A process for preparing an EGFET-based pH sensor

Abstract

The application discloses a preparation process of an EGFET-based pH sensor and belongs to the fields of electrochemistry and semiconductor physics, and comprises the following steps: EGFET conductive substrate preparation, pH sensitive film preparation, pH sensitive particle preparation and EGFET device lead packaging. A high-cost-performance Ti nano layer is used as a lower electrode conductive layer of the EGFET, and a Ta target or a Ta2O5 target is used to prepare a Ta2O5 sensitive film material. The preparation process of the EGFET-based pH sensor overcomes the defects of a traditional pH meter, such as long response time, poor long-term stability, use of fragile glass products and dependence on liquid. Meanwhile, the technical problem that the product performance stability and the preparation cost are difficult to balance in the preparation process of a traditional sensor is solved.

Description

Technical Field

[0001] This invention relates to the fields of electrochemistry and semiconductor physics, and more particularly to a fabrication process for a pH sensor based on EGFET. Background Technology

[0002] Human life, and the life activities of other organisms on Earth, are inseparable from the aquatic environment. The pH level of water is crucial for the life activities of organisms, including animals, plants, and various microorganisms. The acidity or alkalinity of a solution is quantified using pH values. According to the definition of pH, The pH value of an aqueous solution is determined by the amount of H+ in the solution. + The concentration of H+ in a solution. Traditional pH measurement techniques mainly involve pH test strips and pH meters based on glass bulb electrodes. pH test strips are divided into wide-range test strips (measuring range pH = 1–14, accurate to 1 pH) and precision test strips (measuring in intervals, accurate to 0.1 pH). pH test strips are for single use only, and exceeding the measurement range will render the strip invalid. Glass electrode pH meters are based on the Nernst equation to measure the concentration of H+ in a solution. + Using a reference electrode with no activity response as a baseline, the quantization glass electrode is used to measure the H+ in the test solution. + The activity of the pH meter is measured by a galvanometer, which amplifies the potential difference and displays the analytical results. Glass electrode pH meters offer high accuracy, but due to the unavoidable use of glass in their components and the presence of multiple solutions inside, glass breakage and leakage may occur during transportation and use, increasing the difficulty and obstacles to transportation and use.

[0003] Ion-Sensitive Field Effect Transistors (ISFETs), based on Metal-Oxide-Semiconductor Field-Effect Transistors (MOSFETs), use a gate insulating material with ion-selective capabilities to replace the metal gate. Compared to traditional pH electrodes, ISFETs offer advantages such as high sensitivity, high selectivity, and long-term stability, along with shorter response times. They can be integrated into arrays to simultaneously and quantitatively detect multiple ions, demonstrating significant market potential in industries such as pharmaceuticals, agriculture, food, and the environment.

[0004] Chinese Patent Publication No. CN108565262A discloses an array-type sensor integrated chip for biochemical analysis and its fabrication method. This invention, on the one hand, configures an ISFET sensor with a mirror-symmetric REFET field-effect transistor, and shares the reference electrode of both transistors on the center line of symmetry, allowing the sensitive response of the REFET field-effect transistor to serve as a reference. On the other hand, by providing each ISFET sensor with a separate liquid sample receiving hole, the elevation of the hole wall effectively hinders the flow of adjacent sample solutions. However, the aforementioned ISFET sensor requires two mirror-symmetric field-effect transistors, and ensuring that the reference electrodes of both transistors are positioned on the center line of symmetry results in high manufacturing costs and stringent transistor positioning requirements, making production inconvenient. Furthermore, this sensor requires the use of a solution; during use, the ISFET chip structure must be immersed in the solution being measured, posing a challenge to the isolation and sealing between the device and the solution.

