Method for manufacturing tantalum capacitor cathode sheet, tantalum capacitor cathode sheet, and tantalum capacitor

Abstract

This invention discloses a method for preparing a tantalum capacitor cathode sheet. The method includes: pretreating a tantalum foil; performing ablation processing on the pretreated tantalum foil using a femtosecond laser to form multiple first pore structures on the surface of the tantalum foil, wherein the first pore structures are micron-sized blind holes; performing electrochemical etching on the tantalum foil with the first pore structures to form second pore structures smaller than the first pore structures on the surface of the tantalum foil and the inner wall of the first pore structures, thereby obtaining a hierarchical porous tantalum substrate; and forming a ruthenium dioxide film layer on the surface of the hierarchical porous tantalum substrate using atomic layer deposition to obtain the tantalum capacitor cathode sheet. This invention also discloses a tantalum capacitor cathode sheet and a tantalum capacitor. This invention constructs pore structures of different scales through laser processing and electrochemical etching, and utilizes atomic layer deposition to form ruthenium dioxide on the three-dimensional surface of the hierarchical porous tantalum substrate, which is beneficial to improving the utilization of the newly added surface of the porous tantalum substrate.

Description

Technical Field

[0001] This invention belongs to the field of tantalum capacitor manufacturing technology, and particularly relates to a method for preparing a tantalum capacitor cathode sheet, the tantalum capacitor cathode sheet, and a tantalum capacitor. Background Technology

[0002] Ruthenium dioxide (RuO2) can be used as the cathode active material in all-tantalum electrolytic capacitors and high-energy tantalum hybrid capacitors. RuO2 possesses double-layer capacitance and reversible electrochemical redox pseudocapacitance properties, allowing it to participate in charge storage during cathode operation. When using RuO2 as the cathode active material, in addition to the electrochemical properties of RuO2 itself, its effective loading area on the conductive substrate and its contact interface with the electrolyte also affect the electrochemical performance of the cathode.

[0003] Existing technologies have disclosed methods for forming RuO2 cathode layers on tantalum substrates. For example, CN104409216B discloses a method for preparing a Ta2O5-RuO2 / Ta capacitor, which uses tantalum material as the cathode substrate, applies a solution containing a ruthenium source to the inner wall of the tantalum cathode cylinder, and after drying, performs heat treatment at 500–600 °C to form a RuO2 cathode layer. This technology can form RuO2 active material on the tantalum substrate, but the effective loading area of ​​RuO2 is still affected by the surface structure of the tantalum substrate. To increase the actual surface area of ​​the tantalum substrate, existing technologies have also proposed various methods for preparing porous tantalum foils. For example, CN116288636B discloses a high-voltage resistant ordered porous tantalum foil, its preparation method, and its application, which uses laser-assisted electrochemical etching to form an ordered porous structure on the tantalum foil. CN117558560A discloses a method for preparing ordered porous tantalum foil using high-energy beam assistance, along with its products and applications. The method involves constructing an array-type microstructure on the Ta2O5 oxide layer on the surface of the tantalum foil, followed by electrochemical etching to form an ordered porous tantalum foil. This technology primarily increases the actual surface area of ​​the tantalum foil through structural processing.

[0004] However, for tantalum capacitor cathodes using RuO2 as the active material, simply increasing the porosity and surface area of ​​the tantalum substrate does not automatically transform the newly added surface into a RuO2 active interface. As the pore structure extends into the tantalum foil, RuO2 also needs to enter the pore channels and form on the pore wall surface. When RuO2 is formed using solution coating and subsequent heat treatment, its entry and coverage in the complex pore structure are affected by factors such as pore size, depth, and coating process; while if only a RuO2 film is formed on the planar tantalum foil surface, it is difficult to sufficiently increase the active material loading interface per unit geometric area.

[0005] Therefore, it is necessary to provide a method for preparing a tantalum capacitor cathode sheet that combines the construction of a three-dimensional pore structure of tantalum foil with the formation of a RuO2 active layer, so that the tantalum foil can form pore structures of different sizes and RuO2 can be further formed on the surface of the pore structure, thereby improving the utilization of the new surface of the porous tantalum substrate. Summary of the Invention

[0006] The purpose of this invention is to provide a method for preparing a tantalum capacitor cathode, aiming to solve the technical problem in the prior art where the three-dimensional surface area construction of the tantalum substrate and the formation of the RuO2 active layer are independent, and the increased surface area of ​​the porous structure is difficult to fully utilize. This invention uses a femtosecond laser to form micron-sized blind holes on a tantalum foil, further forms a smaller pore structure through electrochemical etching, and then uses atomic layer deposition to form a RuO2 film on the surface of the resulting hierarchical porous tantalum substrate.

