Micro-flow sensing chip based on thermal feedback and digital power distribution and control method

Abstract

The invention discloses a micro-flow sensing chip based on thermal feedback and digital power distribution and a control method, the chip comprises a microstrip line assembly and an interface circuit which are arranged on a substrate, and the interface circuit comprises an amplifier, a comparator, a controller and a phase inverter; a connection point between the first fixed-value resistor and the fourth thermistor and a connection point between the second fixed-value resistor and the first thermistor are respectively connected with two input ends of an amplifier; the connecting end of the first fixed-value resistor and the second fixed-value resistor is connected with a voltage-stabilized power supply; the output end of the amplifier is connected with the positive input end of the comparator; the output end of the comparator is connected with one connecting end of the controller; the other connecting end of the controller is connected with the input end of the phase inverter and one end of the second thermistor; the output end of the phase inverter is connected with one end of the third thermistor. According to the flow sensing microsystem, the flow sensing chip is connected with the exclusive interface circuit in the thermal feedback mode, the signal stability of the integrated sensing microsystem is enhanced, and the inherent temperature drift problem is solved.

Description

Technical Field

[0001] The present invention relates to the technical field of integrated circuits, and in particular to a micro-flow sensor chip and a control method based on thermal feedback and digital power distribution. Background Art

[0002] Flow sensors have broad application potential in many fields such as industry, medicine and biology. At present, there are many kinds of working principles of flow sensors, among which thermal flow sensor chips have attracted widespread attention due to their advantages such as no moving parts, high stability and high repeatability. In order to ensure the optimal performance of thermal flow sensors, it is usually necessary to design appropriate heating strategies and interface circuits. At present, there are two main working modes of common thermal flow sensor chips: one is to drive the microheater on the chip by constant voltage (CV) or constant power (CP). In this mode, as the flow rate increases, the temperature of the microheater gradually decreases, but it is easy to saturate at high flow rates, resulting in reduced sensitivity and limited measurement range. The other mode is to keep the microheater at a constant temperature (CT) or constant temperature difference (CTD). Although this method can improve the measurement accuracy, it requires additional on-chip temperature sensors and complex circuit design to mitigate the temperature drift problem.

[0003] In recent years, a variety of micro-flow sensor chip systems based on thermal feedback (TF) mode have been launched one after another. With its significant advantages in measurement range, stability and response time, thermal feedback mode has become a powerful choice for improving sensor performance. In this mode, the sensor system can automatically adjust the power consumption of the microheater to eliminate the temperature gradient caused by fluid flow, thereby effectively reducing nonlinear distortion, reducing temperature drift, and enhancing the stability of the sensor. However, most existing thermal flow sensors use analog signal distribution during the thermal feedback process, which often leads to decreased signal stability and noise immunity. For example, X. Wang et al. proposed a flow sensor based on thermal feedback and analog voltage distribution. Although the design simplifies the electronic interface and has the advantages of fast response, the output stability is poor. Similarly, S. Wang et al. developed a wind speed sensor based on thermal feedback mode. Although two independent analog heating circuits were used, the output temperature drift of the system was still obvious. Therefore, the flow sensor in the thermal feedback mode in the prior art method has the problems of poor output stability and large signal temperature drift. Summary of the invention

[0004] The embodiment of the present invention provides a micro flow sensor chip and a control method based on thermal feedback and digital power distribution, aiming to solve the problems of poor output stability and large output temperature drift of flow sensors in thermal feedback mode in the prior art methods.

[0005] In a first aspect, an embodiment of the present application provides a micro flow sensor chip based on thermal feedback and digital power distribution, wherein the micro flow sensor chip includes a microstrip line component and an interface circuit disposed on a substrate, and the interface circuit includes an amplifier, a comparator, a controller and an inverter;

[0006] The microstrip line component is composed of a first thermistor, a second thermistor, a third thermistor and a fourth thermistor which are arranged in parallel in sequence, and the four thermistors are all arranged in parallel on the bottom cavity of the substrate in the form of a micro-suspension bridge; a first fixed value resistor, a second fixed value resistor, the first thermistor and the fourth thermistor are respectively arranged in series on the first bridge arm, the second bridge arm, the third bridge arm and the fourth bridge arm of the Wheatstone bridge;

[0007] The connection point between the first fixed value resistor and the fourth thermistor and the connection point between the second fixed value resistor and the first thermistor are respectively connected to the two input terminals of the amplifier; the connection terminal between the first fixed value resistor and the second fixed value resistor is connected to a voltage-stabilized power supply; the voltage-stabilized signal input terminal of the amplifier and the negative input terminal of the comparator are both connected to a reference voltage terminal, and the output terminal of the amplifier is connected to the positive input terminal of the comparator;

[0008] The output end of the comparator is connected to one connection end of the controller; the other connection end of the controller is connected to the input end of the inverter and one end of the second thermistor; the output end of the inverter is connected to one end of the third thermistor; the connection point between the first thermistor and the fourth thermistor, the other end of the second thermistor and the other end of the third thermistor are all grounded.

