阅读说明：本技术 一种mems工艺的穿透式多通道气体传感器 (Penetration type multi-channel gas sensor of MEMS (micro-electromechanical systems) process ) 是由 李兴华 余隽 王媛媛 刘旭 霍智慧 于 2020-12-30 设计创作，主要内容包括：一种MEMS工艺的穿透式多通道气体传感器,解决了现在由于气流只能从气体传感器阵列芯片的封装外壳的上表面经过,气体分子到达气体传感器的气敏材料表面主要通过气体扩散传质,导致气体传感器对低浓度气体的响应时间和恢复时间长的问题,其包括Si衬底、下表面腐蚀窗、通孔和气敏薄膜,所述Si衬底以及通孔的上表面均设置有第一层Si-3O-4薄膜,第一层Si-3O-4薄膜的表面均设置有Pt薄膜加热丝,第一层Si-3O-4薄膜和Pt薄膜加热丝的表面均设置有第二层Si-3O-4薄膜,Au薄膜气敏电极的表面设置有气敏薄膜,由第一层Si-3O-4薄膜、Pt薄膜加热丝、第二层Si-3O-4薄膜、Au薄膜气敏电极以及气敏薄膜构成的多层复合薄膜被上表面腐蚀窗穿过从而具有桥式结构。(A penetration type multi-channel gas sensor of an MEMS (micro-electromechanical system) process solves the problem that the response time and the recovery time of a gas sensor to low-concentration gas are long due to the fact that gas flow can only pass through the upper surface of a packaging shell of a gas sensor array chip and gas molecules reach the surface of a gas sensitive material of the gas sensor and mainly transfer mass through gas diffusion, and comprises a Si substrate, a lower surface corrosion window, a through hole and a gas sensitive film, wherein the upper surfaces of the Si substrate and the through hole are respectively provided with a first layer of Si 3 O 4 Film, first layer Si 3 O 4 The surface of the film is provided with Pt film heating wires and a first layer of Si 3 O 4 The surfaces of the film and the Pt film heating wire are provided with second layers of Si 3 O 4 The surface of Au film gas-sensitive electrode is equipped with gas-sensitive film, which is composed of first layer of Si 3 O 4 Film, Pt film heater wire, second layer Si 3 O 4 Film(s)The multilayer composite film formed by the Au film gas-sensitive electrode and the gas-sensitive film is penetrated by the upper surface corrosion window so as to have a bridge structure.)

1. A penetration type multi-channel gas sensor of MEMS process comprises a Si substrate (1) and a first layer of Si₃O₄A film (2), a Pt film heating wire (3) and a second layer Si₃O₄Film (4), Au film gas-sensitive electrode (5), upper surface corruption window (6), lower surface corruption window (7), through-hole (8) and gas-sensitive film (9), its characterized in that: the upper surfaces of the Si substrate (1) and the through hole (8) are provided with a first layer of Si₃O₄Film (2), first layer Si₃O₄The surface of the film (2) is provided with Pt film heating wires (3), and the first layer of Si₃O₄The surfaces of the film (2) and the Pt film heating wire (3) are both provided with a second layer of Si₃O₄Film (4), second layer Si₃O₄An Au thin film gas-sensitive electrode (5) is arranged on the surface of the thin film (4), a gas-sensitive thin film (9) is arranged on the surface of the Au thin film gas-sensitive electrode (5), and a first layer of Si is formed₃O₄A film (2), a Pt film heating wire (3) and a second layer Si₃O₄A multilayer composite film consisting of the film (4), the Au film gas-sensitive electrode (5) and the gas-sensitive film (9) is penetrated by an upper surface corrosion window (6) to form a bridge structure, and a first layer of Si is arranged on the lower surface of the Si substrate (1)₃O₄Film (2) and second layer Si₃O₄The film (4) is penetrated by the lower surface corrosion window (7) so as to have a hole structure, the upper surface corrosion window (6), the lower surface corrosion window (7) and the through hole (8) are connected to form a penetration channel, and a plurality of structures are simultaneously manufactured on the Si substrate (1) so as to form the penetration multi-channel gas sensor.

