MEMS resonator and preparation method thereof

Abstract

The invention relates to the technical field of resonators, and discloses an MEMS resonator and a preparation method thereof, and the preparation method comprises the steps: forming a first wafer which at least comprises a first monocrystalline silicon layer; forming a second wafer, wherein the second wafer at least comprises a second monocrystalline silicon layer and a piezoelectric material layer located on the second monocrystalline silicon layer; bonding the first wafer and the second wafer to form a laminated structure at least comprising a first monocrystalline silicon layer, a piezoelectric material layer and a second monocrystalline silicon layer, and performing high doping treatment on the first monocrystalline silicon layer and the second monocrystalline silicon layer before or after bonding; deep reactive ion etching is conducted on the laminated structure, a resonator body, a connecting beam and an anchoring part are formed, the resonator body is arranged in a suspended mode, and the resonator body is connected with the anchoring part through the connecting beam. According to the invention, the electromechanical coupling efficiency and the quality factor of the MEMS resonator are improved, and the temperature stability of the MEMS resonator is ensured.

Description

Technical Field

[0001] The present application relates to the technical field of resonators, and in particular to a MEMS resonator and a method for preparing the same. Background Art

[0002] Micro-electro-mechanical systems (MEMS) can integrate mechanical components, drive components, electronic control systems, digital processing systems, etc. into an integrated micro unit. An example of such a device is a MEMS resonator. As a type of MEMS resonator, the working principle of a piezoelectric resonator is that an electrical signal passes through electrodes to stimulate acoustic wave oscillations in the piezoelectric material, thereby achieving resonance of a specific frequency and wavelength. Piezoelectric resonators are widely used, such as for timing reference, signal filtering, mass sensing, biosensing, motion sensing, etc. With the development of electronic technology, the requirements for the size and frequency stability of piezoelectric resonators have been significantly improved.

[0003] The piezoelectric resonator body structure in the related art is a piezoelectric material-metal composite structure arranged on a silicon-based material, with the metal serving as the electrode. However, due to the excessively high thermal expansion coefficient of the metal material, which poorly matches the thermal expansion coefficient of the piezoelectric material layer, the stiffness (elastic modulus) is too high, and it is prone to hardening with use, resulting in problems such as low electromechanical coupling efficiency and low quality factor (Q value) in the piezoelectric resonator. Summary of the Invention

[0004] In view of this, the present application provides a MEMS resonator and a preparation method thereof to solve the above-mentioned technical problems.

[0005] In a first aspect, an embodiment of the present application discloses a method for preparing a MEMS resonator, comprising: forming a first wafer, wherein the first wafer includes at least a first single crystal silicon layer; forming a second wafer, wherein the second wafer comprises at least a second single crystal silicon layer and a piezoelectric material layer located on the second single crystal silicon layer; Bonding the first wafer and the second wafer to form a stacked structure comprising at least the first single crystal silicon layer, the piezoelectric material layer, and the second single crystal silicon layer, and performing a high-doping treatment on the first single crystal silicon layer and the second single crystal silicon layer before or after the bonding; The stacked structure is subjected to deep reactive ion etching to form a resonator body, a connecting beam and an anchoring piece. The resonator body is suspended in the air, and the resonator body is connected to the anchoring piece via the connecting beam.

[0006] In a possible example, the first wafer includes at least a first single crystal silicon layer and a piezoelectric material layer formed on the first single crystal silicon layer.

[0007] In one possible example, the forming the first wafer comprises: providing a first silicon-on-insulator wafer comprising at least a first silicon layer, forming a groove on the first silicon layer; providing a second silicon-on-insulator wafer comprising the first single-crystal silicon layer, and a first dielectric layer on the first single-crystal silicon layer; bonding a side of the first silicon layer with the groove and the first dielectric layer to form the first wafer in a silicon-on-insulator type, and the groove forms a cavity in the first wafer.

[0008] In one possible example, the forming the second wafer comprises: providing a third silicon-on-insulator wafer comprising at least a second silicon layer, sequentially forming a second dielectric layer and the second single-crystal silicon layer on the second silicon layer; depositing an aluminum nitride layer on the second single-crystal silicon layer to form the piezoelectric material layer.

[0009] In one possible example, after the bonding the first wafer and the second wafer, further comprising: etching and removing the second silicon layer and the second dielectric layer.

