Capacitive microfluid pressure sensor based on polymer bonding technology and manufacturing method thereof

Abstract

The invention belongs to the technical field of electronic components, and discloses a capacitive microfluid pressure sensor based on a polymer bonding technology and a manufacturing method thereof.The capacitive microfluid pressure sensor comprises a sensor body obtained by sequentially connecting an upper layer, a middle layer and a lower layer through polymer bonding layers, and the upper layer comprises a lead hole, a microchannel inlet and outlet and a first groove; the top of the middle layer is provided with a second groove communicated with the first groove, and the bottom is provided with an upper electrode lead groove; the polymer layer between the lower layer and the middle layer comprises a lower electrode, a strip and a lower electrode lead groove, and the upper layer lead hole, the middle layer lead hole and the lower layer lead hole are communicated. And the lower-layer lead hole penetrates from the middle layer to the lower layer. And a suspended part between the micro-channel and the groove of the lower electrode is used as a pressure sensing diaphragm. According to the technical scheme, the whole device is compact and integrated, the performance is stable, and efficient integration and real-time pressure sensing of the microchannel and the electrode system can be achieved.

Description

Technical Field

[0001] The present invention belongs to the technical field of electronic components, and in particular relates to a capacitive microfluidic pressure sensor based on polymer bonding technology and a manufacturing method thereof. Background Art

[0002] In recent years, microfluidic devices have achieved rapid development in many fields such as micropumps, microheat exchangers, and microreactors. Pressure monitoring plays a vital role in the design of microfluidic devices, the control of the working state of microfluidic devices, and the study of microfluidic flow laws. Traditional pressure gauges are bulky and often cannot be integrated with microchannels. They can only measure the pressure of microchannels by draining through catheters. In this process, pressure loss is very likely to occur. Moreover, when measuring the pressure along the microchannel, it is necessary to drill holes in the microchannel wall and connect the catheter, which further destroys the initial morphology of the microchannel. In order to achieve accurate measurement of the fluid pressure in the microchannel, the best way is to arrange the pressure sensor on the inner wall of the microchannel, perform in-situ measurement of the microfluid, and have little impact on the initial morphology of the microchannel.

[0003] Capacitive pressure sensors typically consist of a movable electrode and a fixed electrode, forming a capacitor. The movable electrode is embedded in a pressure-sensing diaphragm. A pressure difference across the diaphragm causes it to deform, causing the movable electrode to deform as well. This changes the distance between the two electrodes, and the capacitance of the capacitive pressure sensor changes as well, converting the pressure signal into a capacitance signal.

[0004] As for the manufacture of capacitive pressure sensors, traditional methods often require a groove to be etched on the surface of a wafer to form a gap between the two electrodes, and then it is bonded to another wafer using technologies such as silicon-to-silicon bonding and anodic bonding. These steps have high requirements for the verticality, depth, and flatness of the etching, and the bonding process requires high temperature and tedious pretreatment of the bonding surface. Compared with silicon-silicon bonding and anodic bonding, polymer bonding has lower requirements for the bonding surface and temperature, and does not require the application of voltage. Polymer bonding is achieved by applying a uniform layer of polymer on the bonding surface, and promoting the bonding of the two bonding surfaces under certain temperature and pressure. During the bonding process of existing capacitive pressure sensors, pressure cannot be applied to the groove part of the fluid microchannel, and thus the bonding effect between the bottom surface of the fluid microchannel groove and the underlying wafer is poor, and the performance of the prepared microfluidic pressure sensor is unstable. Summary of the Invention

[0005] The purpose of the present invention is to provide a capacitive microfluidic pressure sensor based on polymer bonding technology and a manufacturing method thereof, so as to solve the problems existing in the above-mentioned prior art.

[0006] To achieve the above objectives, the present invention provides a capacitive microfluidic pressure sensor based on polymer bonding technology, comprising an upper structure, an intermediate structure, and a lower structure sequentially connected by a polymer bonding layer; an upper lead hole, a microchannel inlet, and a microchannel outlet are defined at the top of the upper structure; a first groove is defined in the polymer bonding layer between the upper structure and the intermediate structure, and both the microchannel inlet and the microchannel outlet are connected to the first groove;

[0007] The middle layer structure has a second groove and a middle layer lead hole on the top, and an upper electrode lead groove on the bottom; the second groove is connected to the first groove to form a microchannel;

[0008] The polymer adhesive layer between the lower structure and the intermediate structure is provided with a lower electrode groove, a strip groove and a lower electrode lead groove which are connected in sequence;

[0009] The upper layer lead hole, the middle layer lead hole and the lower electrode lead groove are connected in sequence; a lower layer lead hole is opened between the middle layer structure and the lower end surface and the lower end surface of the lower layer structure; and the suspended part between the microchannel and the lower electrode groove is used as a pressure sensing diaphragm.

