Multi-mode multi-frequency Lamb wave resonator based on interdigital electrode structure with different intervals

Abstract

The invention belongs to the technical field of micro-electro-mechanical systems (MEMS), and discloses a multi-mode multi-frequency lamb wave resonator of a non-same-interval interdigital electrode structure, which is used for solving the problems of large size, single frequency, low integration level and the like of the existing resonator. The multimode multi-frequency Lamb wave resonator comprises a Lamb wave resonator main body 1, a silicon substrate 2, a microstrip metal transmission line 4, a signal metal electrode 301 and a grounding metal electrode disc 302, wherein the Lamb wave resonator main body 1 is integrated on a silicon substrate and is provided with interdigital electrode structures at different intervals; and the signal metal electrode 301 and the grounding metal electrode disc 302 are arranged at two ends of the resonator. According to the invention, the resonator main body 1 is suspended on the middle hollow silicon substrate through the left anchor point and the right anchor point, and the resonator is ensured to have the advantages of low energy leakage and high quality factor (Q value) based on the isolation of an air gap and a surrounding structure; areas with different interdigital electrode center distances are designed, and the effects of multi-mode and multi-frequency output and equal-frequency distance distribution of the resonator are achieved.

Description

Technical Field

[0001] The invention belongs to the technical field of Micro-Electro-Mechanical Systems (MEMS), and particularly relates to a multi-mode and multi-frequency Lamb wave resonator based on a non-uniform pitch interdigital electrode structure. Background Art

[0002] As a core component of a frequency source, a resonator can provide stable clock signals and local oscillation signals for an electronic communication system, so it has become an indispensable device in a radio frequency communication module and is known as the "heart" of an electronic system. Along with the development trend of the integration and miniaturization of electronic devices, an electronic system often has multiple working modes and frequency bands, which has given rise to the application demand for multi-frequency resonators and made multi-mode resonators with small size, low power consumption, and high quality factor (Q value) become a research hotspot and received extensive attention from the academic and industrial communities. Currently, common resonators are mainly divided into traditional quartz crystal resonators, integrated RLC resonators, MEMS capacitive resonators, and MEMS piezoelectric resonators. Traditional quartz crystal resonators have long been used as the clock source of electronic products due to their very high Q value and very low temperature drift characteristics. However, quartz crystal resonators are relatively large in size and not easy to integrate, which does not conform to the development trend of the miniaturization of electronic systems. In addition, the thickness of a quartz crystal resonator is limited by the process, its upper frequency limit is relatively low (generally less than 150 MHz), and there is only one mode, so it cannot meet the application requirements of multi-mode and high frequency. Although the RLC resonator based on integrated circuit technology has high integration and small size, its Q value is very low, resulting in a large noise of the output signal, and it is often only suitable for occasions with low requirements for frequency accuracy and noise and difficult to meet the requirements of high-performance resonators. The MEMS capacitive resonator can achieve an extremely high Q value, so it has unique advantages in the field of clock sources. However, its dynamic impedance is very large, and vacuum packaging and an additional DC bias voltage are required, resulting in a high cost of the processing and packaging process. The MEMS piezoelectric resonator has the characteristics of small size, high Q value, low dynamic impedance, and a wide working frequency range, and is mainly divided into surface acoustic wave (SAW) resonators and bulk acoustic wave (BAW) resonators. The resonant frequency of a traditional BAW resonator is determined by the thickness of the piezoelectric material, and it is difficult to achieve the characteristic of multi-frequency output on a single chip; the traditional SAW resonator uses interdigital electrodes as transducers, and its resonant frequency is regulated by the center pitch of the interdigital electrodes. Therefore, resonators with different resonant frequencies can be fabricated on the same chip. However, the mechanical vibration mode and resonant frequency of a single SAW resonator are fixed.

