A multi-parameter MEMS sensor for groundwater and detection method

Abstract

The application provides a groundwater multi-parameter MEMS sensor and a detection method. The sensor comprises a silicon substrate, an insulating layer, a plurality of resistance bodies, a heater and a reference electrode. The reference electrode is arranged in a central region of the insulating layer. The heater is arranged around the periphery of the reference electrode. The plurality of resistance bodies are symmetrically distributed in the periphery of the heater in a circumferential direction. Each resistance body is provided with a first lead end and a second lead end. The first lead end and the second lead end are respectively connected to an external circuit through metal leads. The first lead end and the second lead end of each resistance body are electrically connected to a switch assembly to switch between an electrode working mode and a resistance working mode under the control of the switch assembly. In the resistance working mode, the first lead end and the second lead end are connected to the external circuit, so that the resistance body works as a resistance element. In the electrode working mode, the first lead end and the second lead end are electrically connected to each other, so that the resistance body forms an equipotential electrode.

Description

Technical Field

[0001] This application relates to the field of water quality monitoring technology, and in particular to a multi-parameter MEMS sensor for groundwater and a detection method thereon. Background Technology

[0002] In recent years, with the continuous introduction of national policies on water environment monitoring and management, the demand for measuring various water quality indicators has increased in industries such as environmental protection, industry, fishery, and sewage treatment.

[0003] Existing multi-parameter water quality sensors mostly employ discrete device designs, resulting in problems such as large size, high power consumption, and low integration. Although MEMS (Micro-Electro-Mechanical System) technology has attempted to integrate conductivity, temperature, and ORP (Oxidation-Reduction Potential) onto a single chip, the independent function of each electrode represents simple integration. Furthermore, most water quality sensors lack flow rate and direction detection capabilities. Finally, with electrodes constantly immersed in groundwater, scale easily forms on the electrode surface, and current technologies lack effective automated cleaning methods. Summary of the Invention

[0004] The technical problem to be solved by the embodiments of this application is to provide a groundwater multi-parameter MEMS sensor and detection method, so as to solve the problems that existing water quality multi-parameter detection sensors mostly adopt discrete device design, which have problems such as large size, high power consumption, low integration and troublesome cleaning.

[0005] In a first aspect, embodiments of this application provide a multi-parameter MEMS sensor for groundwater, the sensor comprising: a silicon substrate, an insulating layer, multiple resistors, a heater, and a reference electrode, wherein... The insulating layer covers the surface of the silicon substrate, and the reference electrode, the heater, and the plurality of resistors are all disposed on the side of the insulating layer away from the silicon substrate; The reference electrode is disposed in the central region of the insulating layer, the heater is arranged around the periphery of the reference electrode, and the plurality of resistive elements are symmetrically distributed around the periphery of the heater; Each of the resistors is provided with a first lead end and a second lead end, and the first lead end and the second lead end are respectively connected to an external circuit through metal leads; The first lead and the second lead of each of the resistors are configured to be electrically connected to a switching assembly to switch between an electrode operating mode and a resistor operating mode under the control of the switching assembly. In the resistor operating mode, the first lead end and the second lead end are connected to an external circuit, so that the resistor body works as a resistor element. In the electrode operating mode, the first lead end and the second lead end are electrically connected to each other, so that the resistive body forms an equipotential electrode.

[0006] Secondly, embodiments of this application provide a detection method applied to the sensor described in the first aspect, comprising: The connection state between the first lead and the second lead of the target resistive element is controlled by a switching assembly to put the target resistive element into a target operating mode; wherein, the target resistive element is at least one of the multiple resistive elements of the groundwater multi-parameter MEMS sensor; The fluid parameters of the target water area are detected by the target resistivity.

[0007] Compared with the prior art, the embodiments of this application have the following advantages: In this embodiment, the reference electrode, heater, and multiple resistors are highly integrated on a silicon substrate using a center-periphery symmetrical layout, which solves the problems of large size and low integration of traditional discrete devices. Furthermore, the analog switch array is used to control the resistors to flexibly switch between resistance and electrode operating modes (i.e., "resistance and electrode" are defined by the series and parallel relationship of leads) to achieve device function reuse. While realizing the miniaturization, low power consumption, and high integration of aquatic multi-parameter MEMS sensor, it can also realize the functions of temperature, conductivity, ORP measurement and electrode cleaning, meeting the urgent need of water environment monitoring networks for high-performance sensors.

[0008] It should be understood that the above general description and the following detailed description are exemplary and explanatory only, and do not limit this application. Attached Figure Description

[0009] Figure 1 This is a schematic diagram of the structure of a groundwater multi-parameter MEMS sensor provided in an embodiment of this application; Figure 2 This is a schematic diagram of another groundwater multi-parameter MEMS sensor provided in an embodiment of this application; Figure 3 A flowchart illustrating the steps of a detection method provided in this application embodiment; Figure 4 This is a timing diagram of an in-situ self-cleaning electrode provided in an embodiment of this application. Detailed Implementation

[0010] To make the above-mentioned objectives, features and advantages of this application more apparent and understandable, the application will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0011] The terminology used in the embodiments of this application is for the purpose of describing particular embodiments only and is not intended to be limiting of this application. The singular forms “a,” “the,” and “the” used in the embodiments of this application and the appended claims are also intended to include the plural forms unless the context clearly indicates otherwise.

[0012] Reference Figure 1 The diagram illustrates the structure of a multi-parameter MEMS sensor for groundwater provided in an embodiment of this application. Figure 1 As shown, the groundwater multi-parameter MEMS sensor may include: a silicon substrate 16, an insulating layer 15, multiple resistors 11, a heater 12, and a reference electrode 14, wherein, The insulating layer 15 can cover the surface of the silicon substrate 16, and the reference electrode 14, heater 12, and multiple resistors 11 are all disposed on the side of the insulating layer 15 away from the silicon substrate 16.

