Gas sensor with three-dimensional structure and preparation method thereof

Abstract

The invention relates to the technical field of gas sensors, in particular to a gas sensor with a three-dimensional structure and a preparation method of the gas sensor. The gas sensor structure with the three-dimensional structure comprises a substrate with a flow channel groove, a supporting layer arranged on one side, with the flow channel groove, of the substrate, a heating electrode arranged on one side, deviating from the flow channel groove, of the supporting layer, and a diffusion tower arranged on one side, deviating from the supporting layer, of the heating electrode, and the part, provided with the heating electrode, of the supporting layer is suspended above the runner groove. The diffusion tower is arranged on the side, away from the supporting layer, of the heating electrode, so that heat of the heating electrode is diffused to the diffusion tower, the size of the sensor is reduced, machining material loss is reduced, meanwhile, the contact area between a sensing area and airflow is increased, and the performance of the sensor is improved. In addition, the gas sensor structure provided with the flow channel groove is more suitable for stable and relatively high-flow-speed use scenes.

Description

Technical Field

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

[0002] Gas sensors can be divided into optical, acoustic, electrochemical and thermal conductivity types according to their working principles. Among them, thermal conductivity gas sensors have the advantages of low cost, simple structure, high reliability, high sensitivity and fast response recovery speed. They are one of the most widely studied and applied gas sensors. The intelligent and portable application trend of gas sensors has put forward higher requirements for small size and low power consumption, so it is necessary to introduce micro-electromechanical system (MEMS) technology. MEMS refers to an engineering system that uses components with micron size to perform electronic and mechanical functions. It has the characteristics of miniaturization, integration, mass production and strong compatibility. Combining it with the design and production of thermal conductivity gas sensors can lay a solid foundation for the further application of gas sensors.

[0003] In order to ensure the performance of thermal conductivity gas sensors, materials with high temperature coefficient of resistance (TCR) are generally used as heating electrodes. In order to enhance the perception of gas changes, the current common practice of traditional thermal conductivity sensors is to increase the heating area, i.e., the sensing area, in the thermal conductivity gas sensor. Although this design can improve the performance of the sensor to a certain extent, since the sensing area is a plane, it will inevitably increase the volume of the sensor. At the same time, in order to ensure low power consumption and temperature and control the heat loss of solid heat conduction, additional support structures cannot be added, which will further reduce the stability and durability of the sensor.

[0004] Therefore, the prior art still needs to be improved and developed. Summary of the invention

[0005] In view of the above-mentioned deficiencies in the prior art, an object of the present invention is to provide a gas sensor with a three-dimensional structure and a preparation method thereof, aiming to solve the problem that the existing gas sensors are large in size and poor in stability.

[0006] The technical solution of the present invention is as follows:

[0007] A gas sensor structure with a three-dimensional structure includes a substrate with a flow channel, a support layer arranged on the side of the substrate with the flow channel, a heating electrode arranged on the side of the support layer away from the flow channel, and a diffusion tower arranged on the side of the heating electrode away from the support layer; the part of the support layer where the heating electrode is provided is suspended above the flow channel.

[0008] The gas sensor structure with a three-dimensional structure, wherein the substrate includes a base layer, a first side wall arranged on the base layer, and a second side wall symmetrically arranged with the first side wall; the base layer and the first side wall and the second side wall enclose the flow channel.

[0009] The gas sensor structure with a three-dimensional structure, wherein the support layer includes a substrate support layer arranged on the side of the first side wall and the second side wall away from the base layer, a plurality of support beams extending from the substrate support layer toward the center of the flow channel, and a sensing area support layer formed by the plurality of support beams extending together; the heating electrode is arranged on the side of the sensing area support layer away from the flow channel.

[0010] In the gas sensor structure with a three-dimensional structure, the heating electrodes are distributed in a serpentine shape on the supporting layer.

[0011] The gas sensor structure with a three-dimensional structure, wherein the diffusion tower includes a plurality of metal columns perpendicular to the support layer and connected to the heating electrode.

