High-sensitivity thermal flow sensing element and preparation method thereof

Abstract

The invention relates to a high-sensitivity thermal flow sensing element and a preparation method thereof.The sensing element is composed of a flow chip and a flow channel piece, and in order to obtain the advantage of high sensitivity, a thermosensitive film with the high TCR characteristic is selected as a temperature measuring unit material; selecting a material with low thickness, low thermal conductivity and low thermal capacity as a chip substrate; the sensor chip is prepared by adopting multilayer pattern photoetching and thin film growth, a heating unit in the prepared sensor chip provides a stable temperature field, meanwhile, a high-sensitivity temperature measuring unit more accurately and quickly measures the change of the temperature field in real time, and the flow velocity and the flow direction are obtained according to a temperature difference signal, so that the measurement of the flow with lower flow velocity is facilitated. The problem that the sensitivity of a traditional silicon-based substrate flow sensing chip can be improved only through complex micro-nano machining procedures such as etching and thinning is effectively solved, the performance and the preparation efficiency of the thermal flow sensing chip are improved, the cost is greatly reduced, and the thermal flow sensing chip has industrial popularization value.

Description

Technical Field

[0001] The patent of this invention belongs to the field of gas flow monitoring, and specifically relates to a high-sensitivity thermal flow sensor element and a preparation method thereof. Background Art

[0002] With the rapid development of the Internet of Things, big data and artificial intelligence technologies, flow sensors are gradually becoming miniaturized and intelligent. In industries such as chemical, petroleum, and food processing, real-time monitoring of flow changes of fluids (such as gases and liquids) in pipelines or industrial equipment is essential to 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 monitoring and control of the flow of blood, respiratory gases, chemical reagents, etc., and the requirements for high precision are also more stringent.

[0003] Thermal flow sensors use the heat transfer principle of gas, that is, the exchange relationship between the flow rate and heat between the gas and the heat source to measure the flow rate of the gas, and usually have high sensitivity and reliability. Its working principle is to provide a constant temperature field to the heating unit, and the temperature sensing unit measures the on-chip temperature difference formed 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 resistors or thermopiles as temperature measurement units to prepare flow sensors. However, due to the high thermal conductivity and large specific heat capacity of silicon materials, the interference of substrate heat transfer is relatively large, which has a great impact on the measurement of low flow rates. At the same time, due to the thickness of standard silicon wafers and other issues, high-precision flow sensors generally need to be thinned or etched cavities, which reduces the mechanical strength of the sensor chip and is more easily damaged, and is not suitable for extremely harsh environments. At the same time, temperature measurement methods such as platinum resistors and thermopiles also have the disadvantages of being expensive and not having high temperature sensitivity. Other temperature-sensitive materials can be selected for replacement. Summary of the invention

[0004] The purpose of the present invention is to provide a highly sensitive thermal flow sensor element and a preparation method thereof in view of the existing problems. The sensor element is composed of two major parts: a flow chip and a flow channel part. In order to obtain the advantages of high sensitivity performance, the present invention selects a thermosensitive film with high TCR characteristics as the temperature measurement unit material, and selects a material with low thickness, low thermal conductivity, and low heat capacity as the chip substrate. The preparation is completed by multi-layer graphic lithography and thin film growth. The heating unit in the prepared sensor chip provides a stable temperature field. At the same time, the highly sensitive temperature measurement unit measures the change of the temperature field more accurately and quickly in real time, and obtains the flow rate and flow direction according to the temperature difference signal, which is conducive to measuring the flow rate with a lower flow rate. It effectively avoids the problem that the traditional silicon-based substrate flow sensor chip needs to go through complex micro-nano processing procedures such as etching and thinning to achieve sensitivity improvement, improves the performance and preparation efficiency of the thermal flow sensor chip, greatly reduces the cost, and has industrial promotion value.