[0007] In a first aspect, the present invention provides a method for preparing a tantalum capacitor cathode sheet, comprising: Pre-treatment of tantalum foil; The pre-treated tantalum foil is directly ablated using a femtosecond laser to form multiple first hole structures on the surface of the tantalum foil. The first hole structures are micron-sized blind holes. Electrochemical etching is performed on a tantalum foil with a first pore structure to form a second pore structure with a smaller scale than the first pore structure on the surface of the tantalum foil and the inner wall of the first pore structure, thereby obtaining a hierarchical porous tantalum substrate. A RuO2 film was formed on the surface of the hierarchical porous tantalum substrate using atomic layer deposition to obtain a tantalum capacitor cathode.

[0008] In one embodiment, the step of using a femtosecond laser to ablate the pretreated tantalum foil to form a plurality of first hole structures on the surface of the tantalum foil includes: The surface of the pretreated tantalum foil is scanned; Based on the scanning results, as well as the target dot spacing and target array arrangement, a femtosecond laser is used to sequentially ablate the pre-treated tantalum foil to form multiple first hole structures on the surface of the tantalum foil, and all the first hole structures form a blind hole array.

[0009] In one embodiment, the step of using a femtosecond laser to ablate the pretreated tantalum foil to form a plurality of first hole structures on the surface of the tantalum foil includes: The surface of the pretreated tantalum foil is scanned; Based on the scanning results, as well as the target hole depth, target dot matrix spacing, and target array arrangement, a femtosecond laser is used to sequentially perform ablation processing on the thickness direction of the pre-processed tantalum foil, forming multiple first hole structures on the surface of the tantalum foil. All the first hole structures form a blind hole array.

[0010] In one embodiment, the step of electrochemically etching the tantalum foil having the first pore structure includes: The platinum sheet and the tantalum foil with the first pore structure are placed together in a preset electrode solution. The saturated calomel electrode is used as the reference electrode, the tantalum foil with the first pore structure is used as the working electrode, and the platinum sheet is used as the counter electrode. The tantalum foil with the first pore structure is etched using a pulsed potential.

[0011] In one embodiment, the preset electrode solution is a propanol solution containing potassium chloride and deionized water.

[0012] In one embodiment, the step of forming a ruthenium dioxide film on the surface of the hierarchical porous tantalum substrate using atomic layer deposition includes: Isopropanol is introduced into the reaction chamber in a pulsed manner, so that the isopropanol comes into contact with the surface of the hierarchical porous tantalum substrate; The reaction chamber was evacuated for the first time; Ruthenium tetroxide is introduced into the reaction chamber in a pulsed manner, causing the ruthenium tetroxide to react with the surface treated with isopropanol. The reaction chamber is evacuated a second time; Repeat the above steps to form a ruthenium dioxide film on the surface of the hierarchical porous tantalum substrate.

[0013] In one embodiment, the step of pretreating the tantalum foil includes: The tantalum foil was sequentially placed in toluene and anhydrous ethanol for ultrasonic cleaning. The ultrasonically cleaned tantalum foil was immersed in a NaOH solution. The tantalum foil after immersion treatment was rinsed with deionized water and then dried.

[0014] In one embodiment, prior to the step of forming a ruthenium dioxide film on the surface of the hierarchical porous tantalum substrate using atomic layer deposition, the method includes: The chamber walls of the reaction chamber are preheated and maintained at 80°C, and the delivery pipeline is heated to 60°C.

[0015] In a second aspect, the present invention provides a tantalum capacitor cathode sheet, which is prepared by the preparation method described in any one of the first aspects.

[0016] Thirdly, the present invention provides a tantalum capacitor, the tantalum capacitor comprising the tantalum capacitor cathode plate described in the second aspect.

[0017] Compared with the prior art, the present invention has the following beneficial effects: (1) In this invention, a femtosecond laser is first used to directly ablate the tantalum foil substrate to form micron-sized blind holes (first hole structure) with a certain pore size and depth on the surface of the tantalum foil. Then, electrochemical etching is used to form smaller hole structures on the surface of the tantalum foil and the inner wall of the blind holes. The two processing methods act on different scales, which is beneficial to increase the actual surface area that can be used to load RuO2 while maintaining the continuous tantalum substrate.

[0018] (2) In this invention, an atomic layer deposition method is used to form a RuO2 film. Isopropanol and RuO4 are alternately introduced into the reaction chamber in a pulsed manner, and evacuation or purging is performed between the two reactant pulses. The gaseous reactants can enter the pore structure that is connected to the outside, which is conducive to the formation of RuO2 along the outer surface of the tantalum foil, the inner wall of the micron-scale blind hole (first pore structure), and the surface of the smaller pore structure, thereby improving the utilization of the surface provided by the hierarchical porous structure.

