Miniature capacitive pressure sensor and method of making the same

Abstract

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

Description

Technical Field

[0001] This invention relates to the field of sensor technology, and in particular to a miniature capacitive pressure sensor and its fabrication method. Background Technology

[0002] A sensor is a detection device that can sense the information being measured and transform that information into an electrical signal or other required form of output according to a certain rule, in order to meet the requirements of information transmission, processing, storage, display, recording, and control. The development and application of sensors have given objects senses such as touch, taste, and smell, making them feel alive; sensors are an extension of human senses.

[0003] Based on the detected variable, application scenario, and nature of the output, sensors can be subdivided into many types. Among them, pressure sensors are used to measure the pressure of liquids and gases, while capacitive pressure sensors are pressure sensors that use capacitance as a sensitive element, converting the measured pressure into a change in capacitance. Capacitive pressure sensors typically use a metal thin film or a metal-plated thin film as one electrode of a capacitor. When the thin film senses pressure and deforms, the distance between the thin film and the fixed electrode changes, resulting in a change in capacitance. This change is then transmitted through a measuring circuit to output an electrical signal that is proportional to the voltage.

[0004] However, when the diaphragm of a traditional capacitive pressure sensor is deformed under pressure, the capacitance changes unevenly at different points because the deformation is large at the center and small at the edges. This results in poor linearity and sensitivity of the sensor. Summary of the Invention

[0005] This invention provides a miniature capacitive pressure sensor and its fabrication method, which can overcome the technical problems existing in the prior art and improve the linearity and sensitivity of the miniature capacitive pressure sensor.

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

[0007] This invention provides a miniature capacitive pressure sensor, comprising, 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 sealed cavity formed by bonding the single-crystal silicon thin film layer and the silicon dioxide insulating layer together.

[0008] This invention also provides a method for fabricating a miniature capacitive pressure sensor, comprising:

[0009] A silicon dioxide insulating layer is oxidized on a single-crystal silicon substrate to serve as the first substrate;

[0010] A concave arc-shaped cavity is etched into the silicon dioxide insulating layer of the first substrate;

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

[0012] An upper electrode metal layer is formed 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 miniature capacitive pressure sensor and its fabrication method provided in this invention, since the single-crystal silicon thin film layer and the silicon dioxide insulating layer are bonded together to form a concave arc-shaped sealed cavity, the problem of large deformation at the center and small deformation at the edges of the thin film no longer exists when the thin film of the miniature capacitive pressure sensor is deformed under pressure. The capacitance at each point changes and the displacement is equal, which greatly improves the linearity of the miniature capacitive pressure sensor. In addition, a very small pressure can cause a large deformation and capacitance change, which greatly improves the sensitivity of the miniature capacitive pressure sensor. Attached Figure Description

[0015] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

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

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

[0018] Figure 3 A flowchart illustrating the fabrication method of the miniature capacitive pressure sensor provided in an embodiment of the present invention;

[0019] Figure 4 A schematic diagram illustrating the specific process of etching a concave arc-shaped cavity on the silicon dioxide insulating layer of the first substrate during the fabrication of the miniature capacitive pressure sensor provided in this embodiment of the invention.

[0020] Figure 5 A schematic diagram illustrating the specific process of forming a concave arc-shaped sealed cavity during the fabrication of the miniature capacitive pressure sensor provided in this embodiment of the invention;

[0021] Figure 6This is a schematic diagram illustrating the process of forming upper and lower electrode metal layers during the fabrication of the miniature capacitive pressure sensor provided in this embodiment of the invention.

[0022] Figure 7 This is a schematic diagram illustrating the process of forming a uniform thin-film insulating layer during the fabrication of a miniature capacitive pressure sensor according to another embodiment of the present invention. Detailed Implementation

[0023] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0024] Furthermore, the terms "first," "second," etc., are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. In the following descriptions of embodiments, "a plurality of" means two or more, unless otherwise explicitly defined.