[0005] The present invention discloses a highly sensitive thermal flow sensor element, which is composed of two major parts: a flow chip (1) and a flow channel component (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 component (6) is composed of a fixing foot (8) and an airflow channel (7); a thermal 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 position of the thermal film layer (9), the heating units (3) are symmetrically arranged on the insulating layer (5), the temperature measuring units (4) are arranged at equal distances on the thermal film layer (9), the temperature measuring units (4) are arranged at the central hollow position of the insulating layer (5), an airflow channel (7) is arranged in the flow channel component (6), the flow chip (1) is fixed at the bottom of the flow channel component (6), and symmetrical fixing feet (8) are arranged at the bottom of the flow channel component (6), and the specific operation is carried out according to the following steps:

[0006] a. growing a thermal-sensitive thin film layer (9) on the surface of the substrate (2) by sputtering, evaporation or epitaxy, and performing high-temperature annealing at a temperature of 200-850° C., preparing a pattern mask of the insulating layer (5) by photolithography at the center of the thermal-sensitive thin film layer (9) coated on the substrate (2), performing annealing at a temperature of 200-650° C. after stripping the photoresist, performing photolithography on the surface of the insulating layer (5), and growing a heating unit (3) by sputtering, evaporation or epitaxy, performing annealing in a nitrogen atmosphere at a temperature of 200-650° C. after stripping the photoresist, and finally preparing a patterned electrode on the thermal-sensitive thin film layer (9) by photolithography to obtain a complete temperature measurement unit (4), thereby completing the flow chip (1);

[0007] b. Fix the flow chip (1) at the bottom of the flow channel (6) to allow airflow to 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, and the temperature measuring units (4) on both sides measure the temperature change. The temperature difference change of the two temperature measuring units (4) corresponds to the change in fluid flow rate. When the airflow direction is different, the temperature difference change of the temperature measuring unit is opposite, so as to judge the flow direction.

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

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

[0010] The temperature measuring unit 4 is a pair of thin film thermistors, which are composed of a thermosensitive film layer (9) and a patterned electrode to form a complete temperature measuring unit (4). The material is an NTC thermistor or a platinum resistor, 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 purpose of the present invention is achieved through the following technical solutions:

[0013] A highly sensitive thermal flow sensor element, the element comprises a highly sensitive thermal flow sensor chip of a main body and a flow channel component. The thermal flow sensor chip comprises a substrate, an insulating layer, a heating unit and a temperature measuring unit. The substrate selects mica, polyimide-based materials and other materials with low thickness, low thermal conductivity and low specific heat capacity as the device substrate, which reduces the substrate heat transfer interference compared with the traditional silicon substrate, and can greatly reduce the difficulty of MEMS process processing in the device preparation process while obtaining excellent performance. The heating unit is a thin film heating resistor, which provides a constant temperature field for the sensor. The temperature measuring unit is a pair of thin film thermistors, which are respectively located on the left and right sides of the heating unit at an equal distance, and can accurately measure the temperature field changes caused by the upstream and downstream airflows of the heat source. The thermistor and the heating film resistor are sequentially grown on the same substrate, and the insulating layer is between the heating film resistor and the thermistor, which simultaneously increases the adhesion and electrical insulation effect. The flow sensor chip is fixed inside the flow channel component for passing gas, 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 substrate, 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) may be made of alloy materials or other low TCR materials, including but not limited to tantalum nitride, nickel-chromium alloy, copper-manganese alloy and the like.

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

[0017] Preferably, the insulating layer (5) is made of an insulating thin film material having the characteristics of 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, wherein the functional layers of the temperature measuring unit (4) and the heating unit (3) and the insulating layer (5) therebetween are sequentially prepared on the surface of the substrate (2) by a physical vapor deposition method, including but not limited to sputtering, evaporation and the like, and the thin film is annealed, wherein the annealing temperature ranges of the temperature measuring unit (4), the heating unit (3) and the insulating layer (5) are 200-850° C., 200-650° C. and 200-650° C., respectively. Each functional layer, the insulating layer and the electrode layer are patterned by a photolithography process.

