Flexible micro-needle tip array electrode based on composite multilayer metal and preparation method of flexible micro-needle tip array electrode

Abstract

The invention belongs to the technical field of micromachining, and discloses a flexible micro needle tip array electrode based on composite multi-layer metal and a preparation method of the flexible micro needle tip array electrode. The flexible micro needle tip array electrode comprises a flexible substrate and a silicon micro needle tip array structure arranged on the flexible substrate, each silicon micro needle tip in the silicon micro needle tip array structure is provided with composite multilayer metal capable of conducting electricity and conducting signals, and the composite multilayer metal sequentially comprises a seed layer, a structural layer, an adhesion layer and a contact layer from inside to outside; the material of the seed layer is Cr, Ti, Ni, Mo, Ta, W, Fe, Cu, Au, Ag or Pt, the material of the structural layer is Cu, Ag or Au, the material of the adhesion layer is Cr, Ni, Ti, Mo, Ta or W, and the material of the contact layer is Au, Ag or AgCl. According to the invention, the composite multi-layer metal is used as the conductive layer of the flexible micro-needle-point array electrode, so that the contact impedance of the flexible micro-needle-point array electrode is reduced.

Description

Technical Field

[0001] The present invention belongs to the field of micromachining technology, relates to the field of flexible micro-needle tip array electrodes, and particularly relates to a flexible micro-needle tip array electrode based on composite multilayer metal and a preparation method thereof. Background Art

[0002] Flexible microneedle array electrode (FMAE) is a new type of biomedical sensor that combines micro-nano processing technology with flexible electronics. It has the advantages of minimal invasiveness, high throughput, high sensitivity and good biocompatibility, and has shown broad application prospects in the fields of neural signal recording, electrophysiological monitoring, drug delivery and biosensing.

[0003] At present, in the existing flexible micro-needle tip array electrode structure, the conductive layer is generally selected as Au / Cr layer or Au layer, and the thickness of Au is relatively thin. The reason is that Au has very low resistance but high cost. The thinner Au conductive layer makes the contact impedance of the electrode higher. In addition, the flexible micro-needle tip structure is relatively complex, such as the structural partition including the columnar needle body and the needle tip at the top, and the process is cumbersome, requiring the use of technologies such as mechanical scribing, multiple (three or more) photolithography, and high-precision laser drilling, resulting in high processing costs and low efficiency.

[0004] As a specific example, brain-computer interfaces (BCIs), which bridge the brain with external devices, are becoming a research hotspot in scientific research and medicine. Non-invasive BCI technology, with its advantages of being non-invasive and easy to use, has shown great potential for application in a wide range of fields, including medical diagnosis, rehabilitation therapy, and human-computer interaction. Existing non-invasive BCIs primarily interact with the brain by collecting EEG signals from the scalp surface. However, the application of the aforementioned flexible microtip array electrodes still presents several challenges. Specifically, the thickness of the Au conductive layer in existing flexible microtip array electrode structures presents an untunable conflict with cost. The thin Au conductive layer increases the overall contact impedance of the electrode, which in turn affects the accuracy of EEG signal acquisition during actual use. This makes it impossible to obtain high-quality, high-resolution EEG signals, leading to significant errors in the analysis and interpretation of brain activity, making it difficult to meet the requirements for accurate diagnosis of brain diseases and complex BCI tasks. For example, subtle EEG signal changes are crucial in the early diagnosis of neurological diseases such as epilepsy and Parkinson's disease, but the low precision of existing electrodes makes it easy to miss this critical information. The improved solution of reducing the contact impedance of the electrode by increasing the thickness of the Au layer will greatly increase the cost of the electrode, limiting the promotion and popularization of EEG detection as an examination and treatment option. On the other hand, the complex structure and cumbersome preparation process of existing flexible micro-needle tip array electrodes further increase the cost of electrode preparation. In summary, there is an urgent need to develop a new technical solution to reduce the contact impedance and manufacturing cost of the electrode, while improving the manufacturing efficiency of the electrode. Summary of the Invention

[0005] The present invention aims to provide a flexible microtip array electrode based on a composite multilayer metal and a method for preparing the same, thereby resolving one or more of the aforementioned technical problems. In the technical solution disclosed in the present invention, the composite multilayer metal serves as the conductive layer of the flexible microtip array electrode, significantly increasing the thickness of the conductive layer for electrical signal transmission and reducing the contact impedance of the flexible microtip array electrode. Furthermore, the present invention provides a method for preparing the flexible microtip array electrode, reducing manufacturing costs and improving manufacturing efficiency.

[0006] In order to achieve the above object, the present invention adopts the following technical solutions: In a first aspect, the present invention provides a flexible micro-needle tip array electrode based on a composite multilayer metal, comprising: a flexible substrate and a silicon micro-needle tip array structure disposed on the flexible substrate; Among them, each silicon microneedle tip in the silicon microneedle tip array structure is provided with a composite multilayer metal that can conduct electricity and transmit signals, and the composite multilayer metal is composed of a seed layer, a structural layer, an adhesion layer and a contact layer from the inside to the outside; the material of the seed layer is Cr, Ti, Ni, Mo, Ta, W, Fe, Cu, Au, Ag or Pt, the material of the structural layer is Cu, Ag or Au, the material of the adhesion layer is Cr, Ni, Ti, Mo, Ta or W, and the material of the contact layer is Au, Ag or AgCl.

[0007] A further improvement of the technical solution of the present invention is that the seed layer is grown on the surface of the silicon microneedle tip, the structural layer is grown on the surface of the seed layer by electrochemical plating, the adhesion layer is grown on the surface of the structural layer by vapor deposition, and the contact layer is grown on the surface of the adhesion layer by vapor deposition.