2. A MEMS process of a penetration type multi-channel gas sensor of the MEMS process comprises the following steps:

1) selecting materials: selecting a single-side polished silicon wafer with the thickness of 500 microns, the diameter of 100 millimeters and the crystal orientation of 100 for later use;

2) making the first layer Si₃O₄Film (2): in (1)Depositing Si on the upper and lower surfaces of a silicon substrate (1) of a silicon wafer₃O₄The film (2) is processed by chemical vapor deposition such as LPCVD or PECVD to obtain low-stress Si with the thickness of 300 nanometers₃O₄A film (2);

3) manufacturing a Pt film heating wire (3): manufacturing a Pt thin film heating wire (3) on the upper surface of the silicon wafer after the step (2), coating photoresist and photoetching to ensure that the silicon wafer is only exposed at the position where the heating wire needs to be sputtered, and the other parts are well protected by the photoresist; sputtering a chromium metal transition layer and a Pt film, wherein the thickness is 100 nanometers; soaking the silicon wafer in a photoresist corrosive liquid, finishing the graphical processing of the Pt film in a stripping mode, and cleaning the silicon wafer by using alcohol and deionized water;

4) production of the second Si3N4 thin film (4): depositing Si on the upper and lower surfaces of the silicon wafer after the step (3)₃O₄A film is formed by chemical vapor deposition such as LPCVD or PECVD, and Si₃O₄The thickness of the film is 300 nanometers;

5) preparing an Au thin film gas-sensitive electrode (5): manufacturing an Au thin film gas-sensitive electrode on the upper surface of the silicon wafer after the step (4), coating photoresist and photoetching to ensure that the silicon wafer is only exposed at the position where the gas-sensitive electrode needs to be deposited, and the other parts are well protected by the photoresist; sputtering a chromium metal transition layer and an Au film, wherein the thickness is 100 nanometers; soaking the silicon wafer in a photoresist corrosive liquid, finishing the graphical processing of the Au thin film in a stripping mode, and cleaning the silicon wafer by using alcohol and deionized water;

6) manufacturing an upper surface corrosion window (6) and a lower surface corrosion window (7): respectively photoetching the upper surface of the silicon wafer after the step (5), defining an upper surface etching window (6), and etching Si by adopting a dry etching process₃O₄A film is formed until the silicon substrate and the bonding pad of the metal heating wire are exposed; photoetching the lower surface of the silicon wafer, defining a lower surface etching window (7), and etching Si by adopting a dry etching process₃O₄A thin film until the silicon substrate (1) is exposed;

7) etching the Si substrate to form a through hole (8): soaking the silicon wafer after the step (6) in TMAH with the concentration of 20 percent to obtain (CH)₃)₄NOH solution, selected at 85 daysWater bath of degree of's centigrade, etching time 4-6 hours, making silicon substrate penetrate to form through hole (8), and the first layer Si on the through hole (8)₃O₄A film (2), a Pt film heating wire (3) and a second layer Si₃O₄The multilayer composite film consisting of the film (4) and the Au film gas-sensitive electrode (5) is completely suspended;

8) production of gas-sensitive film (9): finishing the processing of the gas-sensitive film above the suspended multilayer composite film of the silicon chip after the step (7) by adopting a gas-sensitive ink printing mode to finish the processing of the multi-channel penetrating gas sensor;

9) slicing and packaging: cutting the silicon wafer after the step (8) into a multi-channel penetrating gas sensor chip (10) by adopting a laser cutting process; coating silver paste at the non-through hole on the bottom surface of the chip, aligning the through hole with the through hole of the packaging shell, pasting the through hole on a base (13), starting from the room temperature of 25 ℃ by using a muffle furnace, heating the through hole to 150 ℃ after 30 minutes, keeping the temperature for one hour at 150 ℃, and then naturally cooling to finish annealing and curing of the silver paste; connecting a bonding pad of the chip with a bonding pad of the packaging base by using a gold wire ball bonding machine; the cover (12) of the packaging shell is fixed above the base (13) in an adhering way.

Technical Field

The invention relates to a gas sensor, in particular to a penetration type multi-channel gas sensor of an MEMS (micro-electromechanical system) process.

