Digital micro-fluidic chip with vertically opposed thermal feedback structure and temperature control system thereof

Abstract

The invention discloses a digital micro-fluidic chip with a vertically opposed thermal feedback structure and a temperature control system of the digital micro-fluidic chip, and relates to the technical field of digital micro-fluidic chips. A heating element and a driving electrode of the digital micro-fluidic chip are integrated on the inner side of the lower polar plate in a same-side different-layer mode, and a temperature sensor is integrated on the inner side of the upper polar plate. The core of the device is that the heating element and the temperature sensor are vertically and oppositely arranged, orthographic projections of the heating element and the temperature sensor are overlapped, and a point-to-point vertical thermal feedback path is constructed by utilizing liquid drops in a cavity. According to the structure, thermal hysteresis is eliminated on the physical level, high-precision temperature control of + / -0.3 DEG C is achieved within the temperature range of RT-100 DEG C in cooperation with the shielding effect of the grounding electrode layer, power consumption is greatly reduced, and meanwhile cost is reduced through non-noble metal materials. The invention further provides a temperature control system for the digital micro-fluidic chip, deep fusion of high-voltage driving, precise ADC acquisition and PID closed-loop control is achieved through a high-density FPC interface, the integration level and portability of detection equipment are remarkably improved, and the digital micro-fluidic chip is suitable for PCR, enzymatic reaction and other scenes.

Description

Technical Field

[0001] This invention belongs to the field of digital microfluidic chip technology, and more specifically, relates to a digital microfluidic chip with a vertically opposed thermal feedback structure and its temperature control system. Background Technology

[0002] Digital microfluidics (DMF) technology is an advanced technique for manipulating tiny droplets based on the electrowetting effect, widely used in biomedical detection, chemical analysis, and drug screening. Its core advantage lies in its ability to precisely control microdroplets, significantly reducing reagent consumption, shortening reaction time, and improving detection sensitivity. However, many biochemical reactions (such as polymerase chain reaction (PCR) and enzymatic reactions) are highly temperature-dependent; for example, the three stages of PCR require three temperature zones. Therefore, achieving precise temperature control on digital microfluidic chips has become one of the key challenges in the development of this technology.

[0003] In existing technologies, heating methods are mainly divided into two types: external heating and integrated heating. External heating typically uses devices such as heating plates or TECs (thermal energy coolers) to heat the entire chip through heat conduction or convection. While this method is simple, it suffers from problems such as large size, slow response speed, and high power consumption, making it difficult to meet the requirements of precise temperature control. Integrated heating achieves localized heating by integrating heating elements (such as platinum metal wires, thin-film resistors, etc.) on the chip, for example, using platinum metal as both a heating element and a temperature sensor. First, platinum metal is expensive. More seriously, existing on-chip temperature control structures using integrated heating have fundamental thermal defects in their layout design:

[0004] 1. Thermal feedback hysteresis: Although some solutions (such as CN201810037707) have temperature control elements set on the upper and lower plates, they are horizontally offset. Heat needs to diffuse laterally and then be conducted by droplets. The sensor obtains "outdated" temperature with obvious phase delay, which cannot meet the second-level thermal cycling requirements of PCR.

[0005] 2. Signal coupling interference: In the same-side integrated solution (such as US20210060556A1), the heating and temperature sensing electrodes are coplanar and closely spaced. The large current pulse of the heating element can easily cause electromagnetic crosstalk to the weak temperature measurement analog signal.

[0006] 3. High thermal resistance: In back-side integrated solutions (such as CN202111024813), the temperature control element and the droplet are separated by a thick substrate, resulting in extremely high thermal resistance and sluggish feedback.

[0007] Therefore, how to achieve efficient integration of heating and temperature measurement functions on digital microfluidic chips, and ensure high heating efficiency, accurate temperature measurement, timely temperature control, and low cost, has become an urgent problem to be solved in the current technology field. Summary of the Invention

[0008] The technical problem to be solved by the present invention is to provide a digital microfluidic chip with a vertically opposed thermal feedback structure and its temperature control system. By vertically locking the physical space, the technical pain points of existing digital microfluidic chip integrated temperature control systems, such as thermal response hysteresis, electromagnetic signal crosstalk and significant substrate thermal resistance, are solved, thereby achieving high-precision steady-state temperature control at the ±0.3℃ level and low-cost integration.

