Micromechanical resonator considering thermal elastic loss and preparation method thereof

Abstract

The invention discloses a micromechanical resonator considering thermal elastic loss and a preparation method thereof, the resonator comprises a substrate layer, a buried oxide layer and a device layer, the substrate layer has a cavity structure, the device layer comprises a resonant oscillator suspended above the cavity structure, and the structure of the resonant oscillator is along lt; 100 gt; reaching to lt; 110gt, 110gt; according to the specific track distribution of the single crystal silicon material and the specific track distribution of the crystal orientation, the track distribution is adjusted according to the anisotropy of the single crystal silicon material and the vibration characteristics of different modes, so that the contour of the resonant oscillator is of an irregular rectangular and / or circular structure. According to the micro-mechanical resonator, under the condition that the process difficulty and the manufacturing cost are not increased, the track distribution of the resonator structure along different crystal orientations is adjusted, so that the equivalent stiffness of the resonator structure along different crystal orientations is changed, the stress distribution can be balanced, the temperature gradient generated by stress is reduced, the thermal elastic loss is reduced, and the Q value is remarkably improved.

Description

Technical Field

[0001] The invention relates to the technical field of resonators, and in particular to a micromechanical resonator taking thermoelastic loss into consideration and a preparation method thereof. Background Art

[0002] Clocks are key components in digital circuits, providing frequency references and time references. Micromechanical resonators based on microelectromechanical systems (MEMS) are the basic elements of clocks, generating stable frequency signals through vibration. The resonator combined with peripheral circuits can form an oscillator, output a fixed frequency signal, and drive the operation of digital systems. In the current information age, micromechanical resonators, as a key micro-nanostructure component, are widely used in wireless communications, sensor technology, clock systems, and inertial navigation. These applications place increasingly higher demands on the performance of resonators. The improvement of resonator performance is directly related to the reliability and accuracy of these application systems, especially in the context of the growing demand for high precision, high stability, and low noise.

[0003] Quality factor (Q) is a key indicator for measuring the performance of MEMS resonators. A high Q value can reduce the dynamic impedance of the resonator, reduce the phase noise of the system and improve the frequency stability of the oscillator. Therefore, improving the Q value has become one of the core goals of resonator design. The energy loss mechanism of the MEMS resonator Q value mainly consists of five parts: air damping loss (Q air ), thermoelastic loss (Q TED ), material loss (Q material ), anchor loss (Q anchor ) and electrical load losses (Q loaded ),Right now: , Reducing the thermoelastic loss of the resonator is crucial to improving the Q value of the resonator. Thermoelastic loss is closely related to the vibration frequency and mode of the resonator. High-frequency vibration usually increases thermoelastic loss because frequent stress and temperature changes will cause more energy dissipation. Different vibration modes will also lead to different stress and temperature distributions, which will affect the magnitude of thermoelastic loss. The geometry of the resonator also has an important impact on thermoelastic loss. Complex geometric shapes may cause stress concentration and non-uniform temperature distribution, thereby increasing thermoelastic loss. Optimizing the geometry of the resonator for different vibration modes can reduce stress concentration and heat conduction paths, thereby reducing thermoelastic loss. Single crystal silicon material is one of the most common materials for MEM resonators, and its material properties depend on the orientation relative to the lattice. Due to the anisotropy of single crystal silicon material properties, the stress distribution between structures in different crystal directions of traditional resonators is uneven, resulting in a large temperature gradient, which in turn leads to increased thermoelastic loss. These problems limit the further improvement of resonator performance and cannot meet the increasingly stringent application requirements.

[0004] In order to solve these problems, a method is needed to flexibly design and adjust the resonator structure, balance the stress distribution of the resonator structure, reduce the temperature gradient caused by stress, and reduce the thermoelastic loss to achieve an improvement in the Q value. The present invention proposes an innovative micromechanical resonator structure and a design method thereof to address the above problems. Summary of the invention

[0005] The purpose of the present invention is to provide a micromechanical resonator and a preparation method thereof that takes thermoelastic loss into consideration in view of the problems existing in the prior art. The innovation of the present invention is that the geometric parameters of the resonator structure along different crystal directions are precisely controlled so as to adjust the equivalent stiffness of the resonator structure along different crystal directions, so that the resonator can achieve a better stress distribution when resonating, reduce the temperature gradient, and effectively reduce the thermoelastic loss. Specifically, on the basis of the traditional annular or plate-shaped resonator, according to the anisotropy of the single crystal silicon material and the vibration mode of the resonator, the geometric parameters such as the width, radius and thickness of the resonator structure along different crystal directions are adjusted, and by using optimization methods such as finite element analysis, the resonator structure can be subjected to detailed stress and thermoelastic loss analysis to ensure the accuracy and effectiveness of the design.