[0010] In one possible example, the bonding the first wafer and the second wafer comprises: fusion bonding the first single-crystal silicon layer of the first wafer and the piezoelectric material layer of the second wafer; or, fusion bonding the piezoelectric material layer on the first single-crystal silicon layer and the piezoelectric material layer on the second single-crystal silicon layer.

[0011] In one possible example, the deep reactive ion etching the stacked structure comprises: forming a first isolation groove on the second single-crystal silicon layer of the second wafer, the first isolation groove divides a part of the second single-crystal silicon layer as a driving electrode, and divides another part of the second single-crystal silicon layer as a sensing electrode.

[0012] In one possible example, the deep reactive ion etching the stacked structure comprises: identifying a region corresponding to the resonator body at a top of the stacked structure as a target region, and a region other than the target region as a peripheral region; forming a second isolation groove on the second single-crystal silicon layer of the target region through a first mask, the second isolation groove being connected to the piezoelectric material layer; forming a ground electrode hole in the peripheral region by a second mask, the ground electrode hole being connected to the first dielectric layer by the second single crystal silicon layer; depositing electrode material on top of the stack structure by a third mask, forming a ground electrode on the ground electrode hole, forming a drive electrode and a sense electrode on both sides of the second isolation trench in the target region; forming a first release hole and a second release hole on the stack structure by a fourth mask, the first release hole being connected to the first silicon layer by the second single crystal silicon layer, the second release hole being connected to the cavity by the second single crystal silicon layer, to release the area of the resonator body, forming the resonator body, the connecting beam and the anchor.

[0013] In one possible example, after the forming a first release hole and a second release hole on the stack structure by a fourth mask, the method further comprises: introducing an acid etching gas into the second release hole to remove the first dielectric layer in the cavity.

[0014] In a second aspect, the embodiments of the present application disclose a MEMS resonator prepared by the MEMS resonator preparation method described in any of the above embodiments, comprising: a resonator body, a connecting beam and an anchor, the resonator body being suspended, and the resonator body being connected to the anchor through the connecting beam; the resonator body is a stack structure formed by bonding a first wafer and a second wafer, the stack structure at least comprising a first single crystal silicon layer, a piezoelectric material layer and a second single crystal silicon layer, the first single crystal silicon layer, the piezoelectric material layer and the second single crystal silicon layer being sequentially stacked.

[0015] In summary, compared with the prior art, the present application discloses a MEMS resonator preparation method, comprising forming a first wafer, the first wafer at least comprising a first single crystal silicon layer, forming a second wafer, the second wafer at least comprising a second single crystal silicon layer and a piezoelectric material layer on the second single crystal silicon layer, bonding the first wafer and the second wafer to form a stack structure comprising at least a first single crystal silicon layer, a piezoelectric material layer and a second single crystal silicon layer, and before or after bonding, performing high-doping treatment on the first single crystal silicon layer and the second single crystal silicon layer, and performing deep reactive ion etching on the stack structure to form a resonator body, a connecting beam and an anchor, wherein the resonator body is suspended, and the resonator body is connected to the anchor through the connecting beam, that is, by bonding the first wafer and the second wafer, the high-doped single crystal silicon layer replaces the traditional metal electrode, the matching degree of the thermal expansion coefficient with the piezoelectric material layer is optimized, and the electromechanical coupling efficiency and the quality factor of the MEMS resonator are improved. BRIEF DESCRIPTION OF DRAWINGS

[0016] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the following will briefly introduce the drawings needed in the embodiment description. Obviously, the drawings in the following description only represent some embodiments of the present application, and for those skilled in the art, other drawings can also be obtained from these drawings without creative effort.

[0017] Figure 1 is a flow chart of the MEMS resonator preparation method of the present application; Figure 2 is a structural schematic diagram of the first laminated structure of the present application; Figure 3 is a structural schematic diagram of the second laminated structure of the present application; Figure 4 is a structural schematic diagram of the first MEMS resonator of the present application; Figure 5 is a structural schematic diagram of the second MEMS resonator of the present application; Figure 6 is a preparation structural variation diagram of the first wafer of the present application; Figure 7 is a preparation structural variation diagram of the laminated structure of the present application; Figure 8 is an etching structural schematic diagram of the first laminated structure of the present application; Figure 9 is an etching structural schematic diagram of the second laminated structure of the present application; Figure 10 is an etching structural schematic diagram of the third laminated structure of the present application; Figure 11 is an etching structural schematic diagram of the fourth laminated structure of the present application; Figure 12 is an etching structural schematic diagram of the fifth laminated structure of the present application. DETAILED DESCRIPTION

[0018] The exemplary embodiments will be described in detail herein with reference to the drawings. Unless otherwise specified, the same numbers in different drawings indicate the same or similar elements. The embodiments described in the following exemplary embodiments do not represent all the embodiments consistent with the present application. Rather, they are merely examples of apparatuses and methods consistent with some aspects of the present application as detailed in the claims.