[0009] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is: a digital microfluidic chip with a vertically opposed thermal feedback structure, comprising an upper electrode plate and a lower electrode plate arranged in parallel opposite directions, forming a sealed chamber for containing droplets between the upper electrode plate and the lower electrode plate, and the upper electrode plate having an injection hole communicating with the sealed chamber; the upper electrode plate, facing the sealed chamber, sequentially stacks a first substrate, a transparent FPC flexible circuit board, a temperature sensor, a ground electrode layer, and a first hydrophobic coating, and the lower electrode plate, facing the sealed chamber, sequentially stacks a second substrate, a heating element, a dielectric layer, a driving electrode, and a second hydrophobic coating; the heating element is disposed between the second substrate and the dielectric layer, and the driving electrode is disposed on the side of the dielectric layer away from the second substrate, realizing same-side heterogeneous layer integration.

[0010] The temperature sensor and the heating element's central axis coincide, or the horizontal offset distance between the central axes is less than a preset threshold, and the orthogonal projection of the temperature sensor on the lower electrode plate is within the projection range of the heating element, so that the heating element, the droplet, and the temperature sensor form a vertical coaxial thermal feedback path. The preset threshold is determined according to the size of the heating element, preferably less than or equal to 100 μm. The control drive electrode moves the droplet to directly above the heating element, and the heating element heats the droplet vertically upward. The opposing temperature sensor captures the thermal signal passing through the droplet in real time, thus constructing a vertical closed-loop feedback.

[0011] Preferably, there are several heating elements arranged in a continuous, sequential layout, with the heating area not less than the projected area of ​​the corresponding driving electrode, and the effective heating area of ​​the heating element covering at least one driving electrode.

[0012] Preferably, the number of temperature sensors is not less than the number of heating elements, and each heating element corresponds to at least one temperature sensor.

[0013] Preferably, the temperature sensor is located between the ground electrode layer and the first substrate; the ground electrode layer is located between the temperature sensor and the driving electrode below, forming an electromagnetic shielding layer for physically isolating the driving electrical signal from interfering with the temperature sensor.

[0014] Preferably, the dielectric layer is a tightly sealed encapsulating layer surrounding the heating element to block the electromigration of metal atoms and prevent high-temperature oxidation. The material of the dielectric layer includes inorganic dielectric materials, organic polymer materials, or composite materials thereof. Preferably, the inorganic dielectric material includes at least one of metal oxides, metal nitrides, or semiconductor oxides. The organic polymer material includes at least one of photoresist, elastomer materials, or parylene-based materials, and is processed by magnetron sputtering, spin coating, blade coating, spraying, or other methods. This encapsulation structure can effectively block the electromigration path of metal atoms under continuous current and prevent oxidation reactions on the metal surface at high temperatures. Actual measurements show that after 500 hours of continuous operation at a constant temperature of 95°C, the resistance change rate of the heating element is less than 0.5%, ensuring the long-term calibration accuracy of the temperature control system.

[0015] Preferably, a metal transition layer is provided between the heating element and the second substrate, and between the heating element and the dielectric layer. The thickness of the metal transition layer is 5nm-500nm, and the material includes, but is not limited to, titanium, chromium, titanium-tungsten alloy, tantalum nitride, or other non-precious metals and combinations thereof. This metal transition layer serves as a stress buffer layer to coordinate the shear stress caused by the difference in thermal expansion coefficients between the metal film and the inorganic dielectric layer and the substrate, preventing interlayer delamination under high-frequency thermal cycling. Furthermore, to reduce processing steps, the surface of the second substrate can be subjected to oxygen plasma activation treatment to enhance the physical bonding force between the layers.

[0016] Preferably, the heating element is a metal wire with a resistance of 5-2000Ω, fabricated by magnetron sputtering + photolithography etching, sputtering deposition, or printing processes; the material of the heating element is copper, titanium, chromium, molybdenum, aluminum, indium tin oxide, or combinations thereof and alloys thereof, and the distance between the heating element and the droplet is 1-200μm; the driving electrode material is copper, titanium, chromium, molybdenum, aluminum, indium tin oxide, or combinations thereof and alloys thereof, and the shape is rectangular, circular, serrated, polygonal, or arbitrary geometric shape, processed by photolithography and etching, sputtering deposition, or electroplating processes.