[0019] (3) In this invention, femtosecond laser ablation, electrochemical etching, and RuO2 atomic layer deposition are sequentially arranged. The first two are used to form a three-dimensional porous tantalum substrate with different scales, and the latter is used to form a RuO2 active layer on the three-dimensional surface, so that the construction of the pore structure of the tantalum substrate and the formation of the active material are interconnected in terms of process. At the same time, the RuO2 atomic layer deposition adopts a lower substrate temperature, which helps to reduce the risk of thermal impact on the tantalum foil substrate caused by higher temperature processing. Attached Figure Description

[0020] Figure 1 This is a schematic flowchart of a method for preparing a tantalum capacitor cathode sheet according to an embodiment of the present invention; Figure 2 This is a flowchart illustrating the preprocessing steps in one embodiment of the present invention; Figure 3 This is a schematic diagram of the processing flow of the first hole structure in one embodiment of the present invention; Figure 4 This is a schematic diagram of the processing flow of the first hole structure in one embodiment of the present invention; Figure 5 This is a schematic diagram of the RuO2 atomic layer deposition cycle in one embodiment of the present invention; Figure 6 This is a schematic diagram of the surface structure of the cathode plate of a tantalum capacitor in one embodiment of the present invention. Detailed Implementation

[0021] The present invention will now be described in conjunction with specific embodiments and accompanying drawings. These specific embodiments are used to illustrate the technical solutions of the present invention and are not intended to limit the scope of protection of the present invention.

[0022] In a first aspect, the present invention provides a method for preparing a tantalum capacitor cathode sheet. For example... Figure 1 As shown, the preparation method includes: S100, pretreatment of tantalum foil; In this step, tantalum foil serves as the conductive substrate and structural framework of the cathode sheet, and high-purity tantalum foil with a thickness of 0.3 mm and a purity of not less than 99.95% is preferably used.

[0023] Pretreatment is mainly used to remove oil and residual contaminants from the surface of tantalum foil and to adjust the surface condition before subsequent processing; Reference Figure 1 The S100 includes: S111, the tantalum foil is placed in toluene and anhydrous ethanol in sequence for ultrasonic cleaning; Specifically, the tantalum foil was ultrasonically cleaned in toluene for 15 minutes to remove oily contaminants from the surface; after removal, it was ultrasonically cleaned in anhydrous ethanol for another 15 minutes to further clean the surface of the tantalum foil.

[0024] S112, the ultrasonically cleaned tantalum foil is immersed in NaOH solution for treatment; In this step, the tantalum foil is immersed in a 1 mol / L NaOH solution at 90 °C for 30 seconds. This treatment is mainly used to further clean and adjust the surface condition of the tantalum foil, providing a relatively consistent substrate surface for subsequent femtosecond laser processing and electrochemical etching.

[0025] S113, the tantalum foil after immersion treatment is rinsed with deionized water and then dried.

[0026] After the immersion treatment is completed, the tantalum foil is repeatedly rinsed with deionized water to remove residual solution from the surface, and then the tantalum foil is dried in a vacuum oven at 60 ℃.

[0027] S200 uses a femtosecond laser to directly ablate the pre-treated tantalum foil, forming multiple first hole structures on the surface of the tantalum foil. The first hole structures are micron-sized blind holes. S300, electrochemical etching is performed on the tantalum foil with the first pore structure to form a second pore structure with a smaller scale than the first pore structure on the surface of the tantalum foil and the inner wall of the first pore structure, thereby obtaining a hierarchical porous tantalum substrate. S200 and S300 both involve processing the pore structure of tantalum foil, including forming a first pore structure / micron-sized blind hole using a femtosecond laser (S200) and then performing electrochemical etching on this basis (S300) to form a porous tantalum substrate with pore structures of different scales. The micron-sized blind hole (first pore structure) formed by the femtosecond laser mainly provides a larger-scale three-dimensional structure. On this basis, the microstructure of the outer surface of the tantalum foil and the inner wall of the blind hole is further changed by electrochemical etching to form a micropore structure (second pore structure) with a scale smaller than the micron-sized blind hole.

[0028] Reference Figure 3 In one embodiment, S200 includes: S211, Scan the surface of the pretreated tantalum foil; The scanning is primarily used to acquire the position and size information of the area to be processed, providing a positioning basis for subsequent laser processing according to a preset array arrangement. This scanning is an auxiliary positioning step before femtosecond laser processing and is not limited to using a specific image recognition method.

[0029] S212, based on the scanning results, the target dot matrix spacing and the target array arrangement, a femtosecond laser is used to sequentially ablate the pre-processed tantalum foil to form multiple first hole structures on the surface of the tantalum foil, and all the first hole structures form a blind hole array.

[0030] In this step, based on the scanning results (length and width information of the tantalum foil) and the target dot spacing and target array arrangement, the execution end of the femtosecond laser processing equipment is controlled to sequentially perform ablation processing on the surface of the tantalum foil to form a micron-scale blind hole array. It should be noted that the holes are blind holes, and their depth is less than the thickness of the tantalum foil. Finally, a blind hole array is processed, which uniformly covers the surface of the tantalum foil. The core of this step is to construct a three-dimensional atomic layer deposition platform with regular geometric topology. The uniformly distributed blind hole array provides an equalized microscopic reaction environment for atomic layer deposition, improves the consistency of performance between units, and fully utilizes the three-dimensional conformal advantages of atomic layer deposition technology to provide a stable structural foundation for subsequent processes.

