A multi-channel thermal sensor with micro-suspension structure and its preparation method

Abstract

The present invention discloses a multi-channel thermal sensor with a micro-suspension structure and a preparation method thereof, comprising a microchannel inlet, a microchannel and a microchannel outlet, wherein a plurality of microchannels are connected between the microchannel inlet and the microchannel outlet, the microchannel comprises a microfluidic channel top cover, a microfluidic channel wall and a microfluidic channel bottom plate, a suspended bridge structure substrate is arranged at the bottom of the microfluidic channel bottom plate, the microfluidic channel top cover and the edge of the microfluidic channel bottom plate are connected with the microfluidic channel wall, a reference thermocouple and a main thermocouple are arranged inside the microfluidic channel cavity, and a heater and a grounding point are arranged on both sides of the top of the microfluidic channel bottom plate. The sensor of the present invention contains a microfluidic channel with a suspended bridge structure, which realizes the improvement of sensitivity and the reduction of heat loss; the sensitive measurement of small volume liquid samples is performed through the microfluidic measurement chamber to minimize the loading dose of biofluidic samples, which will help portable medical care applications.

Description

Technical Field

[0001] The invention relates to the field of thermal sensors, and in particular to a multi-channel thermal sensor with a micro-suspension structure and a preparation method thereof. Background Art

[0002] Thermal sensors are devices that can collect and analyze temperature difference information between the sample to be tested and the detection element. With the development of materials science, electronic science and other disciplines, thermal sensors have become a research hotspot. In recent years, various new thermal detection sensors with superior performance have emerged, and the requirements for the accuracy, detection speed and volume of thermal sensors have become increasingly higher. With the development of integrated technology, providing sensors with small size, light weight and high detection accuracy has become a development trend.

[0003] With the development of micro-electro-mechanical systems (MEMS), higher requirements have been placed on the performance and processing technology of various microstructures due to the requirements of microsystem performance or structure. Among them, micro-suspension structures are widely needed because they can effectively avoid the influence and heat transfer between molecules and surfaces between the substrate and increase the contact area with the surrounding environment. Due to the relative isolation of the suspension structure from the substrate, it can minimize the heat flow caused by other external factors and improve the detection accuracy of the sensor. Combining the suspension structure with a thermal sensor can effectively detect the heat dissipated in the heat transfer and improve the detection accuracy and sensitivity of the sensor.

[0004] Existing processes for manufacturing suspended structures between microstructures include bulk silicon etching, electrospinning, chemical vapor deposition, etc. Due to the high equipment or experimental conditions required, the process costs are often high, or it is difficult to establish accurate and strong mechanical bonding and effective electrical contact between the micro-suspended structure and the microstructure.

[0005] With the continuous improvement of MEMS technology, compared with bulky traditional thermal sensors, micro-suspension structure thermal sensors combine micro-channel structure with micro-suspension structure by relying on MEMS technology, and have many advantages such as high performance, small size, low cost and high stability.

[0006] In micro-suspended thermal sensors, the sensor is usually prepared on a suspended membrane structure to improve the thermal insulation of the device to increase the sensitivity of the sensor, and the microchannel is usually directly bonded above the sensor as a container and reaction chamber for the reactant sample, which is convenient for manipulating the reactant sample. The suspended structure can effectively improve the thermal insulation of the device and reduce the heat capacity of the device, thereby increasing the thermal sensitivity of the device. At present, different substrate materials such as silicon, glass, and polymers have been maturely applied to the processing and manufacturing of microfluidic structures. Silicon is a relatively common material with outstanding thermal stability, chemical inertness, and good thermal conductivity. At present, there is a complete set of mature processing technology. Glass is relatively cheap, easy to process, and has good biocompatibility. Polymers have the advantages of low cost, good processability, high optical transparency, simple processing steps, and good biocompatibility. They have become commonly used microfluidic chip substrate materials, such as PDMS materials and SU-8 materials. PDMS materials are resistant to high and low temperatures, do not harden at low temperatures, do not deform or soften at high temperatures, always maintain flexible characteristics, and have good dielectric properties and certain air permeability. SU-8 material has high transparency, large refractive index and low loss at a certain wavelength, and is considered to be a good material for optical waveguide applications.

