A high-robustness photoresist for physiological electrodes, a manufacturing method and an in-situ manufacturing method for physiological electrodes

Abstract

The application provides a high-robustness photoresist for physiological electrodes, a manufacturing method and an in-situ manufacturing method of physiological electrodes, and can prepare two layers of photoresists with an undercut structure by stacking two layers of photoresists on each other, wherein the two layers of photoresists only differ in the concentration of photosensitizers, the concentration difference is adjusted according to the required undercut profile, and the mass percentage components include 3-10% film-forming resin, 90-97% deionized water, 0.1-1% diazo photosensitizer and 0.1-1% surfactant. The surface of a flexible substrate is cleaned by using an ion beam etching technology; a photoresist with low photosensitizer content is spin-coated to obtain a defect-free low-interface-adhesion transferable photoresist film; the photoresist with high photosensitizer content is transferred to the flexible substrate loaded with the photoresist with low photosensitizer content; the flexible substrate loaded with the two layers of photoresists is attached to a hard master mask plate, and is exposed, so that the pattern of the hard master mask plate is transferred to the photoresists, a two-layer stacked photoresist pattern with an undercut structure is formed, high-fidelity replication of the photoetching mask plate structure is realized, and subsequent peeling is facilitated.

Description

Technical Field

[0001] This invention relates to the field of micro-nano manufacturing, and more particularly to a photoresist for a highly robust physiological electrode, a manufacturing method thereof, and a method for in-situ manufacturing of the physiological electrode. Background Technology

[0002] Physiological electrodes, as core devices in the field of bioengineering, efficiently and stably convert weak electrical signals generated in the body into measurable physiological electrical signals. They can not only monitor vital signs, but also provide key support for cutting-edge research such as brain-computer interfaces, neuromodulation therapy, and soft robots. Their performance directly determines signal quality, system reliability, and patient experience, and is an important cornerstone for promoting the rapid development of precision medicine, remote health management, and bioelectronic medicine.

[0003] Currently, mainstream bioelectrodes can be divided into wet electrodes and dry electrodes. Wet electrodes (represented by Ag / AgCl gel electrodes) utilize a gel layer to create a low-impedance conductive channel between the electrode and the skin, exhibiting an extremely high signal-to-noise ratio, capable of meeting the precise acquisition requirements for short-term monitoring of electromyography, electrocardiography, and electroencephalography. However, their gel components (usually water or solvents) are prone to evaporation over time, leading to increased interfacial impedance and signal quality degradation. Furthermore, long-term contact can cause skin irritation or allergic reactions, making them unsuitable for dynamic or continuous monitoring. Dry electrodes, on the other hand, consist of a metal conductive layer and a flexible polymer substrate, offering better biocompatibility and wearability. They represent a key focus for the development of next-generation physiological signal acquisition systems. However, to operate stably in complex application environments, they must simultaneously meet high robustness requirements such as low contact impedance, resistance to motion artifacts, and mechanical and chemical durability. Insufficient interfacial adhesion between the conductive layer and the soft polymer material has become a key bottleneck for performance improvement.

[0004] The traditional electrode manufacturing method of "preparing a metal layer first and then transferring it to a flexible polymer substrate" is non-in-situ integration, which has the following challenges: (1) the adhesion problem of the conductive layer-substrate interface in electrode manufacturing: due to the difference in thermal expansion coefficient and poor interface compatibility between the metal and the polymer substrate, insufficient adhesion is easily caused; (2) the robustness and reliability problems of the electrode during use: after multiple deformations of the electrode, the interface will experience fatigue accumulation, resulting in a decrease in conductivity or even complete failure; in addition, long-term environmental factors (such as humidity and temperature fluctuations) will further aggravate interface degradation, thereby affecting the life and reliability of the device. Summary of the Invention

[0005] Based on this, the present invention provides a photoresist for a highly robust physiological electrode, a manufacturing method thereof, and an in-situ manufacturing method for the physiological electrode, to enhance the adhesion between the subsequent metal and polymer thin film substrates, improve the interfacial bonding strength and device reliability, and ensure stable signal acquisition under complex deformation and sweat erosion.

[0006] To achieve the above objectives, in a first aspect, the present invention provides a photoresist for a highly robust physiological electrode, which can be stacked in two layers and has an undercut structure. The upper and lower layers of the photoresist are prepared with the only difference in photosensitizer concentration. The concentration difference is adjusted according to the required undercut profile. Its mass percentage components include: 3-10% film-forming resin, 90-97% deionized water, 0.1-1% diazo photosensitizer, and 0.1-1% surfactant.

[0007] Optionally, the film-forming resin is at least one of polyvinyl alcohol 1788 and polyvinyl alcohol 1799.