[0008] A further improvement of the technical solution of the present invention is that in the silicon microtip array structure, each silicon microtip is an octagonal pyramid silicon microtip, the tip height is 50 μm to 500 μm, and the tip spacing is 150 μm to 1000 μm.

[0009] A further improvement of the technical solution of the present invention is that the thickness of the seed layer is 10 nm to 300 nm, the thickness of the structural layer is 1 μm to 50 μm, the thickness of the adhesion layer is 10 nm to 50 nm, and the thickness of the contact layer is 50 nm to 400 nm.

[0010] A further improvement of the technical solution of the present invention is that the material of the flexible substrate is parylene, polyimide or polydimethylsiloxane.

[0011] A further improvement of the technical solution of the present invention is that the flexible micro-needle tip array electrode is provided with one or more independent channels, and one or more connected silicon micro-needle tips in the silicon micro-needle tip array structure serve as an independent channel.

[0012] In a second aspect, the present invention provides a method for preparing a flexible micro-needle tip array electrode based on a composite multilayer metal, comprising the following steps: Step 1: Based on a selected silicon wafer, a thin film is grown on one side of the silicon wafer using a vapor deposition method, and the other side of the silicon wafer is bonded to a selected bonding sacrificial layer; wherein the thin film is pure silicon nitride, pure silicon oxide, or a mixture of silicon oxide and silicon nitride; Step 2: Photolithography and dry etching are performed on the film surface to form a patterned mask layer with a square array; wet etching is performed based on the patterned mask layer to obtain an initial silicon microneedle tip array with a preset height; Step 3: On the surface of each silicon microtip of the initial silicon microtip array, a metal electrode pattern is formed by photolithography, a seed layer of metal is grown on the surface of each silicon microtip by vapor deposition, a metal with a predetermined good conductivity is grown on the surface of the seed layer by electrochemical plating as a structural layer, and an adhesion layer and a contact layer of metal are sequentially grown on the metal surface of the structural layer in the metal electrode area by a lift-off process to form a silicon microtip array structure; Step 4: Laterally etch the bonding sacrificial layer to form a groove at the bottom of the silicon microneedle tip array structure; deposit a flexible substrate using vapor deposition or spin coating to wrap the silicon microneedle tips and fill the groove; Step 5: remove the bonding sacrificial layer to prepare a flexible micro-needle tip array electrode based on composite multilayer metal.

[0013] A further improvement of the technical solution of the present invention is that in step 1, the selected silicon wafer is a silicon wafer with a (001) crystal orientation and a thickness of 100 μm to 500 μm, and the thickness of the grown film ranges from 10 nm to 300 nm.

[0014] A further improvement of the technical solution of the present invention is that in step 2, in the step of performing wet etching based on the patterned mask layer to obtain an initial silicon microtip array of a preset height, a potassium hydroxide solution with a mass percentage concentration of 20% to 40% is used for wet etching to obtain an initial silicon microtip array with a height of 50 μm to 500 μm; Among them, the concentration of potassium hydroxide determines the angle between the side and bottom of the pyramid-shaped tip (that is, the sharpness of the tip). A potassium hydroxide concentration lower than 20% or higher than 40% will cause the angle between the side and bottom of the octagonal pyramid tip to become smaller, that is, the tip becomes blunt; during wet etching, the potassium hydroxide solution needs to be magnetically stirred at a stirring speed of 200 r / min ~ 5000 r / min; the temperature for wet etching is 60 ℃ ~ 95 ℃; in the initial silicon microtip array, each silicon microtip is an octagonal pyramid silicon microtip.

[0015] A further improvement of the technical solution of the present invention is that in step 3, the thickness of the seed layer is 10 nm to 300 nm, the thickness of the structural layer is 1 μm to 50 μm, the thickness of the adhesion layer is 10 nm to 50 nm, and the thickness of the contact layer is 50 nm to 400 nm.

[0016] Compared with the prior art, the present invention has the following beneficial effects: The present invention discloses a flexible micro-needle array electrode based on a composite multilayer metal. The composite multilayer metal is provided with a seed layer, a structural layer, an adhesion layer, and a contact layer. The composite multilayer metal is used as the conductive layer of the flexible micro-needle array electrode, which can greatly increase the thickness of the conductive layer on the surface of the silicon micro-needle tip for electrical signal transmission. The structural design of the composite multilayer metal of the present invention provides specific materials for the seed layer, the structural layer, the adhesion layer, and the contact layer. The coordinated effect of the materials in each layer helps to reduce the contact impedance. Further explanatory, the resistance of the conductive layer is inversely proportional to the thickness, so the resistance will be reduced, thereby reducing the contact impedance of the flexible micro-needle array electrode. In addition, each metal layer can be selected from metals with good conductivity and low cost according to needs, thereby reducing the impedance while maintaining the low manufacturing cost of the electrode.

