Miniaturized low profile flexible marine galvanic ph sensor and method of making same

Abstract

The application discloses a miniaturized low-profile flexible marine galvanic pH sensor and a preparation method thereof, and aims at solving the problems of large profile thickness and insufficient reliability of the existing flexible pH sensor. In the miniaturized low-profile flexible marine galvanic pH sensor, a working electrode system and a reference electrode system are arranged on a flexible polyimide substrate, the working electrode system comprises an iridium oxide working electrode, a first metal conductive circuit layer and a first metal pad, the iridium oxide working electrode is connected with the first metal pad through the first metal conductive circuit layer, the reference electrode system comprises a reference electrode, a second metal conductive circuit layer and a second metal pad, and the reference electrode is connected with the second metal pad through the second metal conductive circuit layer. The nano-crystalline iridium oxide sensing layer is used to significantly improve the pH response performance, the sensitivity reaches 72.76 mV / pH, and the fast response of 16.84 s is realized in a 3 m / s high-flow marine environment.

Description

Technical Field

[0001] This application claims priority to Chinese Patent Application No. CN202510507422.6, filed on April 22, 2025. This invention belongs to the field of marine monitoring sensor technology, specifically relating to a miniaturized, low-profile, flexible marine electrocouple-type pH sensor and its fabrication method. Background Technology

[0002] Traditional marine pH monitoring relies primarily on columnar sediment sampling and laboratory titration analysis, which suffers from poor timeliness and inability to capture dynamic environmental changes. While existing in-situ sensors employ photometry or glass electrode technology, their large size (typically >50 cm³) and rigid packaging make integration into underwater vehicles difficult. For example, while iridium oxide thin-film-based pH sensors exhibit hydrogen ion sensitivity, their thickness design lacks systematic optimization, leading to passivation after prolonged immersion (drift >10 mV / month), and ion diffusion boundary layer disruption under high flow rates can cause response distortion (error >0.1 pH). Furthermore, traditional electrocoupled sensors often use rigid substrates, lacking conformal bonding capabilities, and are prone to stress cracking when mounted on curved surfaces, severely hindering the miniaturization of deep-sea exploration equipment.

[0003] While flexible pH sensors have achieved deformation adaptability through polyimide substrates in recent years, they still face two major bottlenecks: first, the interfacial bonding strength between the sensitive membrane and the flexible electrode is insufficient, leading to delamination and failure after repeated bending; second, factors such as chloride ion penetration and biofouling in the marine environment cause a decrease in selectivity. Existing technologies, such as CN104914150B, use graphene / polyaniline composite membranes to improve sensitivity, but fail to solve the signal stability problem under dynamic flow velocities; CN 119534582 A utilizes a breathable and moisture-permeable flexible nanofiber substrate to set the polyaniline sensitive layer, but the profile thickness increases to over 50 μm, which cannot meet the requirements for low profile (<6 μm). Therefore, there is an urgent need to develop a flexible pH sensor that combines miniaturization, anti-interference, and high reliability to overcome the technical barriers of in-situ monitoring in the complex hydrodynamic environment of the ocean. Summary of the Invention

[0004] This invention addresses the problem of large profile thickness and insufficient reliability of existing flexible pH sensors by providing a miniaturized, low-profile flexible marine electrocouple pH sensor and its fabrication method. This electrocouple pH sensor features miniaturization, low profile, and good flexibility, and can be used for long-term real-time pH detection in marine environments while ensuring good hydrogen ion response.

[0005] The miniaturized low-profile flexible marine electrocouple pH sensor of the present invention includes a flexible polyimide substrate, a working electrode system and a reference electrode system, wherein the working electrode system and the reference electrode system are disposed on the flexible polyimide substrate and are spaced apart.

[0006] The working electrode system includes iridium oxide (IrO). x The iridium oxide working electrode consists of a working electrode, a first metal conductive circuit layer, and a first metal pad. The iridium oxide working electrode is connected to the first metal pad through the first metal conductive circuit layer. The iridium oxide working electrode is composed of, from bottom to top, a Cr metal adhesion layer, a Pt metal adhesion layer, and iridium oxide (IrO). x The sensing layer forms a stacked structure;

[0007] The reference electrode system includes a reference electrode, a second metal conductive circuit layer, and a second metal pad. The reference electrode is connected to the second metal pad through the second metal conductive circuit layer. The reference electrode is a stacked structure formed from bottom to top 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.

