Ion sensing system of monolithic three-dimensional integrated differential amplification circuit and preparation method thereof

Abstract

The application discloses a kind of monolithic three-dimensional integrated differential amplification circuit ion sensing system and preparation method thereof, belong to MEMS technical field, including differential amplification circuit and ion-sensitive field effect transistor, by setting molybdenum disulfide layer in differential amplification circuit, and ion-sensitive field effect transistor is set on molybdenum disulfide layer, through the two ion-sensitive membranes set on two gates synchronous work under differential amplification circuit, one ion-sensitive membrane senses ion signal in the liquid to be measured, another ion-sensitive membrane senses environmental noise, through ion-sensitive field effect transistor and differential amplification circuit, the difference of two end output signals is extracted and amplified, while retaining target ion response signal, environmental noise is inhibited, high-precision, high-sensitivity detection to target ion concentration is realized;And the whole ion sensing system only occupies the area of two FETs, reduces chip plane area, realizes the chip-level miniaturization and high integration of ion sensing system.

Description

Technical Field

[0001] This invention belongs to the field of MEMS technology, specifically relating to an ion sensing system based on a two-dimensional material field-effect transistor monolithic three-dimensional integrated differential amplifier circuit and its fabrication method. Background Technology

[0002] In precision medicine, environmental monitoring, and life science research, potassium ions (K+) in body fluids such as blood are studied. + Sodium ions (Na) + ) and calcium ions (Ca 2+ Real-time, rapid, and highly sensitive quantitative detection of key electrolytes such as ions is of significant clinical and scientific importance. These ions are core regulators of cellular electrophysiological activity, nerve conduction, muscle contraction, and fluid balance; abnormal concentrations are crucial for diagnosing heart and kidney dysfunction, electrolyte imbalances, and various endocrine disorders. While traditional techniques such as flame photometry, ion-selective electrode methods, and ion chromatography are widely used in clinical testing, they still have significant shortcomings when facing the demands of point-of-care testing and wearable continuous monitoring. These limitations include reliance on large equipment and complex pretreatment, insufficient sensitivity, stability, and integration, as well as issues like potential drift and ion interference, making it difficult to meet the requirements of next-generation detection that demands miniaturization, real-time monitoring, and high robustness. To overcome these bottlenecks, field-effect transistor (FET) sensors have emerged as a next-generation high-potential sensing platform. Their core principle is to directly convert the surface potential change caused by the binding of the target analyte into a channel current for amplification and reading, thus offering advantages such as high sensitivity, fast response, and ease of miniaturization. Although early silicon-based or metal-oxide FET sensors have been widely used, they still face challenges in terms of stability, sensitivity, and power consumption in liquid environments.

[0003] In recent years, two-dimensional materials, represented by molybdenum disulfide (MoS2), have brought significant breakthroughs to FET sensors due to their atomic-level thickness, high specific surface area, and excellent electrical properties. MoS2 exhibits good chemical stability, and its enormous specific surface area exposes almost all atoms to the environment, making it sensitive to external electrical disturbances. High-performance ion-sensitive field-effect transistors can be constructed by modifying its channel or gate dielectric with an ion-sensitive thin film. When the analyte comes into contact with the sensitive film, the carrier within the film selectively binds to the target ions, causing a change in film potential. This change is equivalent to applying an additional gate voltage, thereby efficiently modulating the carrier density of the MoS2 channel, leading to a significant change in source and drain currents. Quantitative detection of ion concentration can be achieved by measuring the shift in the transfer characteristic curve.

[0004] However, the structural optimization of MoS2FET has reached its limit, making it difficult to further improve its sensitivity (which is insufficient to meet the needs of trace ion detection). On the other hand, when MoS2FET is used to detect complex samples such as serum and sweat, it is easily affected by external interference such as fluctuations in ambient temperature and pH, which seriously affects the reliability and accuracy of the sensor. Summary of the Invention

[0005] In view of one or more of the above-mentioned defects or improvement needs of the prior art, the present invention provides an ion sensing system with a monolithic three-dimensional integrated differential amplifier circuit, which can solve the problems of limited sensitivity, susceptibility to environmental interference, difficulty in miniaturization and integration, and unsuitability for real-time monitoring of complex samples in traditional ion detection technology.

[0006] To achieve the above objectives, one aspect of the present invention provides an ion sensing system with a monolithic three-dimensional integrated differential amplifier circuit, which includes a differential amplifier circuit comprising two first molybdenum disulfide layers spaced apart, wherein one end of each of the two first molybdenum disulfide layers is connected to the same forward bias voltage through a first metal electrode, and the other end is output through a second metal electrode.

