Thin film pressure sensor for seawater depth measurement and preparation method thereof

Abstract

The invention discloses a thin film pressure sensor for seawater depth measurement and a preparation method thereof, the thin film pressure sensor comprises an elastic element, and the elastic element is sequentially provided with an insulating film layer, a functional film layer, a protective film layer and an electrode film layer; a convex island is arranged in the middle of the back cavity of the elastic element, and a chamfer is arranged on the peripheral side of the back cavity of the elastic element; and the functional film layer comprises a strain resistor for measuring pressure, a temperature measuring resistor and a sensitivity temperature compensation resistor. Through methods of elastic element material selection, convex island structure design, temperature compensation and the like, the corrosion resistance is improved, the sensitivity is improved, the nonlinearity is reduced, the precision is improved, the temperature drift is reduced, and the use requirement of deep sea long-time measurement is met.

Description

Technical Field

[0001] The present invention mainly relates to the technical field of pressure sensors, and in particular to a thin film pressure sensor for seawater depth measurement and a preparation method thereof. Background Art

[0002] Pressure sensors are often used for depth measurement of deep-sea long-term cruising equipment due to their mature production and preparation technology, high reliability and low cost. They can sense the current ocean depth of the equipment by measuring pressure and control the diving and surfacing of the equipment. At present, several commonly used pressure sensors have the following main disadvantages: The first is a ceramic capacitive sensor, which uses pressure to cause relative displacement of the ceramic flat diaphragm, and the capacitance of the capacitor changes accordingly. Ceramic capacitive sensors have a wide range and small temperature drift, but the circuit for detecting tiny capacitance changes is relatively complex, and the ability to resist harsh environments such as vibration and impact is poor. Although they can meet the requirements of seawater corrosion, they often break due to factors such as seawater undercurrents and impacts, and have low environmental reliability.

[0003] The second type is the silicon piezoresistive pressure sensor. The external pressure is transmitted to the medium silicone oil through the isolation diaphragm, and then to the pressure-sensitive chip inside the silicone oil. The change of the bridge of the pressure-sensitive chip reflects the current pressure. In order to meet the use requirements of the seawater environment, a corrugated diaphragm is gold-plated or a corrugated diaphragm made of tantalum alloy is used. In terms of structural materials, the isolation diaphragm is made of tantalum alloy, 316Ti, 316 stainless steel gold-plated, etc., and the shell is made of Hastelloy, 316L stainless steel, etc. to improve corrosion resistance. This packaging method requires the pressure ring, isolation diaphragm, and shell of the pressure-sensitive core to be welded together. The welding point is often prone to microbial corrosion, which leads to material degradation and weld cracking over a long period of time. In addition, the thickness of the isolation diaphragm is extremely thin, and pitting caused by long-term marine environment can easily cause it to fail.

[0004] The third type is a thin film pressure sensor. In terms of design, the relationship between the range and the thickness of the diaphragm is obtained by combining the theoretical formula of the flat diaphragm with the small disturbance theory, nonlinearity, overload capacity and other indicators. In the actual processing and preparation process, the influence of the chamfer of the edge of the back cavity of the elastic element cannot be ignored. If the chamfer is too small, it is easy to yield due to stress concentration. If the chamfer is too large, the tensile and compressive strains of the diaphragm are sacrificed and the sensitivity is reduced. In terms of design, traditional thin film pressure sensors rarely consider the impact of seawater corrosion on them. Long-term seawater corrosion will increase the diaphragm radius of the elastic element and reduce the diaphragm thickness. Summary of the invention

[0005] In view of the technical problems existing in the prior art, the present invention provides a thin film pressure sensor for seawater depth measurement with reduced nonlinearity and improved sensitivity, and a preparation method thereof.