[0006] In summary, the present invention can solve the problem of stress concentration in plate-shaped or ring-shaped micromechanical resonator structures during resonant operation through innovative structural design and adjustment methods, reduce the temperature gradient caused by stress, reduce thermoelastic losses, and significantly improve the Q value of the resonator, thereby providing micromechanical resonators with higher performance and stability in various application scenarios.

[0007] To achieve the above object, the technical solution adopted by the present invention is: A micromechanical resonator considering thermoelastic loss comprises a substrate layer, a buried oxide layer and a device layer arranged on the substrate layer, wherein the substrate layer has a cavity structure, and the device layer comprises a resonant oscillator suspended above the cavity structure, wherein the structure of the resonant oscillator is along the <100> to <110> The specific trajectory distribution in the crystal direction is adjusted according to the anisotropy of the single crystal silicon material and the vibration characteristics of different modes so that the outline of the resonant oscillator is an irregular rectangular and / or circular structure; the resonant oscillator can be used alone, or form a resonator array, or be used as a mechanical coupling structure to couple with other resonators.

[0008] Without increasing the process difficulty and manufacturing cost, the micromechanical resonator can balance the stress distribution, reduce the temperature gradient caused by stress, reduce the thermoelastic loss, and significantly improve the mechanical properties of the micromechanical resonator. Q value.

[0009] Furthermore, the trajectory distribution adjustment method is suitable for a variety of resonant oscillator structures, including annular or plate structures; the outer contour of the plate resonator and the inner contour and / or outer contour of the annular structure are adjusted, and the inner contour and / or outer contour shrink toward the center respectively, and there are different shrinkage amounts.

[0010] Furthermore, when the main structure of the resonant oscillator is a circular ring or circular plate structure, multiple arc segments of its inner contour and / or outer contour radially shrink; when the main structure of the resonant oscillator is a square ring or square plate structure, the side length of its inner contour and / or outer contour shrinks and changes from a straight line state to a curved state, the side length of the outer contour is a convex curve, and the side length of the inner contour is a concave curve.

[0011] Furthermore, when the structure of the resonant oscillator is coupled with other resonators as a coupling structure, it is connected to other structures through support beams or anchor points, and the inner contour and / or outer contour of the annular or plate-shaped structure of the coupling structure also shrinks toward the center of the coupling structure.

[0012] Furthermore, microholes or grooves are etched on the structure of the resonator along different crystal directions, and doping is performed at different crystal directions by regional doping to adjust the equivalent stiffness of the resonator structure in different crystal directions.

[0013] Furthermore, the trajectories of the resonant oscillator in different crystal directions after adjustment satisfy the following conditions: , In the formula, is the structural parameter of the resonant oscillator, is the vibration modal parameter, for and Function, structure parameters At least width, radius and thickness, is the Young's modulus of each crystal direction, is the trajectory parameter before adjustment, is the reference Young's modulus.

[0014] Furthermore, the resonant oscillator structure is a single-layer single-crystal silicon structure, or a composite thin film structure of metal-piezoelectric layer-single-crystal silicon.

[0015] Furthermore, a support beam may be provided on the periphery of the resonant oscillator, and the support beam is a straight beam, a T-shaped beam or a folded beam arranged at the vibration node of the resonant oscillator, or the support beam is a spoke beam arranged on the inner periphery of the resonant oscillator.

[0016] A method for preparing a micromechanical resonator taking into account thermoelastic loss, when the resonator is a single-crystal silicon single-layer structure, the preparation method is as follows: Providing an SOI wafer, wherein the SOI wafer comprises, from bottom to top, a substrate layer, a buried oxide layer, and a device layer with a thickness of 5-60 μm; Depositing a 1-2µm thick metal layer on the device layer, and forming a metal pad after patterning; The front side of the SOI wafer is etched to selectively etch the device layer until the etching stops on the buried oxide layer, and a microstructure of a desired resonant oscillator is formed in the device layer according to the adjusted trajectory; Back-etching the SOI wafer, selectively etching the substrate layer until the buried oxide layer is etched, forming a through hole or the cavity structure in the substrate layer, and exposing the buried oxide layer; Gaseous hydrofluoric acid is introduced to corrode and release the exposed buried oxide layer, so that the resonant oscillator is released and suspended to obtain a micromechanical resonator structure.