[0019] It should be noted that the terms "comprising", "including", or any other variation thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements does not include only those elements but can include other elements not expressly listed or inherent to such process, method, article, or apparatus. Without further limitation, an element defined by the statement "comprising a" does not exclude the presence of additional identical elements in the process, method, article, or apparatus that includes the element, and components with the same name in different embodiments of the application can have the same meaning or different meanings, which should be determined in the light of their explanation in the specific embodiment or further in conjunction with the context in the specific embodiment.

[0020] It should be understood that the specific embodiments described herein are merely intended to explain the present application and are not intended to limit the present application.

[0021] In the following description, the suffixes used for elements such as "module", "part", or "unit" are used only to facilitate explanation of the present application, and have no specific meaning by themselves. Therefore, "module", "part", or "unit" can be used interchangeably.

[0022] In the description of the present application, it should be noted that the terms "upper", "lower", "left", "right", "inner", "outer", and the like indicate the orientation or positional relationship based on the orientation or positional relationship shown in the drawings, and are only used to facilitate the description of the present application and simplify the description, and do not indicate or imply that the device or element referred to must have a particular orientation, be constructed and operated in a particular orientation, and therefore cannot be understood as a limitation on the present application. In addition, the terms "first", "second", "third" are only for descriptive purposes and cannot be understood as indicating or implying relative importance.

[0023] The technical solutions shown in the present application will be described in detail below through specific embodiments. It should be noted that the order of the following embodiment descriptions is not a limitation on the priority order of the embodiments.

[0024] Reference should be made to Figure 1 , and in combination with Figures 2 to 4 , the MEMS resonator preparation method of the embodiments of the present application comprises: S101, forming a first wafer 1, the first wafer 1 at least comprising a first single crystal silicon layer 11.

[0025] S102, forming a second wafer 2, the second wafer 2 at least comprising a second single crystal silicon layer 21, and a piezoelectric material layer 3 on the second single crystal silicon layer 21.

[0026] S103, bonding the first wafer 1 and the second wafer 2 to form a laminated structure 4 comprising at least the first single crystal silicon layer 11, the piezoelectric material layer 3 and the second single crystal silicon layer 21, and before or after the bonding, high-doping treatment is performed on the first single crystal silicon layer 11 and the second single crystal silicon layer 21.

[0027] S104, deep reactive ion etching is performed on the laminated structure 4 to form the resonator body 10, the connecting beam 20 and the anchor 30, the resonator body 10 is suspended, and the resonator body 10 is connected to the anchor 30 through the connecting beam 20.

[0028] Therefore, the first single crystal silicon layer 11, the piezoelectric material layer 3 and the second single crystal silicon layer 21 are closely combined by bonding, and the high-doped first single crystal silicon layer 11 and the second single crystal silicon layer 21 on both sides of the piezoelectric material layer 3 after bonding are more suitable for the piezoelectric material layer 3, that is, the thermal expansion coefficients of the two single crystal silicon layers on both sides after bonding are closer to the piezoelectric material layer 3, which can significantly reduce the accumulation of thermal stress and avoid warping, cracking, failure and other situations of the resonator in high-temperature processes or long-term work, and the first single crystal silicon layer 11 and the second single crystal silicon layer 21 in the laminated structure 4 after bonding can be selected as electrodes as needed, the interface is reliable, the stability is high, there is no risk of metal electrode migration and peeling, and the symmetric structure of the first single crystal silicon layer 11-piezoelectric material layer 3-second single crystal silicon layer 21 is realized by bonding, so that the resonator is mechanically symmetric and the stress distribution is uniform, which can reduce parasitic loss and stress concentration, improve electromechanical coupling efficiency and quality factor Q.

[0029] Therefore, the bonding process is adopted to realize the close combination of the above-mentioned different material layers, which is more stable than simply depositing or sputtering an electrode layer, and the overall structure formed by bonding has good uniformity, which helps to reduce residual stress and improve resonator consistency and production yield.