[0006] In order to solve the above technical problems, the technical solution proposed by the present invention is: A thin film pressure sensor for seawater depth measurement comprises an elastic element, on which an insulating film layer, a functional film layer, a protective film layer and an electrode film layer are sequentially arranged; a convex island is arranged in the middle of a back cavity of the elastic element, and chamfers are arranged on the circumference of the back cavity of the elastic element; the functional film layer comprises a pressure measuring strain resistor, a temperature measuring resistor and a sensitivity temperature compensation resistor.

[0007] Preferably, the strain resistor comprises an external strain resistor and an internal strain resistor, the external strain resistor 3a is arranged in a region with maximum compressive strain, and the internal strain resistor is arranged in a region with maximum tensile strain.

[0008] Preferably, the external strain resistors and the internal strain resistors are symmetrically distributed on the surface of the functional film layer; the two external strain resistors and the two internal strain resistors form an open-loop Wheatstone bridge, and the series resistors compensate for the zero point of the sensor.

[0009] Preferably, the temperature measuring resistor and the sensitivity temperature compensation resistor are arranged in a non-strain area.

[0010] Preferably, the insulating film layer is a composite insulating dielectric film layer formed of Ta2O5 and SiO2.

[0011] The present invention also discloses a method for preparing a thin film pressure sensor for seawater depth measurement based on the above, including chamfering design: when chamfering, according to the maximum disturbance, maximum nonlinear error and maximum comprehensive stress formula, the nonlinearity and overload multiple design indicators are given to obtain the pressure range. P Diaphragm radius , Diaphragm thickness h The relationship between the maximum stress and the allowable stress is established; a finite element analysis model is established to analyze the maximum stress change under different chamfering conditions; the optimal design value of the chamfer is the chamfer size corresponding to the maximum stress being just the allowable stress.

[0012] Preferably, the corresponding formulas for maximum disturbance, maximum nonlinear error and maximum comprehensive stress are: Maximum disturbance The formula is:

[0013] in, P is the uniform pressure acting on the diaphragm, μ is the Poisson's ratio of the material, R 0 is the diaphragm radius, E is the elastic modulus of the material, h is the diaphragm thickness; Maximum nonlinear error The formula is:

[0014] Maximum comprehensive stress The formula is: .

[0015] Preferably, it also includes convex island design: establishing finite element analysis models with different convex island diameters to obtain radial stress and disturbance on the surface of the elastic element; substituting the disturbance value into the maximum nonlinear error formula to obtain the nonlinear design value at this time; the optimal design value of the convex island is the convex island diameter value corresponding to the nonlinear value that can significantly reduce the maximum tensile and compressive radial stresses under the premise of less sacrifice.

[0016] Preferably, the elastic element design includes: under the premise of meeting the design requirements, the thickness of the diaphragm h , diaphragm radius R 0 is as large as possible to minimize the impact of seawater corrosion on nonlinearity and sensitivity.

[0017] Preferably, it also includes strain resistor arrangement: establishing a finite element model of the elastic element, extracting radial strain, tangential strain and disturbance curves in the radial direction, and seeking The corresponding coordinate position on the diaphragm is the maximum nonlinear area and should be avoided when arranging the strain resistors; the strain resistors are arranged at the coordinate position corresponding to the maximum radial strain value.

[0018] Compared with the prior art, the advantages of the present invention are: The present invention increases a convex island in the back cavity of the elastic element, thereby greatly reducing the maximum disturbance under the condition of reducing the tensile and compressive stresses and making them very weak, that is, without basically sacrificing the sensitivity, thereby reducing the nonlinearity; under the influence of the chamfer and the convex island, the maximum stress area and the maximum nonlinear area of ​​the elastic element change, and the stress-strain and disturbance distribution are obtained by using the finite element simulation analysis method, and the resistor is arranged in the maximum stress area and avoids the maximum nonlinear area, thereby achieving the improvement of sensitivity and reducing the nonlinear requirements. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 It is a three-dimensional structural diagram of a thin film pressure sensor in an embodiment of the present invention.

[0020] Figure 2 It is a top view of the structure of the thin film pressure sensor in an embodiment of the present invention.

[0021] Figure 3 The open-loop Wheatstone bridge structure diagram of the strain resistor of the present invention.

