CN116087840A - Magnetic field sensor based on tuning fork type TPoS resonator - Google Patents

Abstract

The invention belongs to the technical field of micro-electro-mechanical systems, and particularly relates to a magnetic field sensor based on a tuning fork type TPoS resonator. A magnetic field sensor including a silicon substrate, a tuning fork TPoS resonator integrated on the silicon substrate; the magnetic field sensor of the tuning fork type TPoS resonator comprises a metal spiral coil, a first frequency change unit and a second frequency change unit; the first frequency change unit comprises a micro-lever and a three-tuning-fork type TPoS resonator, wherein 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 change unit and the first frequency change unit have the same structural size and are in central symmetry with the first frequency change unit about the metal spiral coil. Compared with the traditional capacitive resonator, the tuning fork type TPoS resonator provided with the two frequency change units reduces the complexity of packaging and external signal processing circuit design, and realizes lower preparation cost.

Description

A Magnetic Field Sensor Based on Tuning Fork TPoS Resonator

technical field

The invention belongs to the technical field of Micro-Electro-Mechanical Systems (MEMS), in particular to a magnetic field sensor based on a tuning fork type TPoS resonator.

Background technique

The electronic compass is a tool to guide the direction. Due to its stable structure, it can be easily connected with other electronic systems. Due to its stable working performance and high precision, it is widely used in smart mobile terminals such as mobile phones, notebook computers, and electronic wearable devices. As the core component of electronic compass, high-performance magnetic field sensor has always been the focus of researchers. Traditional magnetic field sensors include Hall sensors and magnetoresistive sensors. They utilize the Hall effect and the properties of magnetic materials to detect changes in an external magnetic field, respectively. The advantage of the Hall sensor is that the processing and preparation process is mature, the cost is low, and the processing technology is easy to be compatible with the complementary metal oxide semiconductor (Complementary Metal Oxide Semiconductor, CMOS) process; its disadvantage is that it needs to increase its power consumption by increasing its power consumption. Magnetic field resolution. Magnetoresistive sensors have higher magnetic field resolution and wider working range, but the performance of this type of sensor depends on the characteristics of magnetic materials, and it is not easy to integrate with CMOS devices. Compared with the above two traditional magnetic field sensors, the silicon-based resonant magnetic field sensor based on MEMS technology has attracted extensive attention of researchers in recent years because of its advantages of low power consumption, small size, and easy compatibility with CMOS technology.

At present, the resonant magnetic field sensor based on MEMS technology mainly adopts the capacitive energy conversion method, that is, the Lorentz force generated by the external magnetic field drives the resonator to vibrate and causes the change of capacitance. The purpose of detecting the magnetic field is achieved by reading the capacitance change in the device through an external circuit. The disadvantage of the capacitive transduction method is that the electromechanical transduction efficiency is low, and it needs to apply a DC bias voltage and a high vacuum environment to show better performance. Therefore, this puts forward relatively strict requirements on the external signal processing circuit design technology and vacuum packaging technology of the device, resulting in a significant increase in the design complexity and manufacturing cost of this type of magnetic field sensor. Therefore, it is necessary to provide a magnetic field sensor with simple design and low cost.

Contents of the invention

The object of the present invention is to provide a magnetic field sensor based on a tuning fork type TPoS resonator, which utilizes the characteristics of a tuning fork type TPoS resonator with high electromechanical energy conversion efficiency and can achieve a higher quality factor in an atmospheric pressure environment, The complexity of the package and the design of the external signal processing circuit is reduced, and the preparation cost is lower than that of the capacitive resonator.

To achieve the above object, the present invention adopts the following technical solutions:

A magnetic field sensor based on a tuning fork type TPoS resonator, comprising a silicon substrate, and a magnetic field sensor of the tuning fork type TPoS resonator integrated on the silicon substrate;

The magnetic field sensor of the tuning fork type TPoS resonator includes a metal helical 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 helical coil, and the other end is connected to a three-tuning fork TPoS resonator; the second frequency changing unit is exactly the same in size as the first frequency changing unit , and is center-symmetrical with the first frequency changing unit with respect to the metal helical coil.

Further, a deep reactive ion etching process is used to etch the silicon substrate except 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, further Improve the quality factor Q value of the device.

Further, the metal helix constituting the metal helical coil includes, from top to bottom, a metal layer, a first isolation oxide layer and a doped silicon layer; two adjacent coils are connected by silicon connecting beams.