[0010] Optionally, the intermediate layer structure adopts an SOI wafer, which includes, from bottom to top, a lower surface silicon dioxide layer, a device layer, a buried oxide layer, a substrate layer and an upper surface silicon dioxide layer;

[0011] The intermediate layer lead hole penetrates the lower surface silicon dioxide layer, the device layer, the buried oxide layer, the substrate layer and the upper surface silicon dioxide layer, and is respectively connected to the lower electrode lead groove and the upper layer lead hole; the second groove has the buried oxide layer as the bottom surface, penetrates the substrate layer and the upper surface silicon dioxide layer and is connected to the first groove; the upper electrode lead groove has the device layer as the bottom surface, penetrates and extends to the upper end surface of the upper surface silicon dioxide layer;

[0012] The pressure sensing diaphragm comprises a buried oxide layer of a suspended portion, a device layer, and a silicon dioxide layer on the lower surface, and the device layer of the suspended portion serves as an upper electrode.

[0013] Optionally, an upper electrode lead pad is provided in the upper electrode lead groove, and the upper electrode lead pad is electrically connected to the upper electrode through a device layer.

[0014] Optionally, both the upper structure and the lower structure are made of glass wafers.

[0015] Optionally, a lower electrode lead pad is provided in the lower electrode lead groove, a lower electrode is installed in the lower electrode groove, and the lower electrode lead pad is electrically connected to the lower electrode through the strip-shaped groove.

[0016] A method for preparing a capacitive microfluidic pressure sensor based on polymer bonding technology, comprising:

[0017] Step 1: Obtain a first glass wafer, spin-coat a first polymer adhesive layer on the lower surface of the first glass wafer and perform a groove process to obtain a first groove; perform a hole opening on the first glass wafer to obtain an upper layer lead hole, a microchannel inlet, and a microchannel outlet, and perform cleaning and drying to complete the preparation of the upper layer wafer;

[0018] Step 2: Obtain an SOI wafer, construct an upper electrode lead groove and a groove corresponding to the middle layer lead hole on the lower surface of the SOI wafer; generate an upper electrode lead pad in the groove corresponding to the upper electrode lead groove; extend the groove corresponding to the middle layer lead hole to the substrate layer of the SOI wafer based on a spin-on photoresist method and a dry etching method; perform cleaning and spin-drying to complete the preparation of the middle layer wafer;

[0019] Step 3: Obtain a second glass wafer, magnetron sputter a metal film on the upper surface of the second glass wafer through a lift-off process to form a lower electrode, a strip-shaped lead structure, and a lower electrode lead pad; spin-coat a second polymer film adhesive layer and perform patterning to form a lower electrode groove, a strip-shaped groove, and a lower electrode lead groove; laser drill holes on the bottom of the second glass wafer to form lower layer lead holes; clean and spin-dry, completing the preparation of the lower layer wafer;

[0020] Step 4: Bond the lower wafer to the middle wafer based on polymer bonding technology, construct a second groove on the upper surface of the middle wafer, and penetrate the upper surface of the middle wafer to the groove corresponding to the middle layer lead hole to obtain a first bonding body; bond the upper wafer to the first bonding body based on polymer bonding technology to obtain a second bonding body, cut the second bonding body to obtain a number of capacitive microfluidic pressure sensors.

[0021] Optionally, the step 2 specifically includes:

[0022] Silicon dioxide layers are constructed on the upper and lower surfaces of the SOI wafer, the silicon dioxide layer on the upper surface is removed using a BOE solution, and the silicon dioxide layer on the lower surface is patterned to obtain grooves corresponding to upper electrode lead grooves and middle layer lead holes; a metal film is magnetron sputtered in the grooves corresponding to the upper electrode lead grooves using a lift-off process to generate upper electrode lead pads; the grooves corresponding to the middle layer lead holes are extended to the substrate layer of the SOI wafer using a spin-on photoresist method and a dry etching method; and the middle layer wafer is cleaned and dried to complete the preparation.