[0003] As an emerging bulk acoustic wave resonator, the Lamb wave resonator based on the interdigital electrode structure has developed rapidly in recent years and has received extensive attention from the academic and industrial communities. The resonant frequency of the Lamb wave resonator is also regulated by the center spacing of the interdigital electrodes. However, compared with the SAW resonator that uses a metal reflection grating to converge acoustic waves, the Lamb wave resonator uses an air gap to reflect and converge acoustic waves. Therefore, the Lamb wave resonator has a smaller volume and a higher Q value. Similar to the SAW resonator, the mechanical vibration mode and resonant frequency of a single Lamb wave resonator are limited by the fixed center spacing of the interdigital electrodes, and the goal of a single resonator with multiple modes and multiple frequencies cannot be achieved. Summary of the Invention

[0004] In view of the problem that traditional acoustic resonators are difficult to achieve a single resonator with multiple modes and multiple frequencies, the present invention proposes a multi-mode and multi-frequency Lamb wave resonator based on an interdigital electrode structure with non-uniform spacings. The resonator has different center spacings of interdigital electrodes in different regions. By adjusting the center spacings of the metal interdigital electrodes in different regions, the resonant mode frequencies and frequency spacings excited in each region can be changed. Since different interdigital electrode regions are arranged in a specific pattern and the input and output interdigital electrodes in each region are directly connected correspondingly, the resonator can generate multiple resonant modes with different resonant frequencies and appropriate frequency intervals, thus achieving the purpose of a multi-mode and multi-frequency resonator.

[0005] The technical solution adopted by the present invention is as follows:

[0006] A multi-mode and multi-frequency Lamb wave resonator based on an interdigital electrode structure with non-uniform spacings, comprising a Lamb wave resonator body 1, a silicon substrate 2, a signal metal electrode pad 301, a ground metal electrode pad 302, a microstrip metal transmission line 4, and an anchor 6; characterized in that the Lamb wave resonator body 1 has an interdigital electrode structure with non-uniform spacings; there are electrode pads on both sides based on the direction of the interdigital electrodes, including a signal metal electrode pad 301 and a ground metal electrode pad 302, and the ground metal electrode pads 302 are arranged on both sides of the signal metal electrode pad 301; the ground metal electrode pad 302 is directly in contact with the upper surface of the silicon substrate 2, and both the signal metal electrode pad 301 and the microstrip metal transmission line 4 are electrically isolated from the silicon substrate 2 through a first isolation oxide layer 5. The silicon substrate 2 is a flat plate with a hollow in the middle, and the Lamb wave resonator body 1 is suspended at the center position of the silicon substrate 2 through the anchor 6. The doped silicon layer of the Lamb wave resonator is connected to the silicon substrate through single anchors on the left and right sides in the length direction. In addition, the resonator body is isolated from the external structure through an air gap around it. The existence of this air gap helps to reflect the Lamb wave, improve the voltage standing wave ratio, and further increase the Q value of the resonator at the resonant mode; the microstrip metal transmission line 4 passes above the anchor 6 and is used to connect the resonator body and the signal metal electrode pad 301, that is, the microstrip metal transmission line is, from top to bottom, a metal electrode layer, a first isolation oxide layer, and a doped silicon layer.

[0007] The non-uniform pitch interdigital electrode structure specifically includes a set number of interdigital electrode regions. Between the interdigital electrode regions, metal electrode strips perpendicular to the extending direction of the interdigital electrodes are used to connect the left and right interdigital electrode regions in sequence from outside to inside according to an equally spaced arrangement rule. The metal interdigital electrodes in the same region have the same center pitch and electrode width, while the center pitches of the metal interdigital electrodes in different regions are different, and the electrode widths can also be different; the metal electrodes in different regions are correspondingly connected to ensure that the resonance signals generated in each region can be directly superimposed.

[0008] The Lamb wave resonator body 1 is a thin film structure, and its cross-section from bottom to top is a doped silicon layer 103, a piezoelectric material layer 102, and a metal electrode layer 101 respectively;

[0009] Further, the interdigital electrode regions include a left electrode region 7 with a center pitch of 15 μm and a right electrode region 8 with a center pitch of 20 μm; this resonator can obtain four resonance frequencies: 91 MHz, 136 MHz, 209 MHz, and 264 MHz.

[0010] As an improvement of the present invention, the material of the first isolation oxide layer is silicon dioxide, and its thickness can be between 0.2 μm and 1.5 μm.