[0009] In a second aspect, an embodiment of the present application further provides a control method for a micro-flow sensor chip based on thermal feedback and digital power distribution, wherein the control method applies the controller of the micro-flow sensor chip based on thermal feedback and digital power distribution as described in the first aspect; the control method comprises:

[0010] Determining whether the duty cycle of the voltage signal output by the comparator is 50%, so as to determine whether the temperatures of the first thermistor and the fourth thermistor are balanced;

[0011] If the duty cycle of the voltage signal output by the comparator is not 50%, the interface circuit will intelligently adjust the duty cycle of the control signal of the pulse heating signal to the inverter and the second and third thermistors, and return to execute the step of determining whether the duty cycle of the voltage signal output by the comparator is 50%.

[0012] In a third aspect, an embodiment of the present application further provides a method for manufacturing a micro-flow sensor chip based on thermal feedback and digital power distribution, wherein the manufacturing method is used to manufacture the micro-flow sensor chip based on thermal feedback and digital power distribution as described in the first aspect, and the manufacturing method comprises:

[0013] Low stress SiN is grown on a silicon substrate x and a dielectric layer composed of a low temperature oxide;

[0014] Depositing a platinum metal film on the dielectric layer, and patterning the platinum metal film by a lift-off process to obtain a microstrip line component;

[0015] Depositing a SiO2 layer on the microstrip line component;

[0016] The combined low stress SiN x and SiO2 layer to form a surface opening;

[0017] Deep reactive ion etching is used to form a deep groove on a silicon substrate to form a substrate with a bottom cavity;

[0018] The micro-bridge structure suspended in the bottom cavity is released by isotropic XeF2 etching.

[0019] The embodiment of the present invention provides a micro flow sensor chip based on thermal feedback and digital power distribution, the micro flow sensor chip includes a microstrip line component and an interface circuit arranged on a substrate, the interface circuit includes an amplifier, a comparator, a controller and an inverter; the connection point between the first fixed resistor and the fourth thermistor, and the connection point between the second fixed resistor and the first thermistor are respectively connected to the two input ends of the amplifier; the connection end of the first fixed resistor and the second fixed resistor is connected to a voltage-stabilized power supply; the voltage-stabilized signal input end of the amplifier and the negative input end of the comparator are both connected to the reference voltage end, and the output end of the amplifier is connected to the positive input end of the comparator; the output end of the comparator is connected to a connection end of the controller; the other connection end of the controller is connected to the input end of the inverter and one end of the second thermistor; the output end of the inverter is connected to one end of the third thermistor. The above-mentioned micro flow sensor chip significantly improves the signal stability of the integrated sensor system by connecting the flow sensor chip with the exclusive interface circuit of the thermal feedback mode, and effectively reduces the inherent temperature drift characteristics of the integrated sensor system. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings required for use in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other accompanying drawings can be obtained based on these accompanying drawings without paying any creative work.

[0021] Figure 1 A circuit structure diagram of a micro flow sensor chip provided in an embodiment of the present invention;

[0022] Figure 2 A cross-sectional structural diagram of a micro flow sensor chip provided by an embodiment of the present invention;

[0023] Figure 3 An application effect diagram of the micro flow sensor chip provided by an embodiment of the present invention;

[0024] Figure 4 A method flow chart of a control method of a micro flow sensor chip provided by an embodiment of the present invention;

[0025] Figure 5 Another application effect diagram of the micro flow sensor chip provided by an embodiment of the present invention;

[0026] Figure 6 A method flow chart of a method for manufacturing a micro flow sensor chip provided by an embodiment of the present invention;

[0027] Figure 7 A schematic diagram of a process for manufacturing a micro flow sensor chip provided by an embodiment of the present invention;

[0028] Figure 8 Another application effect diagram of the micro flow sensor chip provided by an embodiment of the present invention;

[0029] Fig. 9 Another application effect diagram of the micro flow sensor chip provided by the embodiment of the present invention;

[0030] Fig.10 The following is an effect diagram of the application of the micro flow sensor chip provided by the embodiment of the present invention;

[0031] Fig.11 Another application effect diagram of the micro flow sensor chip provided by the embodiment of the present invention;

[0032] Fig.12 Another application effect diagram of the micro flow sensor chip provided by the embodiment of the present invention;

[0033] Fig.13 This is another application effect diagram of the micro flow sensor chip provided by the embodiment of the present invention.