[0017] A method for preparing a micromechanical resonator taking into account thermoelastic loss, when the resonator is a composite structure of metal-piezoelectric layer-single crystal silicon, the preparation method is as follows: Providing an SOI wafer, wherein the SOI wafer comprises, from bottom to top, a substrate layer, a buried oxide layer, and a device layer with a thickness of 5-60 μm; Depositing a piezoelectric material with a thickness of 0.5-1 µm and an upper electrode with a thickness of 0.15-0.2 µm on the device layer in sequence, then patterning the upper electrode, and then depositing a top oxide layer with a thickness greater than 0.2 µm; Etching the top oxide layer to form an upper electrode through hole to expose the upper electrode; Continue etching the top oxide layer and the piezoelectric material to form a lower electrode through hole to expose the device layer; Depositing a metal layer with a thickness of 1-2 μm in the upper electrode through hole and the lower electrode through hole, and performing patterning to form a metal pad; Performing front etching on the top oxide layer, the piezoelectric material and the device layer until the buried oxide layer is formed, and distributing the microstructure of the required resonant oscillator in the device layer according to the adjusted trajectory; Performing back etching on the substrate layer until the buried oxide layer is reached, forming a through hole or the cavity structure in the substrate layer, and exposing the buried oxide layer; Gaseous hydrofluoric acid is introduced to corrode and release the exposed buried oxide layer, so that the resonant oscillator is released and suspended to obtain a micromechanical resonator structure.

[0018] Compared with the prior art, the beneficial effects of the present invention are as follows: 1. The micromechanical resonator can balance the stress distribution, reduce the temperature gradient caused by stress, reduce the thermoelastic loss, and significantly improve the micromechanical resonator structure by adjusting the trajectory distribution of the resonator structure along different crystal directions and thereby changing the equivalent stiffness of the resonator structure along different crystal directions without increasing the process difficulty and manufacturing cost. Q 2. The resonant oscillator has different track distributions along different crystal directions. The frequency-temperature characteristics of the resonator will be affected by the track distribution. The track distribution can be adjusted to improve the resonator according to different application scenarios. Q The influence of the value and frequency temperature characteristics; 3. The resonant oscillator adjusts its <100> to <110> After the crystal direction trajectory is distributed, its outline is no longer a regular rectangular or circular structure, and the outline has a change in curvature, which is obviously different from the circular geometric trajectory or rectangular geometric trajectory of the existing resonator. The temperature gradient on the adjusted resonant oscillator structure is significantly reduced, the vibration mode of the resonator is effectively improved, and the internal stress distribution of the structure is more balanced; 4. This method has high universality and can be applied to a variety of plate or ring resonator structures. The adjusted structure can also be applied to coupling structures, can be applied to single-layer single-crystal silicon structures, and can also be applied to the structural design of multi-layer composite films. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 A three-dimensional schematic diagram of a micromechanical resonator considering thermoelastic loss according to the present invention; Figure 2 It is a schematic diagram showing the structure of the resonant oscillator of the present invention from the buried oxide layer to the device layer; Figure 3 Schematic diagram of Young's modulus of single crystal silicon material when it is aligned with different crystal directions; Figure 4 A schematic diagram of a circular ring structure after adjusting the outer contour of the resonator structure of the present invention; Figure 5 A schematic diagram of a circular ring structure after adjusting the inner contour of the resonator structure of the present invention; Figure 6 This is a schematic diagram of the circular ring structure after adjusting the inner and outer contours of the resonator structure of the present invention; Figure 7 A schematic diagram of the circular plate structure after adjusting the outer contour of the resonator structure of the present invention; Figure 8 This is a schematic diagram of the square ring structure after the inner contour of the resonator structure of the present invention is adjusted; Fig. 9 This is a schematic diagram of the square ring structure after the outer contour of the resonator structure of the present invention is adjusted; Fig.10 This is a schematic diagram of the square ring structure after the inner and outer contours of the resonator structure of the present invention are adjusted; Fig.11 A schematic diagram of a square plate structure after adjusting the outer contour of the resonator structure of the present invention; Fig.12 A schematic diagram of the coupling structure of the micromechanical resonator structure of the present invention applied to LE-RB; Fig.13 It is a schematic diagram of the coupling structure of the micromechanical resonator structure of the present invention applied to SE-RB; Fig.14 This is a schematic diagram of the structure in which the support beam of the present invention is a straight beam; Fig.15 This is a schematic diagram of the structure in which the support beam of the present invention is a folded beam; Fig.16 It is a structural schematic diagram of the support beam of the present invention being a spoke beam (central anchor point); Fig.17 The radial extension mode temperature gradient and Q before and after adjustment obtained by finite element simulation TED contrast; Figure 18 to Figure 23 The processing flow chart of Example 2 is shown in FIG. Fig.18 The company showcased a customized SOI wafer, including the substrate silicon wafer, buried oxide layer, and device layer; Fig.19 The process of depositing metal on the device layer and forming metal pads is demonstrated; Fig. 20 The structure after front-side etching of the device layer is shown; Fig.21 The structure after back-etching of the substrate layer is shown; Fig. 22 It was demonstrated that after the introduction of gaseous hydrofluoric acid, a micromechanical resonator structure was formed; Fig.23The micromechanical resonator structure of Example 2 prepared by the CSOI process is shown; Figure 24 to Figure 32 This is a processing flow chart of Example 3; in: Fig.24 The company demonstrated customized SOI wafers, including substrate silicon wafer, buried oxide layer and device layer silicon; Fig.25 The process of depositing the piezoelectric layer, top electrode, and top oxide on the device layer is demonstrated; Fig.26 The process of etching the top oxide to form a through hole for the upper electrode and expose the upper electrode is shown; Fig. 27 The process of etching the top oxide and piezoelectric material to form the through hole for the bottom electrode is shown; Fig.28 The process of depositing metal in the upper and lower electrode through holes and patterning to form metal pads is demonstrated; Fig.29 The structure is shown with front-side etching of the top oxide, piezoelectric material, and device layers; Fig.30 The structure of back-side etching of the substrate silicon wafer is shown; Fig.31 It was demonstrated that after the introduction of gaseous hydrofluoric acid, a micromechanical resonator structure was formed; Fig.32 The micromechanical resonator structure of Example 3 prepared by the CSOI process flow is shown; In the figure: 1. resonant oscillator; 2. support beam; 3. bias electrode; 4. inner electrode; 5. outer electrode; 6. device layer; 7. buried oxide layer; 8. substrate layer; 9. support sheet structure; 10. center anchor point. DETAILED DESCRIPTION

