Miniature capacitive pressure sensor and preparation method thereof

Abstract

The invention discloses a miniature capacitive pressure sensor and a preparation method thereof, and relates to the technical field of sensors, the sensor sequentially comprises an upper electrode metal layer, a monocrystalline silicon thin film layer, a vacuum cavity, a silicon dioxide insulating layer, a monocrystalline silicon substrate and a lower electrode metal layer from top to bottom; wherein the vacuum cavity is a concave arc-shaped closed cavity formed by bonding a monocrystalline silicon thin film layer and a silicon dioxide insulating layer together; the structure greatly improves the linearity and sensitivity of the miniature capacitive pressure sensor.

Description

Technical Field

[0001] The present invention relates to the field of sensor technology, and in particular to a miniature capacitive pressure sensor and a preparation method thereof. Background Art

[0002] A sensor is a detection device that can sense the information being measured and convert the sensed information into electrical signals or other required forms of information output according to certain rules to meet the requirements of information transmission, processing, storage, display, recording and control. The application and development of sensors have given objects senses such as touch, taste and smell, making objects come alive. Sensors are an extension of the five senses of human beings.

[0003] Sensors can be subdivided into many types according to the detected variables, application scenarios, the nature of the output, etc. Among them, pressure sensors are sensors used to measure the pressure of liquids and gases, while capacitive pressure sensors are pressure sensors that use capacitors as sensitive elements to convert the measured pressure into changes in capacitance. Capacitive pressure sensors generally use metal film or metal-plated film as an electrode of the capacitor. When the film deforms due to pressure, the distance between the film and the fixed electrode changes, thereby changing the capacitance formed. The measuring circuit can output an electrical signal that is related to the voltage.

[0004] However, when the film of a traditional capacitive pressure sensor is deformed by pressure, the capacitance changes unevenly at each point because the center of the film changes more and the edges change less, resulting in poor linearity and sensitivity of the sensor. Summary of the invention

[0005] The embodiment of the present invention provides a micro capacitive pressure sensor and a method for preparing the same, which can overcome the technical problems existing in the above-mentioned prior art and improve the linearity and sensitivity of the micro capacitive pressure sensor.

[0006] To achieve the above purpose, the technical solution adopted by the present invention is as follows:

[0007] An embodiment of the present invention provides a miniature capacitive pressure sensor, which includes, from top to bottom, an upper electrode metal layer, a single crystal silicon thin film layer, a vacuum cavity, a silicon dioxide insulating layer, a single crystal silicon substrate and a lower electrode metal layer; wherein the vacuum cavity is a concave arc-shaped closed cavity formed by bonding the single crystal silicon thin film layer and the silicon dioxide insulating layer together.

[0008] The embodiment of the present invention further provides a method for preparing a micro capacitive pressure sensor, comprising:

[0009] Oxidizing a silicon dioxide insulating layer on a single crystal silicon substrate as a first substrate;

[0010] Etching a concave arc-shaped cavity on the silicon dioxide insulating layer of the first substrate;

[0011] Bonding the single crystal silicon thin film layer and the silicon dioxide insulating layer of the first substrate together to form a concave arc-shaped closed cavity;

[0012] forming an upper electrode metal layer on the single crystal silicon thin film layer;

[0013] A lower electrode metal layer is formed on the single crystal silicon substrate of the first substrate.

[0014] In the micro-capacitive pressure sensor and its preparation method provided by the embodiments of the present invention, since the single crystal silicon film layer and the silicon dioxide insulating layer are bonded together to form a concave arc-shaped closed cavity, when the film of the micro-capacitive pressure sensor is deformed under pressure, there is no longer the problem of large deformation in the center of the film and small change at the edge. The capacitance at each point changes and the displacement is equal, which greatly improves the linearity of the micro-capacitive pressure sensor. In addition, very small pressure can cause large deformation and capacitance changes, which greatly improves the sensitivity of the micro-capacitive pressure sensor. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative labor.

[0016] Figure 1 A schematic diagram of the structure of a micro capacitive pressure sensor provided in an embodiment of the present invention;

[0017] Figure 2 A schematic structural diagram of a micro capacitive pressure sensor (with a uniform thin film insulating layer) provided in another embodiment of the present invention;

[0018] Figure 3 A flow chart of a method for preparing a micro capacitive pressure sensor provided by an embodiment of the present invention;

[0019] Figure 4 A schematic diagram of a specific process of etching a concave arc-shaped cavity on a silicon dioxide insulating layer of a first substrate when preparing a micro capacitive pressure sensor provided by an embodiment of the present invention;

[0020] Figure 5 A schematic diagram of a specific process of forming a concave arc-shaped closed cavity when preparing a miniature capacitive pressure sensor provided by an embodiment of the present invention;

[0021] Figure 6A schematic diagram of the process of forming upper and lower electrode metal layers when preparing a micro capacitive pressure sensor provided by an embodiment of the present invention.