[0007] Each of the first molybdenum disulfide layers is provided with a first insulating layer, a second molybdenum disulfide layer, a second insulating layer and a gate electrode in sequence from bottom to top. One end of the second molybdenum disulfide layer is grounded through a drain electrode, and the other end is connected to the second metal electrode through a source electrode. An ion-sensitive film is provided on the gate electrode to form an ion-sensitive field-effect transistor on each of the first molybdenum disulfide layers.

[0008] In actual use, the test solution acts on one of the ion-sensitive membranes, while the other ion-sensitive membrane does not interact with the test solution and senses environmental noise. Then, the actual concentration of the target ion in the test solution is determined by the output signal of the two second metal electrodes.

[0009] As a further improvement of the present invention, it also includes a substrate, on which an electrode groove is provided, wherein the first metal electrode, the second metal electrode and the first molybdenum disulfide layer are all embedded in the electrode groove.

[0010] As a further improvement of the present invention, both the drain electrode and the source electrode are disposed on the first insulating layer.

[0011] As a further improvement of the present invention, both the first molybdenum disulfide layer and the second molybdenum disulfide layer are single-atom-layer single-crystal structures, and the thickness of the first molybdenum disulfide layer and the second molybdenum disulfide layer is 0.7 mm.

[0012] As a further improvement of the present invention, the first insulating layer and the second insulating layer are made of any one of aluminum oxide, hafnium oxide, silicon oxide, and silicon nitride, and the thickness of the first insulating layer and the second insulating layer is 30~50nm.

[0013] As a further improvement of the present invention, the first metal electrode, the second metal electrode, the source electrode, the drain electrode and the gate electrode are formed by vertically stacking two layers of metal; wherein the lower metal layer serves as an adhesion layer, and its material is titanium or chromium, and its thickness is 5~10nm; the upper metal layer is made of gold or platinum, and its thickness is 30~40nm.

[0014] As a further improvement of the present invention, the substrate is a SiO2 / Si substrate, wherein the thickness of SiO2 in the SiO2 / Si substrate is 280~320nm.

[0015] Another aspect of the present invention provides a method for fabricating an ion sensing system with a monolithic three-dimensional integrated differential amplifier circuit, for use in the fabrication of the aforementioned ion sensing system with a monolithic three-dimensional integrated differential amplifier circuit, comprising the following steps:

[0016] (1) Photoresist is coated on the substrate surface and patterned, electrode trenches are etched by plasma etching process, and then the first metal electrode and the second metal electrode are prepared on the substrate surface by electron beam evaporation process and lift-off process.

[0017] (2) A single layer of molybdenum disulfide film is transferred to the substrate surface using a wet transfer process. Then, photoresist is coated on the surface of the single layer of molybdenum disulfide film and imaged. The molybdenum disulfide film is etched using a reactive ion etching process to obtain the first molybdenum disulfide layer.

[0018] (3) A metal oxide layer is grown on the substrate surface using atomic layer deposition process, photoresist is coated on the metal oxide surface and patterned, and then the metal oxide is etched using plasma etching process to obtain the first insulating layer.

[0019] (4) Photoresist is coated on the substrate surface and patterned, and source and drain electrodes are prepared by electron beam evaporation and lift-off processes;

[0020] (5) A single layer of molybdenum disulfide film is transferred to the substrate surface using a wet transfer process. Then, photoresist is coated on the surface of the single layer of molybdenum disulfide film and imaged. The molybdenum disulfide film is etched using a reactive ion etching process to obtain a second molybdenum disulfide layer.

[0021] (6) A metal oxide layer is grown on the substrate surface using atomic layer deposition process, photoresist is coated on the metal oxide surface and patterned, and then the metal oxide is etched using plasma etching process to obtain the second insulating layer.

[0022] (7) Photoresist is coated on the substrate surface and patterned, and gate electrodes are prepared by electron beam evaporation and lift-off processes;

[0023] (8) Drop the target ion-sensitive solution onto the surfaces of the two gate electrodes and dry them to obtain an ion-sensitive film and an inert reference film, thus completing the fabrication of the ion sensing system of a monolithic three-dimensional integrated differential amplifier circuit.

[0024] The aforementioned improved technical features can be combined with each other as long as they do not conflict with each other.

[0025] In summary, the beneficial effects of the above-described technical solutions conceived by this invention compared with the prior art include:

[0026] (1) The ion sensing system of the monolithic three-dimensional integrated differential amplifier circuit of the present invention provides a molybdenum disulfide layer in the differential amplifier circuit and an ion-sensitive field-effect transistor on the molybdenum disulfide layer. At the same time, two ion-sensitive membranes on the two gates work synchronously under the differential amplifier mechanism. One ion-sensitive membrane senses the ion signal in the test liquid, and the other ion-sensitive membrane senses the environmental noise. The difference between the output signals at both ends is extracted and amplified by the ion-sensitive field-effect transistor and the differential amplifier circuit. While effectively retaining the target ion response signal, the system systematically suppresses environmental common-mode interference and device inherent drift, thereby achieving high precision, high sensitivity, high stability and rapid detection of target ion concentration.

