A tpos strain sensor with low temperature drift characteristic

Abstract

This invention belongs to the field of microelectromechanical systems (MEMS) technology, specifically relating to a TPoS strain sensor with low temperature drift characteristics. It includes a silicon substrate and a tuning fork TPoS resonator integrated on the silicon substrate. The tuning fork TPoS resonator comprises a tuning fork TPoS resonator body and a metal electrode disk. A temperature compensation layer, made of a positive temperature coefficient material, is provided on the lower surface of the tuning fork TPoS resonator body. Compared with existing technologies, this invention uses the tuning fork TPoS resonator as the core structure of the strain sensor to detect changes in strain. By employing the tuning fork TPoS resonator as the core structure and using the temperature compensation layer, the frequency shift effect caused by the change in Young's modulus of the silicon layer material during temperature changes is offset, thereby achieving low temperature drift characteristics.

Description

Technical Field

[0001] This invention belongs to the field of micro-electro-mechanical systems (MEMS) technology, specifically relating to a TPoS (Thin-film Piezoelectric-on-Silicon) strain sensor with low temperature drift characteristics. Background Technology

[0002] Strain sensors are sensors used to measure the forces acting on an object. They have wide applications in engineering, science, and medicine. They provide real-time, accurate strain information, helping researchers understand the strain on objects and providing crucial data support for engineering design, scientific research, and medical diagnosis. High-performance strain sensors have consistently attracted the attention of researchers.

[0003] Traditional strain sensors include piezoresistive, fiber optic, and piezoelectric types. Piezoresistive strain sensors utilize the piezoresistive effect of materials—that is, the characteristic that the resistance of a material changes with force—to measure force. Common piezoresistive sensor materials include silicon and silicides. They obtain strain information of a stressed object by measuring changes in resistance, and have advantages such as simple structure, low cost, small size, and wide applicability. However, these sensors have lower accuracy, larger temperature drift, and are susceptible to environmental factors such as temperature and humidity. Fiber optic strain sensors measure strain by utilizing changes in the light signal in an optical fiber under stress. Fiber optic sensors have advantages such as high sensitivity and anti-interference capabilities, and are often used to monitor strain changes in complex structures or high-temperature environments. They are immune to electromagnetic interference, have high-temperature operating capabilities, are corrosion-resistant, and suitable for long-distance transmission. However, they are more expensive, complex to install and debug, and sensitive to light source and fiber optic losses. Piezoelectric strain sensors measure strain using the piezoelectric effect. When piezoelectric materials are subjected to force, charge accumulation or potential changes occur; the magnitude of strain can be obtained by measuring the change in charge or potential. Piezoelectric strain sensors have a wide operating frequency range, high temperature resistance, and strong anti-interference ability, but they are sensitive to changes in temperature and humidity, have relatively low sensitivity, and are easily affected by mechanical vibration.

[0004] Compared with the aforementioned traditional strain sensors, TPoS strain sensors fabricated using microfabrication processes have attracted widespread attention from researchers in recent years due to their advantages such as high sensitivity, low power consumption, small size, and easy compatibility with CMOS processes. However, TPoS strain sensors still face the problem of significant frequency shift with temperature. Therefore, designing a TPoS strain sensor with low temperature drift characteristics is of great importance. Summary of the Invention

[0005] In view of this, the present invention proposes a TPoS strain sensor with low temperature drift characteristics. It utilizes the influence of axial strain on the resonant frequency of a tuning fork TPoS resonator to detect the shift in resonant frequency, thereby realizing the detection of strain magnitude. By preparing a temperature compensation layer at the bottom of the tuning fork TPoS resonator, the influence of temperature on the resonant frequency of the TPoS resonator is suppressed. While ensuring the sensitivity of the TPoS strain sensor, the problem of the resonant frequency shifting significantly with temperature changes is solved.

[0006] The technical solution proposed in this invention is as follows:

[0007] A TPoS strain sensor with low temperature drift characteristics includes a silicon substrate and a tuning fork TPoS resonator integrated on the silicon substrate.

[0008] The silicon substrate is a flat plate with a hollowed-out central space; the tuning fork TPoS resonator includes a tuning fork TPoS resonator body and a metal electrode disk.