[0023] Optionally, a second groove is formed on the upper surface of the middle wafer and penetrates the upper surface of the middle wafer to the groove corresponding to the middle layer lead hole, specifically including:

[0024] Spin-coat photoresist on the upper surface of the middle layer wafer, perform patterning and etching to obtain microchannel grooves and middle layer lead holes, and remove excess photoresist.

[0025] The technical effects of the present invention are:

[0026] The sensor provided by the present invention can be integrated with a microfluidic chip without almost destroying the shape of the microchannel, thereby realizing in-situ real-time dynamic measurement of microfluidic pressure. This embodiment uses a patterned polymer to form the lower electrode groove, the strip groove and the lower electrode lead groove, and does not need to be etched to realize these three structures, which greatly simplifies the process. This embodiment uses a patterned metal layer as the lower electrode. The bonding technology of this sensor adopts polymer bonding technology, which has lower requirements on the process of the bonding surface before bonding, improves bonding stability, lowers bonding cost, takes less time for bonding, and has higher bonding efficiency. The preparation method of this sensor is easier, more stable and more efficient than the existing process, and the cost is also lower. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0028] The accompanying drawings, which constitute part of this application, are intended to provide a further understanding of this application. The exemplary embodiments and descriptions of this application are intended to explain this application and do not constitute an improper limitation on this application. In the accompanying drawings:

[0029] Figure 1 Schematic diagram of the exploded structure of a polymer-bonded capacitive microfluidic pressure sensor according to an embodiment of the present invention;

[0030] Figure 2 1 is a side view of a capacitive microfluidic pressure sensor based on polymer bonding in an embodiment of the present invention;

[0031] Figure 3 Schematic diagram of the planar structure of the processing result of the polymer-bonded capacitive microfluidic pressure sensor in an embodiment of the present invention;

[0032] Figure 4 is a legend diagram corresponding to each material in the embodiment of the present invention;

[0033] Figure 5 This is a process flow chart for processing the upper wafer of a capacitive microfluidic pressure sensor based on polymer bonding in an embodiment of the present invention;

[0034] Figure 6 This is a process flow chart for the middle wafer processing of a capacitive microfluidic pressure sensor based on polymer bonding in an embodiment of the present invention;

[0035] Figure 7 This is a process flow chart for processing the lower wafer of a capacitive microfluidic pressure sensor based on polymer bonding in an embodiment of the present invention;

[0036] Figure 8 This is a process flow chart for multi-layer wafer processing of a capacitive microfluidic pressure sensor based on polymer bonding in an embodiment of the present invention;

[0037] Explanation of reference numerals: 1. Upper lead hole; 2. Microchannel outlet; 3. Microchannel groove; 4. Upper electrode lead pad; 5. Upper electrode lead groove; 6. Strip-shaped lead structure; 7. Lower electrode; 8. Lower lead hole; 9. Patterned lower polymer adhesive layer; 10. Lower electrode groove; 11. Strip-shaped groove; 12. Lower electrode lead groove; 13. Lower electrode lead pad; 14. Middle layer lead hole; 15. Patterned upper polymer adhesive layer; 16. Polymer microchannel groove; 17. Microchannel inlet; 18. Upper structure; 19. Middle structure; 20. Lower structure; 21. Pressure sensing diaphragm; 22. Upper electrode. DETAILED DESCRIPTION

[0038] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as limiting the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0039] It should be understood that the terms described herein are intended only to describe particular embodiments and are not intended to limit the present invention. In addition, for numerical ranges herein, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Each smaller range between any intermediate value within a stated value or stated range and any other stated value or intermediate value within the stated range is also encompassed by the present invention. The upper and lower limits of these smaller ranges may be independently included or excluded within the scope.

[0040] Unless otherwise indicated, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art. Although only preferred methods are described herein, any method similar or equivalent to that described herein may also be used in the practice or testing of the present invention. All documents mentioned in this specification are incorporated by reference to disclose and describe the methods associated with the documents. In the event of any conflict with any incorporated document, the contents of this specification shall prevail.

[0041] It will be apparent to those skilled in the art that various modifications and variations may be made to the specific embodiments of the present invention without departing from the scope or spirit of the invention. Other embodiments will be apparent to those skilled in the art from the present invention. The present description and examples are intended to be illustrative only.

[0042] The words “include,” “including,” “have,” “contain,” etc. used in this article are open-ended terms, meaning including but not limited to.

[0043] It should be noted that, in the absence of conflict, the embodiments and features of the embodiments in this application can be combined with each other. The present application will be described in detail below with reference to the accompanying drawings and in combination with the embodiments.

