Thermal distribution type micro-nano sensor for detecting flow velocity of high-flow-velocity water body and preparation method of thermal distribution type micro-nano sensor

Abstract

The invention provides a thermal distribution type micro-nano sensor for detecting the flow velocity of a high-flow-velocity water body and a preparation method of the thermal distribution type micro-nano sensor. According to the sensor design, an innovative mode of cascading a slow flow area structure and a heat distribution type temperature measuring unit is adopted, and the problem that an existing heat distribution type sensor loses efficacy in a high-flow-speed water body can be effectively solved. The sensor comprises two layers of structures: a substrate electrode layer and a PDMS top layer structure. The base electrode layer is composed of a silicon substrate, a heating unit and a plurality of temperature measuring resistors distributed in the circumferential direction of the heating unit. The PDMS top layer structure comprises a slow flow area and a temperature measurement area which are integrally formed, the slow flow area reduces the flow velocity of a water body through a micro-column array, the preparation method of the sensor comprises magnetron sputtering, photoetching, dry etching and preparation and assembly processes of the PDMS top layer structure, and the sensor is suitable for batch production and has high consistency. The sensor provided by the invention has wide application potential, especially in the fields of hydraulic engineering, environmental monitoring, ship power systems, industrial pipeline transportation and the like.

Description

Technical Field

[0001] This invention relates to the field of micro-nano sensor technology, and more specifically, to a thermally distributed micro-nano sensor for detecting the flow velocity of high-velocity water bodies and its fabrication method. Background Technology

[0002] In fields such as water conservancy projects, environmental monitoring, ship propulsion systems, industrial pipeline transportation, and marine resource development, real-time and accurate measurement of water flow velocity is a core parameter for ensuring the safe operation of systems, optimizing energy efficiency, and assessing ecological effects. For example, early warning of leaks in water transmission networks requires identifying abnormal fluctuations in flow velocity, hydropower station turbine units need to monitor inflow to adjust power generation efficiency, and ocean turbulence research relies on high dynamic response data.

[0003] Current mainstream water flow velocity sensing technologies include ultrasonic time-of-flight / Doppler methods, electromagnetic flow velocity detection, mechanical flow meters (such as turbines and propellers), and thermal distributed flow meters. Among these, mechanical flow sensors suffer from problems such as wear of moving parts, failure due to biofouling, and dead zones at low flow rates. Ultrasonic time-of-flight flow sensors are significantly affected by bubble / particle interference, and electromagnetic flow meters rely on the conductivity of the water and are unsuitable for pure water / oil. Therefore, there is an urgent need to develop novel flow velocity sensing technologies with no moving parts, high sensitivity, and strong interference resistance.

[0004] With the development of micro-nano sensing technology, the use of thermally distributed flow velocity sensors is gradually increasing, especially in the field of gas flow velocity detection. Although thermally distributed sensors have excellent sensing performance in the low flow velocity range (<0.5 m / s), due to limitations in their basic principles, they fail in high-flow-velocity water bodies (1-5 m / s, where 5 m / s is the peak flow velocity in civil water supply networks, the typical flow velocity in ship cooling water systems, and the economic flow velocity threshold for industrial pipelines; beyond this range, mechanical / electromagnetic solutions are recommended). The reason is as follows: because the thermal conductivity of water is much higher than that of air (0.598 W / (m·K) vs. 0.026 W / (m·K)), at higher flow velocities, the fluid heat transport rate increases exponentially. The temperature gradient generated in the heating zone is rapidly smoothed out by the high-speed water flow, causing the temperature difference between the upstream and downstream temperature measurement zones to drop to zero, i.e., the signal-to-noise ratio (SNR) drops below the detection threshold, making flow velocity detection impossible. The obvious solutions to this problem are to increase the heating power of the heater or increase the distance between the upstream and downstream temperature measurement zones. Although the two methods mentioned above are feasible in principle, excessively high heating power will reduce the service life of the thin-film heating metal unit and accelerate substrate aging; it will also increase the physical size of the sensor (exponentially), which goes against the original intention of miniaturized thermal distributed detection and full-range coverage.

[0005] In summary, existing thermally distributed flow velocity sensors for liquid environment detection fail at high flow rates (1-5 m / s) without compromising service life or physical dimensions. Therefore, research is needed to develop novel micro / nano-scale thermally distributed flow velocity sensors to address this issue. Summary of the Invention

[0006] The first technical problem to be solved by the present invention is to provide a thermally distributed micro / nano sensor for detecting the flow velocity of high-velocity water bodies, so as to solve the problem of failure in the detection of high-velocity water bodies in the prior art.

[0007] To overcome the shortcomings of the prior art, the present invention provides a thermally distributed micro / nano sensor for detecting the flow velocity of high-velocity water bodies, comprising a bonded base electrode layer and a PDMS top layer structure; The base electrode layer includes a silicon substrate, on the surface of which heating units and multiple temperature measuring resistors are integrated, and the multiple temperature measuring resistors are distributed circumferentially along the heating unit; The PDMS top layer structure is bonded to the surface of the substrate electrode layer and includes an integrally formed hollow fluid channel structure and a micropillar array. The fluid channel structure includes, in sequence along the water flow direction: Water inlet: located at the beginning of the channel; Slow-flow zone: Its cross-section is trapezoidal, with the narrow end connected to the water inlet and the wide end extending downstream. The micro-column array is provided in this zone to make the water flowing into the slow-flow zone from the water inlet more smoothly and evenly distributed. Temperature measuring zone: Its cross-section is rectangular, its inlet is connected to the wide end of the slow flow zone, and the heating unit and the temperature measuring resistor are located in the temperature measuring zone; Outlet contraction zone: Its cross-section is trapezoidal, with its wide end connected to the outlet of the temperature measurement zone and its narrow end being the water outlet, and the width of the water outlet being greater than the width of the water inlet.