[0027] By setting a molybdenum disulfide layer in a differential amplifier circuit and placing an ion-sensitive field-effect transistor on the molybdenum disulfide layer, and by synchronously operating two ion-sensitive membranes under a differential amplifier mechanism, one ion-sensitive membrane senses the ion signal in the test liquid, while the other ion-sensitive membrane senses environmental noise. By extracting and amplifying the difference between the output signals at both ends, the target ion response signal is effectively preserved while environmental noise is suppressed, achieving high-precision, high-sensitivity, high-stability, and rapid detection of target ion concentration.

[0028] (2) The ion sensing system of the monolithic three-dimensional integrated differential amplifier circuit of the present invention vertically stacks the ion-sensitive field-effect transistors on the differential amplifier circuit through monolithic three-dimensional integration, so that the entire ion sensing system occupies the area of ​​only two FETs, greatly reducing the chip planar area, realizing the "chip-level" miniaturization and high integration of the ion sensing system, and solving the problem that traditional differential amplifier circuits are bulky and difficult to integrate with sensors.

[0029] (3) The ion sensing system of the monolithic three-dimensional integrated differential amplifier circuit of the present invention uses a second molybdenum disulfide layer in the FET to use molybdenum disulfide as a channel material to efficiently convert the small interface potential changes caused by ion binding and / or environmental interference into electrical signals. The first molybdenum disulfide layer is used to further extract and amplify the difference signal between the working and reference channels. While suppressing the substrate noise, the target response is effectively enhanced, and high signal-to-noise ratio detection of low-concentration ions is achieved.

[0030] (4) The ion sensing system of the monolithic three-dimensional integrated differential amplifier circuit of the present invention effectively suppresses environmental interference and amplifies the effective signal through differential signal processing mechanism, which significantly improves the accuracy, repeatability and reliability of ion detection in complex real samples. It provides key support for promoting ion sensing from the laboratory to clinical bedside detection, personal health monitoring and real-time field analysis, and lays an important foundation for the development of a new generation of robust and miniaturized intelligent ion sensing platforms.

[0031] (5) The ion sensing system and its preparation method of the monolithic three-dimensional integrated differential amplifier circuit of the present invention are compatible with standard semiconductor processes, which facilitates wafer-level manufacturing, multi-layer integration and miniaturized packaging. It can build an integrated, chip-based detection platform, laying a technical foundation for large-scale application in scenarios such as portable diagnostic equipment, wearable monitoring and on-site rapid analysis. Attached Figure Description

[0032] To more clearly illustrate the technical solutions in the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0033] Figure 1 This is a schematic diagram of the planar structure of the differential amplifier circuit in an embodiment of the present invention;

[0034] Figure 2 This is a schematic diagram of the planar structure of the ion sensing system of the monolithic three-dimensional integrated differential amplifier circuit in this embodiment of the invention when the second insulating layer and the gate electrode are not provided;

[0035] Figure 3 This is a schematic diagram of the overall planar structure of the ion sensing system with a monolithic three-dimensional integrated differential amplifier circuit in an embodiment of the present invention;

[0036] Figure 4 yes Figure 3 Schematic diagram of section AA;

[0037] Figure 5 yes Figure 3Schematic diagram of the BB section;

[0038] Figure 6 This is a process flow diagram of the fabrication process of the ion sensing system with a monolithic three-dimensional integrated differential amplifier circuit in this embodiment of the invention;

[0039] Figure 7 This is the transfer characteristic curve (Id-Vg) of a field-effect transistor.

[0040] In all the accompanying drawings, the same reference numerals denote the same technical features, specifically: 1, substrate; 2, first metal electrode; 3, second metal electrode; 4, first molybdenum disulfide layer; 5, first insulating layer; 6, source electrode; 7, drain electrode; 8, second molybdenum disulfide layer; 9, second insulating layer; 10, gate electrode; 11, ion-sensitive membrane. Detailed Implementation

[0041] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention. Furthermore, the technical features involved in the various embodiments of this invention described below can be combined with each other as long as they do not conflict with each other.

[0042] In the description of this invention, it should be understood that, unless otherwise expressly specified and limited, the terms "center," "longitudinal," "lateral," "length," "width," "thickness," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," "clockwise," "counterclockwise," "axial," "radial," "circumferential," etc., indicating the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, are only for the convenience of describing this invention and simplifying the description, and are not intended to indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of this invention.

[0043] Furthermore, unless otherwise expressly specified and limited, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one of that feature. In the description of this invention, "a plurality of" means at least two, such as two, three, etc., unless otherwise expressly and specifically limited.