[0034] Figure symbols: Ru, first thermistor; Rhu, second thermistor; Rhd, third thermistor; Rhd, fourth thermistor; R1, first fixed resistor; R2, second fixed resistor; INA, amplifier; CMP, comparator; MCU, controller; INV, high-speed inverter; 101, silicon substrate; 102, silicon nitride; 103, silicon dioxide; 104, platinum metal film; 105, bottom cavity. DETAILED DESCRIPTION

[0035] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0036] It should be understood that when used in this specification and the appended claims, the terms "include" and "comprises" indicate the presence of described features, integers, steps, operations, elements and / or components, but do not exclude the presence or addition of one or more other features, integers, steps, operations, elements, components and / or combinations thereof.

[0037] It should also be understood that the terms used in the present specification are only for the purpose of describing specific embodiments and are not intended to limit the present invention. As used in the present specification and the appended claims, the singular forms "a", "an" and "the" are intended to include the plural forms unless the context clearly indicates otherwise. It should also be further understood that the term "and / or" used in the present specification and the appended claims refers to any combination of one or more of the associated listed items and all possible combinations, and includes these combinations.

[0038] The embodiment of the present application discloses a micro flow sensor chip based on thermal feedback and digital power distribution, wherein the micro flow sensor chip includes a microstrip line component and an interface circuit arranged on a substrate, the interface circuit includes an amplifier INA, a comparator CMP, a controller MCU and an inverter INV; the microstrip line component is composed of a first thermistor Ru, a second thermistor Rhu, a third thermistor Rhd and a fourth thermistor Rhd arranged in parallel in sequence, and the four thermistors are all arranged in parallel on the bottom cavity of the substrate in the form of a micro-suspension bridge; a first fixed resistor R1, a second fixed resistor R2, the first thermistor Ru and the fourth thermistor Rhd are respectively arranged in series on the first bridge arm, the second bridge arm, the third bridge arm and the fourth bridge arm of the Wheatstone bridge; the connection point between the first fixed resistor R1 and the fourth thermistor Rhd, the second fixed resistor R2 and the first The connection points between the thermistors Ru are respectively connected to the two input terminals of the amplifier INA; the connection terminal of the first fixed resistor R1 and the second fixed resistor R2 is connected to a voltage-stabilized power supply; the voltage-stabilized signal input terminal of the amplifier INA and the negative input terminal of the comparator CMP are both connected to the reference voltage terminal, and the output terminal of the amplifier INA is connected to the positive input terminal of the comparator CMP; the output terminal of the comparator CMP is connected to a connection terminal of the controller MCU; the other connection terminal of the controller MCU is connected to the input terminal of the inverter INV and one end of the second thermistor Rhu; the output terminal of the high-speed inverter INV is connected to one end of the third thermistor Rhd; the connection point between the first thermistor Ru and the fourth thermistor Rhd, the other end of the second thermistor Rhu and the other end of the third thermistor Rhd are all grounded.

[0039] In a more specific embodiment, the thermistors are all platinum metal microstrip lines that meander in a serpentine shape. Specifically, the platinum metal microstrip lines are embedded between dielectric films composed of silicon oxide and silicon nitride. The platinum metal microstrip lines have a width of 2.5-5 μm and a thickness of 0.15-0.3 μm; and the dielectric film has a thickness of 2-3 μm.

[0040] In a more specific embodiment, the second thermistor Rhu and the third thermistor Rhd are used as micro-heaters, and the first thermistor Ru and the fourth thermistor Rhd are used as detectors; the resistance value of the micro-heater is smaller than the resistance value of the detector.

[0041] Specifically, the micro flow sensor chip is composed of a silicon substrate 101 and four micro suspension bridges built on a bottom cavity 105 of the silicon substrate 101. The micro suspension bridge is composed of a platinum metal film 104 embedded between silicon nitride 102 and silicon dioxide 103 (i.e. silicon oxide). Silicon oxide and silicon nitride form a dielectric film, and the platinum metal film 104 is embedded in the dielectric film to form a micro suspension bridge (i.e. a thermistor).