[0008] The key innovation of this invention lies in the introduction of a "slow-flow zone" unit. Through a "trumpet-shaped" (trapezoidal) structure and a micro-pillar array design, the slow-flow zone reduces the water flow velocity, resulting in a low and uniform fluid velocity. This allows the temperature measurement zone to accurately reflect the water flow velocity in high-velocity water bodies, slowing down the high-speed water flow before it enters the temperature measurement zone. This design solves the problem of traditional thermal distributed sensors failing in high-velocity environments. The slow-flow zone structure decelerates the water flow before it enters the temperature measurement zone for accurate measurement, ensuring a sufficiently significant temperature gradient, improving the signal-to-noise ratio, and achieving high-velocity detection. The use of a micro-nano sensor design ensures high sensitivity and accuracy, making it particularly suitable for applications requiring high precision and small size, such as microfluidic chips and biomedical devices. Compared to existing technologies, the sensor of this invention has the following technical advantages: Combining a slow-flow zone with a thermally distributed temperature measurement unit: This invention introduces a slow-flow zone structure into the sensor design. This structure decelerates the high-speed fluid before it enters the temperature measurement zone, enabling the acquisition of an effective temperature gradient even in high-flow-rate environments. This solves the technical bottleneck of traditional thermally distributed sensors failing at high flow rates. No moving parts, strong anti-interference: The sensor of this invention does not rely on mechanical parts, avoiding the wear and bio-attachment failure problems of mechanical flow rate sensors. It possesses strong anti-interference capabilities and long-term stability, and is highly adaptable. High flow rate detection performance: The sensor of this invention can operate stably in a flow rate range up to 5 m / s with high detection accuracy, breaking through the limitations of existing technologies in high-flow-rate measurement and enabling its use in various practical application scenarios. Miniaturized design, adaptable to multiple application scenarios: This invention is manufactured using MEMS technology, possessing excellent miniaturization and mass production capabilities. It can adapt to flow rate monitoring applications in confined spaces and has strong market application potential.

[0009] In one possible implementation, the micropillar array is disposed on the slow-flow zone, and the micropillar array is arranged in a gradient increasing manner along the trapezoidal expansion direction of the slow-flow zone. The micropillar array is used to make the water entering the slow-flow zone more smoothly and evenly distributed.

[0010] Compared with existing technologies, the above-mentioned technical solution significantly increases the turbulence of the fluid by increasing the contact surface of the water flow and effectively hinders the rapid flow of water. As the water flow expands from the narrow opening to the wide opening in the slow-flow zone, the gradient arrangement of the micropillar array can gradually slow down the flow velocity during the water flow process, so that the flow of the fluid is gradually slowed down and homogenized, thereby providing a slow-flow environment. This ensures that the fluid can maintain a sufficient velocity difference when the flow velocity is high, avoiding the problem of the temperature gradient being quickly flattened due to the excessive flow velocity in traditional thermal distributed sensors in high-velocity water bodies. Through the gradual deceleration effect of the micropillar array, accurate flow velocity detection is achieved in high-velocity water bodies.

[0011] In one possible implementation, the heating unit is a serpentine Cr-Pt electrode.

[0012] Compared with existing technologies, the above-mentioned technical solution enables the serpentine electrode to uniformly heat the water along the entire heat distribution area of ​​the sensor. By changing the length and width of the electrode, a temperature gradient is gradually formed in the heating area, which effectively solves the problem of temperature instability caused by local overheating or uneven heating in traditional heating units and enhances the accuracy of flow rate measurement.

[0013] In one possible implementation, the number of temperature sensing resistors is at least eight, and the temperature sensing resistors are evenly distributed circumferentially on the outside of the heating unit.

[0014] Compared with the prior art, the above technical solution arranges temperature measuring resistors in the upstream and downstream areas of the heating unit to detect temperature changes as water flows through the heating unit. Using at least eight temperature measuring resistors allows for the distribution of temperature data over a wider area. As water flows through the heating area, the temperature changes, and these changes are monitored simultaneously at multiple temperature measuring points, thus providing more accurate data for flow rate calculation. The temperature measuring resistors are circumferentially distributed on the outside of the heating unit, improving the detection accuracy. All the temperature measuring resistors are either circumferentially or squarely distributed.

[0015] Another technical problem to be solved by the present invention is to provide a method for fabricating a thermally distributed micro / nano sensor for detecting the flow velocity in high-velocity water bodies, so as to solve the problem of flow velocity detection failure in high-velocity environments in the prior art.

[0016] To overcome the shortcomings of the prior art, this invention provides a method for fabricating a thermally distributed micro / nano sensor for detecting the flow velocity of high-velocity water bodies, comprising the following steps: S1: Fabrication of the substrate electrode layer: A metal layer is prepared by magnetron sputtering on the surface of a silicon substrate, and the heating unit and temperature measuring resistor are formed by photolithography and dry etching. S2: Fabrication of the PDMS top layer structure: Photoresist is spin-coated onto the surface of another silicon substrate, and a mold for forming the PDMS top layer structure is formed by photolithography and development. Liquid PDMS is then poured into the mold, and after curing, the PDMS top layer structure is obtained by demolding. The mold includes: fluid channel boundary protrusions: channel sidewalls corresponding to the water inlet, slow flow zone, temperature measurement zone, and outlet contraction zone; and pits for forming the micropillar array: a columnar recess array set at the slow flow zone position to form the micropillar array. S3: Bonding Assembly: The top layer of PDMS and the substrate electrode layer are activated by oxygen plasma, aligned and then hot-pressed to obtain a thermally distributed micro / nano sensor for detecting the flow velocity of high-velocity water bodies.