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

[0026] Figure 1 This is a schematic diagram of the structure of a miniature capacitive pressure sensor provided in an embodiment of the present invention. Figure 1 As shown, the sensor comprises, 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 sealed 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 possesses excellent mechanical properties and is widely used in miniature pressure sensors. The single-crystal silicon thin film layer 401 can pick up external sound vibration signals, realizing the function of receiving ultrasonic signals. Under the drive of an external AC voltage, the single-crystal silicon thin film layer 401 vibrates, generating sound wave signals. In other words, under the action of external sound pressure, the single-crystal silicon thin film layer 401 deforms, and its capacitance changes. By measuring the capacitance value, the sound pressure can be detected.

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

[0029] The upper and lower electrode metal layers can be Al / Si alloys, Ti / Ni / Ag alloys, or Al / Cu alloys, which have good conductivity and are used to collect moving charges to connect to external circuits. The upper electrode metal layer 42 serves as the top layer of the sensor, and it is formed with the single-crystal silicon thin film layer 401 through an ohmic contact. The lower electrode metal layer 43 is located at the bottom layer of the sensor and is formed with the single-crystal silicon substrate 101 through an ohmic contact. It corresponds to the upper electrode metal layer 42 and forms the other electrode of the capacitor.

[0030] A vacuum cavity 103 is formed between the monocrystalline 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 monocrystalline silicon thin film layer 401 and the bottom monocrystalline silicon substrate 101, preventing the upper and lower electrodes from breaking down and short-circuiting.

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

[0032] Furthermore, to increase the adhesion of the metal to the thin film surface, improve the reliability of the device, and simultaneously regulate the driving voltage, a uniform thin film insulating layer 41 is also included between the upper electrode metal layer 42 and the single-crystal silicon thin film layer 401, such as... Figure 2 The diagram shown is a structural schematic 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 flowchart illustrating the fabrication method of the miniature capacitive pressure sensor provided in this embodiment of the invention is shown below. Figure 3 As shown, the specific steps of this method include:

[0034] S1: An insulating layer 102 of silicon dioxide is oxidized on a single-crystal silicon substrate 101 as a first substrate;

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

[0036] S3: Bond 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 sealed cavity;

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

[0038] S5: A lower electrode metal layer 43 is formed on the single-crystal silicon substrate 101 of the first substrate.

[0039] Figure 4 A schematic diagram illustrating the specific process of etching a concave arc-shaped cavity on the silicon dioxide insulating layer of the first substrate during the fabrication of the miniature capacitive pressure sensor provided in this embodiment of the invention is shown below. Figure 4 As shown, the process specifically includes:

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

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

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

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

[0044] 4c: Spherical voids 103 are isotropically etched into the silicon dioxide insulating layer 102 of the first substrate through the small hole 3;

[0045] Isotropic etching refers to etching at the same rate in all directions, which ensures that the etched voids are nearly spherical.

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

[0047] This process utilizes a mask layer and pinholes to guide the etchant for precise etching, ultimately forming the desired concave arc-shaped cavity on the silicon dioxide insulating layer 102. This design not only improves the sensor's sensitivity and stability but also facilitates the realization of smaller and more precise sensors. This precise etching process ensures that the sensor's vacuum cavity has uniform thickness and shape, thereby improving the sensor's overall performance and reliability.

[0048] Figure 5 This is a schematic diagram illustrating the specific process of forming a concave arc-shaped sealed cavity during the fabrication of the miniature capacitive pressure sensor provided in this embodiment of the invention, as shown below. Figure 5 As shown, the process specifically includes:

[0049] 5a: A silicon dioxide insulating layer 402 is oxidized on a single-crystal silicon substrate 403 as a second substrate;

[0050] 5b: A single-crystal silicon thin film layer 401 is formed on the silicon dioxide insulating layer 402 of the second substrate;

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

[0052] 5d: Remove the second substrate, and the monocrystalline silicon thin film layer 401 forms a variable film;

[0053] 5e: The monocrystalline silicon thin film layer 401 is shaped so that the cavity between the monocrystalline silicon thin film layer 401 and the silicon dioxide insulating layer 402 of the first substrate forms a concave arc-shaped sealed cavity.

[0054] Figure 6 This is a schematic diagram illustrating the formation of upper and lower electrode metal layers during the fabrication of the miniature capacitive pressure sensor provided in an embodiment of the present invention. Figure 6 As shown in Figure a, a metal layer is sputtered onto a single-crystal silicon thin film 401 using an electron beam evaporation method, followed by photolithography to form the upper electrode metal layer 42; as shown in Figure a. Figure 6 As shown in Figure b, a lower electrode metal layer 43 is formed by sputtering a metal layer on the single-crystal silicon substrate 101 of the first substrate using an electron beam evaporation method.