[0042] The distance between the micro heater and the detector is 13-34 μm. The present application specifically designs two sensors, wherein the distance between the micro heater and the detector of the two sensors (D sh ) is different, where sensor 1 is designed with D sh The distance is 13 μm, and the D of sensor 2 is designed sh The distance is 34μm.

[0043] The microstrip line assembly consists of four parallel-arranged platinum (Pt) thermistors arranged in a serpentine structure in the center of four micro-bridges. When there is no fluid flow (U = 0), the temperature curve is symmetrically distributed around the two micro-heaters. The second thermistor (heating power is P hu Indicated) and the third thermistor (heating power is P hd The heating power is evenly distributed on the hu =P hd , at this time, the temperature difference between the upstream and downstream detectors (the first heating resistor and the fourth heating resistor) is zero, expressed as ΔT = T d –T u = 0. When there is fluid flow (U≠0), due to thermal imbalance, the power on the second thermistor and the third thermistor will be redistributed, that is, P hu ≠P hd Thus, the temperature difference between the upstream and downstream detectors is rebalanced to zero due to thermal feedback.

[0044] In a preferred embodiment, the thermistor in the micro flow sensor chip can be designed to be made of a platinum (Pt) layer with a thickness of 0.2 μm and a temperature coefficient of resistance (TCR) of 1.8×10 -3 K -1, the wires are also made of a Pt layer. It is worth noting that the Pt layer is embedded in a 2.4μm thick dielectric film composed of silicon oxide and silicon nitride. Two sensor designs, sensor 1 and sensor 2, are implemented on a single chip. They have the same layout structure, and both the microheater and the detector are arranged in a serpentine structure using 4μm wide Pt wires. Specifically, the heating area of ​​each microheater is 712μm×80μm (length×width), and the resistance value of the microheater is 1165Ω; the sensing area of ​​each detector is 712μm×96μm (length×width), and the resistance value of the detector is 1366Ω. The main difference between the two sensor designs is the distance between the microheater and the edge of the detector suspension bridge (D sh ). In sensor 1, the distance D sh is 13 μm, while in sensor 2, the distance D sh It is worth noting that both sensor designs are located on a MEMS cavity with an opening size of 1000μm×800μm (length×width), and the inner distance between the two detectors in each design is fixed at 600μm.

[0045] In order to verify the performance of the sensor designed based on the thermal feedback (TF) mode, nitrogen (N2) was used as the working gas, whose thermal properties (density, viscosity, thermal conductivity, etc.) are automatically adjusted according to temperature changes. At the same time, the heating power allocated to the upstream and downstream microheaters is a function of the temperature difference between the detectors, that is, P hu =P i +G×(T d -T u ) and P hd =P i -G×(T d -T u ). Among them, P i is the initial heating power, G is the amplification factor. The simulation results show that when the gas flow rate is 2.22m / s, the temperature difference between the upstream and downstream detectors will automatically rebalance (ΔT≈0), ΔP=P hu –P hd >0. Figure 3 Figure (a) shows the output ΔP / P of two sensor designs (sensor 1 and sensor 2) as the flow rate U changes from -9m / s to 9m / s. Due to the thermal feedback effect, the temperature difference between the upstream and downstream detectors is suppressed to zero; the temperature difference ΔT of the flow sensor can be accurately controlled within ±5μK at different flow rates (U). At the same time, the second thermistor R hu and the third thermistor R hd The heating power difference ΔP (normalized to ΔP / P) between the two changes monotonically with the fluid flow rate from -9 m / s to 9 m / s, where P = Phu +P hd It is worth noting that sensor 2 has a larger D sh distance, its maximum system output is 1.7 times higher than that of sensor 1. In addition, by considering the thermal properties of the fluid as a function of the ambient temperature during the simulation, the output (ΔP / P) of sensor 2 based on the thermal feedback mode only slightly decreases by 7% in the ambient temperature range of 0 to 50°C (that is, the temperature drift is less than 7%), as shown in Figure 3 The above results show that the sensor with thermal feedback and power distribution can inherently suppress temperature drift without the need for additional compensation.

[0046] Figure 1 The flow sensor system with thermal feedback function and its digital power reading interface circuit are shown. In order to adjust the heating power of the microheater, the system uses a pulse signal with adjustable duty cycle (V hu and V hd ). The two pulse signals have the same frequency but opposite phases, thus ensuring that the total heating power (P) received by the two microheaters remains constant. In the absence of fluid flow, two anti-phase pulse signals with a frequency of 100 Hz and a duty cycle of 50% are applied to the two microheaters respectively. It is worth noting that V hd The signal is inverted via a high speed Figure 1 V hu Pulse signal generation. This design ensures the balance of heating power under static conditions.