Background

The micro-hotplate type gas sensor is a suspended film structure manufactured on a silicon substrate, and the suspended film consists of an upper dielectric layer, a lower dielectric layer, a heating wire in the middle, a gas-sensitive electrode above the gas-sensitive film and the gas-sensitive film. The suspended film structure of the micro-hotplate type gas sensor is mainly divided into three typical structures, namely a bridge structure with a surface sacrificial layer corroded, a bridge structure with a front surface bulk silicon corroded and a diaphragm structure with a back surface bulk silicon corroded, and gas flow cannot penetrate through a gas sensor silicon substrate with the three structures. A plurality of micro-hotplate type gas sensors are manufactured on a micro-hotplate (MHP) on the same chip by utilizing a silicon-based micro-machining technology and are packaged in a packaging shell with air holes on the upper surface to manufacture a gas sensor array chip, and the gas sensor array chip has the advantages of small size, low power consumption, low cost, easiness in integration and the like. When the gas sensor array chip is used, when gas components or gas concentrations in airflow around a package shell of the gas sensor array chip are changed, for example, the concentration of gas a in the airflow is different from the concentration of gas a on the surface of a gas sensing film of the gas sensor, gas molecules a on the surface of the gas sensing film of the gas sensor and gas molecules a in the airflow are diffused due to the concentration difference, mass transfer occurs, the number of gas molecules a adsorbed on the surface of the gas sensing film of the gas sensor is changed, and thus a gas sensing signal is changed. Now, since the gas flow can only pass through the upper surface of the package housing of the gas sensor array chip, the response and recovery time of the gas sensor array chip can be affected. According to the basic law of molecular diffusion, the value of the diffusion flux of gas molecules is proportional to the difference in gas concentration, and therefore, as the difference between the concentration of a gas in the gas stream and the concentration of a gas at the surface of the gas-sensitive film of the gas sensor is smaller, the smaller the gas diffusion flux, resulting in longer response time and recovery time of the gas sensor for low-concentration gases.

Disclosure of Invention

Aiming at the situation, in order to overcome the defects of the prior art, the invention provides a penetration type multi-channel gas sensor of an MEMS (micro-electromechanical systems) process, which effectively solves the problem that the response time and the recovery time of the gas sensor to low-concentration gas are long because gas flow only passes through the upper surface of a packaging shell of a gas sensor array chip and gas molecules reach the surface of a gas sensitive material of the gas sensor and mainly transfer mass through gas diffusion.

In order to achieve the purpose, the invention provides the following technical scheme: the gas sensor comprises a Si substrate, a first layer of Si3N4 film, a Pt film heating wire, a second layer of Si3N4 film, an Au film gas-sensitive electrode, an upper surface corrosion window, a lower surface corrosion window, a through hole and a gas-sensitive film, wherein the first layer of Si is arranged on the upper surfaces of the Si substrate and the through hole₃O₄Film, first layer Si₃O₄The surface of the film is provided with Pt film heating wires and a first layer of Si₃O₄The surfaces of the film and the Pt film heating wire are provided with second layers of Si₃O₄Film, second layer of Si₃O₄An Au film gas-sensitive electrode is arranged on the surface of the film, a gas-sensitive film is arranged on the surface of the Au film gas-sensitive electrode, and the gas-sensitive electrode is composed of a first layer of Si3N4 film, a Pt film heating wire and a second layer of Si₃O₄The multilayer composite film consisting of the film, the Au film gas-sensitive electrode and the gas-sensitive film is penetrated by the upper surface corrosion window to form a bridge structure, and the first layer of Si arranged on the lower surface of the Si substrate₃O₄Film and second layer of Si₃O₄The film is penetrated by the lower surface corrosion window to form a hole structure, the upper surface corrosion window, the lower surface corrosion window and the through hole are connected to form a penetration channel, and a plurality of structures are simultaneously manufactured on the Si substrate to form the penetration type multi-channel gas sensor.

A MEMS process of a penetration type multi-channel gas sensor of the MEMS process comprises the following steps:

1) selecting materials: selecting a single-side polished silicon wafer with the thickness of 500 microns, the diameter of 100 millimeters and the (100) crystal orientation for later use;

2) making the first layer Si₃O₄Film 2: depositing Si on the upper and lower surfaces of the silicon substrate 1 of the silicon wafer in (1)₃O₄The film is prepared by chemical vapor deposition such as LPCVD or PECVD to obtain a low-stress Si3N4 film with the thickness of 300 nm;