[0012] In the gas sensor structure with a three-dimensional structure, the diameter of the metal column is 6 μm-12 μm, and the height of the metal column is 25 μm-150 μm.

[0013] In the gas sensor structure with a three-dimensional structure, the material of the metal column includes one of gold, silver, copper, tungsten, zinc, nickel, iron, platinum, tin, and lead, or an alloy of any two or more thereof.

[0014] The gas sensor structure with a three-dimensional structure, wherein the material of the substrate is single crystal silicon; the material of the support layer is one of silicon nitride and silicon oxide; the material of the heating electrode is one of platinum, nickel-chromium alloy, polycrystalline silicon, and silicon carbide.

[0015] The gas sensor structure with a three-dimensional structure, wherein blocking walls are provided at both ends of the flow channel.

[0016] A method for preparing a gas sensor structure having a three-dimensional structure comprises the steps of:

[0017] providing a substrate;

[0018] depositing a support layer on the substrate;

[0019] Depositing a heating electrode on the support layer, and printing a diffusion tower on the heating electrode to obtain a gas sensor precursor;

[0020] The substrate of the gas sensor precursor is etched to form a suspended membrane structure, thereby obtaining a gas sensor structure.

[0021] Beneficial effects: The present invention provides a gas sensor with a three-dimensional structure and a preparation method thereof. The gas sensor structure with a three-dimensional structure includes a substrate with a flow channel, a support layer arranged on the side of the substrate with the flow channel, a heating electrode arranged on the side of the support layer away from the flow channel, and a diffusion tower arranged on the side of the heating electrode away from the support layer; the part of the support layer where the heating electrode is arranged is suspended above the flow channel. The present invention arranges a diffusion tower on the side of the heating electrode away from the support layer so that the heat of the heating electrode diffuses to the diffusion tower, thereby reducing the volume of the sensor and reducing the loss of processing materials, while increasing the contact area between the sensing area and the airflow, thereby improving the performance of the sensor. In addition, a gas sensor structure with a flow channel is more suitable for stable and relatively high flow rate usage scenarios. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 A schematic diagram of an explosion structure of a gas sensor structure having a three-dimensional structure;

[0023] Figure 2 A schematic diagram of the explosion structure of another gas sensor structure with a three-dimensional structure;

[0024] Figure 3 It is the overall structural schematic diagram of the gas sensor structure;

[0025] Figure 4 A cross-sectional feature dimensioning diagram of a gas sensor structure having a three-dimensional structure;

[0026] Figure 5 This is a schematic diagram of the enlarged structure of the gas sensor;

[0027] Figure 6 This is a schematic diagram of the simulation results after the gas sensor is heated up;

[0028] Figure 7 A simplified model diagram for the force analysis of the metal column of the gas sensor before and after heating;

[0029] Figure 8 This is the heat distribution diagram of the natural air flow of the groove type in Example 1;

[0030] Fig. 9 This is the natural air flow heat distribution diagram of the flow channel type in Example 1;

[0031] Fig.10 This is the heat distribution diagram of the groove type in Example 1 along the positive direction of the Y axis at an air flow rate of 1 m / s;

[0032] Fig.11 This is the heat distribution diagram of the flow channel type in Example 1 along the positive direction of the Y axis at an air flow rate of 1 m / s;

[0033] Fig.12 This is the thermal imaging image of the groove type in Example 1;

[0034] Fig.13 This is a stress test diagram of the sensor with the same number of metal pillars but different heights in Example 2;

[0035] Fig.14 This is a schematic diagram showing the effect of the cross-arch structure of the diffusion tower in Example 3;

[0036] Explanation of the accompanying drawings: flow channel 10, substrate 20, supporting layer 30, substrate supporting layer 31, supporting beam 32, sensing area supporting layer 33, reinforcing structure 34, heating electrode 40, serpentine electrode 41, extension electrode 42, diffusion tower 50, groove 60, sensing area 100. DETAILED DESCRIPTION

[0037] The present invention provides a gas sensor with a three-dimensional structure and a method for preparing the same. To make the purpose, technical solution and effect of the present invention clearer and more specific, the present invention is further described in detail below. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0038] It will be understood by those skilled in the art that, unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as generally understood by those skilled in the art in the art to which the present invention belongs. It should also be understood that terms such as those defined in general dictionaries should be understood to have meanings consistent with the meanings in the context of the prior art, and will not be interpreted with idealized or overly formal meanings unless specifically defined as herein.

