MEMS thermal flow sensor based on glass film structure and preparation method thereof

Abstract

The invention discloses an MEMS thermal flow sensor based on a glass film structure and a preparation method of the MEMS thermal flow sensor. The sensor comprises a glass inner silicon substrate, a back cavity, a silicon through column, a heating resistor, a temperature measurement resistor, an environment temperature measurement resistor, a chromium adhesion layer, a PAD port and a silicon nitride protection layer. Wherein the heating resistor is located in the center, and the temperature measuring resistors are symmetrically distributed on two sides of the heating resistor; the back cavity is located on the back of the glass inner silicon substrate, and the heating resistor, the temperature measuring resistor and the environment temperature measuring resistor lead a PAD port to the back of the glass inner silicon substrate through a silicon through column. A thermal temperature difference principle is adopted, and upstream and downstream temperature measuring resistors form a Wheatstone bridge. When the flow velocity is not zero, the Wheatstone bridge outputs, and the larger the flow velocity is, the larger the output is. Based on the glass and silicon composite substrate, the suspension film structure is formed through the silicon etching process, transmission of heat to the substrate is greatly reduced, and the heat utilization rate is increased.

Description

Technical Field

[0001] The present invention belongs to the technical field of flow sensor preparation, and particularly relates to a MEMS thermal flow sensor prepared by using a high-temperature bonding and thermal reflux process of glass and silicon based on the temperature difference principle. Background Art

[0002] Accurate measurement of flow can provide important information for many fields such as industrial production, scientific research, and medical health. Currently, there are a wide variety of commonly used flow sensors. Among them, the thermal differential flow sensor based on MEMS technology has been widely used due to its many advantages such as simple structure, small size, high precision, fast response, and low power consumption.

[0003] The MEMS thermal flow sensor based on the thermal differential principle can be classified according to different control modes. Common control modes include: constant voltage mode, constant current mode, constant power mode, constant temperature difference mode, and temperature balance mode. Among them, the constant temperature difference mode is the most commonly used. In this mode, the temperature of the sensor is controlled by a feedback loop to be a constant temperature difference higher than the ambient temperature, effectively suppressing the influence of the ambient temperature on the measurement result of the sensor. However, the disadvantage of this mode is that it requires an external ambient temperature sensor, thus increasing the complexity of the system.

[0004] In order to reduce heat dissipation and reduce the heat transfer of the heating resistor to the substrate, thereby improving the output and achieving the purpose of low power consumption, a thermal flow sensor will design an air insulation layer. The traditional MEMS thermal flow sensor uses a suspended bridge thin film structure of silicon dioxide and silicon nitride. However, the silicon dioxide and silicon nitride thin films have residual stress problems, which will cause the thin films to break, greatly reducing the reliability of the sensor. Summary of the Invention

[0005] The purpose of the present invention is to provide a preparation method of a MEMS thermal flow sensor based on a glass thin film structure. Through the low thermal conductivity of the back cavity and the glass, the heat transfer to the substrate is effectively reduced, improving the performance of the product. At the same time, since the MEMS flow sensor has a complete thin film and the thickness of the thin film can be above 50um, the stability and reliability of the sensor structure are effectively improved to solve the technical problems existing in the background art.

[0006] To solve the above technical problems, the specific technical solutions of the present invention are as follows:

[0007] A MEMS thermal flow sensor based on a glass thin film structure of the present invention includes: a glass inner silicon substrate, a silicon through-column, a back cavity, a thermistor, a chromium adhesion layer, a PAD port, and a silicon nitride protective layer. The silicon through-column is embedded at the edge of the glass inner silicon substrate, and the silicon through-column leads the PAD port to the back of the glass inner silicon substrate. The thermistor includes a heating resistor, a temperature measuring resistor, and an ambient temperature measuring resistor. The silicon nitride protective layer is located on the surface of the glass inner silicon substrate to protect the thermistor. The back cavity is located at the center of the back of the glass inner silicon substrate, thereby forming a suspended thin film. The heating resistor, the temperature measuring resistor, and the ambient temperature measuring resistor are located directly above the back cavity. The heating resistor is located at the center directly above the back cavity, and the temperature measuring resistors are distributed on both sides of the heating resistor. The ambient temperature measuring resistors are distributed at the peripheral position above the back cavity, that is, at the edge of the glass inner silicon substrate. A chromium adhesion layer is provided between the glass inner silicon substrate and the thermistor. The PAD port is located on the back of the glass inner silicon substrate and is connected to both ends of the thermistor for connection to an external circuit.