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

[0020] Preferably, the internal channel size of the flow channel member (6) is adjustable. According to the processing accuracy, the channel height can be set to vary from 0.5 mm to above. The channel length and width are 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 the present invention are:

[0022] The substrate material with low thermal conductivity and low heat capacity is selected, and the minimum substrate thickness is 10um. Compared with the traditional silicon-based substrate, the influence of substrate heat transfer on gas flow measurement is greatly reduced, and excellent performance improvement is achieved. There is no need for complex process steps such as thinning or etching, and the preparation is completed through multi-layer graphic lithography and thin film growth, and the process difficulty is low. The heating unit in the prepared sensor chip provides a stable temperature field. At the same time, the highly sensitive temperature measurement unit measures the changes in the temperature field more accurately and quickly in real time, and obtains the flow rate and flow direction based on the temperature difference signal, which is conducive to measuring the flow rate at a lower flow rate. BRIEF DESCRIPTION OF THE DRAWINGS

[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-section structure of the flow chip of the present invention;

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

[0026] Figure 4 This is the flow rate calibration test result of the present invention.

[0027] Markings and corresponding component names in the attached drawings: 1-flow chip, 2-substrate, 3-heating unit, 4-temperature measuring unit, 5-insulating layer, 6-flow channel part, 7-air flow channel, 8-fixing foot, 9-thermosensitive film layer. DETAILED DESCRIPTION

[0028] In order to facilitate the understanding of those skilled in the art, the present invention is further described below in conjunction with embodiments and drawings. The contents mentioned in the implementation modes are not intended to limit the present invention.

[0029] The invention is further described in detail below in conjunction with the following examples.

[0030] Example 1

[0031] A highly sensitive thermal flow sensor element described in the present invention is composed of two major parts: a flow chip 1 and a flow channel component 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 component 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 position of the thermosensitive film layer 9, the heating units 3 are symmetrically arranged on the insulating layer 5, the temperature measuring units 4 are equidistantly arranged on the thermosensitive film layer 9, the temperature measuring units 4 are arranged at the central hollow position of the insulating layer 5, an airflow channel 7 is arranged in the flow channel component 6, the flow chip 1 is fixed at the bottom of the flow channel component 6, and symmetrical fixing feet 8 are arranged at the bottom outside the flow channel component 6. The specific operation is carried out according to the following steps:

[0032] a. A layer of thermosensitive film layer 9 is grown on the surface of a mica substrate 2 with a thickness of 10 μm and a size of 1 mm by a sputtering method, and a high-temperature annealing is performed at a temperature of 850° C. A pattern mask of a silicon oxide insulating layer 5 is prepared by photolithography at the center position of the thermosensitive film layer 9 coated on the mica substrate 2, and an annealing treatment is performed at a temperature of 650° C. After the photoresist is stripped, photolithography is performed on the surface of the silicon oxide insulating layer 5, and a tantalum nitride heating unit 3 is grown by a sputtering method. After the photoresist is stripped, an annealing treatment is performed in a nitrogen atmosphere at a temperature of 650° C. Finally, a patterned electrode is prepared on the thermosensitive film layer 9 by a photolithography process to obtain a complete NTC thermistor temperature measurement unit 4, and a flow chip 1 is completed;

[0033] b. Fix the flow chip 1 at the bottom of the flow channel 6 so that the air flow can flow in for flow testing. The heating unit 3 starts heating to make the temperature of the flow chip 1 reach about 45°C. The specific temperature is measured by the temperature measuring unit 4 at the center. After the gas is introduced, when the air flow in the air flow channel 7 flows, the temperature field generated by the tantalum nitride heating unit 3 in the flow chip 1 changes. The NTC thermistor temperature measuring units 4 on both sides measure the temperature change. The temperature difference change of the two NTC thermistor temperature measuring units 4 corresponds to the change of the fluid flow rate. The results are as follows: Figure 4 As shown in , monitoring within the flow rate range of 0.01 m / s-1 m / s can be achieved; wherein when the airflow direction is different, the temperature difference of the NTC thermistor temperature measuring unit 4 changes in the opposite direction, thereby determining the flow direction.

