A high-sensitivity thermal flow sensing element and a method of manufacturing the same

Abstract

The present application relates to a kind of high sensitivity thermal flow sensing element and its preparation method, the sensing element is by flow chip and flow passage piece two big parts, for obtaining high sensitivity performance advantage, the present application selects the thermal sensitive film with high TCR characteristics as temperature measurement unit material, selects low thickness, low thermal conductivity, low heat capacity material as chip substrate;Multiple layer pattern photolithography and thin film growth are used to complete preparation, the sensing chip prepared by heating unit provides stable temperature field, while high sensitivity temperature measurement unit is more accurate, fast real-time measurement temperature field change, and flow rate and flow direction are obtained according to temperature difference signal, it is favorable to measure lower flow rate flow.It effectively avoids the problem that traditional silicon substrate flow sensing chip needs to be realized sensitivity promotion by etching, thinning and other complex micro-nano processing procedures, improves the performance of thermal flow sensing chip and preparation efficiency, greatly reduces cost, has industrialization popularization value.

Description

Technical Field

[0001] This invention patent belongs to the field of gas flow monitoring, specifically relating to a highly sensitive thermal flow sensing element and its preparation method. Background Technology

[0002] With the rapid development of IoT, big data, and AI technologies, flow sensors are gradually becoming miniaturized and intelligent. In industries such as chemical, petroleum, and food processing, real-time monitoring of fluid (such as gas and liquid) flow changes in pipelines or industrial equipment is crucial for improving production efficiency and ensuring production safety. In the medical and biochemical fields, highly sensitive and fast-response flow sensors are often used to measure the real-time flow of blood, respiratory gases, chemical reagents, etc., requiring even more stringent precision.

[0003] Thermal flow sensors utilize the principle of gas heat transfer, specifically the exchange of heat and velocity between the gas and a heat source, to measure gas flow rate. They typically offer high sensitivity and reliability. Their working principle involves a heating unit providing a constant temperature field, while a temperature sensing unit measures the on-chip temperature difference created by the gas flow to determine the flow rate. Traditional thermal flow sensors generally use silicon wafers as substrates, platinum or nickel-chromium alloys as heating wires, and platinum resistance thermometers or thermopile as the temperature sensing unit. However, due to silicon's high thermal conductivity and specific heat capacity, substrate heat transfer interference is relatively significant, greatly impacting low-velocity measurements. Furthermore, limitations in the thickness of standard silicon wafers necessitate thinning or cavitation etching for high-precision flow sensors, reducing the sensor chip's mechanical strength and making it more susceptible to damage, thus unsuitable for extreme environments. Additionally, platinum resistance thermometers and thermopile temperature sensing methods are expensive and lack sufficient temperature sensitivity; alternative temperature-sensitive materials can be chosen to address these issues. Summary of the Invention

[0004] The purpose of this invention is to address existing problems by providing a highly sensitive thermal flow sensing element and its fabrication method. This sensing element consists of two main parts: a flow chip and a flow channel component. To achieve high sensitivity, this invention selects a thermally sensitive thin film with high thermal conductivity (TCR) as the temperature sensing unit material and a material with low thickness, low thermal conductivity, and low heat capacity as the chip substrate. The chip is fabricated using multilayer patterning photolithography and thin film growth. The heating unit in the fabricated sensing chip provides a stable temperature field, while the highly sensitive temperature sensing unit more accurately and quickly measures changes in the temperature field in real time. Flow velocity and direction are obtained based on the temperature difference signal, which is beneficial for measuring flow rates at lower velocities. This effectively avoids the problem of traditional silicon-based substrate flow sensing chips requiring complex micro-nano processing steps such as etching and thinning to improve sensitivity. It improves the performance and fabrication efficiency of thermal flow sensing chips, significantly reduces costs, and has industrialization potential.