[0017] The present invention further discloses a method for preparing a flexible micro-needle tip array electrode based on a composite multilayer metal. The method is a scheme that first performs anodic bonding, and then prepares a silicon micro-needle tip array structure through a single photolithography and wet etching. This greatly reduces the process flow of flexible micro-needle tip array manufacturing and reduces the complexity of manufacturing. This process scheme further reduces manufacturing costs and improves manufacturing efficiency. At the same time, the manufactured silicon micro-needle tip array structure is simpler and more reliable. In summary, the technical solution of the present invention, based on the economic efficiency of material selection and the optimization of the preparation method, effectively reduces manufacturing costs and improves manufacturing efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] In order to more clearly illustrate the technical solutions in the present invention or the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below; obviously, the drawings described below are some embodiments of the present invention, and for ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0019] Figure 1 1 is a schematic diagram of a cross-sectional two-dimensional structure of a flexible micro-tip array electrode based on composite multi-layer metal in an embodiment of the present invention; Figure 2 1 is a schematic diagram of a preparation process of a flexible micro-needle tip array electrode based on composite multilayer metal in an embodiment of the present invention; Figure 3 Schematic diagram of a circuit channel arrangement scheme of a flexible micro-needle tip array electrode based on composite multilayer metal in an embodiment of the present invention; wherein, Figure 3 (a) is a schematic diagram of the entire chip array as a channel. Figure 3 (b) is a schematic diagram of a solution in which part of the needle tip is used as a channel (specifically, for example, each row or each column). Figure 3 (c) is a schematic diagram of the scheme in which each needle tip serves as a channel; Figure 4 1 is a sample schematic diagram of a silicon microtip array in an embodiment of the present invention; Figure 5 is a scanning electron microscope (SEM) image of a silicon microtip array in an embodiment of the present invention; Figure 6 1 is a photographic schematic diagram of a flexible micro-needle tip array electrode based on composite multi-layer metal in an embodiment of the present invention; Figure 7 1 is a schematic diagram comparing the resistance of 4-layer composite metal layers and 2-layer composite metal layers (Comsol calculation) in an embodiment of the present invention; Figure 8 This is the EEG during the eyes-open / eye-closed process obtained from the test in the embodiment of the present invention; compared with the commercial wet electrode, the flexible micro-needle tip array electrode disclosed in the technical solution of the embodiment of the present invention has a stronger signal and a higher signal-to-noise ratio; The explanations of the reference numerals in the figures are as follows: 1. silicon microneedle tip; 2. seed layer; 3. structural layer; 4. adhesion layer; 5. contact layer; 6. flexible substrate. DETAILED DESCRIPTION

[0020] In order to make the purpose, technical solutions and advantages of the present invention clearer, the technical solutions of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention; it is obvious that the described embodiments and technical solutions are only part of the embodiments of the present invention, not all of the embodiments.

[0021] All other embodiments obtained by persons of ordinary skill in the art based on the technical solutions disclosed in the embodiments of the present invention without creative effort shall fall within the scope of protection of the present invention. In addition, the terms "including" and "having" and any variations thereof are intended to cover non-exclusive inclusions. For example, a process, method, system, product, or apparatus that includes a series of steps or units is not necessarily limited to those steps or units explicitly listed, but may include other steps or units that are not explicitly listed or that are inherent to these processes, methods, products, or apparatuses.

[0022] See also Figure 1 , an embodiment of the present invention provides a flexible micro-needle tip array electrode based on a composite multilayer metal, comprising: a flexible substrate 6 and a silicon micro-needle tip array structure provided on the flexible substrate 6; Among them, each silicon microneedle tip 1 in the silicon microneedle tip array structure is provided with a composite multilayer metal that can conduct electricity and transmit signals, and the composite multilayer metal is composed of a seed layer 2, a structural layer 3, an adhesion layer 4 and a contact layer 5 from the inside to the outside; the material of the seed layer 2 is Cr, Ti, Ni, Mo, Ta, W, Fe, Cu, Au, Ag or Pt, the material of the structural layer 3 is Cu, Ag or Au, the material of the adhesion layer 4 is Cr, Ni, Ti, Mo, Ta or W, and the material of the contact layer 5 is Au, Ag or AgCl.

[0023] To address the technical challenge of the prior art's conflict between the thickness and cost of the conductive layer in microtip arrays, the present invention utilizes a silicon microtip array structure with a composite multilayer metal structure. This design approach reduces the resistance of the conductive layer by increasing its thickness, thereby lowering the contact impedance of the flexible microtip array electrode. Furthermore, by using low-cost metal materials, the overall manufacturing cost of the electrode is reduced. The composite multilayer metal structure of the present invention comprises, from the inside out, a seed layer 2, a structural layer 3, an adhesion layer 4, and a contact layer 5. Each metal layer has its own function. The seed layer 2 exhibits excellent adhesion and conductivity, allowing it to adhere well to the silicon microtip surface and also serves as a conductive layer during the deposition of the structural layer 3. The structural layer 3 is grown using electrochemical plating, primarily increasing the thickness of the overall conductive layer and reducing the electrode resistance. Metals with varying cost, stability, and conductivity can be selected based on specific application requirements. The adhesion layer 4 exhibits excellent adhesion and conductivity, ensuring strong adhesion of the contact layer 5 to the surface of the structural layer 3. The contact layer 5, which comes into direct contact with the human body during use, exhibits excellent conductivity and biocompatibility, ensuring safe contact with the human body and low impedance.

[0024] In the specific exemplary technical scheme of the embodiment of the present invention, the seed layer is grown on the surface of each silicon microtip in the silicon microtip array structure, the structural layer is grown on the surface of the seed layer by electrochemical plating, the adhesion layer is grown on the surface of the structural layer by vapor deposition, and the contact layer is grown on the surface of the adhesion layer by vapor deposition; wherein the seed layer, the structural layer, the adhesion layer, and the contact layer together constitute a composite multilayer metal.

[0025] As a preferred technical solution of an embodiment of the present invention, the silicon microtip array structure is specifically an octagonal pyramid silicon microtip array structure; wherein each silicon microtip is specifically an octagonal pyramid silicon microtip, the tip height is 50 μm to 500 μm, and the tip spacing is 150 μm to 1000 μm; in a further preferred technical solution, the thickness of the seed layer is 10 nm to 300 nm, the thickness of the structural layer is 1 μm to 50 μm, the thickness of the adhesion layer is 10 nm to 50 nm, and the thickness of the contact layer is 50 nm to 400 nm. In addition, the material of the flexible substrate is parylene, polyimide, or polydimethylsiloxane.