[0017] Preferably, the thickness of the first substrate is 0.2-5 mm, and the material is glass, inorganic non-metallic material or plastic; the height of the sealed chamber is 0.1-5 mm, and the height of the sealed chamber is controlled by the thickness of the support structure; the assembly alignment tolerance of the upper electrode plate and the lower electrode plate in the horizontal plane is less than or equal to ±500 μm.

[0018] Preferably, the grounding electrode layer is made of a transparent conductive thin film or a conductive grid structure, preferably silver nanowires, conductive polymers, indium tin oxide, or carbon nanotubes; the temperature sensor is a semiconductor element or metal thin film element with thermosensitive properties, specifically a thin film resistance thermometer, a thermistor, a thermocouple, or an infrared sensor, with a temperature sensing end and a droplet distance of 1-500 μm; the first and second hydrophobic coatings are made of fluoropolymers, polyalkylsiloxanes, or hydrophobic nanocoating materials, with a thickness of 0.01-30.0 μm.

[0019] A temperature control system for the aforementioned digital microfluidic chip includes a control motherboard electrically connected to the digital microfluidic chip. The control motherboard includes a high-voltage drive module, an ADC acquisition module, and a PID control module. The ADC acquisition module acquires temperature sensor signals, the PID control module uses a PID algorithm to adjust the pulse duty cycle applied to both ends of the heating element, and the high-voltage drive module is electrically connected to a transparent FPC flexible circuit board to control the drive electrodes and achieve precise planning of the droplet's movement path.

[0020] The beneficial effects of adopting the above technical solution are as follows:

[0021] 1. This invention abandons the traditional approach of placing the temperature control element on the outside of the substrate or offset it in the horizontal plane. Instead, it integrates the heating element on the inner surface of the lower electrode substrate (i.e., the inner surface of the second substrate) in a "same-side, different-layer" manner, and isolates it from the driving electrode through a micron-level dielectric layer, so that the heat source and the droplet are separated by only a micron-level functional thin layer. At the same time, the temperature sensor is integrated on the inner side of the upper electrode. By aligning the heating element and the temperature sensor in the vertical axis and overlapping their orthographic projections, a vertical "point-to-point" thermal feedback path with the shortest path through the droplet is constructed. In addition, non-precious metals such as copper, titanium, chromium, molybdenum, aluminum, and indium tin oxide are used for the heating element instead of expensive platinum, significantly reducing mass production costs.

[0022] 2. Zero-Delay Feedback: In this invention, the heating element and temperature sensor project and overlap with each other and are aligned at the center, achieving a "point-to-point" opposing layout in the vertical axis. This creates the shortest heat conduction path through the droplet, allowing heat flow to pass directly through the droplet and be captured, almost without needing to undergo lateral conduction through the substrate. This structure physically eliminates the unavoidable lateral heat diffusion lag in traditional offset layouts, improving the temperature control feedback response speed by more than 20%. Experimental results demonstrate that a steady-state temperature accuracy of ±0.3°C can be stably achieved within the RT–100°C range, with a typical entry time into the control zone of no more than 70 seconds, ensuring the stringent requirements of biochemical reactions for instantaneous temperature rise.

[0023] 3. Three-dimensional electrical decoupling and high signal-to-noise ratio: The temperature sensor is placed on the upper electrode plate, using the grounded electrode layer as a physical shield, and is vertically positioned away from the driving electrode below, achieving spatial shielding of the high-voltage drive and heating signals. This completely solves the signal coupling and crosstalk problem caused by close wiring in same-side layouts, ensuring the authenticity of the sampled data.

[0024] 4. Extremely narrow temperature zone edges and high spatial resolution: In PCR multi-temperature zone applications, this vertically opposed structure limits the ineffective spread of heat energy along the substrate direction, confining heat energy within a specific vertical columnar space. At the same time, the use of non-polar oil medium filled in the sealed chamber as a natural insulation layer significantly reduces the lateral thermal crosstalk between adjacent temperature zones, making the lateral thermal crosstalk between adjacent temperature zones ≤1°C. This results in sharper temperature zone switching edges, supports higher density temperature zone integration, and solves the pain point of thermal field coupling in miniaturized chips.