[0039] A gas sensor is a device that can identify a certain gas molecule and detect its concentration, and can convert gas signals into electrical signals. Since gas is closely related to human daily life and labor production, gas sensors are widely used. Gas sensors can be used to monitor outdoor environmental pollution, and can also detect flammable and explosive gases in closed environments and indoors, such as mine operations and gas leaks. The gradual improvement of human living standards has also expanded the application areas of gas sensors and made them more closely integrated with daily life. For example, the detection of food freshness, the detection and analysis of exhaled gas from patients with bad breath, asthma, and diabetes in biomedicine, and the future application in smart devices such as wearable devices can make gas detection more convenient and quick.

[0040] Currently, most thermal conductivity sensors are limited by the processing method, and their structure is an approximately two-dimensional planar design. The projection area of ​​this design on the normal plane in the direction of the airflow velocity is very small. In order to improve the detection limit and performance, the sensing area is generally increased. Since the airflow will exchange heat with the sensing area of ​​the thermal conductivity sensor when it flows through the sensing area, the temperature difference between the airflow at the rear of the sensing area and the sensing area is small, resulting in structural performance loss; at the same time, the increase in the sensing area will increase the physical cost and structural volume.

[0041] Based on this, Figure 1 As shown, the present invention provides a gas sensor structure with a three-dimensional structure, including a substrate 20 with a flow channel 10, a support layer 30 arranged on the side of the substrate 20 with the flow channel, a heating electrode 40 arranged on the side of the support layer 30 away from the flow channel 10, and a diffusion tower 50 arranged on the side of the heating electrode 40 away from the support layer 30; the part of the support layer 30 where the heating electrode 40 is provided is suspended above the flow channel 10.

[0042] In this embodiment, a diffusion tower is provided on the side of the heating electrode away from the support layer, so that the heat of the heating electrode diffuses to the diffusion tower, which reduces the volume of the sensor and the loss of processing materials, increases the contact area between the sensing area and the airflow, and improves the performance of the sensor. In addition, the gas sensor structure with a flow channel groove is more suitable for stable and relatively high flow rate usage scenarios.

[0043] In some embodiments, Figure 2 As shown, baffles are provided at both ends of the flow channel 10. The baffles are provided to form a groove 60, and the sensing area of ​​the gas sensor is located above the groove, which helps to reduce the power consumption of the sensor and improve the heat exchange of the airflow.

[0044] Specifically, Figure 3As shown, the sensing area 100 of the gas sensor structure is mainly composed of a suspended support layer, a heating electrode and a diffusion tower; before working, the heating electrode is energized to heat the sensor to a predetermined temperature, and then the detection gas is introduced. Due to the different thermal conductivity of different gases, the heat dissipation of the sensor changes, and the resulting temperature difference causes the resistance of the heating electrode to change, thereby calculating one or more gas concentrations by detecting the change in resistance. In addition, the present invention sets a diffusion tower on the side of the heating electrode away from the support layer, so that the sensing area of ​​the gas sensor structure is a three-dimensional structure with a longitudinal structural design. The structure is that when the area of ​​the sensing area remains unchanged, the three-dimensional structure can very effectively increase the body surface area ratio of the sensing area, so that its contact area with the airflow is close to or exceeds that of a thermal conductivity sensor with a larger plane sensing area; in addition, the three-dimensional structure can make the sensor without structural redundancy, which not only saves material waste and reduces costs, but also helps to further reduce the volume of the sensor, and is more conducive to the integration of miniaturized sensors.

[0045] In some embodiments, the substrate includes a base layer, a first side wall disposed on the base layer, and a second side wall symmetrically disposed with respect to the first side wall; the base layer, the first side wall, and the second side wall form the flow channel. Preferably, the base layer, the first side wall, and the second side wall are integrally formed, and the flow channel is obtained by etching the substrate, and this structure helps to reduce the power consumption of the sensor and improve the heat exchange of the airflow.