[0011] The materials of the piezoelectric material layer include but are not limited to AlN, ZnO, PZT, PVDF, LiNbO3, LiTaO3, etc., and the thickness is 0.5 μm to 3 μm;

[0012] The metal materials include but are not limited to metals such as silver, copper, gold, aluminum, nickel, and lead, and the thickness can be between 0.5 μm and 2 μm.

[0013] The doping methods of the doped silicon layer include but are not limited to N-type doping, P-type doping, etc., and the thickness can be between 4 μm and 12 μm.

[0014] Based on the above technical solutions, the present invention has the following advantages and beneficial effects:

[0015] 1. On the basis that the Lamb wave resonator of the present invention has a high Q value (in an atmospheric pressure environment), high frequency, low dynamic impedance, small volume and is compatible with the integrated circuit process, a non-uniform pitch interdigital electrode structure is adopted to excite multiple Lamb wave resonance modes. By adjusting the center pitch of the interdigital electrodes in each region, the present invention has the advantage of fabricating a multi-mode and multi-frequency resonator with equal frequency spacing.

[0016] 2. Since the Lamb waves excited by the interdigital electrodes mainly propagate in the direction perpendicular to the extension of the electrodes, and the different electrode regions in the resonator of the present invention are arranged in sequence along the direction of the extension of the interdigital electrodes, that is, the main transmission direction of the excited Lamb waves is perpendicular to the arrangement direction of the electrode regions. Therefore, there is almost no mutual coupling and interference between the Lamb waves excited by different electrode regions in the resonator of the present invention. Therefore, any number of interdigital electrode regions with different center spacings (arranged in the direction of the extension of the interdigital electrodes) can be designed within the limit that the resonator anchor can support, so as to realize specific numbers and frequencies of resonance modes, and further broaden the frequency band range and application scenarios of the resonator. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the following will briefly introduce the drawings required for the description of the embodiments. The drawings described herein are used to provide a further understanding of the embodiments of the present invention, form a part of this application, and do not limit the embodiments of the present invention. In the drawings:

[0018] Figure 1 is a three-dimensional structure diagram of a multi-mode and multi-frequency Lamb wave resonator with a non-uniform pitch interdigital electrode structure provided by the present invention;

[0019] Figure 2 is Figure 1 a top view of;

[0020] Figure 3 is Figure 1 a three-dimensional structure diagram of the remaining part after cutting off the right part along the AA' direction;

[0021] Figure 4 is Figure 2 a symmetric Lamb wave main mode vibration pattern diagram of the left electrode region in;

[0022] Figure 5 is Figure 2 an anti-symmetric Lamb wave main mode vibration pattern diagram of the left electrode region in;

[0023] Figure 6 is Figure 2 a symmetric Lamb wave main mode vibration pattern diagram of the right electrode region in;

[0024] Figure 7 is Figure 2 an anti-symmetric Lamb wave main mode vibration pattern diagram of the right electrode region in;

[0025] Figure 8 is a Y21 parameter curve diagram of a Lamb wave resonator with an interdigital electrode center spacing of 15 μm;

[0026] Figure 9It is a graph of the Y21 parameter of a Lamb wave resonator with a center pitch of 20 μm between interdigital electrodes;

[0027] Figure 10 It is a graph of the Y21 parameter of a multi-mode and multi-frequency Lamb wave resonator with a non-uniform pitch interdigital electrode structure provided by the present invention;

[0028] Marks in the accompanying drawings and corresponding component names:

[0029] 1 - Lamb wave resonator body; 101 - metal electrode layer; 102 - piezoelectric material layer; 103 - doped silicon layer; 2 - silicon substrate; 301 - signal metal electrode pad; 302 - ground metal electrode pad; 4 - microstrip metal transmission line; 5 - first isolation oxide layer; 6 - anchor point; 7 - left electrode region; 8 - right electrode region. Detailed implementation manners

[0030] In the following, the term "comprising" or "may comprise" that can be used in various embodiments of the present invention indicates the presence of the functions, operations or elements of the present invention, and does not limit the addition of one or more functions, operations or elements. In addition, as used in various embodiments of the present invention, the terms "comprising", "having" and their cognates are only intended to indicate specific features, numbers, steps, operations, elements, components or combinations of the foregoing items, and should not be construed as first excluding the existence of one or more other features, numbers, steps, operations, elements, components or combinations of the foregoing items or the possibility of adding one or more features, numbers, steps, operations, elements, components or combinations of the foregoing items.