[0025] 5. Significantly Improved System Energy Efficiency: The "same-side, different-layer" integration scheme reduces the distance between the heating source and the droplet to the micrometer level (≤50μm), greatly reducing thermal resistance. Typical steady-state power consumption is only about 0.4W at 40°C and only about 1.5W at 95°C, significantly better than traditional external heat source solutions.

[0026] 6. The heating element uses non-precious metals such as copper, titanium, chromium, molybdenum, aluminum, and indium tin oxide instead of platinum. Combined with simplified manufacturing processes, this significantly reduces mass production costs while ensuring performance. This chip's sealed chamber design isolates it from external contamination, making it perfectly suited for PCR, cell culture, and various portable biochemical detection scenarios. Attached Figure Description

[0027] Figure 1 This is a schematic diagram of the structure of the first embodiment of the digital microfluidic chip of the present invention;

[0028] Figure 2 This is a schematic diagram of the 40℃ temperature control verification and heating power curve of the first embodiment;

[0029] Figure 3 This is a schematic diagram of the structure of the second embodiment of the digital microfluidic chip of the present invention;

[0030] Figure 4 This is a schematic diagram of the 65℃ temperature control verification and heating power curve of the second embodiment;

[0031] Figure 5 This is a schematic diagram of the 75°C temperature control verification and heating power curve for the second embodiment;

[0032] Figure 6 This is a schematic diagram of the 95℃ temperature control verification and heating power curve of the second embodiment;

[0033] Figure 7This is a schematic diagram of the steady-state power comparison curves in the three temperature zones of the second embodiment;

[0034] Figure 8 A schematic block diagram of a digital microfluidic integrated temperature control system;

[0035] In the figure: 1. First substrate, 2. Transparent FPC flexible circuit board, 3. Ground electrode layer, 4. First hydrophobic coating, 5. Support structure, 6. Droplet, 7. Dielectric layer, 8. Driving electrode, 9. Heating element, 10. Second substrate, 11. Temperature sensor, 12. Second hydrophobic coating. Detailed Implementation

[0036] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of this application.

[0037] First embodiment of a digital microfluidic chip:

[0038] like Figure 1 As shown, the upper electrode plate includes a first substrate 1, a temperature sensor 11, a ground electrode layer 3, and a first hydrophobic coating 4. All components are disposed on the inner side of the first substrate 1 facing the cavity (i.e., inside the chip).

[0039] The first substrate 1 is a 0.5mm thick transparent glass substrate for easy observation. A rectangular liquid injection through-hole with dimensions of 2.0x2.0mm is formed on the first substrate 1 using laser processing to inject reaction droplets 6 into the chamber. The temperature sensor 11 is a surface-mount NTC thermistor (0.6mm×0.3mm×0.3mm), integrated onto the transparent FPC flexible circuit board 2 (facing the chamber) using a soldering process. The distance between the temperature-sensing end of the NTC thermistor and the subsequent chamber is approximately 30μm. The ground electrode layer 3 is a 15μm thick indium tin oxide film based on PET, fixed to the inner surface of the first substrate 1 using a vacuum bonding process. The first hydrophobic coating 4 is a polytetrafluoroethylene solution, coated onto the inner surface of the indium tin oxide film based on PET using a spin coating process, with a coating thickness of 2μm.

[0040] The lower electrode includes a second substrate 10, a heating element 9, a dielectric layer 7, a driving electrode 8, and a second hydrophobic coating 12. All components are disposed on the inner side of the second substrate 10 facing the cavity (i.e., inside the chip).

[0041] The second substrate 10 is a transparent quartz glass substrate with a thickness of 1.0 mm. The heating element 9 is made of copper metal (a non-precious metal, the same material as the driving electrode 8) and is fabricated as a serpentine line structure with its ends connected. The serpentine line has a thickness of 0.32 μm, a line width of 60 μm, and a total length of 11.2 cm. It is fabricated on the inner surface of the second substrate 10 by magnetron sputtering and photolithography etching. The heating element 9 has a resistance of 100 Ω, and its effective heating area covers the three rectangular driving electrodes 8.

[0042] In this embodiment, a 20nm thick titanium adhesion transition layer is deposited between the heating element 9 and the second substrate 10. Experimental data shows that after 1000 thermal cycles at 25℃-95℃, no visible cracks or delamination appeared in the heating area. Furthermore, because the assembly alignment tolerance of the upper and lower plates is controlled to be less than or equal to ±500μm, the temperature sensor 11 is always positioned at the core of the vertical thermal field, ensuring accurate temperature control.