[0046] In some embodiments, Figure 4 As shown, the cross section of the flow channel perpendicular to the flow channel direction of the flow channel is trapezoidal; preferably, the angle between the side wall of the flow channel and the bottom of the flow channel is 125.26°. The flow channel with a trapezoidal cross section is conducive to the heat exchange between the airflow and the sensing area.

[0047] In some embodiments, the support layer 30 includes a substrate support layer 31 arranged on the side of the first side wall and the second side wall away from the base layer, a plurality of support beams 32 extending from the substrate support layer 31 toward the center of the flow channel 10, and a sensing area support layer 33 formed by the plurality of support beams 32 extending together; the heating electrode 40 is arranged on the side of the sensing area support layer 33 away from the flow channel 10.

[0048] Specifically, the substrate support layer 31, the support beam 32 and the sensing area support layer 33 are integrally formed, and a plurality of support beams formed by extending the substrate support layer are used to provide sufficient mechanical support to the sensing area support layer, thereby improving the stability of the sensing area. In addition, a plurality of support beam structures are used to suspend the sensing area support layer above the flow channel, thereby helping to reduce sensor power consumption and improve airflow heat exchange.

[0049] In some embodiments, Figure 5 As shown, a reinforcing structure 34 is provided at the transition between the support beam 32 and the substrate support layer 31 , and the cross-sectional area of ​​the reinforcing structure gradually decreases from the substrate support layer to the support beam, thereby improving the stability of the sensor structure.

[0050] In a preferred embodiment, the support beams include four, which can provide sufficient structural support while saving materials.

[0051] In some embodiments, the heating electrodes are distributed in a serpentine shape on the support layer. The use of serpentine-shaped heating electrodes can improve the heating efficiency and conduct heat to the diffusion tower, thereby forming a heat exchange with the airflow together with the diffusion tower, increasing the contact area between the airflow and the sensing area and improving the sensor performance.

[0052] In some embodiments, Figure 5 As shown, the heating electrode 40 includes a serpentine electrode 41 and an extended electrode 42; the serpentine electrode 41 is arranged on the sensing area support layer 33, and the extended electrode 42 is extended from the serpentine electrode 41 along the support beam 31 and is arranged on the side of the substrate support layer 31 away from the substrate.

[0053] In some embodiments, the diffusion tower includes a plurality of metal columns perpendicular to the support layer and connected to the heating electrode. By using a plurality of metal columns arranged perpendicular to the support layer to obtain a sensor with a three-dimensional structure, the surface area ratio of the sensing area can be effectively increased without changing the area of ​​the sensor area, so that the contact area with the airflow is close to or exceeds that of a thermal conductivity sensor with a larger plane sensing area; at the same time, the three-dimensional structure can make the sensor without structural redundancy, which not only saves material waste and reduces costs, but also helps to further reduce the volume of the sensor, which is more conducive to miniaturization and integration.

[0054] In some embodiments, the diameter of the metal pillar is 6 μm-12 μm, and the height of the metal pillar is 25 μm-150 μm.

[0055] Specifically, the sensing area of ​​the gas sensor structure is composed of a serpentine heating electrode and a metal column arranged on the heating electrode. When the airflow flows through the sensing area, the structure of the metal column will generate additional torque at the connection between it and the heating electrode, which may cause breakage or damage to the heating electrode under extreme conditions. Therefore, the diameter of the metal column is set to 6μm-12μm, and the height is set to 25μm-150μm on the premise of ensuring structural stability to meet the requirements under different conditions. Furthermore, when the operating temperature of the gas sensor is higher, the height of the metal column is set lower, such as Figure 6 and Figure 7 As shown (where Figure 7 The left picture is before heating, and the right picture is after heating). Because the degree of thermal expansion is positively correlated with temperature, the stress increase at the connection between the metal column and the heating electrode is positively correlated. Lowering the height at high temperature can reduce the height of the center of mass of the metal column and thus reduce the gravitational moment caused by the tilt of the metal column due to thermal expansion.