[0022] Figure 4 is the thickness of the diaphragm of the present invention h , diaphragm radius R 0Change diagram.

[0023] Figure 5 2 is a graph showing the chamfer size and the maximum stress of the elastic element in the present invention.

[0024] Figure 6 Graph showing radial stress on the surface of the elastic element at different convex island diameters in the present invention.

[0025] Figure 7 This is a disturbance diagram of the elastic element surface at different convex island diameters in the present invention.

[0026] Figure 8 It is a curve diagram of radial strain, tangential strain and disturbance in the radial direction in the present invention.

[0027] Fig. 9 It is a schematic diagram of the division of compressive strain, tensile strain and non-strain areas in the present invention.

[0028] Legend: 1. Elastic element; 1a. Chamfer; 1b. Convex island; 2. Insulating film layer; 3. Functional film layer; 3a. External strain resistor; 3b. Internal strain resistor; 3c. Temperature measuring resistor; 3d. Sensitivity temperature compensation resistor; 4. Protective film layer; 5. Electrode film layer. DETAILED DESCRIPTION

[0029] The present invention is further described below in conjunction with the accompanying drawings and specific embodiments.

[0030] like Figure 1 As shown, the thin film pressure sensor for seawater depth measurement provided by the embodiment of the present invention mainly comprises an elastic element 1, on which an insulating film layer 2, a functional film layer 3, a protective film layer 4 and an electrode film layer 5 are sequentially arranged; The material of the elastic element 1 is a corrosion-resistant titanium alloy with high elastic limit strength, 316LV and the like; there are chamfers 1a and convex islands 1b in the back cavity of the elastic element 1; like Figure 2 As shown, the functional film layer 3 includes an external strain resistor 3a and an internal strain resistor 3b for measuring pressure, a temperature measuring resistor 3c (such as a platinum resistor), and a sensitivity temperature compensation resistor 3d; the platinum resistor is used for temperature measurement and temperature compensation of the sensor; the thin film strain resistor forms an open-loop Wheatstone bridge, which can be zero-point compensated by connecting resistors in series and parallel; the sensitivity temperature compensation resistor 3d reduces the change of sensitivity with temperature by means of voltage division; like Fig. 9 As shown, the external strain resistor 3a is arranged in the maximum compressive strain area, the internal strain resistor 3b is arranged in the maximum tensile strain area, the platinum resistor and the sensitivity temperature compensation resistor 3d are arranged in the non-strain area; the external strain resistor 3a and the internal strain resistor 3b are symmetrically distributed on the surface of the functional film layer 3. Fig. 9In the figure, A′ is the maximum compressive strain area (the junction between the middle part of the elastic element 1 and the circumferential annular ring), and the negative sign represents compression; B′ is the maximum tensile strain area (the junction between the elastic element 1 and the convex island 1b), and the positive sign represents compression; C′ has extremely small strain, which is generally called the non-strain area (the outside of the circumferential annular ring of the elastic element 1).

[0031] like Figure 3 As shown, two external strain resistors 3a and two internal strain resistors 3b form an open-loop Wheatstone bridge. When external pressure acts on the back cavity of the elastic element 1, the output of the Wheatstone bridge on the surface of the elastic element 1 changes, thereby realizing pressure value measurement. Resistors can be connected in series or in parallel at the C or D end to perform zero point compensation and thermal sensitivity drift compensation.

[0032] The outer strain resistor 3a and the inner strain resistor 3b are both fan-shaped resistor grids, and the long grids are arranged in the radial direction; the outer strain resistor 3a and the inner strain resistor 3b are made of titanium oxynitride, nickel-chromium alloy and its improved alloy, platinum-tungsten alloy or palladium-chromium alloy; The material of the sensitivity temperature compensation resistor 3d is nickel material with a large temperature coefficient. It is connected in series to the negative end of the bridge power supply. When the temperature rises, its resistance value increases, and the bridge power supply is reduced through the voltage division effect, and the output is reduced, which plays a sensitivity temperature compensation effect; The insulating film layer 2 is a composite insulating dielectric film layer formed by Ta2O5 and SiO2. First, a Ta2O5 film with a thermal expansion coefficient smaller than that of the elastic element 1 is deposited by focused oxygen ion beam sputtering, with a film thickness of 30nm; then, an SiO2 insulating film with a film thickness of 30nm is deposited by argon ion beam sputtering.