[0044] Example 1

[0045] like Figure 1 - Figure 8 As shown, in this embodiment, a capacitive microfluidic pressure sensor based on polymer bonding technology is provided, comprising an upper structure 18, an intermediate structure 19 and a lower structure 20 connected in sequence by a polymer adhesive layer; the top of the upper structure 18 is provided with an upper lead hole 1, a microchannel inlet and a microchannel outlet 2, a first groove is provided in the polymer adhesive layer between the upper structure 18 and the intermediate structure 19, and the microchannel inlet and the microchannel outlet 2 are both connected to the first groove; the top of the intermediate structure 19 is provided with a second groove and an intermediate lead hole 14, and the bottom is provided with a Upper electrode lead groove 5; the second groove and the first groove are connected to form a microchannel; the polymer adhesive layer between the lower structure 20 and the intermediate layer structure 19 is provided with a lower electrode groove 10, a strip groove 11 and a lower electrode lead groove 12 which are connected in sequence, and the upper lead hole 1, the intermediate layer lead hole 14 and the lower electrode lead groove 12 are connected in sequence; a lower layer lead hole 8 is provided between the intermediate layer structure 19 and the lower end surface and the lower end surface of the lower structure 20; the suspended part between the microchannel and the lower electrode groove 10 is used as a pressure sensing diaphragm 21.

[0046] A method for preparing a capacitive microfluidic pressure sensor based on polymer bonding technology, comprising:

[0047] Obtain a first glass wafer, spin-coat a first polymer adhesive layer on the lower surface of the first glass wafer and perform a groove process to obtain a first groove; perform a hole drilling on the first glass wafer to obtain an upper layer lead hole 1, a microchannel inlet, and a microchannel outlet 2, and perform cleaning and drying to complete the preparation of the upper layer wafer;

[0048] Obtain an SOI wafer, construct an upper electrode lead groove 5 and a groove corresponding to the middle layer lead hole 14 on the lower surface of the SOI wafer; generate an upper electrode lead pad 4 in the groove corresponding to the upper electrode lead groove 5; extend the groove corresponding to the middle layer lead hole 14 to the substrate layer of the SOI wafer based on a spin-on photoresist method and a dry etching method; perform cleaning and spin-drying to complete the preparation of the middle layer wafer;

[0049] A second glass wafer is obtained, and a metal film is magnetron sputtered on the upper surface of the second glass wafer using a lift-off process to form a lower electrode 7, a strip-shaped lead structure 6, and a lower electrode lead pad 13. A second polymer film adhesive layer is spin-coated and patterned to form a lower electrode groove 10, a strip-shaped groove 11, and a lower electrode lead groove 12. Laser drilling is performed on the bottom of the second glass wafer to form a lower layer lead hole 8. The second glass wafer is then cleaned and dried to complete the preparation of the lower layer wafer.

[0050] Based on polymer bonding technology, the lower wafer is bonded to the middle wafer, a second groove is constructed on the upper surface of the middle wafer, and the groove passes through the upper surface of the middle wafer to the groove corresponding to the middle layer lead hole 14 to obtain a first bonding body; based on polymer bonding technology, the upper wafer and the first bonding body are bonded to obtain a second bonding body, and the second bonding body is cut to obtain a number of capacitive microfluidic pressure sensors.

[0051] The sensor provided in this embodiment can be integrated with a microfluidic chip without almost destroying the shape of the microchannel, thereby realizing in-situ real-time dynamic measurement of microfluidic pressure. This embodiment uses a patterned polymer to form the lower electrode groove, the strip groove and the lower electrode lead groove. There is no need to implement these three structures by etching, which greatly simplifies the process. This embodiment uses a patterned metal layer as the lower electrode. The bonding technology of this sensor adopts polymer bonding technology, which has lower requirements on the process of the bonding surface before bonding, improves bonding stability, lowers bonding cost, takes less time for bonding, and has higher bonding efficiency. The preparation method of this sensor is easier, more stable and more efficient than the existing process, and the cost is also lower. This sensor is also the first microfluidic pressure sensor that integrates a pressure sensor with a microchannel using polymer bonding technology.