[0031] It should be noted that the term "uniform" should be understood as follows: on a macroscopic scale, the areal density of blind holes on the tantalum foil surface remains basically consistent, without large-area sparse or dense regional differences, thereby ensuring that the entire substrate surface has a balanced specific surface area expansion effect.

[0032] In a preferred embodiment of this step, the blind holes can be arranged according to a regular geometric lattice (such as a rectangular array, a honeycomb array, etc.), in which case the center distance between adjacent blind holes remains consistent. The regular array layout provides the atomic layer deposition process with optimized mass transfer path consistency, so that the gaseous precursor in the reaction chamber can obtain equivalent diffusion conditions and reactant supply in each blind hole, which is beneficial to achieving uniform deposition of film thickness and quality on a large-area substrate.

[0033] However, a regular, evenly spaced arrangement is not the only way to achieve the objectives of this invention. As an alternative implementation, blind vias can also be irregularly distributed on the tantalum foil surface. That is, the spacing between adjacent blind vias is allowed to vary within a certain range, but the overall premise of "uniformly covering the surface" must still be met. This means that the areal density of the blind vias must be statistically consistent, without local clusters or obvious gaps. This irregular but generally uniform distribution can still achieve the basic effect of expanding the specific surface area and providing a three-dimensional platform for atomic layer deposition. Furthermore, in some applications, the irregular via layout can help break the modal resonance or stress concentration effects that periodic structures may cause, further improving the reliability and stability of the device.

[0034] It should be noted that the specific arrangement of blind holes, the numerical range of adjacent spacing, and the absolute dimensions of hole depth can all be adaptively adjusted according to actual process requirements and flow field characteristics of atomic layer deposition equipment. This step only limits the spatial distribution uniformity of blind holes and their three-dimensional structural functions, and should not be understood as being limited to a specific arrangement geometry or depth specification.

[0035] In this embodiment, a femtosecond laser is used to perform lattice ablation processing on the pretreated tantalum foil. The laser power is set to 8 W, the pulse frequency to 1 kHz, the wavelength to 1030 nm, the scanning spacing to 0.15 mm, and the laser spot's duration of action at a single processing position to 0.6 ms.

[0036] The depth of the blind hole is less than the thickness of the tantalum foil, so that the tantalum foil forms a three-dimensional hole structure while still retaining a continuous tantalum substrate, which is used to provide structural support and conductive path.

[0037] Reference Figure 4 In one embodiment, S200 includes: S221, Scan the surface of the pretreated tantalum foil; The scanning is primarily used to acquire the position and size information of the area to be processed, providing a positioning basis for subsequent laser processing according to a preset array arrangement. This scanning is an auxiliary positioning step before femtosecond laser processing and is not limited to using a specific image recognition method.

[0038] S222, based on the scanning results, as well as the target dot matrix spacing, target hole depth, and target array arrangement, a femtosecond laser is used to sequentially perform ablation processing on the thickness direction of the pre-processed tantalum foil, forming multiple first hole structures on the surface of the tantalum foil, and all the first hole structures form a blind hole array.

[0039] In this step, based on the scanning results, as well as the target hole depth and target array arrangement, the execution end of the femtosecond laser processing equipment is controlled to perform a preset number of ablation processes in the thickness direction of the pre-processed tantalum foil to form a micron-level blind hole array.

[0040] In this embodiment, a femtosecond laser is used to perform lattice ablation processing on the pretreated tantalum foil. The laser power is set to 8 W, the pulse frequency to 1 kHz, the wavelength to 1030 nm, and the scanning spacing to 0.15 mm.

[0041] During the processing, after each processing step, the laser focus is moved 10μm along the thickness direction of the tantalum foil before the next processing step is performed. A total of 6 processing steps are performed to form a micron-sized blind hole (first hole structure) with a diameter of about 100μm and a depth of about 60μm on the surface of the tantalum foil.

[0042] The depth of the blind hole is less than the thickness of the tantalum foil, so that the tantalum foil forms a three-dimensional hole structure while still retaining a continuous tantalum substrate, which is used to provide structural support and conductive path.

[0043] In this step, by pre-setting the target aperture depth and matching the corresponding laser parameters (such as power, frequency, wavelength, dwell time, scanning spacing, etc.), the depth of each blind aperture is no longer a random or fixed result, but can be actively designed and precisely controlled according to the specific needs of the subsequent atomic layer deposition process. Different target aperture depths directly determine the aspect ratio of the blind aperture, which in turn affects the mass transfer resistance of the vapor precursor diffusing into the aperture during atomic layer deposition and the uniformity of the final film coverage on the aperture wall and bottom. Operators can flexibly set the optimal aperture depth parameters according to the type of functional material being deposited, the deposition temperature window, and the performance requirements of the target device, greatly expanding the process adaptability range.