[0022] Figure 7 A schematic diagram of a process for forming a uniform thin film insulating layer when preparing a micro capacitive pressure sensor provided by another embodiment of the present invention. DETAILED DESCRIPTION

[0023] In order to make the purpose, technical solution and advantages of the embodiments of the present invention clearer, the technical solution in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0024] In addition, the terms "first", "second", etc. are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of technical features indicated. In the description of the following embodiments, the meaning of "multiple" is two or more, unless otherwise clearly and specifically defined.

[0025] The following specific embodiments may be combined with each other, and the same or similar concepts or processes may not be described in detail in some embodiments. To make the technical solution of the present invention clearer, the embodiments of the present invention are described in detail below in conjunction with the accompanying drawings.

[0026] Figure 1 The schematic diagram of the structure of the micro capacitive pressure sensor provided by the embodiment of the present invention is shown in FIG. Figure 1 As shown, the sensor includes, from top to bottom, an upper electrode metal layer 42, a single crystal silicon thin film layer 401, a vacuum cavity 103, a silicon dioxide insulating layer 102, a single crystal silicon substrate 101 and a lower electrode metal layer 43; wherein the vacuum cavity 103 is a concave arc-shaped closed cavity formed by bonding the single crystal silicon thin film layer 401 and the silicon dioxide insulating layer 102 together.

[0027] The single crystal silicon thin film layer 401 is a highly doped material. As a deformation material, it has good mechanical properties and is widely used in micro pressure sensors. The single crystal silicon thin film layer 401 can pick up external sound vibration signals and realize the reception function of ultrasonic signals; under the drive of external AC voltage, the single crystal silicon thin film layer 401 vibrates and generates sound wave signals, that is, under the action of external sound pressure, the single crystal silicon thin film layer 401 will deform and the capacitance value will change. The purpose of detecting sound pressure is achieved by measuring the capacitance value.

[0028] The single crystal silicon substrate 101 serves as the basic support layer of the sensor, providing mechanical support and thermal stability, thereby ensuring the overall structural stability of the sensor.

[0029] The upper and lower electrode metal layers can be Al / Si alloy, Ti / Ni / Ag alloy or Al / Cu alloy, which have good conductivity and are used to collect mobile charges to connect external circuits. The upper electrode metal layer 42 is the top layer of the sensor, and is in ohmic contact with the single crystal silicon thin film layer 401; the lower electrode metal layer 43 is located at the bottom layer of the sensor, and is in ohmic contact with the single crystal silicon substrate 101, and corresponds to the upper electrode metal layer 42 to form the other pole of the capacitor.

[0030] A vacuum cavity 103 is formed between the single crystal silicon thin film layer 401 and the silicon dioxide insulating layer 102. The silicon dioxide insulating layer 102 at the bottom of the vacuum cavity 103 helps to isolate the top single crystal silicon thin film layer 401 and the bottom single crystal silicon substrate 101 to prevent the upper and lower electrodes from being short-circuited due to breakdown.

[0031] Since the vacuum cavity 103 between the single crystal silicon film layer 401 and the silicon dioxide insulating layer 102 is a concave arc-shaped closed cavity, when the film of the micro-capacitive pressure sensor is deformed under pressure, there is no longer the problem of large deformation in the center of the film and small change at the edge. The capacitance at each point changes and the displacement is equal, which greatly improves the linearity of the micro-capacitive pressure sensor. In addition, very small pressure can cause large deformation and capacitance changes, which greatly improves the sensitivity of the micro-capacitive pressure sensor.

[0032] Furthermore, in order to increase the adhesion of the metal on the film surface, improve the reliability of the device, and adjust the driving voltage, a uniform thin film insulating layer 41 is further included between the upper electrode metal layer 42 and the single crystal silicon film layer 401, such as Figure 2 , which is a schematic structural diagram of a miniature capacitive pressure sensor (with a uniform thin film insulating layer) provided in another embodiment of the present invention.