[0005] The present invention discloses a high-sensitivity thermal flow sensing element, which is composed of two main parts: a flow chip (1) and a flow channel (6). The flow chip (1) is composed of a substrate (2), an insulating layer (5), a heating unit (3), and a temperature measuring unit (4). The flow channel (6) is composed of fixing feet (8) and an airflow channel (7). A thermal thin film layer (9) is coated on the surface of the substrate (2) of the flow chip (1). An insulating layer (5) is provided at the center of the thermal thin film layer (9). Heating units (3) are symmetrically arranged on the insulating layer (5). Temperature measuring units (4) are arranged at equal intervals on the thermal thin film layer (9). A temperature measuring unit (4) is provided at the center of the insulating layer (5). An airflow channel (7) is provided inside the flow channel (6). The flow chip (1) is fixed at the bottom inside the flow channel (6). Symmetrical fixing feet (8) are provided at the bottom outside the flow channel (6). The specific operation is carried out according to the following steps:

[0006] a. A thermosensitive thin film layer (9) is grown on the surface of the substrate (2) by sputtering, vapor deposition or epitaxy and then annealed at high temperature (200-850℃). A pattern mask of insulating layer (5) is prepared by photolithography at the center of the thermosensitive thin film layer (9) on the substrate (2). After the photoresist is removed, annealing is performed at temperature (200-650℃). Photolithography is performed on the surface of insulating layer (5) and heating unit (3) is grown by sputtering, vapor deposition or epitaxy. After the photoresist is removed, annealing is performed in nitrogen atmosphere at temperature (200-650℃). Finally, a patterned electrode is prepared on the thermosensitive thin film layer (9) by photolithography to obtain a complete temperature measuring unit (4) and complete the flow chip (1).

[0007] b. Fix the flow chip (1) at the bottom of the flow channel component (6) so that air can flow in for flow testing. When the airflow in the airflow channel (7) flows, the temperature field generated by the heating unit (3) in the flow chip (1) changes. The temperature measurement units (4) on both sides measure the temperature change. The temperature difference between the two temperature measurement units (4) corresponds to the change in fluid flow rate. When the airflow direction is different, the temperature difference of the temperature measurement units changes in opposite directions. This is used to determine the flow direction.

[0008] The substrate (2) is selected from mica or polyimide-based materials, with a thickness of 10μm-200μm and a size of 1mm-10mm.

[0009] The heating unit (3) is a thin-film heating resistor, i.e., tantalum nitride, nickel-chromium alloy or copper-manganese alloy material.

[0010] The temperature measuring unit 4 is a pair of thin-film thermistors, which together form a complete temperature measuring unit (4) consisting of a thermistor thin film layer (9) and patterned electrodes. The material is an NTC thermistor or a platinum resistance thermometer, and the number of resistor pairs can be adjusted according to requirements.

[0011] The insulating layer (5) is made of silicon oxide, aluminum nitride, aluminum oxide or silicon nitride.

[0012] The practical objective of this invention is achieved through the following technical solution:

[0013] A high-sensitivity thermal flow sensing element is disclosed, comprising a high-sensitivity thermal flow sensing chip as the main body and a flow channel component. The thermal flow sensing chip includes a substrate, an insulating layer, a heating unit, and a temperature measuring unit. The substrate is selected from materials with low thickness, low thermal conductivity, and low specific heat capacity, such as mica or polyimide-based materials, which reduces substrate heat transfer interference compared to traditional silicon substrates. This significantly reduces the difficulty of MEMS fabrication while achieving excellent performance. The heating unit is a thin-film heating resistor, providing a constant temperature field for the sensor. The temperature measuring unit consists of a pair of thin-film thermistors, located equidistantly on the left and right sides of the heating unit, enabling precise measurement of temperature field changes caused by upstream and downstream airflow from the heat source. The thermistor and heating thin-film resistors are sequentially grown on the same substrate, with the insulating layer positioned between them, simultaneously increasing adhesion and providing electrical insulation. The flow sensing chip is fixed inside the flow channel component for gas introduction, and the internal channel size can be designed and adjusted to control the gas flow rate and flow range.

[0014] Preferably, the substrate (2) is made of a material with low thickness, low thermal conductivity and low specific heat capacity, including but not limited to mica, polyimide-based materials, or ultra-thin aluminum nitride, aluminum oxide substrates, etc., with a minimum thickness of 10 μm and a maximum thickness of 200 μm. The lower the thickness, the higher the sensitivity.

[0015] Preferably, the heating unit (3) can be made of alloy materials or other low TCR materials, including but not limited to tantalum nitride, nickel-chromium alloy, copper-manganese alloy, etc.

[0016] Preferably, the temperature measuring unit (4) uses a thermistor material as the functional layer material, such as a manganese-based spinel-type negative temperature coefficient thermistor film material, which has high temperature sensitivity and good stability.