[0047] Under this condition, due to the thermal coupling between the microheater and the detector, the Wheatstone bridge generates a periodic approximately sinusoidal signal (ΔV) and amplifies it, as shown in Figure 5 As shown in the figure. Figure 5 Indicates the change in the signal waveform output by the MEMS flow sensor chip when there is or is not thermal feedback. The amplified signal is processed by the comparator to generate a pulse signal Vc. In this state, the duty cycle of Vc is 50%, indicating ΔT = 0, because in the time period t0, V o With V ref The integral value of is zero:

[0048]

[0049] The embodiment of the present invention further provides a control method, which is applied to the controller of the micro flow sensor chip based on thermal feedback and digital power distribution as described in the above embodiment, such as Figure 4 As shown, the control method includes steps S110-S120.

[0050] S110, determining whether the duty cycle of the voltage signal output by the comparator is 50%, so as to determine whether the temperatures of the first thermistor and the fourth thermistor are balanced;

[0051] S120. If the duty cycle of the voltage signal output by the comparator is not 50%, the interface circuit will intelligently adjust the duty cycle of the pulse heating signal to the inverter and the second and third thermistors, and return to execute the step of determining whether the duty cycle of the voltage signal output by the comparator is 50%.

[0052] In a more specific embodiment, step S120 includes sub-steps: if the duty cycle of the voltage output signal exceeds 50%, increasing the duty cycle of the control signal on the second thermistor, and synchronously reducing the duty cycle of the control signal on the third thermistor; if the duty cycle of the voltage signal is less than 50%, reducing the duty cycle of the control signal on the second thermistor, and synchronously increasing the duty cycle of the control signal on the third thermistor.

[0053] When there is fluid flow (U>0), the first thermistor R u and the fourth thermistor R d The thermal imbalance between V o Changes such as Figure 1 If there is no thermal feedback, V c The duty cycle of V will exceed 50%, at which point ΔT>>0. In contrast, when the sensor system operates in thermal feedback mode, the controller continuously monitors V c As input signal, it automatically increases V through PID control hu duty cycle, while reducing V hd until it reaches P hu >P hd state, so that V c The duty cycle of is rebalanced to 50%. Similarly, for the case with reverse fluid flow (U<0), it can be foreseen that P hu <P hd It should be emphasized that the pulse signal V under different flow rates c The duty cycle will be precisely adjusted to 50% through thermal feedback to ensure the stability and accuracy of the system.

[0054] The embodiment of the present invention also provides a method for manufacturing a micro flow sensor chip based on thermal feedback and digital power distribution, and the manufacturing method is used to manufacture the micro flow sensor chip based on thermal feedback and digital power distribution as described in the above embodiment. Figure 6 As shown, the manufacturing method includes steps S210-S260.

[0055] S210, low stress SiN grown on silicon substratex and a dielectric layer composed of a low temperature oxide.

[0056] S220, depositing a platinum metal film on the dielectric layer, and patterning the platinum metal film through a lift-off process to obtain a microstrip line component.

[0057] S230, depositing a SiO2 layer on the microstrip line component.

[0058] S240, low stress SiN composite by reactive ion etching process x The SiO2 layer is processed to form a surface opening.

[0059] S250, using deep reactive ion etching to make deep grooves on the silicon substrate to form a substrate with a bottom cavity.

[0060] S260, releasing the micro-suspended bridge structure suspended in the bottom cavity by isotropic etching with XeF2.

[0061] The processing of flow sensor chip based on thermal feedback (TF) is as follows Figure 7 First, a low stress SiN x and a dielectric layer composed of a low temperature oxide, such as Figure 7 Next, a 200 nm thick Pt film is deposited and patterned by a lift-off process to form microheaters and detectors, as shown in Figure 2. Figure 7 As shown in Figures (b) and (c), PR is the photolithography pattern layer. Subsequently, an additional SiO2 layer is deposited as a passivation layer to assist in the subsequent release of the MEMS structure, as shown in Figures (b) and (c), where PR is the photolithography pattern layer. Figure 7 As shown in Figure (d), the combined low stress SiN x and SiO2 layers to define the cavity openings, such as Figure 7 As shown in Figure (e). Finally, Figure 7 As shown in Figure (f), deep reactive ion etching (DRIE) technology is used to make deep trenches on the silicon substrate, and XeF2 isotropic etching is used to release the suspended micro-bridge structure.