[0008] Optionally, the surfactant is at least one of Pronic F68 and Pronic F127.

[0009] Secondly, the present invention provides a method for producing a photoresist for highly robust physiological electrodes, the production steps of which include: S110. According to the predetermined ratio, accurately weigh the film-forming resin and deionized water into a beaker, and stir at 98°C for 20-40 min to form a film-forming resin mixture. S120. Weigh the film-forming resin mixture and diazo photosensitizer into a beaker according to the ratio, and stir at 40℃ for 15-25 min to obtain the photoresist mixture system; S130. Weigh the photoresist mixture and surfactant according to the ratio, stir at 40℃ for 15-25 min to obtain a uniform near-zero adhesion photoresist resin. S140. Use a paper funnel to filter out air bubbles from the obtained photoresist and place it in a dark and room temperature environment for 24 hours before use.

[0010] Thirdly, the present invention provides an in-situ manufacturing method for a highly robust physiological electrode, characterized by comprising the following steps: S210. Pretreatment of flexible electrode substrate: The surface of the flexible polymer substrate is cleaned using ion beam etching technology; S220. Silicon substrate cleaning: Ultrasonically clean the silicon substrate with deionized water and dry it with nitrogen gas to keep the surface of the silicon substrate dry and clean. S230. Coating: A low-photosensitizer content photoresist is spin-coated using a static spin-coating method to obtain a uniformly distributed, defect-free, low-interfacial-adhesion transferable photoresist film on a silicon substrate; S240. Pre-baking: After the adhesive is applied, place it on a hot plate at 80°C to remove the solvent from the adhesive layer; S250. Transfer 1: Slowly and bubble-free conformally bond the flexible stamp to the photoresist surface and peel it off from the silicon substrate to transfer the photoresist onto the flexible stamp; S260. Transfer 2: Slowly and without bubbles, conformally bond the flexible stamp carrying photoresist to the surface of the flexible substrate, place it on a hot plate and heat it at 80°C. The flexible stamp loses its stickiness, and the photoresist is transferred to the flexible substrate. S270. Transfer 3: Repeat S220-S260 to transfer the high photosensitizer content photoresist onto a flexible substrate loaded with low photosensitizer content photoresist; S280. Exposure: The flexible substrate loaded with double-layer photoresist is bonded to the rigid master mask, and exposed for 2-15 seconds using an ultraviolet lithography machine to transfer the pattern of the rigid master mask onto the photoresist, forming a double-layer stacked photoresist pattern with an undercut structure. S290. Development: Immersion development is used to develop the exposed photoresist in the developing solution for 3-20 seconds, and the pattern of the hard master mask is copied onto the photoresist. S2100. Metal deposition: Depositing metal via ion beam sputtering; S2110. Dry stripping: The metal and photoresist outside the structure are slowly peeled off with tape to obtain a highly robust flexible physiological electrode.

[0011] Furthermore, the substrate in S210 includes at least one of a polydimethylsiloxane film and a polyimide film.

[0012] Furthermore, the substrate in S220 includes at least one of a silicon wafer and a silicon dioxide wafer.

[0013] Furthermore, the flexible stamp in S250, S260 or S270 includes at least one of a polydimethylsiloxane film and a heat-releasing material.

[0014] Furthermore, the metal coating method described in S2100 is ion beam sputtering, the sputtered metal is gold, and the thickness is 50-200 nm.

[0015] Furthermore, the dry adhesive stripping tape in S2110 includes at least one of heat-release tape, polyimide tape, and UV-release tape.

[0016] The technical advantages of the photoresist for highly robust physiological electrodes, the manufacturing method, and the in-situ manufacturing method of physiological electrodes provided by this invention are at least reflected in the following aspects: Firstly, ion beam etching technology is used to clean the surface of the flexible polymer substrate. This process can effectively remove surface contaminants while avoiding swelling or damage caused by solvent cleaning, achieving a non-contact, anisotropic cleaning effect to enhance the adhesion between the subsequent metal and polymer film substrates.

[0017] Secondly, by using ultraviolet contact lithography, a transferable photoresist with near-zero adhesion is used as an intermediate medium film. By controlling the content of photosensitizer, a double-layer stacked photoresist pattern with an undercut structure is constructed, achieving high-fidelity replication of the photomask structure. This process has extremely high pattern resolution and can realize the fabrication of high-density patterns at the micro-nano scale, meeting the manufacturing requirements of highly integrated devices.

[0018] Thirdly, ion beam sputtering technology is used to directly deposit metal and pattern it through a stripping process. High-energy metal atoms are then injected into the polymer surface to form a metal-polymer substrate gradient mechanical interlocking structure, which improves the interfacial bonding strength and device reliability. Attached Figure Description

[0019] To more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings used in the following description of the embodiments will be briefly introduced. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0020] Figure 1 This is a flowchart of the in-situ manufacturing process of the highly robust physiological electrode in Example 1.