[0017] This application discloses a method for fabricating a thermally distributed micro / nano sensor for high-velocity water flow velocity detection. Compared with existing technologies, this method maintains excellent flow velocity detection performance in high-velocity water environments, solving the problem that existing thermally distributed sensors cannot operate stably in high-velocity environments. It provides an accurate, reliable, and low-cost solution for high-velocity water flow velocity detection, greatly improving the applicability and accuracy of flow velocity detection under complex fluid conditions. It has the following advantages: Improved high flow velocity detection capability: Traditional thermal distributed sensors cannot maintain a stable temperature gradient in high flow velocity environments, while this invention effectively reduces the water flow velocity by setting a micro-pillar array in the slow flow zone, ensuring that the temperature gradient can be maintained when the fluid passes through the temperature measurement zone, thereby realizing effective flow velocity detection of high flow velocity water. Increased measurement accuracy and reliability: In the preparation method of this invention, the micropillar array improves the accuracy of flow velocity detection by increasing the degree of fluid turbulence. This design can maintain a high signal-to-noise ratio under complex flow velocity conditions, enabling the sensor to work stably under different flow velocities. The manufacturing process is simplified and the cost is reduced: The preparation method of this invention uses PDMS material to prepare the top layer structure and utilizes photolithography and casting technology to achieve relatively simple mass production. Compared with traditional mechanical sensors, micro-nano sensors are smaller in size, can adapt to smaller installation spaces, and have lower costs. High sensitivity and wide applicability: Because the micro-nano sensor in the preparation method of this invention adopts MEMS (microelectromechanical systems) technology, the sensor has high sensitivity and is applicable to various conductive and non-conductive liquids, and can be widely used in water conservancy, environmental protection, industrial pipelines, marine resource development and other fields.

[0018] In one possible implementation, in step S1, the silicon substrate is a silicon wafer that has been double-sided polished and oxidized.

[0019] Compared with existing technologies, the above technical solution can significantly improve the surface flatness and smoothness of the silicon substrate after double-sided polishing. Through oxidation treatment, a uniform silicon oxide layer is formed on the surface of the silicon substrate, which provides better chemical stability, enhances the corrosion resistance of the silicon wafer, and improves the service life and reliability of the sensor.

[0020] In one possible implementation, in step S1, the metal layer is a Cr-Pt metal layer with a thickness of 85±65μm.

[0021] Compared with existing technologies, the above technical solution uses Cr-Pt metal layer as the material for heating unit and temperature measuring resistor. Due to its excellent thermal stability, good electrical conductivity and low coefficient of thermal expansion, it exhibits extremely high stability in high temperature and high flow rate environments. Furthermore, the optimization of the metal layer thickness (85±65μm) can ensure that the heating unit responds quickly and adapts to instantaneous flow rate changes in high flow rate environments.

[0022] In one possible implementation, in step S2, the photoresist is SU-8 photoresist with a thickness of 250±50μm.

[0023] Compared with existing technologies, the above technical solution uses SU-8 photoresist, which has excellent chemical stability and mechanical strength. Its polymer structure allows it to remain stable in high-temperature and high-flow-rate environments. Photolithography and development using this photoresist under ultraviolet light irradiation can form high-precision microstructures. Furthermore, the thickness of the photoresist is 250±50μm, which ensures the formation of a relatively robust PDMS mold structure, while having sufficient strength to support the micropillar array and fluid channel structure.

[0024] In one possible implementation, in step S2, the conditions for demolding after curing are: curing at a temperature of 90±10℃ for 2 hours, and the pouring thickness of the liquid PDMS is 1±0.1mm.

[0025] Compared with existing technologies, the above technical solution ensures complete curing of PDMS by curing at 90±10℃ for 2 hours, forming a structure with stable physical properties during the curing process. The casting thickness of liquid PDMS is 1±0.1mm. This thickness design helps to form a mold with high mechanical strength and good microstructure fidelity. Too thin a PDMS layer may cause the mold to be unstable and easily deformed under stress; too thick a layer may affect the accuracy and operability of the microstructure.

[0026] In one possible implementation, in step S3, the hot-press bonding condition is: hot-pressing with a 100g weight at a temperature of 80°C for more than 10 hours.

[0027] Compared with existing technologies, the above-mentioned technical solution, when bonding the PDMS top layer and the substrate electrode layer, applies appropriate pressure at 80°C using a 100g weight and maintains hot-pressing for more than 10 hours, ensuring a strong bond between the PDMS and the silicon substrate electrode layer. In this invention, the hot-pressing process, through the synergistic effect of temperature and pressure, promotes enhanced intermolecular forces between the PDMS and the substrate surface, thereby achieving a firm bond between the two layers. Furthermore, the combination of weight mass and hot-pressing time improves the final bonding strength. Attached Figure Description

[0028] Figure 1 This is a schematic diagram of the sensor detection principle of the present invention; Figure 2 This is a top sectional view of the sensor in Embodiment 1 of the present invention; Figure 3 This is a side sectional view of the sensor of the present invention; Figure 4 This is a flowchart of the sensor fabrication method of the present invention; Figure 5 This is a top sectional view of the sensor in Embodiment 2 of the present invention; Figure 6 This is a top sectional view of the sensor in Embodiment 3 of the present invention; Explanation of reference numerals in the attached figures: Figure 2 , Figure 3 , Figure 5 , Figure 6 In the middle, 1. Water inlet, 2. Base electrode layer, 3. PDMS top layer structure, 4. Micropillar array, 5. Slow flow zone, 6. Temperature sensing resistor, 61. Upstream resistor, 62. Downstream resistor, 7. Heating unit, 8. Temperature sensing zone, 9. Water outlet, 10. Outlet contraction zone. Figure 4 In the diagram, 11, SiO2; 12, Si; 13, metal layer; 14, electrode; 15, SU-8 photoresist; 16, PDMS. Detailed Implementation

[0029] First, those skilled in the art should understand that these embodiments are merely used to explain the technical principles of the embodiments of this application and are not intended to limit the scope of protection of the embodiments of this application. Those skilled in the art can make adjustments as needed to adapt to specific application scenarios.

[0030] In the description of the embodiments of this application, it should be noted that, unless otherwise explicitly specified and limited, the terms "connected" and "linked" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium. Those skilled in the art can understand the specific meaning of the above terms in the embodiments of this application based on the specific circumstances.

[0031] In the embodiments of this application, unless otherwise expressly specified and limited, "above" or "below" the second feature can mean that the first feature is in direct contact with the second feature, or that the first feature is in indirect contact with the second feature through an intermediate medium. Furthermore, "above," "on top of," and "over" the second feature can mean that the first feature is directly above or diagonally above the second feature, or simply that the first feature is at a higher horizontal level than the second feature. "Below," "below," and "under" the second feature can mean that the first feature is directly below or diagonally below the second feature, or simply that the first feature is at a lower horizontal level than the second feature.

