheet, and the step of preparing the heater layer 2 on a surface of the substrate 1 by a first process includes: preparing the heater layer 2 by screen printing on the Al2O3 ceramic sheet, leveling for 10-15 minutes after printing, drying at 80°C for 10-15 minutes after leveling, and sintering at 850°C for 10 minutes after drying. The heater layer 2 material (such as a resistor material) is printed on the surface of the Al2O3 ceramic sheet by screen printing. The screen printing process is simple, low-cost, and can quickly produce large-area patterns, which is suitable for the preparation of heaters 21 or electrodes. The printed heater layer 2 needs to be leveled for 10-15 minutes to ensure uniform coating, and then dried at 80°C for 10-15 minutes. This step is to remove solvents or moisture and ensure the quality of film formation. Sintering at 850°C for 10 minutes is to enhance the structural stability and adhesion of the heater layer 2. High-temperature sintering can fuse material particles and improve their conductivity and heat resistance.

[0091] In some embodiments, the step of preparing the protective layer 3 on the heater layer 2 by a second process includes: preparing the protective layer 3 on the heater layer 2 by screen printing, leveling for 10-15 minutes after printing, drying at 80°C for 10-15 minutes after leveling, and sintering at 600°C for 10 minutes after drying. The function of the protective layer 3 is to protect the heater layer 2 from damage by the external environment, especially to prevent direct contact between the gas or other substances and the heater layer 2. Similar to the heater layer 2, the protective layer 3 needs to be leveled and dried after printing to ensure that the film layer is uniform and free of bubbles. Sintering at 600°C for 10 minutes, the sintering temperature is lower than that of the heater layer 2. This sintering process helps to improve the structural density and heat resistance of the protective layer 3.

[0092] In some embodiments, the step of preparing the measuring electrode layer 4 on the protective layer 3 by a third process includes: preparing the measuring electrode layer 4 on the protective layer 3 by screen printing, leveling for 10-15 minutes after printing, drying at 80°C for 10-15 minutes after leveling, and sintering at 850°C for 10 minutes after drying. The measuring electrode layer 4 requires a conductive material (such as a metal or alloy) to transmit electrical signals, so a conductive electrode is prepared on the protective layer 3 using a screen printing process. The accuracy and conductivity of the electrode layer directly affect the response speed and stability of the sensor. As mentioned above, the leveling and drying steps are necessary processes to ensure that the film layer is uniform and bubble-free. Sintering at 850°C for 10 minutes, the higher sintering temperature helps to improve the conductivity of the electrode material and ensure good adhesion between the electrode and the protective layer 3.

[0093] In some embodiments, the step of preparing the sensitive material layer 5 on the measuring electrode layer 4 by the fourth process includes: preparing the sensitive material layer 5 on the measuring electrode layer 4 by screen printing, leveling for 10-15 minutes after printing, drying at 80°C for 10-15 minutes after leveling, and sintering at 500°C for 120 minutes after drying. The last step is to print the sensitive material layer 5, which is used in the gas sensor to respond to different gas changes. Coating the sensitive material on the electrode can make the sensor react to the presence of a specific gas, thereby affecting the current or voltage. Like other layers, the sensitive material layer 5 also needs to be leveled and dried to ensure uniform coating and remove excess solvent. Sintering at 500°C for 120 minutes, the sintering temperature is low and the sintering time is long, the purpose is to promote the crystallization and stabilization of the sensitive material. This helps to improve the performance of the sensitive material, so that it has higher sensitivity and selectivity in gas detection.

[0094] In the above embodiment, in the process of preparing the multilayer structure, the heater layer 2, the protective layer 3, the measuring electrode layer 4 and the sensitive material layer 5 are prepared layer by layer by screen printing. Each step includes leveling, drying and sintering treatment to ensure the uniformity, stability and good adhesion of each layer. The sintering process is crucial to improving the physical and chemical properties of the material, especially in the preparation of the heater layer 2 and the electrode layer. This process flow is suitable for manufacturing high-temperature, corrosion-resistant sensors, especially in applications that require fine control of the thickness of each layer and the material properties. This process flow is relatively simple, effectively reduces the production cost, and is conducive to improving the performance of the sensor.

[0095] By using the above preparation method, a methane sensor was prepared with SnO2 as the sensitive material. The gas sensitive response of the sensor to 300-1000ppm methane gas at an operating temperature of 320℃ was tested. The response results are shown in the attached figure. Figure 7 shown. Figure 8 The graph is a gas-sensitive response curve of the methane sensor prepared by the preparation method in the embodiment of the present invention. The test results show that at the working temperature, the gas-sensitive response of the methane sensor of the new laminated structure to 300, 500, and 1000 ppm methane can reach 4.7, 5.6, and 7.2 respectively. This result shows that the methane sensor of the new laminated structure has excellent gas-sensitive performance.

[0096] The MOS gas sensor with a laminated structure in the embodiment of the present invention can be applied to fields such as air quality monitoring, industrial leak detection, environmental protection, automobile exhaust monitoring and safety monitoring. In the field of air quality monitoring, it can be used to detect harmful gases in indoor and outdoor air, such as carbon monoxide, nitrogen oxides, volatile organic compounds (VOCs), etc.; in the field of industrial leak detection, it can be used to detect the leakage of industrial gases such as natural gas and coal gas; in the field of environmental protection, it can be used to monitor atmospheric pollutants and assess pollution sources; in the field of automobile exhaust monitoring, it can be used to detect and control the emission of harmful gases in automobile emissions; in the field of safety monitoring, it can be used in household natural gas leak alarms, fire alarm systems, etc. The sensor can also be combined with Internet of Things technology. The integrated and intelligent development of MOS gas sensors will make its application scope more extensive, and it can be interconnected with smart devices to realize automatic gas monitoring and alarm.