[0056] In a preferred embodiment, the diameter of the metal column is 7 μm, and the height of the metal column is 60 μm.

[0057] In some embodiments, the material of the metal column includes one of gold, silver, copper, tungsten, zinc, nickel, iron, platinum, tin, and lead, or an alloy of any two or more thereof. The above metals or alloys are all heat-conducting materials, which can diffuse the heat of the heating electrode to the metal column, increase the contact area between the airflow and the sensing area, and thus improve the performance of the sensor.

[0058] In a preferred embodiment, the metal column is made of gold, which can prevent oxidation and ensure stability during long-term use.

[0059] In some embodiments, the substrate is made of single crystal silicon; the support layer is made of silicon nitride or silicon oxide; the heating electrode is made of platinum, which can be replaced by high resistivity metals such as nickel-chromium alloys and polycrystalline silicon, and the diffused resistor can also be replaced by semiconductor materials such as silicon carbide.

[0060] In summary, the three-dimensional structure formed by the diffusion tower arranged on the heating electrode can increase the surface area ratio of the thermal conductivity gas sensor, reduce the size of the thermal conductivity gas sensor and the demand for airflow, which is beneficial to improving the sensor performance; and the diffusion tower is highly customizable, and the three-dimensional structure can be changed according to actual use conditions; at the same time, the three-dimensional structure helps to reduce the deformation of the heating electrode and the silicon nitride film due to thermal expansion, thereby suppressing the stress increase of the two, and improving the long-term stability of the sensor.

[0061] In addition, the present invention also provides a method for preparing a gas sensor structure having a three-dimensional structure, comprising the steps of:

[0062] Step S10: providing a substrate;

[0063] Step S20: depositing a support layer on the substrate;

[0064] Step S30: depositing a heating electrode on the support layer, and printing a diffusion tower on the heating electrode to obtain a gas sensor precursor;

[0065] Step S40: etching the substrate of the gas sensor precursor to form a suspended membrane structure, thereby obtaining a gas sensor structure.

[0066] In this embodiment, the gas sensor structure is prepared by deposition and printing, which has the advantages of simple process and mass production; and by arranging a diffusion tower on the side of the heating electrode away from the support layer, the heat of the heating electrode is diffused to the diffusion tower, which reduces the volume of the sensor and reduces the loss of processing materials, while increasing the contact area between the sensing area and the airflow, thereby improving the performance of the sensor. In addition, the gas sensor structure with a flow channel groove is more suitable for stable and relatively high flow rate usage scenarios.

[0067] Specifically, the preparation of gas sensors with three-dimensional structures is divided into two parts. The first part is the processing of the basic mechanism. The sensor is processed and prepared using MEMS technology, which can realize the miniaturization, integration and mass production of the sensor. The second part is additive processing on the central sensing area. The three-dimensional structure is processed using nano-metal particles, which can achieve high-precision, high-surface-area ratio structural processing.

[0068] In some embodiments, before step S10, the substrate is cleaned; specifically, the cleaning comprises: firstly, soaking the substrate in a SCl solution (NH3 H2O / H2O2) to remove particles on the surface of the silicon wafer, rinsing the substrate, and then soaking the substrate in a SC2 solution (HCl / H2O2) to remove residual metal elements on the surface of the silicon wafer, and then rinsing the substrate and then using an air gun to blow off the surface moisture and drying the substrate.

[0069] In a preferred embodiment, since the sensor structure has a flow channel or groove structure, an anisotropic etching process of silicon is required, so a 4-inch P-type silicon wafer with a crystal plane of (100) and a thickness of 500 μm is selected.

[0070] In some embodiments, a silicon nitride film is selected as a supporting layer in the sensor, which also serves as an electrical insulating layer; depositing the supporting layer on the substrate specifically includes: preparing the silicon nitride film by LPCVD technology, the deposition temperature is 700-800°C, and the prepared silicon nitride film has the characteristics of high density, good uniformity, good electrical properties, low hydrogen content, low stress, etc.