[0005] Chinese Patent Publication No. CN 112179956 B discloses a method for fabricating a MEMS formaldehyde sensor based on an aluminum-doped zinc oxide porous nanofilm. The sensor, from bottom to top, consists of a SiO2-Si3N4 masking layer, a Si substrate, an insulating layer consisting of a double layer of SiO2-Si3N4, a heating electrode, a sensitive electrode, a temperature-measuring electrode, a sensitive material, and a noble metal dopant. Polystyrene microspheres are used as the masking layer. The diameter of the microspheres is adjusted using oxygen plasma etching. A composite sensitive film is deposited between the reduced-diameter microspheres using magnetron co-sputtering of ZnO and Al2O3. The microstructure of the composite film is adjusted by controlling the sputtering power, time, substrate temperature, and sputtering pressure during the ZnO and Al2O3 sputtering process. The aluminum-doped zinc oxide film is doped and its surface modified using Pd noble metal. However, the aforementioned sensor fabrication method uses ZnO and Al2O3 as composite sensitive films. Since Al2O3 is an amphoteric oxide, it is easily corroded in acidic and alkaline environments and has poor chemical stability. Furthermore, the use of Pd noble metal for doping and surface modification of the aluminum-doped zinc oxide film increases the fabrication cost. Moreover, because ZnO and Al2O3 are the main electrode materials, their conductivity is poor. While Pd noble metal is used to modify the surface of ZnO and Al2O3 to enhance conductivity and improve sensor sensitivity, if the sputtered deposition thickness of the Pd noble metal is too thin or the Pd noble metal layer cannot be uniformly covered, good conductivity and sensor sensitivity cannot be guaranteed. If the sputtered deposition thickness is too thick, it will increase the fabrication cost. Furthermore, the bonding strength between the Pd noble metal and the ZnO and Al2O3 oxide layers needs to be ensured, further increasing the difficulty and cost of sensor fabrication. In addition, the aforementioned bonding layer is relatively fragile during use and is easily scratched and damaged due to improper handling. Summary of the Invention

[0006] To overcome the shortcomings of existing technologies, the technical problem this invention aims to solve is to propose a pH sensor fabrication process based on EGFETs. This process, based on extended gate field-effect transistors, enables the fabrication of a high-performance, high-stability pH sensor, overcoming the drawbacks of traditional pH meters such as long response time, poor long-term stability, use of fragile glass components, and reliance on liquids. Simultaneously, it solves the technical challenge of balancing product performance stability and fabrication cost in traditional sensor fabrication processes.

[0007] To achieve this objective, the present invention adopts the following technical solution:

[0008] The present invention provides a fabrication process for a pH sensor based on EGFET, comprising the following steps:

[0009] EGFET conductive substrate preparation: After dust removal and cleaning of the silicon wafer, a Ti nanolayer electrode is deposited on the single-sided surface of the silicon wafer by plasma magnetron sputtering to form an EGFET conductive substrate.

[0010] pH-sensitive film preparation: A Ta2O5 sensitive film was deposited on the lower electrode of the Ti nanolayer using a Ta-containing target on the EGFET conductive substrate by plasma magnetron sputtering to form a pH-sensitive film.

[0011] Preparation of pH-sensitive particles: The pH-sensitive membrane is cut to obtain pH-sensitive particles;

[0012] EGFET device lead packaging: After electrically connecting the gate of MOSFET chip 4 to electrode 1 under Ti nanolayer, it is encapsulated to form a pH sensor.

[0013] A preferred embodiment of the present invention is that the pH sensor includes a PCB board 3 and a MOSFET chip 4 disposed on the PCB board 3.

[0014] The drain of the MOSFET chip is fixed to a pad on the PCB board by silver paste;

[0015] The source of the MOSFET chip is connected to another pad on the PCB board via an ultrasonic bonding wire;

[0016] The gate of the MOSFET chip is connected to the electrode under the Ti nanolayer via ultrasonic bonding wire.

[0017] The preferred embodiment of this invention is that the process parameters for depositing the lower electrode of the Ti nanolayer by plasma magnetron sputtering on a silicon wafer are as follows:

[0018] The sputtering power is 80W to 150W, the sputtering working gas is high-purity argon, and the sputtering working gas pressure is 0.0060 Torr to 0.0100 Torr.

[0019] The thickness of the Ti nanolayer electrode deposited by plasma magnetron sputtering is ≥29 nm.

[0020] The preferred embodiment of the present invention is that the Ta-containing target material is a Ta target;

[0021] The process parameters for coating using a Ta target on an EGFET conductive substrate are as follows:

[0022] The working gas is a mixture of O2 and Ar, wherein the flow ratio of O2 to Ar is 5:95 to 30:70;

[0023] The total gas flow rate is 30 sccm to 100 sccm, and the power is 30 W to 200 W.

[0024] The preferred embodiment of the present invention is that the Ta-containing target is a Ta2O5 target;

[0025] The process parameters for coating using a Ta2O5 target on an EGFET conductive substrate are as follows:

[0026] The working gas is a mixture of O2 and Ar, with an O2 flow rate of 0 sccm to 30 sccm, a total gas flow rate of 30 sccm to 80 sccm, and a power of 30 W to 130 W.

[0027] The preferred technical solution of the present invention is to remove dust and clean the silicon wafer, including: firstly, removing dust from the surface of the monocrystalline silicon wafer using a high-pressure nitrogen gun, and then cleaning the silicon wafer using the RCA cleaning method.