[0044] 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, unless otherwise explicitly limited. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0045] In this invention, unless otherwise explicitly specified and limited, "above" or "below" the second feature can mean that the first feature is in direct contact with the second feature, or that the first feature is in indirect contact with the second feature through an intermediate medium. Furthermore, "above," "over," and "on top" of the second feature can mean that the first feature is directly above or diagonally above the second feature, or simply that the first feature is at a higher horizontal level than the second feature. "Below," "below," and "under" the second feature can mean that the first feature is directly below or diagonally below the second feature, or simply that the first feature is at a lower horizontal level than the second feature.

[0046] Example:

[0047] Please see Figures 1-7 The ion sensing system of the monolithic three-dimensional integrated differential amplifier circuit in the preferred embodiment of the present invention includes a vertically stacked differential amplifier circuit and two ion-sensitive field-effect transistors. One ion-sensitive field-effect transistor acts on the target ion in the test liquid, and the other is used to sense environmental noise. The signals output by both are sent to the differential amplifier circuit including two first molybdenum disulfide layers 4. By extracting and amplifying the difference between the output signals at both ends, the specific response signal of the target ion is amplified while suppressing environmental common-mode interference and device inherent drift.

[0048] Specifically, such as Figure 1 As shown, the differential amplifier circuit in the preferred embodiment includes two first molybdenum disulfide layers 4 spaced apart on the substrate 1, serving as resistors in two branches of the differential amplifier circuit. One end of each of the two first molybdenum disulfide layers 4 is connected to a forward bias voltage VDD through a first metal electrode 2, providing operating power for the entire differential amplifier circuit; the other ends of the two first molybdenum disulfide layers 4 are output through a second metal electrode 3, forming symmetrical branches in the differential amplifier circuit. Figure 1 As shown, one end of a second metal electrode 3 is the output terminal V. out1 One end of the other second metal electrode 3 is the output terminal V. out2 .

[0049] Preferably, an electrode groove is provided on the substrate 1, and the first metal electrode 2, the second metal electrode 3 and the first molybdenum disulfide layer 4 are all embedded in the electrode groove to increase the stability of the differential amplifier circuit on the substrate 1 and reduce the thickness of the ion sensor.

[0050] Furthermore, such as Figures 2-5 As shown, a first insulating layer 5, a second molybdenum disulfide layer 8, a second insulating layer 9, and a gate electrode 10 are sequentially disposed from bottom to top on each first molybdenum disulfide layer 4. A drain electrode 7 and a source electrode 6 are disposed on the first insulating layer 5. One end of the second molybdenum disulfide layer 8 is grounded through the drain electrode 7 to provide a common reference point for the current of the two ion-sensitive field-effect transistors, ensuring normal circuit operation. The other end of the second molybdenum disulfide layer 8 is connected to the second metal electrode 3 through the source electrode 6. Meanwhile, an ion-sensitive film 11 is disposed on the gate electrode 10 to form an ion-sensitive field-effect transistor on each first molybdenum disulfide layer 4. Preferably, the two ion-sensitive field-effect transistors are symmetrically arranged.

[0051] It is understandable that by setting a first insulating layer 5 between the first molybdenum disulfide layer 4 and the ion-sensitive field-effect transistor, while realizing the vertical stacking between the ion-sensitive field-effect transistor and the differential amplifier circuit, the first insulating layer 5 physically achieves vertical isolation between the molybdenum disulfide resistor layer and the transistor layer, electrically preventing short circuits and mutual interference between the two, so that they can work together as independent circuit elements.

[0052] In practical use, one ion-sensitive field-effect transistor on the first molybdenum disulfide layer 4 serves as the working FET. The test liquid acts on the ion-sensitive membrane 11 in the working FET to sense the ion signal in the test liquid. The other ion-sensitive field-effect transistor on the first molybdenum disulfide layer 4 serves as the reference FET. The ion-sensitive membrane 11 in the reference FET does not interact with the test liquid and senses environmental noise to provide a noise sample. Then, the actual concentration of the target ion in the test liquid is determined by the output signal of the two second metal electrodes 3. This allows the ion sensing system to accurately distinguish and eliminate interference introduced by the environment and the device itself, thereby ensuring that the final output signal is true and reliably reflects the concentration change of the target ion.

[0053] Understandably, the second molybdenum disulfide layer 8 serves as the conductive channel of the FET, and its conductivity is extremely sensitive to the voltage of the gate electrode 10. When the potential of the gate electrode 10 changes due to ion bonding or environmental interference, the channel resistance will change significantly, thereby modulating the current of the source electrode 6 and the drain electrode 7, realizing the conversion and amplification from chemical / physical disturbance (potential change) to electrical signal (current change). The first molybdenum disulfide layer 4 located below the second molybdenum disulfide layer 8 serves as the load resistor of the FET, amplifying the change in the FET channel current and converting it into a change in voltage signal, which is then output through the second metal electrode 3.