[0033] Figure 3 A flow chart of a method for preparing a micro capacitive pressure sensor according to an embodiment of the present invention is shown in FIG. Figure 3 As shown, the method specifically comprises the following steps:

[0034] S1: Oxidizing a silicon dioxide insulating layer 102 on a single crystal silicon substrate 101 as a first substrate;

[0035] S2: etching a concave arc-shaped cavity on the silicon dioxide insulating layer 102 of the first substrate;

[0036] S3: bonding the single crystal silicon thin film layer 401 and the silicon dioxide insulating layer 102 of the first substrate together to form a concave arc-shaped closed cavity;

[0037] S4: forming an upper electrode metal layer 42 on the single crystal silicon thin film layer 401;

[0038] S5: forming a lower electrode metal layer 43 on the single crystal silicon substrate 101 of the first substrate.

[0039] Figure 4 A schematic diagram of a specific process of etching a concave arc-shaped cavity on the silicon dioxide insulating layer of the first substrate when preparing the micro capacitive pressure sensor provided by an embodiment of the present invention, as shown in FIG. Figure 4 As shown, the process specifically includes:

[0040] 4a: coating a mask layer 2 on the silicon dioxide insulating layer 102 of the first substrate;

[0041] The mask layer is usually made of photoresist or other appropriate materials, and its function is to protect areas that do not need to be etched during the etching process.

[0042] 4b: Etching a small hole 3 on the mask layer;

[0043] This small hole is the channel for gas or liquid etchant to enter during the subsequent etching process. The position and size of the small hole need to be precisely controlled to ensure that the final concave arc-shaped cavity meets the design requirements.

[0044] 4c: isotropically etching a spherical cavity 103 on the silicon dioxide insulating layer 102 of the first substrate through the small hole 3;

[0045] Isotropic etching means that the etching rate is the same in all directions, which ensures that the shape of the etched cavity is close to a perfect sphere.

[0046] 4d: The mask layer 2 is removed, and a concave arc-shaped cavity is formed on the silicon dioxide insulating layer 102 of the first substrate.

[0047] This process method uses a mask layer and a small hole to guide the etchant to perform precise etching, and finally forms the required concave arc-shaped cavity on the silicon dioxide insulating layer 102. This design not only improves the sensitivity and stability of the sensor, but also helps to achieve a smaller size and higher precision sensor. Through this precise etching process, it can be ensured that the vacuum cavity of the sensor has a uniform thickness and shape, thereby improving the overall performance and reliability of the sensor.

[0048] Figure 5 A schematic diagram of a specific process of forming a concave arc-shaped closed cavity when preparing a micro capacitive pressure sensor provided by an embodiment of the present invention, as shown in FIG. Figure 5 As shown, the process specifically includes:

[0049] 5a: Oxidizing a silicon dioxide insulating layer 402 on a single crystal silicon substrate 403 as a second substrate;

[0050] 5b: forming a single crystal silicon thin film layer 401 on the silicon dioxide insulating layer 402 of the second substrate;

[0051] 5c: bonding the single crystal silicon thin film layer 401 to the silicon dioxide insulating layer 102 of the first substrate;

[0052] 5d: The second substrate is removed, and the single crystal silicon thin film layer 401 forms a variable membrane;

[0053] 5e: shaping the single crystal silicon thin film layer 401 so that the cavity between the single crystal silicon thin film layer 401 and the silicon dioxide insulating layer 402 of the first substrate forms a concave arc-shaped closed cavity.

[0054] Figure 6 Schematic diagram of forming upper and lower electrode metal layers when preparing the micro capacitive pressure sensor provided by an embodiment of the present invention. Figure 6 As shown in FIG. 1 , a metal layer is sputtered on the single crystal silicon film 401 by electron beam evaporation, and then the metal layer is photoetched to form an upper electrode metal layer 42; Figure 6 As shown in FIG. 2 b, a metal layer is sputtered on the single crystal silicon substrate 101 of the first substrate by electron beam evaporation to form a lower electrode metal layer 43.

[0055] Furthermore, in order to increase the adhesion of the metal on the film surface, improve the reliability of the device, and adjust the driving voltage, a uniform thin film insulating layer 41 is further included between the upper electrode metal layer 42 and the single crystal silicon thin film layer 401 .

[0056] like Figure 7 As shown in a, a silicon dioxide insulating layer 41 is formed on the exposed single crystal silicon thin film layer 401 by chemical vapor deposition; chemical vapor deposition is a commonly used thin film deposition technology that generates a thin film on the surface of a substrate through a chemical reaction. This method can form a uniform, high-quality silicon dioxide insulating layer 41 on the single crystal silicon thin film layer 401.

