A magnetic field sensor based on a tuning fork TPoS resonator

Abstract

The application belongs to the technical field of microcomputer electromechanical, and particularly relates to a magnetic field sensor based on a tuning fork type TPoS resonator. The magnetic field sensor based on the tuning fork type TPoS resonator comprises a silicon substrate and a tuning fork type TPoS resonator integrated on the silicon substrate; the magnetic field sensor based on the tuning fork type TPoS resonator comprises a metal spiral coil, a first frequency changing unit and a second frequency changing unit; the first frequency changing unit comprises a micro lever and a three-tuning fork type TPoS resonator, one end of the micro lever is connected with the metal spiral coil, and the other end of the micro lever is connected with the three-tuning fork type TPoS resonator; the second frequency changing unit is completely same in structure size with the first frequency changing unit, and is centrally symmetrical with the first frequency changing unit about the metal spiral coil. Compared with a traditional capacitive resonator, the tuning fork type TPoS resonator arranged in the two frequency changing units can reduce the complexity of packaging and external signal processing circuit design, and realize lower preparation cost.

Description

Technical Field

[0001] This invention belongs to the field of micro-electro-mechanical systems (MEMS) technology, specifically relating to a magnetic field sensor based on a tuning fork TPoS resonator. Background Technology

[0002] An electronic compass is a directional tool that, due to its stable structure, can be easily connected to other electronic systems. Because of its stable performance and high accuracy, it is widely used in smart mobile terminals such as mobile phones, laptops, and wearable devices. As a core component of the electronic compass, high-performance magnetic field sensors have always been a focus of researchers. Traditional magnetic field sensors include Hall effect sensors and magnetoresistive sensors. They utilize the Hall effect and the properties of magnetic materials, respectively, to detect changes in the external magnetic field. The advantages of Hall effect sensors are mature fabrication processes, low cost, and easy compatibility with Complementary Metal Oxide Semiconductor (CMOS) processes; its disadvantage is that it requires increasing power consumption to improve its magnetic field resolution. Magnetoresistive sensors have high magnetic field resolution and a wide operating range, but their performance depends on the properties of the magnetic material and they are not easily integrated with CMOS devices. Compared to the two traditional magnetic field sensors mentioned above, silicon-based resonant magnetic field sensors based on MEMS technology have received widespread attention from researchers in recent years due to their low power consumption, small size, and easy compatibility with CMOS processes.

[0003] Currently, resonant magnetic field sensors based on MEMS technology mainly employ capacitive transduction, where the Lorentz force generated by an external magnetic field drives the resonator to vibrate, causing a change in capacitance. The change in capacitance within the device is then read by an external circuit to detect the magnetic field. The disadvantage of capacitive transduction is its low electromechanical transduction efficiency, requiring a DC bias voltage and a high vacuum environment to exhibit good performance. Therefore, this places stringent requirements on the design of external signal processing circuits and vacuum packaging techniques, significantly increasing the design complexity and fabrication cost of this type of magnetic field sensor. Therefore, it is necessary to provide a magnetic field sensor that is simple to design and low in cost. Summary of the Invention

[0004] The purpose of this invention is to provide a magnetic field sensor based on a tuning fork TPoS resonator. This sensor utilizes the high electromechanical conversion efficiency and high quality factor of the tuning fork TPoS resonator under atmospheric pressure, thereby reducing the complexity of packaging and external signal processing circuit design and achieving a lower manufacturing cost than capacitive resonators.

[0005] To achieve the above objectives, the present invention adopts the following technical solution:

[0006] A magnetic field sensor based on a tuning fork TPoS resonator includes a silicon substrate and a magnetic field sensor with a tuning fork TPoS resonator integrated on the silicon substrate.

[0007] The magnetic field sensor of the tuning fork TPoS resonator includes a metal spiral coil, a first frequency changing unit, and a second frequency changing unit.

[0008] The first frequency changing unit includes a micro lever and a three-tuning-fork TPoS resonator. One end of the micro lever is connected to a metal spiral coil, and the other end is connected to the three-tuning-fork TPoS resonator. The second frequency changing unit has the same structural dimensions as the first frequency changing unit and is centrally symmetrical with respect to the metal spiral coil.