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

[0056] like Figure 7 As shown in Figure a, a silicon dioxide insulating layer 41 is formed on the exposed monocrystalline silicon thin film layer 401 using chemical vapor deposition. Chemical vapor deposition is a commonly used thin film deposition technique that generates a thin film on the substrate surface through a chemical reaction. This method can form a uniform and high-quality silicon dioxide insulating layer 41 on the monocrystalline 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 presence of the silicon dioxide insulating layer 41 also ensures the insulation between the two and prevents electrical short circuits.

[0058] The miniature capacitive pressure sensor prepared by the above method has the following advantages: since the vacuum cavity 103 between the single-crystal silicon thin film layer 401 and the silicon dioxide insulating layer 102 is a concave arc-shaped sealed cavity, when the thin film of the miniature capacitive pressure sensor is deformed under pressure, the problem of large deformation at the center and small deformation at the edge of the thin film no longer exists. The capacitance at each point changes and the displacement is equal, which greatly improves the linearity of the miniature capacitive pressure sensor. In addition, a very small pressure can cause a large deformation and capacitance change, which greatly improves the sensitivity of the miniature capacitive pressure sensor.

[0059] Other embodiments of the invention will readily occur to those skilled in the art upon consideration of the specification and practice of the invention disclosed herein. This invention is intended to cover any variations, uses, or adaptations of the invention that follow the general principles of the invention and include common knowledge or customary techniques in the art not disclosed herein. The specification and examples are to be considered exemplary only, and the true scope and spirit of the invention are indicated by the following claims.

[0060] It should be understood that the present invention is not limited to the precise structure described above and shown in the accompanying drawings, and various modifications and changes can be made without departing from its scope. The scope of the invention is limited only by the appended claims.

Claims

1. A micro-capacitive pressure sensor, characterized by, From top to bottom, it includes: upper electrode metal layer, single crystal silicon thin film layer, vacuum cavity with uniform thickness and shape, silicon dioxide insulating layer, single crystal silicon substrate and lower electrode metal layer; 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, when the thin film of the micro capacitive pressure sensor is deformed under pressure, the capacitances of each point between the center and the edge of the thin film change, and the displacement amounts are equal.

2. The micro-capacitive pressure sensor according to claim 1, characterized in that, The upper electrode metal layer and the single crystal silicon thin film layer further include a uniform thin film insulating layer.

3. A method of manufacturing a micro-capacitive pressure sensor as claimed in claim 1 or 2, characterized in that, It includes: Oxidizing a silicon dioxide insulating layer on a single crystal silicon substrate as a first substrate; Coating a mask layer on the silicon dioxide insulating layer of the first substrate; Etching a small hole on the mask layer; using isotropic etching to form a spherical cavity on the silicon dioxide insulating layer of the first substrate through the small hole; removing the mask layer, and a concave arc-shaped cavity is formed on the silicon dioxide insulating layer of the first substrate; Bonding a 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, when the thin film of the prepared micro capacitive pressure sensor is deformed under pressure, the capacitances of each point between the center and the edge of the thin film change, and the displacement amounts are equal; Forming an upper electrode metal layer on the single crystal silicon thin film layer; Forming a lower electrode metal layer on the single crystal silicon substrate of the first substrate.

4. The method of claim 3, wherein, The bonding of 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 the 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 and the silicon dioxide insulating layer of the first substrate together; Removing the second substrate, and the single crystal silicon thin film layer forms a variable diaphragm; Shaping the single crystal silicon thin film layer to form a concave arc-shaped closed cavity between the single crystal silicon thin film layer and the silicon dioxide insulating layer of the first substrate.

5. The method of claim 3, wherein, 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 an electron beam evaporation method, and then photoetching the metal layer to form the upper electrode metal layer.

6. The method of claim 3, wherein, 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 an electron beam evaporation method to form the lower electrode metal layer.

7. The method according to any one of claims 3 to 6, characterized in that, Before forming the upper electrode metal layer on the single crystal silicon thin film layer, it further includes: oxidizing a uniform thin film insulating layer on the single crystal silicon thin film layer.

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