[0008] Further, the material of the suspended thin film is glass.

[0009] Further, the temperature measuring resistors are symmetrically located on both sides of the heating resistor, including an upstream temperature measuring resistor and a downstream temperature measuring resistor, and are symmetrically distributed at the same distance from the heating resistor.

[0010] Further, the heating resistor, the temperature measuring resistor, and the ambient temperature measuring resistor are processed into a meandering pin pattern.

[0011] Further, the silicon through-column serves as a conductive channel to lead the PAD to the back of the glass inner silicon substrate, reducing the influence of the PAD port on the air flow and making the measured flow rate of the sensor more accurate.

[0012] Further, the material of the PAD port is one or several alloy materials of nickel, titanium, tungsten, chromium, platinum, aluminum, or gold; the heating resistor, the temperature measuring resistor, and the ambient temperature measuring resistor all use the material platinum.

[0013] A preparation method of a MEMS thermal flow sensor based on a glass thin film structure of the present invention includes the following steps:

[0014] S1. Prepare a wafer of a low-resistance silicon wafer: Specifically, clean an N-type silicon wafer with a 100 crystal orientation.

[0015] S2. Spin-coat photoresist on the front side, align the silicon wafer, and then develop, expose, and etch to form a central etch area pit.

[0016] S3. Spin-coat photoresist on the front side, align the silicon wafer, and then develop, expose, and etch to leave the silicon through-column and the central silicon column, which will be etched away in the subsequent process to form a thin film structure.

[0017] S4. After anodic bonding the silicon wafer and the glass wafer, thermally reflux and fill the silicon wafer, perform thermal annealing to eliminate thermal stress, and then thin and polish the composite substrate of the glass and the silicon.

[0018] S5. Spin-coat photoresist on the front side, align with the silicon wafer and then develop and expose the patterns of the heating resistor, temperature-measuring resistor, and ambient temperature-measuring resistor, and sputter chromium metal film and platinum metal film on the front side.

[0019] S6. Use the lift-off process to fabricate the required chromium adhesion layer, heating resistor, temperature-measuring resistor, and ambient temperature-measuring resistor.

[0020] S7. Deposit a silicon nitride protective layer on the front side by plasma-enhanced chemical vapor deposition process.

[0021] S8. Spin-coat photoresist on the back side, align with the silicon wafer and then develop and expose the pattern of the PAD port, and sputter a metal film on the front side.

[0022] S9. Use the lift-off process to fabricate the required PAD port.

[0023] S10. Spin-coat photoresist on the back side, align with the silicon wafer and then develop and expose to etch away the central silicon pillar to form a back cavity, leaving the glass thin film structure.

[0024] A MEMS thermal flow sensor based on a glass thin film structure and its preparation method according to the present invention have the following advantages: In the MEMS thermal flow sensor of the present invention, a suspended thin film structure is formed by the back cavity, and the substrate used is a glass-in-silicon substrate, which has a very low thermal conductivity, effectively reduces the heat transfer to the substrate, reduces power consumption, improves the output of the Wheatstone bridge, and effectively improves the performance of the sensor; the suspended bridge thin film in the present invention is a complete thin film and there is no problem of residual stress, and it has better structural stability compared with silicon oxide and silicon nitride thin films; the PAD port in the present invention is led to the back side of the glass-in-silicon substrate through a silicon through-column, reducing the influence of the connection between the sensor and the circuit on fluids and gases, making the output of the sensor more accurate; the silicon nitride protective layer resistor and the substrate contribute to improving the stability and lifespan of the sensor. Description of the Drawings

[0025] Figure 1 It is a schematic side view of a MEMS thermal flow sensor based on a glass thin film structure disclosed in an embodiment of the present invention;

[0026] Figure 2 It is a process flow model diagram of a MEMS thermal flow sensor based on a glass thin film structure disclosed in an embodiment of the present invention;

[0027] Figure 33D structural schematic diagram of the first MEMS thermal flow sensor based on a glass thin film structure disclosed in the embodiments of the present invention;

[0028] Figure 4 3D structural schematic diagram of the second MEMS thermal flow sensor based on a glass thin film structure disclosed in the embodiments of the present invention;

[0029] Figure 5 3D structural schematic diagram of the third MEMS thermal flow sensor based on a glass thin film structure disclosed in the embodiments of the present invention;

[0030] Figure 6 3D structural schematic diagram of the fourth MEMS thermal flow sensor based on a glass thin film structure disclosed in the embodiments of the present invention.

