A MEMS thermal temperature difference type flow sensor and a manufacturing method thereof

Abstract

The present invention discloses a MEMS thermal temperature difference type flow sensor and a manufacturing method thereof. The flow sensor includes: a substrate provided with a heat insulation cavity; a dielectric layer formed on the upper surfaces of the substrate and the heat insulation cavity; a micro heater and a thermistor formed on the upper surface of the dielectric layer, and the micro heater and the thermistor are partially located above the heat insulation cavity; platinum black covering at least part of the micro heater and the thermistor. The flow sensor disclosed by the present invention has a simple preparation process, strong controllability and high compatibility. By forming platinum black on the micro heater and the thermistor, it is beneficial to increase their surface areas, thereby accelerating the heat exchange efficiency with gas molecules and improving the sensitivity of the device. In addition, the increase in the surface area is also beneficial to improving the thermal utilization rate of the micro heater, thereby playing a role in reducing power consumption.

Description

Technical Field

[0001] The present invention relates to the technical field of flow measurement, and particularly relates to a MEMS thermal differential flow sensor and a manufacturing method thereof. Background Art

[0002] Flow measurement is a basic requirement in industrial production and scientific research. There are various types of flow sensors. Among them, the thermal differential flow sensor fabricated based on MEMS technology has been widely used due to its many advantages such as simple structure, small size, high precision, and fast response speed.

[0003] The physical basis of the MEMS thermal differential flow sensor is heat transfer. Its structure mainly includes three elements integrated on the same substrate: a micro heater located in the center and temperature sensing elements (thermistors or thermopiles) symmetrically distributed upstream and downstream of the micro heater. The micro heater provides a certain amount of power to make the surface temperature higher than the ambient temperature. When there is no gas flow, the surface temperature is normally distributed with the micro heater as the center, and the upstream and downstream temperature sensing elements have the same electrical signal; when there is gas flow, the heat exchange of gas molecules causes the temperature distribution on the surface to shift, and the electrical signals of the upstream and downstream temperature sensing elements will then show differences. Using this difference, the gas flow can be calculated.

[0004] High sensitivity and low power consumption are the most important application requirements and development directions of flow sensors. For this purpose, various effective technical solutions have been proposed, such as using a suspended film structure with a smaller thermal conductivity to reduce the heat dissipation of the substrate; using thermoelectric materials with a higher Seebeck coefficient; using a larger area or a denser arrangement to increase the number of thermopiles. However, with the continuous popularization and in-depth application, the performance of flow sensors such as sensitivity and power consumption urgently needs to be further improved. Summary of the Invention

[0005] To solve the above technical problems, the present invention provides a MEMS thermal differential flow sensor and a manufacturing method thereof to achieve the purpose of improving the sensitivity of the flow sensor and reducing the power consumption of the flow sensor.

[0006] To achieve the above object, the technical solution of the present invention is as follows:

[0007] A MEMS thermal differential flow sensor, comprising:

[0008] A substrate provided with a heat insulation cavity;

[0009] A dielectric layer formed on the upper surface of the substrate and the heat insulation cavity;

[0010] A micro heater and a thermistor formed on the upper surface of the dielectric layer, and the micro heater and the thermistor are partially located above the heat insulation cavity;

[0011] Platinum black, covering at least part of the micro-heater and the thermistor.

[0012] In the above solution, the substrate is a semiconductor substrate, including one of a silicon substrate, a germanium substrate, a SOI substrate, and a GeOI substrate.

[0013] In the above solution, the heat insulation cavity is formed by recessing a certain depth from the upper surface of the substrate, or formed by penetrating the substrate from the lower surface of the substrate.

[0014] In the above solution, the material of the dielectric layer is one or a combination of two of silicon oxide and silicon nitride.

[0015] In the above solution, the number of the thermistors is two, symmetrically distributed on both sides of the micro-heater.

[0016] In the above solution, the materials of the micro-heater and the thermistor are platinum or titanium / platinum or chromium / platinum.

