Three-dimensional micro-nano multi-stage micro-channel structure and preparation method thereof

Abstract

The application discloses a three-dimensional micro-nano multi-stage micro-channel structure and a preparation method thereof. The channel structure comprises a substrate, a nano honeycomb layer on the surface of the substrate, a Tesla valve micro-channel formed on the nano honeycomb layer and a micro-lattice piece. The micro-lattice piece has a plurality of rib columns arranged close to and along the sidewall direction of the Tesla valve micro-channel. The strong wicking capacity of the nano-porous medium and the macro fluid guiding capacity of the micro-channel are organically combined, so that the fluid can be quickly transported in the multi-stage channel, the liquid transport capacity and heat exchange efficiency are effectively improved, especially during boiling, the liquid replenishment rate and the vapor discharge rate can reach dynamic balance, the friction loss of gas-liquid two-phase flow is reduced, and different heat management requirements are met. In addition, the "nano first and micro then" processing is adopted in the preparation method, high compatibility of structure morphology and material interface is realized, good repeatability and process window are achieved, and the method is suitable for large-area preparation and industrial production.

Description

TECHNICAL FIELD

[0001] The present application relates to multi-stage micro-channel technology, belonging to the field of device heat dissipation, and particularly to a three-dimensional micro-nano multi-stage micro-channel structure and a preparation method thereof. BACKGROUND

[0002] With the improvement of the performance of electronic equipment, especially the increasing power density of integrated circuits and semiconductor devices, the thermal management of electronic components is becoming more and more important. For example, the chip process technology reaches the nanometer level, the number of transistors increases, and the power density increases, so that the heat generated per unit area of the chip increases sharply during use. If the heat dissipation system is not reasonably designed or has poor heat dissipation performance, the temperature of the chip will be too high, which will affect the stability and service life of the equipment.

[0003] Micro-channels are used to achieve ultra-high efficient heat dissipation by integrating micron-scale flow channels on the surface or inside of a device and using forced convection and phase change effects of the cooling liquid in the micro-channels. The micro-channel is an important factor for heat dissipation. To further improve the heat dissipation capacity of the micro-channel, the flow channel needs a special structure to increase the heat exchange area and improve the turbulence heat transfer effect. The Tesla valve micro-channel structure has the characteristics of liquid transportation without moving parts, which can effectively control the distribution and speed of the fluid. For example, CN115397195A discloses a Tesla valve type micro-channel radiator with uniform heat source surface temperature, which discloses that the flow channel structure of the radiator is composed of a rectangular cross-section and a flow channel with a Tesla valve structure. By improving the flow distribution in each flow channel of the micro-channel radiator, the uniformity of the temperature distribution on the heat source surface of the radiator is improved, and the performance, stability and service life of the electronic device are improved.

[0004] However, the existing Tesla valve micro-channel brings the advantage of one-way conduction, but also introduces a large fluid resistance, which limits the fluid transportation capacity and heat exchange efficiency. Especially when boiling occurs, the friction loss of gas-liquid two-phase flow is large, the liquid replenishment is limited, and there is a lack of effective wicking and heat conduction operation, which cannot meet the heat dissipation demand of high heat flux. In addition, traditional preparation processes, such as deep silicon etching, micro-milling or laser processing, usually follow the logic of “micro first, nano second”, that is, first manufacturing micron-scale channels, and then trying to integrate nano structures on the complex groove surface. This method makes it difficult to uniformly and controllably prepare high-quality nano functional layers (such as nano honeycomb structures for strengthening wicking) on three-dimensional topography, has poor process compatibility, and is difficult to realize industrialized production. SUMMARY

[0005] The application aims to provide a three-dimensional micro-nano multi-stage micro-channel structure, which combines the strong wicking capacity of a nano-porous medium and the macro fluid guiding capacity of a micro-channel, so that the fluid can be quickly transported in the multi-stage channel, effectively improving the liquid transport capacity and heat exchange efficiency, especially during boiling, the liquid replenishment rate and vapor discharge rate can reach dynamic balance, reducing the friction loss of gas-liquid two-phase flow, and meeting different heat management needs.

[0006] To achieve the above-mentioned purpose, the three-dimensional micro-nano multi-stage micro-channel structure comprises:

[0007] a substrate;

[0008] a nano honeycomb layer located on the upper surface of the substrate;

[0009] a Tesla valve micro-channel and a micro-lattice piece formed on the nano honeycomb layer;

[0010] The two ends of the Tesla valve micro-channel can be connected with a working medium outlet and a working medium inlet respectively; the micro-lattice piece has a plurality of rib columns arranged close to and along the side wall direction of the Tesla valve micro-channel.

[0011] In some embodiments, the Tesla valve micro-channel has a depth of 100-150 μm;

[0012] The rib column in the micro-lattice piece has a diameter of 5-20 μm, an adjacent spacing of 5-30 μm, and a height consistent with the depth of the Tesla valve micro-channel;

[0013] The nano honeycomb layer has a thickness of 120-160 μm and is greater than the depth of the Tesla valve micro-channel.

[0014] The application aims to provide a preparation method of a three-dimensional micro-nano multi-stage micro-channel structure, which adopts a "nano first and micro then" processing method to avoid the difficulty of preparing a nano structure on an existing complex three-dimensional groove structure, has a clear process flow, good controllability, realizes high compatibility of structure morphology and material interface, has good repeatability and process window, and is suitable for large-area preparation and industrial production.