[0008] The method for fabricating the miniaturized low-profile flexible marine electrocouple pH sensor of the present invention is carried out according to the following steps:

[0009] Step 1: Copper Electrode Magnetron Sputtering Process

[0010] A mask is placed on a flexible polyimide substrate to expose the areas of the first metal conductive circuit layer, the first metal pad, the second metal conductive circuit layer, and the second metal pad. A copper target is used to sputter the first metal conductive circuit layer, the first metal pad, the second metal conductive circuit layer, and the second metal pad using a magnetron sputtering process.

[0011] Step 2: Magnetron sputtering process for chromium adhesion layer

[0012] A second mask was placed on a flexible polyimide substrate to expose the areas of the iridium oxide working electrode and the reference electrode. A chromium target was used, and a magnetron sputtering process was employed to sputter the metal adhesion layer Cr of the iridium oxide working electrode and the reference electrode.

[0013] Step 3: Magnetron sputtering process for platinum conductive layer

[0014] Mask No. 3 was placed on a flexible polyimide substrate to expose the area of ​​the iridium oxide working electrode. Using a platinum target, a metal adhesion layer Pt was sputtered on the metal adhesion layer Cr of the iridium oxide working electrode using a magnetron sputtering process.

[0015] Step 4: Magnetron sputtering process for silver reference layer

[0016] Mask No. 4 was placed on the flexible polyimide substrate to expose the area of ​​the reference electrode. Using a silver target, a metal adhesion layer Ag was sputtered on the metal adhesion layer Cr of the reference electrode using a magnetron sputtering process.

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

[0018] A two-electrode system was adopted, with the metal adhesion layer Ag prepared in step four as the working electrode and the platinum sheet electrode as the reference electrode. In 0.1 mol / L HCl solution, the electrochemical working electrode was oxidized by constant current deposition to form a silver chloride layer on the surface of the metal adhesion layer Ag. After rinsing, it was immersed in KCl solution for aging treatment to form the reference electrode layer AgCl.

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

[0020] A three-electrode system was used, with the Pt metal adhesion layer prepared in step three as the working electrode, the AgCl reference electrode layer prepared in step five as the reference electrode, and a platinum sheet electrode as the auxiliary electrode. Amorphous IrO was formed on the Pt metal adhesion layer by electrodeposition in the plating bath using cyclic voltammetry. x The layer is then thermally crystallized at 300 °C to obtain the iridium oxide sensing layer;

[0021] Step 7: Construction of KCl agarose interface layer

[0022] Add agarose powder to 3.0 mol / L KCl electrolyte and stir in a water bath at 85±5 ℃ until completely dissolved to form a transparent sol. When cooled to the critical temperature of sol-gel transition (48±2 ℃), drop it onto the surface of the reference electrode layer AgCl. After cooling and solidification, a KCl agarose layer is formed.

[0023] Step 8: Semi-permeable membrane integration and device packaging

[0024] A miniaturized, low-profile, flexible marine electrocouple pH sensor was obtained by covering a KCl agarose layer with a cellulose semipermeable membrane and encapsulating it with polyimide tape, with windows opened at the iridium oxide working electrode and the reference electrode.

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

[0026] 1. Combining high sensitivity and stability: Nanocrystalline iridium oxide (IrO) prepared by magnetron sputtering and electrochemical deposition processes xThe sensing layer significantly improves 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). It also achieves a rapid response of 16.84 s in a high-velocity marine environment of 3 m / s and a potential drift of less than 5 mV over 30 days of long-term monitoring, overcoming the shortcomings of traditional sensors in signal instability in dynamic fluid environments.

[0027] 2. Miniaturization and Flexible Structure Innovation: By adopting a 2 μm ultrathin 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 Cr / Pt or Cr / Ag multilayer metal stack design, the performance degradation is less than 4% after 1000 bending tests (curvature radius 3 mm). It can be closely attached to the curved surface of marine equipment to realize in-situ monitoring in complex environments.