[0007] Among the microfluidic substrate materials currently used, the preparation process of silicon-based materials is mature, but the etching process is relatively cumbersome, the environmental requirements are strict, and the processing cycle is long, which limits the large-scale application of this processing technology. In addition, the suspended membrane based on silicon materials is very fragile and the manufacturing process is complicated. Although glass is transparent, it is difficult to etch the vertical section relative to the silicon wafer due to its amorphous nature. Although both silicon wafers and glass can be processed in batches, the sealing process of the objects needs to be carried out in an ultra-clean environment and requires high voltage or high temperature. Compared with silicon-based materials, polymer materials have better tensile strength and lower thermal conductivity, and are easier to be prepared into thin film structures. However, the disadvantage of polymer materials is that they usually require surface modification, and most of them are not resistant to high temperatures. Although PDMS is an excellent material for making microfluidic systems, most organic solutions will swell PDMS. In addition, although PDMS can replicate graphics with high fidelity, some geometric figures are not easy to demold. The prepared PDMS fluid structure requires a bonding process integrated with the sensor chip, which requires ensuring sealing and is difficult to bond to the suspended microstructure. Moreover, the load force of the PDMS fluid system chip will destroy the suspension structure of the thermal sensor and is applied in the suspension structure of the microsensor device.

[0008] Compared to other cantilevers, SU-8 based cantilevers show higher tolerance to temperature changes, which can reduce noise and improve sensitivity. Due to its high chemical resistance, SU-8 polymer is used to fabricate microfluidic systems for microsensor devices. Fabricated microchannels with thin SU-8 covers enable the application of optical and fluorescence detection. Suspended microfluidic structures are integrated with thermocouple sensors, which can reduce heat loss and improve sensitivity compared to traditional bulky PDMS chambers. Summary of the invention

[0009] The technical problem to be solved by the present invention is to overcome the defects of the prior art and provide a multi-channel thermal sensor with a micro-suspension structure and a preparation method thereof.

[0010] In order to solve the above technical problems, the present invention provides the following technical solutions:

[0011] The present invention provides a multi-channel thermal sensor with a micro-suspension structure, comprising a microchannel inlet, a microchannel and a microchannel outlet, wherein a plurality of microchannels are connected between the microchannel inlet and the microchannel outlet, wherein the microchannel comprises a microfluidic channel top cover, a microfluidic channel wall and a microfluidic channel bottom plate, wherein a suspended bridge structure substrate is arranged at the bottom of the microfluidic channel bottom plate, wherein the microfluidic channel top cover is connected to the microfluidic channel wall at the edge of the microfluidic channel bottom plate, and a microfluidic channel cavity is formed inside, wherein a reference thermocouple and a main thermocouple are arranged inside the microfluidic channel cavity, and a heater and a grounding point are respectively arranged at both sides of the top end of the microfluidic channel bottom plate.

[0012] As a preferred technical solution of the present invention, the microchannels are evenly spaced and distributed with a spacing of 200 um.

[0013] As a preferred technical solution of the present invention, the microfluidic channel cavity is in the shape of an elongated strip, and the volume in the middle is larger than that on both sides, and the preparation material of the microfluidic channel is SU-8 photoresist.

[0014] The present invention also provides a method for preparing a multi-channel thermal sensor with a micro-suspension structure, comprising the following steps:

[0015] S1: Prepare the processing substrate, use the insulating silicon wafer as the substrate, use the ion implantation process to dope silicon dioxide in the silicon substrate to reduce the sensor resistance;

[0016] S2: preparing a separation layer, depositing a silicon dioxide film on the substrate as a separation layer by chemical vapor deposition technology, and etching the silicon dioxide layer by buffered hydrofluoric acid etching solution to open a window for the thermocouple electrode;

[0017] S3: realizing the electrode pattern of the heater and the sensor, coating the photoresist on the front side of the silicon dioxide, forming the electrode pattern of the heater by photolithography, and defining the area of ​​the heater electrode;

[0018] S4: Prepare the ports of the thermocouple electrodes, deposit a Cr / Au layer on top by sputtering deposition after the photolithography process, and use a lift-off process of Au / Cr to make the electrode patterns for the heater and sensor;

[0019] S5: Prepare the microfluidic channel support wall, design the microchannel with the same structure, the microchannel wall and separation layer are made of SU-8 photoresist, and the top cantilever structure is made into a bridge structure by BHF etching and silicon etching;

[0020] S6: To achieve the microfluidic channel covering pattern, the SU-8 dry film is covered on the substrate by force and temperature control, and the covering film pattern on the channel is made by photolithography;

[0021] S7: preparing a bottom cavity structure of the silicon dioxide layer, etching the bottom of the silicon dioxide to form a bottom cavity.