[0062] The above manufacturing method can produce a 5×5mm chip, which is embedded in a printed circuit board (PCB) and sealed in a photosensitive resin flow channel made of LEDO 6060 stereolithography (SLA) (dimensions are length×width×height=60mm×12.5mm×2.5mm). The packaged thermal feedback (TF) flow sensor chip was tested using a nitrogen (N2) gas flow. The nitrogen source was delivered to the reference flow meter (AWM5104VN, Honeywell, USA) and the sensor under test through two pressure reducing valves and a single-stage throttle valve. The entire sensor system is powered by a single 5V power supply. During the entire experiment, the PCB with the flow channel was placed in a constant temperature chamber (SH-222, ESPEC, Japan) to simulate ambient temperature changes. To verify the function of the entire sensor chip system with thermal feedback, an oscilloscope (MSO54B, Tektronix, USA) was used to monitor the system signal (V o 、V c 、V hu and V hd ). In addition, the microcontroller unit (STM32, MCU) records the duty cycle of each microheater, and then calculates the power difference ΔP between the upstream and downstream microheaters and determines the relationship between the sensor output and the input flow rate.

[0063] Figure 8 The V measured by the flow sensor chip system with and without airflow is shown. hu 、V o and V c waveform. It should be noted that V hd The waveform of V hu The frequencies are the same but the phases are opposite. Figure 8 Figure (a) shows the output waveform of the thermal feedback flow sensor chip when U = 0m / s. Figure 8 Figure (b) shows the output waveform of the flow sensor chip when U = 2.22m / s. The output ΔP increases from 0% to 40.1% due to thermal feedback. Figure 8 Ⅰ, Ⅱ and Ⅲ correspond to V under different conditions respectively. hu 、V o and V c The waveform of Figure 8 As shown in Figure (a), due to the thermal coupling between the microheater and the detector, the pulse signal (V hu and V hd ) will affect the switching state of the approximately sinusoidal signal (V o ) rises and falls. When there is no fluid flow (U = 0), the power difference between the upstream and downstream microheaters (ΔP = P hu –P hd ) is zero, that is, ΔP / P = 0. In this case, compare Vo and V ref The obtained V c The signal is a pulse signal with a duty cycle of 50%. When there is fluid flow (U = 2.22 m / s), R u and R d The thermal imbalance between V o changes, thus affecting V c The duty cycle of the MCU is adjusted to deviate from the 50% duty cycle in the open-loop configuration. In the closed-loop configuration with thermal feedback, the MCU can quickly and automatically adjust V hu and V hd The duty cycle until V c The duty cycle is restored to 50%, that is, ΔT≈0, as Figure 8 This digital automatic adjustment mechanism ensures that the system can achieve temperature balance under airflow conditions.

[0064] pass Figure 8 After the thermal feedback experiment in the experiment verified the function of the sensor chip, Fig. 9 The output curves of sensor 1 and sensor 2 at 25°C and N2 gas flow range from -9m / s to 9m / s were further plotted. Fig. 9 It shows the output ΔP / P measured by the sensor in the flow range of -9 to 9 m / s when the ambient temperature is 25°C, and its comparison with the theoretical result. Among them, in the linear range of -1.5 to 1.5 m / s, the sensitivity of sensor 1 is S1 = 16.66% / (m / s), while the sensitivity of sensor 2 is S2 = 27.71% / (m / s), which is 1.7 times higher than that of sensor 1. Therefore, compared with sensor 1, the subsequent experimental objects will focus on using sensor 2 with higher sensitivity.

[0065] Fig.10 The zero drift test results of the thermal feedback (TF) flow sensor chip in the temperature range of 0-50°C are shown, and the maximum zero drift (ΔP / P) is less than ±0.2%. In this test, the ambient temperature gradually dropped from 25°C to 0°C, then rose to 50°C, and finally returned to 25°C. The whole process lasted for more than 40 minutes. Fig.11 It further shows the drift of the system output measured in the flow range of -9m / s to 9m / s with temperature changes. As the ambient temperature increases, the sensor output gradually decreases. Taking the output curve of 25℃ (ΔP_T=25℃ / P) as the benchmark, Fig.11 The accompanying inset in Figure 2 shows that the sensor with thermal feedback achieved a temperature drift of less than 4% throughout the test (equivalent to 4% FS of full scale, considering maximum ΔP = 100%). These results show that thermal feedback and digital power distribution strategies effectively suppress the temperature drift of the flow sensor chip.