[0034] Example 2

[0035] The highly sensitive thermal flow sensor element is implemented according to Example 1; the specific operation is performed according to the following steps:

[0036] a. A layer of thermosensitive film layer 9 is grown on the surface of a polyimide-based material substrate 2 with a thickness of 50 μm and a size of 5 mm by evaporation, and high-temperature annealing is performed at a temperature of 500° C. A pattern mask of an aluminum nitride insulating layer 5 is prepared by photolithography at the center position of the thermosensitive film layer 9 coated on the polyimide-based material substrate 2, and annealing is performed at a temperature of 300° C. Photolithography is performed on the surface of the aluminum nitride insulating layer 5, and a nickel-chromium alloy heating unit 3 is grown by evaporation. After the photoresist is stripped, annealing is performed in a nitrogen atmosphere at a temperature of 300° C. Finally, a patterned electrode is prepared on the thermosensitive film layer 9 by photolithography to obtain a complete platinum resistance temperature measurement unit 4, and the flow chip 1 is completed;

[0037] b. Fix the flow chip 1 at the bottom of the flow channel 6 so that the air flow can flow in for flow testing. The heating unit 3 starts heating to make the temperature of the flow chip 1 reach about 45°C. The specific temperature is measured by the temperature measuring unit 4 at the center. After the gas is introduced, when the air flow in the air flow channel 7 flows, the temperature field generated by the nickel-chromium alloy heating unit 3 in the flow chip 1 changes. The platinum resistance temperature measuring units 4 on both sides measure the temperature change. The temperature difference change of the two platinum resistance temperature measuring units 4 corresponds to the change of the fluid flow rate. The result is as follows: Figure 4 As shown in , monitoring can be achieved within the flow rate range of 0.01m / s-1m / s; wherein the temperature difference of the platinum resistance temperature measuring unit 4 changes oppositely when the air flow direction is different, thereby determining the flow direction.

[0038] Example 3

[0039] The highly sensitive thermal flow sensor element is manufactured according to Example 1, and the specific operation is performed according to the following steps:

[0040] a. A layer of thermosensitive film layer 9 is grown on the surface of a mica substrate 2 with a thickness of 100 μm and a size of 8 mm by epitaxial method, and high-temperature annealing is performed at a temperature of 700° C. A pattern mask of an aluminum oxide insulating layer 5 is prepared by photolithography at the center position of the thermosensitive film layer 9 coated on the mica substrate 2, and annealing is performed at a temperature of 450° C. After the photoresist is stripped, photolithography is performed on the surface of the aluminum oxide insulating layer 5, and a copper-manganese alloy heating unit 3 is grown by epitaxial method. After the photoresist is stripped, annealing is performed in a nitrogen atmosphere at a temperature of 450° C. Finally, a patterned electrode is prepared on the thermosensitive film layer 9 by photolithography process to obtain a complete NTC thermistor temperature measurement unit 4, and the flow chip 1 is completed;

[0041] b. Fix the flow chip 1 at the bottom of the flow channel 6 so that the air flow can flow in for flow test. The heating unit 3 starts heating to make the temperature of the flow chip 1 reach about 45°C. The specific temperature is measured by the temperature measuring unit 4 at the center. After the gas is introduced, when the air flow in the air flow channel 7 flows, the temperature field generated by the copper-manganese alloy heating unit 3 in the flow chip 1 changes. The NTC thermistor temperature measuring units 4 on both sides measure the temperature change. The temperature difference change of the two NTC thermistor temperature measuring units 4 corresponds to the change of the fluid flow rate. The result is as follows: Figure 4 As shown in , monitoring within the flow rate range of 0.01 m / s-1 m / s can be achieved; wherein when the airflow direction is different, the temperature difference of the NTC thermistor temperature measuring unit 4 changes in the opposite direction, thereby determining the flow direction.

