CN113175963B - MEMS flow sensor and preparation method thereof - Google Patents

Abstract

The invention relates to a MEMS flow sensor and a preparation method. The silicon substrate of the sensor is provided with a closed cavity, a silicon oxide insulating layer is laid on the silicon substrate, and a thermopile and a first heating resistor are arranged on the silicon oxide insulating layer. and the second heating resistance; the first heating resistance and the second heating resistance are respectively located on both sides of the thermopile, and are arranged symmetrically with the center line of the thermopile as the symmetry axis, and the two ends of the first heating resistance are respectively provided with a first pressure welding The two ends of the second heating resistor are respectively provided with a second pressure-welding block, and the two ends of the thermopile are respectively provided with a third pressure-welding block; the top of the thermopile, the first heating resistance and the second heating resistance are covered with silicon oxide insulation layer, the silicon oxide insulating layer is covered with a silicon nitride protective layer; the thermopile, the first heating resistor and the second heating resistor are provided with a thermal insulation groove on the periphery of the overall structure; the bottom of the thermal insulation groove is sequentially laid with silicon oxide protective layer and silicon nitride protective layer. The present invention improves the measurement accuracy.

Description

A kind of MEMS flow sensor and preparation method thereof

technical field

The invention relates to the technical field of flow sensor preparation, in particular to a MEMS flow sensor and a preparation method.

Background technique

MEMS is an industrial technology that combines mechanical engineering and microelectronics technology, and its operating range is generally at the micro-nano level. MEMS technology is usually based on semiconductor materials, using processes such as surface micromachining, deep etching, and bulk micromachining, as well as related processes in the field of integrated circuits to prepare devices.

Flow measurement is of great significance in industrial production and process control, such as consumer electronics, automotive and medical fields. There are many types of flow sensors commonly used at present, and with the help of MEMS technology, they have a wider development and application space. Common types of flow sensors on the market include: (1) Early flow sensors based on simple physical principles, such as volumetric, turbine, and heat loss flow sensors; (2) Based on emerging science and technology, such as electromagnetic, thermoelectric, and pressure sensors Differential iso-flow sensor. However, these flow sensors have their own advantages in different applications, and their shortcomings are also obvious. For example, volumetric, eddy current, and electromagnetic flow sensors usually exhibit large power consumption and volume; differential pressure flow sensors are more complicated to install, and heat loss flow sensors are greatly affected by external ambient temperature and have low accuracy; Type flow sensor has been widely studied because of its simple structure, no mechanical structure and easy integration. However, in order to suppress the influence of temperature drift, it is usually necessary to add an additional temperature sensor near the flow sensor to measure the temperature of the base.

SUMMARY OF THE INVENTION

The purpose of the present invention is to provide a MEMS flow sensor and its preparation method, which improves the measurement accuracy.

To achieve the above object, the present invention provides the following scheme:

A MEMS flow sensor, comprising: a silicon substrate 6, a thermopile 1, a first heating resistor 21, a second heating resistor 22, a first welding block 31, a second welding block 32 and a third welding block 33, Silicon oxide protective layer 7, silicon nitride protective layer 8 and silicon oxide insulating layer 9;

The inside of the silicon substrate 6 is provided with a closed cavity 5, the silicon oxide insulating layer 9 is laid on the silicon substrate 6, and the thermopile 1, the first A heating resistor 21 and the second heating resistor 22; the first heating resistor 21 and the second heating resistor 22 are respectively located on both sides of the thermopile 1, and the center line of the thermopile 1 is The two ends of the first heating resistor 21 are respectively provided with the first welding block 31, and the two ends of the second heating resistor 22 are respectively provided with the second welding block 32, so The two ends of the thermopile 1 are respectively provided with the third welding block 33; the top of the thermopile 1, the first heating resistor 21 and the second heating resistor 22 is covered with the silicon oxide insulating layer 9 , the silicon oxide insulating layer 9 is covered with the silicon nitride protective layer 8; the periphery of the overall structure composed of the thermopile 1, the first heating resistor 21 and the second heating resistor 22 is provided with heat insulation Groove 4; the bottom of the heat insulating groove 4 is laid with the silicon oxide protective layer 7 and the silicon nitride protective layer 8 in sequence; one side of the first pad 31 is connected to the silicon oxide insulating layer 9, the other side is exposed in the air; one side of the second pressure welding block 32 is bonded to the silicon oxide insulating layer 9, and the other side is exposed in the air; the third pressure welding block 33- One side is attached to the silicon oxide insulating layer 9, and the other side is exposed in the air.