[0052] Selection of wafer material: The material for preparing the upper structure is preferably a glass wafer to realize the visualization of the microfluidic flow. The material for preparing the intermediate layer structure is preferably a double-sided polished SOI wafer with a small device layer resistivity, which is convenient for forming a diaphragm of a microfluidic pressure sensor with controllable thickness and a smooth surface, as well as the subsequent lead conductivity. Due to thermal oxidation during the processing, silicon dioxide layers are generated and retained on the upper and lower surfaces of the SOI wafer. From the perspective of material distribution, the SOI wafer is divided from bottom to top into a silicon dioxide layer on the lower surface, a device layer, a buried oxide layer, a substrate layer, and a silicon dioxide layer on the upper surface. Therefore, the intermediate layer structure is also divided into five layers: a silicon dioxide layer on the lower surface, a device layer (silicon layer), a buried oxide layer (silicon dioxide layer), a substrate layer (silicon layer), and a silicon dioxide layer on the upper surface. The material for preparing the lower structure is preferably a glass wafer. The polymer used for bonding in the embodiment is polydimethylglutarimide (PMGI). During the actual fabrication process, a layer of S1813 photoresist is first spin-coated on the PMGI surface, followed by photolithography and development to pattern the PMGI layer. Optical alignment is used to bond the two wafers together. Before contact, the two wafers are heated to 265°C, then brought into contact and a pressure of 450kPa is applied for three minutes.

[0053] Structural aspect: The microfluidic pressure sensor of this embodiment is a superposition of three-layer structures: an upper layer structure 18, an intermediate layer structure 19 and a lower layer structure 19, wherein the upper layer structure 18 and the intermediate layer structure 19 are connected through a patterned upper polymer adhesive layer 15 in the upper layer structure 18, and the intermediate layer structure 19 and the lower layer structure 19 are connected through a patterned lower polymer adhesive layer 9 in the lower layer structure 19.

[0054] The substrate layer of the SOI wafer is used to form the microchannel groove 3, and the buried oxide layer (silicon dioxide layer) of the middle layer serves as the bottom surface of the microchannel groove 3. The microchannel groove 3 located in the middle layer structure 19, the polymer microchannel groove 3 located in the upper structure 18, and the lower bottom surface of the upper structure 18 form a microchannel. The fluid can enter the microchannel from the microchannel inlet 17 and flow out of the fluid microchannel from the microchannel outlet 2. Except for the part directly above the lower electrode groove 10 of the lower structure, the rest of the lower bottom surface of the microchannel groove 3 is supported and fixed by the upper end surface of the lower structure, and only the part directly above the lower electrode groove 10 of the lower structure is suspended. The suspended part is the pressure sensing diaphragm 21 of the microfluidic pressure sensor, which can be deformed by the pressure difference on both sides.

[0055] The pressure sensing diaphragm 21 of the microfluidic pressure sensor includes a buried oxide layer (silicon dioxide layer) of the SOI wafer located in the suspended part, a device layer of the SOI wafer located in the suspended part, and a silicon dioxide layer on the lower surface of the SOI wafer located in the suspended part. The device layer of the SOI wafer in the suspended part serves as the upper electrode 22 of the variable capacitor. The buried oxide layer (silicon dioxide layer) of the SOI wafer is used to achieve electrical insulation between the fluid microchannel and the variable capacitor. The silicon dioxide layer on the lower surface of the SOI wafer is used to achieve insulation between the upper electrode 22 of the variable capacitor and the lower electrode 7 of the variable capacitor. The bottom surface of the upper electrode lead groove 5 is the device layer of the intermediate layer, so when the external circuit probe contacts the upper electrode lead pad 4, it can be electrically connected to the upper electrode 22 of the variable capacitor.

[0056] The lower structure 20 is made of a glass wafer, the upper surface of which is covered with a patterned lower polymer adhesive layer 9. The lower structure 20 comprises a lower electrode 7, a strip lead structure 6, a lower electrode lead pad 13, a lower electrode groove 10, a strip groove 11, a lower electrode lead groove 12, and a lower lead hole 8. The lower electrode 7, the strip lead structure 6, and the lower electrode lead pad 13 are all patterned metal films. The lower electrode 7 is electrically connected to the lower electrode lead pad 13 via the strip lead structure 6. The lower electrode 7 is located on the upper surface of the lower electrode groove 10, the strip lead structure 6 is located on the upper surface of the strip groove 11, and the lower electrode lead pad 13 is located on the upper surface of the lower electrode lead groove 12.

[0057] The external circuit lead probe is inserted into the upper lead hole 1, passes through the middle lead hole 14, and contacts the lower electrode lead pad 13, thereby achieving electrical conduction between the external circuit and the lower electrode 7. The external circuit lead probe is inserted into the lower lead hole 8, contacts the upper electrode lead pad 4, and achieves electrical conduction with the upper electrode 22.