[0009] The tuning fork TPoS resonator body includes 2n+1 resonant beams, two connection ends, and a temperature compensation layer, where n is an integer greater than zero. The 2n+1 resonant beams are connected in parallel between the two connection ends. Each resonant beam has the same structural dimensions and includes a doped silicon layer and a metal transmission line disposed on the upper surface of the doped silicon layer. The metal transmission line includes two metal electrodes and a strip metal wire located between the two metal electrodes. One end of the strip metal wire is connected to one of the metal electrodes, and the other end is connected to the other metal electrode. A piezoelectric thin film layer is disposed between the two metal electrodes and the doped silicon layer, and an isolation oxide layer is disposed between the strip metal wire and the doped silicon layer. Each of the two connection ends has an anchor point, and the tuning fork TPoS resonator body is connected to the silicon substrate through the anchor points on the connection ends. The temperature compensation layer is made of a positive temperature coefficient material and is disposed on the lower surface of the tuning fork TPoS resonator body.

[0010] The metal electrode disk is disposed on the main body of the tuning fork TPoS resonator, on a non-perforated area of ​​the silicon substrate on one side; an isolation oxide layer is provided between the metal electrode disk and the silicon substrate, including an input metal electrode disk, an output metal electrode disk and two grounded metal electrode disks, the input metal electrode disk and the output metal electrode disk are located between the two grounded metal electrode disks, the input metal electrode disk is connected to the metal transmission lines on n+1 resonant beams, and the output metal electrode disk is connected to the metal transmission lines on the remaining n resonant beams.

[0011] Furthermore, the isolation oxide layer material is silicon dioxide, and the metal transmission line is made of conductive metals such as silver, copper, gold, aluminum, nickel, or lead; the piezoelectric material of the piezoelectric thin film layer is AlN, ZnO, PZT, PVDF, PVDF-TrEE, PVDF-TFE, LiNbO3, or LiTaO3, etc.

[0012] Furthermore, the thickness of the isolation oxide layer is 0.1 μm to 2 μm, the thickness of the metal transmission line is 0.5 μm to 5 μm, and the thickness of the piezoelectric thin film layer is 0.5 μm to 5 μm.

[0013] Furthermore, the thickness of the temperature compensation layer is 0.5μm to 5μm.

[0014] Furthermore, the tuning fork-type TPoS resonator has a centrally symmetrical structure.

[0015] By adopting the above technical solution, the present invention has the following beneficial effects:

[0016] 1. The TPoS strain sensor with low temperature drift characteristics of the present invention utilizes the characteristic that the stress on a tuning fork TPoS resonator changes linearly with the axial force it bears, and that the frequency shift also changes linearly with the axial force. The change in strain is detected by measuring the change in the resonant frequency of the tuning fork TPoS resonator. Compared with existing stress testing sensors, the present invention uses a tuning fork TPoS resonator as the core structure of the strain sensor, giving it advantages such as high electromechanical conversion efficiency, higher quality factor under normal pressure, ease of large-scale mass production, and lower packaging cost.

[0017] 2. The present invention achieves low temperature drift characteristics by providing a temperature compensation layer with a positive temperature coefficient on the lower surface of the tuning fork TPoS resonator body, that is, on the lower surface of each resonant beam and the two connecting ends. This compensates for the frequency shift effect caused by the change of Young's modulus of the silicon layer material of the sensor when the temperature changes. Attached Figure Description

[0018] The accompanying drawings, which are included to provide a further understanding of embodiments of the invention and form part of this application, do not constitute a limitation thereof. In the drawings:

[0019] Figure 1 A three-dimensional structural diagram of the TPoS strain sensor with low temperature drift characteristics provided by the present invention;

[0020] Figure 2 for Figure 1 A-A' and B-B' cross-sectional views;

[0021] Figure 3A curve showing the temperature sensitivity of the tuning fork-type TPoS strain sensor provided by the present invention as a function of the thickness of the temperature compensation layer.

[0022] Figure 4 The present invention provides a curve showing the change in resonant frequency offset of the TPoS strain sensor with temperature when the temperature compensation layer is in different positions.

[0023] Figure 5 The present invention provides a graph showing the resonant frequency shift of the TPoS strain sensor as a function of applied strain when the temperature compensation layer is in different positions.