[0033] The present invention adds a convex island 1b in the back cavity of the elastic element 1, thereby greatly reducing its maximum disturbance under the condition of reducing the tensile and compressive stresses and their slightness, that is, basically without sacrificing sensitivity, thereby reducing nonlinearity; under the influence of the chamfer 1a and the convex island 1b, the maximum stress area and the maximum nonlinear area of ​​the elastic element 1 change, and the stress strain and disturbance distribution are obtained by using the finite element simulation analysis method, and the resistor is arranged in the maximum stress area and avoids the maximum nonlinear area, thereby achieving improved sensitivity and reduced nonlinear requirements.

[0034] In a specific embodiment, when chamfering 1a, according to the maximum disturbance, maximum nonlinear error and maximum comprehensive stress formula, the nonlinearity and overload multiple design indicators are given to obtain the pressure range. P Diaphragm radius , Diaphragm thickness h The relationship between the maximum stress and the maximum stress is established; a finite element analysis model is established to analyze the maximum stress change under different chamfer 1a conditions; the optimal design value of chamfer 1a is the chamfer 1a size corresponding to the maximum stress being the allowable stress. The specific process is: According to the maximum disturbance, maximum nonlinear error, and maximum comprehensive stress formula, the nonlinearity and overload multiple design indicators are given to obtain the pressure range. P With the slice radius , Diaphragm thickness h The specific process is: Maximum disturbance The formula is: (1) in, P is the uniform pressure acting on the diaphragm, μ is the Poisson's ratio of the material, R 0 is the diaphragm radius, E is the elastic modulus of the material, h is the diaphragm thickness.

[0035] The maximum nonlinear error formula is: (2) The maximum comprehensive stress formula is: (3) Given the nonlinearity and overload multiple design indicators, the pressure range can be obtained by combining (1), (2), and (3): P With the slice radius , Diaphragm thickness h relationship.

[0036] Finite element analysis models with different chamfer 1a sizes are established (since the presence of convex island 1b has little effect on the maximum stress, the simulation analysis model can be replaced by a flat diaphragm) to analyze the changes in maximum stress under different chamfer 1a conditions. Figure 5 It is a diagram showing the maximum stress variation of the elastic element 1 at different chamfer angles 1a. Figure 5 In the formula, the allowable stress is the elastic limit strength of the material of the elastic element 1 divided by the overload multiple.

[0037] The optimal design value of chamfer 1a is the size of chamfer 1a corresponding to the maximum stress being just equal to the allowable stress.

[0038] In a specific embodiment, when designing the convex island 1b, a finite element analysis model with different convex island 1b diameters is established to obtain the radial stress and disturbance on the surface of the elastic element 1; the disturbance value is substituted into the maximum nonlinear error formula to obtain the nonlinear design value at this time; the optimal design value of the convex island 1b is the convex island 1b diameter value corresponding to the nonlinear value that can significantly reduce the maximum tensile and compressive radial stress under the premise of less sacrifice. The specific process is: Finite element analysis models with different diameters of the convex island 1b are established, and radial stress and disturbance curves on the surface of the elastic element 1 are extracted along the radial direction. Figure 6is the radial stress diagram on the surface of the elastic element 1 for different diameters of the convex island 1b, Figure 7 The disturbance diagram of the surface of the elastic element 1 at different diameters of the convex island 1b is shown in Figure 2. Substituting the maximum disturbance value at different diameters of the convex island 1b into the maximum nonlinear error formula (2), the nonlinear design value at this time can be obtained.