[0028] 3. Mass production and high efficiency: Based on magnetron sputtering and UV-LIGA micromachining technology, wafer-level sensor arrays can be manufactured with small thickness deviations between metal and functional layers, improved batch consistency compared to traditional processes, and a single-process yield of over 95%, providing reliable technical support for the large-scale deployment of marine monitoring networks. Attached Figure Description

[0029] Figure 1 This is a schematic diagram of mask number one;

[0030] Figure 2 This is a schematic diagram of mask number two;

[0031] Figure 3 This is a schematic diagram of mask number three;

[0032] Figure 4 This is a schematic diagram of mask number four;

[0033] Figure 5 This is a structural diagram of the miniaturized low-profile flexible marine electrocouple pH sensor before packaging in an embodiment of the present invention;

[0034] Figure 6 Iridium oxide (IrO) x )Structural diagram of the working electrode system;

[0035] Figure 7 Iridium oxide (IrO) x Longitudinal cross-sectional view of the working electrode system;

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

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

[0038] Figure 10 This is a voltage test diagram of the flexible marine electrocouple pH sensor in an embodiment of the present invention at different pH values;

[0039] Figure 11 The image shows the rapid response of the flexible marine electrocouple pH sensor, as an example, in a high-velocity marine environment (pH=8) at 16.84 s.

[0040] Figure 12 A graph showing the potential drift test of a flexible marine electrocouple pH sensor over a 30-day long-term monitoring period, as illustrated in this embodiment.

[0041] Figure 13 The image shows the performance degradation test results of the flexible marine electrocouple pH sensor used in this embodiment after 1000 bending tests (curvature radius 3 mm). Detailed Implementation

[0042] Specific Implementation Method 1: The miniaturized low-profile flexible marine electrocouple pH sensor of this implementation method 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 are spaced apart.

[0043] The working electrode system includes iridium oxide (IrO). x The iridium oxide working electrode 1 consists of a working electrode 1, a first metal conductive 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 conductive circuit layer 2. The iridium oxide working electrode 1 is composed of a metal adhesion layer Cr, a metal adhesion layer Pt, and iridium oxide (IrO) from bottom to top. x The sensing layer forms a stacked structure;

[0044] The reference electrode system includes a reference electrode 4, a second metal conductive 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 conductive circuit layer 5. The reference electrode 4 is a stacked structure formed from bottom to top 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.

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

[0046] In this embodiment, there is no conductive contact between the working electrode circuit system and the reference electrode circuit system; the low-profile flexible marine electrocouple pH sensor has reserved an iridium oxide sensing window and a reference electrode liquid interface window, and is encapsulated with 1μm thick polyimide tape.

[0047] In this embodiment, the total thickness of the flexible marine electrocouple pH sensor does not exceed 6 μm.

[0048] Specific Implementation Method Two: This implementation method differs from Specific Implementation Method One in that the materials of the first metal conductive circuit layer 2 and the first metal pad 3 are platinum (Pt) or copper (Cu), and the thickness of the first metal conductive circuit layer 2 is 150~200 nm.

[0049] Specific Implementation Method 3: This implementation method differs from Specific Implementation Method 1 or 2 in that the thickness of the flexible polyimide substrate is 2 μm.

[0050] Specific Implementation Method Four: This implementation method differs from Specific Implementation Methods One to Three in 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] Specific Implementation Method 5: This implementation method differs from Specific Implementation Methods 1 to 4 in that the material of the second metal conductive circuit layer 5 and the second metal pad 6 is platinum (Pt) or copper (Cu), and the thickness of the second metal conductive circuit layer 5 is 150-200 nm.

[0052] Specific Implementation Method Six: This implementation method differs from Specific Implementation Methods One to Five in 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 semipermeable membrane is 200 nm.

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

[0054] Specific Implementation Method Seven: The preparation method of the miniaturized low-profile flexible marine electrocouple pH sensor in this embodiment is carried out according to the following steps:

[0055] Step 1: Copper Electrode Magnetron Sputtering Process

[0056] A mask is placed on a flexible polyimide substrate to expose the areas of the first metal conductive circuit layer 2, the first metal pad 3, the second metal conductive circuit layer 5, and the second metal pad 6. The first metal conductive circuit layer 2, the first metal pad 3, the second metal conductive circuit layer 5, and the second metal pad 6 are formed by sputtering using a copper target and a magnetron sputtering process.

[0057] Step 2: Magnetron sputtering process for chromium adhesion layer

[0058] A second mask was placed on a flexible polyimide substrate to expose the areas of the iridium oxide working electrode 1 and the reference electrode 4. A chromium target was used, and a magnetron sputtering process was employed to sputter the metal adhesion layer Cr of the iridium oxide working electrode 1 and the reference electrode 4.