[0021] Figure 2 This is a schematic diagram, simulation, and cross-sectional characterization of the substrate for the implantation of metal atoms into the physiological electrode in Example 1.

[0022] Figure 3 This is a test diagram of the bonding strength of the metal thin film in Example 1.

[0023] Figure 4 The curves showing the changes in the electrical performance of the physiological electrodes in Example 2 under extreme conditions are shown.

[0024] Figure 5 The graphs show the changes in the electrical performance of the physiological electrodes in Examples 1 and 2 under extreme test conditions.

[0025] Figure 6 This is a comparison chart of the electrophysiological signal monitoring test results of the physiological electrode and the commercial electrode under deformation in Example 1.

[0026] Figure 7 This is a comparison chart of the electrophysiological signal monitoring test results of the physiological electrode and the commercial electrode used in Example 1 after different exercise times. Detailed Implementation

[0027] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. The following description of at least one exemplary embodiment is merely illustrative and is in no way intended to limit the present invention or its application or use. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0028] This invention provides a highly robust photoresist for physiological electrodes, a manufacturing method, and an in-situ manufacturing method for physiological electrodes. The photoresist with a double-layer stacked undercut structure is prepared with the only difference between the upper and lower layers in the photosensitizer concentration. The concentration difference is adjusted according to the required undercut profile. Its mass percentage components include: 3-10% film-forming resin, 90-97% deionized water, 0.1-1% diazo photosensitizer, and 0.1-1% surfactant. In in-situ manufacturing, ion beam etching is first used to clean the surface of the flexible substrate, avoiding swelling or damage problems caused by solvent cleaning and achieving a non-contact, anisotropic cleaning effect. Then, a low-photosensitizer content photoresist is spin-coated to obtain a defect-free, low-interfacial-adhesion, transferable photoresist film. A high-photosensitizer content photoresist is then transferred to the flexible substrate loaded with the low-photosensitizer content photoresist. The flexible substrate loaded with the double-layer photoresist is then bonded to a rigid master mask and exposed. The pattern of the rigid master mask is transferred to the photoresist, forming a double-layer stacked photoresist pattern with an undercut structure. This achieves high-fidelity replication of the photomask structure and facilitates subsequent stripping. Further, ion beam sputtering is used to directly deposit metal and pattern it through a stripping process. High-energy metal atoms are injected into the polymer surface to form a metal-polymer substrate mechanical interlocking structure, improving interfacial bonding strength and device reliability. The fabricated physiological electrodes exhibit improved interfacial bonding strength and device reliability, ensuring stable signal acquisition even under complex deformation and sweat corrosion. Example

[0029] The photoresist with a double-layer stackable undercut structure provided in this embodiment differs from the upper and lower photoresist layers only in the concentration of the photosensitizer. The specific concentration difference needs to be adjusted according to the required undercut profile. The photoresist comprises the following components by mass percentage: Film-forming resin 4.96% Deionized water 94.24% Diazo photosensitizer 0.3% Surfactant 0.5% The film-forming resin is polyvinyl alcohol 1788.

[0030] The surfactant is Pronic F68.

[0031] During the manufacturing process, a certain mass of film-forming resin and deionized water were weighed into a beaker and stirred at 98°C for 20 min to form a film-forming resin mixture. A certain mass of the film-forming resin mixture and diazo photosensitizer were weighed into a beaker and stirred at 40°C for 20 min to form a photoresist mixture. A certain mass of the photoresist mixture and surfactant were weighed into a beaker and stirred at 40°C for 20 min to form a uniform near-zero adhesion photoresist. The near-zero adhesion photoresist was filtered to remove air bubbles using a paper funnel and allowed to stand in a dark, room-temperature environment for 24 h before use.