[0017] A manufacturing method of a MEMS thermal difference type flow sensor includes the following steps:

[0018] S1. Provide a substrate and form a dielectric layer on the substrate;

[0019] S2. Form a micro-heater and a thermistor on the dielectric layer;

[0020] S3. Form platinum black on at least part of the micro-heater and the thermistor;

[0021] S4. Release the substrate to form a heat insulation cavity.

[0022] In the above solution, the materials of the micro-heater and the thermistor are platinum or titanium / platinum or chromium / platinum, and are formed by a lift-off process, or formed by a method of sputtering or evaporation first and then etching.

[0023] In the above solution, the platinum black is formed by an electroplating method.

[0024] In the above solution, the heat insulation cavity is formed by releasing the substrate by a dry etching or wet etching method.

[0025] Through the above technical solution, a MEMS thermal difference type flow sensor and its manufacturing method provided by the present invention have the following beneficial effects:

[0026] 1. The thermal difference type flow sensor manufactured by the present invention based on MEMS technology has the advantages of small volume, high precision, fast response speed, etc., and the preparation process is simple, with strong controllability and high process compatibility.

[0027] 2. The present invention forms platinum black on the micro - heater and thermistor of the flow sensor by using MEMS technology. The porous and loose structure of platinum black is beneficial to increasing the surface area of the micro - heater and thermistor, thereby accelerating the heat exchange efficiency with gas molecules and achieving the purpose of improving the sensitivity of the device. In addition, the increase in surface area enables more heat generated by the heating element to act on the surface of the device, that is, it is beneficial to improving the thermal utilization rate of the heating element, thereby playing a role in reducing power consumption. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] 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 drawings required for use in the description of the embodiments or the prior art.

[0029] Figure 1 It is a schematic flow chart of the manufacturing method of the MEMS thermal - temperature - difference type flow sensor disclosed in the embodiments of the present invention;

[0030] Figure 2a It is a schematic cross - sectional structure diagram of the structure obtained in step S1 in the preparation method disclosed in the embodiments of the present invention;

[0031] Figure 2b It is a schematic three - dimensional structure diagram of the structure obtained in step S1 in the preparation method disclosed in the embodiments of the present invention;

[0032] Figure 3a It is a schematic cross - sectional structure diagram of the structure obtained in step S2 in the preparation method disclosed in the embodiments of the present invention;

[0033] Figure 3b It is a schematic three - dimensional structure diagram of the structure obtained in step S2 in the preparation method disclosed in the embodiments of the present invention;

[0034] Figure 4a It is a schematic cross - sectional structure diagram of the structure obtained in step S3 in the preparation method disclosed in the embodiments of the present invention;

[0035] Figure 4b It is a schematic three - dimensional structure diagram of the structure obtained in step S3 in the preparation method disclosed in the embodiments of the present invention;

[0036] Figure 5a It is a schematic cross - sectional structure diagram of the structure obtained in step S4 in the preparation method disclosed in the embodiments of the present invention;

[0037] Figure 5b It is a schematic three - dimensional structure diagram of the structure obtained in step S4 in the preparation method disclosed in the embodiments of the present invention;

[0038] In the figures, 10 is a silicon substrate; 20 is a dielectric layer; 30 is a micro - heater; 40 is a thermistor; 50 is platinum black; 60 is a heat - insulating cavity. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0039] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention.

[0040] The present invention provides a MEMS thermal temperature difference type flow sensor, as Figure 5a and Figure 5b shown, including:

[0041] A substrate 10, provided with a heat insulation cavity 60;

[0042] A dielectric layer 20, formed on the upper surfaces of the substrate 10 and the heat insulation cavity 60;

[0043] A micro heater 30 and a thermistor 40, formed on the upper surface of the dielectric layer 20, and the micro heater 30 and the thermistor 40 are partially located above the heat insulation cavity 60;

[0044] Platinum black 50, covering at least part of the micro heater 30 and the thermistor 40.

