Miniaturized low-profile flexible ocean galvanic couple type pH sensor and preparation method thereof

Abstract

The invention discloses a miniaturized low-profile flexible ocean galvanic couple type pH sensor and a preparation method thereof, and aims to solve the problems of large profile thickness and insufficient reliability of the conventional flexible pH sensor. A working electrode system and a reference electrode system in the miniaturized low-profile flexible ocean galvanic couple pH sensor are arranged on a flexible polyimide substrate, and the working electrode system comprises an iridium oxide working electrode, a first metal conduction circuit layer and a first metal bonding pad; the iridium oxide working electrode is connected with the first metal bonding pad through the first metal conduction circuit layer, the reference electrode system comprises a reference electrode, a second metal conduction circuit layer and a second metal bonding pad, and the reference electrode is connected with the second metal bonding pad through the second metal conduction circuit layer. The pH response performance is remarkably improved by utilizing the nanocrystalline iridium oxide sensing layer, the sensitivity reaches 72.76 mV / pH, and 16.84 s quick response is realized in a 3m / s high-flow-speed marine environment.

Description

Technical Field

[0001] The present invention belongs to the technical field of marine monitoring sensors, and particularly relates to a miniaturized low-profile flexible marine galvanic pH sensor and a preparation method thereof. Background Art

[0002] Traditional marine pH monitoring mainly relies on columnar sediment sampling and laboratory titration analysis, which has the defects of poor timeliness and inability to capture dynamic environmental changes. Although existing in-situ sensors use photometric methods or glass electrode technologies, they are limited by their large size (usually >50 cm 3 ) and rigid encapsulation structures, making it difficult to integrate them on the surface of underwater vehicles. For example, although the pH sensor based on iridium oxide thin film has hydrogen ion sensitivity, its thickness design lacks systematic optimization, resulting in easy passivation after long-term immersion (drift >10 mV / month), and the destruction of the ion diffusion boundary layer in a high-flow environment will cause response distortion (error >0.1 pH). In addition, most traditional galvanic sensors use hard substrates and lack conformal fitting ability, which is prone to stress cracks during installation on curved carriers, severely restricting the miniaturized application of deep-sea exploration equipment.

[0003] Although flexible pH sensors have achieved deformation adaptability through polyimide substrates in recent years, they still face two major bottlenecks: one is the insufficient interfacial bonding strength between the sensitive film and the flexible electrode, which is prone to delamination and failure after repeated bending; the other is the decrease in selectivity due to factors such as chloride ion penetration and biofouling in the marine environment. Existing technologies such as CN104914150B use graphene / polyaniline composite films to improve sensitivity, but do not solve the signal stability problem under dynamic flow rates; CN 119534582 A uses a breathable and moisture-permeable flexible nanofiber substrate to set up a polyaniline sensitive layer, but the cross-sectional thickness increases to more than 50 μm, unable to meet the low-profile (<6 μm) requirements. Therefore, there is an urgent need to develop a flexible pH sensor with the characteristics of miniaturization, anti-interference, and high reliability to break through the in-situ monitoring technology barrier in the complex hydrodynamic environment of the ocean. Summary of the Invention

[0004] The present invention aims to solve the problems of relatively large cross-sectional thickness and insufficient reliability of existing flexible pH sensors, and provides a miniaturized low-profile flexible marine galvanic pH sensor and a preparation method thereof. The galvanic pH sensor has the characteristics of miniaturization, low profile, and good flexibility, and can be used for long-term real-time pH detection in the marine environment while ensuring good hydrogen ion response ability.

[0005] The miniaturized low-profile flexible marine galvanic pH sensor of the present invention includes a flexible polyimide substrate, a working electrode system, and a reference electrode system. The working electrode system and the reference electrode system are arranged on the flexible polyimide substrate, and the working electrode system and the reference electrode system are arranged at intervals;

[0006] The described working electrode system includes an iridium oxide (IrO x ) working electrode, a first metal conduction circuit layer, and a first metal pad. The iridium oxide working electrode is connected to the first metal pad through the first metal conduction circuit layer. The iridium oxide working electrode is a laminated structure formed by, from bottom to top, a metal adhesion layer Cr, a metal adhesion layer Pt, and an iridium oxide (IrO x ) sensing layer;

[0007] The described reference electrode system includes a reference electrode, a second metal conduction circuit layer, and a second metal pad. The reference electrode is connected to the second metal pad through the second metal conduction circuit layer. The reference electrode is a laminated structure formed by, from bottom to top, a metal adhesion layer Cr, a metal adhesion layer Ag, a reference electrode layer AgCl, a KCl agarose layer, and a semi-permeable membrane.