[0066] To evaluate the resolution of the packaged sensor under flow and zero flow conditions, the long-term stability of the system output (ΔP / P) was tested over 10 minutes at 25°C ambient temperature for sensors with and without thermal feedback. Fig.12 As shown by the jagged curve in , when the input gas flow rate is 1.1m / s, the sensor signal change without thermal feedback is 18.82%. For the sensor without thermal feedback, its sensitivity is measured to be 52.66% / (m / s), and the resolution under flow conditions can be inferred to be 357.38mm / s. This relatively poor resolution is mainly due to the flow disturbance in the channel. Further examining the inherent noise of the sensor system under zero flow conditions, the signal change of the non-thermal feedback sensor is Var. = 0.96%, so it can be inferred that the resolution of the non-thermal feedback flow sensor system under zero flow is 18.23mm / s (resolution = Var. / S).

[0067] After implementing the thermal feedback strategy, the signal fluctuation of the flow sensor system was reduced to 0.76% at a gas flow rate of 1.1 m / s, and further reduced to 0.04% under zero flow conditions. Fig.12 As shown by the fluctuation line in . Since the thermal feedback strategy significantly reduces the system noise, the resolution of the sensor under flow and zero flow conditions is significantly improved to 26.7mm / s and 1.44mm / s respectively. Therefore, through thermal feedback, the stability and resolution of the sensor system are also significantly improved.

[0068] Fig.13 The repeatability of the output of the flow sensor system based on thermal feedback (TF) is shown when the gas flow rate ranges from 0 to 6.6m / s at 25°C. The test results show that the signal change of the sensor system is Var=0.04% at zero flow, and the output is stable without hysteresis during the increase and decrease of flow rate. However, as the flow rate increases, the fluctuation of the system output also increases. This may be due to the fact that the chip is not completely horizontal when embedded in the PCB, and the turbulence caused by the uneven flow channel. The chip packaging and flow channel design will be improved in the subsequent processing technology to enhance the stability of the fluid flow, thereby improving the resolution of the sensor under high airflow conditions.

[0069] This application discloses a micro-flow sensor chip based on thermal feedback and digital power distribution. Based on the above test results, it is shown that by optimizing the design structure, the processed sensor chip exhibits extremely low inherent temperature drift characteristics in the range of 0 to 50°C and ±9m / s gas flow rate. The temperature drift is less than ±4% FS and no additional compensation is required. It is worth noting that the sensor system processes signals in a digital form, which significantly improves the stability and noise resistance of the system. Therefore, this new strategy lays the foundation for the development of a highly robust, highly sensitive, solid-state low-temperature drift flow sensor system, which can be used in harsh flow monitoring environments in the future.

[0070] The embodiment of the present invention provides a micro flow sensor chip based on thermal feedback and digital power distribution, the micro flow sensor chip includes a microstrip line component and an interface circuit arranged on a substrate, the interface circuit includes an amplifier, a comparator, a controller and an inverter; the connection point between the first fixed resistor and the fourth thermistor, and the connection point between the second fixed resistor and the first thermistor are respectively connected to the two input ends of the amplifier; the connection end of the first fixed resistor and the second fixed resistor is connected to a voltage-stabilized power supply; the voltage-stabilized signal input end of the amplifier and the negative input end of the comparator are both connected to the reference voltage end, and the output end of the amplifier is connected to the positive input end of the comparator; the output end of the comparator is connected to a connection end of the controller; the other connection end of the controller is connected to the input end of the inverter and one end of the second thermistor; the output end of the inverter is connected to one end of the third thermistor. The above-mentioned micro flow sensor chip significantly improves the signal stability of the integrated sensor system by connecting the flow sensor chip with the exclusive digital interface circuit of the thermal feedback mode, and effectively reduces the inherent temperature drift characteristics of the integrated sensor system.

[0071] The above is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Any technician familiar with the technical field can easily think of various equivalent modifications or replacements within the technical scope disclosed by the present invention, and these modifications or replacements should be included in the protection scope of the present invention. Therefore, the protection scope of the present invention shall be based on the protection scope of the claims.