[0013] The reference electrode 14 is disposed in the central region of the insulating layer 15, the heater 12 is arranged around the reference electrode 14, and multiple resistors 11 are symmetrically distributed around the heater 12. At the same time, the heater 12 and the reference electrode 14, as well as the multiple resistors 11 and the heater 12, are all arranged at predetermined distances.

[0014] Each resistor element 11 is provided with a first lead end and a second lead end. Figure 1 (not shown in the diagram), the first and second leads of each resistor 11 can be connected to an external circuit via metal leads.

[0015] The first and second leads of each resistor 11 are configured to be electrically connected to a switching assembly to switch between an electrode operating mode and a resistor operating mode under the control of the switching assembly. In this example, an external switching assembly can be set for each resistor for control, and multiple switching assemblies can form a switching array. Of course, these switching assemblies are not part of the sensor, but external components.

[0016] In resistive operation mode, the first lead and the second lead are connected to an external circuit, so that the resistor 11 works as a resistive element.

[0017] In electrode operating mode, the first lead end and the second lead end are electrically connected to each other, so that the resistor 11 forms an equipotential electrode.

[0018] In one implementation of this application, the plurality of resistors can be four, namely: a first resistor, a second resistor, a third resistor, and a fourth resistor. This structure can be as follows: Figure 2As shown, the four resistive elements of the groundwater multi-parameter MEMS sensor are R1, R2, R3, and R4. Each resistive element has two leads. Specifically, the first and second leads of R1 are R1-A and R1-B, respectively; the first and second leads of R2 are R2-A and R2-B, respectively; the first and second leads of R3 are R3-A and R3-B, respectively; and the first and second leads of R4 are R4-A and R4-B, respectively. T1 is a heater. Figure 2 It can be seen that T1 is set around the reference electrode, and the four resistive elements can be symmetrically distributed around the center of heater T1 along the circumference, that is, the four resistive elements surround the center of the sensor (i.e., the central axis of the reference electrode). Figure 1 The four resistive elements (Z-axis) are arranged in a ring-shaped symmetrical distribution. Geometrically, the four resistive elements, the reference electrode, and the heater share the same central axis, forming a large circular arrangement.

[0019] Meanwhile, all four resistors can be thin-film platinum resistance elements.

[0020] In one implementation, both leads can be made of Ti-Pt-Au composite metal material, where titanium (Ti) serves as the bottom adhesion layer to enhance the bonding force between the metal and the substrate insulation layer, platinum (Pt) serves as the middle main layer to provide excellent conductivity and corrosion resistance, and gold (Au) serves as the surface anti-oxidation layer to prevent internal metal oxidation and facilitate connection with external circuits. The combination of the three ensures the high reliability and long-term stability of the leads in complex water quality environments.

[0021] Because the electrodes are submerged in groundwater for extended periods, scale easily forms on their surfaces, and existing technologies lack effective automated cleaning methods. In this embodiment, the resistive element is switched to electrode mode, and a large polarization potential is applied. Bubbles are generated using the oxygen evolution reaction (OER) and hydrogen evolution reaction (HER). The bubble formation process introduces localized shear force, physically stripping away the deposited layer from the electrode surface. Simultaneously, the reactive oxygen generated by oxygen evolution can oxidize and decompose organic pollutants, while the reactive hydrogen generated by hydrogen evolution can reduce oxide deposits such as iron and manganese.

[0022] By controlling the switching components, each resistor can have two operating modes, as shown in Table 1 below: Table 1 Resistor Operating Modes

[0023] As shown in Table 1 above, after the first lead A and the second lead B of each resistor are connected to an external circuit, the resistor can be used as a resistive element for applications such as temperature detection, thermal field sensing, and heating. When the first lead A and the second lead B of each resistor are short-circuited at an external analog switch, the resistor can be used as an electrode element for applications such as conductivity measurement, ORP measurement, and electrochemical cleaning.

[0024] The specific functional multiplexing relationships of each resistor are shown in Table 2 below: Table 2 Resistor Function Multiplexing

[0025] As shown in Table 2, heater T1 operates only in resistance mode to generate a thermal field, while the four resistors (R1 to R4) have dual functions: in resistance mode, they are used for upstream and downstream temperature detection and RTD (Resistance Temperature Detector) compensation, respectively. In electrode mode (by shorting terminals A and B), these resistors can be flexibly switched and reused as conductivity electrodes, cleaning cathode / anode electrodes, or ORP electrodes, thereby greatly improving the sensor's integration and measurement flexibility.

[0026] This application utilizes four resistors symmetrically distributed along the circumference, making the sensor isotropic in spatial structure. This effectively eliminates measurement errors caused by water flow direction, installation angle, or local temperature gradients, improving the uniformity and accuracy of multi-parameter measurements. Simultaneously, the use of thin-film platinum resistance elements not only achieves device miniaturization and rapid thermal response through thin-film technology but also leverages the advantages of platinum's chemical stability, corrosion resistance, and excellent resistance-temperature characteristics. This enables high-precision and high-stability temperature detection and electrochemical measurement in complex water environments. Furthermore, by defining "resistance and electrodes" through series-parallel lead connections, sharing a physical structure, simplifying the process, and achieving high integration, the application enables time-division multiplexing of temperature, conductivity, ORP measurement, and electrode cleaning functions. ORP is an indicator of the oxidizing or reducing power of an aqueous solution, measured in millivolts (mV).