[0020] The technical solution of the present invention will be described clearly and completely below in conjunction with the accompanying drawings of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0021] In the description of the present invention, it should be noted that the directions or positional relationships indicated by the terms "middle", "upper", "lower", "left", "right", "inner", "outer", etc. are based on the directions or positional relationships shown in the drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific direction, be constructed and operated in a specific direction, and therefore cannot be understood as limiting the present invention. In addition, the terms "first", "second", etc. are only used for descriptive purposes and cannot be understood as indicating or implying relative importance. Example 1

[0022] like Figure 1 and 2 As shown, a micromechanical resonator considering thermoelastic loss includes a substrate layer 8, a buried oxide layer 7 and a device layer 6 arranged on the substrate layer 8, the substrate layer 8 has a cavity structure, the device layer 6 includes a resonant oscillator 1 suspended above the cavity structure, an inner electrode 4 is arranged in the middle of the resonant oscillator 1, the resonant oscillator 1 is also connected to a bias electrode 3 through a support beam 2, and an outer electrode 5 is also arranged on the periphery of the resonant oscillator 1; the structure of the resonant oscillator 1 is along <100> to <110> The track distribution in the crystal direction is adjusted so that the outline of the resonant oscillator 1 is an irregular rectangular and / or circular structure.

[0023] Without increasing the process difficulty and manufacturing cost, the micromechanical resonator can balance the stress distribution, reduce the temperature gradient caused by stress, reduce the thermoelastic loss, and significantly improve the mechanical properties of the micromechanical resonator. Q value.

[0024] The resonant oscillator 1 has different track distributions along different crystal directions. The frequency-temperature characteristics of the resonator will be affected by the track distribution. The track distribution can be adjusted to improve the resonator according to different application scenarios. Q The influence of value and frequency-temperature characteristics.