[0044] Based on the scanning results, target dot spacing, preset target hole depth, and laser setting parameters, a preset number of holes are drilled on the tantalum foil surface to form the blind hole array.

[0045] By employing a multi-drilling method with a preset number of passes, the achievement of the total hole depth is decomposed into multiple controllable processing sub-steps. The material removal rate per drill is small, and the instantaneous thermal shock from the interaction between the laser and the material is effectively suppressed, avoiding defects such as material splashing, hole opening melting and expansion, or excessively deep heat-affected zones that might result from a single high-energy input. By accumulating multiple passes to approximate the target depth, the control precision of the final hole depth is significantly improved. Simultaneously, by utilizing scanning results (planar positioning), target dot matrix spacing (horizontal distribution), preset target hole depth (vertical dimension), and laser setting parameters (processing conditions), the planar position, horizontal spacing, vertical depth, and processing quality of the blind holes are coordinated and controlled within the same process. This ensures that the final blind hole array is not only uniformly distributed horizontally but also has a consistent and expected depth dimension in the vertical direction, achieving comprehensive control over the hole structure in three-dimensional space. Furthermore, when there are slight fluctuations in the material properties of the tantalum foil (such as surface hardness, grain orientation, residual stress, etc.) between batches, using a fixed preset number of passes combined with uniform laser parameter settings for each pass can effectively suppress the impact of random disturbances in a single processing step on the final hole depth through the averaging effect of the cumulative effect. This ensures a high degree of consistency in the blind hole depth between different batches of products, thereby guaranteeing the batch-to-batch repeatability of device performance after subsequent atomic layer deposition.

[0046] In this invention, the arrangement of the blind via array should not be narrowly interpreted as limited to a strictly equidistant geometric lattice. As a broader scope of protection, the blind vias on the tantalum foil surface can be arranged in an ordered, regular array (such as a rectangular array or a honeycomb array) or in a disordered, irregular distribution. The key point is that, regardless of whether ordered or disordered, the blind vias must satisfy the prerequisite of "uniformly covering the tantalum foil surface," that is, maintaining a consistent overall areal density in a statistical sense.

[0047] In the two embodiments of the first hole structure processing described above, the surface of the tantalum foil is scanned to obtain its precise length and width geometric information, providing a high-precision positioning reference and layout basis for the subsequent drilling process. For example, by determining the drilling start boundary, it is ensured that the hole array is uniformly and symmetrically arranged on the tantalum foil surface. The precise dimensional information obtained by scanning provides a spatial coordinate reference for constructing a regular blind hole array. By determining a unified start edge and boundary, the subsequent hole array is ensured to be neatly arranged on a macroscopic scale. This overall orderly layout is the basis for achieving uniformity in atomic layer deposition. In the subsequent atomic layer deposition process, the regularly arranged hole array enables the gaseous precursor in the reaction chamber to form a uniform concentration gradient on the substrate surface, avoiding local airflow disturbances or precursor depletion effects caused by irregular substrate boundaries, thereby ensuring the consistency of deposition rate and film quality across a large area of ​​the substrate.

[0048] For example, with a preset target hole depth of 60 μm, the laser settings include: power 8 W, pulse frequency 1 kHz, wavelength 1030 nm, and laser spot dwell time set to 0.6 seconds. Each hole needs to be scanned 6 times to reach the preset target hole depth. The tantalum foil can be scanned using one of the following two paths: 1) Perform 6 consecutive laser scans on a single blind hole position. After each scan, the laser spot moves downwards by 10 μm, returns to its initial height, and moves to the next hole position. This process is repeated for each blind hole position until all holes are processed. In this method, each blind hole completes all 6 scans before the laser focus is removed, and the processing of holes does not interfere with each other. 2) Perform a first scan on all blind hole positions sequentially to initially form the entire array. Then, move the laser spot downwards by 10 μm and perform a second scan on all holes in the same order, and so on, until all 6 scans are completed. In this method, each blind hole undergoes 6 scans, but each scan is performed cyclically across the entire array.

[0049] Optionally, the laser scanning path can be arranged in a straight line, a bow shape, or a serpentine pattern in the X and / or Y directions.

[0050] Optionally, the scanning spacing of the laser spot is set to 0.15 mm, and a regular blind hole array with a diameter of 100 μm, a depth of 60 μm, and a dot pitch of 50 μm is finally manufactured on the tantalum foil surface.

[0051] In S300, the step of electrochemically etching the tantalum foil with the first pore structure includes: The platinum sheet and the tantalum foil with the first pore structure are placed together in a preset electrode solution. The saturated calomel electrode is used as the reference electrode, the tantalum foil with the first pore structure is used as the working electrode, and the platinum sheet is used as the counter electrode. The tantalum foil with the first pore structure is etched using a pulsed potential.