[0008] The preparation method of the miniaturized low-profile flexible marine galvanic pH sensor of the present invention is realized according to the following steps:

[0009] Step 1: Copper electrode magnetron sputtering process

[0010] Cover the first mask template on the flexible polyimide substrate, expose the areas of the first metal conduction circuit layer, the first metal pad, the second metal conduction circuit layer, and the second metal pad, use a copper target, and adopt a magnetron sputtering process to sputter and form the first metal conduction circuit layer, the first metal pad, the second metal conduction circuit layer, and the second metal pad;

[0011] Step 2: Chromium adhesion layer magnetron sputtering process

[0012] Cover the second mask template on the flexible polyimide substrate, expose the areas of the iridium oxide working electrode and the reference electrode, use a chromium target, and adopt a magnetron sputtering process to sputter and form the metal adhesion layer Cr of the iridium oxide working electrode and the reference electrode;

[0013] Step 3: Platinum conductive layer magnetron sputtering process

[0014] Cover the third mask template on the flexible polyimide substrate, expose the area of the iridium oxide working electrode, use a platinum target, and adopt a magnetron sputtering process to sputter and form a metal adhesion layer Pt on the metal adhesion layer Cr of the iridium oxide working electrode;

[0015] Step 4: Silver reference layer magnetron sputtering process

[0016] Cover the fourth mask template on the flexible polyimide substrate, expose the area of the reference electrode, use a silver target, and adopt a magnetron sputtering process to sputter and form a metal adhesion layer Ag on the metal adhesion layer Cr of the reference electrode;

[0017] Step 5: In-situ construction of Ag / AgCl reference electrode

[0018] A two - electrode system is adopted. Using the metal adhesion layer Ag prepared in Step Four as the working electrode and a platinum sheet electrode as the reference electrode, in a 0.1 mol / L HCl solution, anodic electro - oxidation treatment of the working electrode is carried out by the constant - current deposition method to form a silver chloride layer on the surface of the metal adhesion layer Ag. After rinsing, it is immersed in a KCl solution for aging treatment to form a reference electrode layer AgCl.

[0019] Step Six. IrO x Electrodeposition and strengthening of the sensitive layer

[0020] A three - electrode system is adopted. Using the metal adhesion layer Pt prepared in Step Three as the working electrode, the reference electrode layer AgCl prepared in Step Five as the reference electrode, and a platinum sheet electrode as the auxiliary electrode, cyclic voltammetry is used for electrodeposition in the plating solution to form an amorphous IrO x layer on the metal adhesion layer Pt, and then thermally induced crystallization treatment is carried out at 300 °C to obtain an iridium oxide sensing layer.

[0021] Step Seven. Construction of the KCl agarose interface layer

[0022] Agarose powder is added to a 3.0 mol / L KCl electrolyte solution and stirred in a water bath at 85 ± 5 °C until completely dissolved to form a transparent sol. When the temperature is cooled to the critical temperature of the sol - gel transition (48 ± 2 °C), it is drop - coated on the surface of the reference electrode layer AgCl and cooled and solidified to form a KCl agarose layer.

[0023] Step Eight. Integration of the semi - permeable membrane and device packaging

[0024] A cellulose semi - permeable membrane is used to cover the KCl agarose layer, and polyimide tape is used for packaging. Windows are respectively opened at the iridium oxide working electrode and the reference electrode to obtain a miniaturized low - profile flexible marine galvanic pH sensor.

[0025] The miniaturized low - profile flexible marine galvanic pH sensor and its preparation method of the present invention have the following beneficial effects:

[0026] 1. Both high sensitivity and stability: The nanocrystalline iridium oxide (IrO x ) sensing layer prepared by magnetron sputtering and electrochemical deposition processes significantly improves the pH response performance. Experiments show that its sensitivity reaches 72.76 mV / pH, which is 39.9% higher than that of the traditional electrochemical oxidation process (52 mV / pH). And it can achieve a rapid response of 16.84 s in a high - flow marine environment of 3 m / s, and the potential drift during 30 - day long - term monitoring is less than 5 mV, overcoming the defect of signal instability of traditional sensors in a dynamic fluid environment.

[0027] 2. Miniaturization and Flexible Structure Innovation: By using a 2-μm ultra-thin polyimide substrate and micro-nano processing technology, the total thickness of the sensor is controlled within 6 μm, which is 99% thinner than traditional rigid sensors (>500 μm). At the same time, through the design of Cr / Pt or Cr / Ag multi-layer metal stacks, the performance degradation is less than 4% after 1000 bending tests (curvature radius 3 mm), and it can be closely attached to the curved surface of marine equipment to achieve in-situ monitoring in complex environments.

[0028] 3. Batch-Manufacturing with High Efficiency: Based on magnetron sputtering and UV-LIGA microfabrication technologies, wafer-level sensor arrays can be manufactured. The thickness deviation of the metal layer and the functional layer is small, and the batch consistency is improved compared with traditional processes. The yield rate of single processing exceeds 95%, providing reliable technical support for the large-scale deployment of marine monitoring networks. Brief Description of the Drawings

[0029] Figure 1 It is a schematic diagram of the first mask;

[0030] Figure 2 It is a schematic diagram of the second mask;

[0031] Figure 3 It is a schematic diagram of the third mask;

[0032] Figure 4 It is a schematic diagram of the fourth mask;

[0033] Figure 5 It is a structural diagram of the miniaturized low-profile flexible marine galvanic pH sensor before encapsulation in the embodiment of the present invention;

[0034] Figure 6 It is a structural diagram of the iridium oxide (IrO x ) working electrode system;

[0035] Figure 7 It is a structural diagram of the iridium oxide (IrO x ) working electrode system in longitudinal section;

[0036] Figure 8 It is a structural diagram of the reference electrode system;

[0037] Figure 9 It is a longitudinal sectional view of the reference electrode system;