[0031] Marking description in the figure: 100, glass-internal silicon substrate; 101, silicon through-column; 102, back cavity; 201, heating resistor; 202, temperature-measuring resistor; 203, ambient temperature-measuring resistor; 300, chromium adhesion layer; 301, PAD port; 302, silicon nitride protective layer. Detailed implementation manners

[0032] To better understand the purpose, structure and function of the present invention, the following further describes in detail a MEMS thermal flow sensor based on a glass thin film structure of the present invention and its preparation method with reference to the accompanying drawings.

[0033] As Figure 1As shown in the figure, the present invention proposes a MEMS thermal flow sensor based on a glass thin film structure. The sensor includes: a glass-internal silicon substrate 100, a silicon through-column 101, a back cavity 102, a heating resistor 201, a temperature-measuring resistor 202, an ambient temperature-measuring resistor 203, a chromium adhesion layer 300, a PAD port 301, and a silicon nitride protective layer 302. Among them, the silicon through-column 101 is embedded at the edge of the glass-internal silicon substrate 100, and the silicon through-column 101 leads the PAD port 301 to the back of the glass-internal silicon substrate 100. The thermistor 200 includes a heating resistor 201, a temperature-measuring resistor 202, and an ambient temperature-measuring resistor 203; the silicon nitride protective layer 302 is located on the surface of the glass-internal silicon substrate 100 and is used to protect the thermistor 200; the back cavity 102 is located at the center of the back of the glass-internal silicon substrate 100, thus forming a suspended thin film; the heating resistor 201, the temperature-measuring resistor 202, and the ambient temperature-measuring resistor 203 are located directly above the back cavity 102; the heating resistor 201 is located at the center position directly above the back cavity 102, and the temperature-measuring resistor 202 is distributed on both sides of the heating resistor 201; the ambient temperature-measuring resistor 203 is distributed at the peripheral position above the back cavity 102; a chromium adhesion layer 300 is provided between the glass-internal silicon substrate 100 and the thermistor 200; the PAD port 301 is located on the back of the glass-internal silicon substrate 100 and is connected to both ends of the thermistor 200.

[0034] The glass-internal silicon substrate 100 is a composite board formed by lithography, etching of a silicon wafer, and then bonding and thermal reflow with a glass plate;

[0035] The ambient temperature-measuring resistor 203 is distributed at the peripheral position above the back cavity 102, that is, at the edge of the glass-internal silicon substrate 100.

[0036] The temperature-measuring resistor 202 is symmetrically located on both sides of the heating resistor 201, including an upstream temperature-measuring resistor and a downstream temperature-measuring resistor, and is symmetrically distributed at the same distance from the heating resistor 201.

[0037] The PAD port 301 is located on the back and is connected to both ends of the heating resistor 201, the temperature-measuring resistor 202, and the ambient temperature-measuring resistor 203, and is used to connect to the peripheral circuit.

[0038] The heating resistor 201, the temperature-measuring resistor 202, and the ambient temperature-measuring resistor 203 are processed into a meandering needle pattern.

[0039] The silicon through-column 101 serves as a conductive channel to lead the PAD to the back of the glass-internal silicon substrate 100, reducing the influence of the PAD port on the air flow and making the measured flow rate of the sensor more accurate.

[0040] A silicon nitride protective layer 302 for protection is also provided on the glass-internal silicon substrate 100, the heating resistor, the temperature-measuring resistor, and the ambient temperature-measuring resistor, which is used to protect the sensor and improve the reliability of the sensor.