[0043] The dielectric layer 7 is made of SiO2 material with a thickness of 30μm. It is prepared on the side of the heating element 9 facing the sealed chamber by magnetron sputtering and fills the gap between the heating element 9 and the driving electrode 8 to isolate the heating element 9 and the driving electrode 8 and avoid electrical signal interference.

[0044] The driving electrode 8 is made of copper metal and is prepared on the side of the dielectric layer 7 facing the sealed chamber by sputtering deposition process. The size of a single electrode is 2.0mm×2.0mm, and the number can be changed according to the requirements.

[0045] The second hydrophobic coating 12 is made of the same material and process as the first hydrophobic coating 4, namely a polytetrafluoroethylene coating with a thickness of 2μm, which is applied to the surface of the driving electrode 8 by spin coating.

[0046] A sealed chamber is formed between the upper and lower plates of the chip using silicone gaskets, specifically:

[0047] Support structure 5 uses a 0.5mm thick silicone gasket, which is adhered to the edge area of ​​the lower electrode plate using UV-cured adhesive. The inner contour of the silicone gasket matches the effective area of ​​the chamber. After the upper and lower electrodes are fastened together, a sealed chamber with a height of 0.5mm is formed by the silicone gasket. The sealed chamber is connected to the outside only through the liquid injection hole of the upper electrode plate, which can effectively isolate external contamination and prevent droplet evaporation.

[0048] Inject 3 μL of reaction liquid droplets into the sealed chamber, as follows: Figure 1 The droplet 6 shown is driven in the area directly above the heating element 9. The distance between the droplet 6 and the heating element 9 is approximately the thickness of the second hydrophobic coating 12 (2 μm) and the thickness of the dielectric layer 7 (30 μm), with a total distance of less than 50 μm.

[0049] At room temperature, the digital microfluidic chip is connected to a matching integrated temperature control system (such as...) via an FPC interface. Figure 8 First, the high-voltage drive module of the control system sends a timing pulse waveform to the drive electrode 8, automatically driving 3μl of deionized water (illustrated droplet 6) to the target area directly above the heating element 9 using the electrowetting effect. Then, the system enters temperature control mode, and the microprocessor reads the feedback data from the temperature sensor 11 in real time and adjusts the output power of the heating element 9 to stabilize the temperature of droplet 6 at 40℃. Actual test results show (e.g.) Figure 2 Temperature control accuracy is 40℃±0.3℃, and the temperature fluctuation range meets the requirements of single-temperature zone constant temperature reaction; the maximum heating power is less than 2.0W, which is significantly lower than that of traditional external heating plates (above 10W).

[0050] Thanks to the vertical orthographic overlap of the heating element 9 and the temperature sensor 11, the temperature change detected by the system is almost synchronized with the application of the heating voltage, with no significant phase delay. This result proves that the vertically opposed structure physically eliminates the horizontal component of heat conduction, enabling the temperature sensor 11 to reflect the internal temperature rise of the droplet 6 in real time, which is the core guarantee for achieving an accuracy of ±0.3℃. Comparative tests show that if the upper electrode is moved horizontally by 2mm (simulating an offset layout), the time to reach steady state will be extended by approximately 30%.

[0051] Furthermore, since this solution uses copper (Cu) instead of traditional platinum (Pt), combined with the high energy efficiency ratio brought by the vertical feedback structure, the material cost is reduced by about 60% during the single-temperature zone isothermal process, and the typical power consumption (40℃) is as low as 0.4W.

[0052] The measured temperature of the NTC thermistor deviates from that of the standard thermocouple by less than ±0.3℃, meeting the accuracy requirements for temperature measurement.

[0053] This embodiment focuses on verifying the practical feasibility of the heating and temperature measurement scheme of the present invention. Its core optimization direction lies in design improvements that, while simplifying the number of heating and temperature measuring elements, not only effectively reduce the overall structural complexity of the equipment but also simultaneously ensure the uniformity and stability of the heating process, as well as the accuracy of the temperature measurement data.