[0038] Figure 10 It is a voltage test chart of the flexible marine galvanic pH sensor in the embodiment of the present invention at different pH values;

[0039] Figure 11 It is a 16.84-s rapid response test chart of the flexible marine galvanic pH sensor in the embodiment at a high flow rate of 3 m / s in the marine environment (pH = 8);

[0040] Figure 12 Potential drift test chart of the flexible marine galvanic pH sensor in the example for 30 days of long-term monitoring;

[0041] Figure 13 Performance decay test chart of the flexible marine galvanic pH sensor in the example after 1000 bending tests (curvature radius 3 mm). Specific implementation manners

[0042] Specific implementation manner one: The miniaturized low-profile flexible marine galvanic pH sensor in this implementation manner includes a flexible polyimide substrate, a working electrode system, and a reference electrode system. The working electrode system and the reference electrode system are arranged on the flexible polyimide substrate, and the working electrode system and the reference electrode system are arranged at intervals;

[0043] The described working electrode system includes an iridium oxide (IrO x ) working electrode 1, a first metal conduction circuit layer 2, and a first metal pad 3. The iridium oxide working electrode 1 is connected to the first metal pad 3 through the first metal conduction circuit layer 2. The iridium oxide working electrode 1 is a laminated structure formed by, from bottom to top, a metal adhesion layer Cr, a metal adhesion layer Pt, and an iridium oxide (IrO x ) sensing layer;

[0044] The reference electrode system includes a reference electrode 4, a second metal conduction circuit layer 5, and a second metal pad 6. The reference electrode 4 is connected to the second metal pad 6 through the second metal conduction circuit layer 5. The reference electrode 4 is a laminated structure formed by, from bottom to top, a metal adhesion layer Cr, a metal adhesion layer Ag, a reference electrode layer AgCl, a KCl agarose layer, and a semi-permeable membrane.

[0045] In this implementation manner, the square iridium oxide working electrode 1 is connected to the square first metal pad 3 through the linear first metal conduction circuit layer 2; the circular reference electrode 4 is connected to the square second metal pad 6 through the linear second metal conduction circuit layer 5.

[0046] There is no conductive contact between the working electrode circuit system and the reference electrode circuit system in this implementation manner; for the low-profile flexible marine galvanic pH sensor, an iridium oxide sensing window and a reference electrode liquid junction surface window are reserved, and they are encapsulated with a 1-μm-thick polyimide tape.

[0047] The total thickness of the flexible marine galvanic pH sensor in this implementation manner does not exceed 6 μm.

[0048] Specific implementation manner two: The difference between this implementation manner and specific implementation manner one is that the materials of the first metal conduction circuit layer 2 and the first metal pad 3 are platinum Pt or copper Cu, and the thickness of the first metal conduction circuit layer 2 is 150 - 200 nm.

[0049] Embodiment 3: The difference between this embodiment and Embodiment 1 or 2 is that the thickness of the flexible polyimide substrate is 2 μm.

[0050] Embodiment 4: The difference between this embodiment and any one of Embodiments 1 to 3 is that the thickness of the metal adhesion layer Cr in the iridium oxide working electrode 1 is 10 - 30 nm, the thickness of the metal adhesion layer Pt is 120 - 150 nm, and the thickness of the iridium oxide sensing layer is 150 - 220 nm.

[0051] Embodiment 5: The difference between this embodiment and any one of Embodiments 1 to 4 is that the materials of the second metal conduction circuit layer 5 and the second metal pad 6 are platinum Pt or copper Cu, and the thickness of the second metal conduction circuit layer 5 is 150 - 200 nm.

[0052] Embodiment 6: The difference between this embodiment and any one of Embodiments 1 to 5 is that the thickness of the metal adhesion layer Cr in the reference electrode 4 is 10 - 30 nm, the thickness of the metal adhesion layer Ag is 120 - 180 nm, the thickness of the reference electrode layer AgCl is 150 - 180 nm, the thickness of the KCl agarose layer is 1 - 2 μm, and the thickness of the semi-permeable membrane is 200 nm.

[0053] The KCl agarose layer in this embodiment is 3M saturated KCl agarose.

[0054] Embodiment 7: The preparation method of the miniaturized low-profile flexible marine galvanic pH sensor in this embodiment is implemented according to the following steps:

[0055] Step 1: Copper electrode magnetron sputtering process

[0056] Cover the first mask on the flexible polyimide substrate, expose the areas of the first metal conduction circuit layer 2, the first metal pad 3, the second metal conduction circuit layer 5, and the second metal pad 6, use a copper target, and sputter to form the first metal conduction circuit layer 2, the first metal pad 3, the second metal conduction circuit layer 5, and the second metal pad 6 by magnetron sputtering process;

[0057] Step 2: Chromium adhesion layer magnetron sputtering process

[0058] Cover the second mask on the flexible polyimide substrate, expose the areas of the iridium oxide working electrode 1 and the reference electrode 4, use a chromium target, and sputter to form the metal adhesion layer Cr of the iridium oxide working electrode 1 and the reference electrode 4 by magnetron sputtering process;