[0059] Step 3: Magnetron sputtering process for platinum conductive layer

[0060] Mask No. 3 was placed on the flexible polyimide substrate to expose the area of ​​the iridium oxide working electrode 1. Using a platinum target, a metal adhesion layer Pt was formed on the metal adhesion layer Cr of the iridium oxide working electrode 1 by magnetron sputtering.

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

[0062] Mask No. 4 was placed on the flexible polyimide substrate to expose the area of ​​reference electrode 4. Using a silver target, a metal adhesion layer Ag was sputtered on the metal adhesion layer Cr of reference electrode 4 using a magnetron sputtering process.

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

[0064] A two-electrode system was adopted, with the metal adhesion layer Ag prepared in step four as the working electrode and the platinum sheet electrode as the reference electrode. In 0.1 mol / L HCl solution, the electrochemical working electrode was oxidized by constant current deposition to form a silver chloride layer on the surface of the metal adhesion layer Ag. After rinsing, it was immersed in KCl solution for aging treatment to form the reference electrode layer AgCl.

[0065] Step Six, IrO x Electrodeposition and strengthening of sensitive layer

[0066] A three-electrode system was used, with the Pt metal adhesion layer prepared in step three as the working electrode, the AgCl reference electrode layer prepared in step five as the reference electrode, and a platinum sheet electrode as the auxiliary electrode. Amorphous IrO was formed on the Pt metal adhesion layer by electrodeposition in the plating bath using cyclic voltammetry. x The layer is then thermally crystallized at 300 °C to obtain the iridium oxide sensing layer;

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

[0068] Add agarose powder to 3.0 mol / L KCl electrolyte and stir in a water bath at 85±5 ℃ until completely dissolved to form a transparent sol. When cooled to the critical temperature of sol-gel transition (48±2 ℃), drop it onto the surface of the reference electrode layer AgCl. After cooling and solidification, a KCl agarose layer is formed.

[0069] Step 8: Semi-permeable membrane integration and device packaging

[0070] A miniaturized, low-profile, flexible marine electrocouple pH sensor was obtained by covering a KCl agarose layer with a cellulose semipermeable membrane and encapsulating it with polyimide tape. Windows were opened at the iridium oxide working electrode 1 and the reference electrode 4, respectively.

[0071] The No. 1, No. 2, No. 3 and No. 4 masks described in this embodiment are all made using UV-LIGA micromachining technology.

[0072] Specific Implementation Method Eight: This implementation method differs from Specific Implementation Method Seven in that step five uses a constant current deposition method with a polarization current of 0.5 mA and an electrochemical anodic electrode oxidation treatment for 20 min.

[0073] Specific Implementation Method Nine: This implementation method differs from Specific Implementation Methods Seven or Eight in that the preparation process of the plating solution in step six is ​​as follows:

[0074] 0.12 g of iridium tetrachloride (IrCl4·H2O) was dissolved in 80 ml of distilled water and stirred until homogeneous. Then, 0.8 ml of 30%wt H2O2 was added and stirred, followed by the addition of 0.12 g of oxalic acid. The pH of the system was adjusted to 10.5 by adding potassium carbonate, resulting in a (golden yellow) precipitate. The precipitate was placed in a dry, dark place for 56–60 h to allow the IrCl4·H2O to precipitate. 3+ The complex is converted to [Ir(OH)5Cl] 2- Active ions are used to obtain the plating solution.

[0075] Specific Implementation Method 10: This implementation method differs from Specific Implementation Methods 7 to 9 in that the thermal crystallization treatment time in step 6 is 4 to 6 hours.

[0076] Example: The fabrication method of the miniaturized low-profile flexible marine electrocouple pH sensor in this example is carried out according to the following steps:

[0077] Step 1: Copper Electrode Magnetron Sputtering Process

[0078] Mask No. 1 (e.g.) Figure 1 The electrode pattern (as shown) covers a flexible polyimide substrate, exposing the areas of the first metal conductive circuit layer 2, the first metal pad 3, the second metal conductive circuit layer 5, and the second metal pad 6. A copper target is used, and a magnetron sputtering process is employed, with a vacuum level of 5×10⁻⁶. -7After Torr, high-purity argon gas (99.999%) is introduced to the working pressure of 5 mTorr. Under the condition of a target-substrate distance of 70 mm, 150 W DC power is applied to excite the plasma. The deposition rate is monitored in real time and stabilized at 0.8 nm / s. Sputtering is continued for 40 min to form a copper electrode layer. After the process is completed, the pressure is gradually released to atmospheric pressure to avoid interface peeling caused by sudden stress change in the film layer, thereby obtaining the first metal conductive circuit layer 2, the first metal pad 3, the second metal conductive circuit layer 5, and the second metal pad 6.