[0042] Example 4

[0043] The highly sensitive thermal flow sensor element is manufactured according to Example 1, and the specific operation is performed according to the following steps:

[0044] a. A layer of thermosensitive film layer 9 is grown on the surface of a polyimide-based material substrate 2 with a thickness of 200 μm and a size of 10 mm by sputtering, and high-temperature annealing is performed at a temperature of 200° C. A pattern mask of a silicon nitride insulating layer 5 is prepared by photolithography at the center of the thermosensitive film layer 9 coated on the polyimide-based material substrate 2, and annealing is performed at a temperature of 200° C. After the photoresist is stripped, photolithography is performed on the surface of the silicon nitride insulating layer 5, and a tantalum nitride heating unit 3 is grown by sputtering. After the photoresist is stripped, annealing is performed in a nitrogen atmosphere at a temperature of 200° C. Finally, a patterned electrode is prepared on the thermosensitive film layer 9 by photolithography to obtain a complete platinum resistance temperature measurement unit 4, and the flow chip 1 is completed;

[0045] b. Fix the flow chip 1 at the bottom of the flow channel 6 so that the air flow can flow in for flow testing. The heating unit 3 starts heating to make the temperature of the flow chip 1 reach about 45°C. The specific temperature is measured by the temperature measuring unit 4 at the center. After the gas is introduced, when the air flow in the air flow channel 7 flows, the temperature field generated by the tantalum nitride heating unit 3 in the flow chip 1 changes. The platinum resistance temperature measuring units 4 on both sides measure the temperature change. The temperature difference change of the two platinum resistance temperature measuring units 4 corresponds to the change of the fluid flow rate. The result is as follows: Figure 4 As shown in , monitoring can be achieved within the flow rate range of 0.01m / s-1m / s; wherein the temperature difference of the platinum resistance temperature measuring unit 4 changes oppositely when the air flow direction is different, thereby determining the flow direction.

[0046] See also Figure 1 , Figure 2 , Figure 3 and Figure 4 They jointly demonstrated a highly sensitive thermal flow sensor element and its preparation method. Figure 1 The flow chip 1 is shown in the figure, and the structure of the flow chip 1 is shown in detail, including a substrate 2, a heating unit 3, a temperature measuring unit 4, an insulating layer 5 and their positional relationship; Figure 2 The central vertical cross-section of the medium flow chip 1, Figure 3 The middle is the flow channel part 6, Figure 4 The calibration test results of the prepared flow sensor are given in;

[0047] The substrate 2 is made of mica, which can reduce the difficulty of device preparation and processing technology while reducing the influence of substrate heat transfer to obtain better performance parameters;

[0048] The heating unit 3 is a thin film heating resistor, which provides a constant temperature field for the sensor; the temperature measuring unit 4 is a plurality of thin film thermistors, which are respectively located at the center of the heating unit and on the left and right sides at equal distances, 200μm away from the center of the substrate, and can accurately measure the temperature field changes caused by the upstream and downstream airflows of the heat source. The insulating layer 5 is located between the heating film resistor and the thermistor film, and at the same time increases the adhesion and electrical insulation effects;

[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 subjected to high-temperature annealing at 750°C. A graphic mask of the insulating layer 5 is prepared by photolithography in the central area of ​​the flow chip 1, which is grown on the thermosensitive film layer by sputtering, and annealed at 450°C after the photoresist is stripped off; photolithography is performed on the surface of the insulating layer 5, and tantalum nitride is grown by sputtering as the heating unit 3, which is annealed at 450°C in a nitrogen atmosphere after the photoresist is stripped off; finally, a graphic mask of the electrode part 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 preparation of the flow chip 1;

[0050] The flow channel component 6 is connected to the fluid generating system through the fixing foot 8 so that the airflow can flow in for flow testing; the flow chip 1 is fixed inside the airflow channel 7, and the electrode end point is led out through the lead wire, so as to be connected to the data acquisition system;