[0052] The electrochemical etching employs a three-electrode system, and the preset electrode solution is a propanol solution containing potassium chloride and deionized water, specifically using propanol as the solvent, which contains 5 wt% potassium chloride and 1 wt% deionized water.

[0053] Specifically, electrochemical etching was performed at 20–25 °C, with the pulse potential of the tantalum foil working electrode relative to the saturated calomel electrode controlled at 8 V, the pulse frequency at 30 Hz, the duty cycle at 60%, and the etching time at 25 min.

[0054] Figure 4 The pulsed electrochemical etching step shown in this embodiment is specifically performed by controlling the pulsed potential of the tantalum foil working electrode relative to the saturated calomel electrode.

[0055] Through the electrochemical etching, a micropore structure (second pore structure) is further formed on the outer surface of the tantalum foil and the inner wall of the micron-sized blind hole (first pore structure) formed by the femtosecond laser. Thus, the tantalum foil simultaneously has a micron-sized blind hole formed by the femtosecond laser and a second pore structure further formed by electrochemical etching, which together form a porous tantalum substrate with pore structures of different scales.

[0056] Femtosecond laser processing and electrochemical etching play different roles in constructing structures at different scales: femtosecond lasers are mainly used to form micron-sized blind holes with predetermined positions, apertures, and depths, while electrochemical etching further increases the fine structure of the outer surface of the tantalum foil and the inner wall of the blind holes.

[0057] Reference Figure 5 In S400, the step of forming a ruthenium dioxide film layer on the surface of the hierarchical porous tantalum substrate using atomic layer deposition includes: S401, Isopropanol is introduced into the reaction chamber in a pulsed manner, so that the isopropanol comes into contact with the surface of the hierarchical porous tantalum substrate; In this embodiment, isopropanol vapor is used as the first gaseous precursor for atomic layer deposition and is introduced into the reaction chamber in a pulsed manner. The isopropanol pulse duration is 20 s, so that the isopropanol comes into contact with the outer surface of the porous tantalum substrate and the surfaces that can be reached within its pore structure to form an adsorption layer.

[0058] S402, the reaction chamber is evacuated for the first time; In this embodiment, the reaction chamber is evacuated or purged with an inert gas for 60 seconds to reduce isopropanol and other gaseous components that do not participate in the surface process within the reaction chamber.

[0059] S403, Ruthenium tetroxide is introduced into the reaction chamber in a pulsed manner, so that the Ruthenium tetroxide reacts with the surface treated with isopropanol; In this embodiment, RuO4 vapor is used as the second gaseous precursor for atomic layer deposition. It is introduced into the reaction chamber in a pulsed manner with a RuO4 pulse duration of 35 s, so that it reacts with the isopropanol-treated surface to form a RuO2 coating layer.

[0060] S404, the reaction chamber is evacuated for the second time; In this embodiment, the reaction chamber is evacuated again or purged with inert gas for 60 seconds to reduce residual gaseous reactants and reaction byproducts.

[0061] S405, Repeat the above steps to form a ruthenium dioxide film on the surface of the hierarchical porous tantalum substrate.

[0062] In this step, RuO2 is formed on the surface of a porous tantalum substrate as a cathode active material. At least one atomic layer deposition cycle (S401-S404) is performed on the hierarchical porous tantalum substrate to obtain a tantalum capacitor cathode sheet. In addition to evacuating the reaction chamber, purging can also be performed to remove the gaseous reactants remaining in the previous step.

[0063] The atomic layer deposition process involves two gaseous reactants sequentially entering the reaction chamber and reacting on the surface to form a RuO2 film. The gaseous reactants can enter pores that communicate with the outside and contact the solid surfaces they can reach, allowing RuO2 to gradually form along the three-dimensional surface of the porous tantalum substrate.

[0064] Before atomic layer deposition, the porous tantalum substrate with the completed pore structure is placed in the reaction chamber, and the reaction chamber is evacuated to a basic vacuum of approximately 10^ -6 mbar. Preheat the chamber walls to approximately 80 °C, set and stabilize the sample stage or substrate temperature at 90 °C, and heat the reactant delivery lines to approximately 60 °C.

[0065] The RuO2 film can be formed on the outer surface of the tantalum foil, the inner wall of the micron-sized blind holes, and the surface of the second pore structure that can be reached by gaseous reactants. RuO2 mainly forms a film along the solid surface, rather than completely filling the pore structure with particles, so that the pore structure after deposition can still retain space for electrolyte entry and mass transfer.

[0066] In one specific embodiment, a total of 100 atomic layer deposition cycles are performed. Based on a growth rate similar to that of a RuO2 atomic layer deposition system, with a process setting of approximately 2.0 Å / cycle, the target RuO2 film thickness corresponding to 100 cycles is approximately 20 nm. This film thickness can be adjusted by changing the number of atomic layer deposition cycles according to the target loading state.