[0097] It should be clear that the present invention is not limited to the specific configuration and processing described above and shown in the figures. For the sake of simplicity, a detailed description of the known method is omitted here. In the above embodiments, several specific steps are described and shown as examples. However, the method process of the present invention is not limited to the specific steps described and shown, and those skilled in the art can make various changes, modifications and additions, or change the order between the steps after understanding the spirit of the present invention.

[0098] In the present invention, features described and / or illustrated for one embodiment may be used in the same or similar manner in one or more other embodiments, and / or combined with features of other embodiments or replace features of other embodiments.

[0099] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the embodiments of the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A MOS gas sensor with a laminated structure, characterized in that: The MOS gas sensor comprises a substrate and a heater layer, a protective layer, a measuring electrode layer and a sensitive material layer which are arranged layer by layer along the thickness direction of the substrate; Wherein, the heater layer is fixedly arranged on one surface of the substrate, and the heater layer comprises a heater and a heating electrode; The protective layer is fixedly arranged on the heater layer, and is used to wrap all or part of the outer surface of the heater layer, and the protective layer is an insulating structure; The measuring electrode layer is fixedly arranged on the protective layer, and the measuring electrode layer includes measuring electrodes arranged in a set shape; The sensitive material layer is fixedly arranged on the measuring electrode layer and is used for sensing the target gas.

2. The MOS gas sensor of the stacked structure according to claim 1, characterized in that: The area of ​​the protection layer is larger than that of the heater layer, and the protection layer is configured to completely cover the surface and surrounding sides of the heater layer.

3. The MOS gas sensor with a stacked structure according to claim 1, characterized in that: The material of the protective layer is glass glaze; and / or, The heater material is Pt, Au, Ru or alloy; and / or, The material of the sensitive material layer is SnO2; and / or, The substrate is made of Al2O3 ceramic sheet.

4. The MOS gas sensor with a stacked structure according to claim 1, characterized in that: The thickness of the heater layer is between 10-15 μm; and / or, The thickness of the protective layer is between 6 and 8 μm; and / or, The thickness of the measuring electrode layer is between 10-15 μm; and / or, The thickness of the sensitive material layer is between 50-60 μm.

5. The MOS gas sensor with a stacked structure according to claim 1, characterized in that: The heaters of the heater layer are arranged in an S-shaped circuitous manner. Two heating electrodes are provided, which are respectively located on both sides of the heater in the length direction and close to the same length side of the heater layer.

6. The MOS gas sensor with a stacked structure according to claim 5, characterized in that: The protection layer is configured to at least cover the area of ​​the heater and leave a window at a position corresponding to the heating electrode, so that the area of ​​the heating electrode is exposed to the surface of the MOS gas sensor.

7. The MOS gas sensor with a stacked structure according to claim 6, characterized in that: The size of the measuring electrode layer is configured to be fully covered by the area of ​​the heater, the measuring electrodes are arranged in a zigzag shape, and have at least one electrode connection point, the electrode connection point is located on one side of the measuring electrode in the width direction and close to a length side of the measuring electrode layer, and the electrode connection point of the measuring electrode and the heating electrode are respectively located on both sides of the width direction of the MOS gas sensor; The size of the sensitive material layer is configured to be completely covered by the area of ​​the measuring electrode.

8. A method for preparing a MOS gas sensor with a stacked structure according to any one of claims 1 to 7, the method comprising the following steps: preparing the heater layer on a surface of a substrate by a first process; After the heater layer is prepared, the protective layer is prepared on the heater layer by a second process, so that the protective layer wraps all or part of the outer surface of the heater layer; After the protective layer is prepared, the measuring electrode layer is prepared on the protective layer by a third process; After the measuring electrode layer is prepared, the sensitive material layer is prepared on the measuring electrode layer by a fourth process.

9. The preparation method according to claim 8, characterized in that: The first process, the second process, the third process or the fourth process includes any one of screen printing, photolithography, sputtering deposition, spraying, chemical vapor deposition or physical vapor deposition.

10. The preparation method according to claim 9, characterized in that: The substrate is an Al2O3 ceramic sheet, and the step of preparing the heater layer on a surface of the substrate by a first process includes: preparing the heater layer on the Al2O3 ceramic sheet by screen printing, leveling for 10-15 minutes after printing, drying at 80°C for 10-15 minutes after leveling, and sintering at 850°C for 10 minutes after drying; The step of preparing the protective layer on the heater layer by a second process comprises: preparing the protective layer on the heater layer by screen printing, leveling for 10-15 minutes after printing, drying at 80° C. for 10-15 minutes after leveling, and sintering at 600° C. for 10 minutes after drying; The step of preparing the measuring electrode layer on the protective layer by the third process comprises: preparing the measuring electrode layer on the protective layer by screen printing, leveling for 10-15 minutes after printing, drying at 80° C. for 10-15 minutes after leveling, and sintering at 850° C. for 10 minutes after drying; The step of preparing the sensitive material layer on the measuring electrode layer by the fourth process includes: preparing the sensitive material layer on the measuring electrode layer by screen printing, leveling for 10-15 minutes after printing, drying at 80°C for 10-15 minutes after leveling, and sintering at 500°C for 120 minutes after drying.

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