[0017] Preferably, the insulating layer (5) is made of an insulating thin film material that has good adhesion, high thermal conductivity and high temperature resistance. The material includes, but is not limited to, silicon oxide, aluminum nitride, aluminum oxide, silicon nitride, etc.

[0018] Preferably, the temperature measuring unit (4) and the heating unit (3) are divided into two parts: a functional layer and an electrode layer. The functional layer of the temperature measuring unit (4) and the insulating layer (5) in between are sequentially prepared on the surface of the substrate (2) by physical vapor deposition, including but not limited to sputtering, evaporation, etc. The thin film is then annealed, and the annealing temperatures of the temperature measuring unit (4), the heating unit (3) and the insulating layer (5) are 200-850℃, 200-650℃ and 200-650℃, respectively. Each functional layer, insulating layer and electrode layer are patterned by photolithography.

[0019] Preferably, multiple pairs of temperature measuring units (4) are placed according to the test requirements to improve test performance.

[0020] Preferably, the internal channel size of the flow channel component (6) is adjustable. Depending on the processing accuracy, the channel height can be set to 0.5mm or more, and the channel length and width can be adjusted according to the size of the heating unit and the temperature measuring unit to meet the application of different flow rate ranges.

[0021] The beneficial effects of this invention are as follows:

[0022] Choosing a substrate material with low thermal conductivity and low heat capacity, with a minimum substrate thickness of 10µm, significantly reduces the impact of substrate heat transfer on gas flow measurement compared to traditional silicon-based substrates, resulting in superior performance improvements. The process is simple, requiring only multi-layer patterning photolithography and thin film growth, eliminating the need for complex thinning or etching steps. The fabricated sensor chip features a heating unit that provides a stable temperature field, while a highly sensitive temperature measurement unit accurately and rapidly measures temperature field changes in real time. Flow velocity and direction are obtained from the temperature difference signal, facilitating the measurement of lower flow rates. Attached Figure Description

[0023] Figure 1 This is a schematic diagram of the flow chip structure of the present invention;

[0024] Figure 2 This is a schematic diagram of the vertical cross-sectional structure of the flow chip center of the present invention;

[0025] Figure 3 This is a schematic diagram of the flow channel component structure of the present invention;

[0026] Figure 4 The results are from the flow rate calibration test of this invention.

[0027] The labels and corresponding component names in the attached diagram are as follows: 1-Flow chip, 2-Substrate, 3-Heating unit, 4-Temperature measuring unit, 5-Insulating layer, 6-Flow channel component, 7-Airflow channel, 8-Fixing foot, 9-Thermosensitive thin film layer. Detailed Implementation

[0028] To facilitate understanding by those skilled in the art, the present invention will be further described below with reference to embodiments and accompanying drawings. The content mentioned in the embodiments is not intended to limit the present invention.

[0029] The invention will be further described in detail below with reference to the following embodiments.

[0030] Example 1

[0031] The present invention discloses a high-sensitivity thermal flow sensing element, which consists of two main parts: a flow chip 1 and a flow channel 6. The flow chip 1 comprises a substrate 2, an insulating layer 5, a heating unit 3, and a temperature measuring unit 4. The flow channel 6 comprises fixing feet 8 and an airflow channel 7. A thermal thin film layer 9 is coated on the surface of the substrate 2 of the flow chip 1. An insulating layer 5 is disposed at the center of the thermal thin film layer 9. Heating units 3 are symmetrically arranged on the insulating layer 5. Temperature measuring units 4 are arranged at equal intervals on the thermal thin film layer 9. A temperature measuring unit 4 is disposed at a hollowed-out position in the center of the insulating layer 5. An airflow channel 7 is disposed inside the flow channel 6. The flow chip 1 is fixed at the bottom inside the flow channel 6. Symmetrical fixing feet 8 are disposed at the bottom outside the flow channel 6. The specific operation is performed according to the following steps:

[0032] a. A thermistor thin film layer 9 with a thickness of 10μm and a size of 1mm is grown on the surface of a mica substrate 2 by sputtering and then annealed at a high temperature of 850℃. A pattern mask of silicon oxide insulating layer 5 is prepared at the center of the thermistor thin film layer 9 on the mica substrate 2 by photolithography. After the photoresist is removed, the substrate is annealed at a temperature of 650℃. A tantalum nitride heating unit 3 is grown on the surface of the silicon oxide insulating layer 5 by photolithography and sputtering. After the photoresist is removed, the substrate is annealed in a nitrogen atmosphere at a temperature of 650℃. Finally, a patterned electrode is prepared on the thermistor thin film layer 9 by photolithography to obtain a complete NTC thermistor temperature measuring unit 4, thus completing the flow chip 1.