[0032] like Figure 1 As shown, this embodiment provides in-situ fabrication of a highly robust physiological electrode, including the following steps: Step 1. Pretreatment of flexible electrode substrate: The surface of the polydimethylsiloxane substrate is cleaned using ion beam etching technology; Step 2. Silicon substrate cleaning: The silicon substrate is ultrasonically cleaned with deionized water and dried with nitrogen gas to keep the surface of the silicon substrate dry and clean; wherein, the substrate is a silicon wafer; Step 3. Coating: A low-photosensitizer content photoresist is spin-coated using a static spin-coating method to obtain a uniformly distributed, defect-free, low-interface-adhesion transferable photoresist film on the silicon substrate; Step 4. Pre-baking: After the adhesive is applied, place it on a hot plate at 80°C to remove the solvent from the adhesive layer; Step 5. Transfer: Slowly and conformally bond the flexible stamp to the surface of the low photosensitizer content photoresist without bubbles, and peel it off from the silicon substrate and transfer it onto the flexible stamp; Step 6. Transfer: Slowly and conformally bond the flexible stamp carrying low photosensitizer content photoresist to the surface of the flexible substrate without air bubbles, and place it on a hot plate at 80°C. The flexible stamp loses its stickiness, and the photoresist is transferred to the flexible substrate. Step 7. Transfer: Repeat steps 2-6 to transfer the high photosensitizer content photoresist onto the flexible substrate loaded with low photosensitizer content photoresist; the flexible stamp in steps 5, 6, and 7 is a polydimethylsiloxane film; Step 8. Exposure: The flexible substrate loaded with double-layer photoresist is bonded to a rigid master mask, and exposed for 4 seconds using an ultraviolet lithography machine to transfer the pattern of the rigid master mask onto the photoresist, forming a double-layer stacked photoresist pattern with an undercut structure; the exposure method described in step 8 is contact lithography; Step 9. Development: Immersion development is used. The exposed photoresist is developed in the developer for 10 seconds to copy the pattern of the hard master mask onto the photoresist. The developer is deionized water. Step 10. Metal deposition: Deposit metal by ion beam sputtering; the metal deposition method described in Step 10 is ion beam sputtering, the sputtered metal is gold, and the thickness is 50 nm; Step 11. Dry stripping: Use adhesive tape to slowly peel off the metal and photoresist outside the structure to obtain a highly robust flexible physiological electrode. The adhesive tape used for dry stripping is a polyimide tape.

[0033] Figure 1 This is a flowchart of the in-situ fabrication process of the highly robust physiological electrode in Example 1 (simplifying the double-layer photoresist transfer process into one step).

[0034] Figure 2 This is a schematic diagram, simulation, and cross-sectional characterization of the substrate for the implantation of metal atoms into the physiological electrode in Example 1; from Figure 2 It can be seen that metal deposition via ion beam sputtering can form a mechanically interlocked structure for gold atom implantation into a flexible substrate. With gold as the metal target and a polydimethylsiloxane film as the sputtering substrate, simulation results show that gold atoms are implanted into the polydimethylsiloxane substrate via ion beam sputtering, with an average implantation depth of approximately 1.5 nm. The cross-sectional characterization diagram of the gold-polydimethylsiloxane film shows that the sample surface is gold. As etching time increases, the gold signal gradually attenuates and overlaps with the silicon signal, indicating that gold has been partially implanted into the silicon-containing polymer substrate, forming a mixed interface structure.

[0035] Figure 3 Here is a test diagram of the metal thin film bonding strength in Example 1: Figure 3 To test the bonding strength between metal films and polymer substrates using the tape method, the tape peeling of gold films prepared by vacuum thermal evaporation (with and without a seed layer) and ion beam sputtering (with and without a seed layer) was compared. It can be seen that the gold films prepared by ion beam sputtering have high interfacial bonding strength.

[0036] Figure 5 The graphs show the changes in the electrical properties of the metal thin films in Examples 1 and 3 under extreme test conditions. Figure 5 This demonstrates that the resistance of a low-modulus gold-polydimethylsiloxane film remains consistent with its initial resistance after being stretched to 245% and returning to its original shape. Figure 5 It was demonstrated that after continuous high stretching (200%) cycles, the resistance of the gold-polydimethylsiloxane film after each recovery was not much different from the initial resistance; Figure 5 This demonstrates that the electrical properties of a high-modulus gold-polyimide film remain stable after undergoing up to 100,000 bending cycles.

[0037] Figure 6 This is a comparison chart of the electrophysiological signal monitoring test results of the physiological electrode and the commercial electrode under deformation in Example 1; Figure 7This is a comparison chart of the electrophysiological signal monitoring test results of the physiological electrode and the commercial electrode used in Example 1 after different exercise times. Figure 6 and Figure 7 The use of in-situ manufactured high-robust physiological electrodes for electrophysiological signal monitoring demonstrates the effectiveness of in-situ manufacturing of these high-robust physiological electrodes. These electrodes exhibit high reliability even under deformation and motion monitoring, maintaining stable signal output comparable to or even surpassing commercial electrodes. Example

[0038] The photoresist with a double-layer stackable undercut structure provided in this embodiment differs from the upper and lower photoresist layers only in the concentration of the photosensitizer. The specific concentration difference needs to be adjusted according to the required undercut profile. The photoresist comprises the following components by mass percentage: Film-forming resin 4.96% Deionized water 94.24% Diazo photosensitizer 0.3% Surfactant 0.5% The film-forming resin is polyvinyl alcohol 1788.