[0027] In another implementation of this application, a cross-shaped cantilever beam structure 13 is formed on the surface of the silicon substrate 16 by etching (e.g., Figure 1 As shown), the insulating layer 15 covers the cantilever beam structure 13, and the heater 12 and multiple resistors 11 are arranged in the beam area of ​​the cantilever beam structure 13.

[0028] This application effectively blocks heat conduction to the substrate by etching a cross-shaped cantilever beam structure on the silicon substrate surface. This reduces heater power consumption, improves thermal response speed, and releases thermal stress generated by temperature changes, thereby significantly improving the sensor's measurement accuracy and structural stability.

[0029] In another implementation of this application, the heater 12 can be a segmented concentric annular micro heater, and the heater 12 is made of platinum metal.

[0030] In another implementation of this application, the reference electrode 14 may be made of silver or silver chloride, and the insulating layer 15 may be made of silicon dioxide or silicon nitride.

[0031] The fabrication process for the aforementioned groundwater multi-parameter MEMS sensor may include: 1. Substrate oxidation to prepare silicon oxide insulating layer.

[0032] A single-crystal silicon wafer is selected as the substrate, and a silicon dioxide insulating layer is grown on the front side of the silicon wafer using a thermal oxidation process.

[0033] 2. A silicon nitride passivation layer is deposited on the front side of the first photoresist pattern.

[0034] A silicon nitride thin film is deposited on the surface of a silicon dioxide layer, and then photoresist is spin-coated on the silicon nitride surface. After exposure and development, the photoresist is patterned to form a preliminary mask pattern for subsequent structural processing.

[0035] 3. Preparation of silver reference electrode thin film.

[0036] Using patterned photoresist as a mask, a titanium adhesion layer and a silver film are sputtered sequentially. The photoresist and excess metal on it are removed by a photoresist stripping process to obtain a patterned silver film on the substrate, which serves as a precursor for the silver chloride reference electrode.

[0037] 4. The second version of the photoresist pattern on the front side is used to define the platinum electrode area.

[0038] Photoresist is spin-coated onto the front side of the wafer, and then patterned by exposure and development. The photoresist window area defines the fabrication areas for the platinum heater electrode and the electrochemical detection platinum electrode.

[0039] 5. Preparation of platinum electrode thin films.

[0040] Using the patterned photoresist as a mask, a titanium adhesion layer and a platinum thin film are sequentially sputtered by magnetron sputtering; the photoresist and excess metal on the surface are removed by photoresist stripping process to form a patterned platinum heater electrode (i.e., the resistor in this embodiment) and a platinum working electrode.

[0041] 6. The third version of photoresist patterning on the front side defines the etching windows for the insulating layer. Photoresist is spin-coated again on the front side of the wafer, and the patterning is completed by exposure and development. The photoresist window area corresponds to the completely hollowed-out area of ​​the subsequent cantilever beam, serving as a mask for the dry etching of silicon nitride and silicon dioxide.

[0042] 7. Dry etching of the insulating layer to open the silicon etching window. Using patterned photoresist as an etching mask, dry etching is used to remove the silicon nitride and silicon dioxide layers in the window area, exposing the underlying single-crystal silicon substrate; then the remaining photoresist is removed.

[0043] 8. Photoresist patterning on the back of the silicon wafer to define the cantilever beam release profile. The wafer is flipped over, and photoresist is spin-coated on the back of the silicon wafer. After exposure and development, the photoresist is patterned, and the photoresist pattern defines the boundary profile of the wet etching of the cantilever beam.

[0044] 9. Silicon wet etching releases the cantilever beam structure. Using patterned photoresist on the back as a protective mask, the exposed single-crystal silicon is anisotropically etched using a wet etching process, etching the silicon substrate from the back to the front until the etching window on the front is penetrated, releasing the suspended cantilever beam microstructure, and removing the remaining photoresist on the back.

[0045] 10. Silver thin film chlorination treatment to prepare Ag / AgCl (silver / silver chloride) reference electrode: The patterned metallic silver region on the cantilever beam is chlorinated to convert the surface metallic silver into silver chloride. Finally, the Ag / AgCl reference electrode, platinum working electrode and platinum heating electrode are integrated on the chip to obtain the MEMS electrochemical sensing cantilever beam chip.

[0046] Finally, wire bonding is performed to obtain a multi-parameter MEMS sensor for groundwater.

[0047] The groundwater multi-parameter MEMS sensor provided in this application defines "resistance and electrodes" through a series-parallel connection of leads, sharing a common physical structure, simplifying the manufacturing process, and achieving high integration. It enables time-division multiplexing of temperature, conductivity, ORP measurement, and electrode cleaning functions. Furthermore, it eliminates the need to remove the sensor or add reagents, utilizing water electrolysis to achieve dual physicochemical cleaning, extending the maintenance-free period to several years. Moreover, the sensor's fabrication process is simple, facilitating mass production.

[0048] Reference Figure 3 This document illustrates a flowchart of a detection method provided in an embodiment of this application. This detection method can be applied to the groundwater multi-parameter MEMS sensor described in any of the above embodiments. Figure 3 As shown, the detection method may include steps 301 and 302.

[0049] Step 301: Control the connection state between the first lead end and the second lead end of the target resistor through the switching assembly, so that the target resistor is in the target working mode; wherein, the target resistor is at least one of the multiple resistors of the groundwater multi-parameter MEMS sensor.

[0050] In this embodiment, when performing detection using the groundwater multi-parameter MEMS sensor described in the above embodiments, the connection state between the first lead and the second lead of the target resistive element can be controlled by a switching component to put the target resistive element into the target operating mode. The target resistive element can be at least one of multiple resistive elements of the groundwater multi-parameter MEMS sensor. In this embodiment, the number of resistive elements on the groundwater multi-parameter MEMS sensor is preferably four. When using four resistive elements for measurement, the electrode mode and resistance mode can be switched in the following manner.