[0059] Step 3: Platinum conductive layer magnetron sputtering process

[0060] Cover the third mask on the flexible polyimide substrate, exposing the area of the iridium oxide working electrode 1. Using a platinum target, a metal adhesion layer Pt is sputtered on the metal adhesion layer Cr of the iridium oxide working electrode 1 by magnetron sputtering process;

[0061] Step 4: Magnetron sputtering process of silver reference layer

[0062] Cover the fourth mask on the flexible polyimide substrate, exposing the area of the reference electrode 4. Using a silver target, a metal adhesion layer Ag is sputtered on the metal adhesion layer Cr of the reference electrode 4 by magnetron sputtering process;

[0063] Step 5: In-situ construction of Ag / AgCl reference electrode

[0064] Adopt a two-electrode system, using the metal adhesion layer Ag prepared in Step 4 as the working electrode, a platinum sheet electrode as the reference electrode, in a 0.1mol / L HCl solution, electrochemical anodic oxidation treatment of the working electrode is carried out by constant current deposition method, a silver chloride layer is formed on the surface of the metal adhesion layer Ag, and after rinsing, it is immersed in KCl solution for aging treatment, thus forming a reference electrode layer AgCl;

[0065] Step 6: Electrodeposition and strengthening of IrO x sensitive layer

[0066] Adopt a three-electrode system, using the metal adhesion layer Pt prepared in Step 3 as the working electrode, the reference electrode layer AgCl prepared in Step 5 as the reference electrode, and a platinum sheet electrode as the auxiliary electrode, and carry out electrodeposition in the plating solution by cyclic voltammetry to form an amorphous IrO x layer on the metal adhesion layer Pt, and then perform thermally induced crystallization treatment at 300 °C to obtain an iridium oxide sensing layer;

[0067] Step 7: Construction of KCl agarose interface layer

[0068] Add agarose powder to 3.0mol / L KCl electrolyte solution, stir in a water bath at 85±5 °C until completely dissolved to form a transparent sol. When the temperature is lowered to the critical temperature of sol-gel transition (48±2 °C), it is drop-coated on the surface of the reference electrode layer AgCl, and after cooling and solidifying, a KCl agarose layer is formed;

[0069] Step 8: Integration of semi-permeable membrane and device encapsulation

[0070] Cover the KCl agarose layer with a cellulose semi-permeable membrane, and encapsulate it with polyimide tape. Windows are respectively opened at the iridium oxide working electrode 1 and the reference electrode 4 to obtain a miniaturized low-profile flexible marine galvanic pH sensor.

[0071] The first mask, the second mask, the third mask, and the fourth mask described in this embodiment are all fabricated by UV-LIGA micromachining technology.

[0072] Specific Embodiment 8: The difference between this embodiment and Specific Embodiment 7 is that in Step 5, the constant current deposition method is used, the polarization current is 0.5 mA, and the electrochemical anodic working electrode is oxidized for 20 min.

[0073] Specific Embodiment 9: The difference between this embodiment and Specific Embodiment 7 or 8 is that the preparation process of the plating solution in Step 6 is as follows:

[0074] Dissolve 0.12 g of iridium tetrachloride IrCl4·H2O in 80 ml of distilled water and stir evenly. Add 0.8 ml of 30% wt H2O2, stir, and then add 0.12 g of oxalic acid. Adjust the pH of the system to 10.5 by adding potassium carbonate to obtain a (golden yellow) deposition solution. The deposition solution is placed in a dry and light-proof place for 56 - 60 h to convert the Ir 3+ complex into [Ir(OH)5Cl] 2- active ions to obtain the plating solution.

[0075] Specific Embodiment 10: The difference between this embodiment and any one of Specific Embodiments 7 to 9 is that the thermally induced crystallization treatment time in Step 6 is 4 - 6 hours.

[0076] Example: The preparation method of the miniaturized low-profile flexible marine galvanic pH sensor in this example is implemented according to the following steps:

[0077] Step 1: Copper electrode magnetron sputtering process

[0078] Cover the first mask (as shown in the Figure 1 electrode pattern) on the flexible polyimide substrate, exposing the areas of the first metal conduction circuit layer 2, the first metal pad 3, the second metal conduction circuit layer 5, and the second metal pad 6. Use a copper target and adopt the magnetron sputtering process. After evacuating to 5×10 -7 Torr, introduce high-purity argon (99.999%) to a working pressure of 5 mTorr. Under the condition of a target-substrate distance of 70 mm, apply a 150 W DC power to excite the plasma. Monitor the deposition rate in real time and keep it stable at 0.8 nm / s. Continuously sputter for 40 min to form the copper electrode layer. After the process is completed, release the pressure gradually to atmospheric pressure to avoid interface peeling caused by sudden changes in film stress, thereby obtaining the first metal conduction circuit layer 2, the first metal pad 3, the second metal conduction circuit layer 5, and the second metal pad 6;

[0079] Step 2: Chromium adhesion layer magnetron sputtering process

[0080] Cover the second mask (as shown in the Figure 2The area covering the indium oxide working electrode 1 and the reference electrode 4 is exposed on the flexible polyimide substrate. Using a chromium target, a magnetron sputtering process is employed. The vacuum chamber is evacuated to 5×10 - 7 Torr, and the working pressure of argon gas is maintained at 5 mTorr. A short sputtering (5 min) is carried out under the conditions of a target-substrate distance of 70 mm and a DC power of 100 W to obtain an ultra-thin chromium layer. The metal adhesion layer Cr of the indium oxide working electrode 1 and the reference electrode 4 is sputtered to form. This adhesion layer forms a strong interfacial bond with the polyimide substrate through Cr-O chemical bonds (bonding force > 30 MPa), providing an anchoring foundation for the subsequent metal layer;