[0024] Figure label:

[0025] 1. Tuning fork TPoS resonator; 101. Input metal electrode disk; 102. Output metal electrode disk; 103. Grounding metal electrode disk; 104. Strip metal wire; 105. Isolation oxide layer; 106. Metal electrode; 2. Piezoelectric layer; 3. Anchor point; 4. Silicon substrate; 401. Doped silicon layer; 5. Temperature compensation layer. Detailed Implementation

[0026] In the following, the terms “comprising” or “may include” as used in various embodiments of the invention indicate the presence of an inventive function, operation, or element, and do not limit the addition of one or more functions, operations, or elements. Furthermore, as used in various embodiments of the invention, the terms “comprising,” “having,” and their cognates are intended only to indicate a specific feature, number, step, operation, element, component, or combination of the foregoing, and should not be construed as primarily excluding the presence of one or more other features, numbers, steps, operations, elements, components, or combinations of the foregoing, or adding one or more combinations of the foregoing.

[0027] In various embodiments of the invention, the expression "or" or "at least one of A and / or B" includes any combination or all combinations of the words listed simultaneously. For example, the expression "A or B" or "at least one of A and / or B" may include A, may include B, or may include both A and B.

[0028] The expressions used in the various embodiments of the present invention (such as "first," "second," etc.) may modify various constituent elements in the various embodiments, but do not limit the corresponding constituent elements. For example, the above expressions do not limit the order and / or importance of the elements. The above expressions are only used for the purpose of distinguishing one element from other elements. For example, a first user device and a second user device refer to different user devices, although both are user devices. For example, a first element may be referred to as a second element without departing from the scope of the various embodiments of the present invention, and similarly, a second element may also be referred to as a first element.

[0029] It should be noted that if a description is made of "connecting" one component to another, then the first component can be directly connected to the second component, and a third component can be "connected" between the first and second components. Conversely, when a component is "directly connected" to another component, it can be understood that there is no third component between the first and second components.

[0030] The terminology used in the various embodiments of the invention is for the purpose of describing particular embodiments only and is not intended to limit the various embodiments of the invention. As used herein, the singular form is intended to include the plural form as well, unless the context clearly indicates otherwise. Unless otherwise defined, all terms used herein (including technical and scientific terms) have the same meaning as commonly understood by one of ordinary skill in the art to which the various embodiments of the invention pertain. The terms (such as those defined in a generally used dictionary) are to be interpreted as having the same meaning as in the context of the relevant technical field and are not to be interpreted as having an idealized or overly formal meaning, unless clearly defined in the various embodiments of the invention.

[0031] To make the objectives, technical solutions, and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the embodiments and accompanying drawings. The illustrative embodiments and descriptions of the present invention are only used to explain the present invention and are not intended to limit the present invention.

[0032] Example 1

[0033] like Figure 1 As shown, this embodiment provides a TPoS strain sensor with low temperature drift characteristics, including a silicon substrate 4 and a tuning fork TPoS resonator 1 integrated on the silicon substrate 4.

[0034] The silicon substrate 4 is a flat plate with a hollowed-out central space; the tuning fork TPoS resonator 1 includes a tuning fork TPoS resonator body and metal electrodes. The tuning fork TPoS resonator 1 includes a tuning fork TPoS resonator body and a metal electrode disk;

[0035] The tuning fork TPoS resonator body 1 includes 2n+1 resonant beams, two connection ends, and a temperature compensation layer 5, where n is an integer greater than zero. The 2n+1 resonant beams are connected in parallel between the two connection ends. Each resonant beam has the same structural dimensions and includes a doped silicon layer 401 and a metal transmission line disposed on the upper surface of the doped silicon layer 401. The metal transmission line includes two metal electrodes 106 and a strip metal conductor 104. The two metal electrodes are a first metal electrode 106 and a second metal electrode, respectively. One end of the strip metal conductor 104 is connected to the first metal electrode, and the other end is connected to the second metal electrode. A piezoelectric thin film layer 2 is disposed between the two metal electrodes and the doped silicon layer 401, and an isolation oxide layer 105 is disposed between the strip metal conductor 104 and the doped silicon layer 401. Each of the two connection ends has an anchor point 3, and the tuning fork TPoS resonator body is connected to the silicon substrate 4 through the anchor points 3 on the connection ends. Temperature compensation layer 5 is provided on the lower surface of the tuning fork TPoS resonator body, that is, a temperature compensation layer with a positive temperature coefficient is provided on the lower surface of each resonant beam and the two connection ends.