[0032] This invention provides a thermally distributed micro / nano sensor for detecting the flow velocity of high-velocity water bodies, comprising a bonded base electrode layer 2 and a PDMS top layer structure 3; The base electrode layer 2 includes a silicon substrate, on the surface of which a heating unit 7 and a plurality of temperature measuring resistors 6 are integrated, and the plurality of temperature measuring resistors 6 are distributed circumferentially along the heating unit 7. The PDMS top layer structure 3 is bonded to the surface of the substrate electrode layer 2, and includes an integrally formed hollow fluid channel structure and a micropillar array 4. The fluid channel structure includes, in sequence along the water flow direction: Water inlet 1: Located at the beginning of the channel; Slow-flow zone 5: Its cross-section is trapezoidal, with the narrow end connected to the water inlet 1 and the wide end extending downstream. The micro-column array 4 is provided in this area, which is used to reduce the water flow velocity. Temperature measuring zone 8: Its cross-section is rectangular, its inlet is connected to the wide end of the slow flow zone 5, and the heating unit 7 and the temperature measuring resistor 6 are located in the temperature measuring zone 8; The outlet contraction zone 10 has a trapezoidal cross-section. Its wide end is connected to the outlet of the temperature measurement zone 8, and its narrow end is the water outlet 9. The width of the water outlet 9 is greater than the width of the water inlet 1.

[0033] As a preferred embodiment, the micro-pillar array 4 is disposed on the slow-flow zone 5, and the micro-pillar array 4 is arranged in a gradient increasing manner along the trapezoidal expansion direction of the slow-flow zone 5. The micro-pillar array 4 is used to reduce the water flow velocity.

[0034] As a preferred embodiment, the heating unit 7 is a serpentine Cr-Pt electrode.

[0035] As a preferred embodiment, the number of temperature measuring resistors 6 is at least 8, and the temperature measuring resistors 6 are evenly distributed circumferentially on the outside of the heating unit 7, which improves the detection accuracy. All the temperature measuring resistors 6 are evenly distributed in a circle or square.

[0036] This invention proposes an innovative flow velocity sensor that cascades a slow-flow zone unit and a thermally distributed temperature sensing unit, forming a two-layer structure. The sensor comprises a heating unit 7 and a temperature-sensing resistor 6 on a silicon substrate, as well as a slow-flow zone unit fabricated from materials such as PDMS or acrylic. The key reason this sensor can achieve high flow velocity measurement is that… Figure 2 , 3 As shown, a "trumpet-shaped" slow-flow zone 5 is designed in front of the distributed thermal measurement zone. When high-speed water enters from the water inlet 1 and flows out from the water outlet 9, the water pressure remains constant, and the width of the water outlet 9 is much larger than the width of the water inlet 1, resulting in a significantly lower flow velocity at the water outlet 9 section compared to the water inlet 1. Furthermore, the micro-pillar array 4 within the slow-flow zone effectively ensures the uniformity of the water flow at the water outlet 9 section and avoids dead zones within the slow-flow zone. The decelerated water flows out from the water outlet 9 and into the distributed thermal measurement zone, thus achieving accurate flow velocity detection.

[0037] It is worth noting that, since there is a one-to-one correspondence between the flow velocity of the water body to be measured, the flow velocity at section 9 of the outlet in the slow-flow zone, and the flow velocity in the temperature measurement zone, the sensor design of this invention can accurately detect the flow velocity of high-velocity water bodies, solving the technical problem that existing thermally distributed velocity sensors cannot function properly under high-velocity conditions. Therefore, this invention not only promotes the development of sensor technology but also provides significant value for practical applications in related fields.

[0038] Furthermore, by integrating the thermally distributed micro / nano sensor of the present invention for detecting high-velocity water flow, full-range thermally distributed detection of water flow velocity can be achieved with comparable physical size.

[0039] The present invention also provides a method for fabricating the aforementioned thermally distributed micro / nano sensor for detecting high-velocity water flow, comprising the following steps: S1: Fabrication of the base electrode layer 2: A metal layer is prepared by magnetron sputtering on the surface of a silicon substrate, and the heating unit 7 and the temperature measuring resistor 6 are formed by photolithography and dry etching; S2: Fabrication of PDMS top layer structure 3: Photoresist is spin-coated onto the surface of another silicon substrate, and a mold for forming PDMS top layer structure 3 is formed by photolithography and development. Liquid PDMS is then poured into the mold, and after curing, the mold is demolded to obtain PDMS top layer structure 3. The mold includes: fluid channel boundary protrusions: corresponding to the channel sidewalls of water inlet 1, slow flow zone 5, temperature measurement zone 8 and outlet contraction zone 10; and pits for forming micropillar array 4: a columnar recess array set at the position of the slow flow zone 5 to form micropillar array 4. S3: Bonding Assembly: The top layer of PDMS and the substrate electrode layer 2 are activated by oxygen plasma, aligned and then hot-pressed to obtain a thermally distributed micro / nano sensor for detecting the flow velocity of high-velocity water bodies.

[0040] One of the core technologies of this invention is the method for preparing the PDMS top layer structure 3. Considering the compatibility of mass production and processes, this invention selects PDMS as the main material for the slow flow region and test region of the electrode top layer: First, a patterned SU-8 photoresist mold is prepared on a silicon wafer using photolithography. The mold includes a trapezoidal structure of the slow flow region 5, a micropillar array 4 (corresponding to a micro-hole array on the mold), and a rectangular structure of the temperature measurement region 8. Then, liquid PDMS is poured into the mold, and after thermal curing, it is demolded to complete the preparation of the top layer structure. This method can ensure the accuracy of the structure and has high production efficiency, making it suitable for large-scale mass production.

[0041] The second key technology of this invention is the fabrication method of the thermally distributed temperature sensing electrode array. To ensure the stability and reliability of the heating unit 7 and the temperature sensing resistor 6, Pt material with negative temperature characteristics is selected as the material for the heating unit 7 and the temperature sensing resistor 6. A metal thin film is prepared by magnetron sputtering technology, and then the serpentine electrode is patterned by photolithography and dry etching technology. In order to further improve the quality of the thin film electrode, an annealing process can be used to improve the conductivity and thermal stability of the electrode, ensuring that the metal electrode array has excellent performance.