Optionally, the thermopile 1 includes a plurality of thermocouples, and each of the thermocouples is connected in series. The thermocouple includes a semiconductor arm 12 and a metal arm 11, and one end of the semiconductor arm 12 is connected to the metal arm. One end of 11 is connected by metal wire 13.

Optionally, the semiconductor arm 12 and the metal arm 11 are horizontally arranged on the same plane.

Optionally, the metal arm 11 is disposed above the semiconductor arm 12, and the metal arm 11 and the semiconductor arm 12 are separated by an insulating medium layer.

Optionally, the lower surface of the heat insulation groove 4 is a rectangular frame.

The present invention also discloses a method for preparing a MEMS flow sensor, the preparation method is used to prepare the MEMS flow sensor, comprising:

Etching grooves on the silicon substrate;

growing a layer of single crystal silicon on the groove, so that the groove forms a closed cavity;

A layer of silicon oxide is grown on the silicon substrate forming a closed cavity inside to form a silicon oxide insulating layer;

By photolithography, ion implantation into polysilicon and metal sputtering, a first heating resistor, a second heating resistor and a thermopile are formed on the silicon oxide insulating layer, and the two ends of the first heating resistor respectively form a first pad, so The two ends of the second heating resistor respectively form a second welding block, and the two ends of the thermopile respectively form a third welding block; the first heating resistor and the second heating resistor are respectively located in the thermopile The two sides of the thermopile are arranged symmetrically with the center line of the thermopile as the axis of symmetry;

A thermal insulation groove is formed on the periphery of the overall structure composed of the thermopile, the first heating resistor and the second heating resistor by using deep etching technology, and the bottom of the thermal insulation groove extends into the silicon substrate ;

Depositing and photoetching silicon oxide above the heat insulation groove, the thermopile, the first heating resistor, and the second heating resistor to form a silicon oxide protective layer, and making the first pad, The upper surfaces of the second pad and the third pad are exposed in the air;

Depositing and photoetching silicon nitride on the silicon oxide protective layer to form a silicon nitride protective layer;

Optionally, the etching a groove on the silicon substrate specifically includes:

Etching an initial groove on the silicon substrate by using an anisotropic reactive ion etching method;

Continue etching at the bottom of the initial groove by using an isotropic etching method to form the groove.

Optionally, the thermopile includes a plurality of thermocouples, each of the thermocouples is connected in series, the thermocouple includes a semiconductor arm and a metal arm, and one end of the semiconductor arm is connected to one end of the metal arm through a metal wire connection.

Optionally, the first heating resistor, the second heating resistor and the thermopile are formed on the silicon oxide insulating layer through photolithography, ion implantation into polysilicon and metal sputtering, and the two ends of the first heating resistor respectively form a second heating resistor. A pressure welding block, the two ends of the second heating resistance respectively form a second pressure welding block, and the two ends of the thermopile respectively form a third pressure welding block; the first heating resistance and the second heating resistance They are respectively located on both sides of the thermopile, and are arranged symmetrically with the center line of the thermopile as a symmetrical axis, specifically including:

Perform photolithography and ion implantation on the silicon oxide insulating layer to form the semiconductor arm of the thermopile, the ohmic contact area between the metal wire of the thermopile and the semiconductor arm, the first heating resistor and the first heating resistor. Two heating resistors; the semiconductor arm of the first heating resistor, the second heating resistor and the thermopile is the first polysilicon, the ohmic contact area is the second polysilicon, and the second polysilicon The conductive metal concentration doped with silicon is greater than the conductive metal concentration doped with the first polysilicon;

By sputtering metal aluminum, the metal arm, the metal wire, the first pressure welding block, the second pressure welding block and the third pressure welding block of the thermopile are formed.