[0051] When using one resistor (e.g., R1) for measurement, and the others are idle, the switching assembly can be controlled to connect terminals A and B of the target resistor R1 to the external measurement circuit (resistance mode), or to directly short-circuit terminals A and B (electrode mode). Simultaneously, the switching assembly disconnects terminals A and B of non-target resistors R2, R3, and R4 (placing them in a high-resistance state or floating), placing them in an open-circuit idle state. This avoids interference from parasitic capacitance and leakage current, and reduces the overall system power consumption.

[0052] When using four resistive elements for measurement, in resistance mode, terminals A and B of R1 to R4 can be connected to an external multi-channel acquisition circuit via a switching assembly to achieve simultaneous multi-point temperature detection or temperature gradient analysis. In electrode mode, terminals A and B of R1 to R4 can be internally shorted via a switching assembly to form four independent equipotential electrodes, which can be combined into a four-electrode conductivity measurement array to eliminate polarization effects and improve measurement accuracy. In mixed mode, terminals A and B of some resistive elements (such as R1 and R3) can be shorted via a switching assembly to act as electrodes, while terminals A and B of other elements (such as R2 and R4) can be connected to the circuit to act as temperature sensing resistors, achieving simultaneous detection of multiple parameters.

[0053] Step 302: Detect the fluid parameters of the target water area using the target resistivity.

[0054] After the target resistivity is configured to a specific working mode, fluid parameters (such as flow velocity, flow direction, conductivity, temperature, ORP, etc.) of the target water body (such as underground water body) can be detected through the target resistivity.

[0055] Of course, in the external control device, flow and direction detection units, conductivity detection units, ORP detection units, temperature detection units and electrochemical cleaning units can be set up separately. These can be virtual units, used to control the groundwater multi-parameter MEMS sensor separately to realize the detection of different functions.

[0056] This application defines "resistance and electrodes" through the series and parallel connection of leads, sharing a physical structure, simplifying the process, and achieving high integration. At the same time, it realizes time-division multiplexing of temperature, conductivity, and ORP measurement functions.

[0057] In one implementation of this application, the target operating mode is a resistance operating mode, the fluid parameters are flow velocity parameters and flow direction parameters, the target resistor is four resistors, and the above step 302 may include: sub-steps A1 to A6.

[0058] Sub-step A1: Control the heater to heat at a specified power.

[0059] In this embodiment, the target operating mode is the resistance operating mode, the fluid parameters are the flow velocity and flow direction parameters of the fluid in the target water area (i.e., the speed and direction of the water flow), and the target resistivity is four resistivity elements (i.e., the four resistivity elements of the groundwater multi-parameter MEMS sensor are used for measurement).

[0060] When measuring flow velocity and flow direction parameters, the fluid in the target water area can be in a static state. After switching the resistance mode in step 101, a constant current is then supplied to the heater of the groundwater multi-parameter MEMS sensor, causing it to heat up continuously at a preset power. This creates an initial symmetrical thermal field around the four resistive elements on the sensor surface, which is higher than the ambient water temperature. The temperatures measured by the four resistive elements are basically equal.

[0061] Sub-step A2: Obtain the temperature values ​​of the four resistors in the resistor operating mode.

[0062] During continuous heating, the real-time resistance values ​​of four resistive elements in resistance mode can be simultaneously collected. Utilizing the temperature resistance characteristics of platinum resistance thermometers (i.e., the resistance of platinum metal exhibits a highly stable linear or quasi-linear relationship with temperature changes), these values ​​are accurately converted into corresponding real-time temperature values ​​(denoted as T1, T2, T3, and T4, respectively). Specifically, fluid flow is generated in the target water area. The forced convection of the fluid disrupts the original symmetrical thermal field. Heat is continuously carried away by the fluid on the upstream side, causing its temperature to decrease. Heat accumulates on the downstream side, causing its temperature to rise, resulting in differences in the output temperatures of the various temperature-sensing resistors. At this point, the real-time temperature values ​​of the four resistive elements can be collected.

[0063] Sub-step A3: Perform differential calculation on the temperature values ​​corresponding to the two resistors symmetrically distributed along the first direction to obtain the first temperature difference signal.

[0064] The temperature difference signal refers to the difference in temperature measured by two resistive elements on the same axis of symmetry, which is used to reflect the degree of spatial asymmetry in the heat carried away by the water flow.

[0065] After recording the real-time temperature value, the temperature values ​​of two resistors (such as R1 and R3) that are symmetrically distributed along the first direction (such as the X-axis) can be extracted and subtracted (such as ΔTx=T1-T3) to obtain the first temperature difference signal that reflects the difference in heat loss in that direction.

[0066] Sub-step A4: Perform differential calculation on the temperature values ​​corresponding to the two resistive elements symmetrically distributed along the second direction to obtain the second temperature difference signal; wherein the first direction and the second direction are orthogonal to each other.

[0067] The first and second directions are two mutually orthogonal axes of symmetry of the four resistive elements distributed on the circumference.

[0068] At the same time, the temperature values ​​of two other resistive elements (such as R2 and R4) that are symmetrically distributed along the second direction (such as the Y-axis, which is orthogonal to the X-axis) can be extracted and subtracted (such as ΔTy=T2-T4) to obtain a second temperature difference signal that reflects the difference in heat loss in this direction.

[0069] Sub-step A5: Determine the flow velocity parameters of the fluid in the target water area based on the first temperature difference signal and the second temperature difference signal.