[0036] The metal electrode disk is disposed on the non-perforated area of ​​the silicon substrate 4 on one side of the tuning fork resonator body. An isolation oxide layer 105 is provided between the metal electrode disk and the silicon substrate 4, including an input metal electrode disk 101, an output metal electrode disk 102, and two grounded metal electrode disks 103. The input metal electrode disk 101 and the output metal electrode disk 102 are located between the two grounded metal electrode disks 103. The input metal electrode disk 101 is connected to the metal transmission lines on n+1 resonant beams, and the output metal electrode disk 103 is connected to the metal transmission lines on the remaining n resonant beams.

[0037] In this embodiment, the tuning fork TPoS resonator has a centrally symmetrical structure. The insulating oxide layer is made of silicon dioxide with a thickness of 0.1 μm to 2 μm. The metal transmission line is made of conductive metals such as silver, copper, gold, aluminum, nickel, or lead, with a thickness of 0.5 μm to 5 μm. The piezoelectric thin film layer is made of piezoelectric materials such as AlN, ZnO, PZT, PVDF, PVDF-TrEE, PVDF-TFE, LiNbO3, or LiTaO3, with a thickness of 0.5 μm to 5 μm. The temperature compensation layer is made of materials including, but not limited to, silicon dioxide and other materials with a positive temperature coefficient, with a thickness of 0.5 μm to 5 μm.

[0038] In use, external axial strain is applied to the tuning fork TPoS resonator 1 through anchor point 3, causing changes in the intrinsic material parameters of the tuning fork TPoS resonator 1, such as stiffness and density, thereby altering the characteristic frequency of the tuning fork TPoS resonator 1. The mode used is an out-of-plane antiphase vibration mode, which has significant advantages over other vibration modes, such as high Q value, high signal strength, and high force sensitivity. The characteristic frequency of the out-of-plane antiphase vibration mode can be expressed by the formula:

[0039]

[0040] Among them, L t W is the length of the resonant beam of the tuning fork TPoS resonator. t Let t be the width of the resonant beam. Si E represents the thickness of the tuning fork TPoS resonator. Si It is the equivalent Young's modulus of a tuning fork TPoS resonator.

[0041] When an axial force F is applied to the anchor point at one end of a tuning fork TPoS resonator s When affected, its resonant frequency will change, which can be defined by the formula:

[0042]

[0043] Taking advantage of the fact that the stress on a tuning fork TPoS resonator changes linearly with the axial force it bears, and that the frequency shift also changes linearly with the axial force it bears, the change in strain can be detected by measuring the change in the resonant frequency of the tuning fork TPoS resonator.

[0044] Figure 2 The upper part shows the three-dimensional structure of the tuning fork TPoS resonator 1, and the lower part shows the cross-sections of the resonant beam of the tuning fork TPoS resonator at two points. Figure 2 As shown, in this embodiment, a temperature compensation layer 5 is prepared on the lower surface of the doped silicon 401. The main purpose of preparing the temperature compensation layer 5 is to suppress temperature drift. The principle of suppressing temperature drift in this embodiment is as follows:

[0045] The main reason for temperature drift is that the Young's modulus of the material changes when the external temperature rises. For the material used in the tuning fork TPoS resonator 1, its Young's modulus gradually decreases as the temperature increases, as shown in the following formula:

[0046]

[0047] Among them, L t W is the length of the resonant beam of the tuning fork TPoS resonator. t Let t be the width of the resonant beam. Si E represents the thickness of the tuning fork TPoS resonator.Si It is the equivalent Young's modulus of a tuning fork TPoS resonator.

[0048] As can be seen from the formula, the Young's modulus gradually decreases with increasing temperature, and f0 is affected by temperature. Based on this, this embodiment incorporates materials with positive temperature coefficients, such as silicon dioxide, into the film structure of the strain sensor to counteract the influence of negative material temperature coefficients, reducing the temperature sensitivity of the strain sensor's resonant frequency and achieving temperature compensation, thereby suppressing the influence of temperature on the sensor's sensitivity. The mode used is an out-of-plane inverse vibration mode, whose energy is mainly concentrated on the lower surface of the doped silicon 401. Since the overall Young's modulus is obtained by weighted averaging of the Young's moduli of each thin film material, when a certain material is located where the energy is most concentrated, its Young's modulus will have a greater impact on the proportion of the overall Young's modulus.