[0071] Specifically, in this embodiment, a LPCVD method is used to grow a 1 μm low-stress silicon nitride layer on the surface of the substrate as a supporting layer.

[0072] In some embodiments, in the step S30, depositing the heating electrode on the support layer involves an imaging process of a metal film, which can be divided into three steps: photolithography, coating, and lift-off. First, a photolithography process is used to transfer the pattern of the heating electrode on the photolithography mask to the silicon substrate through processes such as coating, exposure, and development. In order to make it easy to peel off after coating, a double-layer coating process is used during coating. After that, electron beam evaporation (ebeam) is used to deposit a 200nm Pt layer as a heating electrode. Since the adhesion between Pt and the silicon nitride support film is poor, 15nm Ti or Ta needs to be deposited as an adhesion layer before depositing Pt. Finally, a positive photoresist stripping solution is used to strip the photoresist to complete the graphical production of the heating electrode.

[0073] In some embodiments, in step S30, taking gold as the metal column material as an example, the step of printing a diffusion tower on the heating electrode includes:

[0074] First, a borosilicate glass tube with an outer diameter of 1 mm was pulled into a hollow needle tip using a needle puller, and a needle with an inner diameter of 6 μm was selected for printing. A pipette was used to inject the metal nanoparticle solution into the needle tube from the end of the needle, and then ventilation was performed to fill the needle with gold nanoparticles and exhaust the air in the needle.

[0075] Then, the needle filled with gold nanoparticles is installed on a homemade printing platform. After the gold particle solution is loaded, a meniscus-shaped liquid surface is formed at the tip of the needle, causing the needle to gradually approach the substrate. When it reaches a certain distance (usually a few microns), a capillary bridge is formed at the intersection of the needle tip and the glass substrate. The solvent evaporates at the intersection, and the resulting continuous ink inflow causes the gold nanoparticles to accumulate on the substrate. The heating platform is heated to an operating temperature of 50 degrees Celsius to accelerate the accumulation of particles. The printing platform can move along the XYZ axis and rotate along the XY axis, with a total of five degrees of freedom.

[0076] Afterwards, the needle and the processing surface are positioned and aligned using the printing platform's dual-camera positioning system, which consists of a color low-magnification lens and a high-magnification grayscale lens, placed crosswise.

[0077] Finally, by slowly lowering the substrate in the vertical direction to increase the distance between the needle tip and the substrate, gold nanoparticles can be continuously deposited in the direction perpendicular to the substrate. Using a printing speed of 1 μm / s, gold nanoparticles are evenly printed on the surface of the Pt heating electrode to form gold columns. Repeating the operation can obtain a gold column array, i.e., a diffusion tower.

[0078] In some embodiments, between step S30 and step S40, the gas sensor precursor is also heat treated; since the diffusion tower structure just printed is not stable, it will absorb moisture in the air, causing the structure to collapse. Therefore, after printing, a muffle furnace is required for heat treatment, including the steps of: heating the printed gas sensor precursor to 100°C, and transferring the crucible to the muffle furnace and heating it to 100°C. Afterwards, the heated crucible is directly taken out and the gas sensor precursor is immediately moved from the printing platform to the crucible, and then quickly put back into the muffle furnace together to prevent the printed sample from absorbing moisture in the air and causing the structure to collapse. Then heat from 100°C to 400°C at 5°C / min, then keep warm at 400°C for 10 minutes, and then cool naturally. Finally, the gas sensor structure is obtained.

[0079] In some embodiments, in step S40, the step of etching the substrate of the gas sensor precursor to form a suspended membrane structure is completed by anisotropic etching of silicon. Anisotropic etching refers to the different etching rates of various crystallographic planes of the silicon wafer in anisotropic etching liquid. There are three commonly used crystal planes in the manufacture of MEMS devices: (100) crystal plane, (111) crystal plane and (110) crystal plane. Among them, the etching rates of (100) and (110) crystal planes are faster, and the etching rate of (111) crystal plane is the slowest. The angle between the (111) crystal plane and the (100) crystal plane after etching should be 54.7°. Commonly used anisotropic etching liquids include KOH etching liquid (KOH+IPA+H2O), EPW (ethylenediamine+catechol+water) and TMAH (tetramethylammonium hydroxide+water). KOH etching liquid has the characteristics of low cost, simple operation and non-toxicity, and is widely used. Therefore, a 40% concentration KOH solution is used to etch the (100) crystal surface silicon wafer, and the etching rate is about 0.69um / min.