[0015] The preparation method of the three-dimensional micro-nano multi-stage micro-channel structure specifically comprises the following steps:

[0016] S1, pretreating the substrate surface: sequentially depositing a metal layer on the substrate, using titanium or chromium metal layer as a bonding layer, and using copper or gold conductive layer as a seed layer;

[0017] S2, opal template self-assembly: configure the PS microsphere suspension, place the substrate in the suspension in step S1, or slowly drop the suspension on the substrate in step S1, evaporate the solvent under temperature control, and after the liquid phase is completely evaporated, the PS microspheres self-assemble on the substrate surface to form a face-centered cubic crystal opal template;

[0018] S3, sinter the substrate loaded with the opal template, then use the sintered opal template as a deposition skeleton, and perform pulse / direct current electrodeposition in a cold electrolyte by a three-electrode system, then remove the opal template to form a nanometer honeycomb layer on the surface of the substrate;

[0019] S4, on the surface of the nanometer honeycomb layer, the structure of the Tesla valve microchannel and the micrometer fence is processed by a patterning and etching process, and finally the three-dimensional micro-nano multi-stage microchannel structure is obtained.

[0020] In some embodiments, the pretreatment in step S1 further comprises: before the deposition of the metal layer, using a buffer oxide etching solution to clean the substrate, first soaking at room temperature for 30-60s, then performing ultrapure water rinsing and nitrogen blowing dry;

[0021] The buffer oxide etching solution is obtained by mixing hydrofluoric acid and ammonium fluoride.

[0022] In some embodiments, in step S1, the substrate after deposition is subjected to hydrophilic adjustment treatment, so that the contact angle of the substrate surface is significantly reduced to <10°;

[0023] The hydrophilic adjustment treatment selects oxygen plasma treatment or sulfuric acid-hydrogen peroxide solution.

[0024] In some embodiments, in step S2, the diameter of the PS microspheres is selected to be 300-800nm, and the suspension concentration is controlled to be 3-4wt%, and the evaporation assembly is performed naturally at 65℃.

[0025] In some embodiments, in step S3, the substrate loaded with the opal template is placed in a constant temperature device and sintered at a temperature of 103-105℃ for 30-90min.

[0026] In some embodiments, in step S3, the thickness of the adhesive layer is 8-12nm, and the thickness of the seed layer is 40-60nm.

[0027] In the three-electrode system, the working cathode is a copper seed layer, the reference electrode is Ag / AgCl, and the counter electrode is a platinum plate.

[0028] The electrolyte contains Cu 2+The ion source and acidic environment, and the addition of polyethylene glycol organic inhibitors; deposition current density control at 7.5-8.5 mA / cm2, room temperature control deposition time for 30-120 minutes.

[0029] In some embodiments, the step S3, when removing the opal template, using organic solvent tetrahydrofuran or chlorobenzene solution, under the assistance of ultrasonic immersion for more than 12 hours;

[0030] The nano honeycomb layer formed on the substrate surface is subjected to CuO oxidation treatment to form a nano CuO film layer with superhydrophilicity.

[0031] In some embodiments, the step S4, when using metal wet etching or reactive ion etching processing, specifically includes the following steps:

[0032] S4-1, a layer of hard mask material is deposited on the surface of the nano honeycomb layer, and then photoresist is spin-coated;

[0033] S4-2, using a mask plate with a Tesla valve microchannel and microlattice pattern, aligning and exposing the exposure system, then developing with an alkaline developer to form a target pattern of the Tesla valve microchannel with microlattice, and then using metal wet etching or reactive ion etching technology, taking the patterned photoresist as a mask to etch the underlying nano honeycomb layer;

[0034] S4-3, removing the photoresist and the remaining hard mask, and obtaining the three-dimensional micro-nano multi-level microchannel structure after surface cleaning;

[0035] When using femtosecond laser direct writing processing, the following steps are specifically included:

[0036] S4-1, a layer of high-viscosity resist is coated on the surface of the nano honeycomb layer as a mask;

[0037] S4-2, using femtosecond laser direct writing technology, the pattern of the Tesla valve microchannel and microlattice on the resist mask in step S4-1 is directly drawn;

[0038] S4-3, using the drawn resist as a mask, the nano honeycomb layer material in the exposed area is removed by metal etching technology;

[0039] S4-4, removing the remaining resist mask to obtain the three-dimensional micro-nano multi-level microchannel structure.

[0040] Compared with the prior art, the three-dimensional micro-nano multi-stage micro-channel structure has the following advantages: on one hand, a nano honeycomb layer is arranged on the surface of the substrate, the nano honeycomb layer has liquid wicking characteristics, and in the boiling process, liquid can be quickly transported in the honeycomb hole structure through multi-stage channels; on the other hand, a Tesla valve micro-channel and a micrometer barrier are formed on the nano honeycomb layer, the Tesla valve micro-channel can reduce fluid backflow in flow control, and the micrometer barrier can strengthen capillary flow, so that the fluid can be supplemented to ensure uniform heat dissipation, and the Tesla valve micro-channel with the micrometer barrier is combined with the nano honeycomb layer, the whole has a large heat exchange specific surface area, the liquid supplement rate and the vapor discharge rate in the boiling process reach a dynamic balance, the gas-liquid competition flow is eliminated, the liquid transport capacity and the heat exchange efficiency are effectively improved, the friction loss of the gas-liquid two-phase flow is reduced, and different heat management requirements are met.