[0070] After obtaining the first and second temperature difference signals, the fluid velocity can be calculated based on these two signals, thus obtaining the velocity parameters. For example, based on a fluid dynamics heat transfer model, the first and second temperature difference signals can be vector-synthesized (the modulus of the temperature difference vector can be calculated). This modulus has a specific functional relationship with the rate at which the fluid carries away heat. The velocity parameters (velocity) of the fluid in the target water area can then be calculated using a built-in algorithm or by looking up a table.

[0071] Sub-step A6: Determine the flow direction parameters of the fluid in the target water area based on the orientation of the resistor corresponding to the maximum temperature value among the temperature values ​​of each resistor.

[0072] Simultaneously, the temperature values ​​of the four resistors can be compared, and the maximum temperature value can be selected from the corresponding temperature values ​​of each resistor. Since the water flow carries the heat generated by the heater downstream, resulting in the highest temperature of the resistor on the downstream side, the flow direction parameter of the fluid in the target water area can be directly determined based on the physical orientation angle of the resistor on the circumference corresponding to this maximum temperature value.

[0073] In practical applications, during the flow rate and direction measurement phase, the four components are used only as temperature measuring resistors. The switching network cuts off all electrode-related paths, and the conductivity, ORP, and electrochemical cleaning units are completely disconnected to avoid mutual interference between circuits.

[0074] This application achieves high-precision, two-dimensional vector measurement of water flow velocity and direction without the need for additional mechanical structures by controlling four resistors to operate in resistive mode and continuously heating them with a heater. This greatly improves the measurement reliability and integration of the sensor in complex aquatic environments.

[0075] In one implementation of this application, the target operating mode is a resistance operating mode, the fluid parameter is temperature, and the target resistive element is any one of the multiple resistive elements of a groundwater multi-parameter MEMS sensor. Step 302 may include sub-step B1 and sub-step B2.

[0076] Sub-step B1: Obtain the resistance value of the target resistor in the resistor operating mode.

[0077] In this embodiment, when measuring fluid temperature, in step 101, the external temperature detection unit can connect the first and second leads of the selected target resistor (such as R1) to the external measurement circuit through an analog switch array, while placing the remaining non-target resistors in an open circuit or high resistance state to eliminate interference.

[0078] Subsequently, a small and constant excitation current can be applied to the target resistive element, and a high-precision analog-to-digital converter acquires the voltage across its terminals in real time. Based on Ohm's law (R=U / I), the microprocessor uses the measured voltage value and the known constant current value to accurately calculate the current real-time resistance value of the target resistive element.

[0079] Sub-step B2: Determine the temperature of the fluid in the target water area based on the preset correspondence between resistance and temperature and the resistance value.

[0080] After acquiring the resistance value, a pre-defined resistance-temperature correspondence can be used. Through table lookup and interpolation, the real-time resistance value is accurately mapped and converted into the corresponding temperature value, thereby obtaining the real-time temperature of the fluid in the target water area.

[0081] This application enables rapid and accurate detection of water temperature by switching a single resistor in a multi-parameter MEMS groundwater sensor to a resistive operating mode.

[0082] In one implementation of this application, the target operating mode is an electrode operating mode, the fluid parameter is conductivity, and the target resistive body consists of four resistive bodies: a first and a third resistive body symmetrically distributed along a first direction, and a second and a fourth resistive body symmetrically distributed along a second direction, wherein the first and second directions are orthogonal to each other. Step 302 may include sub-steps C1 to C5.

[0083] Sub-step C1: Apply a first AC excitation signal between the first resistor and the third resistor, and detect the first response current.

[0084] In this embodiment, when measuring conductivity, the four resistors of the groundwater multi-parameter MEMS sensor can be used as target resistors. The target operating mode of these four resistors is the electrode operating mode. These four resistors are a first resistor and a third resistor symmetrically distributed along a first direction, and a second resistor and a fourth resistor symmetrically distributed along a second direction, with the first direction and the second direction being orthogonal to each other.

[0085] The AC excitation signal is an alternating voltage or current signal applied between the electrode pairs. AC is used to avoid the electrolysis and polarization effects on the electrode surface caused by DC.

[0086] The response current is an alternating current formed between two electrodes as the current passes through the target water body under the action of an AC excitation signal.

[0087] When measuring conductivity, a first AC excitation signal (usually a constant voltage AC signal) of a specific frequency and amplitude can be applied between the first and third resistive elements, and a detection circuit (such as a transimpedance amplifier) ​​can be used to collect the first response current flowing through the water body in real time.

[0088] Sub-step C2: Apply a second AC excitation signal between the second resistor and the fourth resistor, and detect the second response current.

[0089] Simultaneously, a second AC excitation signal (usually consistent with the frequency and amplitude of the first signal) can be applied between R2 and R4, and the corresponding second response current can be detected.

[0090] Sub-step C3: Determine the first conductivity based on the amplitude of the first AC excitation signal and the first response current.

[0091] After obtaining the first response current, the voltage amplitude of the first AC excitation signal and the amplitude of the first response current can be calculated according to Ohm's law to obtain the water impedance (or conductance) in the first direction. Then, the first conductivity can be calculated by multiplying or dividing by the geometric electrode constant of the electrode pair.

[0092] Sub-step C4: Determine the second conductivity based on the amplitude of the second AC excitation signal and the second response current.

[0093] Similar to the calculation method for the first conductivity, the amplitude of the second AC excitation signal and the second response current are used to calculate the water impedance in the second direction, and the second conductivity is obtained by combining the electrode constant.

[0094] Understandably, for ease of calculation and consistency, the amplitudes of the first AC excitation signal and the second AC excitation signal can be the same.