3) manufacturing a Pt film heating wire 3: manufacturing a Pt heating wire on the upper surface of the silicon wafer after the step (2), coating photoresist and photoetching to ensure that the silicon wafer only exposes the position needing sputtering of the heating wire, and the other parts are well protected by the photoresist; sputtering a chromium metal transition layer and a Pt film, wherein the thickness is 100 nanometers; soaking the silicon wafer in a photoresist corrosive liquid, finishing the graphical processing of the Pt film in a stripping mode, and cleaning the silicon wafer by using alcohol and deionized water;

4) making a second Si3N4 film 4: depositing Si on the upper and lower surfaces of the silicon wafer after the step (3)₃O₄A film is formed by chemical vapor deposition such as LPCVD or PECVD, and Si₃O₄The thickness of the film is 300 nanometers; the completion scheme is shown in FIG. 7;

5) manufacturing an Au thin film gas-sensitive electrode 5: manufacturing an Au thin film gas-sensitive electrode on the upper surface of the silicon wafer after the step (4), coating photoresist and photoetching to ensure that the silicon wafer is only exposed at the position where the gas-sensitive electrode needs to be deposited, and the other parts are well protected by the photoresist; sputtering a chromium metal transition layer and an Au film, wherein the thickness is 100 nanometers; soaking the silicon wafer in a photoresist corrosive liquid, finishing the graphical processing of the Au thin film in a stripping mode, and cleaning the silicon wafer by using alcohol and deionized water;

6) manufacturing an upper surface corrosion window 6 and a lower surface corrosion window 7: respectively photoetching the upper surface of the silicon wafer after the step (5), defining an upper surface etching window 6, and etching Si by adopting a dry etching process₃O₄A film is formed until the silicon substrate and the bonding pad of the metal heating wire are exposed; photoetching the lower surface of the silicon wafer, defining a lower surface etching window 7, and etching Si by dry etching process₃O₄A film is formed until the silicon substrate 1 is exposed;

7) etching the silicon substrate to form the through hole 8: soaking the silicon wafer after the step (6) in TMAH with the concentration of 20 percent to obtain (CH)₃)₄The NOH solution is selected to be in water bath at 85 ℃ and is etched for 4-6 hours, so that the silicon substrate penetrates through to form a through hole 8, and the first layer of Si is arranged on the through hole 8₃O₄Film 2, Pt film heating wire 3 and second layer Si₃O₄The multilayer composite film consisting of the film 4 and the Au film gas-sensitive electrode 5 is completely suspended;

8) manufacturing a gas-sensitive film 9: finishing the processing of the gas-sensitive film above the suspended multilayer composite film of the silicon chip after the step (7) by adopting a gas-sensitive ink printing mode to finish the processing of the multi-channel penetrating gas sensor;

9) slicing and packaging: cutting the silicon wafer after the step (8) into a multi-channel penetrating gas sensor chip 10 by adopting a laser cutting process; coating silver paste at a non-through hole on the bottom surface of the chip, aligning a through hole of the chip with a through hole of the packaging shell, adhering the through hole to the base 13, starting from 25 ℃ at room temperature by using a muffle furnace, heating the through hole to 150 ℃ after 30 minutes, keeping the temperature for one hour at 150 ℃, and then naturally cooling to finish annealing and curing of the silver paste; connecting a bonding pad of the chip with a bonding pad of the packaging base by using a gold wire ball bonding machine; the lid 12 of the package is adhesively secured over the base 13.

Of course, the thickness of the Si3N4 film can be 100 nm-500 nm, and the material can also be SiO2 film; the thickness of the Pt film heating wire can be 100 nm-500 nm, and other high-temperature-resistant metals such as W can also be adopted; the thickness of the Au thin film gas-sensitive electrode can be 100 nm-500 nm, and other gas-sensitive electrode materials such as Pt can also be adopted; the patterning process of the film heating wire and the film gas-sensitive electrode can also adopt an etching process; the thickness of the Si substrate can be 200-600 microns.

Has the advantages that: the penetration type multi-channel gas sensor prepared by the invention adopts the penetration type gas channel formed by combining the front side with the back side in a corrosion way, so that gas flow can vertically penetrate through the penetration type multi-channel gas sensor, the gas molecular flow flux is in direct proportion to the product of gas concentration and gas flow speed, and therefore, compared with the prior gas sensor mainly relying on gas diffusion mass transfer, the penetration type multi-channel gas sensor has larger gas molecular flow flux, and is favorable for obtaining faster gas response speed and recovery speed during the detection of low-concentration gas; the adoption of the penetrating type multi-channel gas sensor is matched with a corresponding packaging structure with an air flow penetrating effect, the purposes of improving the gas response speed and the recovery speed of the sensor can be achieved, the sensor chip can be in quick and effective contact with the air flow formed by the introduced test gas, the response effect is improved, and meanwhile, the device has the characteristics of low cost, small size, low power consumption and the like.