Further, the three-tuning fork resonator includes a base, a resonant beam and two connecting ends;

There are 4 rectangular metal sheets on the base, two of the 4 rectangular metal sheets are used as ground electrode plates, and the other two are input electrode plates and output electrode plates;

There are 3 resonant beams, including two side beams and a middle beam; the 3 resonant beams are connected in parallel between the two connection ends; each resonant beam has the same structure, and they are all made of doped silicon and doped in the same layer. Composed of metal electrodes and strip-shaped transmission lines on miscellaneous silicon, the metal electrodes are located at both ends of the beam and connected by strip-shaped transmission lines; a piezoelectric film layer is set between the metal electrodes and doped silicon, and the strip-shaped transmission line and doped silicon There is a first isolation oxide layer; the metal electrodes on the two side beams are input electrodes, and the electrodes on the middle beam are output electrodes;

The two connection ends are respectively 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 The first connection end is connected to the input electrode disk, and one end of the output electrode is connected to the output electrode disk through the first connection end.

Furthermore, the micro-lever includes a first-stage micro-lever and a second-stage micro-lever, and the first-stage micro-lever and the second-stage micro-lever are connected through a lever connector; the first-stage micro-lever is provided with an input end and the first support beam, the input end is directly connected to the metal spiral coil, and the first support beam is fixed on the silicon substrate; the length of the second-stage micro-lever is much larger than that of the first micro-lever, and an output end and a second support beam are arranged on it, 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.

Furthermore, the material of the first isolation oxide layer is silicon dioxide with a thickness of 0.3 μm to 1.5 μm; the metal electrode and the strip transmission line are made of silver, copper, gold, aluminum, nickel or lead and other metals, The thickness is 0.5 μm-2 μm; the piezoelectric material of the piezoelectric film is AlN, ZnO, PZT, PVDF, LiNbO ₃ or LiTaO ₃ , and the thickness is 0.5 μm-2 μm.

Further, the silicon substrate includes substrate silicon, a second isolation oxide layer, and a doped silicon layer stacked sequentially from bottom to top.

After adopting the above technical scheme, the present invention has the following beneficial effects:

1. The present invention utilizes the characteristic that the tuning fork type TPoS resonant appliance has high electromechanical energy conversion efficiency and can realize a higher quality factor (Q value) in an atmospheric pressure environment. In the two first frequency changing units, each adopts A tuning-fork TPoS resonator reduces the complexity of packaging and external signal processing circuit design compared to traditional capacitive resonators, and achieves lower manufacturing costs than capacitive resonators.

2. The invention realizes the connection between two adjacent coils of the multi-turn wiring in the metal spiral coil through the silicon connecting beam pair, and realizes the superimposed conduction of the Lorentz force, thereby achieving the effect of improving the magnetic field sensitivity of the device. And on this basis, the metal helical coil is coupled with the micro-lever to realize the re-amplification of the superimposed Lorentz force and further improve the sensitivity of the magnetic field sensor.

Description of drawings

Fig. 1 is a three-dimensional structure diagram of a magnetic field sensor based on a tuning fork type TPoS resonator provided by the present invention;

Fig. 2 is a top view of Fig. 1;

Fig. 3 is the interconnection diagram of the metal helical coil provided by the present invention;

Fig. 4 is the structural diagram of the secondary micro-lever provided by the present invention;

Fig. 5 is the three-dimensional structural diagram of the three-tuning fork resonator provided by the present invention;

Fig. 6 is A-A' and B-B' sectional view of Fig. 5;

Fig. 7 is the change diagram of the admittance parameter of the three-tuning fork resonator provided by the present invention along with the magnetic field;

Fig. 8 is a diagram of the frequency shift of the three-tuning fork resonator provided by the present invention for different magnetic fields.

Reference signs:

1. Metal spiral coil; 101. Metal layer; 102. Silicon connection beam; 103. First isolation oxide layer; 104. First metal pad; 105. Second metal pad; 2. First micro lever; 201. 202, second-stage micro-lever; 203, input end; 204-first support beam; 205, lever connection beam; 206, second support beam; 207, output end; 3, second micro-lever ;4, the first three tuning fork TPoS resonator; 401, input electrode; 402, output electrode; 403, output electrode plate; 404, input electrode plate; 405, ground electrode plate; 406, strip transmission line; 407, anchor point; 5. The second three-tuning fork TPoS resonator; 6. Silicon substrate; 601, doped silicon layer; 7. Piezoelectric film.

Detailed ways

Hereinafter, the terms "comprising" or "may include" that may be used in various embodiments of the present invention indicate the existence of invented functions, operations or elements, and do not limit the existence of one or more functions, operations or elements. Increase. In addition, as used in various embodiments of the present invention, the terms "comprising", "having" and their cognates are only intended to represent specific features, numbers, steps, operations, elements, components or combinations of the foregoing, And it should not be understood as first excluding the existence of one or more other features, numbers, steps, operations, elements, components or combinations of the foregoing or adding one or more features, numbers, steps, operations, elements, components or a combination of the foregoing possibilities.