[0041] The preparation method adopts a 'nano first and then micro' method, that is, a uniform nano honeycomb layer is first prepared on a large-area substrate to ensure the quality and consistency of the bottom functional structure, and then a micrometer structure is processed on the nano honeycomb layer, so that the difficulty of preparing a nano structure on an existing complex three-dimensional groove structure is avoided; the preparation method has a clear process flow and good controllability, realizes high compatibility of structure morphology and material interface, has good repeatability and process window, is suitable for large-area preparation and industrial production, and in addition, the method is convenient for adjusting the parameters of the nano honeycomb layer and then accurately controlling liquid flow and heat transfer performance. In the pretreatment of the preparation method, the substrate is cleaned by using a buffer oxide etching liquid, so that the surface silicon dioxide impurities can be selectively removed, and at the same time, the main silicon structure is not obviously corroded, so that the integrity of the microstructure is maintained, the substrate interface is planarized and the surface is activated, so as to facilitate subsequent process processing; in addition, the hydrophilic adjustment treatment is performed on the deposited substrate, so that favorable conditions are provided for the opal template self-assembly. BRIEF DESCRIPTION OF DRAWINGS

[0042] Figure 1 is a whole schematic view of the three-dimensional micro-nano multi-stage micro-channel structure of the present application;

[0043] Figure 2 is a schematic view of the nano honeycomb layer in the three-dimensional micro-nano multi-stage micro-channel structure of the present application;

[0044] Figure 3 is a flow chart of the first stage of the 'nano first and then micro' process in the embodiment 1 of the present application;

[0045] Figure 4 is a rendering schematic view of the three-dimensional micro-nano multi-stage micro-channel structure finally obtained through the first stage and the second stage in the preparation method of the present application;

[0046] Figure 5 is a comparison chart of the critical heat flux density and the heat transfer coefficient of the present application and the ordinary micro-channel.

[0047] Figure 6 This is a comparison chart of the dynamic thermal performance curves of the present invention and ordinary microchannels;

[0048] In the diagram: 10. Substrate;

[0049] 20. Tesla valve microchannel;

[0050] 30. Micrometer-sized fence components; 31. Ribs;

[0051] 40. Nanocellular layer. Detailed Implementation

[0052] To make the objectives, technical solutions, and advantages of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. The same reference numerals in the drawings represent the same components. It should be noted that the described embodiments are only some, not all, of the embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the described embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0053] Unless otherwise defined, the technical or scientific terms used herein shall have the ordinary meaning understood by one of ordinary skill in the art to which this invention pertains. The terms “first,” “second,” and similar terms used in this patent application specification and claims do not indicate any order, quantity, or importance, but are merely used to distinguish different components. Similarly, “an” or “a” and similar terms do not necessarily indicate a quantity limitation. Terms such as “comprising” or “including” mean that the element or object preceding the word encompasses the element or object listed following the word and its equivalents, without excluding other elements or objects. Terms such as “connected” or “linked” are not limited to physical or mechanical connections, but can include electrical connections, whether direct or indirect. Terms such as “upper,” “lower,” “left,” and “right” are used only to indicate relative positional relationships; these relative positional relationships may change accordingly when the absolute position of the described object changes.

[0054] Reference Figure 1 , Figure 2 As shown, the present invention provides a three-dimensional micro / nano multi-level microchannel structure, comprising:

[0055] substrate 10;

[0056] The nano-honeycomb layer 40 is located on the upper surface of the substrate 10;

[0057] Tesla valve microchannels 20 and micron-sized barrier elements 30 are formed on nano-honeycomb layers 40;

[0058] The two ends of the Tesla valve microchannel 20 can be connected with the working medium outlet and the working medium inlet respectively; the micrometer barrier 30 has a plurality of rib columns 31 arranged close to and along the side wall direction of the Tesla valve microchannel 20;

[0059] Specifically, the substrate 10 can be a metal substrate 10 (such as copper, aluminum) with good thermal conductivity, or a silicon wafer, quartz, or other substrate with a metal conductive seed layer;

[0060] As shown in Figure 2 The nanometer honeycomb layer 40 on the upper surface of the substrate 10 is a porous metal layer with inverse opal structure, and its regular nanometer pore network can provide a large specific surface area and strong capillary wicking capacity, responsible for efficiently and continuously transporting liquid to the heating surface during boiling; Figure 2 The nanometer honeycomb layer 40 is a schematic diagram, and the actual nanometer honeycomb layer 40 is more complex and smaller in size, so it is not possible to accurately draw the corresponding graph;

[0061] The Tesla valve microchannel 20 and the micrometer barrier 30 are microscale flow channels further processed on the basis of the nanometer honeycomb layer 40; the two ends of the Tesla valve microchannel 20 can be connected with the working medium outlet and the working medium inlet respectively, and the special geometric shape is used to realize the one-way conduction of the fluid, that is, the forward flow resistance is small, and the reverse flow resistance is large, which helps to guide the steam to be quickly and directionally discharged from the outlet, while suppressing backflow and reducing the resistance loss of gas-liquid interaction;

[0062] The Tesla valve microchannel 20 can be multiple groups, that is, multiple groups of Tesla valve microchannels 20 are arranged in parallel and at equal intervals, and the two ends of each group of Tesla valve microchannels 20 are connected with the working medium outlet and the working medium inlet, so that the cooling fluid can enter from the working medium inlet, pass through the Tesla valve microchannel 20, and then be discharged from the working medium outlet. The fluid entering the Tesla valve microchannel 20 in the forward direction can pass smoothly, and when flowing in the reverse direction, it has a large resistance and is limited;

[0063] The micrometer barrier 30 has a plurality of rib columns 31 arranged close to and along the side wall direction of the Tesla valve microchannel 20; the micrometer barrier 30 is the rib column 31 structure left over when the nanometer honeycomb layer 40 is etched, and is arranged along the side wall of the microchannel. These rib columns 31 are also composed of porous materials, which can further strengthen the capillary action, assist the lateral transport of liquid, ensure the wetting of the channel wall surface, and prevent local drying;

[0064] The three-dimensional micro-nano multi-stage micro-channel structure has the nano honeycomb layer 40 on the surface of the substrate 10, the nano honeycomb layer 40 has liquid wicking characteristics, and in the boiling process, the liquid can be quickly transported in the honeycomb hole structure through the multi-stage channel, and the Tesla valve micro-channel 20 and the micron fence 30 are formed on the nano honeycomb layer 40, the Tesla valve micro-channel 20 can reduce fluid backflow in flow control, and the micron fence 30 can strengthen capillary flow, so that the fluid can be supplemented to ensure uniform heat dissipation, the Tesla valve micro-channel 20 with the micron fence 30 is combined with the nano honeycomb layer 40, the whole has a large heat exchange specific surface area, the liquid transport capacity and the heat exchange efficiency are effectively improved, the friction loss of the gas-liquid two-phase flow is reduced, and different heat management requirements are met.