[0095] Sub-step C5: Determine the conductivity of the fluid in the target water area based on the average of the first conductivity and the second conductivity.

[0096] Electrical conductivity is a physical quantity that characterizes the ability of water to conduct electric current and is an important water quality indicator that reflects the total concentration of dissolved solids (ions) in water.

[0097] After obtaining the first conductivity and the second conductivity, the average value of the first conductivity and the second conductivity can be calculated, and this average value can be used as the conductivity of the fluid in the target water area.

[0098] Of course, in practical applications, only two resistive elements can be used as target resistive elements for conductivity measurement, such as the first and third resistive elements, or the second and fourth resistive elements. Two resistive elements can also measure fluid conductivity, but the accuracy is slightly lower than that of measuring with four resistive elements.

[0099] This application constructs a dual-channel conductivity measurement array using four orthogonally symmetrically distributed resistive elements. It effectively overcomes the electrode polarization effect by utilizing AC excitation and improves the accuracy, stability, and spatial representativeness of conductivity measurement through dual-channel data fusion and averaging.

[0100] In one implementation of this application, the target operating mode is the electrode operating mode, the fluid parameter is the oxidation-reduction potential (ORP) parameter, and the target resistivity is any one of a plurality of resistivityes (i.e., using one resistivity as the target resistivity for ORP parameter measurement). Step 302 above may include sub-steps D1 and D2.

[0101] Sub-step D1: Obtain the potential difference between the target resistive element and the reference electrode.

[0102] In this embodiment, the potential difference refers to the open-circuit voltage generated by the galvanic cell formed by the working electrode (target resistivity) and the reference electrode in the water body to be tested.

[0103] When measuring the ORP parameter, in step 101, the first and second leads of the selected target resistive element (such as R1) can be short-circuited to make it an equipotential working electrode.

[0104] The working electrode and the reference electrode can then be connected to an external high-input-impedance voltage measurement circuit. Since the water acts as an electrolyte solution, a galvanic cell will form between the working electrode and the reference electrode. The high-input-impedance circuit accurately acquires and amplifies the open-circuit potential difference between the two electrodes with almost no current consumption (to avoid polarization), thus obtaining the raw ORP measurement value.

[0105] Sub-step D2: Determine the ORP parameters of the fluid in the target water area based on the sum of the potential difference and the preset reference electrode potential compensation value.

[0106] The reference electrode potential compensation value is the correction value required to convert the potential of the currently used reference electrode (such as Ag / AgCl) to the potential of the standard hydrogen electrode (SHE).

[0107] After obtaining the original potential difference, a pre-stored reference electrode potential compensation value can be acquired (this compensation value can be dynamically calculated or obtained by looking up a table based on the water temperature measured in real time by the sensor, in order to eliminate the influence of temperature on the reference electrode potential). The original potential difference is then algebraically added to this compensation value, thereby converting the measurement result into an absolute redox potential value relative to the standard hydrogen electrode (SHE), which is the final determined ORP parameter of the fluid in the target water area.

[0108] This application achieves high-precision measurement of water oxidation-reduction potential by reusing a thin-film platinum resistance thermometer as the working electrode of ORP, combined with high input impedance measurement and reference electrode potential compensation algorithm, without adding an additional electrode structure, further improving the multi-parameter integration and space utilization of the sensor.

[0109] In one implementation of this application, the aforementioned groundwater multi-parameter MEMS sensor can be used for in-situ self-cleaning of electrodes. The cleaning method may include steps E1 and E2.

[0110] Step E1: Switch the operating mode of the resistor to be cleaned among the plurality of resistors to the electrode operating mode using the switching assembly.

[0111] In this embodiment, the in-situ self-cleaning principle of the electrodes of the groundwater multi-parameter MEMS sensor is as follows: the resistive element is switched to electrode mode, a large polarization potential is applied, and bubbles are generated using oxygen evolution reaction (OER) and hydrogen evolution reaction (HER). The bubble generation process brings local shear force, which physically peels off the deposited layer on the electrode surface; at the same time, the active oxygen generated by oxygen evolution can oxidize and decompose organic pollutants, and the active hydrogen generated by hydrogen evolution can reduce oxide deposits such as iron and manganese. Through alternating polarization between electrodes, hydrogen and oxygen are alternately generated on different electrode surfaces, enhancing the cleaning effect brought about by bubble disturbance.

[0112] During in-situ electrode cleaning, the operating mode of the resistor to be cleaned among multiple resistors can be switched to the electrode operating mode using a switching assembly. For example, the first and second leads of the resistor to be cleaned (such as R1) can be physically shorted internally, transforming it from an independent temperature-sensing resistor into an equipotential overall working electrode. At the same time, the reference electrode can be connected to the common reference terminal of the cleaning drive circuit, completing the electrode state and circuit configuration before cleaning.

[0113] Step E2: Apply a cleaning drive potential between the resistor to be cleaned and the reference electrode to cause an electrochemical reaction on the surface of the resistor to be cleaned and generate bubbles, so as to clean the resistor through the bubbles.

[0114] After switching the electrode operating mode, a DC or pulsed cleaning drive potential higher than the water electrolysis threshold can be applied between the resistor to be cleaned and the reference electrode, forcing a vigorous water electrolysis reaction to occur on the surface of the resistor to be cleaned (oxygen is evolved if it is the anode, and hydrogen is evolved if it is the cathode). A large number of microbubbles generated in situ grow, merge, and rapidly detach on the surface of the platinum electrode. In this process, strong mechanical shearing forces and microfluidic disturbances are generated, which effectively physically peel off and wash away biofilms, dirt, deposits, or aging products attached to the surface of the resistor, achieving efficient in-situ self-cleaning and restoring the activity of the electrode surface.