In various embodiments of the present invention, the expression "or" or "at least one of A or/and B" includes any or all combinations of words listed at the same time. For example, the expression "A or B" or "at least one of A or/and B" may include A, may include B, or may include both A and B.

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

It should be noted that if it is described that one constituent element is "connected" to another constituent element, the first constituent element may be directly connected to the second constituent element, and there may be "connection" between the first constituent element and the second constituent element. "The third component. Conversely, when one constituent element is "directly connected" to another constituent element, it can be understood that there is no third constituent element between the first constituent element and the second constituent element.

The terms used in the various embodiments of the present invention are for the purpose of describing particular embodiments only and are not intended to be limiting of the various embodiments of the present invention. As used herein, singular forms are intended to include plural forms as well, unless the context clearly dictates otherwise. Unless otherwise defined, all terms (including technical terms and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which various embodiments of the present invention belong. The terms (such as those defined in commonly used dictionaries) will be interpreted as having the same meaning as the contextual meaning in the relevant technical field and will not be interpreted as having an idealized meaning or an overly formal meaning, Unless clearly defined in various embodiments of the present invention. In order to make the purpose, technical solutions and advantages of the present invention clearer, the present invention will be further described in detail below in conjunction with the examples and accompanying drawings. As a limitation of the present invention.

Example 1

As shown in FIG. 1 and FIG. 2 , a magnetic field sensor based on a tuning fork TPoS resonator provided in this embodiment includes a silicon substrate 6 and a magnetic field sensor of a tuning fork TPoS resonator integrated on the silicon substrate 6 .

The magnetic field sensor of the tuning fork type TPoS resonator includes a metal helical coil 1 , a first frequency changing unit and a second frequency changing unit. The first frequency change 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 helical coil 1, and the other end is connected to the first three-tuning-fork TPoS resonator 4. The second frequency variation 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 helical 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 size as the first frequency changing unit, and is center-symmetrical to the first frequency changing unit with respect to the metal helical coil.

When in use, the Lorentz force generated by the current in the metal helical coil under the action of the measured magnetic field is amplified by the first micro-lever 2, and axially loaded on the first TPoS three-tuning fork resonator 4, so that the first three The stiffness inside the tone TPoS fork resonator changes, thereby changing the characteristic frequency of the first three-tone TPoS fork resonator 4; after being amplified by the second micro-lever 3, it is axially loaded on the second TPoS three-tone fork resonator 5, The stiffness inside the second three-tone TPoS fork resonator is changed to change the characteristic frequency of the second three-tone TPoS fork resonator 5 .

Since the second frequency changing unit has the same structural size as the first frequency changing unit, and is center-symmetric with the first frequency changing unit with respect to the metal helical coil, the sensitivity to the Lorentz force is the same. Therefore, the resonant frequency offset of the two three-tuning fork resonators is also the same. During the magnetic field test, the output signals of the two three-tuning fork resonators are superimposed through an external signal processing circuit, which can improve the signal-to-noise ratio of the sensor output signal , effectively improving test efficiency.

如图3所示，通过硅连接梁102对金属螺旋线圈上N圈走线上的洛伦兹力进行叠加传导，同时考虑到力的损耗，通过计算仿真得知最终约有70％的洛伦兹力可传入二级微杠杆2，以使整个器件获得更高灵敏度。In this embodiment, the metal helix constituting the metal helical coil includes, from top to bottom, a metal layer 101 , a first isolation oxide layer 103 and a doped silicon layer 601 . Two adjacent coils are connected by silicon connecting beams 102 . The micro-lever is directly connected to the metal layer of the metal helical coil. In order to facilitate the measurement of the magnetic field, a metal pad 104 and a metal pad 105 are added at the center of the metal helical coil. The metal pad 104 is connected to the starting end of the metal helical coil, and the metal pad 105 is connected to the terminal of the metal helical coil. When in use, the current enters the metal spiral coil through the metal pad 104, and is output along the wire through the metal pad 105, and is connected to an external circuit. At present, only the working condition of the first three-tuning fork TPoS resonator 4 is considered; when the magnetic field exists, the Lorentz force on each circle on the metal helical coil is calculated according to the formula _FL =BIL, taking into account that the two ends of the wiring are fixed , then the magnitude of the force in the middle of each circle on the metal helical coil is

As shown in Figure 3, the Lorentz force on the N-turn traces on the metal helical coil is superimposed and conducted through the silicon connecting beam 102. At the same time, considering the loss of force, it is known through calculation and simulation that there will be about 70% of the Lorentz force in the end. The Z force can be transmitted to the secondary micro-lever 2 to obtain higher sensitivity of the whole device.