[0028] The preferred technical solution of the present invention is to cut the pH-sensitive film, including: cutting the pH-sensitive film with a diamond cutter or a laser scribing machine, and cutting the pH-sensitive film into individual pH-sensitive particles according to the size designed by the mask template.

[0029] The preferred technical solution of the present invention is that the window size of the mask template is 50μm×50μm~5mm×5mm.

[0030] The preferred technical solution of the present invention is that the thickness of the Ta2O5 sensitive film is 60nm to 200nm.

[0031] A preferred embodiment of the present invention is that the MOSFET chip and the pH-sensitive particle are respectively encapsulated with encapsulating adhesive to form a pH sensor, wherein the encapsulating adhesive is silicone or epoxy resin.

[0032] The beneficial effects of this invention are as follows:

[0033] 1. This invention uses a cost-effective Ti nanolayer as the lower electrode conductive layer of EGFET. The cost is lower than that of precious metals such as Au and Pt, the performance is better than that of conductive oxides, and it can form an ohmic contact with sensitive materials.

[0034] 2. Using a Ta2O5 target, a Ta2O5 sensitive membrane material with controllable oxygen vacancies was prepared; using a metallic Ta target, the oxygen vacancies concentration in the Ta2O5 sensitive membrane was controlled by adjusting the O2:Ar ratio in the working gas, and the optimal performance of the Ta2O5 sensitive membrane material was formulated.

[0035] 3. The device contains no aqueous solution or glassware and can be reused. Attached Figure Description

[0036] Figure 1 This is a schematic diagram of the principle of an EGFET pH sensor in the prior art, where V DS V represents the drain voltage. Ref This represents the reference electrode voltage.

[0037] Figure 2 This is a schematic flowchart of the fabrication process of the pH sensor based on EGFET provided in a specific embodiment of the present invention.

[0038] Figure 3 This is a schematic diagram of the pH sensor in Embodiment 1 of the present invention.

[0039] Figure 4 This is a partially enlarged cross-sectional view of the pH-sensitive particulate material in Embodiment 1 of the present invention.

[0040] Figure 5 This is a schematic diagram of the voltammetric transfer curves measured multiple times in different pH solutions by the pH sensor in Embodiment 1 of the present invention, where the horizontal axis V GS Represents voltage, ordinate i D Represents electric current.

[0041] Figure 6 This is a schematic diagram illustrating the sensitivity and linearity of the pH sensor in Embodiment 1 of the present invention, where the horizontal axis pH represents the acidity or alkalinity of the solution, and the vertical axis V GS Represents voltage.

[0042] Figure 7 This is a schematic diagram of the pH sensor in Embodiment 2 of the present invention.

[0043] Figure 8 This is a schematic diagram of the voltammetric transfer curves obtained by the pH sensor in different pH solutions in Embodiment 2 of the present invention, where the horizontal axis V GS Represents voltage, ordinate i D Represents electric current.

[0044] Figure 9 This is a schematic diagram illustrating the sensitivity and linearity of the pH sensor in Embodiment 2 of the present invention, where pH represents the acidity or alkalinity of the solution, and the vertical axis V GS Represents voltage.

[0045] Figure 10 This is a schematic diagram of the voltammetric transfer curves of a pH sensor using Pt as the conductive electrode in different pH solutions measured multiple times, where the horizontal axis V GS Represents voltage, ordinate i D Represents electric current.

[0046] Figure 11 This is a schematic diagram of the voltammetric transfer curves of a pH sensor using ITO as the conductive electrode in different pH solutions measured multiple times, where the horizontal axis V... GS Represents voltage, ordinate i D Represents electric current.

[0047] In the picture:

[0048] 1. Ti nanolayer electrode; 2. Ta2O5 sensitive film; 3. PCB board; 4. MOSFET chip; 5. MOSFET chip assembly; 51. Source; 52. Gate; 53. Drain; 6. pH sensitive material assembly; 7. Reference electrode. Detailed Implementation

[0049] The technical solution of the present invention will be further described below with reference to the accompanying drawings and specific embodiments.

[0050] like Figures 1 to 11 As shown, in order to reduce the manufacturing cost of pH sensors, make the performance of sensitive materials more stable, reduce the manufacturing difficulty, and make the sensors reusable, usable outside of liquids, with high product strength, good long-term stability, and greater durability, this embodiment further provides a pH sensor manufacturing process based on EGFET. The pH sensor manufacturing process includes the following steps:

[0051] (S1) EGFET conductive substrate preparation: After dust removal and cleaning of the silicon wafer, Ti nanolayer lower electrode 1 is deposited on the single-surface of the silicon wafer by plasma magnetron sputtering to form EGFET conductive substrate.