[0080] In some embodiments, before etching, in order to form a suspended membrane structure, it is necessary to open a window on the silicon nitride layer to expose part of the silicon substrate to facilitate subsequent wet etching. Deep Reactive Ion Etching (DRIE) can form a plasma through glow discharge with a gas that reacts chemically with the etched material, and uses the dual effects of physical bombardment of the etched material by charged ions and chemical reaction of active free radicals with the etched material to perform etching. Inductively coupled plasma etching (ICP) can pass radio frequency current into the inductor coil, generate a high-frequency oscillating magnetic field near the coil in the reaction chamber, thereby obtaining a high-density, high-energy and uniformly distributed plasma, and has become the most widely used equipment in the DRIE process. Therefore, the ICP method is used to dry etch a total of 1450nm of silicon nitride layer.

[0081] In addition, the present invention also provides an application of the gas sensor with a three-dimensional structure in gas chromatography.

[0082] The following examples are further given to illustrate the present invention in detail. It should also be understood that the following examples are only used to further illustrate the present invention and cannot be understood as limiting the scope of protection of the present invention. Some non-essential improvements and adjustments made by those skilled in the art based on the above content of the present invention belong to the scope of protection of the present invention.

[0083] Example 1

[0084] The natural air flow heat distribution experiment was conducted with a gas sensor structure with a flow channel (flow channel type) and a gas sensor structure with a groove (groove type), wherein the substrate is made of single crystal silicon; the support layer is made of silicon nitride; the heating electrode is made of platinum, and the diffusion tower is made of gold. The results are as follows:

[0085] The heat distribution diagram of the natural air flow of the groove type is as follows Figure 8 As shown, the natural air flow heat distribution diagram of the flow channel type is as follows Fig. 9 As shown; In addition, the heat distribution diagram of the groove type along the Y axis with an air flow rate of 1m / s is as follows Fig.10 As shown, the heat distribution diagram of the flow channel type along the Y axis with an air flow rate of 1m / s is as follows Fig.11 As shown; at the same time, the thermal imaging of the groove type is as follows Fig.12 shown.

[0086] In the calculation results, the temperature distribution in the static state is consistent with the actual test; in the flow condition, the through-channel design can reduce the inhibitory effect on the airflow, so that the airflow flowing through the sensing area can flow fully and avoid the influence of low-energy turbulence on the airflow.

[0087] In the calculation results, the thermal conductivity sensor with a three-dimensional structure and gold pillars has a higher airflow utilization rate (better heat exchange effect). The groove type is blocked by the silicon substrate, and its airflow is hindered. Since the material of the heating electrode is Pt, which has a high TCR coefficient, the better heat exchange effect brought by sufficient airflow will cause the temperature drop of the heating electrode to be greater, and the resistance value of the heating electrode will increase. In addition, when the voltage remains unchanged, the current changes more. Therefore, the thermal conductivity gas sensor with a flow channel structure has better sensitivity.

[0088] Example 2

[0089] The material of the substrate is single crystal silicon; the material of the support layer is silicon nitride; the material of the heating electrode is platinum, and the material of the metal column is gold. The gas sensor structure with grooves (groove type) and the sensors with the same number of metal columns but different heights are subjected to mechanical analysis. The results are as follows Fig.13 described.

[0090] The calculation results show that the stress value at the connection between the outer gold column and the heating electrode is higher, which is consistent with Figure 7 The mechanical analysis of the results shows that reducing the height of the gold pillar can significantly improve the stress surge caused by the influence of the additional torque and the thermal expansion of the heating electrode. That is, after heating, with the same number of gold pillars, the shorter the height ( Fig.13 The stress performance of the high altitude ( Fig.13 (right picture in the figure).

