A nanoscale air flow sensor and its preparation method

Abstract

The present invention relates to a nano-scale airflow sensor, comprising: 4×N airflow sensing units (6), wherein N is an integer greater than or equal to 1; the airflow sensing unit (6) comprises: a supporting substrate (2); a bearing portion (3) formed on the supporting substrate (2); a piezoresistive film (5) formed on the bearing portion (3); an electrode (4) formed on the piezoresistive film (5); the bearing portion (3), the piezoresistive film (5) and the electrode (4) together form a suspended part; the suspended part has three free sides and a folded edge; the electrode (4) is arranged parallel to the folded edge of the suspended part perpendicularly; the airflow sensing units (6) are symmetrically distributed in a manner of equally dividing a circle. The present invention also relates to a method for preparing the nano-scale airflow sensor of the present invention. The nano-scale airflow sensor provided by the present invention has high sensitivity; each nano-scale airflow sensing unit has a different curvature and can distinguish the direction of airflow.

Description

Technical Field

[0001] The invention relates to the field of airflow sensors, and in particular to a nano-scale airflow sensor and a preparation method thereof. Background Art

[0002] Accurate wind speed and direction information can prevent loss of human life and property safety, and can better provide safety protection for meteorology, ocean, environment, airports, ports, industry, agriculture and transportation.

[0003] In today's society, wind speed and direction are measured using traditional methods, and wind direction is observed using a wind vane. A wind vane is a device for measuring the direction of wind. A wind vane is basically an asymmetrically shaped object with its center of gravity fixed on a vertical axis. When the wind blows, the end that creates greater resistance to air flow will rotate downwind, showing the wind direction. The disadvantage is that humans observe wind direction information and cannot automatically transmit it. Wind speed uses the principle of windmill rotation. It is difficult to measure the speed at which the wind moves in 1 second, but it is relatively simple to measure its speed in 10 minutes. Meteorological departments often use wind cup rotation to measure wind speed. The distance that the wind cup rotates in one circle is fixed, and the number of circles rotated in 10 minutes can be recorded by the counter at the bottom of the central axis. The distance divided by the time gives the speed at which the wind moves per second. The disadvantage is that only the average wind speed can be calculated, and the instantaneous wind speed cannot be measured. Summary of the invention

[0004] The object of the present invention is to provide a nanometer-scale airflow sensor with high sensitivity and a preparation method thereof.

[0005] In a first aspect, the present invention provides a nanoscale airflow sensor, comprising: 4×N airflow sensing units (6), wherein N is an integer greater than or equal to 1;

[0006] The airflow sensing unit (6) comprises:

[0007] A supporting substrate (2);

[0008] A carrier portion (3) formed on the supporting substrate (2);

[0009] A piezoresistive film (5) formed on the bearing portion (3);

[0010] An electrode (4) formed on the piezoresistive film (5);

[0011] The bearing portion (3), the piezoresistive film (5) and the electrode (4) together form a suspended portion; the suspended portion has three free sides and a folded edge;

[0012] The electrode (4) is arranged perpendicularly and parallel to the folded edge of the suspended part;

[0013] The airflow sensing units (6) are symmetrically distributed in a manner of equally dividing the circumference.

[0014] Preferably, in the nanoscale airflow sensor of the present invention, the supporting substrate is a double-sided polished silicon wafer and / or a single-sided polished silicon wafer.

[0015] Preferably, in the nanoscale airflow sensor of the present invention, the thickness of the silicon wafer is greater than 300 um, the crystal orientation is

[100] , and the resistivity is less than 100 Ω·cm.

[0016] Preferably, in the nanoscale airflow sensor of the present invention, the bearing portion is formed of a silicon nitride film and / or a silicon oxide film.

[0017] Preferably, in the nanoscale airflow sensor of the present invention, the piezoresistive film may be composed of a film having a piezoresistive effect, for example, a graphene film.

[0018] Preferably, in the nanoscale airflow sensor of the present invention, the stress of the bearing portion is less than or equal to 50 MPa.

[0019] Preferably, in the nanoscale airflow sensor of the present invention, the N airflow sensing units are structurally separated from each other and have uncoupled signals.

[0020] Preferably, in the nanoscale airflow sensor of the present invention, the suspended portion is in a rectangular shape.