Drawings

The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and together with the description serve to explain the principles of the invention and not to limit the invention. In the drawings:

FIG. 1 is a schematic cross-sectional view of a transmissive multi-channel gas sensor of the present invention;

FIG. 2 is a schematic plan view of the upper surface of the transmissive multi-channel gas sensor of the present invention;

FIG. 3 is a schematic plan view of the lower surface of the transmissive multi-channel gas sensor of the present invention;

FIG. 4 is a schematic cross-sectional view of a transmission multi-channel gas sensor of the present invention in a transmission package housing;

FIGS. 5 to 11 are schematic cross-sectional views illustrating the effects achieved in steps (2) to (8) according to the corresponding embodiment of the present invention;

reference numbers in the figures: 1. a Si substrate; 2. first layer of Si₃O₄A film; 3. a Pt film heating wire; 4. second layer of Si₃O₄A film; 5. an Au thin film gas-sensitive electrode; 6. an upper surface erosion window; 7. a lower surface erosion window; 8. a through hole; 9. a gas-sensitive film; 10. a multi-channel penetrating gas sensor chip; 11. a pad of the package housing; 12. a cover; 13. a base; 14. a through hole on the base.

Detailed Description

The following description of the present invention will be made in detail with reference to the accompanying drawings 1 to 11.

Embodiments, as shown in fig. 1 to 11, the present invention provides a transmissive multi-channel gas sensor for MEMS process, comprising a Si substrate 1, a first Si3N4 thin film 2, a Pt thin film heater wire 3, and a second Si layer₃O₄The gas sensor comprises a film 4, an Au film gas-sensitive electrode 5, an upper surface corrosion window 6, a lower surface corrosion window 7, a through hole 8 and a gas-sensitive film 9, wherein the upper surfaces of a Si substrate 1 and the through hole 8 are respectively provided with a first layer of Si₃O₄Film 2, first layer Si₃O₄The surface of the film 2 is provided with a Pt film heating wire 3, and the first layer of Si₃O₄The surfaces of the film 2 and the Pt film heating wire 3 are both provided with a second layer of Si3N4 film 4₃O₄An Au thin film gas-sensitive electrode 5 is arranged on the surface of the thin film 4, a gas-sensitive thin film 9 is arranged on the surface of the Au thin film gas-sensitive electrode 5, and a first layer of Si is formed₃O₄A multilayer composite film consisting of a film 2, a Pt film heating wire 3, a second layer Si3N4 film 4, an Au film gas-sensitive electrode 5 and a gas-sensitive film 9 penetrates through an upper surface corrosion window 6 to have a bridge structure, and a first layer Si is arranged on the lower surface of the Si substrate 1₃O₄Film 2 and second layer Si₃O₄The film 4 is penetrated by the lower surface etching window 7 to have a hole structure, the upper surface etching window 6, the lower surface etching window 7 and the through hole 8 are connected to form a penetration channel, and a plurality of the structures are simultaneously manufactured on the Si substrate 1 to form the penetration multi-channel gas sensor.

A MEMS process of a penetration type multi-channel gas sensor of the MEMS process comprises the following steps:

1) selecting materials: selecting a single-side polished silicon wafer with the thickness of 500 microns, the diameter of 100 millimeters and the (100) crystal orientation for later use;

2) making a first Si3N4 film 2: depositing Si3N4 films on the upper and lower surfaces of the silicon substrate 1 of the silicon wafer in the step (1), and completing the process by chemical vapor deposition such as LPCVD or PECVD to obtain low-stress Si with the thickness of 300 nanometers₃O₄A film;

3) manufacturing a Pt film heating wire 3: manufacturing a Pt heating wire on the upper surface of the silicon wafer after the step (2), coating photoresist and photoetching to ensure that the silicon wafer only exposes the position needing sputtering of the heating wire, and the other parts are well protected by the photoresist; sputtering a chromium metal transition layer and a Pt film, wherein the thickness is 100 nanometers; soaking the silicon wafer in a photoresist corrosive liquid, finishing the graphical processing of the Pt film in a stripping mode, and cleaning the silicon wafer by using alcohol and deionized water;