Claims

1. A micro flow sensor chip based on thermal feedback and digital power distribution, characterized in that: The micro flow sensor chip includes a microstrip line component and an interface circuit arranged on a substrate, and the interface circuit includes an amplifier, a comparator, a controller and an inverter; The microstrip line component is composed of a first thermistor, a second thermistor, a third thermistor and a fourth thermistor which are arranged in parallel in sequence, and the four thermistors are all arranged in parallel on the bottom cavity of the substrate in the form of a micro-suspension bridge; a first fixed value resistor, a second fixed value resistor, the first thermistor and the fourth thermistor are respectively arranged in series on the first bridge arm, the second bridge arm, the third bridge arm and the fourth bridge arm of the Wheatstone bridge; The connection point between the first fixed value resistor and the fourth thermistor and the connection point between the second fixed value resistor and the first thermistor are respectively connected to the two input terminals of the amplifier; the connection terminal between the first fixed value resistor and the second fixed value resistor is connected to a voltage-stabilized power supply; the reference signal input terminal of the amplifier and the negative input terminal of the comparator are both connected to the reference voltage terminal, and the output terminal of the amplifier is connected to the positive input terminal of the comparator; The output end of the comparator is connected to one connection end of the controller; the other connection end of the controller is connected to the input end of the inverter and one end of the second thermistor; the output end of the inverter is connected to one end of the third thermistor; the connection point between the first thermistor and the fourth thermistor, the other end of the second thermistor and the other end of the third thermistor are all grounded.

2. The micro flow sensor chip based on thermal feedback and digital power distribution according to claim 1 is characterized in that: The thermistors are all platinum metal microstrip lines that meander in a serpentine shape.

3. The micro flow sensor chip based on thermal feedback and digital power distribution according to claim 2 is characterized in that: The platinum metal microstrip line is embedded between dielectric films composed of silicon oxide and silicon nitride.

4. The micro flow sensor chip based on thermal feedback and digital power distribution according to claim 3 is characterized in that: The platinum metal microstrip line has a width of 2.5-5 μm and a thickness of 0.15-0.3 μm.

5. The micro flow sensor chip based on thermal feedback and digital power distribution according to claim 4 is characterized in that: The thickness of the dielectric film is 2-3 μm.

6. The micro flow sensor chip based on thermal feedback and digital power distribution according to any one of claims 2 to 5, characterized in that: The second thermistor and the third thermistor are used as micro heaters, and the first thermistor and the fourth thermistor are used as detectors; the resistance value of the micro heater is smaller than the resistance value of the detector.

7. The micro flow sensor chip based on thermal feedback and digital power distribution according to claim 6 is characterized in that: The distance between the micro heater and the detector is 13-34 μm.

8. A control method for a micro flow sensor chip based on thermal feedback and digital power distribution, the control method being applied to a controller of a micro flow sensor chip based on thermal feedback and digital power distribution as claimed in any one of claims 1 to 7, characterized in that: The control method comprises: Determining whether the duty cycle of the voltage signal output by the comparator is 50%, so as to determine whether the temperatures of the first thermistor and the fourth thermistor are balanced; If the duty cycle of the voltage signal output by the comparator is not 50%, the interface circuit will intelligently adjust the duty cycle of the control signal of the pulse heating signal to the inverter and the second and third thermistors, and return to execute the step of determining whether the duty cycle of the voltage signal output by the comparator is 50%.

9. The control method according to claim 8, characterized in that: The duty cycle of the pulse heating signal to the control signal of the inverter includes: If the duty cycle of the voltage output signal exceeds 50%, increasing the duty cycle of the control signal on the second thermistor, and simultaneously reducing the duty cycle of the control signal on the third thermistor; If the duty cycle of the voltage signal is less than 50%, the duty cycle of the control signal on the second thermistor is reduced, and the duty cycle of the control signal on the third thermistor is increased synchronously.

10. A method for manufacturing a micro flow sensor chip based on thermal feedback and digital power distribution, characterized in that: The manufacturing method is used to manufacture the micro flow sensor chip based on thermal feedback and digital power distribution as described in any one of claims 1 to 7, and the manufacturing method comprises: Low stress SiN is grown on a silicon substrate x and a dielectric layer composed of a low temperature oxide; Depositing a platinum metal film on the dielectric layer, and patterning the platinum metal film by a lift-off process to obtain a microstrip line component; Depositing a SiO2 layer on the microstrip line component; The combined low stress SiN x and SiO2 layer to form a surface opening; Deep reactive ion etching is used to form a deep groove on a silicon substrate to form a substrate with a bottom cavity; The micro-bridge structure suspended in the bottom cavity is released by isotropic XeF2 etching.

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