[0021] In a preferred embodiment of the present invention, the supporting substrate is a double-sided polished silicon wafer, which can form a supporting frame to support the gas sensing unit; the bearing portion is composed of a silicon nitride film and supported by the supporting frame; the piezoresistive film is composed of a graphene film and supported by the silicon nitride film. The electrode can transmit the electrical signal of the nanoscale airflow sensing unit; the graphene film can generate a piezoresistive effect to realize the sensing signal. The airflow sensing unit in the present invention can realize the measurement of the gas flow velocity signal.

[0022] In another preferred embodiment of the present invention, the nanoscale airflow sensor of the present invention includes two relative nanoscale airflow sensing units, which constitute an axial nanoscale airflow sensor, so that two mutually perpendicular axial nanoscale airflow sensors realize two-axis measurement; the four nanoscale airflow sensing units are structurally separated from each other and have uncoupled signals.

[0023] In a second aspect, the present invention provides a method for preparing the nanoscale airflow sensor of the present invention, comprising the following steps:

[0024] A. forming a bearing portion on both sides of the supporting substrate;

[0025] B. forming a piezoresistive film on the carrier portion, and then patterning the piezoresistive film;

[0026] C. forming an electrode on the piezoresistive body and then patterning the electrode;

[0027] D. Etching the bearing part and corroding the supporting substrate to form a suspended part, wherein the bearing part, the piezoresistive film and the electrode together form the suspended part.

[0028] Preferably, in the method of the present invention, the forming of the carrier in step A is performed by adopting a low-pressure vapor phase chemical deposition method.

[0029] Preferably, in the method of the present invention, the forming of the piezoresistive film in step B is performed by adopting a chemical vapor deposition method; preferably, the patterning is performed by adopting a focused ion beam method.

[0030] Preferably, in the method of the present invention, the forming of the electrode in step C is performed by electron beam evaporation; preferably, the patterning is performed by a lift-off process.

[0031] Preferably, in the method of the present invention, before forming the bearing parts on both sides of the supporting substrate, it also includes cleaning the supporting substrate by using standard RCA.

[0032] Preferably, in the method described in the present invention, the etching in step D is performed by a method comprising the following steps: preparing a photoresist pattern by ultraviolet lithography, and then etching by reactive ions; the etching in step D is performed by KOH wet etching.

[0033] In a preferred embodiment of the present invention, the graphene film in the nanoscale airflow sensor of the present invention is formed and patterned by the following methods: (1) chemical vapor deposition method is used to realize the film; (2) focused ion beam method is used to realize patterning. The electrode in the nanoscale airflow sensor of the present invention is formed and patterned by the following methods: (1) electron beam evaporation method is used to realize the electrode film; (2) stripping process is used to realize patterning.

[0034] The nanoscale airflow sensor provided by the present invention has the following advantages:

[0035] High sensitivity; each nanometer-scale airflow sensing unit has a different curvature and a different sensitivity to airflow, and can distinguish the direction of airflow. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] The embodiments of the present invention are described in detail below with reference to the accompanying drawings, wherein:

[0037] Figure 1 is a diagram of a nanoscale airflow sensor according to an embodiment of the present invention;

[0038] FIG. 2 is a preparation flow chart according to an embodiment of the present invention.

[0039] Figure 3 is a schematic diagram of a nanoscale airflow sensor according to an embodiment of the present invention;

[0040] Figure 4 is a schematic diagram of a nanoscale airflow sensor according to an embodiment of the present invention;

[0041] Description of reference numerals:

[0042] 1 Nanoscale airflow sensor

[0043] 2 Support substrate

[0044] 3 Load-bearing part

[0045] 4 Electrodes

[0046] 5 Piezoresistive film

[0047] 6 Air flow sensing unit DETAILED DESCRIPTION

[0048] Now, with reference to the accompanying drawings, a schematic scheme of the nanoscale airflow sensor disclosed in the present invention is described in detail. Although the accompanying drawings are provided to present some embodiments of the present invention, the accompanying drawings do not have to be drawn according to the dimensions of the specific implementation scheme. Some components in the accompanying drawings can be adjusted in position according to actual needs without affecting the technical effect. The phrase "in the accompanying drawings" or similar terms appearing in the specification do not necessarily refer to all drawings or examples.