[0039] The surfactant is Pronic F127.

[0040] The photoresist manufacturing method provided in this embodiment involves weighing a certain mass of film-forming resin and deionized water into a beaker, stirring at 98°C for 20 min to form a film-forming resin mixture; weighing a certain mass of the film-forming resin mixture and diazo photosensitizer into a beaker, stirring at 40°C for 20 min to form a photoresist mixture; weighing a certain mass of the photoresist mixture and surfactant into a beaker, stirring at 40°C for 20 min to form a uniform near-zero adhesion photoresist; filtering the near-zero adhesion photoresist to remove air bubbles using a paper funnel, and allowing it to stand in a dark, room-temperature environment for 24 h before use.

[0041] The in-situ fabrication of the highly robust physiological electrode provided in this embodiment includes the following steps: Step 1: Pretreatment of flexible electrode substrate: The surface of the polydimethylsiloxane substrate is cleaned using ion beam etching technology.

[0042] Step 2: Silicon substrate cleaning: The silicon substrate is ultrasonically cleaned with deionized water and dried with nitrogen gas to keep the surface of the silicon substrate dry and clean. The substrate in Step 2 is a silicon wafer. Step 3: Coating: A low-photosensitizer content photoresist is spin-coated using a static spin-coating method to obtain a uniformly distributed, defect-free, low-interfacial-adhesion transferable photoresist film on the silicon substrate; Step 4: Pre-baking: After the adhesive is applied, place it on a hot plate at 80 ℃ to heat and remove the solvent in the adhesive layer; Step 5: Transfer: Slowly and without bubbles, conformally bond the flexible stamp to the surface of the low photosensitizer content photoresist and peel it off from the silicon substrate, transferring it onto the flexible stamp; Step 6: Transfer: Slowly and conformally bond the flexible stamp carrying low photosensitizer content photoresist to the surface of the flexible substrate without air bubbles, and place it on a hot plate at 80°C. The flexible stamp loses its stickiness and the photoresist is transferred to the flexible substrate. Step 7: Transfer: Repeat steps 2-6 to transfer the high photosensitizer content photoresist onto the flexible substrate loaded with low photosensitizer content photoresist; the flexible stamp in steps 5, 6, and 7 is a polydimethylsiloxane film; Step 8: Exposure: The flexible substrate loaded with double-layer photoresist is bonded to the rigid master mask, and exposed for 4 seconds using an ultraviolet lithography machine to transfer the pattern of the rigid master mask onto the photoresist, forming a double-layer stacked photoresist pattern with an undercut structure; the exposure method described in Step 8 is contact lithography. Step 9: Development: Immersion development is used. The exposed photoresist is developed in the developer for 10 seconds to copy the pattern of the hard master mask onto the photoresist. The developer in Step 9 is deionized water. Step 10: Metal deposition: Deposit metal by ion beam sputtering; the metal deposition method described in Step 10 is ion beam sputtering, the sputtered metal is gold, and the thickness is 50 nm; Step 11: Dry stripping: Use adhesive tape to slowly peel off the metal and photoresist outside the structure to obtain a highly robust flexible physiological electrode. The adhesive tape used for dry stripping is a polyimide tape.

[0043] Based on this embodiment, ion beam etching technology is used to clean the surface of the flexible polymer substrate. This process can effectively remove surface contaminants (such as organic residues, oxides, and adsorbed water films) while avoiding the swelling or damage problems caused by solvent cleaning. It achieves a non-contact, anisotropic cleaning effect, significantly improving the adhesion between the subsequently deposited metal and the polymer substrate. Based on ultraviolet contact lithography and near-zero adhesion transferable photoresist, by controlling the photosensitizer content, a double-layer stacked pattern with an undercut structure is formed, thereby achieving high-precision, high-density pattern fabrication. Example

[0044] The photoresist with a double-layer stackable undercut structure provided in this embodiment differs from the upper and lower photoresist layers only in the concentration of the photosensitizer. The specific concentration difference needs to be adjusted according to the required undercut profile. The photoresist comprises the following components by mass percentage: Film-forming resin 4.96% Deionized water 94.24% Diazo photosensitizer 0.3% Surfactant 0.5% Preferably, the film-forming resin is polyvinyl alcohol 1788.

[0045] Preferably, the surfactant is Pronico F68.