[0065] In some examples of the present application, the depth of the Tesla valve micro-channel 20 is 100-150 μm;

[0066] The diameter of the rib column 31 in the micron fence 30 is 5-20 μm, the adjacent spacing is 5-30 μm, and the height is consistent with the depth of the Tesla valve micro-channel 20;

[0067] The thickness of the nano honeycomb layer 40 is controllable in the range of 120 μm to 200 μm, preferably 120 μm to 160 μm, which can be achieved by adjusting the PS template ball diameter, sintering time and electrodeposition thickness in the preparation method to adapt to the heat transfer requirements in different application scenarios; it is explained that the thickness of the nano honeycomb layer 40 is greater than the depth of the Tesla valve micro-channel 20;

[0068] The local minimum liquid channel size of the longitudinal main flow channel of the Tesla valve micro-channel 20 is dp=2-3 μm, which corresponds to the liquid main channel size, preferably, the minimum liquid channel size dp=2 μm of the longitudinal main flow channel of the Tesla valve micro-channel 20; the throat aperture of the vapor escape path in the nano honeycomb layer 40 is dn=100-300 nm; the geometric mutation dp is much larger than dn, which helps to form a capillary pressure difference, to push the liquid phase to the wall, and to realize the two-phase separation mechanism of the gas phase flowing along the center.

[0069] As shown in Figure 4 The preparation method of the three-dimensional micro-nano multi-stage micro-channel structure specifically includes the following steps:

[0070] S1, pretreating the surface of the substrate 10: sequentially depositing a metal layer on the substrate 10, using titanium or chromium metal layer as the bonding layer, and using copper or gold conductive layer as the seed layer;

[0071] S2, opal template self-assembly: configure a PS microsphere suspension, the PS microsphere is a highly dispersed microsphere made of polystyrene material, which can be used in the fields of ordered nanostructure, template material, self-assembly, surface functionalization, etc.; then place the substrate 10 in the suspension in step S1, or slowly drop the suspension on the substrate 10 in step S1, evaporate the solvent under temperature control, and after the liquid phase is completely evaporated, the PS microspheres self-assemble on the surface of the substrate 10 to form a face-centered cubic crystal opal template;

[0072] S3, sinter the substrate 10 loaded with the opal template, then use the sintered opal template as a deposition skeleton, and perform pulse / direct current electrodeposition in a cold electrolyte by using a three-electrode system, and then remove the opal template to form a nanometer honeycomb layer 40 on the surface of the substrate 10;

[0073] S4, on the surface of the nanometer honeycomb layer 40, the structure of the Tesla valve microchannel 20 and the micrometer fence piece 30 is processed and formed by high-precision patterning and etching process, and finally the three-dimensional micro-nano multi-stage microchannel structure is obtained, as shown in Figure 1 、 Figure 2 、 Figure 4

[0074] Specifically, the preparation method adopts the innovative process sequence of "nanometer first and microsecond", first, the uniform nanometer honeycomb layer 40 is prepared on the substrate 10 by steps of metal layer deposition, PS microsphere self-assembly, electrodeposition and removal of the opal template; on this basis, the Tesla valve microchannel 20 and the micrometer fence piece 30 are directly constructed on the nanometer honeycomb layer 40 by using femtosecond laser direct writing or photolithography and etching high-precision processing technology, and finally the three-dimensional micro-nano multi-stage microchannel structure is obtained. The method is different from the traditional process, solves the technical problem of uniformly preparing high-quality nanometer functional layer on the existing complex microstructure, realizes high compatibility of structure morphology and material interface, the process is controllable, has good repeatability and process window, and is suitable for large-area preparation and industrial production.

[0075] Example 1

[0076] This embodiment is used to describe the first stage of the "nanometer first and microsecond" process of the application, that is, to prepare the core nanometer honeycomb layer 40 on the substrate 10, which specifically includes the following steps:

[0077] As shown in Figure 3 , in step S1, the substrate 10 can be selected from copper substrate 10 or N-type / P-type monocrystalline silicon wafer with good thermal conductivity and resistivity in the range of 1-100 Ω·cm;

[0078] ​In metal layer deposition, to achieve good electrical connection in electrochemical deposition, a continuous and strongly adherent metal layer must be deposited on the surface of the microchannel. Depositing a titanium (Ti) or chromium (Cr) layer as a bonding layer not only provides good adhesion to silicon, but also prevents the subsequent copper seed layer from peeling off due to weak interface. Then, a copper (Cu) or gold (Au) layer is deposited on top as a seed layer for the cathode base of the electrodeposited copper honeycomb structure.

[0079] This process can be carried out using magnetron sputtering equipment under vacuum conditions, with the metal layer thickness controlled at approximately 10 nm and 50 nm, respectively, while maintaining the deposition temperature below 150 °C. The deposited layer needs to have continuity, uniformity, and excellent electrical conductivity. Preferably, a titanium or chromium metal layer with a thickness of 8-12 nm is used as the binder layer, and a copper or gold conductive layer with a thickness of 40-60 nm is used as the seed layer.