[0054] Because the two ion-sensitive field-effect transistors and the two branches of the differential amplifier circuit are highly matched in terms of materials, structure and electrical characteristics, when there is only common-mode interference in the environment (such as temperature drift, pH fluctuation, non-specific adsorption, device inherent drift, etc.) and no target ions, the two ion-sensitive field-effect transistors are exposed to the same environment and the magnitude of the current generated is nearly equal. Therefore, the voltage at the output terminals of the two second metal electrodes 3 is also roughly the same, and the voltage difference output by the differential amplifier circuit is almost zero, thereby effectively suppressing environmental noise.

[0055] When the ion-sensitive membrane 11 is exposed to a test solution containing the target ion, the gate of the working FET senses the concentration change, generating an additional voltage and causing a change in its channel current, while the current of the reference FET remains unchanged. At this time, the voltages at the two output terminals are no longer equal, and a voltage difference is generated between them. The magnitude of this final differential output voltage is proportional to the difference in current between the two FETs, and this difference directly reflects the actual concentration of the target ion in the test solution.

[0056] Preferably, both the first molybdenum disulfide layer 4 and the second molybdenum disulfide layer 8 are single-atom-layer single-crystal structures with a thickness of 0.7 nm.

[0057] Preferably, the materials of the first insulating layer 5 and the second insulating layer 9 can be any one of alumina, hafnium oxide, silicon oxide, and silicon nitride, and the thickness is 30~50nm.

[0058] Preferably, the materials of the first metal electrode 2, the second metal electrode 3, the source electrode 6, the drain electrode 7, and the gate electrode 10 are all vertically stacked double-layer metals, wherein the lower metal is titanium (Ti) or chromium (Cr) as an adhesion layer with a thickness of 5~10nm, and the upper metal is gold (Au) or platinum (Pt) with a thickness of 30~40nm.

[0059] Preferably, the substrate 1 is a SiO2 / Si substrate, specifically consisting of an upper SiO2 insulating layer and a lower silicon substrate, wherein the thickness of the SiO2 insulating layer is 280~320μm.

[0060] Furthermore, the present invention also relates to a method for fabricating an ion sensing system based on a monolithic three-dimensional integrated differential amplifier circuit, used in the aforementioned fabrication of a monolithic three-dimensional integrated differential amplifier circuit, such as... Figure 6 As shown, the specific steps include the following:

[0061] (1) Photoresist is coated on the surface of substrate 1 and patterned. Electrode grooves are etched by plasma etching process. Then, the first metal electrode 2 and the second metal electrode 3 are prepared on the surface of substrate 1 by electron beam evaporation process and stripping process.

[0062] In a preferred embodiment, the substrate 1 is first cleaned to remove impurities and contaminants from its surface. Specifically, the SiO2 / Si substrate 1 is immersed in an acetone solution and ultrasonically cleaned for 10 minutes to ensure the cleanliness of the substrate 1 surface; then, the substrate 1 is immersed in anhydrous ethanol solution and ultrasonically cleaned for 10 minutes to dissolve any acetone residue on the substrate 1 surface; finally, the substrate 1 is rinsed with deionized water and dried with a nitrogen gun.

[0063] Before preparation, the cleaned substrate 1 was placed on a hot plate at 100°C and baked for 10 min to ensure that the surface of substrate 1 was dry.

[0064] Then, a layer of negative photoresist NR9-3000PY was spin-coated onto the surface of SiO2 / Si substrate 1 (the spin coater speed was set to low speed 500 rpm / min, spin coating time 5 s, acceleration 500 rpm / s; high speed 3000 rpm / min, spin coating time 40 s, acceleration 1500 rpm / s); it was then preheated at 120℃ for 2 min, exposed for 25 s, then baked at 120℃ for 2 min, and immersed in RD6 developer for 45 s to pattern it; subsequently, the SiO2 layer was etched using a plasma etching machine with CH4 gas introduced, the etching rate was approximately 3 nm / s, and the etching time was set to 15 s;

[0065] A 5nm thick Ti and a 40nm thick Au were deposited using an electron beam evaporation device. After the deposition was completed, the substrate 1 was immersed in an acetone solution and ultrasonicated with low power. After the metal on the photoresist was stripped off, it was successively immersed in anhydrous ethanol and deionized water for cleaning to obtain the first metal electrode 2 and the second metal electrode 3.

[0066] (2) A single layer of molybdenum disulfide film is transferred to the surface of substrate 1 using a wet transfer process. Then, photoresist is coated on the surface of the single layer of molybdenum disulfide film and imaged. The molybdenum disulfide film is etched using a reactive ion etching process to obtain the first molybdenum disulfide layer 4.