[0009] Furthermore, a deep reactive ion etching process is used to etch the silicon substrate except for the contact area of ​​the magnetic field sensor of the tuning fork TPoS resonator, so that the magnetic field sensor of the tuning fork TPoS resonator is suspended on the silicon substrate, thereby further improving the quality factor Q value of the device.

[0010] Furthermore, the metal helix that constitutes the metal helical coil includes, from top to bottom, a metal layer, a first insulating oxide layer, and a doped silicon layer; adjacent coils are connected by silicon connecting beams.

[0011] Furthermore, the three tuning fork resonator includes a base, a resonant beam, and two connecting ends;

[0012] Four rectangular metal plates are provided on the substrate. Two of the four rectangular metal plates serve as ground electrode plates, and the other two are the input electrode plate and the output electrode plate, respectively.

[0013] There are three resonant beams, including two side beams and one middle beam. The three resonant beams are connected in parallel between two connection ends. Each resonant beam has the same structure, consisting of doped silicon, metal electrodes disposed on the doped silicon in the same layer, and strip transmission lines. The metal electrodes are located at both ends of the beam and connected by the strip transmission lines. A piezoelectric thin film layer is provided between the metal electrodes and the doped silicon, and a first isolation oxide layer is provided between the strip transmission lines and the doped silicon. The metal electrodes on the two side beams are the input electrodes, and the electrodes on the middle beam are the output electrodes.

[0014] The two connection ends are the first connection end and the second connection end, and both are provided with anchor points. The first connection end is connected to the substrate through the anchor point, and the second connection end is connected to the micro lever through the anchor point. One end of the input electrode is connected to the input electrode disk through the first connection end, and one end of the output electrode is connected to the output electrode disk through the first connection end.

[0015] Furthermore, the micro-lever includes a first-stage micro-lever and a second-stage micro-lever, which are connected by a lever connector. The first-stage micro-lever has an input end and a first support beam. The input end is directly connected to a metal spiral coil, and the first support beam is fixed on the silicon substrate. The second-stage micro-lever is much longer than the first micro-lever and has an output end and a second support beam. The second support beam is also fixed on the silicon substrate, and the output end is directly connected to the anchor point of the second connection end of the three-tuning-fork TPoS resonator.

[0016] Furthermore, the first isolation oxide layer is made of silicon dioxide with a thickness of 0.3 μm to 1.5 μm; the metal electrode and the strip transmission line are made of metals such as silver, copper, gold, aluminum, nickel or lead with a thickness of 0.5 μm to 2 μm; the piezoelectric thin film is made of AlN, ZnO, PZT, PVDF, LiNbO3 or LiTaO3 with a thickness of 0.5 μm to 2 μm.

[0017] Furthermore, the silicon substrate includes, from bottom to top, a substrate silicon, a second isolation oxide layer, and a doped silicon layer.

[0018] By adopting the above technical solution, the present invention has the following beneficial effects:

[0019] 1. This invention utilizes the characteristics of tuning fork TPoS resonators, which have high electromechanical conversion efficiency and can achieve a high quality factor (Q value) under atmospheric pressure. In each of the two first frequency change units, a tuning fork TPoS resonator is used. Compared with traditional capacitive resonators, this reduces the complexity in packaging and external signal processing circuit design, and achieves a lower manufacturing cost than capacitive resonators.

[0020] 2. This invention connects adjacent coils in a multi-turn metal helical coil using silicon connecting beams, achieving superposition and transmission of the Lorentz force, thereby enhancing the magnetic field sensitivity of the device. Furthermore, by coupling the metal helical coil with a micro-lever, the superimposed Lorentz force is amplified again, further improving the sensitivity of the magnetic field sensor. Attached Figure Description

[0021] Figure 1 A three-dimensional structural diagram of a magnetic field sensor based on a tuning fork TPoS resonator provided by this invention;

[0022] Figure 2 for Figure 1 Top view;

[0023] Figure 3 The interconnection diagram of the metal spiral coils provided by the present invention;

[0024] Figure 4 A diagram of a two-stage micro-lever structure provided for this invention;

[0025] Figure 5 A three-dimensional structural diagram of the three-tuning fork resonator provided by the present invention;

[0026] Figure 6 for Figure 5 A-A' and B-B' cross-sectional views;

[0027] Figure 7 A graph showing the variation of the admittance parameter of the three tuning fork resonator as a function of the magnetic field, provided by the present invention.