[0033] b. Fix the flow chip 1 at the bottom of the flow channel component 6 to allow airflow for flow testing. The heating unit 3 starts heating, raising the temperature of the flow chip 1 to approximately 45°C. The specific temperature is measured by the temperature measuring unit 4 at the center. When gas is introduced, the temperature field generated by the tantalum nitride heating unit 3 in the flow chip 1 changes as the airflow flows through the air channel 7. The NTC thermistor temperature measuring units 4 on both sides measure the temperature change. The temperature difference between the two NTC thermistor temperature measuring units 4 corresponds to the change in fluid velocity. The results are as follows: Figure 4 As shown, it can monitor flow velocities from 0.01 m / s to 1 m / s; the temperature difference of the NTC thermistor temperature measuring unit 4 changes oppositely when the airflow direction is different, thereby determining the flow direction.

[0034] Example 2

[0035] The high-sensitivity thermal flow sensing element described herein is based on Embodiment 1; the specific operation is performed according to the following steps:

[0036] a. A thermistor thin film layer 9 is grown on the surface of a polyimide-based material substrate 2 with a thickness of 50μm and a size of 5mm by vapor deposition and then annealed at a high temperature of 500℃. A pattern mask of aluminum nitride insulating layer 5 is prepared by photolithography at the center of the thermistor thin film layer 9 on the polyimide-based material substrate 2. After the photoresist is removed, annealing is performed at a temperature of 300℃. Photolithography is performed on the surface of aluminum nitride insulating layer 5, and a nickel-chromium alloy heating unit 3 is grown by vapor deposition. After the photoresist is removed, annealing is performed in a nitrogen atmosphere at a temperature of 300℃. Finally, a patterned electrode is prepared on the thermistor thin film layer 9 by photolithography to obtain a complete platinum resistance temperature measuring unit 4, thus completing the flow chip 1.

[0037] b. Fix the flow chip 1 at the bottom of the flow channel component 6 to allow airflow for flow testing. The heating unit 3 starts heating, raising the temperature of the flow chip 1 to approximately 45°C. The specific temperature is measured by the temperature measuring unit 4 at the center. When gas is introduced, the temperature field generated by the nickel-chromium alloy heating unit 3 in the flow chip 1 changes as the airflow flows through the air channel 7. The platinum resistance temperature measuring units 4 on both sides measure the temperature change. The temperature difference between the two platinum resistance temperature measuring units 4 corresponds to the change in fluid velocity, as shown in the figure. Figure 4 As shown, it can monitor flow velocities from 0.01 m / s to 1 m / s; the temperature difference of the platinum resistance temperature measuring unit 4 changes in opposite directions when the airflow direction is different, thereby determining the flow direction.

[0038] Example 3

[0039] The high-sensitivity thermal flow sensing element described herein is based on Embodiment 1, and the specific operation is performed according to the following steps:

[0040] a. A thermistor thin film layer 9 with a thickness of 100μm and a size of 8mm is grown on the surface of a mica substrate 2 using an epitaxial method and then annealed at a high temperature of 700℃. A pattern mask of an alumina insulating layer 5 is prepared at the center of the thermistor thin film layer 9 on the mica substrate 2 by photolithography. After the photoresist is removed, the substrate is annealed at a temperature of 450℃. A copper-manganese alloy heating unit 3 is grown on the surface of the alumina insulating layer 5 by photolithography and then grown using an epitaxial method. After the photoresist is removed, the substrate is annealed in a nitrogen atmosphere at a temperature of 450℃. Finally, a patterned electrode is prepared on the thermistor thin film layer 9 by photolithography to obtain a complete NTC thermistor temperature measuring unit 4, thus completing the flow chip 1.