[0022] S8: Stripping the photoresist at the bottom of the silicon dioxide layer to complete the preparation of the MEMS thermal sensor with a suspended structure cavity

[0023] As a preferred technical solution of the present invention, in step S1, the ion implantation conditions of the silicon substrate are 100kev voltage and 1020cm -3 Carrier concentration

[0024] Compared with the prior art, the present invention has the following beneficial effects:

[0025] 1: The sensor of the present invention contains a microfluidic channel with a suspended bridge structure, which achieves improved sensitivity and reduced heat loss.

[0026] 2: The present invention uses a microfluidic measurement chamber to perform sensitive measurements on small volume liquid samples to minimize the loading dose of biofluidic samples, which will facilitate portable healthcare applications.

[0027] 3: The sensor of the present invention contains multiple microfluidic channels, which can achieve rapid response and small volume sample detection, can process multiple solutions at the same time, and perform component detection, thus solving the problem of traditional MEMS thermal sensors with little detection information and long processing time.

[0028] 4. The standard MEMS process can realize one-time mass production of sensors. At the same time, the production cost is low and it can be produced without complex equipment, so it has the potential for widespread use. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] The accompanying drawings are used to provide a further understanding of the present invention and constitute a part of the specification. Together with the embodiments of the present invention, they are used to explain the present invention and do not constitute a limitation of the present invention. In the accompanying drawings:

[0030] Figure 1 It is a schematic diagram of the structure of the MEMS thermal sensor of the present invention;

[0031] Figure 2 is a front view structural schematic diagram of a multi-channel thermal sensor with a micro-suspension structure of the present invention;

[0032] Figure 3 It is a structural exploded diagram of a single microfluidic channel of a multi-channel thermal sensor with a micro-suspension structure of the present invention;

[0033] Figure 4 It is a preparation process diagram of the multi-channel thermal sensor with a micro-suspension structure of the present invention;

[0034] Figure 5 is the response time of the microfluidic channel of the multi-channel thermal sensor of the micro-suspension structure of the present invention;

[0035] Figure 6 It is the sensitivity test result of the microfluidic channel of the multi-channel thermal sensor of the micro-suspension structure of the present invention;

[0036] In the figure: 1. microfluidic channel inlet; 3. microfluidic channel; 4. microfluidic channel outlet; 6. heater; 7. microfluidic channel top cover; 8. microfluidic channel wall; 9. grounding point; 10. microfluidic channel bottom plate; 11. reference thermocouple; 12. main thermocouple; 13. microfluidic channel cavity. DETAILED DESCRIPTION

[0037] The preferred embodiments of the present invention are described below in conjunction with the accompanying drawings. It should be understood that the preferred embodiments described herein are only used to illustrate and explain the present invention, and are not used to limit the present invention.

[0038] Example 1

[0039] like Figure 1-3 As shown, the present invention provides a multi-channel thermal sensor with a micro-suspension structure, including a microchannel inlet 1, a microchannel 3 and a microchannel outlet 4, wherein a plurality of microchannels 3 are connected between the microchannel inlet 1 and the microchannel outlet 4, the microchannel 3 includes a microfluidic channel top cover 7, a microfluidic channel wall 8 and a microfluidic channel bottom plate 10, a suspended bridge structure substrate is arranged at the bottom of the microfluidic channel bottom plate 10, the microfluidic channel top cover 7 and the edge of the microfluidic channel bottom plate 10 are connected with the microfluidic channel wall 8, and a microfluidic channel cavity 13 is formed inside, a reference thermocouple 11 and a main thermocouple 12 are arranged inside the microfluidic channel cavity 13, and a heater 6 and a grounding point 9 are arranged on both sides of the top of the microfluidic channel bottom plate 10.

[0040] Furthermore, the microchannels 3 are evenly spaced and spaced apart by 200 um.