[0025] The resonant oscillator 1 adjusts its <100> to <110> After the crystal direction trajectory is distributed, its outline is no longer a regular rectangular (rectangular or square) or circular structure, and the outline has a change in curvature, which is obviously different from the circular geometric trajectory or rectangular geometric trajectory of the existing resonator. The resonator is simulated using finite element method, and the radial extension mode and temperature gradient before and after adjustment are obtained as follows: Fig.17 As shown, it can be seen that before the ring structure resonator is adjusted, the temperature gradient on the resonant oscillator structure is greater than the temperature gradient after adjustment by adopting the technical solution of the present invention. By adopting the technical solution of the present invention, the vibration mode of the resonator is effectively improved, and the stress distribution inside the structure is more balanced. QTED Obtained significant improvement.

[0026] After the trajectory distribution of the resonant oscillator 1 is adjusted, the shapes of the electrodes inside and outside the resonant oscillator 1 will also be adjusted accordingly. In addition, the resonator adopts the structure of internal and external electrodes, and the internal electrode and the external electrode are not in direct contact with the resonant oscillator.

[0027] In this embodiment, the resonant oscillator is prepared in the middle of the device layer according to the pattern of track distribution, the bias electrode 3 and the external electrode 5 are respectively arranged in four symmetrical positions, the four bias electrodes 3 are distributed at 0°, 90°, 180° and 270°, and the four external electrodes 5 are distributed at 45°, 135°, 225° and 315°; the inner diameter of the cavity structure is larger than the outer diameter of the resonant oscillator 1, the cavity structure is etched out in the substrate layer, and the buried oxide layer at the corresponding position is released in the subsequent etching process, so that the resonant oscillator 1 is suspended in the substrate layer. The state on the cavity structure, the support beam 2 on the periphery of the resonant oscillator 1 extends outside the cavity structure to the buried oxide layer 7, and then connects to the bias electrode 3. The periphery of the resonant oscillator 1 is provided with a support sheet structure 9 in the area between adjacent bias electrodes 3. The inner side of the support sheet structure 9 is arc-shaped and maintains a gap with the periphery of the resonant oscillator 1. The two straight sides and the top corners of the support sheet structure 9 are arranged on the buried oxide layer 7 and a rectangular support platform is provided at the top corner to support the external electrode 5. The support sheet structure 9 is also a structure etched on the device layer 6 to support and connect the external electrode 5. The internal electrode 4 is in the middle area of ​​the resonant oscillator, and it itself is not directly connected to the inner periphery of the resonant oscillator. It can also be supported or connected by a support structure or an external structure.

[0028] Furthermore, the resonant oscillator 1 includes an annular main body structure, and the inner contour and / or outer contour of the annular main body structure shrinks toward the center respectively, and there are different shrinkage amounts.

[0029] That is, the contour of the annular main structure changes from a standard circular or rectangular structure to a contour with a curvature change, which can be adjusted according to the anisotropy of the single crystal silicon material. When the annular main structure is a circular ring structure, multiple arc segments of its inner contour and / or outer contour shrink radially; when the annular main structure is a square ring structure, the side length of its inner contour and / or outer contour shrinks and changes from a straight line state to a curved state, the side length of the outer contour is an outward convex curve, and the side length of the inner contour is an inward concave curve.

[0030] Specifically, taking the radial extension mode of the resonant oscillator 1 as an example, Figure 4As shown, the traditional ring structure is a standard circle 0. According to the anisotropy of the single crystal silicon material, the structure of the adjusted resonant oscillator 1 is obviously different from the geometric trajectory of the circular resonator. The adjusted resonant oscillator 1 has four arcs indented in the radial direction. Figure 5 The circular trajectory of the resonant oscillator 1 after adjusting the inner contour is shown, and it also has four arc segments showing morphological changes. Figure 6 The figure shows the annular trajectory of the resonant oscillator 1 after adjusting both the inner and outer contours. At this time, the ring is no longer a standard circular ring, but a special-shaped ring with a variable width. The positions of the arc segments where the inner and outer contours vary are staggered, so that the width of the adjusted resonant oscillator is slightly larger at the positions of 0°, 90°, 180° and 270°, which are the positions where the support beam is connected. These positions are also the vibration node positions of the resonant oscillator. Such an arrangement can improve its vibration characteristics and stress state.