[0081] Step 3. Magnetron sputtering process of the platinum conductive layer

[0082] Cover the flexible polyimide substrate with the third mask template (as shown in the Figure 3 electrode pattern). Expose the area of the indium oxide working electrode 1. Using a platinum target, a magnetron sputtering process is adopted. Maintaining an argon gas environment of 5 mTorr and a target-substrate distance of 70 mm, continuous deposition is carried out at a power of 100 W for 30 min. A metal adhesion layer Pt is sputtered on the metal adhesion layer Cr of the indium oxide working electrode 1. During the sputtering process, the film thickness uniformity is ensured by substrate rotation (10 rpm) (deviation < ±3%), and finally a highly conductive interface with a sheet resistance of 0.15 Ω / sq is obtained, meeting the low-impedance transmission requirements of flexible devices;

[0083] Step 4. Magnetron sputtering process of the silver reference layer

[0084] Cover the flexible polyimide substrate with the fourth mask template (as shown in the Figure 4 electrode pattern). Expose the area of the reference electrode 4. Using a silver target, a magnetron sputtering process is adopted. Maintaining an argon gas environment of 5 mTorr and a target-substrate distance of 70 mm, continuous deposition is carried out at a power of 100 W for 30 min. A metal adhesion layer Ag is sputtered on the metal adhesion layer Cr of the reference electrode 4. This layer serves as the precursor of the Ag / AgCl reference electrode, and subsequently, an active silver chloride layer (Cl - doping concentration > 1×10 21 cm -3 ) is formed through electrochemical oxidation to achieve a stable reference potential output (drift < 0.5 mV / h);

[0085] Step 5. In-situ construction of the Ag / AgCl reference electrode

[0086] Adopting a two-electrode system, using the metal adhesion layer Ag prepared in Step 4 as the working electrode and a platinum sheet electrode as the reference electrode. In a 0.1 mol / L HCl solution, a constant current polarization deposition method is used to apply a constant current of 0.5 mA for 20 min for electrochemical anodic oxidation treatment of the working electrode. Through an interfacial reaction (Ag + Cl- →AgCl + e - ) A dense silver chloride layer is formed. After ultrasonic cleaning with deionized water, the electrode is immersed in a 3 mol / L KCl solution and aged for 24 h to form a Cl⁻ concentration gradient inside the AgCl layer (from 5×10 20 to 1×10 22 cm -3 ). Finally, a highly stable reference electrode with an open-circuit potential drift < 0.3 mV / h is obtained, and the reference electrode layer AgCl is formed;

[0087] Step Six: Electrodeposition and Strengthening of the IrO x Sensing Layer

[0088] Cover the first metal conduction circuit layer connected to the iridium oxide working electrode system, the first metal pad connected to the first metal conduction circuit layer, the second metal conduction circuit layer connected to the reference electrode system, and the second metal pad connected to the second metal conduction circuit layer with Teflon to prevent electroplating;

[0089] (1) Plating solution formula: Dissolve 0.12 g of iridium tetrachloride IrCl₄·H₂O in 80 ml of distilled water and add it to a three-necked flask. Stir well at room temperature on a magnetic stirrer for about 40 min. Measure 0.8 ml of H₂O₂ (30% wt), add it and stir magnetically for 10 min, then weigh 0.12 g of oxalic acid, add it and stir magnetically for 20 min. Finally, adjust the pH to 10.5 by adding potassium carbonate to obtain a golden deposition solution. The newly prepared deposition solution is placed in a dry and dark place for 72 h to convert the Ir 3+ complex into [Ir(OH)₅Cl] 2- active ions. Wait until the deposition solution turns blue-black before use;

[0090] (2) Electroplating method: Use a three-electrode system. The working electrode is the platinum electrode prepared in deposition step three, the reference electrode is the silver chloride electrode prepared in step five, and the auxiliary electrode is a platinum sheet electrode. Add 60 ml of the deposition solution to a 100 ml beaker. Set the cyclic voltammetry potential scanning range from 0.2 V to 0.75 V, and the scanning rate is 50 mV·s -1 , scan 100 cycles to obtain an amorphous IrO x layer;

[0091] (3) Thermal crystallization: Heat up at a gradient of 5 °C / min to 300 °C and keep it for 5 h to promote the transformation of IrO x from amorphous to nanocrystalline state, improve the film-substrate bonding strength, and then cool to 25 °C to obtain the iridium oxide sensing layer;

[0092] The nanocrystalline iridium oxide sensing layer formed by electroplating in the present invention has significant advantages compared to the iridium oxide sensing layer deposited by magnetron sputtering. Electrochemical deposition can achieve more uniform IrO x film growth at a lower temperature, promoting the nanocrystalline iridium oxide IrO x to have a higher surface area and better electrochemical activity, thereby improving the sensitivity of the sensor. In addition, the hydrated iridium oxide IrO x formed by electroplating, compared with the non-hydrated iridium oxide obtained by magnetron sputtering, significantly improves the electron conductivity and reactivity due to the inclusion of water molecules in its structure, thereby enhancing the adsorption and conversion efficiency of hydrogen ions. The electrochemically deposited hydrated iridium oxide IrO x has more superior sensitivity and response characteristics in sensor applications.