[0052] (S2) pH-sensitive film preparation: On the EGFET conductive substrate, a Ta2O5 sensitive film 2 is deposited on the Ti nanolayer lower electrode 1 using a plasma magnetron sputtering method with a Ta-containing target through a mask to form a pH-sensitive film.

[0053] (S3) Preparation of pH-sensitive particles: The pH-sensitive film is cut to obtain pH-sensitive particles;

[0054] (S4) EGFET device lead packaging: After the gate of MOSFET chip 4 is electrically connected to the electrode 1 under the Ti nanolayer, it is encapsulated to form a pH sensor.

[0055] In step (S1), the preparation of the pH-sensitive material requires a clean and dust-free environment; otherwise, the device will fail. Therefore, the silicon wafer needs to be cleaned by dust removal and washing.

[0056] In practical testing, the selection of the lower electrode metal material is also crucial, as it relates to the stability of material properties, preparation cost, and preparation difficulty. In this application, Ti was chosen as the optimal choice for the lower electrode metal material based on the following aspects:

[0057] First, compared to precious metals such as Pt and Au, Ti metal has a lower cost. Second, Ti metal has a higher Mohs hardness (6.0), significantly better than Au (2.5) and Pt (3.5), making the device less prone to scratches and damage during use. Third, the conductivity of the Ti metal layer (resistivity 0.0234×10⁻⁶) is relatively high. -6 The resistivity ( / Ωcm) is superior to that of electro-oxide FTO (resistivity 4.3×10). -3 / Ωcm) or ITO (resistivity 1.0×10 -2 / Ωcm), etc.; Fourth, due to the intrinsic oxygen defect of Ta2O5, it will exhibit N-type conductive semiconductor. The work function of Ti metal (4.33eV) is lower than the Fermi level of Ta2O5 (4.4eV), which makes it easy to form ohmic contacts and ensures better conductivity.

[0058] In existing technologies, pH-sensitive materials are generally SiO2, Al2O3, Si3N4, Ta2O5, and SnO2. The selection of the pH-sensitive material is crucial in practical testing, as it affects parameters such as sensitivity, drift, and hysteresis. In this application, Ta2O5 is chosen as the optimal pH-sensitive material because: SiO2 has relatively low sensitivity (approximately 40 mV / pH); Si3N4 has high sensitivity (53–55 mV / pH), but also significant drift (1 mV / h); Al2O3 and Ta2O5 both have high sensitivity (56–59 mV / pH), and their drift is only 0.1–0.2 mV / h. Considering that Al2O3 is an amphoteric oxide and Ta2O5 has strong resistance to acid and alkali corrosion, Ta2O5, which has a sensitivity close to the Nernst limit (59.16 mV / pH) and the best stability (drift of 0.03 to 0.05 pH / day), was selected here.

[0059] Based on this, step (S2) is adopted, since the coordination difference between O and Ta can form a semiconductor, and a Ta2O5 sensitive film 2 can be deposited by bombarding the Ta-containing target with plasma.

[0060] In step (S3), the silicon wafer after being coated with Ta2O5 sensitive film 2 forms a pH sensitive film, which can be cut into individual pH sensitive material particles according to the size designed by the mask template on a diamond cutter or laser scribing machine.

[0061] In step (S4), the MOSFET chip 4 and pH-sensitive particles are connected and installed, and then encapsulated with encapsulating glue to ensure better isolation and sealing performance between the device and the solution, improve the device's resistance to acid and alkali corrosion, and ensure good long-term stability.

[0062] Through the above process, the voltammetric transfer curves of the conductive electrode of the pH sensor in this application are more concentrated in multiple measurements in different pH solutions, indicating better device stability. This results in lower manufacturing costs, more stable performance of sensitive materials, and reduced manufacturing difficulty for the pH sensor. Furthermore, the sensor is reusable, can be used without liquid, has high product strength, good long-term stability, and is more durable.

[0063] Preferably, in step (S4), the pH sensor includes a PCB board 3, and a MOSFET chip 4 is disposed on the PCB board 3. The drain of the MOSFET chip 4 is fixed to a pad on the PCB board 3 with silver paste. The source of the MOSFET chip 4 is connected to another pad on the PCB board 3 via an ultrasonic bonding wire. The gate of the MOSFET chip 4 is connected to the Ti nanolayer electrode 1 via an ultrasonic bonding wire. The coverage area of ​​the Ta2O5 sensing film 2 is smaller than the area of ​​the Ti nanolayer electrode 1, so that the gate of the MOSFET chip 4 can be connected to the Ti nanolayer electrode 1 via the ultrasonic bonding wire, achieving good conductivity. Through the above process, the MOSFET chip 4, the pH sensing particle, and the PCB board 3 are interconnected and assembled, and then encapsulated with encapsulating adhesive to ensure better isolation and sealing performance between the device and the solution, improve the device's resistance to acid and alkali corrosion, and enhance long-term stability.