[0042] The third key technology is the two-layer assembly process. Through the Si-PDMS bonding process, a strong bond is achieved between the electrode array and the PDMS structure: First, the PDMS and silicon wafer surfaces are activated by oxygen plasma to generate Si-OH and PDMS-OH hydrophilic groups. Then, the two are precisely aligned and thermo-pressed to form an integrated structure. After completion, electrode leads are connected to finally fabricate the entire sensor, which can be used for actual flow rate experimental testing.

[0043] The beneficial effects of the fabrication method of this invention lie in its provision of a thermally distributed micro / nano sensor capable of accurately detecting the flow velocity of high-velocity water bodies. This successfully solves the problem of traditional thermally distributed sensors failing under high-velocity conditions. Based on innovative design, this invention provides a highly efficient sensor fabrication method, employing standard MEMS process procedures, and possessing significant advantages such as excellent mass production capabilities, low cost, and high consistency. This not only helps reduce production costs but also ensures the large-scale application of high-performance sensors.

[0044] As a preferred embodiment, in step S1, the metal layer is a Cr-Pt metal layer with a thickness of 85±65μm.

[0045] As a preferred embodiment, in step S2, the photoresist is SU-8 photoresist with a thickness of 250±50μm.

[0046] As a preferred embodiment, in step S2, the conditions for demolding after curing are: curing at a temperature of 90±10℃ for 2 hours, and the pouring thickness of the liquid PDMS is 1±0.1mm.

[0047] As a preferred embodiment, in step S3, the hot-press bonding condition is: hot-pressing with a 100g weight at a temperature of 80°C for more than 10 hours.

[0048] The following will provide embodiments incorporating specific data and structures to further elaborate on the above-described technical solutions of the present invention: Example 1: This embodiment provides a thermally distributed micro / nano sensor for detecting flow velocity in high-velocity water bodies and its fabrication method. The micro / nano sensor includes a substrate electrode layer 2 and a PDMS top layer structure 3. The sensor's structural design, through an innovative cascaded configuration of a flow-retarding zone and a thermally distributed temperature measurement unit, effectively solves the problem of existing thermally distributed sensors failing in high-velocity water environments. The structure and components of this sensor will be described in detail below.

[0049] Substrate electrode layer 2: Substrate electrode layer 2 consists of a silicon substrate, heating unit 7, and multiple temperature sensing resistors 6. A Cr-Pt metal layer is deposited on the surface of the silicon substrate using magnetron sputtering technology, serving as the basis for the heating unit 7 and the temperature sensing resistors 6. The heating unit 7 adopts a serpentine Cr-Pt electrode structure, which has excellent thermal stability and conductivity. The temperature sensing resistors 6 are distributed circumferentially along the heating unit 7, and there are eight of them. Figure 2 , Figure 3 As shown, Figure 2 In this configuration, eight temperature-sensing resistors 6 are distributed circumferentially around the heating unit 7. Specifically, with the heating unit 7 as the center, the temperature-sensing resistors 6 are evenly distributed around the heating unit 7 in a ring array with equal angles, and the central angle between adjacent temperature-sensing resistors 6 is 45°. The resistors 61 closest to the water outlet 9 are upstream resistors, and the resistors 62 closest to the water outlet 9 are downstream resistors. This allows for precise measurement of temperature changes in the upstream and downstream regions of the heating unit 7, thereby providing accurate data for flow rate calculation.

[0050] PDMS Top Layer Structure 3: The PDMS top layer structure 3 is made of PDMS material and bonded to the surface of the substrate electrode layer 2. The top layer structure includes a one-piece molded hollow fluid channel structure and a micropillar array 4, specifically comprising four rows of micropillars arranged parallel to each other in the slow-flow zone 5, following the direction of water flow. The number of micropillars in each row increases progressively. Figure 1 As shown, specifically from left to right (i.e. from the direction of water flow at the water inlet), the micropillars of the micropillar array increase in size step by step. This structure is mainly used to control the deceleration of the water flow and ensure accurate measurement of the flow velocity. The fluid channel structure includes, in sequence along the direction of water flow, a water inlet 1, a slow-flow zone 5, a temperature measurement zone 8, and an outlet contraction zone 10.

[0051] Water inlet 1: Located at the beginning of the fluid channel, used to guide water flow into the sensor.

[0052] Slow-flow zone 5: The cross-section of the slow-flow zone is trapezoidal, with the narrow end connected to the water inlet 1 and the wide end extending downstream. This zone utilizes a micro-pillar array 4 to reduce water velocity. The micro-pillar array 4 is arranged in a gradient increasing pattern along the trapezoidal expansion direction of the slow-flow zone, effectively increasing the water contact surface, enhancing fluid turbulence, gradually slowing the flow velocity, and ensuring a more uniform and smooth flow of water entering the inlet. Through this design, the flow velocity is sufficiently reduced and homogenized when the water enters the temperature measurement zone, thus ensuring a significant temperature gradient and preventing the rapid disappearance of the temperature gradient at high flow velocities.

[0053] Temperature measurement zone 8: The inlet of this zone is connected to the wide end of the slow flow zone 5, and the heating unit 7 and the temperature measuring resistor 6 are located in the temperature measurement zone 8. In this zone, the temperature measuring resistor 6 inverts the flow velocity by monitoring the temperature change of the water flow.

[0054] Outlet contraction zone 10: This zone has a trapezoidal cross-section, with the wide end connected to the outlet of temperature measurement zone 8 and the narrow end being the water outlet 9. The width of the water outlet 9 is greater than the width of the water inlet 1, ensuring that the flow velocity of the water is effectively slowed down when it flows out of the outlet, thus avoiding turbulence at the outlet.