[0093] Step 7: Construction of the KCl agarose interface layer

[0094] Add 2.5 wt% agarose powder (5 g) to 3.0 mol / L KCl electrolyte (56 g KCl / 200 mL deionized water), and continuously stir magnetically (300 rpm) in a water bath at 85 ± 5 °C until completely dissolved to form a transparent sol. When the solution cools down to the critical temperature of the sol-gel transition (48 ± 2 °C), precisely drop-coat it on the surface of the Ag / AgCl electrode with a micro syringe, control the thickness of the gel layer, and after natural cooling and solidification, a three-dimensional interpenetrating network structure (pore size 0.5 - 1.2 μm) is formed to achieve controllable ion exchange between the internal electrolyte and the outside world, forming a KCl agarose layer;

[0095] Step 8: Integration of the semi-permeable membrane and device encapsulation

[0096] Cover the agarose layer with a cellulose semi-permeable membrane with a molecular weight cut-off of 500 Da. Synchronously open a square IrO x sensing window with a side length of 800 μm and a circular reference electrode liquid junction window with a diameter of 1000 μm on the polyimide tape by laser micromachining (wavelength 355 nm). Finally, encapsulate it with a 1-μm-thick polyimide tape with windows opened to form a leak-proof barrier. After encapsulation, a miniaturized low-profile flexible marine galvanic pH sensor is obtained.

[0097] In this embodiment, the flexible substrate is polyimide, with a size of 1 cm × 2.2 cm and a thickness of 2 μm. The first to fourth masks are prepared using UV-LIGA micromachining technology. The thickness of the copper layer is 165 nm, the thickness of the chromium layer is 17 nm, the thickness of the platinum layer is about 134 nm, and the thickness of the silver layer is 143 nm. The thickness of the iridium oxide on the working electrode is 180 nm, the thickness of the silver chloride on the reference electrode is 172 nm, the thickness of the KCl agarose is 1.3 μm, and the thickness of the semi-permeable membrane is 200 nm, with a total thickness of 5.0 μm.

[0098] As shown Figure 5 in the figure, it is the structural diagram of the miniaturized low-profile flexible marine galvanic pH sensor before encapsulation prepared in the embodiment. The miniaturized low-profile flexible marine galvanic pH sensor includes a flexible polyimide substrate, and a working electrode system and a reference electrode system spaced on the surface of the flexible polyimide substrate. The working electrode circuit system includes: an iridium oxide (IrO x ) working electrode system 1; a first metal conduction circuit layer 2 connected to the iridium oxide (IrO x ) working electrode system; a first metal pad 3 connected to the first metal conduction circuit layer; the reference electrode circuit system includes: a reference electrode system 4; a second metal conduction circuit layer 5 connected to the reference electrode system; a second metal pad 6 connected to the second metal conduction circuit layer.

[0099] Figure 6 The figure is the structural diagram of the iridium oxide (IrO x ) working electrode system, including: a metal adhesion layer Cr adhered to the polyimide flexible substrate, a metal adhesion layer Pt provided on the metal adhesion layer Cr, and an iridium oxide (IrO x ) sensing layer provided on the metal adhesion layer Pt.

[0100] Figure 7 The figure shows the longitudinal sectional view of the iridium oxide (IrO x ) working electrode system. From bottom to top, they are: a metal adhesion layer Cr, a metal adhesion layer Pt, and an iridium oxide (IrO x ) sensing layer. Among them, the Cr / Pt metal stack realizes an interfacial contact resistance of <0.5Ω / sq through gradient sputtering technology. This design synergistically combines the electron tunneling effect of the Pt conductive layer and the proton-coupled redox characteristics of IrO x to enable the sensor to obtain a super Nernst response sensitivity of 72.76mV / pH, while ensuring the electrochemical stability of the flexible substrate under a 3mm curvature bend (sensitivity attenuation <4% after 1000 cycles).

[0101] Figure 8 The figure is the structural diagram of the reference electrode system, including: a metal adhesion layer Cr adhered to the polyimide flexible substrate, a metal adhesion layer Ag provided on the metal adhesion layer Cr, and a silver chloride AgCl reference electrode layer provided on the metal adhesion layer Ag. Figure 9The longitudinal sectional view of the reference electrode system is shown. From bottom to top, they are: metal adhesion layer Cr, metal adhesion layer Ag, silver chloride AgCl reference electrode layer, 3 mol / L KCl agarose gel electrolyte layer, and 500 Da cut-off molecular weight semi-permeable membrane. The Cr / Ag laminate realizes nanoscale interfacial bonding through the magnetron sputtering process, and the AgCl layer provides a stable reference potential; the KCl agarose gel forms a three-dimensional porous network (porosity > 80%) after curing, which not only blocks the leakage of internal electrolyte but also maintains the ion conduction path; the surface semi-permeable membrane selectively permeates H + and Cl - (the permeation rate is two orders of magnitude higher than that of Na + / K + ), effectively shielding the interference of Ca 2+ , Mg 2+ and organic macromolecules in seawater, and ensuring the long-term stability of the potential signal (drift < 5 mV in 30 days).