[0041] Furthermore, the microfluidic channel cavity 13 is in the shape of an elongated strip, and the volume in the middle is larger than that on both sides. The middle is a cubic cavity with a side length of 500 um and a height of 50 um. The preparation material of the microchannel 3 is SU-8 photoresist.

[0042] Specifically, the heater 6 cooperates with the grounding point 9 to evaluate the sensor after production and simulate the reaction heat generated; when the thermal sensor starts working, the patient's eye fluid to be tested is first injected into the microchannel inlet 1 by titration, and then injected into each microchannel 3 after diversion, so that the solution fills the entire microfluidic channel cavity 13 and the flow channel; at this time, the five chambers are filled with various types of enzymes, and the enzymes are placed in the middle area of ​​the microfluidic channel cavity 13, one of which is the experimental group and the remaining four are the control group. Different enzymes react with the solution to generate reaction heat, and then the reference thermocouple 11 and the main thermocouple 12 sense the heat, and the released heat is detected, and finally the electrical signal is transmitted to the computer for processing.

[0043] like Figure 4-6 As shown, the present invention also provides a method for preparing a multi-channel thermal sensor with a micro-suspension structure, comprising the following steps:

[0044] S1: Reference Figure 4 (a) A substrate for processing is prepared, with a silicon-on-insulator (SOI) substrate as the substrate. The thickness of the silicon-on-insulator (SOI) substrate is 10 μm, 1 μm, and 400 μm, respectively. The device layer of the silicon-on-insulator (SOI) substrate is N-type silicon.

[0045] S2: Reference Figure 4 (b) Preparing a separation layer, a 500 nm SiO2 film is deposited on the substrate by chemical vapor deposition as a separation layer, and a 500 nm silicon dioxide (SiO2) layer is etched by a buffered hydrofluoric acid (BHF) etching solution to open an ion implantation window to prepare a PN junction;

[0046] S3: Reference Figure 4 (c) realizing the electrode pattern of the heater and the sensor, coating the photoresist on the front side of the silicon dioxide, forming the electrode pattern of the heater by photolithography, and defining the area of ​​the heater electrode;

[0047] S4: Reference Figure 4(d) preparing the port of the thermocouple electrode, a 200 nm chromium / gold (Cr-Au) layer is deposited on the top by sputtering deposition after the photolithography process, specifically, a 40 nm thick chromium (Cr) layer is first sputtered on the front side of a 500 μm thick silicon dioxide by using a sputtering device, and then a 160 nm thick gold (Au) layer is sputtered on the chromium (Cr) layer, and finally a chromium / gold (Cr-Au) metal film is deposited, and a chromium / gold (Cr-Au) etching solution is used to remove the chromium / gold (Cr-Au) layer not covered by the photoresist mask, and the substrate is heated to 450° C. and maintained for 1 minute to achieve ohmic contact of the thermocouple sensor;

[0048] S5: Reference Figure 4 (e), preparation of microfluidic channel support wall, according to the design, the microchannel has the same structure, the microchannel wall and separation layer are made of SU-8 photoresist, photolithography 50μm, after the substrate cleaning process, the SU-8 wall is manufactured on the substrate by photolithography process, the width of the microchannel is 50μm, and the height is 50μm. The top cantilever structure is made into a bridge structure by buffered hydrofluoric acid (BHF) etching and silicon etching;

[0049] S6: Reference Figure 4 (f) To achieve the microfluidic channel covering pattern, the channel cover thickness was prepared by a dry SU-8 film (50 μm). First, the dry SU-8 film with a support film was covered on the channel at 55 °C for 3 min. After exposure for 80 s, the substrate was pre-baked at 85 °C for 30 s. After that, the support film was removed and the substrate was heated at 95 °C for 5 min to harden the pattern on the substrate.

[0050] S7: Reference Figure 4 (g) preparing a cavity structure at the bottom of the silicon dioxide layer, etching the bottom of the silicon dioxide to form a bottom cavity, using SU-8 developer to develop the SU-8 film, and after 10 minutes, washing away the developer to complete the preparation of the hollow structure on the substrate;

[0051] S8: Reference Figure 4 (h) The photoresist at the bottom of the silicon dioxide layer is stripped off, and a MEMS thermal sensor with a bridge structure is fabricated through backside silicon etching and buffered hydrofluoric acid (BHF) etching processes.