[0031] In various embodiments of the present invention, the expression "or" or "at least one of A or / and B" includes any combination or all combinations of the recited words. 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.

[0032] Expressions (such as "first", "second", etc.) used in various embodiments of the present invention may modify various components in various embodiments, but do not limit the corresponding components. 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, the first user device and the second user device indicate different user devices, although both are user devices. For example, without departing from the scope of various embodiments of the present invention, the first element may be referred to as the second element, and similarly, the second element may also be referred to as the first element.

[0033] It should be noted that: If a description "connects" one component to another component, the first component can be directly connected to the second component, and a third component can be "connected" between the first component and the second component. Conversely, when a component is "directly connected" to another component, it can be understood that there is no third component between the first component and the second component.

[0034] The terms used in the various embodiments of the present invention are only for the purpose of describing specific embodiments and are not intended to limit the various embodiments of the present invention. As used herein, the singular forms are intended to also include the plural forms unless the context clearly indicates otherwise. Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which the various embodiments of the present invention belong. The terms (such as those defined in a general use dictionary) 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 the various embodiments of the present invention.

[0035] To make the objectives, technical solutions and advantages of the present invention more clear and understandable, the present invention will be further described in detail below in conjunction with embodiments and drawings. The illustrative embodiments and descriptions of the present invention are only used to explain the present invention and do not serve as a limitation to the present invention.

[0036] The technical solutions of the present invention will be described in detail below in conjunction with the drawings.

[0037] As Figure 1 As shown, a multi-mode multi-frequency Lamb wave resonator based on a non-uniform pitch interdigital electrode structure includes a Lamb wave resonator body 1, a silicon substrate 2, a signal metal electrode pad 301, a ground metal electrode pad 302, and a microstrip metal transmission line 4. The resonator body includes a non-uniform pitch interdigital electrode structure. There are electrode pads on both sides based on the direction of the interdigital electrodes. The arrangement of the electrode pads meets the requirements of the radio frequency probe station standard GSG (ground-signal-ground) probe test, facilitating high-precision electrical characteristic characterization. Specifically, ground metal electrode pads 302 are arranged on both sides of the signal metal electrode pad 301. Among them, the ground metal electrode pad 302 is directly in contact with the upper surface of the silicon substrate 2. The signal metal electrode pad 301 and the microstrip metal transmission line 4 are both electrically isolated from the silicon substrate 2 through a first isolation oxide layer 5 to avoid short circuit between the signal metal electrode pad 301 and the silicon substrate 2. The microstrip metal transmission line 4 is connected to the metal electrode layer 101 in the resonator body and the signal metal electrode pad 301 via above an anchor point 6. The silicon substrate 2 is a three-layer structure, and the cross-section from top to bottom is a doped silicon layer 103, a second isolation oxide layer, and an insulating silicon layer.

[0038] CombinedFigure 1 With Figure 3 , the Lamb wave resonator body 1 is a thin film structure, and the cross-section of this structure from bottom to top is a doped silicon layer 103, a piezoelectric material layer 102 grown or assembled on the doped silicon layer, and a metal electrode layer 101 on the piezoelectric material layer. In this embodiment, the doping type of the doped silicon is N-type doping, and the thickness is 10 μm; the piezoelectric material is aluminum nitride (AlN), and the thickness is 0.5 μm; the material of the metal electrode (including the microstrip metal transmission line, the interdigital electrode, and the metal electrode pad) is aluminum, and the thickness is 1 μm.

[0039] By applying an alternating voltage signal to the interdigital electrode, the piezoelectric material layer 102 generates periodic vibrations under the inverse piezoelectric effect, and then generates Lamb waves propagating in all directions. The bottom of the resonator body 1 is suspended, effectively preventing the leakage of Lamb wave energy in the direction of the silicon substrate 2. Except for the anchor point 6, the periphery is isolated from the silicon substrate 2 through an air gap, so that the excited Lamb waves are significantly reflected when propagating to the boundary, and are superimposed with the incident waves to form a standing wave, triggering resonance, and ensuring a high quality factor (Q value).