[0031] Figure 7 The structure of the plate-shaped resonant oscillator after the outer contour is adjusted is shown. Figures 8 to 11 They are schematic diagrams of the square ring structure after adjusting the inner contour of the resonant oscillator, the square ring structure after adjusting the outer contour, the square ring structure after the inner and outer contours, and the square plate structure after the outer contour. It can be seen that the sides of the square ring structure are no longer straight edges, but arc edges with varying widths.

[0032] Furthermore, the periphery of the annular main structure is also connected to a mechanical coupling ring structure through the support beam or anchor point, and the inner contour and / or outer contour of the mechanical coupling ring structure also shrinks toward the center of the mechanical coupling ring structure, and the bias electrode is arranged at the location of the mechanical coupling ring structure.

[0033] Specifically, Fig.12 and Fig.13 As shown, the contour adjustment form of the mechanical coupling ring structure is basically similar to the contour adjustment form of the resonant oscillator, so that its contour is no longer a standard circle or rectangle, and electrodes are provided on the mechanical coupling ring structure.

[0034] Further, such as Fig.14 and 15 As shown, the support beam 2 is a straight beam, a T-shaped beam or a folded beam arranged at the vibration node of the resonant oscillator; Fig.16 As shown, the support beam 2 may also be a spoke beam arranged on the inner periphery of the resonant oscillator, and a central anchor point 10 is used for support at the middle intersection of the spoke beam.

[0035] Furthermore, the inner electrodes and the outer electrodes are symmetrically arranged on the periphery of the resonant oscillator, and one outer electrode is arranged between adjacent inner electrodes.

[0036] Furthermore, the resonator structure is adjusted along <100> to <110> The trajectory distribution of the crystal direction includes but is not limited to etching microholes or grooves on the structure of the resonator along different crystal directions, using regional doping to dope at different crystal direction positions, and adjusting the equivalent stiffness of the resonator structure in different crystal directions to balance the stress distribution and reduce thermoelastic losses.

[0037] Preferably, the single crystal silicon material is N-type or P-type heavily or super heavily doped, and the doping concentration includes but is not limited to 4.0×10 19 / cm 3 Up to 2.0×10 20 / cm 3 .

[0038] Preferably, the resonator structure can be used alone, or can form a resonator array or be coupled with other resonators as a mechanical coupling structure, so as to adjust the overall performance of the coupled resonator.

[0039] Preferably, the vibration modes of the resonator include but are not limited to extension modes, shear modes, and combined modes.

[0040] The structure of the resonant oscillator is not limited to a specific type of resonator, including but not limited to piezoelectric, capacitive and piezoresistive resonator designs. When a piezoelectric resonator design is adopted, the device structure includes but is not limited to a composite thin film structure of metal-piezoelectric layer-single crystal silicon.

[0041] Furthermore, the trajectories of the resonant oscillator 1 in different crystal directions after adjustment satisfy the following conditions: , In the formula, is the structural parameter of the resonant oscillator, is the vibration modal parameter, for and Function, structure parameters At least width, radius and thickness, is the Young's modulus of each crystal direction, is the trajectory parameter before adjustment, For reference Young's modulus, the Young's modulus of single crystal silicon is as follows Figure 3 shown. Example 2

[0042] A method for preparing a micromechanical resonator taking into account thermoelastic loss, the method being applied to a device structure that is not limited to a specific type of resonator, including but not limited to piezoelectric, capacitive, and piezoresistive resonator designs. When a piezoelectric resonator design is used, the device structure includes but is not limited to a composite thin film structure of metal-piezoelectric layer-single crystal silicon.

[0043] When the resonator is a single-crystal silicon single-layer structure, the preparation method is as follows: (1) If Fig.18 As shown, a SOI wafer is provided, wherein the SOI wafer includes, from bottom to top, a substrate layer 501 (substrate silicon wafer), a buried oxide layer, and a device layer 503 (device layer silicon) having a thickness of 5-60 μm; (2) If Fig.19 As shown, a 1-2µm thick metal layer is deposited on the device layer 501, and after being processed by a patterning process, metal pads 504 are formed. These metal pads will be used for electrical connection in subsequent steps; (3) If Fig. 20 As shown, the front side of the SOI wafer is etched, and the device layer 503 is selectively etched until the etching stops on the buried oxide layer 502, and the microstructure of the required resonant oscillator is formed in the device layer 503 according to the adjusted trajectory. This step ensures that the required microstructure is formed in the device layer while protecting the buried oxide layer below; (4) If Fig.21 As shown, the back side of the SOI wafer is etched, the substrate layer 501 is selectively etched until the buried oxide layer 502 is etched, a through hole or the cavity structure is formed in the substrate layer 501, and the buried oxide layer 502 is exposed to prepare for the subsequent release process; (5) If Fig. 22 As shown, gaseous hydrofluoric acid is introduced to corrode and release the exposed buried oxide layer 502, so that the resonant oscillator is released and suspended to obtain a micromechanical resonator structure. Gaseous hydrofluoric acid can effectively remove the buried oxide layer, realize the release and suspension of the device, and thus complete the resonator structure.