[0026] As a preferred embodiment of the present invention, the flexible microtip array electrode is provided with one or more independent channels, and one or more silicon microtips connected together serve as an independent channel. Explanatoryally, in the technical solution of the embodiment of the present invention, at least one silicon microtip is used as an independent channel, and multiple or all silicon microtips can be connected together to serve as an independent channel. In addition, multiple independent channels can enable the electrode to have the ability to detect different types of signals simultaneously, thereby achieving the effect of simultaneously collecting multiple targeted signals.

[0027] In summary, compared with the existing technical solutions, the technical solutions provided by the embodiments of the present invention have the following advantages: (1) Excellent electrical conductivity and biocompatibility; Explanatoryally, the seed layer, structural layer, adhesion layer and contact layer of the embodiments of the present invention are made of specific metal materials, such as Cr, Ti, etc. for the seed layer, Cu for the structural layer, Cr, etc. for the adhesion layer, and Au, Ag, etc. for the contact layer. These materials have good electrical conductivity, stability and biocompatibility, and can effectively ensure the performance and service life of the electrode.

[0028] (2) Precise needle tip structure and higher needle tip density; Explanation: The needle tip height, spacing and angle of the octagonal pyramid silicon micro needle tip array structure can be achieved by precisely controlling the preparation process parameters, ensuring the efficient collection of bioelectric signals by the electrode. For example, the needle tip height is 50 μm ~ 500 μm, and the needle tip spacing is 150 μm ~ 1000 μm, which can be optimized and adjusted according to different application scenarios and needs; in the minimum 5×5 mm 2 Up to 144 needle tips can be integrated within an area, which can collect bioelectric signals more comprehensively and accurately, greatly improving the efficiency and accuracy of signal acquisition compared to traditional electrodes.

[0029] (3) More and more flexible channels; Explanation: Each needle tip can become an independent channel, or multiple needle tips can be customized to become one channel. Compared with traditional single-channel electrodes and two-channel interdigitated electrodes, the multi-channel high-density flexible micro-needle tip array electrode based on composite multi-layer metal disclosed in the embodiment of the present invention is at a minimum of 5×5 mm. 2 Up to 144 independent channels can be integrated in a small area, allowing for simultaneous measurement of multiple parameters.

[0030] (4) Good flexibility; explanatory note: using polyparaxylene, polyimide or polydimethylsiloxane as a flexible substrate enables the electrode to better fit the skin surface, reducing signal interference caused by poor contact between the electrode and the skin, improving the stability of signal acquisition, and also increasing the comfort of the user.

[0031] (5) Broad application prospects: Explanation-wise, the electrodes of the embodiments of the present invention can be used to collect various bioelectric signals such as EEG, ECG, and EMG, and have broad application prospects in the fields of medical diagnosis, biomedical research, neuroscience, etc., and can provide strong technical support for the development of related fields.

[0032] To sum up, the embodiment of the present invention specifically provides a multi-channel high-density flexible micro-needle tip array electrode based on composite multi-layer metal, which has high integration, good flexibility and precise signal acquisition performance, and can effectively solve the problems of existing bioelectric signal acquisition electrodes in terms of channel number, flexibility and signal acquisition accuracy.

[0033] See also Figures 2 to 6 The present invention provides a method for preparing a multi-channel high-density flexible micro-needle tip array electrode based on composite multi-layer metal, which specifically includes the following steps: Step 1: On a silicon wafer with a (001) crystal orientation and a thickness of 100 μm to 500 μm, silicon nitride is grown on one side using a vapor deposition method, and the other side is bonded to BF33 glass; Step 2: performing photolithography and dry etching on the silicon nitride surface to form a patterned silicon nitride mask layer in a square array; Step 3: Wet etching is performed using potassium hydroxide having a concentration (e.g., mass percentage concentration) of 20% to 40% to obtain a silicon microneedle tip array having a height of 50 to 500 μm. Specifically, the silicon microneedle tip may be an octagonal pyramid tip structure. Step 4: Setting a metal electrode pattern on the surface of the silicon microtip array by photolithography, growing a seed layer of metal on the surface of the silicon microtip using a vapor deposition method, and then stripping the metal and photoresist in other areas; Step 5: growing a metal with good conductivity as a structural layer on the surface of the seed layer by electrochemical plating; Step 6: Using a lift-off process, an adhesion layer and a contact layer metal are grown on the metal surface of the structural layer in the metal electrode area. Step 7: Using hydrofluoric acid or buffered oxide etchant (BOE) solution, the BF33 is laterally etched to form grooves at the bottom of the octagonal pyramid silicon micro-needle tip array structure and the composite multilayer metal; Step 8, using vapor deposition or spin coating to deposit a flexible substrate to wrap the needle tip and fill the groove; Step 9: If the vapor deposition method is used in step 8, the sample is subjected to photolithography to expose the flexible substrate material at the needle tip, and the remaining area is covered with photoresist; the flexible substrate material in the needle tip area is removed by oxygen plasma etching; and the photoresist is removed; Step 10: Use hydrofluoric acid or BOE solution to remove the BF33 glass at the bottom to release the high-density multi-channel flexible micro-tip array electrode. Figure 4 、 Figure 5 、 Figure 6 shown.

[0034] In the product prepared by the embodiment of the present invention, the seed layer, the structural layer, the adhesion layer, and the contact layer together constitute a composite multilayer metal, which can conduct electricity and transmit signals. The bottom of the octagonal pyramid silicon microneedle tip array structure covered with the composite multilayer metal is wrapped by a flexible substrate. Through a series of precise preparation steps, such as photolithography, etching, evaporation, peeling and other processes, the embodiment of the present invention can accurately control the structure and performance of the electrode, ensure the consistency and reliability of each electrode, and facilitate large-scale production and application. Specifically, for example, the high-density multi-channel flexible microneedle tip array electrode proposed in the embodiment of the present invention can be in a minimum of 5×5 mm 2 The device integrates up to 144 independent channels in a tiny area, greatly improving the density and comprehensiveness of signal acquisition; its high-precision design can obtain high-quality EEG signals, laying the foundation for accurate diagnosis of brain diseases and more complex and efficient brain-computer interaction; in addition, its good flexibility enables the electrodes to fit tightly to the scalp, effectively reducing signal interference and ensuring stable acquisition of EEG signals. In summary, the technical solutions of the embodiments of the present invention have important practical significance for promoting the development of non-invasive brain-computer interface technology and expanding its application in more fields.