[0055] In this embodiment, the sensor has a two-layer structure, including a base electrode layer 2 and a PDMS top layer structure 3, which are bonded together by a Si-PDMS bonding process. First, the surfaces of the PDMS top layer and the base electrode layer 2 are activated by oxygen plasma to generate hydrophilic groups, ensuring good bonding between the two layers. Then, the two layers are strongly bonded together by a hot-pressing process under appropriate temperature and pressure, ultimately forming an integral sensor structure. This structure design can effectively avoid the loss of temperature gradient caused by high-flow-rate water, ensuring that the sensor can still work normally in high-flow-rate environments and provide accurate flow rate detection. The following provides a method for fabricating the aforementioned sensor: S1: Fabrication of substrate electrode layer 2: Selecting the substrate material: First, select a silicon wafer that has been double-polished and oxidized (e.g., ...). Figure 4 (a) As shown, the silicon wafer includes SiO2 and Si12. The surface flatness of the silicon wafer is less than 1 μm, and the oxide layer thickness is about 1 μm to ensure good surface smoothness and chemical stability. Magnetron sputtering of the metal layer: Next, an 85 nm thick Cr-Pt metal layer 13 was prepared on the surface of the silicon oxide wafer using magnetron sputtering technology (e.g., ...). Figure 4 (b) As shown, the metal layer 13 serves as the base material for the subsequent heating unit 7 and the temperature measuring resistor 6. The Cr-Pt alloy, due to its excellent thermal stability and good electrical conductivity, can effectively meet the requirements of the sensor in high-flow-rate water. Electrode patterning: Subsequently, photoresist (positive resist) is coated onto the substrate metal layer, and photolithography is used to form electrode layer windows. Next, a dry etching process is used to remove areas of metal layer 13 not protected by photoresist (such as...). Figure 4 (c) As shown, a serpentine electrode 14 with the desired shape is finally formed. In this process, photolithography and dry etching techniques can precisely control the size and shape of the electrode to ensure the accuracy of the electrode structure.

[0056] Annealing treatment: In order to further improve the conductivity and thermal stability of the metal electrode, the metal electrode is treated with an annealing process. Through the annealing process, the conductivity and thermal stability of the Cr-Pt electrode 14 are further improved, ensuring that it can work stably for a long time in practical applications.

[0057] S2: Preparation of PDMS top layer structure 3: Preparation of the photolithography mold: A 250μm thick layer of SU-8 photoresist 15 is spin-coated onto a double-sided polished silicon wafer, followed by photolithography and development processes to form a patterned mold (e.g., ...). Figure 4 (d) shows that the mold includes a slow-flow zone 5 structure, a micropillar array 4 (corresponding to a micro-hole array) and a temperature measurement zone 8 structure. SU-8 photoresist has good mechanical strength and chemical stability, ensuring that the mold can work stably in high-flow-rate water environments;

[0058] PDMS casting and curing: Pour liquid PDMS16 into the above photoresist mold, ensuring a casting thickness of 1mm (e.g., Figure 4 (e) As shown, the mold is then placed in a 90°C thermosetting oven for 2 hours to ensure that the PDMS is completely cured and forms a stable top layer structure. Demolding and cleaning: After curing, PDMS16 is demolded from the mold (e.g.) Figure 4 (f) shows that a top-level structure with micropillar array 4 and fluid channels is obtained. At this time, the surface of the top-level structure has high microstructure fidelity and can accurately replicate the pattern of the photolithography mold.

[0059] S3: Bonding assembly: The PDMS top layer is bonded to the substrate electrode layer 2 through a single oxygen plasma activation treatment (e.g., Figure 4 (g) As shown, hydrophilic groups are generated on the PDMS and silicon surface under the action of oxygen plasma, ensuring that the two can be firmly bonded. Then, the PDMS top layer is precisely aligned with the substrate electrode layer 2, and the bonding process is completed by hot pressing (at 80°C, with a 100g weight applied, hot pressing 11 sales); this process ensures strong bonding and good mechanical stability of the two-layer structure.

[0060] Example 2: Example 2 provides a thermally distributed micro / nano sensor for detecting the flow velocity of high-velocity water and its fabrication method. The structure of the micro / nano sensor is similar to that of Example 1, except that there are 16 temperature-sensing resistors 6, which are arranged circumferentially outside the heating unit 7. Specifically, the 16 temperature-sensing resistors 6 are arranged circumferentially outside the heating unit 7 with the geometric center of the heating unit 7 as the center, and the central angle between adjacent temperature-sensing resistors 6 is 22.5°. The micro-pillar array 4 includes 4 columns of micro-pillars, and the 4 columns of micro-pillars are arranged in parallel in the slow-flow zone 5, with the number of micro-pillars in each column increasing in the direction of water flow (from left to right).

[0061] The following provides a method for fabricating the aforementioned sensor: S1: Fabrication of substrate electrode layer 2: Selecting the substrate material: First, select a silicon wafer that has been polished and oxidized on both sides. The surface flatness of the silicon wafer is less than 1μm, and the oxide layer thickness is about 1μm to ensure good surface smoothness and chemical stability. Magnetron sputtering metal layer: A 150 nm thick Cr-Pt metal layer 13 is prepared on the surface of silicon oxide wafer by magnetron sputtering technology. This metal layer serves as the base material for the subsequent heating unit 7 and temperature measuring resistor 6. Due to its excellent thermal stability and good electrical conductivity, the Cr-Pt alloy can effectively meet the requirements of the sensor in high-flow-rate water. Electrode patterning: Next, photoresist (positive photoresist) is coated on the substrate metal layer, and an electrode layer window is formed using a photolithography development process; subsequently, the area in the metal layer 13 not protected by the photoresist is removed by a dry etching process, and finally a serpentine electrode 14 of the desired shape is formed. Annealing treatment: In order to further improve the conductivity and thermal stability of the metal electrode, the metal electrode is treated with annealing process. Through the annealing process, the conductivity and thermal stability of Cr-Pt electrode 14 are further improved, ensuring that it can work stably for a long time in practical applications.

