Thermal flow velocity sensor and preparation method thereof

Abstract

The invention discloses a thermal flow velocity sensor and a preparation method thereof, the thermal flow velocity sensor comprises a sensing chip, an interlayer and a cover plate, the sensing chip comprises a chip body, a heating unit, a temperature sensing unit, a temperature compensation resistor and an environment temperature resistor, and a microfluid pipeline is formed among the interlayer, the chip body and the cover plate and is communicated with the outside; according to the invention, the double heating units are combined with the microfluid pipeline, and the blocking and viscous effects of the microfluid pipeline are utilized to convert the high external flow velocity into the slow flow velocity in the microfluid pipeline for measurement, so that the sensing range of the thermal flow velocity sensor to the flow field flow velocity signal is greatly increased; and on the other hand, under the low flow velocity of the fluid, the temperature sensing unit exposed in the external flow field and the temperature compensation resistor form a bridge circuit to measure the flow velocity, and the thermal flow velocity sensor has very high sensitivity to the change of the flow velocity, so that the thermal flow velocity sensor 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 velocity sensors are of great significance in monitoring the flow field on the surface of aircraft, and are one of the hardware foundations for aircraft to realize complex flow field recognition and attitude control. The performance of flow velocity sensors, such as sensing accuracy, range, sensitivity and other indicators, directly affect the accuracy of the aircraft flow field sensing system.

[0003] At present, flow sensors can be divided into thermal flow sensors and ciliary flow sensors according to their structures. Thermal flow sensors detect the flow rate by measuring the heat lost by the thermistor on the sensor due to the action of the fluid; thermal flow sensors are usually composed of a heating element and a temperature measuring element. The heating element is usually a heating resistor, which is used to generate heat and is placed in the fluid path. The temperature measuring element includes upstream and downstream temperature-sensitive elements (such as thermistors or thermocouples) to measure the temperature difference caused by the flow of the fluid. When the fluid flows through the heating resistor of the heat loss type sensor, it will take away part of the heat on the heating resistor, so that the flow rate can be inferred by measuring the heat loss; or when the fluid passes, there will be a temperature difference between the upstream and downstream temperature measuring elements. As the flow rate increases, the temperature difference will also increase. 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, the cilia flow rate sensor usually includes a cilia structure and a sensitive element. 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 high-sensitivity 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 improve 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 velocity sensor 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, 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.

[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 comprises 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, the spacing 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, using the thermal flow velocity sensor according to any one of claims 1 to 4, comprising the following steps:

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

[0013] Patterning the silicon nitride film by 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 formed by patterning using a Lift-off process;

[0015] Using the patterned photoresist as a mask, ICP dry-etching the silicon nitride film to form grooves 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 photolithograph 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] The silicon substrate is isotropically etched by dry method to form a suspended structure to reduce the heat conduction along the substrate.

[0020] Preferably, 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 made of Pt / Cr are patterned by a Lift-off process.

[0021] Preferably, the electrode made of Au / Cr is patterned by 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, and utilizes the blocking and viscosity effects of the microfluidic pipeline to convert a relatively high 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 and the fourth temperature sensing unit exposed to the external flow field and a bridge circuit formed with a temperature compensation resistor, which has a 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 technical solutions in the present invention or the prior art, the drawings required for use in the embodiments will be briefly introduced below. 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 creative labor.

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

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

[0027] Figure 3 It is a schematic diagram of the structure 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 plate; 3. partition; 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 wire. DETAILED DESCRIPTION

[0033] 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 only 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.

[0034] The object of the present invention is to provide a thermal flow velocity sensor and a preparation method thereof, so as to improve 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 6A thermal flow velocity sensor 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 which are symmetrically arranged on the left and right sides of the chip body, a first temperature sensing unit and a second temperature sensing unit which are sequentially 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 which are sequentially 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 which are symmetrically arranged on the front and rear sides of the chip body, and an ambient temperature resistor which is 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, and the second temperature sensing unit The first 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; the present invention adopts a dual-heating first heating unit and a second heating unit and combines them with a 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 to 5 , the sensor sensing principle is introduced with the water flow direction from left to right. At low flow rates, the fluid flow takes away the heat of the first temperature sensing unit and the fourth temperature sensing unit exposed to the external field, and due to the blocking and viscosity effect of the microfluidic pipeline, the flow rate in the microfluidic pipeline approaches zero, but the external flow rate will diffuse through the cover plate and take away part of the heat of the second temperature sensing unit and the third temperature sensing unit in the microfluidic pipeline, causing the temperature of the second temperature sensing unit and the third temperature sensing unit 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 velocity 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 velocity sensor has the characteristics of high sensitivity at low flow rates.

[0038] refer to Figure 4 and Figure 6, at high flow rates, the fluid in the microfluidic pipeline flows, and the internal flow rate is positively correlated with the external field flow rate. The flow of fluid in the microfluidic pipeline causes the heat of the second heating unit to diffuse more to the fourth temperature sensing unit and increases the temperature of the fourth temperature sensing unit; however, due to the blocking and viscosity effects of the microfluidic pipeline, the flow rate in the microfluidic pipeline is much smaller than the external flow rate, which expands the perception range of the fourth temperature sensing unit for the external flow rate. Therefore, at high flow rates, the temperature of the first temperature sensing unit continues to decrease as the flow rate increases and tends to the ambient temperature, and the temperature of the fourth temperature sensing unit continues to increase. The first temperature sensing unit and the fourth temperature sensing unit 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 design of the dual heating unit and the microfluidic structure of the flow velocity sensor greatly increase its perception range of 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 layer 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, 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 by low-pressure chemical vapor deposition;

[0044] Patterning the silicon nitride film by 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 formed by patterning using a Lift-off process;

[0046] Using the patterned photoresist as a mask, ICP dry-etching the silicon nitride film to form grooves 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 photolithograph 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] The silicon substrate is isotropically etched by dry method to form a suspended structure to reduce the 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 made according to actual needs are all within the protection scope of the present invention.

[0054] It should be noted that it is obvious 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 features of the present invention. Therefore, the embodiments should be regarded as exemplary and non-restrictive from any point of view, and the scope of the present invention is defined by the appended claims rather than the above description, and it is intended that all changes falling within the meaning and scope of the equivalent elements of the claims are included in the invention. Any reference numeral in a claim should not be regarded as limiting the claim to which it relates.

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 which are symmetrically arranged on the left and right sides of the chip body, a first temperature sensing unit and a second temperature sensing unit which are sequentially 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 which are sequentially 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 which are symmetrically arranged on the front and back sides of the chip body, and an ambient temperature resistor which is 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, 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 layer 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 spacing between the edge plates and the middle plate forms a branch microfluidic pipeline, and the branch microfluidic pipeline 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 by low-pressure chemical vapor deposition; Patterning the silicon nitride film by 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 grooves 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 photolithograph 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; The silicon substrate is isotropically etched by dry method to form a suspended structure to reduce the heat conduction along the substrate.

6. The method for preparing a thermal flow velocity sensor according to claim 5, characterized in that: 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, are patterned by a lift-off process.

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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