[0035] The embodiment of the present invention is based on an optimized manufacturing process, and its main feature is that it first performs anodic bonding, and then prepares an octagonal pyramid silicon needle tip array through a single photolithography and wet etching method. This greatly reduces the process flow of flexible micro needle tip array manufacturing, reduces manufacturing cost and difficulty, and the manufactured integrated micro needle tip has higher reliability. Specifically, the present invention maintains a low-cost advantage while reducing contact impedance by constructing a conductive layer composed of a composite multilayer metal as the surface of the micro needle tip electrode; at the same time, the optimized solution of preparing an octagonal pyramid silicon needle tip array based on a single photolithography and wet etching method greatly shortens the preparation process, the needle tip electrode structure is simple, and the manufacturing difficulty and cost are reduced. The electrode prepared by the present invention has an extremely high degree of integration and can be manufactured in a minimum of 5×5 mm 2 The device integrates up to 144 independent channels in a tiny area, greatly improving the density and comprehensiveness of signal acquisition. Its high-precision design can obtain high-quality EEG signals, laying the foundation for accurate diagnosis of brain diseases and more complex and efficient brain-computer interaction. In addition, the good flexibility allows the electrodes to fit closely to the scalp, effectively reducing signal interference and ensuring stable acquisition of EEG signals. Therefore, the present invention has important practical significance for promoting the development of non-invasive brain-computer interface technology and expanding its application in more fields.

[0036] As a preferred embodiment of the present invention, in steps 1, 4, 6, and 8, the vapor deposition methods used to grow the thin film include chemical vapor deposition (CVD) and physical vapor deposition (PVD) methods, wherein the CVD method includes but is not limited to low-pressure chemical vapor deposition, plasma-enhanced chemical vapor deposition, organometallic compound chemical vapor deposition, and atomic layer deposition, and the PVD method includes but is not limited to vacuum evaporation coating, sputtering coating, and pulsed laser deposition.

[0037] As a preferred embodiment of the present invention, in step 1, the thickness of the silicon wafer determines the upper limit of the needle tip height; specifically, illustratively, the types of thin films grown include but are not limited to: pure silicon nitride, silicon oxide and silicon nitride or pure silicon oxide, and the thickness of the grown film ranges from 10 nm to 300 nm.

[0038] As a preferred embodiment of the present invention, in step 2, the side length of the square silicon nitride mask layer determines the height of the needle tip, the center distance of the square determines the center distance of the needle tip, and the number of squares determines the number of needle tips. While ensuring that the needle tip height is ≥ 200 μm, the minimum height can be 5×5 mm. 2 Up to 144 needle tips can be integrated into the area; the corresponding microneedle tip density can reach up to 576 microneedles / cm 2The increase in electrode area and the decrease in needle tip height can further increase the number of needle tips. Specifically, in step 2, the dry etching method includes but is not limited to: reactive ion etching, inductively coupled plasma etching, ion beam etching, and plasma etching.

[0039] As a preferred embodiment of the present invention, in step 3, the concentration of potassium hydroxide determines the angle between the side and bottom of the pyramid-shaped needle tip (i.e., the sharpness of the needle tip). A potassium hydroxide concentration lower than 20% or higher than 40% will cause the angle between the side and bottom of the octagonal pyramid needle tip to become smaller, that is, the needle tip becomes blunt. During wet etching, the potassium hydroxide solution needs to be magnetically stirred at a stirring speed of 200 to 5000 r / min. The temperature for wet etching is 60 to 95 ° C, and the temperature determines the silicon etching rate. Specifically, illustratively, the needle tip height of the octagonal pyramid silicon micro needle tip array structure is 50 μm to 500 μm, and the needle tip spacing is 150 μm to 1000 μm.

[0040] As a preferred embodiment of the present invention, in step 4, the pre-set photolithographic pattern determines the number of channels of the final electrode, and at least one needle tip is used as an independent channel, or all needle tips can be connected together as a channel. The material of the seed layer is Cr, Ti, Ni, Mo, Ta, W, Fe, Cu, Au, Ag or Pt, and the thickness of the seed layer is 10 ~ 300 nm. In addition, in step 4, at least one needle tip is used as an independent channel, or all needle tips can be connected together as a channel or individual needle tips can be customized as independent channels. Multiple independent channels can allow the needle tip to have the ability to detect different types of signals at the same time, thereby achieving the effect of collecting multiple signals at the same time. Specifically, for example, Figure 3 shown.

[0041] In a preferred embodiment of the present invention, in step 5, when the structural layer is grown using electrochemical plating, the plating solution temperature is controlled between 20°C and 40°C, the current density is controlled between 0.5 and 10 amperes per square decimeter, and the thickness of the final grown structural layer is 1 to 50 μm. Electroplating materials include, but are not limited to, Cu, Ag, and Au.

[0042] As a preferred embodiment of the present invention, in step 6, the material of the adhesion layer includes but is not limited to Cr, Ni, Ti, Mo, Ta, and W, and the thickness of the adhesion layer is 10 to 50 nm; the material of the contact layer is Au, Ag, and AgCl, and the thickness of the contact layer is 50 to 400 nm.