[0067] This embodiment uses a sample stage or substrate temperature of 90 °C to form the RuO2 film. This temperature is lower than some existing processes that use higher temperature heat treatment to form RuO2, which helps to reduce the risk of thermal impact on the tantalum foil substrate caused by higher temperature treatment.

[0068] like Figure 6 As shown, the tantalum capacitor cathode obtained by the above method includes a hierarchical porous tantalum substrate, a first pore structure formed on the hierarchical porous tantalum substrate, a second pore structure formed on the outer surface of the hierarchical porous tantalum substrate and the inner wall of the first pore structure, and a RuO2 film layer formed on the porous surface.

[0069] S200, S300, and S400 are interconnected in terms of process. S200 and S300 form porous tantalum substrates with different pore structures through femtosecond laser processing and electrochemical etching; S400 then forms a RuO2 film on the surface of the porous tantalum substrate by atomic layer deposition, so that the increased surface area of ​​the tantalum substrate due to the pore structure can be further used to load RuO2 active materials.

[0070] A complete implementation of S100 to S400 is specifically as follows: High-purity tantalum foil with a thickness of 0.3 mm and a purity of not less than 99.95% was selected. The tantalum foil was ultrasonically cleaned in toluene for 15 min, then removed and ultrasonically cleaned again in anhydrous ethanol for 15 min. Subsequently, the tantalum foil was immersed in a 1 mol / L NaOH solution at 90 ℃ for 30 s. After treatment, it was repeatedly rinsed with deionized water and dried in a vacuum oven at 60 ℃. The pretreated tantalum foil was fixed on the sample stage of the femtosecond laser processing equipment. The area to be processed was scanned and positioned, and the tantalum foil was ablated by femtosecond laser according to the preset dot matrix processing path. The laser power was set to 8 W, the pulse frequency to 1 kHz, the wavelength to 1030 nm, and the scanning interval to 0.15 mm. After each processing, the laser focus was moved 10 μm along the thickness direction of the tantalum foil, and a total of 6 processings were performed to form a micron-sized blind hole with a diameter of about 100 μm and a depth of about 60 μm on the surface of the tantalum foil. A tantalum foil processed by femtosecond laser was used as the working electrode, a large-area platinum sheet as the counter electrode, and a saturated calomel electrode as the reference electrode. An electrolyte solution containing 5 wt% potassium chloride and 1 wt% deionized water was used for electrochemical etching at 20–25 °C. The pulse potential of the tantalum foil working electrode relative to the saturated calomel electrode was controlled at 8 V, the pulse frequency at 30 Hz, and the duty cycle at 60%, lasting for 25 min. This further formed a microporous structure on the outer surface of the tantalum foil and the inner wall of the micron-sized blind holes, resulting in a porous tantalum substrate. The porous tantalum substrate was placed in an atomic layer deposition (ALD) reaction chamber. The chamber was evacuated to a basic vacuum of approximately 10⁻⁶ mbar, the chamber walls were maintained at approximately 80 °C, the sample stage or substrate temperature was set and stabilized at 90 °C, and the reactant delivery line was heated to approximately 60 °C. Isopropanol vapor was introduced into the reaction chamber for 20 s, followed by evacuation or purging for 60 s; then RuO₄ vapor was introduced for 35 s, followed by evacuation or purging again for 60 s, completing one ALD cycle. This ALD cycle was repeated 100 times to form a RuO₂ film on the surface of the porous tantalum substrate, with a target film thickness of approximately 20 nm, thus obtaining a tantalum capacitor cathode.

[0071] For different tantalum foil specifications, target hole structures, and RuO2 loading states, the femtosecond laser processing parameters, electrochemical etching conditions, and atomic layer deposition cycle numbers can be adjusted accordingly based on the actual processing conditions.

[0072] Secondly, the present invention provides a tantalum capacitor cathode sheet.

[0073] The tantalum capacitor cathode includes a tantalum substrate. Multiple first pore structures are formed on the tantalum substrate, and second pore structures with smaller dimensions are formed on the outer surface of the tantalum substrate and the inner wall of the first pore structures. The first and second pore structures together form a porous structure with pores of different dimensions.

[0074] A RuO2 film is formed on at least a portion of the surface of the porous structure. The RuO2 film is formed along the outer surface of the tantalum substrate, the inner wall of the first pore structure, and the surface of the second pore structure that the gaseous reactants can reach, while the interior of the pore structure still retains pore spaces that communicate with the outside.

[0075] In one embodiment, the tantalum substrate has a thickness of 0.3 mm, and the first pore structure has a diameter of approximately 100 μm and a depth of approximately 60 μm.

[0076] In one embodiment, the target thickness of the RuO2 film is approximately 20 nm.

[0077] Thirdly, the present invention provides a tantalum capacitor, the tantalum capacitor comprising the aforementioned tantalum capacitor cathode plate.

[0078] The tantalum capacitor cathode can be assembled with tantalum anode, electrolyte, isolation structure, lead-out structure, and casing to form a tantalum capacitor. Except for the cathode, the remaining structures can be configured according to the specific specifications and usage requirements of the tantalum capacitor.

