A thermal flow velocity sensor and its preparation method

Abstract

The present invention discloses a thermal flow rate sensor and a preparation method thereof, comprising a sensor chip, an interlayer and a cover plate, wherein the sensor chip comprises a chip body, a heating unit, a temperature sensing unit, a temperature compensation resistor and an ambient temperature resistor, and a microfluidic pipeline is formed between the interlayer and the chip body and the cover plate and is connected to the outside world; the present invention adopts a dual heating unit and combines it with the microfluidic pipeline, and utilizes the blocking and viscosity effects of the microfluidic pipeline to convert the higher external flow rate into a slow flow rate in the microfluidic pipeline for measurement, which greatly increases the perception range of the thermal flow rate sensor for flow field flow rate signals; on the other hand, under low fluid flow rate, the flow rate is measured by utilizing the temperature sensing unit exposed to the external flow field and the temperature compensation resistor to form a bridge circuit, which has high sensitivity to flow rate changes. Therefore, the thermal flow rate sensor of the present invention has the huge advantages of high sensitivity and wide range.

Description

Technical Field

[0001] The present invention relates to the technical field of flow velocity sensors, and in particular to a thermal flow velocity sensor and a preparation method thereof. Background Art

[0002] Flow sensors are crucial for monitoring the flow field on a vehicle's surface. They form the hardware foundation for complex flow field recognition and attitude control. Flow sensor performance, such as accuracy, range, and sensitivity, directly impacts the accuracy of a vehicle's flow field sensing system.

[0003] Currently, flow sensors can be divided into thermal flow sensors and ciliary flow sensors based on their structure. Thermal flow sensors detect flow velocity by measuring the heat lost by the sensor's thermistor due to the action of the fluid. Thermal flow sensors typically consist of a heating element and a temperature measuring element. The heating element is usually a heating resistor that generates heat and is placed in the fluid path. The temperature measuring element includes upstream and downstream temperature-sensitive elements (such as thermistors or thermocouples) that measure the temperature difference caused by the fluid flow. When the fluid flows through the heating resistor of a heat loss sensor, it removes some of the heat from the heating resistor, allowing the flow rate to be inferred by measuring the heat loss. Alternatively, as the fluid passes through, a temperature difference will appear between the upstream and downstream temperature measuring elements. The temperature difference increases with the flow rate, and the flow rate is inferred by measuring this temperature difference. Bionic cilia structures based on the biological hair sensing principle are widely used in the design of flow rate sensors. The cilia structure deforms under the action of fluid-solid coupling, and the deformation of the cilia structure is converted into a corresponding electrical signal using sensitive principles such as piezoresistance, capacitance, and piezoelectricity, thereby realizing the perception of flow rate. Therefore, cilia-type flow rate sensors usually include cilia structures and sensitive elements. The cilia structure is the unit for the interaction between the sensor and the fluid, and is responsible for transmitting the fluid stimulus to the sensitive layer. The sensitive element converts the corresponding fluid stimulus into an electrical signal output.

[0004] In order to solve the above problems, the present invention provides a thermal flow velocity sensor and a preparation method thereof. By combining the design of a dual heating unit with a microfluidic structure, the range of the flow velocity sensor is greatly increased while ensuring high sensitivity, thereby achieving highly sensitive and wide-range perception of flow field velocity information. Summary of the Invention

[0005] The object of the present invention is to provide a thermal flow velocity sensor and a preparation method thereof, so as to achieve the purpose of improving the sensitivity and perception of flow velocity information of a flow field.

[0006] To achieve the above object, the present invention provides the following solutions:

[0007] A thermal flow rate sensor includes a sensor chip, an interlayer and a cover plate that are sequentially bonded from bottom to top, the sensor chip including a chip body, a first heating unit and a second heating unit symmetrically arranged on the left and right sides of the chip body, a first temperature sensing unit and a second temperature sensing unit symmetrically arranged on both sides of the first heating unit from left to right, a third temperature sensing unit and a fourth temperature sensing unit symmetrically arranged on both sides of the second heating unit from left to right, a first temperature compensation resistor and a second temperature compensation resistor symmetrically arranged on the front and back sides of the chip body, and an ambient temperature resistor arranged on the chip body, a microfluidic channel is formed between the interlayer, the chip body and the cover plate and is connected to the outside world, the second temperature sensing unit and the third temperature sensing unit are both arranged in the microfluidic channel, and the first temperature sensing unit and the fourth temperature sensing unit are exposed to the external flow field.

[0008] Preferably, the first temperature sensing unit, the second temperature sensing unit, the third temperature sensing unit, the fourth temperature sensing unit, the first heating unit, the second heating unit, the first temperature compensation resistor, the second temperature compensation resistor and the ambient temperature resistor are all connected to the leads on the chip body.