[0079] Step 2: Magnetron sputtering process for chromium adhesion layer

[0080] Apply the second mask (such as...) Figure 2 The electrode pattern shown is applied to a flexible polyimide substrate, exposing the areas of the iridium oxide working electrode 1 and the reference electrode 4. A chromium target is used, and a magnetron sputtering process is employed. The vacuum chamber is evacuated to 5 × 10⁻⁶. -7 Torr, argon working pressure maintained at 5 mTorr, short-time sputtering (5 min) was performed under target-substrate distance of 70 mm and DC power of 100 W to obtain an ultrathin chromium layer. The sputtering formed the metal adhesion layer Cr of the iridium oxide working electrode 1 and the reference electrode 4. This adhesion layer formed a strong interfacial bond with the polyimide substrate through Cr-O chemical bonds (adhesion force > 30 MPa), providing an anchoring basis for the subsequent metal layer.

[0081] Step 3: Magnetron sputtering process for platinum conductive layer

[0082] Apply the third mask (as shown) Figure 3 The electrode pattern shown is covered on a flexible polyimide substrate, exposing the area of ​​the iridium oxide working electrode 1. A platinum target is used, and a magnetron sputtering process is employed. An argon atmosphere of 5 mTorr and a target-substrate distance of 70 mm are maintained. The deposition is carried out continuously at 100 W power for 30 min to form a metal adhesion layer Pt on the metal adhesion layer Cr of the iridium oxide working electrode 1. During the sputtering process, the substrate is rotated (10 rpm) to ensure the uniformity of the film thickness (deviation < ±3%). Finally, a high conductivity interface with a sheet resistance of 0.15 Ω / sq is obtained, which meets the low impedance transmission requirements of flexible devices.

[0083] Step 4: Magnetron sputtering process for silver reference layer

[0084] Apply mask number four (such as...) Figure 4The electrode pattern shown is applied to a flexible polyimide substrate, exposing the area of ​​reference electrode 4. A silver target is used, and magnetron sputtering is employed, maintaining a 5 mTorr argon atmosphere and a 70 mm target-substrate distance. Deposition is carried out continuously at 100 W for 30 min, sputtering to form a metal adhesion layer Ag on the Cr metal adhesion layer of reference electrode 4. This layer serves as the precursor for the Ag / AgCl reference electrode, which is subsequently electrochemically oxidized to generate a silver chloride active layer (Cl). - Doping concentration > 1×10 21 cm -3 This achieves a stable reference potential output (drift < 0.5 mV / h).

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

[0086] A two-electrode system was used, with the Ag metal adhesion layer prepared in step four as the working electrode and a platinum sheet electrode as the reference electrode. Electrochemical oxidation of the working electrode was performed in a 0.1 mol / L HCl solution using a constant current polarization deposition method, applying a constant current of 0.5 mA for 20 min. The oxidation was achieved 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 for 24 h to age, causing Cl to form inside the AgCl layer. - Concentration gradient (from surface to interior, 5 × 10⁻⁶) 20 Up to 1×10 22 cm -3 Finally, a highly stable reference electrode with an open-circuit potential drift of <0.3 mV / h was obtained, forming a reference electrode layer AgCl;

[0087] Step Six, IrO x Electrodeposition and strengthening of sensitive layer

[0088] The first metal conductive circuit layer connected to the iridium oxide working electrode system, the first metal pad connected to the first metal conductive circuit layer, the second metal conductive circuit layer connected to the reference electrode system, and the second metal pad connected to the second metal conductive circuit layer are covered with Teflon to prevent electroplating.

[0089] (1) Plating solution formulation: Dissolve 0.12 g of iridium tetrachloride (IrCl4·H2O) in 80 ml of distilled water and add it to a three-necked flask. Stir thoroughly with a magnetic stirrer at room temperature 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-yellow precipitate. Place the freshly prepared precipitate in a dry, light-protected place for 72 h to allow the IrCl4·H2O to precipitate. 3+ The complex is converted to [Ir(OH)5Cl] 2- Active ions should be used after the sedimentation solution turns blue-black.