[0064] Preferably, in step (S1), the process parameters for the lower electrode 1 of the plasma magnetron sputtering deposition of the Ti nanolayer on the silicon wafer are as follows:

[0065] The sputtering power is 80W to 150W, the sputtering working gas is high-purity argon, and the sputtering working gas pressure is 0.0060 Torr to 0.0100 Torr.

[0066] The plasma magnetron sputtering deposition thickness of the Ti nanolayer under electrode 1 is ≥29 nm.

[0067] Ti metal thin films can be deposited on silicon wafers by bombarding Ti-containing targets with plasma to form Ti nanolayer electrodes 1, wherein the power is preferably 80W to 150W.

[0068] In this application, the plasma magnetron sputtering deposition thickness of the electrode 1 under the Ti nanolayer is preferably not less than 29 nm. Based on the continuous metal film resistivity ρ F With the resistivity ρ of bulk metal B The functional relationship between the film thickness d and the film thickness d

[0069] ρ F = B [1+3λ(1-P) / 8]

[0070] Where λ is the mean free path of the electron, and P is the specular reflection coefficient. Neglecting elastic scattering, i.e., complete diffuse reflection of electrons at the thin film surface (spectral reflection coefficient P = 0), when d = λ, ρ F Ratio ρ B The increase is approximately 40%. For Ti material, λ is approximately 29 nm. In this application, the minimum plasma magnetron sputtering deposition thickness of electrode 1 under the Ti nanolayer is set to 29 nm. This is because if the thickness is less than 29 nm, the resistance will increase, leading to severe heat generation and thus reducing device sensitivity.

[0071] Meanwhile, for thinner Ti metal films, the effect of surface scattering on the film resistivity cannot be underestimated. In practical films, P≠0; therefore, for the same film, improving surface smoothness and increasing the value of P can reduce the film resistivity.

[0072] Preferably, in step (S2), the Ta-containing target material is a Ta target;

[0073] The process parameters for coating the conductive substrate of EGFET using a Ta target are as follows:

[0074] The working gas is a mixture of O2 and Ar, wherein the flow ratio of O2 to Ar is 5:95 to 30:70;

[0075] The total gas flow rate is 30 sccm to 100 sccm, and the power is 30 W to 200 W.

[0076] A Ta2O5 sensitive film 2 can be deposited by bombarding a Ta target with plasma. The preferred power is 60W to 150W. This is because excessive power can easily damage the Ti nanolayer that serves as the conductive substrate, while insufficient power will result in too few Ta particles generated by plasma bombardment of the Ta target, making it difficult to effectively form the Ta2O5 sensitive film 2 on the EGFET conductive substrate.

[0077] Meanwhile, the total gas flow rate is preferably 30 sccm to 100 sccm. This is because if the flow rate is too low, there will be less plasma bombarding the target material, which will not be able to effectively generate the required Ta particles, resulting in a low film deposition rate. If the flow rate is too high, the collision between sputtered Ta particles will be enhanced, leading to a decrease in the actual deposition rate.

[0078] Preferably, in step (S2), the Ta-containing target is a Ta2O5 target;

[0079] The process parameters for coating using a Ta2O5 target on an EGFET conductive substrate are as follows:

[0080] The working gas is a mixture of O2 and Ar, with an O2 flow rate of 0 sccm to 30 sccm, a total gas flow rate of 30 sccm to 80 sccm, and a power of 30 W to 130 W.

[0081] A Ta2O5 sensitive film 2 can be deposited by bombarding a Ta2O5 target with plasma. The power is preferably 60W to 120W. This is because excessive power can easily damage the Ta2O5 ceramic target, while insufficient power will result in too few plasmas bombarding the Ta2O5 target, making it difficult to effectively deposit the Ta2O5 sensitive film 2 on the EGFET conductive substrate.

[0082] Meanwhile, the working gas is high-purity argon, and oxygen can be introduced when oxygen defects need to be regulated. The O2 flow rate is 0 sccm to 30 sccm, and the total gas flow rate is preferably 30 sccm to 80 sccm. In particular, when the O2 flow rate is 0 sccm, the working gas is high-purity argon, and oxygen defects generally exist in the deposited Ta2O5 film under these conditions.