[0052] After step S8, the MEMS thermal sensor is simulated and tested using simulation software, such as Figure 5 As shown, the response time test of the multi-target detection MEMS thermal sensor described in the embodiment is carried out; it can be seen that when a step temperature is input, the sensor can react to the temperature change very quickly. In less than 200ms, the thermocouple detects the temperature change and outputs a response signal, which is then converted into an electrical signal output. The results show that the thermal sensor has a fast response and good thermal characteristics.

[0053] like Figure 6 As shown, the sensitivity test of the multi-target detection MEMS thermal sensor described in the embodiment was carried out, and the test results showed that the sensor had extremely high thermal characterization accuracy, confirming that the prepared microsensor can measure the catalytic reaction heat of the enzyme, and the suspended bridge structure proposed in the present invention can improve the sensitivity of thermal detection.

[0054] Finally, it should be noted that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art can still modify the technical solutions described in the aforementioned embodiments or replace some of the technical features therein by equivalents. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A multi-channel thermal sensor with a micro-suspension structure, characterized in that: The invention comprises a microfluidic channel inlet (1), a microfluidic channel (3) and a microfluidic channel outlet (4); a plurality of microfluidic channels (3) are connected between the microfluidic channel inlet (1) and the microfluidic channel outlet (4); the microfluidic channel (3) comprises a microfluidic channel top cover (7), a microfluidic channel wall (8) and a microfluidic channel bottom plate (10); a suspended bridge structure substrate is arranged at the bottom of the microfluidic channel bottom plate (10); the microfluidic channel top cover (7) and the microfluidic channel bottom plate (10) are connected at their edges with the microfluidic channel wall (8); a microfluidic channel cavity (13) is formed inside the microfluidic channel cavity (13); a reference thermocouple (11) and a main thermocouple (12) are arranged inside the microfluidic channel cavity (13); a heater (6) and a grounding point (9) are arranged at both sides of the top of the microfluidic channel bottom plate (10).

2. The multi-channel thermal sensor with a micro-suspension structure according to claim 1, characterized in that: The microchannels (3) are evenly spaced and distributed with a spacing of 200 um.

3. The multi-channel thermal sensor with a micro-suspension structure according to claim 2, characterized in that: The microfluidic channel cavity (13) is in the shape of an elongated strip, and the volume in the middle is larger than that on both sides. The preparation material of the microfluidic channel (3) is SU-8 photoresist.

4. A method for preparing a multi-channel thermal sensor with a micro-suspension structure, characterized in that: The method comprises the following steps: S1: Prepare a substrate for processing, use an insulating silicon wafer as the substrate, and use an ion implantation process to dope silicon dioxide into the silicon substrate to reduce the sensor resistance; S2: preparing a separation layer, depositing a silicon dioxide film on the substrate as a separation layer by chemical vapor deposition technology, and etching the silicon dioxide layer by buffered hydrofluoric acid etching solution to open a window for the thermocouple electrode; S3: realizing the electrode pattern of the heater and the sensor, coating the photoresist on the front side of the silicon dioxide, forming the electrode pattern of the heater by photolithography, and defining the area of ​​the heater electrode; S4: Prepare the ports of the thermocouple electrodes, deposit a Cr / Au layer on top by sputtering deposition after the photolithography process, and use a lift-off process of Au / Cr to make the electrode patterns for the heater and sensor; S5: Prepare the microfluidic channel support wall, design the microchannel with the same structure, the microchannel wall and separation layer are made of SU-8 photoresist, and the top cantilever structure is made into a bridge structure by BHF etching and silicon etching; S6: To achieve the microfluidic channel covering pattern, the SU-8 dry film is covered on the substrate by force and temperature control, and the covering film pattern on the channel is made by photolithography; S7: preparing a cavity structure at the bottom of the silicon dioxide layer, etching the bottom of the silicon dioxide to form a bottom cavity; S8: Peeling off the photoresist at the bottom of the silicon dioxide layer to complete the preparation of the MEMS thermal sensor with a suspended structure cavity.

5. The method for preparing a multi-channel thermal sensor with a micro-suspension structure according to claim 4, characterized in that: In step S1, the ion implantation conditions of the silicon substrate are 100kev voltage and 1020cm -3 Carrier concentration.

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