[0028] Figure 8 The frequency shift diagram of the three tuning fork resonator provided by the present invention for different magnetic fields.

[0029] Figure label:

[0030] 1. Metal spiral coil; 101. Metal layer; 102. Silicon connecting beam; 103. First isolation oxide layer; 104. First metal pad; 105. Second metal pad; 2. First micro lever; 201. First stage micro lever; 202. Second stage micro lever; 203. Input end; 204. First support beam; 205. Lever connecting beam; 206. Second support beam; 207. Output end; 3. Second micro lever; 4. First three-tuning-fork TPoS resonator; 401. Input electrode; 402. Output electrode; 403. Output electrode disk; 404. Input electrode disk; 405. Ground electrode disk; 406. Strip transmission line; 407. Anchor point; 5. Second three-tuning-fork TPoS resonator; 6. Silicon substrate; 601. Doped silicon layer; 7. Piezoelectric thin film. Detailed Implementation

[0031] 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.

[0032] 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.

[0033] 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.

[0034] 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.

[0035] The terminology used in the various embodiments of this 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. To make the objectives, technical solutions, and advantages of the invention clearer, the invention will be further described in detail below with reference to embodiments and accompanying drawings. The illustrative embodiments and descriptions of the invention are for explaining the invention only and are not intended to limit the invention.

[0036] Example 1

[0037] like Figure 1 , Figure 2 As shown, this embodiment provides a magnetic field sensor based on a tuning fork TPoS resonator, including a silicon substrate 6 and a magnetic field sensor with a tuning fork TPoS resonator integrated on the silicon substrate 6.

[0038] The magnetic field sensor of the tuning fork TPoS resonator includes a metal spiral coil 1, a first frequency changing unit, and a second frequency changing unit. The first frequency changing unit includes a first micro-lever 2 and a first three-tuning-fork TPoS resonator 4. One end of the first micro-lever 2 is connected to the first end of the metal spiral coil 1, and the other end is connected to the first three-tuning-fork TPoS resonator 4. The second frequency changing unit includes a second micro-lever 3 and a second three-tuning-fork TPoS resonator 5. One end of the second micro-lever 3 is connected to the second end of the metal spiral coil 1, and the other end is connected to the second three-tuning-fork TPoS resonator 5. The second frequency changing unit has the same structural dimensions as the first frequency changing unit and is centrally symmetrical with respect to the metal spiral coil.

[0039] In use, the Lorentz force generated by the current in the metal spiral coil under the action of the measured magnetic field is amplified by the first micro lever 2 and axially applied to the first TPoS three-tone fork resonator 4, causing a change in the internal stiffness of the first three-tone TPoS three-tone fork resonator 4, thereby changing the characteristic frequency of the first three-tone TPoS three-tone fork resonator 4; after being amplified by the second micro lever 3, it is axially applied to the second TPoS three-tone fork resonator 5, causing a change in the internal stiffness of the second three-tone TPoS three-tone fork resonator 5, thereby changing the characteristic frequency of the second three-tone TPoS three-tone fork resonator 5.

[0040] Since the second frequency changing unit has the same structural dimensions as the first frequency changing unit and is centrally symmetrical about the metal spiral coil, it has the same sensitivity to the Lorentz force. Therefore, the resonant frequency offsets of the two tuning fork resonators are also the same. During magnetic field testing, the output signals of the two tuning fork resonators can be superimposed by an external signal processing circuit, which can improve the signal-to-noise ratio of the sensor output signal and effectively improve the testing efficiency.

[0041] In this embodiment, the metal spiral coil comprising the metal spiral coil includes, from top to bottom, a metal layer 101, a first isolation oxide layer 103, and a doped silicon layer 601. Adjacent coils are connected by a silicon connecting beam 102. A micro-lever is directly connected to the metal layer of the metal spiral coil. To facilitate magnetic field measurement, metal pads 104 and 105 are added at the center of the metal spiral coil. Metal pad 104 connects to the starting end of the metal spiral coil, and metal pad 105 connects to the end of the metal spiral coil. In use, current enters the metal spiral coil through metal pad 104, travels along its path, outputs through metal pad 105, and connects to an external circuit. Currently, only the operation of the first three-tuning-fork TPoS resonator 4 is considered; when a magnetic field exists, according to formula F... L =BIL calculates the magnitude of the Lorentz force on each turn of a metal spiral coil, taking into account that the ends of the trace are fixed. Therefore, the magnitude of the force in the middle of each turn of the metal spiral coil is: like Figure 3 As shown, the Lorentz force on the N turns of the metal spiral coil is superimposed and transmitted through the silicon connecting beam 102. Considering the force loss, the simulation results show that about 70% of the Lorentz force can be transmitted to the secondary micro lever 2, so that the whole device can obtain higher sensitivity.