[0049] Certain directional terms used to describe the drawings below, such as "on", "above" and other directional terms, will be understood to have their normal meanings and refer to those directions involved when the drawings are normally viewed. Unless otherwise specified, the directional terms described in this specification are basically in accordance with the conventional directions understood by those skilled in the art.

[0050] Figure 1 A nanoscale airflow sensor provided by the present invention is shown, referring to Figure 1 In the embodiment shown, the nanoscale airflow sensor 1 is composed of four airflow sensing units 6. Of course, in other embodiments, the nanoscale airflow sensor may include eight or sixteen airflow sensing units. The schematic diagram of the nanoscale airflow sensor composed of eight airflow sensing units can be referred to. Figure 3 The schematic diagram of the nanoscale airflow sensor consisting of 16 airflow sensing units can be found in Figure 4 .exist Figure 1 In the figure, the airflow sensing unit 6 includes: a supporting substrate 2, a bearing part 3 formed on the supporting substrate 2, a piezoresistive film 5 formed on the bearing part 3, and an electrode 4 formed on the piezoresistive film 5. The airflow sensing unit 6 has a suspended part, and the suspended part has three free sides and a folded edge. The suspended part is rectangular, and the suspended part includes the bearing part 3, the piezoresistive film 5 and the electrode 4. The electrode 4 is arranged in parallel and perpendicular to the folded edge. The four airflow sensing units 6 are symmetrically distributed in a manner of equally dividing the circumference, that is, two relative nanoscale airflow sensing units constitute an axial nanoscale airflow sensor, so two mutually perpendicular axial nanoscale airflow sensors realize two-axis measurement. The four nanoscale airflow sensing units are structurally separated from each other and have uncoupled signals.

[0051] exist Figure 1 In the embodiment shown, the support substrate 2 is a double-sided polished silicon wafer. The thickness of the silicon wafer is 500um, the crystal orientation is

[100] , and the resistivity is 5Ω·cm. Of course, in other embodiments, the silicon wafer may also have a resistivity of other values, for example, silicon wafers with a resistivity of 1-10Ω·cm are suitable for the present invention. The bearing portion 3 is composed of a silicon nitride film with a stress within 50MPa. The piezoresistive film 5 is composed of a graphene film.

[0052] If the nanoscale airflow sensor provided by the present invention is used to measure wind speed, wind blowing from a certain direction acts on the airflow sensing unit 6, the silicon nitride film 3 is deformed, causing the graphene film 5 to deform to change the resistivity, thereby converting the airflow signal of the wind into an electrical signal and transmitting it to the signal processing terminal through the electrode 4.

[0053] In addition, refer to Figure 2 of the present invention, which is a preparation flow chart according to an embodiment of the present invention. As shown in the figure, the preparation process of the nanoscale airflow sensor includes: a step of depositing a silicon nitride film 3 on both sides of a supporting substrate 2 by a low-pressure vapor phase chemical deposition method, as shown in Figure 2 (1); a step of forming a graphene film 5 on the formed silicon nitride film 3, as shown in Figure 2 (2); a step of forming an electrode 4 on the graphene film 5, as shown in Figure 2 (3); a step of preparing a suspended part of the airflow sensing unit, as shown in Figure 2 (4); a step of releasing the suspended part so that the suspended part has three degrees of freedom and a folded edge, as shown in Figure 2 (5).

[0054] The specific steps include:

[0055] Step A, as shown in FIG2(1), firstly, a double-sided polished silicon wafer with a thickness of 500 um, a crystal orientation of

[100] , a resistivity of 1-10 Ω·cm, and cleaned by standard RCA is used as a supporting substrate 2; then, a silicon nitride film 3 is deposited by a low-pressure vapor chemical deposition method;

[0056] Step B, as shown in FIG2 (2), firstly, a graphene film 5 is prepared by chemical vapor deposition method, and then patterned by focused ion beam method;

[0057] Step C, as shown in FIG. 2 (3), firstly, a photoresist pattern is realized by ultraviolet lithography, then an electrode 4 thin film is prepared by electron beam evaporation, and finally a lift-off process is used to realize the pattern of the electrode 4, forming electrodes 4 that are parallel to each other and perpendicular to the folded edges of the suspended parts;

[0058] In step D, as shown in FIG2 (4), a photoresist pattern is first prepared by ultraviolet lithography, and then the silicon nitride film 3 is etched by reactive ion etching, and finally the supporting substrate 2 is wet-etched by KOH to form a suspended portion; the suspended portion includes the silicon nitride film 3, the graphene film 5 and the electrode 4, and the suspended portion has three free sides and a folded edge.