[0083] Preferably, in step (S1), the silicon wafer is dusted and cleaned, including: firstly, using a high-pressure nitrogen gun to remove dust from the surface of the monocrystalline silicon wafer, and then using the RCA cleaning method to clean the silicon wafer. By employing the above dust removal and cleaning steps, the silicon wafer is ensured to be clean and free of contamination, thereby ensuring the detection sensitivity of the material.

[0084] Preferably, in step (S3), the pH-sensitive film is cut, including: cutting the pH-sensitive film using a diamond cutter or laser scribing machine, and cutting the pH-sensitive film into individual pH-sensitive particles according to the dimensions designed in the photomask. Through the above steps, the user can cut the pH-sensitive film into pH-sensitive material particles of corresponding specifications according to actual usage needs.

[0085] Preferably, in step (S2), the window size of the photomask is 50μm×50μm to 5mm×5mm. Users can limit the size of the sensing material by setting different window sizes of the photomask according to actual usage requirements.

[0086] Preferably, in step (S2), the thickness of the Ta2O5 sensitive film 2 is 60 nm to 200 nm. The thickness of the Ta2O5 sensitive film 2 has a significant impact on the performance of the device; therefore, in this application, the thickness of the Ta2O5 sensitive film 2 is preferably 60 nm to 200 nm.

[0087] Preferably, in step (S4), the MOSFET chip 4 and the pH-sensitive particle are encapsulated with encapsulating adhesive to form a pH sensor. The encapsulating adhesive is silicone or epoxy resin. Silicone or epoxy resin has stable chemical properties and can be used to encapsulate components such as the MOSFET chip 4 and the pH-sensitive particle, ensuring better isolation and sealing performance between the device and the solution, improving the device's resistance to acid and alkali corrosion, and providing good long-term stability. Different embodiments are given below to further illustrate the present invention.

[0088] Example 1

[0089] In Example 1, PCB board 3 is designed for testing purposes, such as... Figure 3 As shown, a MOSFET chip 4 is placed in the center of the circuit board. In this example, an N-channel enhancement-mode field-effect transistor (EMT) chip is used. The drain of the MOSFET chip 4 is bonded to the pads on the PCB board 3 using silver paste, and the source of the MOSFET chip 4 is connected to the PCB board 3 using an Al wire from an ultrasonic welding machine. Dust particles on the surface of the 4-inch p-type single-layer polished silicon wafer are blown away using a handheld high-pressure nitrogen gun, and then the wafer is thoroughly cleaned using the RCA cleaning method. Figure 4 As shown, an 85nm Ti nanolayer under-electrode 1 was deposited on a silicon wafer using plasma magnetron sputtering at a sputtering power of 100W and a working gas of high-purity argon at a pressure of 0.0080 Torr. A 175nm thick Ta2O5 sensitive film 2 was deposited on the EGFET conductive substrate using a 4mm × 5mm mask and a Ta2O5 ceramic target. The Ta2O5 target deposition process involved high-purity argon as the working gas, a total gas flow rate of 50 sccm, and a power of 80W. After deposition, the silicon wafer was diced into 4×5mm individual pH-sensitive material particles using a laser dicing machine. Ultrasonic bonding wires were used to connect the Ti nanolayer under-electrode 1 of the EGFET to the gate of the MOSFET chip 4. The N-type MOSFET chip 4 and the Ta2O5 sensitive film 2 were encapsulated in silicone with a sensitive window size of 3mm × 4mm.

[0090] The device was placed in pH buffer solutions with pH values ​​of 2, 4, 6, 8, 10, and 12, and the transfer curves of the EGFET were tested, where V DS =0.1V, repeated 5 times in each solution, results as follows Figure 5 As shown, the horizontal axis V GS Represents voltage, ordinate i D Represents electric current.

[0091] in I DS =Read V at 100uA GS (i.e. V) th The analysis revealed a sensitivity of 59.04 mV / pH and a linearity of [missing information]. Figure 6 As shown, the horizontal axis pH represents the acidity or alkalinity of the solution, and the vertical axis V... GS Represents voltage.

[0092] like Figure 5-6 as well as Figure 10-11 As shown, by comparing the transfer curves of the Ti-based pH sensor in Example 1 with those of the Pt or ITO-based pH sensors, it can be seen that the existing pH sensors using Pt or ITO as conductive electrodes exhibit more dispersed voltammetric transfer curves in different pH solutions, indicating poor device stability. In contrast, the pH sensor in Example 1 using Ti as a conductive electrode shows more concentrated voltammetric transfer curves from multiple measurements in different pH solutions, indicating better device stability.