[0009] Preferably, the ambient temperature resistor includes a first ambient temperature resistor and a second ambient temperature resistor symmetrically arranged on both sides of the first temperature compensation resistor or the second temperature compensation resistor.

[0010] Preferably, the partition includes a circular middle plate and edge plates symmetrically arranged on both sides of the middle plate, the edge plates are spaced apart from the middle plate, and the distance between the edge plates and the middle plate forms a branch microfluidic pipeline, and the branch microfluidic pipeline is connected to the microfluidic pipeline.

[0011] A method for preparing a thermal flow velocity sensor comprises the following steps:

[0012] A low-stress silicon nitride film is formed on a silicon wafer substrate using low-pressure chemical vapor deposition;

[0013] Patterning the silicon nitride film using a lift-off process to form a first heating unit, a second heating unit, a first temperature sensing unit, a second temperature sensing unit, a third temperature sensing unit, and a fourth temperature sensing unit;

[0014] The electrodes are patterned using a lift-off process;

[0015] Using the patterned photoresist as a mask, ICP dry-etching the silicon nitride film to form trenches between the first heating unit, the second heating unit, and the first temperature sensing unit, the second temperature sensing unit, the third temperature sensing unit, and the fourth temperature sensing unit;

[0016] Spin-coat and photolithography SU-8 microfluidic channels and branch microfluidic channels to form a partition layer;

[0017] Use a dicing machine to cut the wafer and separate the devices;

[0018] Bonding cover plate;

[0019] A silicon substrate is isotropically dry-etched to form a suspended structure to reduce heat conduction along the substrate.

[0020] Preferably, the first heating unit, the second heating unit, and the first, second, third and fourth temperature sensing units made of Pt / Cr are patterned by a lift-off process.

[0021] Preferably, the electrodes made of Au / Cr are patterned by using a lift-off process.

[0022] Compared with the prior art, the present invention has achieved the following technical effects:

[0023] 1. The present invention adopts a dual-heating first heating unit and a second heating unit and combines them with a microfluidic pipeline. The blocking and viscosity effects of the microfluidic pipeline are used to convert the higher external flow velocity into a slow flow velocity in the microfluidic pipeline for measurement, which greatly increases the perception range of the thermal flow velocity sensor for the flow field flow velocity signal; on the other hand, under low fluid flow velocity, the flow velocity is measured by using the first temperature sensing unit and the fourth temperature sensing unit exposed to the external flow field and a temperature compensation resistor to form a bridge circuit, which has high sensitivity to flow velocity changes. Therefore, the thermal flow velocity sensor of the present invention has the huge advantages of high sensitivity and wide range. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] In order to more clearly illustrate the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0025] Figure 1 It is a structural schematic diagram of the present invention;

[0026] Figure 2 is an exploded view of the present invention;

[0027] Figure 3 It is a structural schematic diagram of the sensor chip of the present invention;

[0028] Figure 4 It is a schematic diagram of the structure of the present invention during operation;

[0029] Figure 5 is a graph showing the relationship between the temperature difference between the first temperature sensing unit and the temperature compensation resistor and the water flow velocity at low flow velocity of the present invention;

[0030] Figure 6 is a graph showing the relationship between the temperature difference between the first temperature sensing unit and the fourth temperature sensing unit and the water flow velocity at high flow velocity of the present invention;

[0031] Figure 7 This is a flow chart of the method for preparing the thermal flow velocity sensor of the present invention;

[0032] Among them, 1. Thermal flow rate sensor; 2. Cover; 3. Interlayer; 4. Sensor chip; 5. First heating unit; 6. Second heating unit; 7. First temperature sensing unit; 8. Second temperature sensing unit; 9. Third temperature sensing unit; 10. Fourth temperature sensing unit; 11. First ambient temperature resistor; 12. Second ambient temperature resistor; 13. First temperature compensation resistor; 14. Second temperature compensation resistor; 15. Lead. DETAILED DESCRIPTION

[0033] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. All other embodiments obtained by ordinary technicians in this field based on the embodiments of the present invention without making any creative efforts shall fall within the scope of protection of the present invention.

[0034] The object of the present invention is to provide a thermal flow velocity sensor and a preparation method thereof, so as to achieve the purpose of improving the sensitivity and perception of flow velocity information of a flow field.

[0035] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the present invention is further described in detail below with reference to the accompanying drawings and specific embodiments.