[0062] S2: Preparation of PDMS top layer structure 3: Fabrication of the photolithography mold: SU-8 photoresist 15 with a thickness of 250μm is spin-coated on a double-sided polished silicon wafer, and photolithography and development processes are performed to form a patterned mold, which includes a slow flow region 5 structure, a micro pillar array 4 (corresponding to a micro hole array) and a temperature measuring region 8 structure. PDMS casting and curing: Liquid PDMS is poured into the photoresist mold, ensuring a casting thickness of 1 mm. The mold is then placed in a 90°C curing oven for 2 hours to ensure complete curing of PDMS16 and the formation of a stable top layer structure.

[0063] Demolding and cleaning: The cured PDMS16 is demolded from the mold to obtain a top-layer structure with micropillar array 4 and fluid channels.

[0064] S3: Bonding assembly: Oxygen plasma activation: The PDMS top layer is bonded to the substrate electrode layer 2 by three oxygen plasma activation treatments. Under the action of oxygen plasma, hydrophilic groups are generated on the PDMS and silicon surface, ensuring that the two can be firmly bonded. Hot pressing process: Then, the PDMS top layer and the substrate electrode layer 2 are precisely aligned, and the bonding process is completed by hot pressing (at 80°C, a 100g weight is applied, and hot pressing is carried out for 12 hours), which ensures a strong bond and good mechanical stability between the two layers.

[0065] Example 3: Example 3 provides a thermally distributed micro / nano sensor for detecting the flow velocity of high-velocity water bodies and its fabrication method. The structure of the micro / nano sensor is similar to that of Example 1, except that the number of temperature-sensing resistors 6 is 24. Figure 6 As shown, the 24 temperature measuring resistors 6 are arranged circumferentially outside the heating unit 7. Specifically, the 24 temperature measuring resistors 6 are arranged circumferentially outside the heating unit 7 with the geometric center of the heating unit 7 as the center. The central angle between adjacent temperature measuring resistors 6 is 15°. The micro-pillar array 4 includes 4 columns of micro-pillars, and the 4 columns of micro-pillars are arranged in parallel in the slow flow zone 5. The number of micro-pillars in each column increases in the direction of water flow (from left to right).

[0066] The following provides a method for fabricating the aforementioned sensor: S1: Fabrication of substrate electrode layer 2: Selecting the substrate material: First, select a silicon wafer that has been polished and oxidized on both sides. The surface flatness of the silicon wafer is less than 1μm, and the oxide layer thickness is about 1μm to ensure good surface smoothness and chemical stability. Magnetron sputtering metal layer: A 20 nm thick Cr-Pt metal layer was prepared on the surface of a silicon oxide wafer using magnetron sputtering technology. This metal layer serves as the base material for the subsequent heating unit 7 and the temperature sensing resistor 6. Due to its excellent thermal stability and good electrical conductivity, the Cr-Pt alloy can effectively meet the requirements of the sensor for use in high-flow-rate water bodies.

[0067] Electrode patterning: Next, photoresist (positive photoresist) is coated on the substrate metal layer, and an electrode layer window is formed using a photolithography development process; subsequently, the area in the metal layer 13 not protected by the photoresist is removed by a dry etching process, and finally a serpentine electrode 14 of the desired shape is formed. Annealing treatment: To further improve the conductivity and thermal stability of the metal electrode, an annealing process is used to treat the metal electrode. Through the annealing process, the conductivity and thermal stability of the Cr-Pt electrode 14 are further improved, ensuring its long-term stable operation in practical applications.

[0068] S2: Preparation of PDMS top layer structure 3: Fabrication of the photolithography mold: SU-8 photoresist 15 with a thickness of 250μm is spin-coated on a double-sided polished silicon wafer, and photolithography and development processes are performed to form a patterned mold, which includes a slow flow region 5 structure, a micro pillar array 4 (corresponding to a micro hole array) and a temperature measuring region 8 structure. PDMS16 casting and curing: Liquid PDMS is poured into the photoresist mold, ensuring a casting thickness of 1 mm. The mold is then placed in a 90°C curing oven for 2 hours to ensure complete curing of the PDMS and the formation of a stable top layer structure.

[0069] Demolding and cleaning: The cured PDMS16 is demolded from the mold to obtain a top-layer structure with micropillar array 4 and fluid channels; S3: Bonding assembly: Oxygen plasma activation: The PDMS top layer is bonded to the substrate electrode layer 2 through a single oxygen plasma activation treatment. Hydrophilic groups are generated on the PDMS and silicon surface under the action of oxygen plasma, ensuring a strong bond between the two.

[0070] Hot pressing process: Then, the PDMS top layer and the substrate electrode layer 2 are precisely aligned, and the bonding process is completed by hot pressing (at 80°C, a 100g weight is applied, and hot pressing is carried out for 12 hours), which further ensures the strong bonding and good mechanical stability of the two-layer structure.

[0071] The thermally distributed flow velocity sensor of this invention is based on the coupling effect of heat transfer and fluid convection diffusion. It inverts the flow velocity by measuring the temperature field distortion upstream and downstream of the heating unit 7. Specifically, the sensor is designed by setting temperature measuring units upstream and downstream of the heating unit 7 to measure the temperature difference between these regions. This temperature difference has a linear relationship with the flow velocity. The faster the flow velocity, the more obvious the thermal gradient distortion, resulting in a larger temperature difference. This principle enables the thermally distributed flow velocity sensor to accurately and sensitively detect water flow velocity.

[0072] In the sensor of this invention, a slow-flow zone 5 is incorporated. This design, combined with a thermally distributed temperature measurement unit, further enhances the sensor's performance under high flow rate conditions. The slow-flow zone slows down the high-speed fluid and homogenizes the water flow through a trapezoidal structure and micropillar array 4. At high flow rates, the water flow is gradually slowed down in the slow-flow zone, and a significant temperature gradient emerges upon entering the temperature measurement zone. The sensor successfully avoids the signal-to-noise ratio degradation caused by an overly smooth temperature gradient under high flow rate conditions.

[0073] like Figure 1 As shown, when fluid passes through heating unit 7, the temperature field is distorted due to the temperature difference between heating unit 7 and the upstream and downstream temperature measuring electrodes caused by the change in flow velocity. By measuring these temperature differences, combined with the effect of the slow-flow zone, the sensor can accurately infer the water flow velocity. In this process, the slow-flow zone design plays a significant synergistic role, not only slowing down the fluid flow velocity but also making the fluid flow more uniform, providing a more obvious temperature gradient for temperature measurement, thereby ensuring accurate detection of the flow velocity.