Optionally, growing a layer of silicon oxide on the silicon substrate forming a closed cavity inside to form a silicon oxide insulating layer specifically includes:

Polishing the upper surface of the silicon substrate forming a closed cavity inside;

A layer of silicon oxide is grown on the surface of the polished silicon substrate to form a silicon oxide insulating layer.

According to the specific embodiments provided by the invention, the invention discloses the following technical effects:

In the present invention, the first heating resistor and the second heating resistor are arranged symmetrically on both sides of the thermopile in the MEMS flow sensor, which can suppress the influence of temperature drift and improve the measurement accuracy and sensitivity. An airtight cavity is arranged under the heating resistor, and heat insulation grooves are arranged around the surface of the silicon substrate to reduce heat loss and further improve measurement accuracy.

Description of drawings

In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the accompanying drawings required in the embodiments. Obviously, the accompanying drawings in the following description are only some of the present invention. Embodiments, for those of ordinary skill in the art, other drawings can also be obtained according to these drawings without paying creative labor.

Fig. 1 is the A-A sectional view of a kind of MEMS flow sensor of the present invention;

Fig. 2 is a side view of a MEMS flow sensor of the present invention;

Fig. 3 is a kind of flow chart of the preparation method of MEMS flow sensor of the present invention;

Symbol Description:

1. Thermopile, 11, metal arm, 12, semiconductor arm, 13, metal wire, 21, first heating resistor, 22, second heating resistor, 31, first welding block, 32, second pressing welding block, 33. The third welding block, 4. The heat insulation groove, 5. The airtight cavity, 6. The silicon substrate, 7. The silicon oxide protective layer, 8. The silicon nitride protective layer, 9. The silicon oxide insulating layer.

Detailed ways

The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, but not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

The purpose of the present invention is to provide a MEMS flow sensor and its preparation method, which improves the measurement accuracy.

In order to make the above objects, features and advantages of the present invention more clearly understood, the present invention will be described in further detail below with reference to the accompanying drawings and specific embodiments.

Fig. 1 is the A-A sectional view of a kind of MEMS flow sensor of the present invention, and Fig. 2 is the side view of a kind of MEMS flow sensor of the present invention, as shown in Fig. 1-2, a kind of MEMS flow sensor comprises: silicon substrate 6, thermopile 1. The first heating resistor 21, the second heating resistor 22, the first soldering block 31, the second soldering block 32 and the third soldering block 33, the silicon oxide protective layer 7, the silicon nitride protective layer 8 and the silicon oxide insulating layer9.

The inside of the silicon substrate 6 is provided with a closed cavity 5, the silicon oxide insulating layer 9 is laid on the silicon substrate 6, and the thermopile 1, the first A heating resistor 21 and the second heating resistor 22; the thermopile 1 is arranged in the middle of the silicon oxide insulating layer 9; the first heating resistor 21 and the second heating resistor 22 are respectively located in the thermopile 1, and set symmetrically with the central line of the thermopile 1 as the symmetrical axis, the two ends of the first heating resistor 21 are respectively provided with the first pressure welding block 31, and the second heating resistor 22 The two ends of the thermopile 1 are respectively provided with the second welding block 32, and the two ends of the thermopile 1 are respectively provided with the third welding block 33; the thermopile 1, the first heating resistor 21 and the The silicon oxide insulating layer 9 is covered above the second heating resistor 22, and the silicon nitride protective layer 8 is covered above the silicon oxide insulating layer 9; the thermopile 1, the first heating resistor 21 and the The outer periphery of the overall structure formed by the second heating resistor 22 is provided with a heat insulating groove 4; the bottom of the heat insulating groove 4 is laid with the silicon oxide protective layer 7 and the silicon nitride protective layer 8 in sequence; One side of the first pressure welding block 31 is bonded to the silicon oxide insulating layer 9, and the other side is exposed in the air; one side of the second pressure welding block 32 is bonded to the silicon oxide insulating layer 9, and the other side is bonded to the silicon oxide insulating layer 9. One side is exposed in the air; one side of the third bonding pad 33 is attached to the silicon oxide insulating layer 9 , and the other side is exposed in the air.