[0039] The optimal design value of the diameter of the convex island 1b can significantly reduce its nonlinear value under the premise of sacrificing less maximum tensile and compressive radial stresses.

[0040] In a specific embodiment, under the premise of meeting the design requirements, the thickness of the diaphragm is h , diaphragm radius R 0 is as large as possible to minimize the impact of seawater corrosion on nonlinearity and sensitivity. The specific process is: like Figure 4 As shown in the figure, after the seawater corrodes the back cavity of the elastic element 1, the diaphragm radius becomes larger, the diaphragm thickness h becomes smaller, ΔR0 and Δh are the change dimensions of the diaphragm radius and diaphragm thickness respectively; and are the change rates of the diaphragm radius and diaphragm thickness respectively.

[0041] At the center of the diaphragm, radial strain The formula is: (4) Sensitivity is a linear function of strain. From the radial strain formula (4), we can see that the sensitivity change rate is: (5) From the maximum nonlinear error formula (2), we can know that the nonlinear change rate is: (6) because << , the above formula can be simplified to: (7) To minimize the rate of change of both nonlinearity and sensitivity, even if , Less affected by seawater corrosion. Under the premise of meeting the design requirements, the design h , R 0 value should be as large as possible. If h1=1mm, R 01 =7.5mm and h2=2mm, R 02 =15mm corresponding stress, strain value is the same, preferably (h2, R 02 )This set of data.

[0042] In a specific embodiment, the design idea of ​​the strain resistor arrangement area is: establish a finite element model of the elastic element 1, extract the radial strain, tangential strain, and disturbance curve in the radial direction, such as Figure 8 shown.

[0043] seek Corresponding to the coordinate position on the diaphragm, this position is the maximum nonlinear area and should be avoided when arranging resistors; The long grids of the inner and outer strain resistor grids are arranged radially. To ensure maximum sensitivity, the radial strain should be maximized. Figure 8 The black circle in the middle is the strain resistor arrangement area; The design idea of ​​the strain resistor layout area is to establish a finite element model of the elastic element 1, extract the radial strain, tangential strain and disturbance curve in the radial direction, and seek The corresponding coordinate position on the diaphragm is the maximum nonlinear area and should be avoided when arranging the strain resistors. The strain resistors are arranged at the coordinate position corresponding to the maximum radial strain value to ensure maximum sensitivity.

[0044] The thin film pressure sensor in the present invention adopts an elastic element 1 made of corrosion-resistant metal material. Based on the finite element analysis method, the influence of the back cavity chamfer 1a and the convex island 1b of the elastic element 1 on the sensitivity, nonlinearity and overload multiple of the sensor is optimized; by appropriately increasing the diaphragm thickness and diaphragm radius of the elastic element 1, the influence of seawater corrosion on the sensitivity and linearity is reduced; through the selection of materials for the elastic element 1, the design of the island membrane structure, temperature compensation and other methods, the corrosion resistance is improved, the sensitivity is increased, the nonlinearity is reduced, the accuracy is improved, and the temperature drift is reduced, so as to meet the use requirements of deep-sea long-term measurement.

[0045] In the description of the present invention, it should be understood that the terms "length", "width", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside" and "outside" etc., indicating orientations or positional relationships, are based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as a limitation on the present invention.

[0046] In addition, the terms "first" and "second" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features defined as "first" and "second" may explicitly or implicitly include one or more of the features. In the description of the present invention, the meaning of "plurality" is two or more, unless otherwise clearly and specifically defined.

[0047] In the present invention, unless otherwise clearly specified and limited, the terms "assemble", "connect", "connect", "fix" and the like should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium, it can be the internal connection of two elements or the interaction relationship between two elements. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0048] The above are only preferred embodiments of the present invention. The protection scope of the present invention is not limited to the above embodiments. All technical solutions under the concept of the present invention belong to the protection scope of the present invention. It should be pointed out that for ordinary technicians in this technical field, some improvements and modifications without departing from the principle of the present invention should be regarded as the protection scope of the present invention.