[0074] Compared to traditional flow velocity detection methods, the thermally distributed sensor of this invention has the advantage of having no moving parts, avoiding the wear and failure problems of mechanical sensors. It also possesses strong vibration resistance and dirt resistance, resulting in a service life far exceeding that of traditional mechanical sensors. Furthermore, the sensor can operate stably within a microflow velocity range of 0.001 m / s, far exceeding the detection capabilities of ultrasonic and electromagnetic methods, and can meet the measurement needs of both conductive and non-conductive liquids (such as pure water, oil, and chemical solutions).

[0075] Furthermore, the thermally distributed velocity sensor of this invention is manufactured using MEMS technology, enabling the realization of a velocity probe at the millimeter scale. This sensor is ideally suited for embedded monitoring in confined spaces and is widely applicable to scenarios such as microfluidic chips, biomedical devices, and underground pipeline monitoring, possessing irreplaceable technological advantages.

[0076] In summary, through innovative design and synergistic effects, this invention not only solves the problem of flow velocity detection failure in high-velocity water bodies in existing technologies, but also provides a new technical solution for high-precision, long-life, and widely adaptable flow velocity detection, which has broad application prospects and practical value.

[0077] In the description of the embodiments of this application, it should be noted that the terms "inner" and "outer" and other terms indicating direction or positional relationship are based on the direction or positional relationship shown in the drawings. This is only for the convenience of description and does not indicate or imply that the device or component must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, it should not be construed as a limitation of this application.

[0078] In the description of this application, the references to terms such as "an embodiment," "some embodiments," "in this embodiment," "specific example," or "some examples," etc., refer to specific features, structures, materials, or characteristics described in connection with that embodiment or example, which are included in at least one embodiment or example of this application. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in a suitable manner in any one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0079] The above description is merely a specific embodiment of this application, but the scope of protection of this application is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in this application should be included within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the scope of the claims.

Claims

1. A thermally distributed micro / nano sensor for detecting the flow velocity of high-velocity water bodies, characterized in that, It includes a bonded base electrode layer (2) and a PDMS top layer structure (3); The base electrode layer (2) includes a silicon substrate, on the surface of which a heating unit (7) and a plurality of temperature measuring resistors (6) are integrated, and the plurality of temperature measuring resistors (6) are distributed circumferentially along the heating unit (7); The PDMS top layer structure (3) is bonded to the surface of the substrate electrode layer (2) and includes an integrally formed hollow fluid channel structure and a micropillar array (4). The fluid channel structure includes, in sequence along the water flow direction: Water inlet (1): located at the beginning of the channel; Slow-flow zone (5): Its cross-section is trapezoidal, with the narrow end connected to the water inlet (1) and the wide end extending downstream. The micro-column array (4) is provided on the slow-flow zone (5). Temperature measuring zone (8): Its cross-section is rectangular, its inlet is connected to the wide end of the slow flow zone (5), and the heating unit (7) and the temperature measuring resistor (6) are located in the temperature measuring zone (8). Outlet contraction zone (10): Its cross-section is trapezoidal, with the wide end connected to the outlet of the temperature measurement zone (8) and the narrow end being the water outlet (9), and the width of the water outlet (9) is greater than the width of the water inlet (1).

2. The thermally distributed micro / nano sensor for detecting high-velocity water flow according to claim 1, characterized in that, The micropillar array (4) is arranged in a gradient increasing manner along the trapezoidal expansion direction of the slow flow zone (5).

3. The thermally distributed micro / nano sensor for detecting high-velocity water flow according to claim 1, characterized in that, The heating unit (7) is a serpentine Cr-Pt electrode.

4. The thermally distributed micro / nano sensor for detecting high-velocity water flow according to claim 1, characterized in that, The number of temperature measuring resistors (6) is at least 8, and the temperature measuring resistors (6) are evenly distributed circumferentially on the outside of the heating unit (7).

5. A method for fabricating a thermally distributed micro / nano sensor for detecting high-velocity water flow as described in any one of claims 1-4, characterized in that, Includes the following steps: S1: Fabrication of the base electrode layer (2): A metal layer is prepared by magnetron sputtering on the surface of a silicon substrate, and a heating unit (7) and a temperature measuring resistor (6) are formed by photolithography and dry etching. S2: Preparation of PDMS top layer structure (3): Photoresist is spin-coated on the surface of another silicon substrate, and a mold for PDMS top layer structure (3) is formed by photolithography and development. Liquid PDMS is then poured into the mold, and after curing, the PDMS top layer structure (3) is obtained by demolding. S3: Bonding Assembly: The top layer structure (3) of PDMS and the base electrode layer (2) are activated by oxygen plasma, aligned and then hot-pressed to obtain a thermally distributed micro / nano sensor for detecting the flow velocity of high-velocity water bodies.

6. The method for fabricating a thermally distributed micro / nano sensor for detecting high-velocity water flow according to claim 5, characterized in that, In step S1, the silicon substrate is a silicon wafer that has been polished and oxidized on both sides.

7. The method for fabricating a thermally distributed micro / nano sensor for detecting high-velocity water flow according to claim 5, characterized in that, In step S1, the metal layer is a Cr-Pt metal layer with a thickness of 85±65μm.

8. The method for fabricating a thermally distributed micro / nano sensor for detecting high-velocity water flow according to claim 5, characterized in that, In step S2, the photoresist is SU-8 photoresist with a thickness of 250±50μm.

9. The method for fabricating a thermally distributed micro / nano sensor for detecting high-velocity water flow according to claim 5, characterized in that, In step S2, the conditions for demolding after curing are: curing at a temperature of 90±10℃ for 2 hours, and the pouring thickness of the liquid PDMS is 1±0.1mm.

10. The method for fabricating a thermally distributed micro / nano sensor for detecting high-velocity water flow according to claim 5, characterized in that, In step S3, the hot-press bonding condition is: hot-pressing with a 100g weight at a temperature of 80°C for more than 10 hours.

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