[0090] (2) Electroplating method: A three-electrode system was used. The working electrode was the platinum electrode prepared in step three, the reference electrode was the silver chloride electrode prepared in step five, and the auxiliary electrode was a platinum sheet electrode. 60 ml of deposition solution was added to a 100 ml beaker. The cyclic voltammetry scan range was set to 0.2 V to 0.75 V, and the scan rate was 50 mV·s. -1 Amorphous IrO was obtained by scanning 100 cycles. x layer;

[0091] (3) Thermally induced crystallization: The temperature was increased to 300 ℃ at a gradient of 5 ℃ / min and held for 5 h to promote IrO crystallization. x The transformation from amorphous to nanocrystalline state enhances the film-substrate bonding strength, and then the layer is cooled to 25 °C to obtain an iridium oxide sensing layer.

[0092] The nanocrystalline iridium oxide sensing layer formed by electroplating in this invention has significant advantages over the iridium oxide sensing layer deposited by magnetron sputtering. Electrochemical deposition can achieve more uniform IrO at lower temperatures. x Thin film growth promotes the growth of nanocrystalline iridium oxide (IrO). x It possesses a higher surface area and better electrochemical activity, thereby improving the sensor's sensitivity. Furthermore, the hydrated iridium oxide (IrO) formed by electroplating... x Compared to non-hydrated iridium oxide obtained by magnetron sputtering, the presence of water molecules in its structure significantly improves electronic conductivity and reactivity, thereby enhancing the adsorption and conversion efficiency of hydrogen ions. Electrochemically deposited hydrated iridium oxide (IrO) x It exhibits 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 ℃ until completely dissolved to form a transparent sol. When the solution is cooled to the critical temperature for sol-gel transition (48±2 ℃), it is precisely dripped onto the surface of Ag / AgCl electrode using a microsyringe to control the thickness of the gel layer. After natural cooling and solidification, a three-dimensional interpenetrating network structure (pore size 0.5~1.2 μm) is formed, realizing controllable ion exchange between the internal electrolyte and the external environment, forming a KCl agarose layer.

[0095] Step 8: Semi-permeable membrane integration and device packaging

[0096] An agarose layer was coated with a 500 Da molecular weight cutoff cellulose semipermeable membrane, and square IrO with a side length of 800 μm was simultaneously formed on the polyimide tape using laser micromachining (wavelength 355 nm). x The sensing window and the circular reference electrode liquid interface window with a diameter of 1000 μm are finally encapsulated with 1 μm thick polyimide tape with the window opened to form a leak-proof barrier. After encapsulation, a miniaturized low profile flexible marine electrocouple pH sensor is obtained.

[0097] In this embodiment, the flexible substrate is polyimide, with dimensions of 1 cm × 2.2 cm and a thickness of 2 μm. Masks one through four were fabricated using UV-LIGA micromachining technology. The copper layer has a thickness of 165 nm, the chromium layer 17 nm, the platinum layer approximately 134 nm, and the silver layer 143 nm. The working electrode, iridium oxide, has a thickness of 180 nm, the reference electrode, silver chloride, has a thickness of 172 nm, the KCl agarose has a thickness of 1.3 μm, and the semi-permeable membrane has a thickness of 200 nm, for a total thickness of 5.0 μm.

[0098] like Figure 5 The diagram shown is a structural image of the miniaturized low-profile flexible marine electrocouple pH sensor prepared in this embodiment before encapsulation. This miniaturized low-profile flexible marine electrocouple pH sensor includes a flexible polyimide substrate and a working electrode system and a reference electrode system spaced apart on the surface of the flexible polyimide substrate. The working electrode circuit system includes: iridium oxide (IrO₂). x Working electrode system 1; with iridium oxide (IrO) x The reference electrode circuit system includes: a first metal conductive circuit layer 2 connected to the working electrode system; a first metal pad 3 connected to the first metal conductive circuit layer; and a reference electrode circuit system including: a reference electrode system 4; a second metal conductive circuit layer 5 connected to the reference electrode system; and a second metal pad 6 connected to the second metal conductive circuit layer.