[0054] Second embodiment of digital microfluidic chip:

[0055] like Figure 3A schematic diagram of a digital microfluidic chip with parallel electrode plates is presented, showing the integrated heating element 9 and temperature sensor 11 within the chip. The digital microfluidic chip, from top to bottom, comprises a first substrate 1, a transparent FPC flexible circuit board 2, a temperature sensor 11, a ground electrode layer 3, a first hydrophobic coating 4, a support structure 5, a droplet 6, a second hydrophobic coating 12, a dielectric layer 7, a driving electrode 8, a heating element 9, and a second substrate 10.

[0056] The core difference between this embodiment and the first embodiment is that, in order to meet the requirement of temperature control in three temperature zones of denaturation (95°C), annealing (65°C), and extension (75°C) for polymerase chain reaction (PCR), multiple heating elements 9 and temperature sensors 11 are independently designed to achieve efficient PCR reaction; the basic structure is the same as that in the first embodiment (such as the stacked logic of upper and lower plates, the common process of hydrophobic coating, etc.), which will not be described again here.

[0057] like Figure 3 As shown, a transparent FPC flexible circuit board 2 is disposed on the surface of the first substrate 1. Three surface-mount NTC thermistors are soldered on the transparent FPC flexible circuit board 2 as temperature sensors 11, corresponding to three heating elements 9. An indium tin oxide thin film serves as the ground electrode layer 3.

[0058] Specifically, the number of injection wells has been increased to four to accommodate the addition of various reagents required for reactions such as PCR.

[0059] This embodiment is based on the verification results of the first embodiment (the 100Ω copper heating wire process is mature, the temperature control is reliable, and it covers the temperature required for PCR). In order to further reduce the heating power and simplify the design and processing flow, the resistance of the heating element 9 is increased to 400Ω, and three sets of completely identical modular designs are adopted, while also having the flexibility of customizing the temperature range. The specific design differences are as follows:

[0060] Heating element 9 adopts a modular design (the three heating elements are completely identical), which can reuse the same processing flow and does not require separate design for different temperature zones; it continues the copper metal material and magnetron sputtering + photolithography etching process, which is compatible with the process of the first embodiment, reducing the cost of developing new masks; the line thickness is 0.32μm, the line width is 60μm, and the length is 44.8cm; all adopt a serpentine line layout, with the three sets of heating elements distributed in parallel, and the distance between adjacent sets is 2mm, which reduces temperature zone crosstalk; it achieves independent temperature control in three temperature zones: 95℃ in the denaturation zone, 65℃ in the annealing zone, and 75℃ in the extension zone, with crosstalk between adjacent temperature zones ≤1℃.

[0061] At room temperature, the digital microfluidic chip is integrated into a matching electronic control system. Through the host computer interface of the control system, PCR control logic is preset, and the high-pressure drive module sequentially controls three groups of droplets to move directly above the heating elements 9 in three preset temperature zones (65℃, 75℃, and 95℃). The system utilizes multiplexing sampling technology, with the ADC module cyclically reading real-time data from the three opposing temperature sensors 11, and the PID algorithm independently adjusting the PWM duty cycle of the three heating elements 9 to achieve coordinated and precise temperature control of the three temperature zones. Actual test results show (e.g.) Figure 4 , 5 6): Temperature control accuracies are 65℃±0.3℃, 75℃±0.3℃, and 95℃±0.3℃, respectively, and the temperature fluctuation range meets the requirements of PCR reaction; the maximum heating power is less than 4.0W, and is generated by... Figure 7 It can be seen that when heating reaches a steady state, the average heating power of the three temperature zones is less than 1.5W, which is significantly lower than that of traditional external heating plates (above 10W).

[0062] The vertically opposed layout of this invention vertically locks the "heating-temperature measurement" circuit in space. Since heat flow is primarily conducted vertically, the non-polar oil medium filling the space between the plates forms a natural insulating zone in the horizontal direction. Actual measurement data shows that when the modified region is at a steady state of 95°C, the temperature fluctuation within an adjacent 2mm radius is less than 1°C due to heat. Utilizing the non-polar oil medium filling the chamber as a natural horizontal thermal barrier cuts off the lateral spread of heat along the glass substrate. Simultaneously, Figure 7 A comparison of the power curves after each temperature zone enters steady state is presented, proving that the power output of each temperature zone is extremely low and stable during the collaborative temperature control process, thus solving the lateral thermal crosstalk bottleneck of miniaturized multi-temperature zone digital microfluidic chips.