[0080] In step S2, such as Figure 3 The upper left figure shows the substrate 10 placed in a suspension. The diameter of the PS microspheres ranges from 100 nm to 3 μm, and the solid content is 2-6 wt%. In some examples, the diameter of the PS microspheres is selected as 300-800 nm, and the suspension concentration is controlled at 3-4 wt%.

[0081] like Figure 3 The upper and middle images (after evaporation and sintering) show that the solvent is evaporated at 60-80℃ under temperature control, with a preferred temperature of 62-68℃. After the liquid phase is completely evaporated, the PS microspheres self-assemble on the surface of the substrate 10 to form a face-centered cubic crystalline opal template.

[0082] In step S3, the substrate 10 loaded with the opal template is placed in a constant temperature device and sintered at 100-110°C for 10-120 min, or preferably, sintered at 103-105°C for 30-90 min.

[0083] During sintering, the diameter of the bonding neck between adjacent PS microspheres is precisely controlled by adjusting the sintering time, which accounts for 10-40% of the diameter of the PS microspheres. This allows for the regulation of the pore size of the final inverse opal structure, resulting in a target pore size of 50-300 nm. The high porosity, regular pore structure, and adjustable pore size of the nano-honeycomb layer 40 give it excellent wicking and thermal conductivity.

[0084] like Figure 3 The upper right image (after electrodeposition) shows that a three-electrode system is used to perform pulse / DC electrodeposition in a cold electrolyte (temperature 15-30℃). The electrolyte is an aqueous solution containing copper ion sources (such as copper sulfate and copper pyrophosphate) and additives.

[0085] Cathode: is the copper or gold seed layer mentioned above, preferably a copper seed layer;

[0086] Current density: 5-15 mA / cm² (preferably 7.5-8.5 mA / cm²); Deposition time: 30-180 min;

[0087] Copper nanoparticles are directionally filled in the gaps between PS microspheres to form a continuous metal network. The overall structure thickness is controlled to be 5-100 μm by the deposition time, preferably 20-50 μm.

[0088] like Figure 3 The lower right figure (after template removal) shows that after template removal, the deposited substrate 10 is immersed in an organic solvent and ultrasonically assisted for 1-24 hours to completely dissolve the PS microsphere template. The thickness of the nano-honeycomb layer 40 is 120μm to 200μm, preferably 120μm to 160μm. This range can be achieved by subsequently adjusting the PS template sphere diameter, sintering time and electrodeposition thickness to adapt to the heat transfer requirements of different application scenarios.

[0089] In this example, parameters such as the neck diameter, microcell diameter, porosity, arrangement pattern, and thickness of the nano-honeycomb layer 40 can be adjusted by pretreatment of the substrate 10, self-assembly of the opal template, sintering, and electrodeposition, thereby enabling precise control of liquid flow and heat transfer performance.

[0090] In some examples of the present invention, the pretreatment in step S1 further includes: before the metal layer is deposited, the substrate 10 is cleaned with a buffer oxide etchant, soaked at room temperature for 30-60 seconds, and then rinsed with ultrapure water and dried with nitrogen.

[0091] The buffer oxide etching solution is obtained by mixing hydrofluoric acid and ammonium fluoride. Preferably, it is obtained by mixing 49% hydrofluoric acid and 40% ammonium fluoride at a volume ratio of 6:1.

[0092] Specifically, the surface of substrate 10 is often accompanied by nanoscale silicon dust. Therefore, substrate 10 is cleaned by buffered oxide etchant (BOE). During the cleaning process, BOE can selectively remove surface silicon dioxide impurities without causing significant corrosion to the main silicon structure, thereby maintaining the integrity of the microstructure and achieving interface planarization and surface activation of substrate 10 to facilitate subsequent processing.

[0093] In some examples of the present invention, in step S1, the substrate 10 after deposition is subjected to a hydrophilicity adjustment treatment:

[0094] Choose oxygen plasma treatment or Piranha (sulfuric acid-hydrogen peroxide) solution;

[0095] Specifically, since the self-assembly of the opal template in step S2 depends on the good spreading ability of the liquid on the surface, the hydrophilic treatment on the surface of the substrate 10 is one of the key steps to ensure the ordered assembly of the template;

[0096] The oxygen plasma treatment can be selected to etch the surface by using active oxygen radicals to improve the surface energy, or a Piranha (sulfuric acid-hydrogen peroxide) solution can be selected to remove organic residues and form a hydrophilic oxidation layer by strong oxidation; after the treatment, the contact angle of the surface of the substrate 10 is significantly reduced to <10°, and a uniform high-hydrophilic interface is formed, which provides favorable conditions for the self-assembly of the opal template in step S2.

[0097] In some examples of the present application, in step S2, the PS suspension is slowly added dropwise on the surface of the substrate 10, and by controlling the volume of the droplet and the evaporation speed, the PS microspheres are naturally crystallized into a film in a certain area;

[0098] The diameter of the PS microspheres is selected to be 300-800 nm, and the suspension concentration is controlled to be 3-4 wt%, and the natural evaporation assembly is carried out at 65°C to form a face-centered cubic structure with a regular and controllable pore network.

[0099] In some examples of the present application, in step S3, the thickness of the adhesion layer is 5-20 nm, and the thickness of the seed layer is 30-100 nm;

[0100] Specifically, the preferred thickness of the adhesion layer is 8-12 nm, and the thickness of the seed layer is 40-60 nm;

[0101] In the three-electrode system, the working cathode is a copper seed layer, the reference electrode is Ag / AgCl, and the counter electrode is a platinum sheet;

[0102] The electrolyte contains Cu 2+ ions (such as CuSO4) and an acidic environment (such as H2SO4), and an organic inhibitor such as polyethylene glycol (PEG) is added to improve the deposition morphology; the deposition current density is controlled to be 8.0 mA / cm², the temperature is room temperature to 25°C, and by controlling the deposition time to be 30-120 minutes, the controllable construction of the honeycomb structure with different thicknesses is realized. During the deposition process, copper gradually fills the gaps between the PS microspheres to form a continuous porous metal skeleton, which lays the foundation for subsequent boiling cooling and heat exchange.