[0102] The miniaturized low-profile flexible marine galvanic pH sensor prepared in the example was tested for its response across pH values (3.0 - 10.0). The specific operation process is as follows: First, based on the phosphate buffer system, 9.47 g of Na2HPO4 (disodium hydrogen phosphate) and 9.08 g of KH2PO4 (potassium dihydrogen phosphate) were respectively dissolved in 1000 mL of ultrapure water to prepare two stock mother liquors; then, the mother liquors were mixed in equal volumes of 10 mL, and a high-precision commercial pH meter was used for real-time monitoring. Through the dynamic titration method (dropwise addition of 1 M HCl or 1 M NaOH), the pH of the buffer solution was precisely adjusted to the target gradient value (±0.02 error range) to ensure the stoichiometric accuracy of the test system and provide a standardized environment for subsequent sensor calibration.

[0103] The miniaturized low-profile flexible marine galvanic pH sensor of the example was attached to the surface of a 500 μm thick PET flexible bracket, and then the bracket was placed in a beaker, and the prepared phosphate buffer solution with a pH value of 3 - 10 was poured into the beaker. Using a three-electrode system, the first wire part of the working electrode and the second wire part of the reference electrode in the flexible galvanic pH sensor were respectively connected to the corresponding electrodes of the electrochemical workstation, and a platinum plate electrode was used as the counter electrode. Continuously tested for 150 s in the open-circuit voltage mode of the electrochemical workstation, and the steady-state voltage data of the last 40 s were intercepted to construct the sensor response curve, as Figure 10 shown. The output voltage has a linear relationship with the pH value, and the fitting equation is: y = -72.76x + 889.70, with a sensitivity of 72.76 mV / pH, which is 39.9% higher than that of the traditional electrochemical oxidation process.

[0104] Furthermore, the dynamic response characteristics were tested in a simulated high-flow marine environment (pH = 8) with a flow rate of 3 m / s ( Figure 11) The voltage signal change time (90% - 10%) only needs 16.84 s, and the recovery time (10% - 90%) is shortened to 12.15 s, proving the interfacial stability of the sensor under fluid shear force. Long-term monitoring data ( Figure 12 ) shows that the potential drift of pH 7.4 / 8.6 / 9.5 solutions within 30 days is less than 5 mV, and after 1000 bending tests with a 3 mm radius of curvature ( Figure 13 ), the sensitivity only decays by 3.74% (70.04 mV / pH), highlighting its mechanical reliability.

[0105] The flexible marine galvanic pH sensor described in the present invention breaks through the thickness limitation of traditional rigid devices (reduced by 99%), can conformally adhere to the curved surface of marine equipment, and provides core technical support for building a high spatio-temporal resolution ocean acidification monitoring network.

[0106] The above embodiments only represent several implementation manners of the present invention. The description is relatively specific and detailed, but it should not be construed as a limitation on the scope of the invention patent. It should be noted that for those of ordinary skill in the art, without departing from the concept of the present invention, several modifications and improvements can still be made, and these all belong to the protection scope of the present invention. Therefore, the protection scope of the present invention patent shall be subject to the appended claims.

Claims

1. A miniaturized low-profile flexible marine galvanic pH sensor, characterized in that The miniaturized low-profile flexible marine galvanic pH sensor includes a flexible polyimide substrate, a working electrode system, and a reference electrode system. The working electrode system and the reference electrode system are disposed on the flexible polyimide substrate, and the working electrode system and the reference electrode system are spaced apart. The working electrode system includes an iridium oxide working electrode (1), a first metal conduction circuit layer (2), and a first metal pad (3). The iridium oxide working electrode (1) is connected to the first metal pad (3) through the first metal conduction circuit layer (2). The iridium oxide working electrode (1) is a laminated structure formed by a metal adhesion layer Cr, a metal adhesion layer Pt, and an iridium oxide sensing layer from bottom to top. The reference electrode system includes a reference electrode (4), a second metal conduction circuit layer (5), and a second metal pad (6). The reference electrode (4) is connected to the second metal pad (6) through the second metal conduction circuit layer (5). The reference electrode (4) is a laminated structure formed by a metal adhesion layer Cr, a metal adhesion layer Ag, a reference electrode layer AgCl, a KCl agarose layer, and a semi-permeable membrane from bottom to top.

2. The miniaturized low-profile flexible marine galvanic pH sensor according to claim 1, characterized in that The materials of the first metal conduction circuit layer (2) and the first metal pad (3) are platinum Pt or copper Cu, and the thickness of the first metal conduction circuit layer (2) is 150 - 200 nm.

3. The miniaturized low-profile flexible marine galvanic pH sensor according to claim 1, characterized in that The thickness of the flexible polyimide substrate is 2 μm.

4. The miniaturized low-profile flexible marine galvanic pH sensor according to claim 1, characterized in that In the iridium oxide working electrode (1), the thickness of the metal adhesion layer Cr is 10 - 30 nm, the thickness of the metal adhesion layer Pt is 120 - 150 nm, and the thickness of the iridium oxide sensing layer is 150 - 220 nm.