[0057] like Figure 7 As shown in b, an upper electrode metal layer 42 is formed on the silicon dioxide insulating layer 41 to ensure good electrical connection between the electrode metal layer and the single crystal silicon thin film layer 401. At the same time, the existence of the silicon dioxide insulating layer 41 also ensures the insulation between the two and prevents electrical short circuit.

[0058] The micro-capacitive pressure sensor prepared by the above method has a vacuum cavity 103 between the single-crystal silicon film layer 401 and the silicon dioxide insulating layer 102 as a concave arc-shaped closed cavity. When the film of the micro-capacitive pressure sensor is deformed by pressure, there is no longer the problem of large deformation in the center of the film and small change at the edge. The capacitance at each point changes and the displacement is equal, which greatly improves the linearity of the micro-capacitive pressure sensor. In addition, very small pressure can cause large deformation and capacitance changes, which greatly improves the sensitivity of the micro-capacitive pressure sensor.

[0059] Those skilled in the art will readily appreciate other embodiments of the present invention after considering the specification and practicing the invention disclosed herein. The present invention is intended to cover any variations, uses or adaptations of the present invention that follow the general principles of the present invention and include common knowledge or customary techniques in the art that are not disclosed by the present invention. The description and examples are to be considered exemplary only, and the true scope and spirit of the present invention is indicated by the following claims.

[0060] It should be understood that the present invention is not limited to the exact construction that has been described above and shown in the drawings, and that various modifications and changes may be made without departing from the scope thereof. The scope of the present invention is limited only by the appended claims.

Claims

1. A miniature capacitive pressure sensor, characterized in that: It includes, from top to bottom: an upper electrode metal layer, a single crystal silicon thin film layer, a vacuum cavity, a silicon dioxide insulating layer, a single crystal silicon substrate and a lower electrode metal layer; Wherein, the vacuum cavity is a concave arc-shaped closed cavity formed by bonding the single crystal silicon thin film layer and the silicon dioxide insulating layer together.

2. The structure according to claim 1, characterized in that: A uniform thin film insulating layer is also included between the upper electrode metal layer and the single crystal silicon thin film layer.

3. A method for preparing a micro capacitive pressure sensor, characterized in that: include: Oxidizing a silicon dioxide insulating layer on a single crystal silicon substrate as a first substrate; Etching a concave arc-shaped cavity on the silicon dioxide insulating layer of the first substrate; Bonding the single crystal silicon thin film layer and the silicon dioxide insulating layer of the first substrate together to form a concave arc-shaped closed cavity; forming an upper electrode metal layer on the single crystal silicon thin film layer; A lower electrode metal layer is formed on the single crystal silicon substrate of the first substrate.

4. The method according to claim 3, characterized in that The step of etching a concave arc-shaped cavity on the silicon dioxide insulating layer of the first substrate specifically comprises: coating a mask layer on the silicon dioxide insulating layer of the first substrate; etching a small hole in the mask layer; isotropically etching a spherical cavity on the silicon dioxide insulating layer of the first substrate through the small hole; After the mask layer is removed, a concave arc-shaped cavity is formed on the silicon dioxide insulating layer of the first substrate.

5. The method according to claim 3, characterized in that: The step of bonding the single crystal silicon thin film layer and the silicon dioxide insulating layer of the first substrate together to form a concave arc-shaped closed cavity specifically includes: Oxidizing a silicon dioxide insulating layer on a single crystal silicon substrate as a second substrate; forming a single crystal silicon thin film layer on the silicon dioxide insulating layer of the second substrate; Bonding the single crystal silicon thin film layer to the silicon dioxide insulating layer of the first substrate; The second substrate is removed, and the single crystal silicon thin film layer forms a variable membrane; The single crystal silicon thin film layer is shaped so that the cavity between the single crystal silicon thin film layer and the silicon dioxide insulating layer of the first substrate forms a concave arc-shaped closed cavity.

6. The method according to claim 3, characterized in that The forming of the upper electrode metal layer on the single crystal silicon thin film layer specifically includes: sputtering a metal layer on the single crystal silicon thin film by electron beam evaporation method, and then photolithography the metal layer to form the upper electrode metal layer.

7. The method according to claim 3, characterized in that The forming of the lower electrode metal layer on the single crystal silicon substrate of the first substrate specifically includes: sputtering a metal layer on the single crystal silicon substrate of the first substrate by electron beam evaporation to form the lower electrode metal layer.

8. The method according to any one of claims 3 to 7, characterized in that: Before forming the upper electrode metal layer on the single crystal silicon thin film layer, the method further includes: oxidizing a uniform thin film insulating layer on the single crystal silicon thin film layer.

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