[0103] In some examples of the present application, in step S3, the opal template is removed by using an organic solvent such as tetrahydrofuran (THF) or chlorobenzene solution and soaking for more than 12 hours under ultrasonic assistance;

[0104] The nano-honeycomb layer 40 formed on the surface of the substrate 10 is then subjected to CuO oxidation treatment to form a nano-CuO film layer with super-hydrophilicity;

[0105] Specifically, after the electrodeposition is completed, the opal template needs to be removed to release the nano honeycomb structure; an organic solvent tetrahydrofuran (THF) or chlorobenzene solution is used to completely dissolve the PS microspheres; in order to prevent the structure from collapsing during the dissolving process, the solvent needs to be replaced intermittently and handled gently;

[0106] The nano CuO film layer is formed on the surface of the honeycomb structure, the contact angle is less than 30°, the super-hydrophilic modification is realized, the liquid film thickness of the hydrophilic CuO film layer is controlled in the sub-micron level, and the thermal resistance is reduced to 10 -5 m 2 K / W. The film layer can provide stronger liquid film holding capacity, reduce thermal resistance, and improve wicking liquid supply rate in boiling cooling.

[0107] Embodiment 2

[0108] This embodiment is used to describe the second stage of the "nano first and micro then" process of the application, that is, the micro-level Tesla valve microchannel 20 and the micron fence 30 are processed on the basis of the nano honeycomb layer 40 prepared in embodiment 1.

[0109] When the metal wet etching or reactive ion etching (RIE) technology is used, the step S4 specifically includes the following steps:

[0110] S4-1, a layer of silicon dioxide or other inorganic hard mask material is pre-deposited on the surface of the nano honeycomb layer 40, and then photoresist is spin-coated;

[0111] On the spin-coated photoresist, AZ4620 series equipment can be used; the spin-coating procedure of the spin-coated photoresist adopts a stepwise uniform coating: the first stage speed is 300 rpm to 800 rpm, the time is 3 s to 10 s, which is used for spreading the photoresist; the second stage speed is 1500 rpm to 4000 rpm, the time is 20 s to 60 s, which is used to obtain the target thickness and uniformity;

[0112] Preferably, the thickness of the photoresist ranges from 3 μm to 15 μm;

[0113] After spin-coating, pre-baking (soft baking) is performed, the temperature range is controlled at 90°C to 120°C, and the time is 60 s to 180 s, so as to remove the solvent and enhance the adhesion of the film, preferably, the temperature is 110°C, and the time is 90 s;

[0114] S4-2, using a mask plate with the pattern of the Tesla valve microchannel 20 and the micron fence 30, the exposure system is exposed, and then developed using an alkaline developer, the target pattern of the Tesla valve microchannel 20 with the micron fence 30 is formed on the hard mask, and then the metal wet etching or reactive ion etching (RIE) technology is used to etch the nano honeycomb layer 40 below with the patterned photoresist as a mask;

[0115] Specifically, in the exposure and development, the mask plate with Tesla valve microchannel 20 and micrometer fence element 30 pattern is exposed to the exposure system, and ultraviolet light exposure can be selected, the wavelength range is g line (436 nm) to i line (365 nm), preferably 365 nm (i line), the exposure energy density range is 100 mJ / cm2to 500 mJ / cm2, preferably 200 mJ / cm2to 400 mJ / cm2;

[0116] After exposure, the alkaline developer is used for development, preferably, the developer is 0.26N to 0.38N aqueous solution of tetramethylammonium hydroxide (TMAH), the development time is 30 s to 120 s, the exposed area photoresist is removed, the target microstructure pattern is formed, that is, the Tesla valve microchannel 20 and micrometer fence element 30 pattern with line width / gap of 5 μm to 50 μm, preferably 10 μm to 30 μm; After development, post-baking (hard baking) can be carried out, the temperature control range is 100℃ to 130℃, the time is 1 min to 5 min, which is used for curing the pattern;

[0117] The patterned photoresist is used as a mask, and the sample is immersed in a copper wet etching solution; the commonly used etching solution is ferric chloride (FeCl3) aqueous solution (concentration 1.0-1.5 mol / L, temperature 30-50℃) or ammonium persulfate ((NH4)2S2O8) solution, the temperature is controlled at 40℃, the etching time is 60 seconds, and the etching depth is controlled in the range of 150-250 μm;

[0118] Among them, the width of the Tesla valve microchannel 20 is 20-100 μm, and the depth is 150-250 μm; the rib column 31 in the micrometer fence element 30 has a width of 5-20 μm, a pitch of 5-30 μm, and a height consistent with the microchannel depth;

[0119] S4-3, remove the photoresist and the remaining hard mask, and obtain the three-dimensional micro-nano multi-stage microchannel structure after surface cleaning, as shown in Figure 4 ;

[0120] Specifically, the residual photoresist is cleaned with acetone, isopropyl alcohol, or ashed with oxygen plasma, and finally the three-dimensional micro-nano multi-stage microchannel structure is obtained.

[0121] The above-mentioned metal wet etching process can realize micro-channel etching of the copper-based nanometer honeycomb layer 40 by preparing a resist pattern in the early stage of photolithography, using ferric chloride or ammonium persulfate and other metal etching solutions, and is suitable for patterning of metal material surfaces, with the advantages of simple operation, low cost and suitability for large-area preparation. However, this method has certain limitations, especially in terms of pattern precision and side etching control, and it is difficult to form high-fidelity steep sidewall microstructures. In addition, due to the high porosity and roughness of the nanometer honeycomb layer 40 surface, the coating and pattern fidelity of the photoresist are affected, and high-viscosity thick glue (such as SU-8) needs to be used and the glue spreading and development process needs to be optimized.