[0058] Technical principle: The microfluidic pressure sensor of this embodiment is based on the same principle as the capacitive pressure sensor for measuring gauge pressure. The technical principle is that the diaphragm acts as an electrode to form a variable capacitor with another electrode. The gap of the variable capacitor is connected to the atmosphere. The pressure difference between the measured pressure and the atmospheric pressure causes the diaphragm to deform, thereby causing the change of the variable capacitor. The upper electrode 22 of the variable capacitor in the pressure-sensing diaphragm 21 of the microfluidic pressure sensor and the lower electrode 7 formed by the patterned metal film serve as the upper and lower electrodes to form a variable capacitor. The gap between the upper and lower electrodes is connected to the external gas through the strip-shaped groove 11. When the microfluid flows through, a pressure difference is formed between the microfluid and the external gas. The pressure-sensing diaphragm 21 is deformed under the action of the pressure difference on both sides, the distance between the upper and lower electrodes changes, and the capacitance value of the variable capacitor changes.

[0059] Manufacturing method: The superposition of the three-layer structure of the microfluidic pressure sensor is based on polymer bonding technology. In the actual operation process, the upper, middle and lower wafers need to be processed separately to form their own microstructures such as through holes and grooves. Afterwards, the lower wafer is bonded to the middle wafer using polymer bonding technology, and then dry etching is used to form microchannel grooves 3 and middle layer lead holes 14. The wafer is bonded to the upper wafer using polymer bonding technology, and finally the multi-layer wafer is cut to form multiple separate wafers such as Figure 1 The microfluidic pressure sensor shown.

[0060] The processing flow of the superstructure is as follows Figure 5 As shown, including:

[0061] Step 1: Prepare the wafer;

[0062] Step 2: Spin-coating a 2 μm thick LOR 20B polymer film and patterning the polymer film with S1813 photoresist to form a patterned upper polymer adhesive layer 15 and construct a polymer microchannel groove 16;

[0063] Step 3: Laser drilling is performed to form the microchannel outlet 2, the microchannel inlet 17 and the upper lead hole 1. The wafer is cleaned with deionized water and dried before being prepared for bonding.

[0064] The processing flow of the intermediate layer structure is as follows Figure 6 As shown, including:

[0065] Step 1: Prepare a double-sided polished SOI wafer with low device layer resistivity;

[0066] Step 2: Dry thermal oxidation to form a 0.5 micron thick silicon dioxide layer on the upper and lower surfaces of the wafer;

[0067] Step 3: Use BOE solution to remove the silicon dioxide layer on the upper surface of the wafer and pattern the silicon dioxide layer on the lower surface of the wafer, completely removing the silicon dioxide layer on the upper surface so that the two parts of the lower surface of the wafer corresponding to the upper electrode lead groove 5 and the middle layer lead hole 14 are exposed;

[0068] Step 4: magnetron sputtering a metal film and patterning it through a lift-off process to form an upper electrode lead pad 4;

[0069] Step 5: Spin-coat photoresist and expose the portion corresponding to the middle layer lead hole 14 by patterning, and dry-etch the lower surface of the wafer so that the portion corresponding to the middle layer lead hole 14 is etched to the silicon dioxide layer in the middle of the SOI wafer;

[0070] Step 6: Use BOE solution to etch the silicon dioxide exposed in the previous step, clean the wafer with deionized water, and dry it before bonding.

[0071] The processing flow of the lower structure is as follows Figure 7 As shown, including:

[0072] Step 1: Prepare the glass wafer;

[0073] Step 2: magnetron sputtering a metal film and patterning it through a lift-off process to form a lower electrode 7, a strip-shaped lead structure 6, and a lower electrode lead pad 13;

[0074] Step 3: Spin coating a polymer film; patterning the polymer film to form a patterned lower polymer adhesive layer 9, constructing a lower electrode groove 10, a strip groove 11, and a lower electrode lead groove 12;

[0075] Step 4: Laser drilling is performed to form the lower layer lead holes 8. The wafer is cleaned with deionized water and dried before being prepared for bonding.