[0045] Specifically, the substrate 10 is a common semiconductor substrate, including but not limited to one of a silicon substrate, a germanium substrate, a SOI substrate, and a GeOI substrate; in the embodiment of the present invention, the substrate 10 is a double-sided polished single-crystalline silicon substrate.

[0046] Specifically, the heat insulation cavity 60 is formed by recessing a certain depth from the upper surface of the substrate 10, or is formed by penetrating the substrate 10 from the lower surface of the substrate 10; in the embodiment of the present invention, the heat insulation cavity 60 is formed by penetrating the substrate 10 from the lower surface of the substrate 10.

[0047] Specifically, the material of the dielectric layer 20 is one or a combination of two of silicon oxide and silicon nitride; in the embodiment of the present invention, the dielectric layer 20 is composed of a composite of silicon oxide and silicon nitride.

[0048] Specifically, the number of thermistors 40 is two, symmetrically distributed on both sides of the micro heater 30; the materials of the micro heater 30 and the thermistor 40 are platinum or titanium / platinum or chromium / platinum. In this embodiment, the materials of the micro heater 30 and the thermistor 40 are both platinum.

[0049] It should be noted that part of the micro heater 30 and the thermistor 40 are used as electrodes to achieve electrical connection with an external circuit during application.

[0050] It should be noted that the platinum black 50 is in a loose microporous shape, which is beneficial to increasing the surface areas of the micro heater 30 and the thermistor 40, thereby accelerating the heat exchange efficiency with gas molecules and improving the sensitivity of the flow sensor; in addition, the increase in the surface area is also beneficial to improving the thermal utilization rate of the micro heater 30, thereby playing a role in reducing power consumption.

[0051] The present invention also provides a manufacturing method for the above-mentioned MEMS thermal difference type flow sensor, as Figure 1 shown, including the following steps:

[0052] S1. Provide a substrate 10, and form a dielectric layer 20 on the substrate 10, as Figure 2a and Figure 2b shown;

[0053] Specifically, the substrate 10 adopts a common semiconductor substrate, including but not limited to one of a silicon substrate, a germanium substrate, an SOI substrate, and a GeOI substrate; in an embodiment of the present invention, the substrate 10 adopts a double-sided polished single-crystal silicon substrate.

[0054] Specifically, the material of the dielectric layer 20 is one or a combination of two of silicon oxide and silicon nitride. Among them, silicon oxide can be formed by thermal oxidation, low-pressure chemical vapor deposition, or plasma chemical vapor deposition methods, and silicon nitride can be formed by low-pressure chemical vapor deposition or plasma chemical vapor deposition methods; in an embodiment of the present invention, the dielectric layer 20 is composed of a composite of silicon oxide and silicon nitride, wherein silicon oxide is formed by thermal oxidation, and silicon nitride is formed by low-pressure chemical vapor deposition.

[0055] S2. Form a micro-heater 30 and a thermistor 40 on the dielectric layer 20, as Figure 3a and 3b shown;

[0056] Specifically, the number of thermistors 40 is two, symmetrically distributed on both sides of the micro-heater 30; the materials of the micro-heater 30 and the thermistor 40 are platinum or titanium / platinum or chromium / platinum, and are formed by a lift-off process, or by a method of sputtering or evaporation followed by etching; in an embodiment of the present invention, the materials of the micro-heater 30 and the thermistor 40 are both platinum and are formed by a lift-off process.

[0057] S3. Form platinum black 50 on at least part of the micro-heater 30 and the thermistor 40, as Figure 4a and Figure 4b shown;

[0058] Specifically, platinum black 50 is formed by electroplating; the porous structure of platinum black 50 is beneficial to increasing the surface area of the micro-heater 30 and the thermistor 40, thereby accelerating the heat exchange efficiency with gas molecules and improving the sensitivity of the flow sensor; in addition, the increase in surface area is also beneficial to improving the thermal utilization rate of the micro-heater 30, thereby playing a role in reducing power consumption.