[0091] Example 3

[0092] For the structure of the diffusion tower, nano-metal particle 3D processing can print a variety of shapes and structures, not limited to columnar printing. The processing shape can be customized according to actual use needs. Fig.14 The cross-arch structure shown illustrates the feasibility of custom fabrication.

[0093] In summary, the present invention provides a gas sensor with a three-dimensional structure and a preparation method thereof. The gas sensor structure with a three-dimensional structure includes a substrate with a flow channel, a support layer arranged on the side of the substrate with the flow channel, a heating electrode arranged on the side of the support layer away from the flow channel, and a diffusion tower arranged on the side of the heating electrode away from the support layer; the part of the support layer where the heating electrode is provided is suspended above the flow channel. The present invention arranges a diffusion tower on the side of the heating electrode away from the support layer so that the heat of the heating electrode diffuses to the diffusion tower, thereby reducing the volume of the sensor and reducing the loss of processing materials, while increasing the contact area between the sensing area and the airflow, thereby improving the performance of the sensor. In addition, a gas sensor structure with a flow channel is more suitable for stable and relatively high flow rate usage scenarios.

[0094] It should be understood that the application of the present invention is not limited to the above examples. For ordinary technicians in this field, improvements or changes can be made based on the above description. All these improvements and changes should fall within the scope of protection of the claims attached to the present invention.

Claims

1. A gas sensor structure having a three-dimensional structure, characterized in that: It includes a substrate with a flow channel, a support layer arranged on the side of the substrate with the flow channel, a heating electrode arranged on the side of the support layer away from the flow channel, and a diffusion tower arranged on the side of the heating electrode away from the support layer; the part of the support layer where the heating electrode is arranged is suspended above the flow channel.

2. The gas sensor structure with a three-dimensional structure according to claim 1, characterized in that: The substrate comprises a base layer, a first side wall arranged on the base layer, and a second side wall arranged symmetrically to the first side wall; the base layer, the first side wall and the second side wall form the flow channel.

3. The gas sensor structure with a three-dimensional structure according to claim 2, characterized in that: The support layer includes a substrate support layer arranged on the side of the first side wall and the second side wall away from the base layer, a plurality of support beams extending from the substrate support layer toward the center of the flow channel, and a sensing area support layer formed by the plurality of support beams extending together; the heating electrode is arranged on the side of the sensing area support layer away from the flow channel.

4. The gas sensor structure with a three-dimensional structure according to claim 1, characterized in that: The heating electrodes are distributed in a serpentine shape on the supporting layer.

5. The gas sensor structure with a three-dimensional structure according to claim 1, characterized in that: The diffusion tower includes a plurality of metal columns which are perpendicular to the support layer and connected to the heating electrodes.

6. The gas sensor structure with a three-dimensional structure according to claim 5, characterized in that: The diameter of the metal column is 6 μm-12 μm, and the height of the metal column is 25 μm-150 μm.

7. The gas sensor structure with a three-dimensional structure according to claim 5, characterized in that: The material of the metal column includes one of gold, silver, copper, tungsten, zinc, nickel, iron, platinum, tin, and lead, or an alloy of any two or more thereof.

8. The gas sensor structure with a three-dimensional structure according to claim 1, characterized in that: The material of the substrate is single crystal silicon; the material of the support layer is one of silicon nitride and silicon oxide; the material of the heating electrode is one of platinum, nickel-chromium alloy, polycrystalline silicon and silicon carbide.

9. The gas sensor structure with a three-dimensional structure according to claim 1, characterized in that: Both ends of the flow channel are provided with blocking walls.

10. A method for preparing a gas sensor structure having a three-dimensional structure as claimed in any one of claims 1 to 8, characterized in that: Includes steps: providing a substrate; depositing a support layer on the substrate; Depositing a heating electrode on the support layer, and printing a diffusion tower on the heating electrode to obtain a gas sensor precursor; The substrate of the gas sensor precursor is etched to form a suspended membrane structure, thereby obtaining a gas sensor structure.

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