[0046] In the photoresist manufacturing process, a certain mass of film-forming resin and deionized water are weighed into a beaker and stirred at 98°C for 20 min to form a film-forming resin mixture. A certain mass of the film-forming resin mixture and diazo photosensitizer are weighed into a beaker and stirred at 40°C for 20 min to form a photoresist mixture. A certain mass of the photoresist mixture and surfactant are weighed into a beaker and stirred at 40°C for 20 min to form a uniform near-zero adhesion photoresist. The near-zero adhesion photoresist is filtered to remove air bubbles using a paper funnel and then allowed to stand in a dark, room-temperature environment for 24 h before use.

[0047] The in-situ fabrication of the highly robust physiological electrode provided in this embodiment includes the following steps: Step 1: Pretreatment of flexible electrode substrate: The surface of the polyimide substrate is cleaned using ion beam etching technology.

[0048] Step 2: Silicon substrate cleaning: The silicon substrate is ultrasonically cleaned with deionized water and dried with nitrogen gas to keep the surface of the silicon substrate dry and clean; the substrate is a silicon wafer. Step 3: Coating: A low-photosensitizer content photoresist is spin-coated using a static spin-coating method to obtain a uniformly distributed, defect-free, low-interfacial-adhesion transferable photoresist film on the silicon substrate; Step 4: Pre-baking: After the adhesive is applied, place it on a hot plate at 80°C to remove the solvent from the adhesive layer; Step 5: Transfer: Slowly and without bubbles, conformally bond the flexible stamp to the surface of the low photosensitizer content photoresist and peel it off from the silicon substrate, transferring it onto the flexible stamp; Step 6: Transfer: Slowly and conformally bond the flexible stamp carrying low photosensitizer content photoresist to the surface of the flexible substrate without air bubbles, and place it on a hot plate at 80°C. The flexible stamp loses its stickiness and the photoresist is transferred to the flexible substrate. Step 7: Transfer: Repeat steps 2-6 to transfer the high photosensitizer content photoresist onto the flexible substrate loaded with low photosensitizer content photoresist; the flexible stamp in steps 5, 6, and 7 is a polydimethylsiloxane film; Step 8: Exposure: The flexible substrate loaded with double-layer photoresist is bonded to the rigid master mask, and exposed for 4 seconds using an ultraviolet lithography machine to transfer the pattern of the rigid master mask onto the photoresist, forming a double-layer stacked photoresist pattern with an undercut structure; wherein the exposure method is contact lithography. Step 9: Development: Immersion development is used. The exposed photoresist is developed in the developer for 10 seconds to copy the pattern of the hard master mask onto the photoresist. The developer is deionized water. Step 10: Metal deposition: Deposit metal by ion beam sputtering; wherein the metal deposition method is ion beam sputtering, the sputtered metal is gold, and the thickness is 150 nm; Step 11: Dry stripping: Use adhesive tape to slowly peel off the metal and photoresist outside the structure to obtain a highly robust flexible physiological electrode. The dry stripping tape is a polyimide tape.

[0049] Figure 4 The following are the electrical performance curves of the metal film in Example 3 under extreme conditions: (a) Sheet resistance of the metal film after immersion in different pH buffer solutions for different times; (b) Sheet resistance of the metal film at different cleaning test times; (c) Resistance of the metal film at different temperatures.

[0050] Figure 4 This study demonstrates that the gold-polyimide film maintains stable electrical properties and strong environmental adaptability under conditions of pH 1.68-12.45, high temperature (400℃), and continuous water flow and agitation. Referring to Examples 1 and 3, it can be seen that the in-situ fabrication method of the high-robust physiological electrode of this invention involves cleaning the substrate using ion beam etching technology; constructing a double-layer stacked photoresist pattern with an undercut structure by controlling the photosensitizer content, achieving high-fidelity replication of the photomask structure, which can be directly used to prepare high-precision, high-density micro / nano patterns; and injecting metal atoms into the polymer substrate through ion beam sputtering to form a mechanically interlocked hybrid interface structure, significantly improving the interfacial bonding strength between the deposited metal and the polymer substrate. The prepared electrode exhibits excellent electrical stability and environmental adaptability under extreme chemical, thermal, water flow, and mechanical environments, demonstrating high reliability and performance comparable to commercial electrodes in actual electrophysiological signal monitoring. This fully verifies the application potential of this in-situ fabrication strategy in the field of flexible electronics, providing a new paradigm for flexible electronic devices under extreme environments. Example

[0051] The photoresist with a double-layer stackable undercut structure provided in this embodiment differs from the upper and lower photoresist layers only in the concentration of the photosensitizer. The specific concentration difference needs to be adjusted according to the required undercut profile. The photoresist comprises the following components by mass percentage: Film-forming resin 4.96% Deionized water 94.24% Diazo photosensitizer 0.3% Surfactant 0.5% Preferably, the film-forming resin is polyvinyl alcohol 1788.

[0052] Preferably, the surfactant is Pronico F127.