The thermopile 1 includes a plurality of thermocouples, each of the thermocouples is connected in series, and the thermocouple includes a semiconductor arm 12 and a metal arm 11, and one end of the semiconductor arm 12 passes through an end of the metal arm 11. Metal wire 13 is connected.

As a specific embodiment, the semiconductor arm 12 and the metal arm 11 are arranged horizontally on the same plane, or the metal arm 11 is arranged above the semiconductor arm 12, and between the metal arm 11 and the semiconductor arm 12 separated by an insulating layer. In Fig. 1, the situation where the semiconductor arm 12 and the metal arm 11 are horizontally arranged on the same plane, when the liquid or gas flows from left to right, the left and right ends are respectively located at the upstream and downstream of the flowing liquid or gas, when the liquid Or when the gas flows from right to left, the left and right ends are respectively located at the downstream and upstream of the flowing liquid or gas.

Both the first heating resistor 21 and the second heating resistor 22 are strip-shaped and placed parallel to each other, and the first heating resistor 21 and the second heating resistor 22 are identical.

The airtight cavity 5 is located in the silicon substrate 6 below the thermopile 1, the airtight cavity 5 extends beyond the first heating resistor 21 and the second heating resistor 22 in the lateral direction, and the airtight cavity 5 Capable of covering the projections of the thermopile 1, the first heating resistor 21 and the second heating resistor 22 on the vertical and horizontal planes, extending to the upper and lower ends of the first heating resistor 21 and the second heating resistor 22 in the longitudinal direction, without reaching the heating resistor (the first heating resistor 21). One heating resistor 21 and the second heating resistor 22) at the pressure welding blocks (the first pressure welding block 31, the second pressure welding block 32 and the third pressure welding block 33) at the upper and lower ends.

Described silicon substrate 6 is P-type monocrystalline silicon, and the metal arm 11 of thermopile 1 can adopt metals such as Al or Ti, and semiconductor arm 12 can adopt semiconductors such as N+ polysilicon or P+ polysilicon; In addition, the two arms of thermopile 1 N+polysilicon and P+polysilicon two kinds of semiconductor materials can also be used; in a specific embodiment, the metal arm 11 and the semiconductor arm 12 are selected to form the thermopile 1, and the material of the metal arm 11 is Al, and the material of the semiconductor arm 12 is N+polysilicon.

As a specific embodiment, the doping type of the heating resistor and the semiconductor arm 12 is N-type lightly doped, and the designed doping concentration is about 10 ¹² -10 ¹⁵ cm ^-3 .

As a specific embodiment, the doping type of the ohmic contact region between the semiconductor arm 12 and the metal wire 13 is N-type heavy doping, and the design doping concentration is about 10 ¹⁷ ~ 10 ¹⁹ cm ^-3 , which can make a good formation between the two. ohmic contact.

A MEMS flow sensor of the present invention is provided with a thermopile in the middle of the silicon oxide insulating layer, and two heating resistors are symmetrically placed at the left and right ends of the thermopile, and the heating resistors are all energized to generate heat, and when the liquid or gas flows, the heat will be transferred from the The temperature difference between the left and right ends of the thermopile is caused by the upstream to the downstream, and the thermopile converts the temperature difference into an output thermoelectric potential. By measuring the positive and negative values of the thermoelectric potential, the direction and flow rate of the liquid or gas can be judged, and then can be obtained flow within a period of time; two heating resistors placed symmetrically are used to eliminate the influence of the external temperature on the sensor, so that in the present invention, no additional design of a temperature sensor is required to measure the temperature of the base, which improves the measurement sensitivity and accuracy and reduces the manufacturing cost; The heat insulation groove and the airtight cavity are used to reduce heat loss and further improve the measurement accuracy, and the manufacture of the flow sensor is compatible with the silicon-based circuit process; therefore, the MEMS flow sensor has miniaturization, low power consumption, high precision and low cost Features.