[0043] In a preferred embodiment of the present invention, in step 7, when hydrofluoric acid etching is used, the hydrofluoric acid concentration (mass fraction) is 40% to 60%, the etching temperature is 20°C to 40°C, and the final groove width is 50 to 200 μm. In step 8, the material of the flexible substrate includes, but is not limited to, parylene, polyimide, or polydimethylsiloxane.

[0044] The electrode tips prepared by the embodiment of the present invention have high consistency, low impedance, and high density, and can detect different types of signals at the same time. The embodiment of the present invention has successfully developed a high-density multi-channel flexible micro-needle tip array electrode and its preparation method. Through micro-nano processing technologies such as photolithography, dry etching, deposition, and peeling, the construction of each part of the electrode is accurately realized, including an octagonal pyramid silicon micro-needle tip array structure, a composite metal layer including a seed layer, a metal layer, an adhesion layer and a conductive layer, and a flexible substrate. The prepared electrode can be at a minimum of 5×5 mm while ensuring that the tip height is ≥200 μm. 2 Up to 144 independent channels are integrated within an area with high integration. The parameters such as the tip height and spacing of its octagonal pyramid silicon microtip array structure can be precisely controlled. Combined with the selection of specific materials, such as suitable metal materials for the seed layer, metal layer, adhesion layer and conductive layer, the electrodes can be used to collect bioelectric signals such as EEG, ECG, and EMG with high accuracy, and can test changes in bioelectric signals of varying degrees of subtlety. At the same time, the flexible substrate is made of polyparaxylene, polyimide or polydimethylsiloxane, which gives the electrodes good flexibility, allowing them to fit closely to the skin, reduce signal interference caused by poor contact, and improve the stability and accuracy of signal acquisition. With the above-mentioned excellent performance, the electrode has important value in fields such as non-invasive and non-invasive brain-computer interfaces. It can not only provide high-quality EEG signal support for the early and accurate diagnosis of brain diseases, but also facilitate more complex and efficient brain-computer interaction applications. It has broad application prospects in many fields such as medical diagnosis, biomedical research, and neuroscience, and will promote the development of related fields. Specific embodiment 1 An embodiment of the present invention provides a method for preparing a high-density multi-channel flexible micro-tip array electrode, comprising the following steps: Step 1: On a silicon wafer with a (001) crystal orientation, a resistance of 1 to 10 Ω·cm, and a thickness of 100 μm, 10 nm of silicon nitride and 10 nm of silicon oxide are grown on one side using plasma-enhanced chemical vapor deposition, and the other side is bonded to BF33 glass.

[0046] Step 2: Perform photolithography and reactive ion etching on the silicon nitride surface to remove a portion of the silicon nitride to form a square masking layer. The side length of the square masking layer is 200 μm, the center distance of the square is 240 μm, and the number of squares is 12×12.

[0047] In step 3, potassium hydroxide with a mass percentage concentration of 20% is used for wet etching. The potassium hydroxide solution needs to be magnetically stirred at a stirring speed of 200 r / min. The temperature for wet etching is 60°C to obtain an octagonal pyramid tip with a height of 100 μm.

[0048] In step 4, a photolithography process is performed, covering the areas where the seed layer is not needed with photoresist. Plasma-enhanced chemical vapor deposition is then used to grow a 10 nm layer of Ni metal on the surface of the structural layer as a seed layer. The unnecessary photoresist and the metal on the surface are then stripped away, and all the needle tips are connected to form a channel.

[0049] In step 5, Cu is grown on the surface of the seed layer using electrochemical plating as a structural layer. The plating solution temperature is controlled at 20°C, the current density is controlled at 0.5 amperes per square decimeter, and the thickness of the final grown structural layer is 1 μm.

[0050] Step 6: Use photolithography to cure the photoresist in areas where the adhesion layer and contact layer are not required, use vapor deposition to grow Cr as the adhesion layer and Ag as the contact layer on the surface of the structural layer with thicknesses of 10 nm and 50 nm respectively, and use a stripping process to remove excess photoresist and metal.

[0051] In step 7, the BF33 glass was laterally etched using a BOE solution to form grooves at the bottom of the octagonal pyramid silicon microtip array structure and the composite multilayer metal. The final groove width was 50 μm.

[0052] In step 8, polyimide is grown as a flexible substrate using a spin coating method to wrap the needle tip and fill the groove.

[0053] In step 9, 60% by mass hydrofluoric acid is used to remove the BF33 glass at the bottom, releasing the high-density multi-channel flexible microtip array electrode. Specific embodiment 2 An embodiment of the present invention provides a method for preparing a high-density multi-channel flexible micro-tip array electrode, comprising the following steps: Step 1: On a silicon wafer with a (001) crystal orientation, a resistance of 1 to 10 Ω·cm, and a thickness of 200 μm, 100 nm of silicon nitride is grown on one side using low-pressure chemical vapor deposition, and the other side is bonded to BF33 glass.

[0055] Step 2: Photolithography and inductively coupled plasma etching are performed on the silicon nitride surface to remove a portion of the silicon nitride to form a square masking layer. The side length of the square masking layer is 400 μm, the center distance of the square is 440 μm, and the number of squares is 12×12.

[0056] In step 3, wet etching is performed using potassium hydroxide having a concentration of 40%. The potassium hydroxide solution needs to be magnetically stirred at a stirring speed of 3000 r / min and the temperature for wet etching is 80°C. An octagonal pyramid tip with a height of 200 μm is obtained.

[0057] In step 4, photolithography is performed, covering areas where a seed layer is not needed with photoresist. A 30 nm thick Mo metal seed layer is grown on the surface of the structural layer using vacuum evaporation. The unneeded photoresist and metal are then stripped away, and each row of 12 needle tips is connected to form an independent channel.