[0067] In a specific embodiment, a wet transfer process is used to transfer a single-layer molybdenum disulfide film onto the surface of substrate 1. LOR 3B primer is then spin-coated onto the surface of the molybdenum disulfide film (spin coater speed set to low speed 500 rpm / min, spin coat time 5 s, acceleration 800 rpm / s; high speed 2000 rpm / min, spin coat time 30 s, acceleration 1500 rpm / s), and baked on a hot plate at 97°C for 1 min. Subsequently, AZ 5214 photoresist is spin-coated (spin coater speed set to low speed 1500 rpm / min, spin coat time 15 s, acceleration 800 rpm / s; high speed 4000 rpm / min, spin coat time 30 s, acceleration 1500 rpm / s), and then baked on a hot plate at 97°C for 2 min, with an exposure time of 5.2 s. Finally, it is developed in a solution of AZ 400K and water at a 1:4 ratio for 24 s.

[0068] In a mixed atmosphere of Ar and O2, a single layer of molybdenum disulfide film was etched for 30 seconds using a reactive ion etching machine, followed by cleaning with acetone, anhydrous ethanol and deionized water to complete the patterning of the first molybdenum disulfide layer 4.

[0069] (3) A metal oxide layer is grown on the surface of substrate 1 using atomic layer deposition process, photoresist is coated on the surface of metal oxide and patterned, and then plasma etching process is used to etch the metal oxide to obtain the first insulating layer 5.

[0070] In a specific embodiment, 30nm aluminum oxide is grown on the surface of substrate 1 using atomic layer deposition (ALD). A layer of positive photoresist AZ 5214 is spin-coated onto the surface of substrate 1 (the spin coater speed is set to 1500rpm / min at low speed, spin coating time is 15s, and acceleration is 800rpm / s; and 4000rpm / min at high speed, spin coating time is 30s, and acceleration is 1500rpm / s). The substrate is then baked in front of a hot plate at 97°C for 2min, with an exposure time of 5.2s. Subsequently, the substrate is developed in a solution of AZ 400K and water at a ratio of 1:4 for 35s.

[0071] In a mixed atmosphere of BCl3 and Ar, aluminum oxide was etched for 150 seconds using a plasma etching machine; then it was cleaned sequentially with acetone, anhydrous ethanol and deionized water to complete the patterning of the first insulating layer 5.

[0072] (4) Photoresist is coated on the surface of substrate 1 and patterned. Source electrode 6 and drain electrode 7 are prepared by electron beam evaporation and stripping process.

[0073] In a specific embodiment, a layer of negative photoresist NR9-3000PY is spin-coated onto the surface of substrate 1 (the spin coater speed is set to low speed 500 rpm / min, spin coating time 5s, acceleration 500 rpm / s, high speed 3000 rpm / min, spin coating time 40s, acceleration 1500 rpm / s), baked in front of a hot plate at 120°C for 2 min, exposed for 25s, then baked in a hot plate at 120°C for 2 min, and then immersed in RD6 developer for 45s to pattern it;

[0074] 5 nm of Ti and 40 nm of Au were deposited using an electron beam evaporation apparatus. After the deposition was completed, the substrate 1 was immersed in an acetone solution. After the metal on the photoresist was completely stripped off, the substrate 1 was placed in anhydrous ethanol and deionized water for cleaning in sequence to prepare the source electrode 6 and the drain electrode 7.

[0075] (5) A single layer of molybdenum disulfide film is transferred to the surface of substrate 1 using a wet transfer process. Then, photoresist is coated on the surface of the single layer of molybdenum disulfide film and imaged. The molybdenum disulfide film is etched using a reactive ion etching process to obtain the second molybdenum disulfide layer 8.

[0076] In a specific embodiment, a wet transfer process is used to transfer a monolayer molybdenum disulfide film onto the surface of substrate 1. LOR 3B adhesive is then spin-coated onto the surface of the monolayer molybdenum disulfide film (spin coater speed set to low speed 500 rpm / min, spin coat time 5 s, acceleration 800 rpm / s; high speed 2000 rpm / min, spin coat time 30 s, acceleration 1500 rpm / s), and baked on a hot plate at 97°C for 1 min. Subsequently, AZ 5214 photoresist is spin-coated (spin coater speed set to low speed 1500 rpm / min, spin coat time 15 s, acceleration 800 rpm / s; high speed 4000 rpm / min, spin coat time 30 s, acceleration 1500 rpm / s) and baked on a hot plate at 97°C for 2 min, with an exposure time of 5.2 s. Finally, it is developed in a solution of AZ 400K and water at a 1:4 ratio for 24 s.