When the MEMS flow sensor is working, the same voltage is applied to the welding blocks at both ends of the two heating resistors, so that the heating resistors generate heat through the current, and the two heating resistors at both ends of the thermopile can suppress the influence of temperature drift to a certain extent. Therefore, there is no need to design an additional temperature sensor to measure the temperature of the base in this structure; if the liquid or gas is in a static state, the temperature at the left and right ends of the thermopile is the same; if the liquid or gas flows to the right, the heat will be absorbed by the liquid or gas From the left end of the thermopile to the right, so that the temperature of the right end of the thermopile is higher than the temperature of the left end; on the contrary, if the liquid or gas flows to the left, the heat will be carried by the liquid or gas from the right end of the thermopile to the left end, making the temperature of the thermopile The left end temperature is higher than the right end temperature. And the temperature difference between the left and right ends is positively correlated with the flow velocity of the liquid or gas. It can also be seen from the Seebeck effect that the output thermoelectric potential of the thermopile is proportional to the temperature difference between the left and right ends of the thermopile, so the output thermoelectric potential of the thermopile is positively correlated with the flow rate of the liquid or gas. Therefore, by measuring the thermoelectric potential between the two pressure welding blocks on the upper and lower sides of the thermopile, the direction and flow rate of the liquid or gas flow can be judged according to the positive and negative values of the thermoelectric potential and the flow rate, and then it can be obtained within a period of time. The volume of a liquid or gas that passes through. The thermal insulation grooves around the surface of the silicon substrate and the airtight cavity in the silicon substrate all play the role of increasing thermal resistance, reducing heat loss and improving measurement accuracy.

The lower surface of the heat insulation groove 4 is a rectangular frame.

The invention relates to a MEMS flow sensor, which is used for measuring the flow of liquid or gas. The flow sensor adopts a completely passive structure. The whole structure is located on a silicon substrate. A silicon oxide insulating layer is arranged on the surface of the silicon substrate. A thermopile composed of a semiconductor arm, a metal arm and a metal wire is placed on the insulating layer. Both ends of the stack are provided with a heating device composed of heating resistors, a closed cavity is provided under the thermopile in the middle of the silicon substrate, and a heat insulation groove is provided around the surface of the silicon substrate. Both are covered with a silicon oxide protective layer and a silicon nitride protective layer. When the sensor is working, the two heating resistors are energized to generate heat, and the temperature distribution is symmetrical about the thermopile, so that the temperature at the left and right ends of the thermopile is the same (that is, the temperature difference is zero), and the output thermoelectric potential of the thermopile is zero at this time; When liquid or gas flows, the original symmetrical temperature distribution will be disturbed, and the temperature upstream of the flow direction will be lower than the temperature downstream, causing a temperature difference between the left and right ends of the thermopile, and the output thermoelectric potential of the thermopile is not zero at this time , by measuring the positive and negative values and magnitude of the thermoelectric potential, the direction and flow rate of the liquid or gas flow can be obtained, and then the volume of the liquid or gas passing through it can be obtained within a period of time.

Fig. 3 is a flow chart of a MEMS flow sensor preparation method of the present invention, as shown in Fig. 3, a kind of MEMS flow sensor preparation method comprises:

Step 100: Etching grooves on the silicon substrate.

Wherein, step 100 specifically includes:

Etching an initial groove on the silicon substrate by using an anisotropic reactive ion etching method;

Continue etching at the bottom of the initial groove by using an isotropic etching method to form the groove.

Optionally, the thermopile includes a plurality of thermocouples, each of the thermocouples is connected in series, the thermocouple includes a semiconductor arm and a metal arm, and one end of the semiconductor arm is connected to one end of the metal arm through a metal wire connection.

Step 200: growing a layer of single crystal silicon on the groove, so that the groove forms a closed cavity.

Step 300: growing a layer of silicon oxide on the silicon substrate forming a closed cavity inside to form a silicon oxide insulating layer.

Wherein, step 300 specifically includes:

Polishing the upper surface of the silicon substrate forming a closed cavity inside;

A layer of silicon oxide is grown on the surface of the polished silicon substrate to form a silicon oxide insulating layer.