[0058] In step 5, Cu is grown on the seed layer using electrochemical plating as a structural layer. The plating solution temperature is controlled at 25°C, and the current density is controlled at 1 ampere per square decimeter. The resulting structural layer has a thickness of 10 μm.

[0059] Step 6: Use photolithography to cure the photoresist in areas where the adhesion layer and contact layer are not required, use vapor deposition to grow Ti as the adhesion layer and Au as the contact layer on the surface of the structural layer, with thicknesses of 20 nm and 200 nm respectively, and use a stripping process to remove the cured photoresist and all metal on the photoresist.

[0060] In step 7, the BF33 was laterally etched using a BOE solution to form grooves on the bottom of the octagonal pyramid silicon microtip array structure and the composite multilayer metal. The final groove width was 100 μm.

[0061] In step 8, chemical vapor deposition is used to grow parylene as a flexible substrate to wrap the needle tip and fill the groove.

[0062] Step 9: Photolithography is performed on the sample to expose the needle tip and cover the rest of the area with photoresist. Inductively coupled plasma etching is used to perform oxygen plasma etching to remove the flexible substrate not protected by the photoresist and remove the photoresist.

[0063] In step 10, hydrofluoric acid with a mass fraction of 60% is used to remove the BF33 glass at the bottom, releasing the high-density multi-channel flexible micro-tip array electrode. Specific embodiment 3 An embodiment of the present invention provides a method for preparing a high-density multi-channel flexible micro-tip array electrode, comprising the following steps: In step 1, a 300 nm layer of silicon oxide was grown on one side of a 500 μm thick silicon wafer with a (001) crystal orientation and a resistance of 1 to 10 Ω·cm. The other side was bonded to BF33 glass.

[0065] Step 2: Photolithography and plasma etching are performed on the silicon nitride surface to remove a portion of the silicon nitride to form a square mask layer. The side length of the square mask layer is 1000 μm, the center distance of the square is 1040 μm, and the number of squares is 12×12.

[0066] In step 3, wet etching was performed using 40% potassium hydroxide. The potassium hydroxide solution was magnetically stirred at a speed of 5000 rpm. The wet etching temperature was 95°C. An octagonal pyramid tip with a height of 500 μm was obtained.

[0067] In step 4, a photolithography process is performed, covering the areas where a seed layer is not needed with photoresist. Atomic layer deposition is then used to grow a 300 nm thick layer of W metal on the surface of the structural layer as a seed layer. The unnecessary photoresist and the metal on the surface are then stripped away, leaving each needle tip as an independent channel.

[0068] In step 5, Ag is grown on the seed layer using electrochemical plating as a structural layer. The plating solution temperature is controlled at 30°C and the current density is controlled at 5 amperes per square decimeter. The resulting structural layer has a thickness of 50 μm.

[0069] Step 6: Use photolithography to cure the photoresist in areas where the adhesion layer and contact layer are not required. Use vapor deposition to grow Ta as the adhesion layer and AgCl as the contact layer on the surface of the structural layer with thicknesses of 50 nm and 400 nm, respectively. Use a stripping process to remove the cured photoresist and all metal on the photoresist.

[0070] In step 7, 40% hydrofluoric acid was used to laterally etch the BF33, forming grooves on the bottom of the octagonal pyramid silicon microtip array structure and the composite multilayer metal. The final groove width was 200 μm.

[0071] In step 8, chemical vapor deposition is used to grow polydimethylsiloxane as a flexible substrate to wrap the needle tip and fill the groove.

[0072] Step 9: Photolithography is performed on the sample to expose the needle tip and cover the rest of the area with photoresist. Oxygen plasma etching is used to remove the flexible substrate not protected by the photoresist and remove the photoresist.

[0073] In step 10, hydrofluoric acid with a mass fraction of 60% is used to remove the BF33 glass at the bottom, releasing the high-density multi-channel flexible micro-tip array electrode.

[0074] See also Figure 7 and Figure 8 , Figure 7The figure shows a comparison of the resistance of a four-layer composite metal layer and a two-layer composite metal layer (Comsol calculation). After adding the structural layer Cu and the seed layer Cr, the thickness of the composite metal layer increases by two orders of magnitude (composite metal layer type 1), thereby reducing the resistance of the four-layer composite metal electrode by about two orders of magnitude. Figure 8 The EEG obtained during the eyes-open / eye-closed process is of better quality due to the low impedance characteristics of the flexible micro-tip array electrode of the embodiment of the present invention, and its ability to pierce the high-impedance stratum corneum and directly contact the epidermis. Compared with commercial wet electrodes, the flexible micro-tip array electrode disclosed in the technical solution of the embodiment of the present invention has a stronger signal and a higher signal-to-noise ratio, and is more comfortable. In summary, the embodiment of the present invention discloses a multi-channel high-density flexible micro-tip array electrode based on composite multi-layer metal and its preparation method. The electrode comprises a flexible substrate, an octagonal pyramid silicon micro-tip array, and a composite multi-layer metal on the surface; wherein the composite multi-layer metal comprises a seed layer, a structural layer, an adhesion layer, and a contact layer. The electrode preparation method includes: first growing silicon nitride on one side of a silicon wafer with a specific crystal orientation, resistance value, and thickness, and bonding the other side to BF33 glass; forming a patterned silicon nitride mask layer on the silicon nitride surface by photolithography and dry etching, and then using wet etching of silicon to obtain an octagonal pyramid silicon microneedle tip array; sequentially preparing a seed layer, a structural layer, an adhesion layer, and a contact layer metal by a lift-off process; and completing the flexible preparation of the electrode by lateral etching of the BF33 glass, growing a flexible material layer, photolithography, oxygen plasma etching of the flexible material layer on the top of the needle tip, and removing the BF33 glass. The electrode of the present invention can be used in a minimum of 5×5 mm 2 The electrodes integrate up to 144 independent channels within a single area, enabling the collection of bioelectric signals such as EEG, ECG, and myoelectricity. Combining the excellent biocompatibility, electrical properties, and mechanical properties of various materials, the electrodes offer high integration, excellent flexibility, and sensitive signal acquisition performance, promising broad application prospects in related bioelectric signal collection fields.