[0042] Micro-levers are used to amplify the Lorentz force generated by a metal helical coil, thereby improving the sensitivity of the entire magnetic field sensor. Considering the differences in structure and working principle between micro-lever structures and macro-lever structures, as well as limitations in manufacturing processes, the micro-lever is made of a curved flexible beam. Due to the elastic deformation within the flexible beam, and taking into account factors such as amplification factor, device area, and structural flexibility, simulations determined that the optimal micro-level is two stages. At stage two, the amplification factor is best, approximately 200. The two-stage micro-lever structure is as follows. Figure 4 As shown, the micro-lever includes a first-stage micro-lever 201 and a second-stage micro-lever 202. The first-stage micro-lever 201 has an input end 203 and a first support beam 204. The input end 203 is directly connected to a metal spiral coil, and the first support beam is fixed to the silicon substrate. The second-stage micro-lever 202 is much longer than the first micro-lever 201. It has an output end 207 and a second support beam 206, which is also fixed to the silicon substrate. The output end 204 is connected to the anchor point of the three-tuning-fork TPoS resonator. The first-stage micro-lever 201 and the second-stage micro-lever 202 are connected by a lever connector 205.

[0043] like Figure 5 and Figure 6 The figures show the three-dimensional structure of the three-tone tuning fork resonator and two cross-sections of the resonant beam. The characteristic frequency of the three-tone tuning fork resonator is determined by the mechanical vibration mode during operation, the length and width of the resonant beam, and the material of the resonator. The vibration mode used in this example is the out-of-plane antiphase vibration mode. The out-of-plane antiphase vibration mode 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:

[0044]

[0045] Among them, L t W is the length of the resonant beam of the three-tuning-fork resonator. t Let t be the width of the resonant beam. Si E represents the thickness of the three-tuning-fork resonator. Si This is the Young's modulus of the three tuning fork resonator.

[0046] When an axial force F is applied to the anchor point at one end of the tuning fork resonator sWhen affected, its resonant frequency will change, which can be defined by the formula:

[0047]

[0048] Taking advantage of the fact that the resonant frequency shift of a tuning fork resonator changes linearly with the axial force borne by the anchor point, the resonant frequency of the tuning fork resonator can be changed by the Lorentz force generated by the magnetic field, and the change in the magnetic field can be detected by measuring the change in the resonant frequency of the tuning fork resonator.

[0049] The TPoS resonator can be driven by both the piezoelectric and inverse piezoelectric effects. Applying a voltage to the input electrodes causes mechanical deformation of the piezoelectric material due to the inverse piezoelectric effect, which in turn drives the entire three-tone fork resonator to vibrate according to specific modes. Simultaneously, the output metal electrodes collect the charge generated by the piezoelectric film through the piezoelectric effect, and the polarity of the collected charge changes periodically over time, ultimately forming a current that is output through the output metal electrode disk. The ratio of the output current to the input voltage is the admittance. Figure 7 This is a graph showing the admittance parameter of the three-tuning-fork TPoS resonator as a function of the magnetic field. In this example, the resonant frequency of the three-tuning-fork resonator at zero magnetic field is 55.5 kHz. The graph showing the resonant frequency of the three-tuning-fork resonator as a function of the magnetic field shift is shown below. Figure 8 As shown.

[0050] The method proposed in this embodiment uses a three-tuning-fork resonator based on a TPoS structure. It leverages the characteristic that the resonant frequency of a three-tuning-fork resonator is affected by axial force, utilizing the Lorentz force generated by a magnetic field in a metal spiral to change the resonant frequency. Ultimately, the magnetic field detection is achieved by detecting the shift in the resonant frequency. In practical applications, the metal spiral coil, the first isolation oxide layer of the two tuning fork resonators, and the doped silicon layer can be directly utilized from a silicon substrate. This reduces fabrication processes and lowers costs. Compared to traditional capacitive resonators, this magnetic field sensor reduces dependence on a vacuum environment, and its advantages such as low power consumption, small size, and easy compatibility with CMOS processes are likely to attract widespread attention in the application market.