[0041] The material of the PAD port 301 is one or several alloy materials among nickel, titanium, tungsten, chromium, platinum, aluminum or gold; the heating resistor 201, the temperature measuring resistor 202, and the ambient temperature measuring resistor 203 all use the material platinum.

[0042] The chromium adhesion layer 300 is located between the thermal resistor 201, the temperature measuring resistor 202, the ambient temperature measuring resistor 203 and the glass inner silicon substrate 100.

[0043] Such as Figure 3 shown, four rows of temperature measuring resistors are placed at different distances from the heating resistor, and a Wheatstone full bridge circuit can be adopted. Compared with Figure 5 the structure of, the sensitivity of the thermal flow sensor is increased by approximately twice, and at the same time, the range of the thermal flow sensor is increased; as Figure 4 shown, four rows of temperature measuring resistors are placed at the same distance from the heating resistor, and a Wheatstone full bridge circuit can be adopted. Compared with Figure 5 the structure of, the sensitivity of the thermal flow sensor is increased to twice; as Figure 5 shown, it is a common structure, two temperature measuring resistors are placed on both sides of the heating resistor, and a Wheatstone half bridge circuit is adopted; as Figure 6 shown, this structure is designed based on a neural network, aiming at maximizing the sensitivity output of the flow sensor, and the key parameters are optimized through the neural network algorithm, including the distance between the temperature measuring resistor and the heating resistor and the resistance arrangement form of the heating resistor. The optimized structure significantly improves the sensitivity output of the sensor;

[0044] For the first to third invention embodiments, in terms of structure, only the thermal resistor 201 and the temperature measuring resistor 202 are arranged differently. In terms of process implementation, only the mask layout is inconsistent, and other process steps are the same. The fourth one is to optimize the distance between the temperature measuring resistor and the heating resistor and the arrangement form of the heating resistor through the neural network algorithm to improve the sensitivity output of the flow sensor.

[0045] The present invention also provides a preparation method for a MEMS thermal flow sensor based on a glass thin film structure. As Figure 2 shown, this method includes the following steps:

[0046] S1. Prepare a wafer of low-resistance silicon wafer: Specifically, clean the N-type silicon wafer with a 100 crystal orientation;

[0047] S2. Spin-coat photoresist on the front side, align the silicon wafer and then develop, expose and etch to form a central etching area pit;

[0048] S3. Spin-coat photoresist on the front side, align the silicon wafer and then develop, expose and etch, leaving the silicon through-column 101 and the central silicon column, which will be etched away in the subsequent process to form a thin film structure;

[0049] S4. After anodic bonding of the silicon wafer and the glass wafer, thermally reflux to fill the silicon wafer, perform thermal annealing to eliminate thermal stress, and then thin and polish the composite substrate of the glass and the silicon.

[0050] S5. Spin coat photoresist on the front side, align with the silicon wafer and then develop and expose the patterns of the heating resistor 201, the temperature measuring resistor 202, and the ambient temperature measuring resistor 203. Spray chromium metal film and platinum metal film on the front side.

[0051] S6. Use the lift-off process to fabricate the required chromium adhesion layer 300, heating resistor 201, temperature measuring resistor 202, and ambient temperature measuring resistor 203.

[0052] S7. Deposit a silicon nitride protective layer 302 on the front side by plasma enhanced chemical vapor deposition process.

[0053] S8. Spin coat photoresist on the back side, align with the silicon wafer and then develop and expose the pattern of the PAD port 301. Spray a metal film on the front side.

[0054] S9. Use the lift-off process to fabricate the required PAD port 301.

[0055] S10. Spin coat photoresist on the back side, align with the silicon wafer and then develop and etch away the central silicon pillar to form a back cavity 102, leaving the glass film structure.

[0056] It can be understood that the present invention is described through some embodiments. Those skilled in the art know that without departing from the spirit and scope of the present invention, various changes or equivalent substitutions can be made to these features and embodiments. Additionally, under the teaching of the present invention, these features and embodiments can be modified to adapt to specific situations and materials without departing from the spirit and scope of the present invention. Therefore, the present invention is not limited by the specific embodiments disclosed herein, and all embodiments falling within the scope of the claims of this application belong to the scope protected by the present invention.