[0036] refer to Figures 1 to 6, a thermal flow rate sensor, comprising a sensor chip, an interlayer and a cover plate which are sequentially bonded from bottom to top, the sensor chip comprising a chip body, a first heating unit and a second heating unit symmetrically arranged on the left and right sides of the chip body, a first temperature sensing unit and a second temperature sensing unit symmetrically arranged on both sides of the first heating unit from left to right, a third temperature sensing unit and a fourth temperature sensing unit symmetrically arranged on both sides of the second heating unit from left to right, a first temperature compensation resistor and a second temperature compensation resistor symmetrically arranged on the front and back sides of the chip body, and an ambient temperature resistor arranged on the chip body, a microfluidic channel is formed between the interlayer, the chip body and the cover plate and is connected to the outside world, the second temperature sensing unit The first and second temperature sensing units are both arranged in the microfluidic pipeline, and the first temperature sensing unit and the fourth temperature sensing unit are exposed to the external flow field; the present invention adopts a dual-heating first heating unit and a second heating unit and combines them with the microfluidic pipeline, and utilizes the blocking and viscosity effects of the microfluidic pipeline to convert the higher external flow velocity into a slow flow velocity in the microfluidic pipeline for measurement, which greatly increases the perception range of the thermal flow velocity sensor for the flow field flow velocity signal; on the other hand, under low fluid flow velocity, the flow velocity is measured by utilizing the first temperature sensing unit exposed to the external flow field and the temperature compensation resistor to form a bridge circuit, which has high sensitivity to flow velocity changes. Therefore, the thermal flow velocity sensor of the present invention has the huge advantages of high sensitivity and wide range.

[0037] refer to Figures 4 and 5 , the sensor sensing principle is introduced with the water flow direction from left to right. At low flow rates, the fluid flow carries away the heat of the first and fourth temperature sensing units exposed to the external field. Due to the obstruction and viscosity of the microfluidic pipeline, the flow rate in the microfluidic pipeline approaches zero. However, the external flow rate will diffuse through the cover and carry away part of the heat of the second and third temperature sensing units in the microfluidic pipeline, causing the temperature of the second and third temperature sensing units to drop. Therefore, at low flow rates, the first temperature sensing unit directly exposed to the external field and at the front end of the sensor is used as the flow rate sensing element, and a bridge circuit is formed with the temperature compensation resistor to offset the influence of the fluid environment temperature on the sensor and convert the resistance change into a voltage signal output. It can be seen that the flow rate sensor has the characteristic of high sensitivity at low flow rates.

[0038] refer to Figure 4 and Figure 6At high flow rates, the fluid in the microfluidic channel flows, and the internal flow velocity is positively correlated with the external flow velocity. The fluid flow in the microfluidic channel causes more heat from the second heating unit to diffuse to the fourth temperature sensing unit, causing the temperature of the fourth temperature sensing unit to rise. However, due to the obstruction and viscosity of the microfluidic channel, the flow velocity in the microfluidic channel is much lower than the external flow velocity, which expands the fourth temperature sensing unit's sensing range for the external flow velocity. Therefore, at high flow rates, the temperature of the first temperature sensing unit decreases continuously as the flow velocity increases and approaches the ambient temperature, while the temperature of the fourth temperature sensing unit increases continuously. The first and fourth temperature sensing units form a bridge circuit to offset the influence of the fluid ambient temperature on the sensor and convert the resistance change into a voltage signal output. It can be seen that the dual heating unit design and microfluidic structure of the flow sensor greatly increase its sensing range for flow velocity.

[0039] refer to Figure 3 The first temperature sensing unit, the second temperature sensing unit, the third temperature sensing unit, the fourth temperature sensing unit, the first heating unit, the second heating unit, the first temperature compensation resistor, the second temperature compensation resistor and the ambient temperature resistor are all connected to the leads on the chip body.

[0040] refer to Figure 3 The ambient temperature resistor includes a first ambient temperature resistor and a second ambient temperature resistor symmetrically arranged on both sides of the first temperature compensation resistor or the second temperature compensation resistor.

[0041] refer to Figure 2 The partition includes a circular middle plate and edge plates symmetrically arranged on both sides of the middle plate. The edge plates are spaced apart from the middle plate. The distance between the edge plates and the middle plate forms a branch microfluidic pipeline, and the branch microfluidic pipeline is connected to the microfluidic pipeline.

[0042] A method for preparing a thermal flow velocity sensor comprises the following steps:

[0043] A low-stress silicon nitride film is formed on a silicon wafer substrate using low-pressure chemical vapor deposition;

[0044] Patterning the silicon nitride film using a lift-off process to form a first heating unit, a second heating unit, a first temperature sensing unit, a second temperature sensing unit, a third temperature sensing unit, and a fourth temperature sensing unit;

[0045] The electrodes are patterned using a lift-off process;

[0046] Using the patterned photoresist as a mask, ICP dry-etching the silicon nitride film to form trenches between the first heating unit, the second heating unit, and the first temperature sensing unit, the second temperature sensing unit, the third temperature sensing unit, and the fourth temperature sensing unit;

[0047] Spin-coat and photolithography SU-8 microfluidic channels and branch microfluidic channels to form a partition layer;

[0048] Use a dicing machine to cut the wafer and separate the devices;

[0049] Bonding cover plate;

[0050] A silicon substrate is isotropically dry-etched to form a suspended structure to reduce heat conduction along the substrate.