[0075] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit it. Although the present invention has been described in detail with reference to the above embodiments, ordinary technicians in the field should understand that the specific implementation methods of the present invention can still be modified or replaced by equivalents. Any modification or equivalent replacement that does not depart from the spirit and scope of the present invention should be covered by the scope of protection of the claims of the present invention.

Claims

1. A flexible micro-needle tip array electrode based on composite multilayer metal, characterized in that: include: A flexible substrate (6) and a silicon micro-needle tip array structure arranged on the flexible substrate (6); Each silicon microtip (1) in the silicon microtip array structure is provided with a composite multilayer metal capable of conducting electricity and transmitting signals, wherein the composite multilayer metal comprises, from the inside to the outside, a seed layer (2), a structural layer (3), an adhesion layer (4) and a contact layer (5); the material of the seed layer (2) is Cr, Ti, Ni, Mo, Ta, W, Fe, Cu, Au, Ag or Pt, the material of the structural layer (3) is Cu, Ag or Au, the material of the adhesion layer (4) is Cr, Ni, Ti, Mo, Ta or W, and the material of the contact layer (5) is Au, Ag or AgCl.

2. The flexible micro-needle tip array electrode based on composite multi-layer metal according to claim 1, characterized in that: The seed layer (2) is grown on the surface of the silicon microneedle tip (1), the structural layer (3) is grown on the surface of the seed layer (2) by electrochemical plating, the adhesion layer (4) is grown on the surface of the structural layer (3) by vapor deposition, and the contact layer (5) is grown on the surface of the adhesion layer (4) by vapor deposition.

3. The flexible micro-tip array electrode based on composite multi-layer metal according to claim 1, characterized in that: In the silicon microtip array structure, each silicon microtip (1) is an octagonal pyramid silicon microtip, with a tip height of 50 μm to 500 μm and a tip spacing of 150 μm to 1000 μm.

4. The flexible micro-tip array electrode based on composite multi-layer metal according to claim 3, characterized in that: The thickness of the seed layer (2) is 10 nm to 300 nm, the thickness of the structural layer (3) is 1 μm to 50 μm, the thickness of the adhesion layer (4) is 10 nm to 50 nm, and the thickness of the contact layer (5) is 50 nm to 400 nm.

5. The flexible micro-needle tip array electrode based on composite multi-layer metal according to claim 1, characterized in that: The material of the flexible substrate (6) is polyparaxylene, polyimide or polydimethylsiloxane.

6. The flexible micro-tip array electrode based on composite multi-layer metal according to claim 1, characterized in that: The flexible micro-needle tip array electrode is provided with one or more independent channels, and one or more connected silicon micro-needle tips in the silicon micro-needle tip array structure serve as an independent channel.

7. A method for preparing a flexible micro-needle tip array electrode based on composite multilayer metal according to claim 1, characterized in that: The following steps are involved: Step 1: Based on a selected silicon wafer, a thin film is grown on one side of the silicon wafer using a vapor deposition method, and the other side of the silicon wafer is bonded to a selected bonding sacrificial layer; wherein the thin film is pure silicon nitride, pure silicon oxide, or a mixture of silicon oxide and silicon nitride; Step 2: Photolithography and dry etching are performed on the film surface to form a patterned mask layer with a square array; wet etching is performed based on the patterned mask layer to obtain an initial silicon microneedle tip array with a preset height; Step 3: On the surface of each silicon microtip of the initial silicon microtip array, a metal electrode pattern is formed by photolithography, a seed layer of metal is grown on the surface of each silicon microtip by vapor deposition, a metal with a predetermined good conductivity is grown on the surface of the seed layer by electrochemical plating as a structural layer, and an adhesion layer and a contact layer of metal are sequentially grown on the metal surface of the structural layer in the metal electrode area by a lift-off process to form a silicon microtip array structure; Step 4: Laterally etch the bonding sacrificial layer to form a groove at the bottom of the silicon microneedle tip array structure; deposit a flexible substrate using vapor deposition or spin coating to wrap the silicon microneedle tips and fill the groove; Step 5: remove the bonding sacrificial layer to prepare a flexible micro-needle tip array electrode based on composite multilayer metal.

8. The preparation method according to claim 7, wherein In step 1, the selected silicon wafer is a silicon wafer with a (001) crystal orientation and a thickness of 100 μm to 500 μm, and the thickness of the grown film ranges from 10 nm to 300 nm.

9. The preparation method according to claim 8, wherein In step 2, wet etching is performed based on the patterned mask layer to obtain an initial silicon microtip array of a predetermined height, wherein a potassium hydroxide solution with a mass percentage concentration of 20% to 40% is used for wet etching to obtain an initial silicon microtip array with a height of 50 μm to 500 μm; During wet etching, the potassium hydroxide solution needs to be magnetically stirred at a stirring speed of 200 r / min to 5000 r / min; the temperature for wet etching is 60 ℃ to 95 ℃; in the initial silicon microtip array, each silicon microtip is an octagonal pyramid silicon microtip (1).

10. The preparation method according to claim 9, wherein In step 3, the thickness of the seed layer is 10 nm to 300 nm, the thickness of the structural layer is 1 μm to 50 μm, the thickness of the adhesion layer is 10 nm to 50 nm, and the thickness of the contact layer is 50 nm to 400 nm.

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