[0063] Specifically, since the structural design and performance parameters of the three heating elements 9 are completely identical, they have good consistency and interchangeability. This embodiment takes the three-temperature zone precise temperature control scenario required by polymerase chain reaction (PCR) as an example for specific explanation. The heating element 9 supports the free configuration of the target temperature of the three temperature zones according to actual application needs, which can meet the core requirement of multi-temperature zone coordinated temperature control. Its application scenarios are not limited to PCR reaction, but can also be widely adapted to other biochemical reactions, material synthesis, sample processing and other scenarios that require multi-temperature zone precise temperature control, and has strong versatility and adaptability.

[0064] Integrated temperature control system using digital microfluidic chips:

[0065] The digital microfluidic chip of this invention is equipped with a miniaturized integrated electronic control system. This system is physically connected to the chip's edge pads via a high-density flexible printed circuit board (FPC). The control system includes the following integrated modules:

[0066] Integrated electronic control interface: The chip connects to the electronic control board through a ZIF connector, and the high-voltage drive (30V-200V) and the weak temperature sensing signal (mV level) are physically isolated at the interface to suppress electromagnetic coupling interference;

[0067] Precision temperature control sampling and driving circuit: A 24-bit ADC acquisition unit is used to read the resistance change of the temperature sensor 11 in real time, and the pulse width modulation (PWM) duty cycle applied to the heating element 9 is adjusted by a PID closed-loop algorithm.

[0068] Miniaturized feedback control: The system's main control chip incorporates an improved PID algorithm, dynamically adjusting the heating duty cycle based on the zero-delay feedback characteristic provided by the vertically opposed structure. This deep integration of "chip + circuit" design allows the overall biochemical detection equipment to be reduced to a handheld size.

[0069] Specifically, such as Figure 8 As shown, the integrated control system uses a microprocessor (MCU / FPGA) as the control core and interacts with the high-voltage drive module, precision sampling module and power regulation module through an internal bus to realize command interaction.

[0070] 1. High-voltage drive module: Controlled by microprocessor instructions, it generates a high-voltage timing level of 30V-200V, which is applied to the drive electrode 8 of the chip through the FPC interface to realize the precise planning of the movement path of the droplet 6.

[0071] 2. Precision sampling module: It has a built-in 24-bit high-resolution ADC unit, which reads the slight resistance change of the opposite temperature sensor 11 on the chip in real time through the FPC interface and converts it into a digital temperature signal and feeds it back to the microprocessor.

[0072] 3. Power Regulation Module: Based on the deviation between the set target temperature and the feedback temperature, the microprocessor runs a PID closed-loop algorithm and outputs PWM (Pulse Width Modulation) control commands. This module adjusts the DC power applied to the heating element 9 accordingly, achieving high-precision temperature control of ±0.3℃.

[0073] The above are merely preferred embodiments of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A digital microfluidic chip with a vertically opposed thermal feedback structure, characterized in that, It includes an upper electrode plate and a lower electrode plate arranged in parallel opposite directions, and a closed chamber for containing droplets (6) is formed between the upper electrode plate and the lower electrode plate. The upper electrode plate is provided with an injection hole that communicates with the closed chamber. The upper electrode plate is stacked in sequence with the first substrate (1), transparent FPC flexible circuit board (2), temperature sensor (11), ground electrode layer (3) and first hydrophobic coating (4) facing the sealed chamber. The lower electrode plate is stacked in sequence with the second substrate (10), heating element (9), dielectric layer (7), driving electrode (8) and second hydrophobic coating (12) facing the sealed chamber. The driving electrode (8) is disposed on the side of the dielectric layer (7) away from the second substrate (10), realizing same-side heterogeneous layer integration. The temperature sensor (11) and the heating element (9) coincide on the central axis or the horizontal offset distance between the central axes is less than a preset threshold, and the orthogonal projection of the temperature sensor (11) on the lower electrode plate is located within the projection range of the heating element (9), so that the heating element (9), the droplet (6) and the temperature sensor form a vertical coaxial thermal feedback path; the control drive electrode (8) moves the droplet (6) directly above the heating element (9), and the heating element (9) heats the droplet (6) vertically upward, and the opposing temperature sensor (11) captures the thermal signal passing through the droplet (6) in real time, thus constructing a vertical closed-loop feedback.