Step 400: Form a first heating resistor, a second heating resistor, and a thermopile on the silicon oxide insulating layer by photolithography, ion implantation into polysilicon, and metal sputtering, and the two ends of the first heating resistor respectively form a first bonding The two ends of the second heating resistor respectively form a second welding block, and the two ends of the thermopile respectively form a third welding block; the first heating resistor and the second heating resistor are respectively located at the The two sides of the thermopile are arranged symmetrically with the center line of the thermopile as the axis of symmetry.

Wherein, step 400 specifically includes:

Perform photolithography and ion implantation on the silicon oxide insulating layer to form the semiconductor arm of the thermopile, the ohmic contact area between the metal wire of the thermopile and the semiconductor arm, the first heating resistor and the first heating resistor. Two heating resistors; the semiconductor arm of the first heating resistor, the second heating resistor and the thermopile is the first polysilicon, the ohmic contact area is the second polysilicon, and the second polysilicon The conductive metal concentration doped with silicon is greater than the conductive metal concentration doped with the first polysilicon;

By sputtering metal aluminum, the metal arm, the metal wire, the first pressure welding block, the second pressure welding block and the third pressure welding block of the thermopile are formed.

Step 500: Form a thermal insulation groove on the periphery of the overall structure composed of the thermopile, the first heating resistor and the second heating resistor by using deep etching technology, and the bottom of the thermal insulation groove extends into the silicon substrate.

Step 600: Depositing and photoetching silicon oxide on the heat insulation tank, the thermopile, the first heating resistor, and the second heating resistor to form a silicon oxide protective layer, and make the first voltage The upper surfaces of the welding block, the second pressure welding block and the third pressure welding block are exposed in the air.

Step 700: Depositing and photoetching silicon nitride on the silicon oxide protective layer to form a silicon nitride protective layer.

The manufacturing process of the MEMS flow sensor of the present invention is compatible with the silicon-based circuit process. In the preparation process, the single crystal silicon sealing process is used for the airtight cavity, the body etching process is used for the heat insulation groove, and the structures such as thermopile and heating resistance are adopted. Using surface semiconductor technology, it has the characteristics of miniaturization, low power consumption, high precision and low cost.

A method for preparing a MEMS flow sensor of the present invention is described below with specific examples. The preparation process of the shown preparation method is compatible with the silicon-based circuit process, including the following steps:

a. P-type single crystal silicon is selected as the silicon substrate; shallow grooves (initial grooves) are etched on the silicon substrate through an anisotropic reactive ion etching process.

b. On the silicon substrate obtained in step a, protect the side walls of the shallow groove, and then perform isotropic etching on the bottom of the shallow groove of the silicon substrate, thereby forming a cavity (groove) in the silicon substrate.

c. Epitaxially growing a layer of single crystal silicon on the cavity of the silicon substrate obtained in step b to form a closed cavity.

d. On the silicon substrate obtained in step c, use a chemical mechanical polishing process to smooth the upper surface of the silicon substrate, and grow a layer of silicon oxide on the silicon substrate to form a silicon oxide insulating layer.

e. Deposit a layer of polysilicon on the silicon substrate obtained in step d, and perform photolithography and ion implantation twice to form lightly doped and heavily doped polysilicon, wherein lightly doped polysilicon is used to form heating resistors and thermoelectrics The semiconductor arm of the stack, and the heavily doped polysilicon is used to form the ohmic contact area between the metal wire and the semiconductor arm in the thermopile.

f. On the silicon substrate obtained in step e, sputter a layer of metal aluminum and perform photolithography to form metal arms, metal wires and bonding pads of the thermopile.

g. On the silicon substrate obtained in step f, thermal insulation grooves are formed on the surrounding edges of the silicon substrate by deep etching technology.

h. Depositing and photoetching silicon oxide on the silicon substrate obtained in step g, and forming a silicon oxide protective layer on the depressurized solder bump.

i. On the silicon substrate obtained in step h, silicon nitride is deposited and photoetched, and a silicon nitride protective layer is formed at the depressurized solder bump.