The micro-lever is used to amplify the Lorentz force generated by the metal helical coil to improve the sensitivity of the entire magnetic field sensor. Considering the difference in structure and working principle between the micro-lever structure and the macro-lever structure, as well as the limitation of processing technology, the micro-lever is made of a curved flexible beam, because the flexible beam has a certain elastic deformation inside; comprehensively consider the magnification, device Influencing factors such as area and structural flexibility, and through simulation, it is determined that the micro-optimal series is level 2; at the second level, the magnification factor is the best, about 200. The structure of the two-stage micro-lever is shown in FIG. 4 , and the micro-lever includes a first-stage micro-lever 201 and a second-stage micro-lever 202 . The first-stage micro-lever 201 is provided with an input end 203 and a first support beam 204, the input end 203 is directly connected to the metal helical coil, and the first support beam is fixed on the silicon substrate. The length of the second-stage micro-lever 202 is much longer than that of the first micro-lever 201, and an output end 207 and a second support beam 206 are arranged on it. The second support beam 206 is also fixed on the silicon substrate, and the output end 204 is connected to a three-tuning fork TPoS resonance Anchor point of the device. The first-stage micro-lever 201 and the second-stage micro-lever 202 are connected through a lever connecting piece 205 .

As shown in FIG. 5 and FIG. 6 , they are respectively the three-dimensional structural diagram of the three-tuning fork resonator and two cross-sections of the resonance beam of the three-tuning fork resonator. Among them, the characteristic frequency of the three-tuning fork resonator is jointly determined by the mechanical vibration mode of the three-tuning fork resonator, the length and width of the resonant beam of the three-tuning fork resonator, and the material of the three-tuning fork resonator. The vibration mode applied in this example is the out-of-plane anti-phase vibration mode; the out-of-plane anti-phase vibration mode has obvious advantages compared with other vibration modes, such as: high Q value, high signal strength, and high force sensitivity ; The eigenfrequency of the out-of-plane anti-phase vibration mode can be expressed by the formula:

Among them, L _t is the length of the resonant beam of the three tuning fork resonator, W _t is the width of the resonant beam, t _Si is the thickness of the three tuning fork resonator, E _Si is the Young's modulus of the three tuning fork resonator.

When the anchor point at one end of the three-tuning fork resonator is affected by the axial force F _s , its resonant frequency will change, which can be defined by the formula:

Using the characteristic that the resonant frequency offset of the three-tuning fork resonator changes linearly with the axial force borne by the anchor point, the resonant frequency of the three-tuning fork resonator can be changed by the Lorentz force generated by the magnetic field. By measuring the three-tuning fork The amount of change in the resonant frequency of the resonator is used to detect the amount of change in the magnetic field.

Among them, the TPoS resonator can be driven by the piezoelectric effect and the inverse piezoelectric effect. A voltage is applied to the input electrode to drive. Due to the inverse piezoelectric effect, the piezoelectric material produces mechanical deformation, and drives the entire three-tuning fork resonator to vibrate according to a specific mode. At the same time, we use the output metal electrode to collect the charge generated by the piezoelectric film through the piezoelectric effect, and the polarity of the collected charge will also change periodically with time, and finally form a current output through the output metal electrode disk. The ratio of the output current to the input voltage is the admittance. Figure 7 shows the variation of the admittance parameter of the three-tuning fork TPoS resonator with the magnetic field. The resonant frequency of the three-tuning fork resonator used in this example is 55.5kHz at zero magnetic field. Wherein, the shift curve of the resonant frequency of the three-tuning fork resonator with the magnetic field is shown in FIG. 8 .

The method proposed in this embodiment will be based on the three-tuning fork resonator with TPoS structure, which is based on the characteristic that the resonant frequency of the three-tuning fork resonator is affected by the axial force, and uses the Lorentz force generated by the magnetic field in the metal helix to change the three-tuning fork The resonant frequency of the resonator; finally, the purpose of magnetic field detection is realized by detecting the shift of the resonant frequency. In practical applications, the metal helical coil and the first isolation oxide layer and the doped silicon layer of the two tuning fork resonators can directly utilize the silicon substrate. The oxide layer and the doped silicon layer are isolated to reduce manufacturing process and cost. Compared with traditional capacitive resonators, this magnetic field sensor reduces the dependence on the vacuum environment, and its advantages such as low power consumption, small size, and easy compatibility with CMOS processes can also attract wide attention in the application market.