2. The digital microfluidic chip with a vertically opposed thermal feedback structure according to claim 1, characterized in that, There are several heating elements (9), which are arranged in a continuous end-to-end structure. The heating area is not less than the projected area of ​​the corresponding driving electrode (8). The effective heating area of ​​the heating element (9) covers at least one driving electrode (8).

3. The digital microfluidic chip with a vertically opposed thermal feedback structure according to claim 1, characterized in that, The number of temperature sensors (11) is not less than the number of heating elements (9), and each heating element (9) corresponds to at least one temperature sensor (11).

4. The digital microfluidic chip with a vertically opposed thermal feedback structure according to claim 1, characterized in that, The temperature sensor (11) is located between the ground electrode layer (3) and the first substrate (1); the ground electrode layer (3) is located between the temperature sensor (11) and the driving electrode (8) below, forming an electromagnetic shielding layer for physically isolating the driving electrical signal from interfering with the temperature sensor (11).

5. The digital microfluidic chip with a vertically opposed thermal feedback structure according to claim 1, characterized in that, The dielectric layer (7) is a sealed packaging layer that encapsulates the heating element (9) to block the electromigration of metal atoms and prevent high-temperature oxidation; the material of the dielectric layer includes inorganic dielectric materials, organic polymer materials or composite materials thereof; The inorganic dielectric material includes at least one of metal oxide, metal nitride, or semiconductor oxide; the organic polymer material includes at least one of photoresist, elastomer, or parylene-based material, and is processed by magnetron sputtering, spin coating, blade coating, or spray coating.

6. The digital microfluidic chip with a vertically opposed thermal feedback structure according to claim 1, characterized in that, A metal transition layer is provided between the heating element (9) and the second substrate (10), and between the heating element (9) and the dielectric layer (7), and the thickness of the metal transition layer is 5nm-500nm.

7. The digital microfluidic chip with a vertically opposed thermal feedback structure according to claim 1, characterized in that, The resistance of the heating element (9) is 5-2000Ω, and it is prepared by magnetron sputtering and photolithography etching, sputtering deposition or printing process; the material of the heating element (9) is copper, titanium, chromium, molybdenum, aluminum, indium tin oxide or a combination or alloy thereof, and the distance between the heating element (9) and the droplet (6) is 1-200μm; the material of the driving electrode (8) is copper, titanium, chromium, molybdenum, aluminum, indium tin oxide or a combination or alloy thereof, and the shape is rectangular, circular, sawtooth or polygonal, and it is processed by photolithography and etching, sputtering deposition or electroplating process.

8. The digital microfluidic chip with a vertically opposed thermal feedback structure according to claim 1, characterized in that, The thickness of the first substrate (1) is 0.2-5mm, and the material is glass, inorganic non-metallic material or plastic; the height of the sealed chamber is 0.1-5mm, and the height of the sealed chamber is controlled by the thickness of the support structure (5); the assembly alignment tolerance of the upper electrode plate and the lower electrode plate in the horizontal plane is less than or equal to ±500μm.

9. The digital microfluidic chip with a vertically opposed thermal feedback structure according to claim 1, characterized in that, The grounding electrode layer (3) is made of a transparent conductive film or a conductive grid structure, including silver nanowires, conductive polymers, indium tin oxide or carbon nanotubes; the temperature sensor (11) is a semiconductor element or metal thin film element with thermosensitive properties, including thin film resistance thermometers, thermistors, thermocouples or infrared sensors, and the distance between its temperature sensing end and the droplet (6) is 1-500 μm; the first hydrophobic coating (4) and the second hydrophobic coating (12) are made of fluoropolymers, polyalkylsiloxanes or hydrophobic nano-coating materials, with a thickness of 0.01-30.0 μm.

10. A temperature control system based on a digital microfluidic chip with a vertically opposed thermal feedback structure as described in any one of claims 1-9, characterized in that, The control board includes a high-voltage drive module, an ADC acquisition module and a PID control module. The ADC acquisition module acquires the signal from the temperature sensor (11). The PID control module uses the PID algorithm to adjust the pulse duty cycle applied to both ends of the heating element (9). The high-voltage drive module is electrically connected to the transparent FPC flexible circuit board and controls the drive electrode (8) to achieve precise planning of the movement path of the droplet (6).

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