The technical effect of a kind of MEMS flow sensor of the present invention and preparation method is:

(1) The MEMS flow sensor is composed of a completely passive structure. When working, the two heating resistors at the left and right ends of the thermopile are energized and heated to generate heat. The flow of liquid or gas causes a temperature difference between the left and right ends of the thermopile. The temperature difference is converted into a DC thermoelectric potential. By measuring the output thermoelectric potential of the thermopile, the direction and flow rate of the liquid or gas flow can be obtained, and then the volume of the liquid or gas passing through it can be obtained within a period of time.

(2) In the MEMS flow sensor, by designing symmetrical heating resistors at the left and right ends of the thermopile, the influence of temperature drift can be suppressed, so there is no need to design an additional temperature sensor for measuring the base temperature in this structure, which improves the Measurement accuracy and sensitivity, while reducing the chip area and manufacturing cost of the sensor.

(3) In the MEMS flow sensor, a closed cavity is set under the thermopile and the heating resistor, and a heat insulation groove is set around the edge of the surface of the silicon substrate to reduce heat loss and further improve measurement accuracy .

(4) The manufacturing process of the MEMS flow sensor is compatible with the silicon-based circuit process, and has low cost.

The various embodiments in this specification are described in a progressive manner, and each embodiment focuses on the differences from other embodiments, and the same and similar parts between the various embodiments can be referred to each other. In this paper, specific examples have been used to illustrate the principle and implementation of the present invention. The description of the above embodiments is only used to help understand the method of the present invention and its core idea; meanwhile, for those of ordinary skill in the art, according to the present invention Thoughts, there will be changes in specific implementation methods and application ranges. In conclusion, the contents of this specification should not be construed as limiting the present invention.

Claims (10)

1. A MEMS flow sensor, comprising: the device comprises a silicon substrate (6), a thermopile (1), a first heating resistor (21), a second heating resistor (22), a first pressure welding block (31), a second pressure welding block (32), a third pressure welding block (33), a silicon oxide protective layer (7), a silicon nitride protective layer (8) and a silicon oxide insulating layer (9);

a closed cavity (5) is formed in the silicon substrate (6), the silicon oxide insulating layer (9) is laid on the silicon substrate (6), and the thermopile (1), the first heating resistor (21) and the second heating resistor (22) are arranged on the silicon oxide insulating layer (9); the first heating resistor (21) and the second heating resistor (22) are respectively located on two sides of the thermopile (1) and symmetrically arranged by taking the center line of the thermopile (1) as a symmetry axis, the first pressure welding blocks (31) are respectively arranged at two ends of the first heating resistor (21), the second pressure welding blocks (32) are respectively arranged at two ends of the second heating resistor (22), and the third pressure welding blocks (33) are respectively arranged at two ends of the thermopile (1); the silicon oxide insulating layer (9) covers the thermopile (1), the first heating resistor (21) and the second heating resistor (22), and the silicon nitride protective layer (8) covers the silicon oxide insulating layer (9); a heat insulation groove (4) is arranged on the periphery of the whole structure formed by the thermopile (1), the first heating resistor (21) and the second heating resistor (22); the silicon oxide protective layer (7) and the silicon nitride protective layer (8) are sequentially laid on the bottom of the heat insulation groove (4); one side of the first pressure welding block (31) is attached to the silicon oxide insulating layer (9), and the other side of the first pressure welding block is exposed in the air; one side of the second pressure welding block (32) is attached to the silicon oxide insulating layer (9), and the other side of the second pressure welding block is exposed in the air; one side of the third pressure welding block (33) is attached to the silicon oxide insulating layer (9), and the other side of the third pressure welding block is exposed in the air.

2. MEMS flow sensor according to claim 1, characterised in that the thermopile (1) comprises a plurality of thermocouples, each of which is connected in series with each other, the thermocouples comprising one semiconductor arm (12) and one metal arm (11), one end of the semiconductor arm (12) being connected to one end of the metal arm (11) by means of a metal wire (13).

3. MEMS flow sensor according to claim 2, characterised in that the semiconductor arm (12) is arranged horizontally in the same plane as the metal arm (11).