[0059] S4. Release the substrate 10 on the lower surface of the substrate 10 to form a heat-insulating cavity 60, as Figure 5a and 5b shown;

[0060] Specifically, the substrate 10 can be released by dry etching or wet etching to form the heat insulation cavity 60, and the cross-sectional shape of the heat insulation cavity 60 is rectangular or trapezoidal; in the embodiment of the present invention, the TMAH anisotropic wet etching method is adopted to form the heat insulation cavity 60 with a trapezoidal cross-section.

[0061] The thermal differential flow sensor manufactured based on MEMS technology in the present invention has the advantages of small volume, high precision, fast response speed, etc., and the preparation process is simple, with strong controllability and high process compatibility; in the present invention, platinum black is formed on the micro heater and thermistor of the flow sensor by MEMS process, which is beneficial to increasing the surface areas of the micro heater and thermistor, thereby accelerating the heat exchange efficiency with gas molecules and achieving the purpose of improving the sensitivity of the device; in addition, the increase in surface area enables the heat generated by the heating element to act more on the surface of the device, that is, it is beneficial to improving the thermal utilization rate of the heating element, thereby playing a role in reducing power consumption.

[0062] Therefore, the present invention effectively overcomes various disadvantages in the prior art and has high industrial utilization value.

[0063] The above description of the disclosed embodiments enables those skilled in the art to implement or use the present invention. Various modifications to these embodiments will be obvious to those skilled in the art, and the general principles defined herein can be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention will not be limited to these embodiments shown herein, but rather to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A MEMS thermal temperature difference type flow sensor, characterized in that Comprising: A substrate provided with a heat-insulating cavity; A dielectric layer formed on the upper surfaces of the substrate and the heat-insulating cavity; A micro-heater and a thermistor formed on the upper surface of the dielectric layer, and the micro-heater and the thermistor are partially located above the heat-insulating cavity; Platinum black, which forms a microporous structure by electroplating and covers at least part of the micro-heater and the thermistor.

2. The MEMS thermal temperature difference type flow sensor according to claim 1, characterized in that, The substrate is a silicon substrate or a germanium substrate.

3. A MEMS thermal temperature difference type flow sensor according to claim 1 or 2, characterized in that, The substrate is a SOI substrate or a GeOI substrate.

4. A MEMS thermal temperature difference type flow sensor according to claim 1, wherein The heat-insulating cavity is formed by indenting a certain depth from the upper surface of the substrate, or by penetrating the substrate from the lower surface of the substrate.

5. A MEMS thermal temperature difference type flow sensor according to claim 1, characterized in that, The material of the dielectric layer is one or a combination of two of silicon oxide and silicon nitride.

6. The MEMS thermal temperature difference type flow sensor according to claim 1, wherein The number of the thermistors is two, symmetrically distributed on both sides of the micro-heater.

7. The MEMS thermal temperature difference type flow sensor according to claim 1, wherein The materials of the micro-heater and the thermistor are platinum or titanium / platinum or chromium / platinum.

8. A manufacturing method of the MEMS thermal temperature difference type flow sensor according to claim 1, characterized in that, Including the following steps: S1. Provide a substrate and form a dielectric layer on the substrate; S2. Form a micro-heater and a thermistor on the dielectric layer; S3. Form platinum black with a microporous structure on at least part of the micro-heater and the thermistor by electroplating; S4. Release the substrate to form a heat-insulating cavity.

9. The manufacturing method of a MEMS thermal temperature difference type flow sensor according to claim 8, characterized in that, The materials of the micro-heater and the thermistor are both platinum, formed by a lift-off process, or formed by a method of sputtering first and then etching or evaporating first and then etching.

10. The manufacturing method of a MEMS thermal temperature difference type flow sensor according to claim 8, characterized in that, The heat-insulating cavity is formed by releasing the substrate by dry etching or wet etching.

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