[0093] Example 2

[0094] In Example 2, dust particles on the surface of a 4-inch N-type (100) single-layer polished silicon wafer were first removed using a handheld high-pressure nitrogen gun, followed by thorough cleaning using the RCA cleaning method. A 125nm Ti nanolayer electrode 1 was deposited on the silicon wafer using plasma magnetron sputtering at a power of 120W and a high-purity argon gas pressure of 0.0070 Torr. A 105nm thick Ta₂O₅ sensitive film 2 was deposited on the EGFET conductive substrate using a 4mm×4mm mask and a Ta metal target. The coating process using the Ta target involved a 20:80 O₂:Ar mixed gas flow rate of 70 sccm and a power of 100W. After coating, the silicon wafer was cut into 4mm×4mm individual pH-sensitive material particles according to the dimensions designed in the mask using a diamond cutter. The design is as follows: Figure 7 On the PCB board 3 shown, the drain of the N-type MOSFET chip 4 is fixed to the pad on the back with silver paste, and the source of the MOSFET chip 4 is connected to another pad using an Al wire from an ultrasonic bonding machine. Using an ultrasonic bonding machine, the under-Ti nanolayer electrode 1 of the EGFET is connected to the gate of the MOSFET chip 4. The N-type MOSFET chip 4 and the Ta2O5 sensing film 2 are encapsulated with epoxy resin, with a sensing window of 2mm × 3mm.

[0095] The device was placed in pH buffer solutions of pH = 4.00, 6.86, and 9.18 to test the transfer curves of the EGFET, where V DS=0.1V, repeated 5 times in each solution, results as follows Figure 8 As shown, where the horizontal axis V GS Represents voltage, ordinate i D Represents electric current.

[0096] in I DS =Read V at 100uA GS (i.e. V) th The analysis showed that its sensitivity was 55.28 mV / pH, and its repeatability was good. Figure 9 As shown, the horizontal axis pH represents the acidity or alkalinity of the solution, and the vertical axis V... GS Represents voltage.

[0097] like Figure 8-11 As shown, by comparing the transfer curves of the Ti-based pH sensor in Example 2 with those of the Pt or ITO-based pH sensors, it can be seen that the existing pH sensors using Pt or ITO as conductive electrodes exhibit more dispersed voltammetric transfer curves in different pH solutions, indicating poor device stability. In contrast, the pH sensor in Example 2, using Ti as the conductive electrode, shows more concentrated voltammetric transfer curves across multiple measurements in different pH solutions, indicating better device stability.

[0098] The difference between Example 2 and Example 1 lies in the different Ta target materials used and the different coating process parameters. The stability of the pH sensors prepared by both examples is better than that of pH sensors using Pt or ITO as conductive electrodes in the prior art.

[0099] In this application, silicon wafers are preferably selected as the substrate for the pH-sensitive device, but other rigid or flexible materials can also be used as the pH-sensitive substrate. Specifically, quartz, glass, and other materials can be used as rigid substrate materials, while PI, PET, and other materials can be used as flexible substrate materials.

[0100] This application preferably uses plasma magnetron sputtering to prepare Ti thin films to form Ti nanolayer electrode 1. Alternatively, Ti thin films can be prepared using methods such as electron beam evaporation.

[0101] This invention has been described through preferred embodiments. Those skilled in the art will understand that various changes or equivalent substitutions can be made to these features and embodiments without departing from the spirit and scope of the invention. This invention is not limited to the specific embodiments disclosed herein; other embodiments falling within the scope of the claims are also within the protection scope of this invention.

[0102] It should be noted that any reference signs placed between parentheses in the claims should not be construed as limiting the claims. The word "comprising" does not exclude the presence of components or steps not listed in the claims. The word "a" or "an" preceding a component does not exclude the presence of a plurality of such components. The invention can be implemented by means of hardware comprising several different components and by means of a suitably programmed computer. In a unit claim enumerating several means, several of these means may be embodied by the same item of hardware. The use of the words first, second, and third, etc., does not indicate any order. These words can be interpreted as names.

[0103] Although preferred embodiments of the invention have been described, those skilled in the art, upon learning the basic inventive concept, can make other changes and modifications to these embodiments. Therefore, the appended claims are intended to be interpreted as including both the preferred embodiments and all changes and modifications falling within the scope of the invention.