[0099] Figure 6 Iridium oxide (IrO) x The working electrode system structure diagram includes: a metal adhesion layer Cr bonded to a flexible polyimide substrate, a metal adhesion layer Pt disposed on the metal adhesion layer Cr, and iridium oxide (IrO) disposed on the metal adhesion layer Pt. x Sensing layer.

[0100] Figure 7 The image shows iridium oxide (IrO). x A longitudinal cross-sectional view of the working electrode system, from bottom to top, shows: a Cr metal adhesion layer, a Pt metal adhesion layer, and an iridium oxide (IrO) layer. x The sensing layer consists of a Cr / Pt metal stack that achieves an interfacial contact resistance of <0.5 Ω / sq using gradient sputtering. This design leverages the electron tunneling effect of the Pt conductive layer and the interaction between the Pt and IrO layers. x The synergistic effect of proton coupling redox properties enables the sensor to achieve an ultra-Nernst response sensitivity of 72.76 mV / pH, while ensuring the electrochemical stability of the flexible substrate under 3 mm curvature (sensitivity decay of <4% after 1000 cycles).

[0101] Figure 8 The diagram shows the structure of a reference electrode system, which includes: a metal adhesion layer Cr bonded to a flexible polyimide substrate, a metal adhesion layer Ag disposed on the metal adhesion layer Cr, and a silver chloride (AgCl) reference electrode layer disposed on the metal adhesion layer Ag. Figure 9 The diagram shows a longitudinal cross-section of the reference electrode system. From bottom to top, the layers are: a Cr metal adhesion layer, an Ag metal adhesion layer, a silver chloride (AgCl) reference electrode layer, a 3 mol / L KCl agarose gel electrolyte layer, and a 500 Da molecular weight cutoff semi-permeable membrane. The Cr / Ag stack achieves nanoscale interfacial bonding through magnetron sputtering, while the AgCl layer provides a stable reference potential. After curing, the KCl agarose gel forms a three-dimensional porous network (porosity >80%), which both prevents internal electrolyte leakage and maintains ion conductivity pathways. The surface semi-permeable membrane selectively allows H₂ to pass through through size exclusion effects. + With Cl - (permeability rate compared to Na) + / K + (Two orders of magnitude higher), effectively shielding seawater from Ca. 2+ Mg 2+ It also mitigates interference from organic macromolecules, ensuring the long-term stability of the potential signal (30-day drift <5mV).

[0102] The miniaturized low-profile flexible marine electrocouple pH sensor prepared in the examples was tested across pH values ​​(3.0~10.0). The specific operation procedure is as follows: First, based on the phosphate buffer system, 9.47 g Na2HPO4 (disodium hydrogen phosphate) and 9.08 g KH2PO4 (potassium dihydrogen phosphate) were dissolved in 1000 mL of ultrapure water to prepare two stock solutions. Then, the stock solutions were mixed in equal volumes of 10 mL. The pH of the buffer solution was monitored in real time using a high-precision commercial pH meter. The pH of the buffer solution was precisely adjusted to the target gradient value (±0.02 error range) by dynamic titration (adding 1M HCl or 1M NaOH dropwise) 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 electrocouple pH sensor of this embodiment was attached to the surface of a 500 μm thick PET flexible support. The support was then placed in a beaker, and a prepared phosphate buffer solution with a pH of 3-10 was poured into the beaker. A three-electrode system was used, with the first lead of the working electrode and the second lead of the reference electrode of the flexible electrocouple pH sensor connected to their corresponding electrodes on an electrochemical workstation. A platinum sheet electrode was used as the counter electrode. Continuous testing was performed for 150 seconds in open-circuit voltage mode on the electrochemical workstation. The steady-state voltage data for the last 40 seconds was then used to construct the sensor response curve, as shown below. Figure 10 As shown, the output voltage exhibits a linear relationship with pH value, with the fitted equation being: y = -72.76x + 889.70, achieving a sensitivity of 72.76 mV / pH, which is 39.9% higher than that of traditional electrochemical oxidation processes.

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

[0105] The flexible marine electrocouple-type pH sensor described in this invention breaks through the thickness limitations of traditional rigid devices (reducing thickness by 99%), and can be conformally attached to the curved surface of marine equipment, providing core technical support for building a high spatiotemporal resolution marine acidification monitoring network.

[0106] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the protection scope of the present invention. Therefore, the protection scope of this invention patent should be determined by the appended claims.