[0051] 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 magnetic field sensor based on a tuning fork TPoS resonator, comprising a silicon substrate and a magnetic field sensor with a tuning fork TPoS resonator integrated on the silicon substrate, characterized in that: The magnetic field sensor of the tuning fork TPoS resonator includes a metal spiral coil, a first frequency changing unit, and a second frequency changing unit. The first frequency changing unit includes a micro lever and a three-tuning-fork TPoS resonator. One end of the micro lever is connected to a metal spiral coil, and the other end is connected to the three-tuning-fork TPoS resonator. The second frequency changing unit has the same structural dimensions as the first frequency changing unit and is centrally symmetrical with respect to the metal spiral coil.

2. A magnetic field sensor based on a tuning fork TPoS resonator according to claim 1, characterized in that: Deep reactive ion etching is used to etch the silicon substrate except for the contact area of ​​the magnetic field sensor of the tuning fork TPoS resonator, so that the magnetic field sensor of the tuning fork TPoS resonator is suspended on the silicon substrate.

3. A magnetic field sensor based on a tuning fork TPoS resonator according to claim 1, characterized in that: The metal spiral coil consists of, from top to bottom, a metal layer, a first insulating oxide layer, and a doped silicon layer; adjacent coils are connected by silicon connecting beams.

4. A magnetic field sensor based on a tuning fork TPoS resonator according to claim 1, characterized in that: The three-tuning-fork TPoS resonator includes a base, a resonant beam, and two connection terminals; Four rectangular metal plates are provided on the substrate. Two of the four rectangular metal plates serve as grounding electrode plates, and the other two are the input electrode plate and the output electrode plate, respectively. There are three resonant beams, including two side beams and one middle beam. The three resonant beams are connected in parallel between two connection ends. Each resonant beam has the same structure, consisting of doped silicon, metal electrodes disposed on the doped silicon in the same layer, and strip transmission lines. The metal electrodes are located at both ends of the beam and connected by the strip transmission lines. A piezoelectric thin film layer is provided between the metal electrodes and the doped silicon, and a first isolation oxide layer is provided between the strip transmission lines and the doped silicon. The metal electrodes on the two side beams are the input electrodes, and the electrodes on the middle beam are the output electrodes. The two connection ends are the first connection end and the second connection end, and both are provided with anchor points. The first connection end is connected to the substrate through the anchor point, and the second connection end is connected to the micro lever through the anchor point. One end of the input electrode is connected to the input electrode disk through the first connection end, and one end of the output electrode is connected to the output electrode disk through the first connection end.

5. A magnetic field sensor based on a tuning fork TPoS resonator according to claim 4, characterized in that: The micro-lever includes a first-stage micro-lever and a second-stage micro-lever, which are connected by a lever connector. The first-stage micro-lever has an input end and a first support beam. The input end is directly connected to a metal spiral coil, and the first support beam is fixed on a silicon substrate. The second-stage micro-lever is much longer than the first micro-lever and has an output end and a second support beam. The second support beam is also fixed on a silicon substrate, and the output end is directly connected to the anchor point of the second connection end of the three-tuning-fork TPoS resonator.

6. A magnetic field sensor based on a tuning fork TPoS resonator according to claim 3, characterized in that: The first isolation oxide layer is made of silicon dioxide and has a thickness of 0.3 μm to 1.5 μm.

7. A magnetic field sensor based on a tuning fork TPoS resonator according to claim 4, characterized in that: The metal electrodes and strip transmission lines are made of silver, copper, gold, aluminum, nickel, or lead, with a thickness of 0.5 μm to 2 μm; the piezoelectric thin film is made of AlN, ZnO, PZT, PVDF, LiNbO3, or LiTaO3, with a thickness of 0.5 μm to 2 μm.

8. A magnetic field sensor based on a tuning fork TPoS resonator according to claim 1, characterized in that... The silicon substrate comprises, from bottom to top, a substrate silicon, a second isolation oxide layer, and a doped silicon layer.

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