[0104] Obviously, those skilled in the art can make various modifications and variations to this invention without departing from its spirit and scope. Therefore, if these modifications and variations fall within the scope of the claims of this invention and their equivalents, this invention also intends to include these modifications and variations.

[0105] In this invention, unless otherwise explicitly specified and limited, the terms "installation," "connection," "linking," and "fixing," etc., should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0106] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the present invention. In this specification, the illustrative expressions of the above terms should not be construed as necessarily referring to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0107] The above description is only a preferred embodiment of the present invention. All equivalent changes and modifications made within the scope of the claims of the present invention should be included in the scope of the present invention.

Claims

1. A fabrication process for a pH sensor based on EGFET, characterized in that, The pH sensor fabrication process includes the following steps: After dust removal and cleaning of the silicon wafer, a Ti nano-layer lower electrode (1) is deposited on the single-surface of the silicon wafer by plasma magnetron sputtering to form an EGFET conductive substrate, wherein the plasma magnetron sputtering deposition thickness of the Ti nano-layer lower electrode (1) is ≥29nm; A pH-sensitive film (2) was deposited on the Ti nanolayer under electrode (1) by plasma magnetron sputtering on the EGFET conductive substrate using a Ta-containing target material through a mask. The pH-sensitive film was then cut to obtain pH-sensitive particles. After the gate of the MOSFET chip (4) is electrically connected to the Ti nanolayer lower electrode (1), the pH sensor is formed by encapsulation. The coverage area of ​​the Ta2O5 sensitive film (2) is smaller than the area of ​​the Ti nanolayer lower electrode (1) so that the gate of the MOSFET chip (4) can be connected to the Ti nanolayer lower electrode (1) through ultrasonic pressure welding wire to achieve good conductivity.

2. The fabrication process of the pH sensor based on EGFET according to claim 1, characterized in that: The pH sensor includes a PCB board (3), and the MOSFET chip (4) is disposed on the PCB board (3); The drain of the MOSFET chip (4) is fixed to a pad on the PCB board (3) by silver paste; The source of the MOSFET chip (4) is connected to another pad on the PCB board (3) via an ultrasonic welding lead; The gate of the MOSFET chip (4) is connected to the lower electrode (1) of the Ti nanolayer via ultrasonic welding wire.

3. The fabrication process of the pH sensor based on EGFET according to claim 1, characterized in that: The process parameters for plasma magnetron sputtering deposition of the Ti nanolayer lower electrode (1) on the silicon wafer are as follows: The sputtering power is 80W to 150W, the sputtering working gas is high-purity argon, and the sputtering working gas pressure is 0.0060 Torr to 0.0100 Torr.

4. The fabrication process of the pH sensor based on EGFET according to claim 1, characterized in that: The Ta-containing target material is a Ta target; The process parameters for coating the EGFET conductive substrate using the Ta target are as follows: The working gas is a mixture of O2 and Ar, wherein the flow ratio of O2 to Ar is 5:95 to 30:70; The total gas flow rate is 30 sccm to 100 sccm, and the power is 30 W to 200 W.

5. The fabrication process of the pH sensor based on EGFET according to claim 1, characterized in that: The Ta-containing target is a Ta2O5 target; The process parameters for coating the EGFET conductive substrate using the Ta2O5 target are as follows: The working gas is a mixture of O2 and Ar, with an O2 flow rate of 0 sccm to 30 sccm, a total gas flow rate of 30 sccm to 80 sccm, and a power of 30 W to 130 W.

6. The fabrication process of the pH sensor based on EGFET according to claim 1, characterized in that: Dust removal and cleaning of silicon wafers include: First, a high-pressure nitrogen gun is used to remove dust from the surface of the monocrystalline silicon wafer, and then the RCA cleaning method is used to clean the silicon wafer.

7. The fabrication process of the pH sensor based on EGFET according to claim 1, characterized in that: Cutting the pH-sensitive film includes: The pH-sensitive film is cut using a diamond cutter or a laser scribing machine, and the film is cut into individual pH-sensitive particles according to the dimensions designed by the photomask.

8. The fabrication process of the pH sensor based on EGFET according to claim 1, characterized in that: The window size of the mask template is 50μm×50μm to 5mm×5mm.

9. The fabrication process of the pH sensor based on EGFET according to claim 1, characterized in that: The thickness of the Ta2O5 sensitive film (2) is 60nm to 200nm.

10. The fabrication process of the pH sensor based on EGFET according to claim 1, characterized in that: The MOSFET chip (4) and the pH-sensitive particles are respectively encapsulated with encapsulating adhesive to form the pH sensor; The encapsulating adhesive is silicone or epoxy resin.

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