4. MEMS flow sensor according to claim 2, wherein the metal arm (11) is arranged above the semiconductor arm (12), the metal arm (11) being separated from the semiconductor arm (12) by a dielectric layer.

5. MEMS flow sensor according to claim 1, wherein the lower surface of the thermal shield groove (4) is a rectangular frame.

6. A method for preparing a MEMS flow sensor, the method for preparing the MEMS flow sensor of any one of claims 1-5, comprising:

etching a groove on a silicon substrate;

growing a layer of monocrystalline silicon on the groove to enable the groove to form a closed cavity;

growing a layer of silicon oxide on a silicon substrate with a closed cavity formed inside to form a silicon oxide insulating layer;

forming a first heating resistor, a second heating resistor and a thermopile on a silicon oxide insulating layer by photoetching, ion implantation of polycrystalline silicon and metal sputtering, wherein first pressure welding blocks are respectively formed at two ends of the first heating resistor, second pressure welding blocks are respectively formed at two ends of the second heating resistor, and third pressure welding blocks are respectively formed at two ends of the thermopile; the first heating resistor and the second heating resistor are respectively positioned at two sides of the thermopile and are symmetrically arranged by taking the center line of the thermopile as a symmetry axis;

forming a heat insulation groove on the periphery of an integral structure formed by the thermopile, the first heating resistor and the second heating resistor by adopting a deep etching technology, wherein the bottom of the heat insulation groove extends into the silicon substrate;

depositing and photoetching silicon oxide above the heat insulation groove, the thermopile, the first heating resistor and the second heating resistor to form a silicon oxide protective layer, and exposing the upper surfaces of the first pressure welding block, the second pressure welding block and the third pressure welding block in the air;

and depositing and photoetching silicon nitride above the silicon oxide protective layer to form a silicon nitride protective layer.

7. The method for manufacturing an MEMS flow sensor according to claim 6, wherein the etching a groove on the silicon substrate specifically includes:

etching an initial groove on the silicon substrate by adopting an anisotropic reactive ion etching method;

and continuously etching the bottom of the initial groove by adopting an isotropic etching method to form the groove.

8. The method of making a MEMS flow sensor as recited in claim 6, wherein the thermopile includes a plurality of thermocouples, each of the thermocouples being connected in series, the thermocouples including a semiconductor arm and a metal arm, one end of the semiconductor arm being connected to one end of the metal arm by a metal wire.

9. The method for manufacturing the MEMS flow sensor according to claim 8, wherein a first heating resistor, a second heating resistor and a thermopile are formed on the silicon oxide insulating layer by photolithography, ion implantation of polysilicon and metal sputtering, wherein a first bonding pad is formed at each of two ends of the first heating resistor, a second bonding pad is formed at each of two ends of the second heating resistor, and a third bonding pad is formed at each of two ends of the thermopile; first heating resistor with second heating resistor is located respectively the both sides of thermopile, and use the central line of thermopile sets up as symmetry axis symmetry, specifically includes:

photoetching and ion implantation are carried out on the silicon oxide insulating layer to form a semiconductor arm of the thermopile, an ohmic contact area of a metal wire of the thermopile and the semiconductor arm, the first heating resistor and the second heating resistor; the first heating resistor, the second heating resistor and the semiconductor arm of the thermopile are first polycrystalline silicon, the ohmic contact region is second polycrystalline silicon, and the concentration of the conductive metal doped with the second polycrystalline silicon is greater than that of the conductive metal doped with the first polycrystalline silicon;

and forming a metal arm, a metal lead, a first pressure welding block, a second pressure welding block and a third pressure welding block of the thermopile by sputtering metal aluminum.

10. The method for preparing the MEMS flow sensor according to claim 6, wherein the step of growing a layer of silicon oxide on the silicon substrate with the closed cavity formed therein to form a silicon oxide insulating layer specifically includes:

polishing the upper surface of a silicon substrate with a closed cavity formed inside;

and growing a layer of silicon oxide on the upper surface of the polished silicon substrate to form a silicon oxide insulating layer.

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