[0079] It should be understood that in this embodiment, femtosecond laser processing, electrochemical etching, and atomic layer deposition are performed sequentially according to the above-described process order. Specifically, femtosecond laser processing is used to form the first pore structure, electrochemical etching further forms the second pore structure based on the first pore structure, and atomic layer deposition forms a RuO2 film on the surface of the obtained porous tantalum substrate. Auxiliary operations in each step can be adjusted according to specific equipment and process conditions, but the process connection between the main process steps described above remains unchanged.

[0080] It should be noted that, in this document, the terms “comprising,” “including,” or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or system that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or system.

[0081] The sequence numbers of the above embodiments of the present invention are for descriptive purposes only and do not represent the superiority or inferiority of the embodiments.

[0082] The above are merely preferred embodiments of the present invention and do not limit the patent scope of the present invention. Any equivalent structural or procedural transformations made based on the content of the present invention's specification and drawings, or direct or indirect applications to other related technical fields, are similarly included within the patent protection scope of the present invention.

Claims

1. A method for preparing a tantalum capacitor cathode, characterized in that, include: Pre-treatment of tantalum foil; The pre-treated tantalum foil is ablated using a femtosecond laser to form multiple first hole structures on the surface of the tantalum foil. The first hole structures are micron-sized blind holes. Electrochemical etching is performed on a tantalum foil with a first pore structure to form a second pore structure with a smaller scale than the first pore structure on the surface of the tantalum foil and the inner wall of the first pore structure, thereby obtaining a hierarchical porous tantalum substrate. A ruthenium dioxide film was formed on the surface of the hierarchical porous tantalum substrate using atomic layer deposition to obtain a tantalum capacitor cathode.

2. The preparation method according to claim 1, characterized in that, The step of using a femtosecond laser to ablate the pretreated tantalum foil to form a plurality of first hole structures on the surface of the tantalum foil includes: The surface of the pretreated tantalum foil is scanned; Based on the scanning results, as well as the target dot spacing and target array arrangement, a femtosecond laser is used to sequentially ablate the pre-treated tantalum foil to form multiple first hole structures on the surface of the tantalum foil, and all the first hole structures form a blind hole array.

3. The preparation method according to claim 1, characterized in that, The step of using a femtosecond laser to ablate the pretreated tantalum foil to form multiple first hole structures on the surface of the tantalum foil includes: The surface of the pretreated tantalum foil is scanned; Based on the scanning results, as well as the target hole depth, target dot matrix spacing, and target array arrangement, a femtosecond laser is used to sequentially perform ablation processing on the thickness direction of the pre-processed tantalum foil, forming multiple first hole structures on the surface of the tantalum foil. All the first hole structures form a blind hole array.

4. The preparation method according to claim 1, characterized in that, The step of electrochemically etching the tantalum foil with the first pore structure includes: The platinum sheet and the tantalum foil with the first pore structure are placed together in a preset electrode solution. The saturated calomel electrode is used as the reference electrode, the tantalum foil with the first pore structure is used as the working electrode, and the platinum sheet is used as the counter electrode. The tantalum foil with the first pore structure is etched using a pulsed potential.

5. The preparation method according to claim 4, characterized in that, The preset electrode solution is a propanol solution containing potassium chloride and deionized water.

6. The preparation method according to claim 1, characterized in that, The step of forming a ruthenium dioxide film on the surface of the hierarchical porous tantalum substrate using atomic layer deposition includes: Isopropanol is introduced into the reaction chamber in a pulsed manner, so that the isopropanol comes into contact with the surface of the hierarchical porous tantalum substrate; The reaction chamber was evacuated for the first time; Ruthenium tetroxide is introduced into the reaction chamber in a pulsed manner, causing the ruthenium tetroxide to react with the surface treated with isopropanol. The reaction chamber is evacuated a second time; Repeat the above steps to form a ruthenium dioxide film on the surface of the hierarchical porous tantalum substrate.

7. The preparation method according to claim 1, characterized in that, The pretreatment step of the tantalum foil includes: The tantalum foil was sequentially placed in toluene and anhydrous ethanol for ultrasonic cleaning. The ultrasonically cleaned tantalum foil was immersed in a NaOH solution. The tantalum foil after immersion treatment was rinsed with deionized water and then dried.

8. The preparation method according to claim 6, characterized in that, Before the step of forming a ruthenium dioxide film on the surface of the hierarchical porous tantalum substrate using atomic layer deposition, the following steps are included: The chamber walls of the reaction chamber are preheated and maintained at 80°C, and the delivery pipeline is heated to 60°C.

9. A tantalum capacitor cathode plate, characterized in that, The tantalum capacitor cathode sheet is prepared by the preparation method according to any one of claims 1-8.

10. A tantalum capacitor, characterized in that, The tantalum capacitor includes the tantalum capacitor cathode plate as described in claim 9.

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