[0059] The nanometer-scale airflow sensor prepared by the present invention has high sensitivity, each nanometer-scale airflow sensing unit has a different curvature direction and a different airflow sensing sensitivity, and has the advantage of distinguishing the direction of airflow.

[0060] The above description is only an illustrative embodiment of the present invention and is not intended to limit the scope of the present invention. Any equivalent changes, modifications and combinations made by any person skilled in the art without departing from the concept and principle of the present invention shall fall within the scope of protection of the present invention.

Claims

1. A nanoscale airflow sensor (1), comprising: 4×N airflow sensing units (6), wherein N is an integer greater than or equal to 1; The airflow sensing unit (6) comprises: A supporting substrate (2); A carrier portion (3) formed on the supporting substrate (2); A piezoresistive film (5) formed on the bearing portion (3); An electrode (4) formed on the piezoresistive film (5); The bearing portion (3), the piezoresistive film (5) and the electrode (4) together form a suspended portion; the suspended portion has three free sides and a folded edge; The electrode (4) is arranged perpendicularly and parallel to the folded edge of the suspended part; The airflow sensing units (6) are symmetrically distributed in a manner of equally dividing the circumference; Two opposite nano-scale airflow sensing units form an axial nano-scale airflow sensor, and two mutually perpendicular axial nano-scale airflow sensors realize two-axis measurement; 4×N nano-scale airflow sensing units are structurally separated from each other and have uncoupled signals; The suspended portion is in a rectangular shape.

2. The nanoscale airflow sensor (1) according to claim 1, characterized in that: The supporting substrate (2) is a double-sided polished silicon wafer and / or a single-sided polished silicon wafer.

3. The nanoscale airflow sensor (1) according to claim 2, characterized in that: The silicon wafer has a thickness greater than 300um, a crystal orientation of [100], and a resistivity less than 100Ω·cm.

4. The nanoscale airflow sensor (1) according to claim 1, characterized in that: The bearing part (3) is composed of a silicon nitride film and / or a silicon oxide film.

5. The nanoscale airflow sensor (1) according to claim 1, characterized in that: The piezoresistive film (5) is made of a graphene film.

6. The nanoscale airflow sensor (1) according to any one of claims 1 to 5, characterized in that: The stress of the bearing portion (3) is less than or equal to 50 MPa.

7. A method for preparing the nanoscale airflow sensor (1) according to any one of claims 1 to 6, comprising the following steps: A. forming a bearing portion (3) on both sides of a supporting substrate (2); B. forming a piezoresistive film (5) on the carrier (3), and then patterning the piezoresistive film (5); C. forming an electrode (4) on the piezoresistive film (5), and then patterning the electrode (4); D. Etching the bearing part (3) and corroding the supporting substrate (2) to form a suspended part, wherein the bearing part (3), the piezoresistive film (5) and the electrode (4) together form the suspended part.

8. The method according to claim 7, characterized in that The forming of the carrier part (3) in step A is carried out by adopting a low-pressure vapor phase chemical deposition method.

9. The method according to claim 7, characterized in that: The formation of the piezoresistive film (5) in step B is carried out by adopting a chemical vapor deposition method.

10. The method according to claim 7, characterized in that The patterning in step B is performed by using a focused ion beam method.

11. The method according to claim 7, characterized in that The forming of the electrode (4) in the step C is performed by using an electron beam evaporation method.

12. The method according to claim 7, characterized in that The patterning in step C is performed by adopting a lift-off process.

13. The method according to claim 7, characterized in that The etching in step D is performed by a method comprising the following steps: preparing a photoresist pattern by ultraviolet lithography, and then etching by reactive ions; the etching in step D is performed by KOH wet etching.

14. The method according to claim 7, characterized in that Before forming the bearing parts (3) on both sides of the supporting substrate (2), the method further includes cleaning the supporting substrate (2) using standard RCA.

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