[0040] The non-uniform pitch interdigital electrode structure specifically includes a set number of interdigital electrode regions, and the interdigital electrode regions have different interdigital electrode center pitches; between the interdigital electrode regions, metal electrode strips perpendicular to the extension direction of the interdigital electrodes are used and arranged in an equal-spacing pattern to connect the left and right interdigital electrode regions from outside to inside in sequence. The metal interdigital electrodes in the same region have the same center pitch and electrode width, and the center pitches of the metal interdigital electrodes in different regions are different, and the electrode widths can also be different; the metal electrodes in different regions are correspondingly connected to ensure that the resonance signals generated in each region can be directly superimposed. One implementation is as Figure 2 shown. The Lamb wave resonator body 1 is fixed to the silicon substrate 2 through the anchor point 6. In order to implement a multi-interdigital electrode structure, there are a left electrode region 7 and a right electrode region 8 in the resonator body 1. In order to directly connect the input and output electrodes in the left and right regions correspondingly and not affect the electrical performance of the resonator, in this embodiment, metal electrode strips perpendicular to the extension direction of the interdigital electrodes are used between these two electrode regions, and the corresponding electrodes in the left and right regions are connected from outside to inside in sequence according to an equal-spacing arrangement rule.

[0041] Figure 4 With Figure 5 shown are respectively the three-dimensional vibration mode diagrams and cross-sectional vibration mode diagrams of the symmetric Lamb wave main mode (S0) and the anti-symmetric Lamb wave main mode (A0) in the left electrode region 7 of the resonator body 1. In this embodiment, the interdigital electrode center pitches in the left electrode region 7 are 15 μm respectively.

[0042] Figure 6 With Figure 7The figures respectively show the three-dimensional vibration mode diagrams and cross-sectional vibration mode diagrams of the symmetric Lamb wave main mode (S0) and the anti-symmetric Lamb wave main mode (A0) in the right electrode region 8 of the resonator body 1. In this embodiment, the center spacing of the interdigital electrodes in the right electrode region 8 is 20 μm respectively.

[0043] Based on Figures 4 - 7 the magnitude of the deformation in the vibration mode diagrams indicates that when the left electrode region 7 resonates, the deformation in the right electrode region 8 is very weak, and vice versa. That is to prove that the Lamb waves excited in each region mainly propagate along the width direction of the thin film (i.e., perpendicular to the extending direction of the interdigital electrodes), and the energy leakage of the Lamb waves along the arrangement direction of the electrode regions is less. Therefore, it shows that different regions with different interdigital electrode center spacings can normally excite the S0 and A0 modes without mutual influence on other regions. This is beneficial to designing different multiple electrode regions based on the calculation and simulation results and optimizing the resonator structure by region.

[0044] Under the condition of ensuring that the material properties of each layer of the resonator, other dimensions, and the external environment remain unchanged, the resonance frequencies of the above-mentioned symmetric Lamb wave main mode (S0) and anti-symmetric Lamb wave main mode (A0) are only regulated by the center spacing of the interdigital electrodes. Here, the calculation formula for the resonance frequency of the S0 mode is briefly listed:

[0045]

[0046] Among them, V p is the phase velocity of the Lamb wave excited during resonance, λ is the wavelength of the Lamb wave, C is the elastic modulus of the piezoelectric thin film, ρ is the density of the piezoelectric thin film, and p is the center spacing of the interdigital electrodes.

[0047] Figure 8 、 9 are the schematic diagrams of the Y21 curves of Lamb wave resonators with the same structure and material having a single interdigital electrode center spacing of 15 μm and 20 μm respectively. Figure 10 is the schematic diagram of the Y21 curve of the Lamb wave resonator designed in this embodiment with a non-uniform spacing interdigital electrode structure (including two electrode center spacings of 15 μm and 20 μm).