[0122] In contrast, femtosecond laser direct writing technology can directly realize high-precision microstructure writing on the nanometer honeycomb copper layer without a mask, thanks to its extremely short pulse width (<200 fs) and nonlinear multi-photon absorption mechanism. This technology has extremely small heat affected zone, nanoscale ablation precision and arbitrary pattern flexible processing capability, and is particularly suitable for complex honeycomb structures, uneven surfaces and difficult-to-fit masks.

[0123] When using femtosecond laser direct writing technology, the step S4 specifically includes the following steps:

[0124] S4-1, a layer of high-viscosity resist glue is coated on the surface of the nanometer honeycomb layer 40 as a mask;

[0125] Specifically, a layer of high-viscosity resist glue SU-8 (such as SU-82075) can be selectively spin-coated on the surface of the nanometer honeycomb layer 40 to form a protective layer with a thickness of 10-20 μm, preferably 15 μm, to buffer laser impact, suppress burr formation and assist in forming regular patterns;

[0126] The spin-coating procedure is as follows: first stage, 300 rpm for 5 seconds; second stage, 2500 rpm for 40 seconds; after spin-coating, soft baking at 95°C for 2-3 minutes to remove solvents and enhance adhesion;

[0127] S4-2, using femtosecond laser direct writing technology, the patterns of the Tesla valve micro-channel 20 and the micron fence 30 are directly drawn on the resist glue mask in step S4-1;

[0128] Specifically, a femtosecond laser (such as PHAROS, Spirit, etc.) with a pulse width of 120 fs and a wavelength of 800 nm is used to scan the surface of the resist glue mask sample according to the CAD pattern to form the patterns of the Tesla valve micro-channel 20 and the micron fence 30, with the following settings: laser average power is 250 mW, scanning speed is controlled at 1500 μm / s, focusing spot diameter is about 1 μm, scanning path overlap rate is 80%-90%, and pulse repetition frequency is set to 100-500 kHz;

[0129] Femtosecond laser realizes direct material ablation and stripping on the nanocell layer 40 by nonlinear multi-photon absorption mechanism without a mask, forming a high-precision channel pattern; the laser can penetrate the SU-8 resist layer and be written to the honeycomb metal surface, realizing one-piece forming of the structure;

[0130] S4-3, using the etched resist as a mask, the nanocell layer 40 material in the exposed area is removed by metal etching technology;

[0131] To further deepen the pattern depth and remove the laser ablation residue, the sample after laser writing can be immersed in a copper metal etching solution, such as 1.2 mol / L ferric chloride or ammonium persulfate solution, and etched at 30-45°C for 30-90 seconds. This step is used to expand the microchannel to the target depth (150-250 μm) and trim the channel bottom edge.

[0132] S4-4, remove the remaining resist mask;

[0133] Specifically, when using SU-8 resist, acetone or PGMEA organic solvent can be used for ultrasonic-assisted dissolution and cleaning, and if necessary, oxygen plasma ashing (power 100 W, time 60 seconds) can be used to remove residual organic matter to ensure the cleanliness of the channel and the honeycomb orifice;

[0134] In this example, femtosecond laser direct writing technology does not require a mask process and can efficiently construct high-precision Tesla valve microchannels 20 and micron fence pieces 30 structures with a channel width of 10-100 μm and a rib column 31 diameter of 5-20 μm on the nanocell layer 40. It has the advantages of high processing precision, small thermal influence, flexible pattern, etc., and is particularly suitable for constructing complex micron structures on the surface of high specific surface area nanomaterials. In addition, femtosecond laser direct writing technology is suitable for honeycomb metal layers with a thickness of not more than 50 μm. If the thickness of the nanocell layer 40 exceeds this range, the laser power should be appropriately increased to 300-350 mW, or multiple scans should be performed to ensure the etching depth and pattern integrity. This method is highly compatible with the "first nanometer and then micro" preparation method of the present application, and can realize the coordinated construction of multi-level structures, improve the channel heat exchange efficiency and microsuction liquid supply performance;

[0135] In summary, in the second stage of the "first nanometer and then micro" process, femtosecond laser direct writing is more suitable for complex structures, high precision requirements, or honeycomb layer surfaces that are not suitable for mask processing, and has strong process compatibility and product quality. Wet etching of metal is suitable for large channels, regular patterns, shallow honeycomb structures, and moderate pattern fidelity requirements.

[0136] Example 3

[0137] As Figure 5 , Figure 6As shown, the ordinary microchannel and the three-dimensional micro-nano multilevel microchannel structure are compared to examine the critical heat flux density (CHF) and heat transfer coefficient (HTC) of the two under the same operating conditions, as well as the change of HTC of the microchannel with heat flux density.

[0138] like Figure 5 As shown, compared to ordinary microchannels, the critical heat flux density and heat transfer coefficient of this three-dimensional micro / nano-level microchannel structure are significantly improved, such as... Figure 6 As shown, the heat transfer coefficient of this three-dimensional micro / nano-level microchannel structure continuously increases with changes in heat flux density without performance degradation; therefore, this three-dimensional micro / nano-level microchannel structure has significant advantages in thermodynamic performance, flow characteristics, and reliability. The foregoing description, with reference to preferred embodiments, details an exemplary implementation of the three-dimensional micro / nano-level microchannel structure and its fabrication method proposed in this invention. However, those skilled in the art will understand that various modifications and variations can be made to the above specific embodiments without departing from the spirit of this invention, and various combinations can be made to the various technical features and structures proposed in this invention without exceeding the scope of protection of this invention, which is determined by the appended claims.