Claims

1. A thin film pressure sensor for seawater depth measurement, It is characterized in that The invention comprises an elastic element (1), on which an insulating film layer (2), a functional film layer (3), a protective film layer (4) and an electrode film layer (5) are sequentially provided; a convex island (1b) is provided in the middle of a back cavity of the elastic element (1), and a chamfer (1a) is provided on the peripheral side of the back cavity of the elastic element (1); the functional film layer (3) comprises a strain resistor for measuring pressure, a temperature measuring resistor (3c) and a sensitivity temperature compensation resistor (3d).

2. The thin film pressure sensor for seawater depth measurement according to claim 1, It is characterized in that The strain resistor comprises an external strain resistor (3a) and an internal strain resistor (3b); the external strain resistor (3a) is arranged in a region with maximum compressive strain, and the internal strain resistor (3b) is arranged in a region with maximum tensile strain.

3. The thin film pressure sensor for seawater depth measurement according to claim 2, It is characterized in that The external strain resistors (3a) and the internal strain resistors (3b) are symmetrically distributed on the surface of the functional film layer (3); the two external strain resistors (3a) and the two internal strain resistors (3b) form an open-loop Wheatstone bridge, and the series resistors compensate for the zero point of the sensor.

4. The thin film pressure sensor for seawater depth measurement according to claim 1, 2 or 3, It is characterized in that The temperature measuring resistor (3c) and the sensitivity temperature compensation resistor (3d) are arranged in the non-strain area.

5. The thin film pressure sensor for seawater depth measurement according to claim 1, 2 or 3, It is characterized in that The insulating film layer (2) is Ta 2 O 5 and SiO 2 A composite insulating dielectric film layer is formed.

6. A method for preparing a thin film pressure sensor for seawater depth measurement according to any one of claims 1 to 5, It is characterized in that Including chamfer (1a) design: When performing chamfer (1a), according to the maximum disturbance, maximum nonlinear error and maximum comprehensive stress formula, the nonlinearity and overload multiple design indicators are given to obtain the pressure range. P Diaphragm radius , Diaphragm thickness h relationship; A finite element analysis model is established to analyze the maximum stress variation under different chamfer (1a) conditions; the optimal design value of the chamfer (1a) is the chamfer (1a) size corresponding to the maximum stress being just equal to the allowable stress.

7. The preparation method according to claim 6, It is characterized in that The corresponding maximum disturbance, maximum nonlinear error and maximum comprehensive stress formulas are: Maximum disturbance The formula is: in, P is the uniform pressure acting on the diaphragm, μ is the Poisson's ratio of the material, R 0 is the diaphragm radius, E is the elastic modulus of the material, h is the diaphragm thickness; Maximum nonlinear error The formula is: Maximum comprehensive stress The formula is: 。 8. The preparation method according to claim 6 or 7, It is characterized in that It also includes the design of the convex island (1b): establishing a finite element analysis model with different convex island (1b) diameters to obtain the radial stress and disturbance on the surface of the elastic element (1); substituting the disturbance value into the maximum nonlinear error formula to obtain the nonlinear design value at this time; The optimal design value of the convex island (1b) is the diameter value of the convex island (1b) corresponding to the nonlinear value which can be significantly reduced under the premise of less sacrifice of the maximum tensile and compressive radial stresses.

9. The preparation method according to claim 6 or 7, It is characterized in that Including elastic element (1) design: Under the premise of meeting the design requirements, the diaphragm thickness h , diaphragm radius R 0 As large as possible to minimize the impact of seawater corrosion on nonlinearity and sensitivity.

10. The preparation method according to claim 6 or 7, It is characterized in that It also includes strain resistor arrangement: establishing a finite element model of the elastic element (1), extracting radial strain, tangential strain and disturbance curves in the radial direction, and seeking The corresponding coordinate position on the diaphragm is the maximum nonlinear area and should be avoided when arranging the strain resistors; the strain resistors are arranged at the coordinate position corresponding to the maximum radial strain value.

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