[0051] Furthermore, a lift-off process is used to pattern the first heating unit, the second heating unit, the first temperature sensing unit, the second temperature sensing unit, the third temperature sensing unit and the fourth temperature sensing unit, which are made of Pt / Cr.

[0052] Furthermore, a lift-off process is used to pattern and form electrodes made of Au / Cr.

[0053] Adaptive changes based on actual needs are all within the scope of protection of the present invention.

[0054] It should be noted that it will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above and that the present invention can be implemented in other specific forms without departing from the spirit or essential characteristics of the present invention. Therefore, the embodiments should be considered in all respects as illustrative and non-restrictive, and the scope of the present invention is defined by the appended claims, not the foregoing description, and it is intended that all variations within the meaning and range of equivalents of the claims be encompassed therein. Any reference signs in the claims should not be construed as limiting the claim to which they relate.

Claims

1. A thermal flow velocity sensor, characterized in that: The invention comprises a sensor chip, an interlayer and a cover plate which are sequentially bonded from bottom to top, wherein the sensor chip comprises a chip body, a first heating unit and a second heating unit symmetrically arranged on the left and right sides of the chip body, a first temperature sensing unit and a second temperature sensing unit symmetrically arranged on both sides of the first heating unit from left to right, a third temperature sensing unit and a fourth temperature sensing unit symmetrically arranged on both sides of the second heating unit from left to right, a first temperature compensation resistor and a second temperature compensation resistor symmetrically arranged on the front and back sides of the chip body, and an ambient temperature resistor arranged on the chip body, a microfluidic pipeline is formed between the interlayer, the chip body and the cover plate and is connected to the outside world, the second temperature sensing unit and the third temperature sensing unit are both arranged in the microfluidic pipeline, and the first temperature sensing unit and the fourth temperature sensing unit are exposed to the external flow field.

2. A thermal flow velocity sensor according to claim 1, characterized in that: The first temperature sensing unit, the second temperature sensing unit, the third temperature sensing unit, the fourth temperature sensing unit, the first heating unit, the second heating unit, the first temperature compensation resistor, the second temperature compensation resistor and the ambient temperature resistor are all connected to the leads on the chip body.

3. A thermal flow velocity sensor according to claim 2, characterized in that: The ambient temperature resistor includes a first ambient temperature resistor and a second ambient temperature resistor symmetrically arranged on both sides of the first temperature compensation resistor or the second temperature compensation resistor.

4. A thermal flow velocity sensor according to claim 3, characterized in that: The partition includes a circular middle plate and edge plates symmetrically arranged on both sides of the middle plate, the edge plates are spaced apart from the middle plate, and the spacing between the edge plates and the middle plate forms a branch microfluidic pipeline, which is connected to the microfluidic pipeline.

5. A method for preparing a thermal flow velocity sensor, characterized in that: The application of the thermal flow velocity sensor according to any one of claims 1 to 4 comprises the following steps: A low-stress silicon nitride film is formed on a silicon wafer substrate using low-pressure chemical vapor deposition; Patterning the silicon nitride film using a lift-off process to form a first heating unit, a second heating unit, a first temperature sensing unit, a second temperature sensing unit, a third temperature sensing unit, and a fourth temperature sensing unit; The electrodes are patterned using a lift-off process; Using the patterned photoresist as a mask, ICP dry-etching the silicon nitride film to form trenches between the first heating unit, the second heating unit, and the first temperature sensing unit, the second temperature sensing unit, the third temperature sensing unit, and the fourth temperature sensing unit; Spin-coat and photolithography SU-8 microfluidic channels and branch microfluidic channels to form a partition layer; Use a dicing machine to cut the wafer and separate the devices; Bonding cover plate; A silicon substrate is isotropically dry-etched to form a suspended structure to reduce heat conduction along the substrate.

6. The method for preparing a thermal flow velocity sensor according to claim 5, characterized in that: A lift-off process is used to pattern and form a first heating unit, a second heating unit, a first temperature sensing unit, a second temperature sensing unit, a third temperature sensing unit and a fourth temperature sensing unit made of Pt / Cr.

7. The method for preparing a thermal flow velocity sensor according to claim 6, characterized in that: The Au / Cr electrodes are patterned using a lift-off process.

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