[0053] In the photoresist manufacturing process, a certain mass of film-forming resin and deionized water are weighed into a beaker and stirred at 98°C for 20 min to form a film-forming resin mixture. A certain mass of the film-forming resin mixture and diazo photosensitizer are weighed into a beaker and stirred at 40°C for 20 min to form a photoresist mixture. A certain mass of the photoresist mixture and surfactant are weighed into a beaker and stirred at 40°C for 20 min to form a uniform near-zero adhesion photoresist. The near-zero adhesion photoresist is filtered to remove air bubbles using a paper funnel and then allowed to stand in a dark, room-temperature environment for 24 h before use.

[0054] In-situ fabrication of highly robust physiological electrodes includes the following steps: Step 1: Pretreatment of flexible electrode substrate: The surface of the polydimethylsiloxane substrate is cleaned using ion beam etching technology.

[0055] Step 2: Silicon substrate cleaning: The silicon substrate is ultrasonically cleaned with deionized water and dried with nitrogen gas to keep the surface of the silicon substrate dry and clean; the substrate is a silicon wafer. Step 3: Coating: A low-photosensitizer content photoresist is spin-coated using a static spin-coating method to obtain a uniformly distributed, defect-free, low-interfacial-adhesion transferable photoresist film on the silicon substrate; Step 4: Pre-baking: After the adhesive is applied, place it on a hot plate at 80 ℃ to heat and remove the solvent in the adhesive layer; Step 5: Transfer: Slowly and without bubbles, conformally bond the flexible stamp to the surface of the low photosensitizer content photoresist and peel it off from the silicon substrate, transferring it onto the flexible stamp; Step 6: Transfer: Slowly and conformally bond the flexible stamp carrying low photosensitizer content photoresist to the surface of the flexible substrate without air bubbles, and place it on a hot plate at 80°C. The flexible stamp loses its stickiness and the photoresist is transferred to the flexible substrate. Step 7: Transfer: Repeat steps 2-6 to transfer the high photosensitizer content photoresist onto the flexible substrate loaded with low photosensitizer content photoresist; the flexible stamp in steps 5, 6, and 7 is a polydimethylsiloxane film; Step 8: Exposure: The flexible substrate loaded with double-layer photoresist is bonded to the rigid master mask, and exposed for 4 seconds using an ultraviolet lithography machine to transfer the pattern of the rigid master mask onto the photoresist, forming a double-layer stacked photoresist pattern with an undercut structure; wherein the exposure method is contact lithography. Step 9: Development: Immersion development is used. The exposed photoresist is developed in the developer for 10 seconds to copy the pattern of the hard master mask onto the photoresist. The developer is deionized water. Step 10: Metal deposition: Deposit metal by ion beam sputtering; the metal deposition method described in Step 10 is ion beam sputtering, the sputtered metal is gold, and the thickness is 150 nm; Step 11: Dry stripping: Use adhesive tape to slowly peel off the metal and photoresist outside the structure to obtain a highly robust flexible physiological electrode. The dry stripping tape is a polyimide tape.

[0056] Furthermore, when directly depositing metal using ion beam sputtering, excessive metal adhesion occurs on the sidewalls, which severely affects the integrity of the patterned structure during subsequent patterning via a lift-off process. Currently, the most effective solution to this problem is to construct a double-layer photoresist undercut structure. However, if the second layer of photoresist is directly coated onto the surface of the first layer, the bottom photoresist will be dissolved by the solvent in the upper layer, causing interface mixing and resulting in pattern distortion. Therefore, this structure typically requires a transfer process to achieve the stacking of the two photoresist layers.

[0057] In addition, by directly injecting metal ions into the surface of a flexible polymer substrate through in-situ ion beam sputtering, a mechanically interlocked structure with a gradient at the interface between the deposited metal and the substrate can be formed. This can maintain excellent adhesion and stability under dynamic conditions such as stretching and bending, thus avoiding the reliability reduction caused by interface delamination or fatigue failure of traditional dry electrodes.

[0058] The electrodes prepared by this method exhibit excellent electrical stability and environmental adaptability under extreme chemical, thermal, water flow, and mechanical environments, ensuring stable signal acquisition even under complex deformation and sweat corrosion. The prepared highly robust physiological electrodes have significant application value in wearable health monitoring, neural interfaces, and electrophysiological diagnostics.

[0059] This document provides a detailed description and uses specific examples to illustrate the principles and implementation methods of the present invention. The above embodiments are only used to help understand the method and core ideas of the present invention. At the same time, for those skilled in the art, there will be changes in the specific implementation methods and application scope based on the ideas of the present invention. Therefore, the content of this specification should not be construed as a limitation of the present invention.