The specific embodiments described above have further described the purpose, technical solutions and beneficial effects of the present invention in detail. It should be understood that the above descriptions are only specific embodiments of the present invention and are not intended to limit the scope of the present invention. Protection scope, within the spirit and principles of the present invention, any modification, equivalent replacement, improvement, etc., shall be included in the protection scope of the present invention.

Claims (8)

1. A tuning fork TPoS resonator-based magnetic field sensor comprising a silicon substrate, and a tuning fork TPoS resonator integrated on the silicon substrate, characterized in that:

the magnetic field sensor of the tuning fork type TPoS resonator comprises a metal spiral coil, a first frequency change unit and a second frequency change unit;

the first frequency change unit comprises a micro-lever and a three-tuning-fork type TPoS resonator, wherein 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 change unit and the first frequency change unit have the same structural size and are in central symmetry with the first frequency change unit about the metal spiral coil.

2. A tuning fork TPoS resonator-based magnetic field sensor according to claim 1, wherein: and etching the silicon substrate except the contact area of the magnetic field sensor of the tuning fork type TPoS resonator by adopting a deep reactive ion etching process so as to enable the magnetic field sensor of the tuning fork type TPoS resonator to be suspended on the silicon substrate.

3. A tuning fork TPoS resonator-based magnetic field sensor according to claim 1, wherein: the metal spiral line forming the metal spiral coil sequentially comprises from top to bottom: the metal layer, the first isolation oxide layer and the doped silicon layer; the adjacent two coils are connected through a silicon connecting beam.

4. A tuning fork TPoS resonator-based magnetic field sensor according to claim 1, wherein: the three tuning fork resonator comprises a substrate, a resonant beam and two connecting ends;

the substrate is provided with 4 rectangular metal sheets, two of the 4 rectangular metal sheets are used as grounding electrode discs, and the other 2 rectangular metal sheets are respectively an input electrode disc and an output electrode disc;

the number of the resonant beams is 3, and the resonant beams comprise two side beams and a middle beam; the 3 resonance beams are connected between the two connecting ends in parallel; each resonant beam has the same structure and consists of doped silicon, a metal electrode and a strip-shaped transmission line, wherein the metal electrode and the strip-shaped transmission line are arranged on the doped silicon in the same layer, and the metal electrode is positioned at two ends of the beam and connected through the strip-shaped transmission line; a piezoelectric film layer is arranged between the metal electrode and the doped silicon, and a first isolation oxide layer is arranged between the strip-shaped transmission line and the doped silicon; the metal electrodes on the two side beams are input electrodes, and the electrodes on the middle beam are output electrodes;

the two connecting ends are a first connecting end and a second connecting end respectively, and are all provided with anchor points, the first connecting end is connected with the substrate through the anchor points, and the second connecting end is connected with the micro-lever through the anchor points; one end of the input electrode is connected with the input electrode disc through a first connecting end, and one end of the output electrode is connected with the output electrode disc through a first connecting end.

5. A tuning fork TPoS resonator-based magnetic field sensor according to claim 4, wherein: the micro-lever comprises a first-stage micro-lever and a second-stage micro-lever, and the first-stage micro-lever and the second-stage micro-lever are connected through a lever connecting piece; the first-stage micro-lever is provided with an input end and a first supporting beam, the input end is directly connected with the metal spiral coil, and the first supporting beam is fixed on the silicon substrate; the length of the second stage micro lever is far longer than that of the first micro lever, an output end and a second supporting beam are arranged on the second stage micro lever, the second supporting beam is also fixed on the silicon substrate, and the output end is directly connected with an anchor point of the second connecting end of the three-tuning fork TPoS resonator.

6. A tuning fork TPoS resonator-based magnetic field sensor according to claim 3, characterized in that: the first isolation oxide layer is made of silicon dioxide, and the thickness of the first isolation oxide layer is 0.3-1.5 mu m.

7. A tuning fork TPoS resonator-based magnetic field sensor according to claim 4, wherein: the metal electrode and the strip-shaped transmission line are made of silver, copper, gold, aluminum, nickel or lead and other metals, and the thickness is 0.5-2 mu m; the piezoelectric material of the piezoelectric film is AlN, znO, PZT, PVDF, liNbO ₃ Or LiTaO ₃ The thickness is 0.5 μm to 2 μm.

8. The tuning fork TPoS resonator-based magnetic field sensor of claim 1 wherein the silicon substrate comprises a substrate silicon, a second isolation oxide layer, and a doped silicon layer laminated in sequence from bottom to top.

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