[0041] b. Fix the flow chip 1 at the bottom of the flow channel component 6 to allow airflow for flow testing. The heating unit 3 starts heating, raising the temperature of the flow chip 1 to approximately 45°C. The specific temperature is measured by the temperature measuring unit 4 at the center. When gas is introduced, the temperature field generated by the copper-manganese alloy heating unit 3 in the flow chip 1 changes as the airflow flows through the air channel 7. The NTC thermistor temperature measuring units 4 on both sides measure the temperature change. The temperature difference between the two NTC thermistor temperature measuring units 4 corresponds to the change in fluid velocity, as shown in the figure. Figure 4 As shown, it can monitor flow velocities from 0.01 m / s to 1 m / s; the temperature difference of the NTC thermistor temperature measuring unit 4 changes oppositely when the airflow direction is different, thereby determining the flow direction.

[0042] Example 4

[0043] The high-sensitivity thermal flow sensing element described herein is based on Embodiment 1, and the specific operation is performed according to the following steps:

[0044] a. A thermistor thin film layer 9 with a thickness of 200 μm and a size of 10 mm is grown on the surface of a polyimide-based material substrate 2 by sputtering and then annealed at a high temperature of 200 °C. A pattern mask of silicon nitride insulating layer 5 is prepared by photolithography at the center of the thermistor thin film layer 9 on the polyimide-based material substrate 2. After the photoresist is removed, annealing is performed at a temperature of 200 °C. Photolithography is performed on the surface of silicon nitride insulating layer 5, and tantalum nitride heating unit 3 is grown by sputtering. After the photoresist is removed, annealing is performed in a nitrogen atmosphere at a temperature of 200 °C. Finally, patterned electrodes are prepared on the thermistor thin film layer 9 by photolithography to obtain a complete platinum resistance temperature measuring unit 4, thus completing the flow chip 1.

[0045] b. Fix the flow chip 1 at the bottom of the flow channel component 6 to allow airflow for flow testing. The heating unit 3 starts heating, raising the temperature of the flow chip 1 to approximately 45°C. The specific temperature is measured by the temperature measuring unit 4 at the center. When gas is introduced, the temperature field generated by the tantalum nitride heating unit 3 in the flow chip 1 changes as the airflow flows through the air channel 7. The platinum resistance temperature measuring units 4 on both sides measure the temperature change. The temperature difference between the two platinum resistance temperature measuring units 4 corresponds to the change in fluid velocity, as shown in the figure. Figure 4 As shown, it can monitor flow velocities from 0.01 m / s to 1 m / s; the temperature difference of the platinum resistance temperature measuring unit 4 changes in opposite directions when the airflow direction is different, thereby determining the flow direction.

[0046] See Figure 1 , Figure 2 , Figure 3 and Figure 4 Together, they demonstrated a highly sensitive thermal flow sensing element and its fabrication method. Figure 1 The middle part is the flow chip 1, which shows in detail the structure on the flow chip 1, including the substrate 2, heating unit 3, temperature measuring unit 4, insulating layer 5 and their positional relationship; Figure 2 Center vertical cross-section of medium flow chip 1 Figure 3 The middle is the flow channel component 6, Figure 4 The calibration test results of the fabricated flow sensor are given in the paper;

[0047] The substrate 2 is made of mica, which can reduce the difficulty of device fabrication and processing while reducing the impact of substrate heat transfer and obtaining better performance parameters.

[0048] The heating unit 3 is a thin-film heating resistor, providing a constant temperature field for the sensor; the temperature measuring unit 4 consists of multiple thin-film thermistors, located at the center of the heating unit and on both sides at equal distances, 200μm from the center of the substrate, enabling precise measurement of temperature field changes caused by upstream and downstream airflow from the heat source. The insulating layer 5 is located between the heating thin-film resistor and the thermistor film, simultaneously increasing adhesion and providing electrical insulation.

[0049] The functional layer material in the temperature measuring unit 4 is a manganese cobalt nickel type negative temperature coefficient thermistor film, which is grown on the mica substrate 2 by sputtering and then annealed at 750°C. In the central region of the flow chip 1, a pattern mask for the insulating layer 5 is prepared by photolithography and grown on the thermistor film layer by sputtering. After the photoresist is removed, it is annealed at 450°C. Photolithography is performed on the surface of the insulating layer 5, and tantalum nitride is grown as the heating unit 3 by sputtering. After the photoresist is removed, it is annealed at 450°C in a nitrogen atmosphere. Finally, the pattern mask for the electrode parts in the temperature measuring unit 4 and the heating unit 3 is prepared by photolithography, and the electrode layer is grown by sputtering to complete the fabrication of the flow chip 1.