[0060] Those skilled in the art will clearly understand that, for the sake of convenience and brevity, the specific working process of the system and unit described above can be referred to the corresponding process in the foregoing method embodiments, and will not be repeated here.

Claims

1. A photoresist for highly robust physiological electrodes, characterized in that: The photoresist with a double-layer stackable undercut structure is prepared with the only difference between the upper and lower layers in the concentration of photosensitizer. The concentration difference is adjusted according to the required undercut profile. Its mass percentage components include: 3-10% film-forming resin, 90-97% deionized water, 0.1-1% diazo photosensitizer, and 0.1-1% surfactant.

2. The photoresist for highly robust physiological electrodes according to claim 1, characterized in that: The film-forming resin is at least one of polyvinyl alcohol 1788 and polyvinyl alcohol 1799.

3. The photoresist for highly robust physiological electrodes according to claim 1, characterized in that: The surfactant is at least one of Pronic F68 and Pronic F127.

4. A method for manufacturing a photoresist for a highly robust physiological electrode, characterized in that, The production steps include: S110. According to the predetermined ratio, accurately weigh the film-forming resin and deionized water into a beaker, and stir at 98°C for 20-40 min to form a film-forming resin mixture. S120. Weigh the film-forming resin mixture and diazo photosensitizer into a beaker according to the ratio, and stir at 40℃ for 15-25 min to obtain the photoresist mixture system; S130. Weigh the photoresist mixture and surfactant according to the ratio, stir at 40℃ for 15-25 min to obtain a uniform near-zero adhesion photoresist resin; S140. Use a paper funnel to filter out air bubbles from the obtained photoresist and place it in a dark and room temperature environment for 24 hours.

5. A method for in-situ fabrication of a highly robust physiological electrode, using the photoresist according to any one of claims 1 to 4, characterized in that, Includes the following steps: S210. Pretreatment of flexible electrode substrate: The surface of the flexible polymer substrate is cleaned using ion beam etching technology; S220. Silicon substrate cleaning: Ultrasonically clean the silicon substrate with deionized water and dry it with nitrogen gas to keep the surface of the silicon substrate dry and clean. S230. Coating: A low-photosensitizer content photoresist is spin-coated using a static spin-coating method to obtain a uniformly distributed, defect-free, low-interfacial-adhesion transferable photoresist film on a silicon substrate; S240. Pre-baking: After the adhesive is applied, place it on a hot plate at 80°C to remove the solvent from the adhesive layer; S250. Transfer 1: Slowly and bubble-free conformally bond the flexible stamp to the photoresist surface and peel it off from the silicon substrate to transfer the photoresist onto the flexible stamp; S260. Transfer 2: Slowly and without bubbles, conformally bond the flexible stamp carrying photoresist to the surface of the flexible substrate, place it on a hot plate and heat it at 80°C. The flexible stamp loses its stickiness, and the photoresist is transferred to the flexible substrate. S270. Transfer 3: Repeat S220-S260 to transfer the high photosensitizer content photoresist onto a flexible substrate loaded with low photosensitizer content photoresist; S280. Exposure: The flexible substrate loaded with double-layer photoresist is bonded to the rigid master mask, and exposed for 2-15 seconds using an ultraviolet lithography machine to transfer the pattern of the rigid master mask onto the photoresist, forming a double-layer stacked photoresist pattern with an undercut structure. S290. Development: Immersion development is used to develop the exposed photoresist in the developing solution for 3-20 seconds, and the pattern of the hard master mask is copied onto the photoresist. S2100. Metal deposition: Depositing metal via ion beam sputtering; S2110. Dry stripping: The metal and photoresist outside the structure are slowly peeled off with tape to obtain a highly robust flexible physiological electrode.

6. The in-situ manufacturing method of the highly robust physiological electrode according to claim 5, characterized in that, The substrate in S210 includes at least one of a polydimethylsiloxane film and a polyimide film.

7. The in-situ manufacturing method of the highly robust physiological electrode according to claim 5, characterized in that, The substrate in S220 includes at least one of silicon wafer and silicon dioxide wafer.

8. The in-situ manufacturing method of the highly robust physiological electrode according to claim 5, characterized in that, The flexible stamps in S250, S260 or S270 include at least one of a polydimethylsiloxane film and a heat-release tape.

9. The in-situ manufacturing method of the highly robust physiological electrode according to claim 5, characterized in that, The metal coating method described in S2100 is ion beam sputtering, where the sputtered metal is gold and the thickness is 50-200 nm.

10. The in-situ manufacturing method of the highly robust physiological electrode according to claim 5, characterized in that, The dry adhesive stripping tape in S2110 includes at least one of heat-release tape, polyimide tape, and UV-release tape.

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