[0076] The overall processing process is as follows Figure 8 As shown, including:

[0077] Step 1: Bond the lower wafer to the middle wafer using polymer bonding technology;

[0078] Step 2: Spin-coating photoresist on the upper surface of the middle layer wafer, patterning the photoresist, and then etching to form the microchannel grooves 3 and the middle layer lead holes 14, and then removing the excess photoresist;

[0079] Step 3: Use polymer bonding technology to bond the upper wafer to the middle and lower wafers;

[0080] Regarding wafer material selection: both the upper and lower wafers are 0.5-micron thick glass wafers. The middle wafer is a double-sided polished SOI wafer with a low resistivity device layer. The SOI wafer has a substrate layer thickness of 390 microns, a buried oxide layer thickness of 1 micron, and a device layer thickness of 8 microns. The device layer resistivity is less than 0.02 ohm·cm.

[0081] In terms of structural dimensions: the radius of the upper lead hole 1 is 1 mm, the radius of the middle lead hole 14 is 2.5 mm, and the radius of the lower electrode lead groove is 2.5 mm. This can better limit the range of the probe and the lead. Similarly, the diameter of the lower lead hole 8 is 4 mm, and the diameter of the upper electrode lead groove 5 is 4 mm. The diameters of the microchannel inlet 17 and the microchannel outlet 2 are both 1 mm, which facilitates fluid entry and exit and sealing. The radius of the lower electrode groove 10 is 400 microns, that is, the diaphragm radius of the microfluidic pressure sensor is 400 microns, and the radius of the pressure measuring point is 400 microns. The depth of the lower electrode groove 10 is 2 microns.

[0082] The upper electrode 22 of the variable capacitor in the pressure sensing diaphragm 21 of the microfluidic pressure sensor provided in this embodiment and the lower electrode 7 formed by the patterned metal film serve as upper and lower electrodes to form a variable capacitor. The gap between the upper and lower electrodes is connected to the external gas through the strip-shaped groove 11. When the microfluid flows through, a pressure difference is formed between the microfluid and the external gas, and the pressure sensing diaphragm 21 is deformed under the action of the pressure difference on both sides, the spacing between the upper and lower electrodes changes, and the capacitance value of the variable capacitor changes. The external circuit analyzes the pressure difference between the microfluid and the external atmosphere at the pressure measuring point by detecting the change in capacitance value. By setting multiple pressure measuring points along the microfluid, that is, forming multiple pressure sensing diaphragms 21 of microfluidic pressure sensors, real-time measurement of the pressure along the microfluid can be achieved.

[0083] The above description is merely a preferred embodiment of the present application, but the scope of protection of the present application is not limited thereto. Any changes or substitutions that can be easily conceived by a person skilled in the art within the technical scope disclosed in the present application should be included in the scope of protection of the present application. Therefore, the scope of protection of the present application should be based on the scope of protection of the claims.

Claims

1. A capacitive microfluidic pressure sensor based on polymer bonding technology, characterized in that: It comprises an upper structure (18), an intermediate structure (19) and a lower structure (20) which are sequentially connected via a polymer adhesive layer; The top of the upper structure (18) is provided with an upper lead hole (1), a microchannel inlet and a microchannel outlet (2); a first groove is provided in the polymer adhesive layer between the upper structure (18) and the intermediate structure (19); the microchannel inlet and the microchannel outlet (2) are both connected to the first groove; The middle layer structure (19) has a second groove and a middle layer lead hole (14) at the top, and an upper electrode lead groove (5) at the bottom; the second groove is connected to the first groove to form a microchannel; A lower electrode groove (10), a strip groove (11) and a lower electrode lead groove (12) which are connected in sequence are provided in the polymer adhesive layer between the lower layer structure (20) and the intermediate layer structure (19); The upper layer lead hole (1), the middle layer lead hole (14) and the lower electrode lead groove (12) are connected in sequence; a lower layer lead hole (8) is provided between the lower end surface of the middle layer structure (19) and the lower end surface of the lower layer structure (20); and the suspended portion between the microchannel and the lower electrode groove (10) is used as a pressure sensing diaphragm (21).

2. A capacitive microfluidic pressure sensor based on polymer bonding technology according to claim 1, characterized in that: The intermediate layer structure (19) adopts an SOI wafer, and comprises, from bottom to top, a lower surface silicon dioxide layer, a device layer, a buried oxide layer, a substrate layer and an upper surface silicon dioxide layer; The intermediate layer lead hole (14) penetrates the lower surface silicon dioxide layer, the device layer, the buried oxide layer, the substrate layer and the upper surface silicon dioxide layer, and is respectively connected to the lower electrode lead groove (12) and the upper layer lead hole (1); the second groove has the buried oxide layer as the bottom surface, penetrates the substrate layer and the upper surface silicon dioxide layer and is connected to the first groove; the upper electrode lead groove (5) has the device layer as the bottom surface, penetrates and extends to the upper end surface of the upper surface silicon dioxide layer; The pressure sensing diaphragm (21) comprises a buried oxide layer of a suspended part, a device layer, and a lower surface silicon dioxide layer, and the device layer of the suspended part serves as an upper electrode (22).