[0077] In a mixed atmosphere of Ar and O2, a single layer of molybdenum disulfide film was etched for 30 seconds using a reactive ion etching machine, followed by cleaning with acetone, anhydrous ethanol and deionized water to complete the patterning of the second molybdenum disulfide layer 8.

[0078] (6) A metal oxide layer is grown on the surface of substrate 1 using atomic layer deposition process, photoresist is coated on the surface of metal oxide and patterned, and then plasma etching process is used to etch the metal oxide to obtain the second insulating layer 9.

[0079] In a specific embodiment, 30 nm aluminum oxide is grown on the surface of substrate 1 using atomic layer deposition (ALD). A layer of positive photoresist AZ 5214 is spin-coated onto the substrate surface (the spin coater speed is set to 1500 rpm / min at low speed, spin coating time is 15 s, and acceleration is 800 rpm / s; and 4000 rpm / min at high speed, spin coating time is 30 s, and acceleration is 1500 rpm / s). The substrate is then baked in front of a hot plate at 97°C for 2 min, with an exposure time of 5.2 s. Subsequently, the substrate is developed in a solution of AZ 400K and water at a ratio of 1:4 for 35 s.

[0080] In a mixed atmosphere of BCl3 and Ar, aluminum oxide was etched for 150 seconds using a plasma etching machine; then it was cleaned sequentially with acetone, anhydrous ethanol and deionized water to complete the patterning of the second insulating layer 9.

[0081] (7) Photoresist is coated on the surface of substrate 1 and patterned. Gate electrode 10 is prepared by electron beam evaporation and stripping process to complete the preparation of ion sensing system of monolithic three-dimensional integrated differential amplifier circuit.

[0082] In a specific embodiment, a layer of negative photoresist NR9-3000PY is spin-coated onto the surface of substrate 1 (the spin coater speed is set to low speed 500 rpm / min, spin coating time 5s, acceleration 500 rpm / s, high speed 3000 rpm / min, spin coating time 40s, acceleration 1500 rpm / s), baked in front of a hot plate at 120°C for 2 min, exposed for 25s, then baked in a hot plate at 120°C for 2 min, and then immersed in RD6 developer for 45s to pattern it.

[0083] 5nm Ti and 40nm Au were deposited using an electron beam evaporation device. After the deposition was completed, the sample was immersed in an acetone solution. After the metal on the photoresist was completely stripped off, the sample was cleaned in anhydrous ethanol and deionized water in sequence to complete the patterning of the gate electrode 10.

[0084] (8) Drop the target ion-sensitive solution onto the surfaces of the two gate electrodes 10 and dry them to obtain two ion-sensitive films 11, thus completing the fabrication of the ion sensing system of the monolithic three-dimensional integrated differential amplifier circuit.

[0085] In a specific embodiment, taking sodium ions as the target ion to be measured as an example, 10 mg of sodium ion carrier X, 5.5 mg of sodium tetrakis(3,5-bis(trifluoromethyl)phenyl)borate (Na-TFPB), 330 mg of polyvinyl chloride (PVC), and 654.5 mg of dioctyl sebacate (DOS) were dissolved in 6.6 mL of tetrahydrofuran (THF), stirred evenly, and placed in a refrigerator at 4°C for 24 h; the above mixture was then dropped onto the surfaces of two gate electrodes 10 through a micromanipulation platform, and after drying in air for 24 h, two thin films were obtained.

[0086] Correspondingly, when preparing other ion-sensitive films 11, simply replace the sodium ion carrier X with other ion carriers (such as valinemycin (potassium ion carrier), calcium ion carrier II, etc.), prepare a sensitive solution of other ions, drop it onto the surface of one of the gate electrodes 10 and dry it to obtain the corresponding ion-sensitive film.

[0087] The electrical characteristics of the ion sensing system with the above-prepared monolithic three-dimensional integrated differential amplifier circuit were tested using a Keysight B1500A semiconductor analyzer. Figure 7 As shown, the fabricated ion-sensitive field-effect transistor has an n-type structure and an on / off ratio of 10. 5 It has good gate control capabilities.

[0088] The ion sensing system of this invention, featuring a monolithic three-dimensional integrated differential amplifier circuit, utilizes a pair of molybdenum disulfide resistors and a pair of molybdenum disulfide FETs with highly matched materials, structures, and electrical properties to form the core of the differential amplifier circuit. By using one of the two FETs as the working FET and the other as the reference FET, and by exposing the working FET to the test solution, the differential amplifier circuit extracts and amplifies the difference between the output signals of the two FETs. This effectively amplifies the target ion signal while significantly suppressing common-mode environmental noise, greatly improving the stability and accuracy of sample detection, and achieving K... + Na + Ca 2+ Highly selective recognition and highly sensitive, highly stable detection of plasma.