Claims

1. A MEMS thermal flow sensor based on a glass film structure, characterized in that: The invention comprises a silicon substrate in glass (100), a silicon through column (101), a back cavity (102), a thermistor (200), a chrome adhesion layer (300), a PAD port (301), and a silicon nitride protective layer (302), wherein the silicon through column (101) is embedded at the edge of the silicon substrate in glass (100), the silicon through column (101) leads the PAD port (301) to the back of the silicon substrate in glass (100), the thermistor (200) comprises a heating resistor (201), a temperature measuring resistor (202), and an environmental temperature measuring resistor (203); the silicon nitride protective layer (302) is located on the surface of the silicon substrate in glass (100) and is used to protect the thermistor (200); the back cavity (102) is located on the glass The invention relates to a glass inner silicon substrate (100) and a thermistor (200). The glass inner silicon substrate (100) is provided at the center of the back side of the thermistor (200), thereby forming a suspended film; the heating resistor (201), the temperature measuring resistor (202) and the environmental temperature measuring resistor (203) are located directly above the back side cavity (102); the heating resistor (201) is located at the center of the back side cavity (102), and the temperature measuring resistor (202) is distributed on both sides of the heating resistor (201); the environmental temperature measuring resistor (203) is distributed at the peripheral position above the back side cavity (102); a chromium adhesion layer (300) is provided between the glass inner silicon substrate (100) and the thermistor (200); and the PAD port (301) is located at the back side of the glass inner silicon substrate (100) and connected to both ends of the thermistor (200).

2. The MEMS thermal flow sensor based on a glass film structure according to claim 1 is characterized in that: The material of the suspended film is glass.

3. The MEMS thermal flow sensor based on a glass film structure according to claim 1, characterized in that: The temperature measuring resistor (202) comprises an upstream temperature measuring resistor and a downstream temperature measuring resistor, which are symmetrically distributed at positions with the same distance from the heating resistor (201).

4. The MEMS thermal flow sensor based on a glass film structure according to claim 1, characterized in that: The heating resistor (201), the temperature measuring resistor (202), and the environmental temperature measuring resistor (203) are processed into a paper clip pattern.

5. The MEMS thermal flow sensor based on a glass film structure according to claim 1, characterized in that: The material of the PAD port (301) is one or more alloy materials selected from nickel, titanium, tungsten, chromium, platinum, aluminum or gold; the heating resistor (201), the temperature measuring resistor (202) and the environmental temperature measuring resistor (203) are all made of platinum.

6. A method for preparing a MEMS thermal flow sensor based on a glass thin film structure, using a MEMS thermal flow sensor based on a glass thin film structure as claimed in any one of claims 1 to 5, characterized in that: The preparation method comprises the following steps: S1. Prepare low-resistance silicon wafers: clean N-type silicon wafers with 100 crystal orientation; S2, applying photoresist on the front side by rotation, aligning with the silicon wafer, developing and exposing, and etching out a pit in the central etching area; S3, applying photoresist on the front surface by rotation, aligning with the silicon wafer, developing, exposing and etching, leaving the silicon through column (101) and the central silicon column; S4, after high-temperature bonding of the silicon wafer and the glass wafer, thermal reflow filling of the silicon wafer, thermal annealing to eliminate thermal stress, and then thinning and polishing the composite substrate of glass and silicon; S5, applying photoresist on the front side by rotation, aligning with the silicon wafer and developing to expose the patterns of the heating resistor (201), the temperature measuring resistor (202), and the environment temperature measuring resistor (203), and sputtering a chromium metal film and a platinum metal film on the front side; S6. Using a stripping process to produce the required chromium adhesion layer (300), heating resistor (201), temperature measuring resistor (202), and environmental temperature measuring resistor (203); S7, depositing a silicon nitride protective layer (302) on the front surface by a plasma enhanced chemical vapor deposition process; S8, smearing photoresist on the back side by rotation, developing and exposing the PAD port (301) pattern after aligning with the silicon wafer, and sputtering a metal film on the front side; S9, using a stripping process to process the required PAD port (301); S10, smearing photoresist on the back side in a rotation manner, aligning the photoresist with the silicon wafer, developing and exposing the photoresist to etch away the central silicon pillar, thereby forming a back side cavity (102), leaving a glass film structure.

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