[0044] The above-mentioned embodiment 2 is a preparation process using the SOI process. The resonator with a single-crystal silicon single-layer structure can also be prepared using the CSOI process. The prepared resonator structure is as follows: Fig.23 shown. Example

[0045] A method for preparing a micromechanical resonator taking into account thermoelastic loss, when the resonator is a composite structure of metal-piezoelectric layer-single crystal silicon, the preparation method is as follows: (1) If Fig.24 As shown, a SOI wafer is provided, and the SOI wafer includes, from bottom to top, a substrate layer 601 (substrate silicon wafer), a buried oxide layer 602, and a device layer 603 (device layer silicon) with a thickness of 5-60 μm; (2) If Fig.25As shown, a piezoelectric material 604 (including but not limited to aluminum nitride and lead zirconate titanate, etc.) with a thickness of 0.5-1µm and an upper electrode 605 (including but not limited to molybdenum) with a thickness of 0.15-0.2µm are sequentially deposited on the device layer 603, and then the upper electrode is patterned, and then a top oxide layer 606 with a thickness greater than 0.2µm is deposited; (3) If Fig.26 As shown, the top oxide layer 606 is etched to form an upper electrode through hole, exposing the upper electrode 605; (4) If Fig. 27 As shown, the top oxide 606 and the piezoelectric material 604 are continuously etched to form a lower electrode through hole, exposing the device layer 603; (5) If Fig.28 As shown, a metal layer (including but not limited to aluminum) with a thickness of 1-2 μm is deposited in the upper electrode through hole and the lower electrode through hole, and patterned to form a metal pad 607; (6) Fig.29 As shown, the top oxide 606, the piezoelectric material 604 and the device layer 603 are etched on the front side until the buried oxide layer 602 is distributed in the device layer according to the adjusted trajectory to form the microstructure of the required resonant oscillator; (7) Fig.30 As shown, the substrate layer 601 is back-etched until the buried oxide layer 602 is reached, a through hole or the cavity structure is formed in the substrate layer 601, and the buried oxide layer 602 is exposed; (8) Fig.31 As shown, gaseous hydrofluoric acid is introduced to corrode and release the exposed buried oxide layer 602, so that the resonant oscillator is released and suspended to obtain a micromechanical resonator structure.

[0046] The above-mentioned embodiment 3 is a preparation process using SOI technology. The metal-piezoelectric layer-single crystal silicon composite thin film structure resonator can also be prepared using CSOI process flow. The prepared resonator structure is as follows: Fig.32 shown.

[0047] Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present invention, and that the scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A micromechanical resonator considering thermoelastic loss, comprising a substrate layer, and a buried oxide layer and a device layer arranged on the substrate layer, wherein the substrate layer has a cavity structure, characterized in that: The device layer includes a resonant oscillator suspended above the cavity structure, and the structure of the resonant oscillator is along the <100> to <110> The trajectory distribution in the crystal direction is adjusted according to the anisotropy of the single crystal silicon material and the vibration characteristics of different modes, so that the outline of the resonant oscillator is an irregular rectangular and / or circular structure; the resonant oscillator is used alone, or forms a resonator array, or is used as a mechanical coupling structure to couple with other resonators.

2. The micromechanical resonator considering thermoelastic loss according to claim 1, characterized in that: The trajectory distribution adjustment method is suitable for a variety of resonant oscillator structures, including ring-shaped or plate-shaped structures; the outer contour of the plate-shaped resonator and the inner contour and / or outer contour of the ring structure are adjusted, and the inner contour and / or outer contour shrink toward the center respectively, and there are different shrinkage amounts.