3. The capacitive microfluidic pressure sensor based on polymer bonding technology according to claim 2, characterized in that: An upper electrode lead pad (4) is provided in the upper electrode lead groove (5), and the upper electrode lead pad (4) is electrically connected to the upper electrode (22) through a device layer.

4. The capacitive microfluidic pressure sensor based on polymer bonding technology according to claim 1, characterized in that: The upper structure (18) and the lower structure (20) are both made of glass wafers.

5. The capacitive microfluidic pressure sensor based on polymer bonding technology according to claim 1, characterized in that: A lower electrode lead pad (13) is provided in the lower electrode lead groove (12), a lower electrode (7) is installed in the lower electrode groove (10), and the lower electrode lead pad (13) is electrically connected to the lower electrode (7) through the strip-shaped groove (11).

6. A method for preparing a capacitive microfluidic pressure sensor based on polymer bonding technology, characterized in that: include: Step 1: obtaining a first glass wafer, spin-coating a first polymer adhesive layer on the lower surface of the first glass wafer and performing a groove process to obtain a first groove; Opening holes on the first glass wafer to obtain upper layer lead holes (1), microchannel inlets and microchannel outlets (2), and cleaning and drying the holes to complete the preparation of the upper layer wafer; Step 2: obtaining an SOI wafer, constructing an upper electrode lead groove (5) and a groove corresponding to the middle layer lead hole (14) on the lower surface of the SOI wafer; generating an upper electrode lead pad (4) in the groove corresponding to the upper electrode lead groove (5); extending the groove corresponding to the middle layer lead hole (14) to the substrate layer of the SOI wafer based on a spin-on photoresist method and a dry etching method; and performing cleaning and drying to complete the preparation of the middle layer wafer; Step 3: Obtain a second glass wafer, magnetron sputter a metal film on the upper surface of the second glass wafer through a lift-off process to generate a lower electrode (7), a strip-shaped lead structure (6) and a lower electrode lead pad (13); spin-coat a second polymer film adhesive layer and perform a patterning process to obtain a lower electrode groove (10), a strip-shaped groove (11) and a lower electrode lead groove (12); perform laser drilling on the bottom of the second glass wafer to obtain a lower layer lead hole (8); perform cleaning and spin drying to complete the preparation of the lower layer wafer; Step 4: Bonding the lower wafer to the middle wafer based on polymer bonding technology, constructing a second groove on the upper surface of the middle wafer, and penetrating the upper surface of the middle wafer to the groove corresponding to the middle layer lead hole (14) to obtain a first bonding body; bonding the upper wafer to the first bonding body based on polymer bonding technology to obtain a second bonding body, cutting the second bonding body to obtain a plurality of capacitive microfluidic pressure sensors.

7. The method for preparing a capacitive microfluidic pressure sensor based on polymer bonding technology according to claim 6, characterized in that: The step 2 specifically includes: Silicon dioxide layers are constructed on the upper and lower surfaces of the SOI wafer, the silicon dioxide layer on the upper surface is removed by a BOE solution, and the silicon dioxide layer on the lower surface is patterned to obtain an upper electrode lead groove (5) and a groove corresponding to an intermediate layer lead hole (14); a metal film is magnetron sputtered in a groove corresponding to the upper electrode lead groove (5) by a lift-off process to generate an upper electrode lead pad (4); the groove corresponding to the intermediate layer lead hole (14) is extended to the substrate layer of the SOI wafer based on a spin-on photoresist method and a dry etching method; and cleaning and drying are performed to complete the preparation of the intermediate layer wafer.

8. The method for preparing a capacitive microfluidic pressure sensor based on polymer bonding technology according to claim 6, characterized in that: A second groove is constructed on the upper surface of the middle layer wafer and penetrates through the upper surface of the middle layer wafer to the groove corresponding to the middle layer lead hole (14), specifically comprising: Photoresist is spin-coated on the upper surface of the middle layer wafer, and patterning and etching are performed to obtain microchannel grooves (3) and middle layer lead holes (14), and excess photoresist is removed.

Images