[0051] The test process is as follows: the heating unit 3 starts heating, so that the chip temperature reaches about 45°C. The specific temperature is measured by the thermistor located at the center of the temperature measuring unit 4. When the gas is introduced, the airflow in the airflow channel 7 flows, and the temperature field generated by the heating unit 3 changes. The temperature measuring unit 4 measures the temperature change. The temperature difference change of the thermistor on both sides corresponds to the change of the fluid flow rate. The results are as follows: Figure 4 As shown in , monitoring can be achieved within the flow rate range of 0.01m / s-1m / s; the temperature difference of the temperature measuring unit changes in the opposite direction when the air flow direction is different, and the flow direction can be judged accordingly.

[0052] The above description is only a preferred embodiment of the present invention and does not constitute any form of limitation to the present invention. Although the present invention is disclosed as a preferred embodiment as above, it is not intended to limit the present invention. Any technician familiar with the profession can make some changes or modifications to equivalent embodiments of equivalent changes by using the technical contents disclosed above without departing from the scope of the technical solution of the invention. However, any simple modification, equivalent changes and modifications made to the above embodiments according to the technology of the present invention, which do not depart from the content of the technical solution of the present invention, are within the scope of the present practical invention.

Claims

1. A highly sensitive thermal flow sensor element, characterized in that: The sensor element is composed of two major parts, namely a flow chip (1) and a flow channel component (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 component (6) is composed of a fixing foot (8) and an airflow channel (7); a thermal 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 position of the thermal film layer (9), the heating units (3) are symmetrically arranged on the insulating layer (5), the temperature measuring units (4) are arranged at equal distances on the thermal film layer (9), the temperature measuring unit (4) is arranged at the central hollow position of the insulating layer (5), an airflow channel (7) is arranged in the flow channel component (6), the flow chip (1) is fixed at the bottom of the flow channel component (6), and symmetrical fixing feet (8) are arranged at the bottom of the flow channel component (6), and the specific operation is performed according to the following steps: a. growing a thermal-sensitive thin film layer (9) on the surface of the substrate (2) by sputtering, evaporation or epitaxy, and performing high-temperature annealing at a temperature of 200-850° C., preparing a pattern mask of the insulating layer (5) by photolithography at the center of the thermal-sensitive thin film layer (9) coated on the substrate (2), performing annealing at a temperature of 200-650° C. after stripping the photoresist, performing photolithography on the surface of the insulating layer (5), and growing a heating unit (3) by sputtering, evaporation or epitaxy, performing annealing in a nitrogen atmosphere at a temperature of 200-650° C., and finally preparing a patterned electrode on the thermal-sensitive thin film layer (9) by photolithography to obtain a complete temperature measurement unit (4), thereby completing the flow chip (1); b. Fix the flow chip (1) at the bottom of the flow channel (6) to allow airflow to 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, and the temperature measuring units (4) on both sides measure the temperature change. The temperature difference change of the two temperature measuring units (4) corresponds to the change in fluid flow rate. When the airflow direction is different, the temperature difference change of the temperature measuring units is opposite, so as to judge the flow direction.

2. A highly sensitive thermal flow sensor element according to claim 1, characterized in that: The substrate (2) is made of mica or polyimide-based material, with a thickness of 10 μm-200 μm and a size of 1 mm-10 mm.

3. A highly sensitive thermal flow sensor according to claim 1, characterized in that: The heating unit (3) is a thin-film heating resistor, namely, tantalum nitride, nickel-chromium alloy or copper-manganese alloy material.

4. A highly sensitive thermal flow sensor element according to claim 1, characterized in that: The temperature measurement unit 4 is a pair of thin-film thermistors, which are composed of a thermosensitive film layer (9) and a patterned electrode to form a complete temperature measurement unit (4). The material is an NTC thermistor or a platinum resistor, and the number of resistor pairs is adjusted according to requirements.

5. A highly sensitive thermal flow sensor element according to claim 1, characterized in that: The insulating layer (5) is made of silicon oxide, aluminum nitride, aluminum oxide or silicon nitride.

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