[0049] The resonator is driven and detected through the direct and inverse piezoelectric effects. Applying a voltage to the input electrode causes deformation of the piezoelectric material through the inverse piezoelectric effect, driving the tuning fork-type TPoS resonator to vibrate according to a specific vibration mode. Simultaneously, the output metal electrode collects the charge generated by the direct piezoelectric effect of the piezoelectric thin film on another beam, forming a current, which is finally output through the output metal electrode.

[0050] Figure 3 To investigate the effect of different temperature compensation layer thicknesses on temperature sensitivity, under the size conditions of the tuning fork TPoS resonator used in this example, a temperature compensation layer thickness of 1.09 μm can completely suppress the temperature drift of the device. The difference in strain sensitivity between devices with and without a temperature compensation layer was also compared, and the results are as follows: Figure 4 , 5 As shown, the strain sensitivity with the temperature compensation layer decreased by 13% compared to the strain sensitivity without the temperature compensation layer.

[0051] Compared to traditional strain sensors, the method proposed in this embodiment reduces the impact of temperature on the sensor, while also offering advantages such as low power consumption, small size, and easy compatibility with CMOS processes.

[0052] The specific embodiments described above further illustrate the purpose, technical solution, and beneficial effects of the present invention. It should be understood that the above description is only a specific embodiment of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A TPoS strain sensor with low temperature drift characteristics, comprising a silicon substrate and a tuning fork TPoS resonator integrated on the silicon substrate, characterized in that: The silicon substrate is a flat plate with a hollowed-out central space; the tuning fork TPoS resonator includes a tuning fork TPoS resonator body and a metal electrode disk. The tuning fork TPoS resonator body comprises 2n+1 resonant beams, two connection ends, and a temperature compensation layer, where n is an integer greater than zero. The 2n+1 resonant beams are connected in parallel between the two connection ends. Each resonant beam has the same structural dimensions and includes a doped silicon layer and a metal transmission line disposed on the upper surface of the doped silicon layer. The metal transmission line includes two metal electrodes and a strip metal conductor located between the two metal electrodes. One end of the strip metal conductor is connected to one of the metal electrodes, and the other end is connected to the other metal electrode. A piezoelectric thin film layer is disposed between the two metal electrodes and the doped silicon layer, and an isolation oxide layer is disposed between the strip metal conductor and the doped silicon layer. Each of the two connection ends has an anchor point, and the tuning fork TPoS resonator body is connected to the silicon substrate through the anchor points on the connection ends. The temperature compensation layer is made of a positive temperature coefficient material and is disposed on the lower surface of the tuning fork TPoS resonator body. The metal electrode disk is disposed on the main body of the tuning fork TPoS resonator, on a non-cutout area of ​​the silicon substrate on one side; an isolation oxide layer is provided between the metal electrode disk and the silicon substrate, including an input metal electrode disk, an output metal electrode disk and two grounded metal electrode disks, the input metal electrode disk and the output metal electrode disk are located between the two grounded metal electrode disks, the input metal electrode disk is connected to the metal transmission lines on n+1 of the resonant beams, and the output metal electrode disk is connected to the metal transmission lines on the remaining n resonant beams.

2. The TPoS strain sensor with low temperature drift characteristics as described in claim 1, characterized in that: The isolation oxide layer is made of silicon dioxide, and the metal transmission line is made of conductive metals such as silver, copper, gold, aluminum, nickel, or lead; the piezoelectric material of the piezoelectric thin film layer is AlN, ZnO, PZT, PVDF, PVDF-TrEE, PVDF-TFE, LiNbO3, or LiTaO3.

3. A TPoS strain sensor with low temperature drift characteristics as described in claim 1, characterized in that: The thickness of the isolation oxide layer is 0.1 μm to 2 μm, the thickness of the metal transmission line is 0.5 μm to 5 μm, and the thickness of the piezoelectric thin film layer is 0.5 μm to 5 μm.

4. A TPoS strain sensor with low temperature drift characteristics as described in any one of claims 1 to 3, characterized in that: The thickness of the temperature compensation layer is 0.5μm to 5μm.

5. A TPoS strain sensor with low temperature drift characteristics as described in claim 1, characterized in that: The tuning fork-type TPoS resonator has a centrally symmetrical structure.

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