5. The miniaturized low-profile flexible marine galvanic pH sensor according to claim 1, characterized in that The materials of the second metal conduction circuit layer (5) and the second metal pad (6) are platinum Pt or copper Cu, and the thickness of the second metal conduction circuit layer (5) is 150 - 200 nm.

6. The miniaturized low-profile flexible marine galvanic pH sensor according to claim 1, wherein In the reference electrode (4), the thickness of the metal adhesion layer Cr is 10 - 30 nm, the thickness of the metal adhesion layer Ag is 120 - 180 nm, the thickness of the reference electrode layer AgCl is 150 - 180 nm, the thickness of the KCl agarose layer is 1 - 2 μm, and the thickness of the semi-permeable membrane is 200 nm.

7. The preparation method of the miniaturized low-profile flexible marine galvanic pH sensor according to claim 1, characterized in that The preparation method of the miniaturized low-profile flexible marine galvanic pH sensor is realized according to the following steps: Step 1: Copper electrode magnetron sputtering process Cover the first mask on the flexible polyimide substrate, expose the areas of the first metal conduction circuit layer (2), the first metal pad (3), the second metal conduction circuit layer (5), and the second metal pad (6), use a copper target, and adopt magnetron sputtering process to sputter and form the first metal conduction circuit layer (2), the first metal pad (3), the second metal conduction circuit layer (5), and the second metal pad (6). Step 2: Chromium adhesion layer magnetron sputtering process Cover the second mask on the flexible polyimide substrate, expose the areas of the iridium oxide working electrode (1) and the reference electrode (4), use a chromium target, and adopt magnetron sputtering process to sputter and form the metal adhesion layer chromium Cr of the iridium oxide working electrode (1) and the reference electrode (4). Step 3: Platinum conductive layer magnetron sputtering process Cover the third mask on the flexible polyimide substrate, exposing the area of the iridium oxide working electrode (1). Using a platinum target, a metal adhesion layer of platinum Pt is sputtered on the chromium Cr metal adhesion layer of the iridium oxide working electrode (1) by magnetron sputtering process; Step 4. Magnetron sputtering process of silver reference layer Cover the fourth mask on the flexible polyimide substrate, exposing the area of the reference electrode (4). Using a silver target, a metal adhesion layer of silver Ag is sputtered on the chromium Cr metal adhesion layer of the reference electrode (4) by magnetron sputtering process; Step 5. In-situ construction of Ag / AgCl reference electrode Adopt a two-electrode system, using the metal adhesion layer Ag prepared in Step 4 as the working electrode and a platinum sheet electrode as the reference electrode. In a 0.1 mol / L HCl solution, electrochemical anodic oxidation treatment of the working electrode is carried out by constant current deposition method to form a silver chloride layer on the surface of the metal adhesion layer Ag. After rinsing, it is immersed in a KCl solution for aging treatment to form a reference electrode layer AgCl; Step 6. Electrodeposition and strengthening of the IrO x sensitive layer A three - electrode system is adopted. The metal adhesion layer Pt prepared in Step 3 is used as the working electrode, the reference electrode layer AgCl prepared in Step 5 is used as the reference electrode, and a platinum sheet electrode is used as the auxiliary electrode. Cyclic voltammetry is used for electrodeposition in the plating solution to form an amorphous IrO x layer on the metal adhesion layer Pt, and then heat - induced crystallization treatment is carried out at 300 °C to obtain an iridium oxide sensing layer; Step 7. Construction of KCl agarose interface layer Add agarose powder to a 3.0 mol / L KCl electrolyte solution, stir in a water bath at 85 ± 5 °C until completely dissolved to form a transparent sol. When the temperature is lowered to the critical temperature of sol-gel transition, it is drop-coated on the surface of the reference electrode layer AgCl, and after cooling and solidifying, a KCl agarose layer is formed; Step 8. Integration of semi-permeable membrane and device encapsulation Cover the KCl agarose layer with a cellulose semi-permeable membrane and encapsulate it with a polyimide tape. Windows are respectively opened at the iridium oxide working electrode (1) and the reference electrode (4) to obtain a miniaturized low-profile flexible marine galvanic pH sensor.

8. The preparation method of the miniaturized low-profile flexible marine galvanic pH sensor according to claim 7, characterized in that In Step 5, the constant current deposition method is adopted, the polarization current is 0.5 mA, and the electrochemical anodic oxidation treatment of the working electrode is carried out for 20 min.

9. The preparation method of the miniaturized low-profile flexible marine galvanic pH sensor according to claim 7, characterized in that The preparation process of the plating solution in Step 6 is as follows: Dissolve 0.12 g of iridium tetrachloride IrCl4·H2O in 80 ml of distilled water and stir evenly. Add 0.8 ml of 30% wt H2O2, stir and then add 0.12 g of oxalic acid. Adjust the pH of the system to 10.5 by adding potassium carbonate to obtain a deposition solution. The deposition solution is placed in a dry and dark place for 56 - 60 h to obtain a plating solution.

10. The preparation method of the miniaturized low-profile flexible marine galvanic pH sensor according to claim 7, characterized in that The thermally induced crystallization treatment time in Step 6 is 4 - 6 hours.

Images