[0050] The flow channel component 6 is connected to the fluid generation system via the fixing foot 8 so that airflow can be introduced for flow testing; the flow chip 1 is fixed inside the airflow channel 7, and the electrode terminals are led out through leads so that it can be connected to the data acquisition system.

[0051] The testing process is as follows: Heating unit 3 begins heating, raising the chip temperature to approximately 45°C. The specific temperature is measured by the thermistor located at the center of temperature measuring unit 4. When gas is introduced, the temperature field generated by heating unit 3 changes as the airflow flows through airflow channel 7. Temperature measuring unit 4 measures this temperature change. The temperature difference between the two thermistor units corresponds to the change in fluid flow rate, and the results are as follows: Figure 4 As shown, it can monitor flow velocities from 0.01 m / s to 1 m / s; the temperature difference of the temperature measuring unit changes in opposite directions when the airflow direction is different, which can be used to determine the flow direction.

[0052] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make some changes or modifications to the above-disclosed technical content to create equivalent embodiments without departing from the scope of the invention. Any simple modifications, equivalent changes, and modifications made to the above embodiments based on the present invention without departing from the scope of the present invention are within the scope of the present invention.

Claims

1. A high sensitivity thermal flow sensing element characterized by, The sensing element is composed of a flow chip (1) and a flow channel piece (6), wherein the flow chip (1) is composed of a substrate (2), an insulating layer (5), a heating unit (3), and a temperature measuring unit (4), and the flow channel piece (6) is composed of a fixing foot (8) and an airflow channel (7); a thermosensitive film layer (9) is coated on the surface of the substrate (2) of the flow chip (1), an insulating layer (5) is arranged at the center of the thermosensitive film layer (9), the heating unit (3) is symmetrically arranged on the insulating layer (5), the temperature measuring unit (4) is arranged at equal distances on the thermosensitive film layer (9), the temperature measuring unit (4) is arranged at the center hollow position of the insulating layer (5), the airflow channel (7) is arranged in the flow channel piece (6), the flow chip (1) is fixed at the bottom of the flow channel piece (6), and the fixing foot (8) is symmetrically arranged at the bottom of the flow channel piece (6). a. A thermosensitive film layer (9) is grown on the surface of the substrate (2) by sputtering, evaporation or epitaxy, and high-temperature annealing is performed at a temperature of 200-850 DEG C. The center position of the thermosensitive film layer (9) coated on the substrate (2) is prepared by photoetching to form a pattern mask of the insulating layer (5). After the photoresist is stripped, annealing treatment is performed at a temperature of 200-650 DEG C. The surface of the insulating layer (5) is photoetched, and the heating unit (3) is grown by sputtering, evaporation or epitaxy. After the photoresist is stripped, annealing treatment is performed in a nitrogen atmosphere at a temperature of 200-650 DEG C. Finally, the patterned electrode is prepared on the thermosensitive film layer (9) by photoetching process to obtain the complete temperature measuring unit (4), and the flow chip (1) is completed. b. The flow chip (1) is fixed at the bottom of the flow channel piece (6) so that the airflow flows in for flow testing. When the airflow in the airflow channel (7) flows, the temperature field generated by the heating unit (3) in the flow chip (1) changes, and the temperature change is measured by the temperature measuring units (4) on both sides. The temperature difference change of the two temperature measuring units (4) corresponds to the change of the fluid flow rate, wherein the temperature difference change of the temperature measuring units is opposite when the airflow flows in different directions, so as to determine the flow direction.

2. A high sensitivity thermal flow sensing element according to claim 1, wherein, The substrate (2) is selected from mica or polyimide-based materials, and has a thickness of 10-200 microns and a size of 1-10 mm.

3. A high sensitivity thermal flow sensing element according to claim 1, wherein, The heating unit (3) is a thin-film heating resistor, which is made of tantalum nitride, nickel-chromium alloy or copper-manganese alloy material.

4. A high sensitivity thermal flow sensing element according to claim 1, wherein, The temperature measuring unit (4) is a pair of thin-film thermistors, which is composed of the thermosensitive film layer (9) and the patterned electrode to form a complete temperature measuring unit (4). The material is NTC thermistor or platinum resistor, and the number of resistance pairs can be adjusted according to requirements.

5. A high sensitivity thermal flow sensing element according to claim 1, wherein, The insulating layer (5) is made of silicon oxide, aluminum nitride, aluminum oxide or silicon nitride.

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