[0048] Combined with Figure 8 、 Figure 9 、 Figure 10 it can be known that the Lamb wave resonator with a non-uniform spacing interdigital electrode structure can be compatible with the Lamb wave modes excited by the same structure resonators with multiple single electrode center spacings, and thus realize more frequency outputs. The Lamb wave resonator with a non-uniform interdigital electrode spacing structure designed in this embodiment can obtain four resonance frequencies of approximately equally spaced distribution: 91 MHz (A0_1), 136 MHz (A0_2), 209 MHz (S0_1), and 264 MHz (S0_2).

[0049] The method proposed in this embodiment applies the non-uniform pitch interdigital electrode structure to the Lamb wave resonator, achieving the effects of multi-resonant frequency output and equally spaced frequency distribution. And anchor points are used for fixing to improve the Q value; a doped silicon layer is used under the piezoelectric material to improve the mechanical stability of the resonator; the SOI substrate is used to make the device have the advantage of being compatible with the integrated circuit process.

[0050] The specific embodiments described above have further elaborated on the purpose, technical solutions, and beneficial effects of the present invention. It should be understood that the above description is only the specific embodiments of the present invention and is not used to limit the protection scope of the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present invention shall be included in the protection scope of the present invention.

Claims

1. A multi-mode multi-frequency Lamb wave resonator based on a non-uniform pitch interdigital electrode structure, comprising a Lamb wave resonator body (1), a silicon substrate (2), a signal metal electrode pad (301), a ground metal electrode pad (302), a microstrip metal transmission line (4), and an anchor point (6); characterized in that, The Lamb wave resonator body (1) has a non-uniform pitch interdigital electrode structure; there are electrode pads on both sides based on the direction of the interdigital electrodes, including a signal metal electrode pad (301) and a ground metal electrode pad (302), and the ground metal electrode pads (302) are arranged on both sides of the signal metal electrode pad (301); the silicon substrate (2) is a flat plate with a hollow in the middle, and the Lamb wave resonator body (1) is suspended at the center of the silicon substrate (2) through an anchor point (6); the microstrip metal transmission line (4) passes above the anchor point (6) and connects the Lamb wave resonator body (1) and the signal metal electrode pad (301).

2. A multimode and multifrequency Lamb wave resonator based on a non-uniform pitch interdigital electrode structure according to claim 1, wherein The non-uniform pitch interdigital electrode structure specifically includes a set number of interdigital electrode regions, and different interdigital electrode regions have different center pitches of interdigital electrodes; between the interdigital electrode regions, metal electrode strips perpendicular to the extending direction of the interdigital electrodes are used and arranged at equal intervals to connect the left and right interdigital electrode regions from outside to inside in turn.

3. The multimode and multi - frequency Lamb wave resonator based on a non - uniform pitch interdigital electrode structure according to claim 2, wherein, The ground metal electrode pad (302) is in direct contact with the upper surface of the silicon substrate (2), and both the signal metal electrode pad (301) and the microstrip metal transmission line (4) are electrically isolated from the silicon substrate (2) through a first isolation oxide layer (5).

4. The multimode and multi-frequency Lamb wave resonator based on a non-uniform pitch interdigital electrode structure according to claim 3, characterized in that, The Lamb wave resonator body (1) is a thin film structure, and its cross-section from bottom to top is a doped silicon layer (103), a piezoelectric material layer (102), and a metal electrode layer (101) respectively.

5. A multimode and multi - frequency Lamb wave resonator based on a non - uniform pitch interdigital electrode structure according to claim 4, characterized in that, The interdigital electrode regions include a left electrode region (7) with a center pitch of 15 μm and a right electrode region (8) with a center pitch of 20 μm; this resonator can obtain four resonance frequencies: 91 MHz, 136 MHz, 209 MHz, and 264 MHz.

6. The multimode and multi - frequency Lamb wave resonator based on a non - uniform pitch interdigital electrode structure according to claim 5, wherein, The anchor point (6) is a doped silicon connecting beam.

7. A multimode and multifrequency Lamb wave resonator based on a non-uniform pitch interdigital electrode structure according to claim 6, characterized in that, The material of the first isolation oxide layer (5) is silicon dioxide, and its thickness is 0.2 μm to 1.5 μm; The doping method of the doped silicon layer (103) includes but is not limited to N-type doping and P-type doping, and its thickness is between 4 μm and 12 μm.

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