4) making a second Si3N4 film 4: depositing Si on the upper and lower surfaces of the silicon wafer after the step (3)₃O₄A film is formed by chemical vapor deposition such as LPCVD or PECVD, and Si₃O₄The thickness of the film is 300 nanometers; the completion scheme is shown in FIG. 7;

5) manufacturing an Au thin film gas-sensitive electrode 5: manufacturing an Au thin film gas-sensitive electrode on the upper surface of the silicon wafer after the step (4), coating photoresist and photoetching to ensure that the silicon wafer is only exposed at the position where the gas-sensitive electrode needs to be deposited, and the other parts are well protected by the photoresist; sputtering a chromium metal transition layer and an Au thin film with the thickness of 100 nanometers; soaking the silicon wafer in a photoresist corrosive liquid, finishing the graphical processing of the Au thin film in a stripping mode, and cleaning the silicon wafer by using alcohol and deionized water;

6) manufacturing an upper surface corrosion window 6 and a lower surface corrosion window 7: respectively photoetching the upper surface of the silicon wafer after the step (5), defining an upper surface etching window 6, and etching Si by adopting a dry etching process₃O₄A film is formed until the silicon substrate and the bonding pad of the metal heating wire are exposed; photoetching the lower surface of the silicon wafer, defining a lower surface etching window 7, and etching Si by dry etching process₃O₄A film is formed until the silicon substrate 1 is exposed;

7) etching the silicon substrate to form the through hole 8: soaking the silicon wafer after the step (6) in TMAH with the concentration of 20 percent to obtain (CH)₃)₄The NOH solution is selected to be in water bath at 85 ℃ and is etched for 4-6 hours, so that the silicon substrate penetrates through to form a through hole 8, and the first layer of Si is arranged on the through hole 8₃O₄Film 2, Pt film heating wire 3 and second layer Si₃O₄The multilayer composite film consisting of the film 4 and the Au film gas-sensitive electrode 5 is completely suspended;

8) manufacturing a gas-sensitive film 9: finishing the processing of the gas-sensitive film above the suspended multilayer composite film of the silicon chip after the step (7) by adopting a gas-sensitive ink printing mode to finish the processing of the multi-channel penetrating gas sensor;

9) slicing and packaging: cutting the silicon wafer after the step (8) into a multi-channel penetrating gas sensor chip 10 by adopting a laser cutting process; coating silver paste at a non-through hole on the bottom surface of the chip, aligning a through hole of the chip with a through hole of the packaging shell, adhering the through hole to the base 13, starting from 25 ℃ at room temperature by using a muffle furnace, heating the through hole to 150 ℃ after 30 minutes, keeping the temperature for one hour at 150 ℃, and then naturally cooling to finish annealing and curing of the silver paste; connecting a bonding pad of the chip with a bonding pad of the packaging base by using a gold wire ball bonding machine; the lid 12 of the package is adhesively secured over the base 13.

Has the advantages that: the penetration type multi-channel gas sensor prepared by the invention adopts the penetration type gas channel formed by combining the front side with the back side in a corrosion way, so that gas flow can vertically penetrate through the penetration type multi-channel gas sensor, the gas molecular flow flux is in direct proportion to the product of gas concentration and gas flow speed, and therefore, compared with the prior gas sensor mainly relying on gas diffusion mass transfer, the penetration type multi-channel gas sensor has larger gas molecular flow flux, and is favorable for obtaining faster gas response speed and recovery speed during the detection of low-concentration gas; the adoption of the penetrating type multi-channel gas sensor is matched with a corresponding packaging structure with an air flow penetrating effect, the purposes of improving the gas response speed and the recovery speed of the sensor can be achieved, the sensor chip can be in quick and effective contact with the air flow formed by the introduced test gas, the response effect is improved, and meanwhile, the device has the characteristics of low cost, small size, low power consumption and the like.

Finally, it should be noted that: although the present invention has been described in detail with reference to the foregoing embodiments, it will be apparent to those skilled in the art that changes may be made in the embodiments and/or equivalents thereof without departing from the spirit and scope of the invention. Any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.