Claims

1. A three-dimensional micro-nano multi-stage microchannel structure, characterized in that, It comprises: a substrate (10); a nanometer honeycomb layer (40) on the upper surface of the substrate (10); a Tesla valve microchannel (20) and a micrometer fence (30) formed on the nanometer honeycomb layer (40); the two ends of the Tesla valve microchannel (20) are respectively connected with the working medium outlet and the working medium inlet; the micrometer fence (30) has a plurality of rib columns (31) arranged close to and along the side wall direction of the Tesla valve microchannel (20); the depth of the Tesla valve microchannel (20) is 100-150μm; the diameter of the rib column (31) in the micrometer fence (30) is 5-20μm, the adjacent spacing is 5-30μm, and the height is consistent with the depth of the Tesla valve microchannel (20); the thickness of the nanometer honeycomb layer (40) is 120-160μm and greater than the depth of the Tesla valve microchannel (20).

2. A method for fabricating a three-dimensional micro / nano hierarchical microchannel structure according to claim 1, characterized in that, It specifically comprises the following steps: S1, pretreatment of the surface of the substrate (10): sequentially depositing a metal layer on the substrate (10), using titanium or chromium metal layer as the bonding layer, and using copper or gold conductive layer as the seed layer; S2, opal template self-assembly: configuring a PS microsphere suspension, placing the substrate (10) in the suspension or slowly dropping the suspension on the substrate (10) in step S1, evaporating the solvent under temperature control, and after the liquid phase is completely evaporated, the PS microspheres are self-assembled on the surface of the substrate (10) to form a face-centered cubic crystal opal template; S3, sintering the substrate (10) loaded with the opal template, then using the sintered opal template as the deposition skeleton, performing pulse / direct current electrodeposition in a cold electrolyte by a three-electrode system, and then removing the opal template to form a nanometer honeycomb layer (40) on the surface of the substrate (10); S4, on the surface of the nanometer honeycomb layer (40), the structure of the Tesla valve microchannel (20) and the micrometer fence (30) is processed by patterning and etching process, and finally the three-dimensional micro-nano multi-stage microchannel structure is obtained.

3. The preparation method of the three-dimensional micro-nano multi-stage microchannel structure according to claim 2, wherein the pretreatment in step S1 further comprises: before the metal layer deposition, using a buffer oxide etching solution to clean the substrate (10), first soaking for 30-60s at room temperature, and then ultrapure water rinsing and nitrogen blowing dry; wherein the buffer oxide etching solution is obtained by mixing hydrofluoric acid and ammonium fluoride.

4. The preparation method of the three-dimensional micro-nano multi-stage microchannel structure according to claim 3, wherein the substrate (10) after deposition in step S1 is subjected to hydrophilic adjustment treatment, so that the contact angle of the substrate surface is significantly reduced to <10°; wherein the hydrophilic adjustment treatment selects oxygen plasma treatment or sulfuric acid-hydrogen peroxide solution.

5. The preparation method of the three-dimensional micro-nano multi-stage microchannel structure according to claim 2, wherein in step S2, the diameter of the PS microspheres is selected to be 300-800nm, and the suspension concentration is controlled to be 3-4wt%, and the evaporation assembly is naturally carried out at 65℃. ​ ​ ​ 6. The method according to claim 2, wherein, In step S3, the substrate (10) loaded with the opal template is placed in a constant temperature device and sintered at a temperature of 103-105℃ for 30-90 min.

7. The method according to claim 2, wherein, In step S3, the thickness of the adhesive layer is 8-12 nm and the thickness of the seed layer is 40-60 nm; In the three-electrode system, the working cathode is a copper seed layer, the reference electrode is Ag / AgCl, and the counter electrode is a platinum plate; The electrolyte contains Cu 2+ The ion source and acidic environment, and the addition of polyethylene glycol organic inhibitors; deposition current density control at 7.5-8.5 mA / cm2, room temperature control deposition time for 30-120 minutes.

8. The method according to claim 2, wherein, In step S3, when removing the opal template, an organic solvent such as tetrahydrofuran or chlorobenzene solution is used for immersion for more than 12 hours under ultrasonic assistance; The nano honeycomb layer (40) formed on the surface of the substrate (10) is then subjected to CuO oxidation treatment to form a nano CuO film layer with superhydrophilicity.

9. The method according to any one of claims 2-8, wherein, In step S4, when using metal wet etching or reactive ion etching, the following steps are included: S4-1, a layer of hard mask material is first deposited on the surface of the nano honeycomb layer (40), and then photoresist is spin-coated; S4-2, a mask plate with the pattern of the Tesla valve microchannel (20) and the micrometer fence (30) is used for exposure treatment by an alignment exposure system, and then developed using an alkaline developer to form a target pattern of the Tesla valve microchannel (20) with the micrometer fence (30), and then using metal wet etching or reactive ion etching technology, the nano honeycomb layer (40) below is etched with the patterned photoresist as a mask; S4-3, after removing the photoresist and the remaining hard mask, the surface is cleaned to obtain the three-dimensional micro-nano multi-level microchannel structure; When using femtosecond laser direct writing, the following steps are included: S4-1, a layer of high-viscosity resist is coated on the surface of the nano honeycomb layer (40) as a mask; S4-2, femtosecond laser direct writing technology is used to directly draw the pattern of the Tesla valve microchannel (20) and the micrometer fence (30) on the resist mask in step S4-1; S4-3, using the drawn resist as a mask, the nano honeycomb layer (40) material in the exposed area is removed by metal etching technology; S4-4, the remaining resist mask is removed to obtain the three-dimensional micro-nano multi-level microchannel structure.

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