3. The micromechanical resonator considering thermoelastic loss according to claim 2, characterized in that: When the main structure of the resonant oscillator is a circular ring or circular plate structure, multiple arc segments of its inner contour and / or outer contour radially shrink; when the main structure of the resonant oscillator is a square ring or square plate structure, the side length of its inner contour and / or outer contour shrinks and changes from a straight line state to a curved state, the side length of the outer contour is a convex curve, and the side length of the inner contour is a concave curve.

4. The micromechanical resonator considering thermoelastic loss according to claim 1, characterized in that: When the structure of the resonant oscillator is coupled with other resonators as a coupling structure, it is connected to other structures through support beams or anchor points, and the inner contour and / or outer contour of the annular or plate-shaped structure of the coupling structure also shrinks toward the center of the coupling structure.

5. The micromechanical resonator considering thermoelastic loss according to claim 1, characterized in that: Microholes or grooves are etched on the structure of the resonator along different crystal directions, and doping is performed at different crystal directions by regional doping to adjust the equivalent stiffness of the resonator structure in different crystal directions.

6. The micromechanical resonator considering thermoelastic loss according to claim 1, characterized in that: The trajectories of the resonant oscillator in different crystal directions after adjustment satisfy the following conditions: ， In the formula, is the structural parameter of the resonant oscillator, is the vibration modal parameter, for and Function, structure parameters At least width, radius and thickness, is the Young's modulus of each crystal direction, is the trajectory parameter before adjustment, is the reference Young's modulus.

7. The micromechanical resonator considering thermoelastic loss according to claim 1, characterized in that: The resonant oscillator structure is a single-layer single-crystal silicon structure, or a composite thin film structure of metal-piezoelectric layer-single-crystal silicon.

8. The micromechanical resonator considering thermoelastic loss according to claim 1, characterized in that: A support beam is provided at the periphery of the resonant oscillator. The support beam is a straight beam, a T-shaped beam or a folded beam arranged at the vibration node of the resonant oscillator, or the support beam is a spoke beam arranged at the inner periphery of the resonant oscillator.

9. A method for preparing a micromechanical resonator taking into account thermoelastic loss according to any one of claims 1 to 8, characterized in that: When the resonator is a single-crystal silicon single-layer structure, the preparation method is as follows: Providing an SOI wafer, wherein the SOI wafer comprises, from bottom to top, a substrate layer, a buried oxide layer, and a device layer with a thickness of 5-60 μm; Depositing a 1-2µm thick metal layer on the device layer, and forming a metal pad after patterning; The front side of the SOI wafer is etched to selectively etch the device layer until the etching stops on the buried oxide layer, and a microstructure of a desired resonant oscillator is formed in the device layer according to the adjusted trajectory; Back-etching the SOI wafer, selectively etching the substrate layer until the buried oxide layer is etched, forming a through hole or the cavity structure in the substrate layer, and exposing the buried oxide layer; Gaseous hydrofluoric acid is introduced to corrode and release the exposed buried oxide layer, so that the resonant oscillator is released and suspended to obtain a micromechanical resonator structure.

10. A method for preparing a micromechanical resonator taking into account thermoelastic loss according to any one of claims 1 to 8, characterized in that: When the resonator is a composite structure of metal-piezoelectric layer-single crystal silicon, the preparation method is as follows: Providing an SOI wafer, wherein the SOI wafer comprises, from bottom to top, a substrate layer, a buried oxide layer, and a device layer with a thickness of 5-60 μm; Depositing a piezoelectric material with a thickness of 0.5-1 µm and an upper electrode with a thickness of 0.15-0.2 µm on the device layer in sequence, then patterning the upper electrode, and then depositing a top oxide layer with a thickness greater than 0.2 µm; Etching the top oxide layer to form an upper electrode through hole to expose the upper electrode; Continue etching the top oxide layer and the piezoelectric material to form a lower electrode through hole to expose the device layer; Depositing a metal layer with a thickness of 1-2 μm in the upper electrode through hole and the lower electrode through hole, and performing patterning to form a metal pad; Performing front etching on the top oxide layer, the piezoelectric material and the device layer until the buried oxide layer is formed, and distributing the microstructure of the required resonant oscillator in the device layer according to the adjusted trajectory; Performing back etching on the substrate layer until the buried oxide layer is reached, forming a through hole or the cavity structure in the substrate layer, and exposing the buried oxide layer; Gaseous hydrofluoric acid is introduced to corrode and release the exposed buried oxide layer, so that the resonant oscillator is released and suspended to obtain a micromechanical resonator structure.

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