[0115] During resistive element cleaning, the potential timing sequence can be as follows: Figure 4 As shown, the horizontal axis Time represents time (i.e., the time axis of the resistive cleaning process), and the vertical axis Voltage represents voltage (representing the driving voltage applied across the electrodes). Figure 2 The voltage range is -1.5V to +1.5V. Potential timing logic: The potential ramps up from 0V to the anodic polarization potential +1.5V (Ag / AgCl), maintains this for a certain time, then ramps down to the cathodic polarization potential -1V (Ag / AgCl), maintains this potential, and then ramps back up to 0V. By alternately applying the anode and cathode potentials, the oxygen evolution and hydrogen evolution reactions are triggered sequentially.

[0116] During cleaning, the first and second resistors can be used as a first group, and the third and fourth resistors as a second group. Each group is cleaned by applying a potential according to the aforementioned potential logic. Furthermore, the first and second resistors, or the third and fourth resistors, can be swapped before performing the above operation to further reduce the polarization effect. In a preferred example of this application, the electrode polarization potential range is -1.5 V to +1.5 V.

[0117] This application eliminates the need to remove the sensor or add reagents. It utilizes water electrolysis to achieve dual physical and chemical cleaning, which can extend the maintenance-free cycle of groundwater multi-parameter MEMS sensors to several years.

[0118] In this embodiment, the complete timing sequence for detection and resistor cleaning using a multi-parameter MEMS sensor for groundwater (containing four resistors) can be shown in Table 3 below: Table 3 Working Sequence

[0119] In Table 3 above, the four resistors are R1, R2, R3, and R4, and T1 is the heater. High resistance (i.e., high impedance state) means that the analog switch completely disconnects both ends A and B of the resistor, so that it is neither connected to any measurement circuit nor to the drive / excitation circuit, and the lead end is in a floating state with an approximately open circuit.

[0120] Phase 1: Flow and direction detection (5~30 seconds). The central heater T1 heats at a constant power, forming a symmetrical steady-state thermal field around the sensor. R1~R3 ​​are all switched to resistance temperature measurement mode, and the temperature values ​​are collected in real time from the four channels.

[0121] Phase 2: Conductivity and Temperature Detection (0.1~3 seconds). Heating stops at T1. R1 and R3 switch to electrode mode (terminals A and B shorted to form an equipotential body), forming a pair of conductivity electrodes. AC excitation is applied between them, and the response current is detected to calculate conductivity. R2 remains in resistance mode to simultaneously measure water temperature, providing temperature compensation for conductivity. R4 is placed in a high-resistance floating state to prevent it from acting as a parasitic electrode, shunting current, or causing polarization interference. R2+R4 can be used alternately to measure another set of conductivity values ​​and average them to improve accuracy.

[0122] Phase 3: ORP Detection (0.1~1 seconds). T1 remains powered off. R4 switches to electrode mode as the ORP working electrode, paired with the central Ag / AgCl reference electrode. The steady-state potential difference between the two is acquired and converted into a redox potential. Since the ORP signal is a high-impedance microvolt-level voltage, R1 and R3 must be in a high-blocking-on state; any leakage current will severely affect measurement accuracy. R2 can remain in resistance mode for backup temperature measurement or temperature compensation. The ORP channel is immediately disconnected after measurement.

[0123] Phase 4: Cleaning Group 1 (1-10 seconds). Power is off at T1. All electrodes (R1-R4) are switched to electrode mode and divided into two groups—R1 paired with R2, and R3 paired with R4. Within each group, the anode and cathode polarization potentials are alternately applied according to a potential sequence of "0V ramp-up to +1.5V maintenance, then ramp-down to -1V maintenance, and finally back to 0V." The anode triggers the oxygen evolution reaction, and the cathode triggers the hydrogen evolution reaction. The deposited layer is physically stripped away using bubble shear force, while active oxygen oxidizes organic matter and active hydrogen reduces iron and manganese oxides. The anode and cathode within each group can be interchanged to reduce unidirectional polarization accumulation.

[0124] Phase 5: Cleaning Group 2 (1-10 seconds). Power is off at T1; only R3 and R4 participate in the cleaning process—R3 acts as the anode, applying a positive potential to trigger oxygen evolution, and R4 acts as the cathode, applying a negative potential to trigger hydrogen evolution. R1 and R2 are completely disconnected and do not participate. Unlike Phase 4, where all four electrodes are cleaned simultaneously, this phase only cleans one group of electrodes, while the other group rests. This avoids overall potential disturbance caused by simultaneous polarization of all electrodes, and allows for cleaning only the most heavily contaminated group of electrodes as needed.

[0125] This application presents a multi-parameter MEMS sensor for groundwater based on a resistor-electrode functional reuse method, along with a detection and cleaning method. The sensor comprises functional resistors R1-R4 with leads at both ends, which can be flexibly reused between "resistance mode" (temperature measurement / heating) and "electrode mode" (electrochemical detection / cleaning after short-circuiting) via an external switch. Based on this, time-division detection of five parameters—flow rate, flow direction, conductivity, temperature, and ORP—is achieved. Furthermore, the hydrogen evolution / oxygen evolution reaction in electrode mode enables in-situ self-cleaning of the electrode. The multi-parameter transmitter provided in this application features ultra-high integration, high-precision temperature measurement, and maintenance-free cleaning, making it suitable for long-term unattended groundwater monitoring.

[0126] Finally, it should be noted that in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or terminal that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or terminal. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or terminal that includes said element.