Claims

1. A method for fabricating a miniaturized, low-profile, flexible marine electrocouple-type pH sensor, characterized in that... The fabrication method of the miniaturized low-profile flexible marine electrocouple pH sensor is carried out according to the following steps: Step 1: Copper Electrode Magnetron Sputtering Process A mask is placed on a flexible polyimide substrate to expose the area of ​​the first metal conductive circuit layer (2), the first metal pad (3), the second metal conductive circuit layer (5), and the second metal pad (6). The first metal conductive circuit layer (2), the first metal pad (3), the second metal conductive circuit layer (5), and the second metal pad (6) are formed by sputtering using a copper target and a magnetron sputtering process. Step 2: Magnetron sputtering process for chromium adhesion layer The second mask was placed on the flexible polyimide substrate to expose the area of ​​the iridium oxide working electrode (1) and the reference electrode (4). Using a chromium target, a chromium Cr metal adhesion layer was sputtered to form the iridium oxide working electrode (1) and the reference electrode (4) using a magnetron sputtering process. Step 3: Magnetron sputtering process for platinum conductive layer The No. 3 mask was placed on the flexible polyimide substrate to expose the area of ​​the iridium oxide working electrode (1). Using a platinum target, a platinum metal adhesion layer was formed on the chromium (Cr) metal adhesion layer of the iridium oxide working electrode (1) by magnetron sputtering. Step 4: Magnetron sputtering process for silver reference layer The No. 4 mask was placed on the flexible polyimide substrate to expose the area of ​​the reference electrode (4). Using a silver target, a silver Ag metal adhesion layer was sputtered on the chromium Cr metal adhesion layer of the reference electrode (4) using a magnetron sputtering process. Step 5: In-situ construction of the Ag / AgCl reference electrode A two-electrode system was adopted, with the metal adhesion layer Ag prepared in step four as the working electrode and the platinum sheet electrode as the reference electrode. The electrochemical working electrode was oxidized by constant current deposition in 0.1 mol / L HCl solution to form a silver chloride layer on the surface of the metal adhesion layer Ag. After rinsing, it was immersed in KCl solution for aging treatment to form the reference electrode layer AgCl. Step Six, IrO x Electrodeposition and strengthening of sensitive layer A three-electrode system was used, with the Pt metal adhesion layer prepared in step three as the working electrode, the AgCl reference electrode layer prepared in step five as the reference electrode, and a platinum sheet electrode as the auxiliary electrode. Amorphous IrO was formed on the Pt metal adhesion layer by electrodeposition in the plating bath using cyclic voltammetry. x The layer is then thermally crystallized at 300 °C to obtain the iridium oxide sensing layer; Step 7: Construction of KCl agarose interface layer Add agarose powder to 3.0 mol / L KCl electrolyte, stir in a water bath at 85±5 ℃ until completely dissolved to form a transparent sol, cool to the critical temperature of sol-gel transition, drop it onto the surface of the reference electrode layer AgCl, and cool and solidify to form a KCl agarose layer; Step 8: Semi-permeable membrane integration and device packaging A miniaturized, low-profile, flexible marine electrocouple pH sensor was obtained by covering a KCl agarose layer with a cellulose semipermeable membrane and encapsulating it with polyimide tape. Windows were opened at the working electrode (1) and the reference electrode (4) of the iridium oxide.

2. The method for fabricating the miniaturized low-profile flexible marine electrocouple pH sensor according to claim 1, characterized in that... In step five, a constant current deposition method was used, with a polarization current of 0.5 mA, and the electrochemical anodic working electrode was oxidized for 20 min.

3. The method for fabricating the miniaturized low-profile flexible marine electrocouple pH sensor according to claim 1, characterized in that... The preparation process of the plating solution in step six is ​​as follows: Dissolve 0.12 g of iridium tetrachloride (IrCl4·H2O) in 80 ml of distilled water and stir until homogeneous. Add 0.8 ml of 30%wt H2O2 and stir. Then add 0.12 g of oxalic acid and adjust the pH of the system to 10.5 by adding potassium carbonate to obtain the deposition solution. Place the deposition solution in a dry, light-protected place for 56-60 h to obtain the plating solution.

4. The method for fabricating the miniaturized low-profile flexible marine electrocouple pH sensor according to claim 1, characterized in that... The thermal crystallization treatment in step six takes 4 to 6 hours.

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