[0089] Those skilled in the art will readily understand that the above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. An ion sensing system with a monolithic three-dimensional integrated differential amplifier circuit, characterized in that, It includes a differential amplifier circuit, which includes two first molybdenum disulfide layers spaced apart. One end of each of the two first molybdenum disulfide layers is connected to the same forward bias voltage through a first metal electrode, and the other end is output through a second metal electrode. Each of the first molybdenum disulfide layers is provided with a first insulating layer, a second molybdenum disulfide layer, a second insulating layer and a gate electrode in sequence from bottom to top. One end of the second molybdenum disulfide layer is grounded through a drain electrode, and the other end is connected to the second metal electrode through a source electrode. An ion-sensitive film is provided on the gate electrode to form an ion-sensitive field-effect transistor on each of the first molybdenum disulfide layers. In actual use, the test solution acts on one of the ion-sensitive membranes, while the other ion-sensitive membrane does not interact with the test solution and senses environmental noise. Then, the actual concentration of the target ion in the test solution is determined by the output signal of the two second metal electrodes.

2. The ion sensing system with a monolithic three-dimensional integrated differential amplifier circuit according to claim 1, characterized in that, It also includes a substrate on which an electrode groove is provided, wherein the first metal electrode, the second metal electrode and the first molybdenum disulfide layer are all embedded in the electrode groove.

3. The ion sensing system with a monolithic three-dimensional integrated differential amplifier circuit according to claim 1, characterized in that, The drain electrode and the source electrode are disposed on the first insulating layer.

4. The ion sensing system with a monolithic three-dimensional integrated differential amplifier circuit according to claim 1, characterized in that, Both the first molybdenum disulfide layer and the second molybdenum disulfide layer are single-atom-layer single-crystal structures, and the thickness of the first molybdenum disulfide layer and the second molybdenum disulfide layer is 0.7 mm.

5. The ion sensing system with a monolithic three-dimensional integrated differential amplifier circuit according to claim 1, characterized in that, The first insulating layer and the second insulating layer are made of any one of aluminum oxide, hafnium oxide, silicon oxide, and silicon nitride, and the thickness of the first insulating layer and the second insulating layer is 30~50nm.

6. The ion sensing system with a monolithic three-dimensional integrated differential amplifier circuit according to claim 1, characterized in that, The first metal electrode, the second metal electrode, the source electrode, the drain electrode, and the gate electrode are formed by vertically stacking two layers of metal; wherein the lower metal layer serves as an adhesion layer, and its material is titanium or chromium, with a thickness of 5~10nm; the upper metal layer is made of gold or platinum, with a thickness of 30~40nm.

7. The ion sensing system with a monolithic three-dimensional integrated differential amplifier circuit according to claim 2, characterized in that, The substrate is a SiO2 / Si substrate, and the thickness of SiO2 in the SiO2 / Si substrate is 280~320nm.

8. A method for fabricating an ion sensing system with a monolithic three-dimensional integrated differential amplifier circuit, used for fabricating the ion sensing system with the monolithic three-dimensional integrated differential amplifier circuit as described in any one of claims 1 to 7, characterized in that, Includes the following steps: (1) Photoresist is coated on the substrate surface and patterned, electrode trenches are etched by plasma etching process, and then the first metal electrode and the second metal electrode are prepared on the substrate surface by electron beam evaporation process and lift-off process. (2) A single layer of molybdenum disulfide film is transferred to the substrate surface using a wet transfer process. Then, photoresist is coated on the surface of the single layer of molybdenum disulfide film and imaged. The molybdenum disulfide film is etched using a reactive ion etching process to obtain the first molybdenum disulfide layer. (3) A metal oxide layer is grown on the substrate surface using atomic layer deposition process, photoresist is coated on the metal oxide surface and patterned, and then the metal oxide is etched using plasma etching process to obtain the first insulating layer. (4) Photoresist is coated on the substrate surface and patterned, and source and drain electrodes are prepared by electron beam evaporation and lift-off processes; (5) A single layer of molybdenum disulfide film is transferred to the substrate surface using a wet transfer process. Then, photoresist is coated on the surface of the single layer of molybdenum disulfide film and imaged. The molybdenum disulfide film is etched using a reactive ion etching process to obtain a second molybdenum disulfide layer. (6) A metal oxide layer is grown on the substrate surface using atomic layer deposition process, photoresist is coated on the metal oxide surface and patterned, and then the metal oxide is etched using plasma etching process to obtain the second insulating layer. (7) Photoresist is coated on the substrate surface and patterned, and gate electrodes are prepared by electron beam evaporation and lift-off processes; (8) Drop the target ion-sensitive solution onto the surfaces of the two gate electrodes and dry them to obtain two ion-sensitive films, thus completing the preparation of the ion sensing system of the monolithic three-dimensional integrated differential amplifier circuit.

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