[0127] The present application has been described in detail above. Specific examples have been used to illustrate the principles and implementation methods of the present application. The description of the above embodiments is only for the purpose of helping to understand the method and core ideas of the present application. At the same time, for those skilled in the art, there will be changes in the specific implementation methods and application scope based on the ideas of the present application. Therefore, the content of this specification should not be construed as a limitation of the present application.

Claims

1. A groundwater multi-parameter MEMS sensor, characterized in that, The sensor includes: a silicon substrate, an insulating layer, multiple resistors, a heater, and a reference electrode, wherein, The insulating layer covers the surface of the silicon substrate, and the reference electrode, the heater, and the plurality of resistors are all disposed on the side of the insulating layer away from the silicon substrate; The reference electrode is disposed in the central region of the insulating layer, the heater is arranged around the periphery of the reference electrode, and the plurality of resistive elements are symmetrically distributed around the periphery of the heater; Each of the resistors is provided with a first lead end and a second lead end, and the first lead end and the second lead end are respectively connected to an external circuit through metal leads; The first lead and the second lead of each of the resistors are configured to be electrically connected to a switching assembly to switch between an electrode operating mode and a resistor operating mode under the control of the switching assembly. In the resistor operating mode, the first lead end and the second lead end are connected to an external circuit, so that the resistor body works as a resistor element. In the electrode operating mode, the first lead end and the second lead end are electrically connected to each other, so that the resistive body forms an equipotential electrode.

2. The sensor according to claim 1, characterized in that, The plurality of resistive elements includes: a first resistive element, a second resistive element, a third resistive element, and a fourth resistive element, wherein, The first resistor and the second resistor are symmetrically distributed along the circumferential direction, and the third resistor and the fourth resistor are symmetrically distributed along the circumferential direction; Each of the resistors is a thin-film platinum resistor.

3. The sensor according to claim 1, characterized in that, A cross-shaped cantilever beam structure is formed on the surface of the silicon substrate by etching. The insulating layer covers the cantilever beam structure, and the heater and the plurality of resistors are arranged in the beam area of ​​the cantilever beam structure.

4. The sensor according to claim 1, characterized in that, The heater is a segmented concentric ring-shaped micro heater, and the heater is made of platinum metal.

5. The groundwater multi-parameter MEMS sensor according to claim 1, characterized in that, The reference electrode is made of silver or silver chloride, and the insulating layer is made of silicon dioxide or silicon nitride.

6. A detection method, applied to the sensor according to any one of claims 1 to 5, characterized in that, include: The connection state between the first lead and the second lead of the target resistive element is controlled by a switching assembly to put the target resistive element into a target operating mode; wherein, the target resistive element is at least one of the multiple resistive elements of the groundwater multi-parameter MEMS sensor; The fluid parameters of the target water area are detected by the target resistivity.

7. The method according to claim 6, characterized in that, The target operating mode is a resistance operating mode, the fluid parameters are flow velocity parameters and flow direction parameters, and the target resistive element is four resistive elements; The detection of fluid parameters of the target water area through the target resistivity includes: Control the heater to heat at a specified power; Obtain the temperature values ​​of the four resistors in the resistor operating mode; The temperature values ​​corresponding to two resistors symmetrically distributed along the first direction are differentially calculated to obtain the first temperature difference signal. The temperature values ​​corresponding to two resistors symmetrically distributed along the second direction are differentially calculated to obtain a second temperature difference signal; wherein the first direction and the second direction are orthogonal to each other. Based on the first temperature difference signal and the second temperature difference signal, the flow velocity parameters of the fluid in the target water area are determined; The flow direction parameters of the fluid in the target water area are determined based on the orientation of the resistor corresponding to the maximum temperature value among the temperature values ​​of each resistor.

8. The method according to claim 6, characterized in that, The target operating mode is a resistance operating mode, the fluid parameter is temperature, and the target resistive element is any one of the plurality of resistive elements; The detection of fluid parameters of the target water area through the target resistivity includes: Obtain the resistance value of the target resistor in the resistor operating mode; The temperature of the fluid in the target water area is determined based on the preset relationship between resistance and temperature and the resistance value.

9. The detection method according to claim 6, characterized in that, The target working mode is the electrode working mode, the fluid parameter is the conductivity, and the target resistive element is four resistive elements. The four resistive elements are a first resistive element and a third resistive element symmetrically distributed along a first direction, and a second resistive element and a fourth resistive element symmetrically distributed along a second direction. The first direction and the second direction are orthogonal to each other. The detection of fluid parameters of the target water area through the target resistivity includes: A first AC excitation signal is applied between the first resistor and the third resistor, and a first response current is detected; A second AC excitation signal is applied between the second resistor and the fourth resistor, and a second response current is detected; The first conductivity is determined based on the amplitude of the first AC excitation signal and the first response current. The second conductivity is determined based on the amplitude of the second AC excitation signal and the second response current. The conductivity of the fluid within the target water area is determined based on the average of the first conductivity and the second conductivity.

10. The detection method according to claim 6, characterized in that, The target operating mode is the electrode operating mode, the fluid parameter is the oxidation-reduction potential (ORP) parameter, and the target resistivity is any one of multiple resistivityes. The detection of fluid parameters of the target water area through the target resistivity includes: Obtain the potential difference between the target resistive element and the reference electrode; The ORP parameters of the fluid in the target water area are determined based on the sum of the potential difference and the preset reference electrode potential compensation value.

11. The detection method according to claim 6, characterized in that, The method further includes: The switching assembly switches the operating mode of the resistor to be cleaned among the plurality of resistors to the electrode operating mode. A cleaning drive potential is applied between the resistor to be cleaned and the reference electrode to cause an electrochemical reaction on the surface of the resistor to be cleaned and generate bubbles, so as to clean the resistor through the bubbles.

Images