[0030] Compared with the metal as the electrode in the related art, the first single crystal silicon layer 11 and the second single crystal silicon layer 21 can effectively adjust the equivalent capacitance, conductivity and thermal expansion coefficient matching degree with the piezoelectric material layer 3 as the electrode by adjusting the doping type, doping concentration and thickness setting without affecting the mechanical properties, and since the hardness of the single crystal silicon layer is stable, the attenuation is small even at high temperature, so that the overall temperature coefficient of the resonator is small, thereby the resonator can have high electromechanical coupling efficiency, quality factor and temperature stability.

[0031] With reference to Figure 4 The laminated structure 4 comprising at least the first single crystal silicon layer 11, the piezoelectric material layer 3 and the second single crystal silicon layer 21 is patterned and processed, deep reactive ion etching is adopted to realize structure separation with high aspect ratio, so as to accurately construct the three-dimensional structure characteristics of the MEMS resonator, that is, the resonator body 10, the connecting beam 20 and the anchor 30.

[0032] It should be noted that the resonator body 10 is composed of at least a first single crystal silicon layer 11, a piezoelectric material layer 3 and a second single crystal silicon layer 21 stacked together, and is released into a suspended state for mechanical resonance under the action of a driving voltage, and the cross-sectional shape of the resonator body 10 can be rectangular, circular or other regular shapes.

[0033] In order to realize the suspended arrangement of the resonator body 10 , a sacrificial layer may be released during the etching process or a groove may be opened from the back side.

[0034] Among them, the anchor 30 is used for fixing and can be directly connected to the base or substrate layer. The connecting beam 20 can be an elastic beam, of course not limited to this. A common piezoelectric resonator adopts a cantilever beam structure, a double-ended fixed beam, a bridge beam and other structures. The connecting beam 20 not only serves as a physical support, but also provides an electrical connection path, so that the single crystal silicon layer extends to the anchor 30.

[0035] The resonator body 10 and the connecting beam 20 may be integrated, and one end thereof is fixedly connected to the anchor 30 .

[0036] In combination with the aforementioned embodiments, the first single crystal silicon layer 11 can serve as the bottom electrode of the MEMS resonator, and the second single crystal silicon layer 21 can serve as the top electrode of the MEMS resonator. The two together constitute an electrical-mechanical energy conversion structure through the intermediate piezoelectric material layer 3. Thus, the first single crystal silicon layer 11 and the second single crystal silicon layer 21 are electrically coupled to the external packaging contacts through the connecting beam 20 and the anchor 30 to correspond to the sensing electrode and the driving electrode of the MEMS resonator, respectively, so that the MEMS resonator can receive the piezoelectric actuation drive signal and can sense the piezoelectric output signal indicating the mechanical movement of the resonant structure externally.

[0037] Furthermore, a conduction path is formed between the first single crystal silicon layer 11 and the second single crystal silicon layer 21 and the external packaging contact through the anchor 30 and the connecting beam 20. For example, the single crystal silicon layer can extend outward from the resonator body 10 and be formed on the connecting beam 20 and the anchor 30, thereby forming a conduction path on the connecting beam 20 and the anchor 30. Then, by applying a driving voltage to generate a potential on the piezoelectric material layer 3, the resonator body 10 is actuated to produce mechanical resonance.

[0038] In one example, reference Figure 3 When deep reactive ion etching is performed on the stacked structure 4, a first isolation groove 5a can be formed on the second single crystal silicon layer 21 of the second wafer 2. The first isolation groove 5a divides a portion of the second single crystal silicon layer 21 into a driving electrode, and divides another portion of the second single crystal silicon layer 21 into a sensing electrode.

[0039] Preferably, the first wafer 1 can serve as a support base of the MEMS resonator in the embodiments of the present application, and the thickness of the first monocrystalline silicon layer 11 includes 18 um, which can provide sufficient support and ensure the formation of microstructures with high aspect ratio in the deep reactive ion etching (DRIE) process, thereby effectively maintaining the suspended state of the resonator body 10.

[0040] Preferably, the thickness of the piezoelectric material layer 3 includes 0.25 um, which can ensure significant piezoelectric effect while avoiding excessive residual stress and energy leakage problems caused by excessive thickness, thereby improving the electromechanical coupling efficiency.

[0041] Preferably, the thickness of the second monocrystalline silicon layer 21 includes 2 um, which can ensure its operation as a low-resistance electrode while reducing the stiffness of the laminated structure 4 to avoid adverse effects on the vibration mode of the resonator body 10.

[0042] In the specific implementation process, the first wafer 1 and the second wafer 2 are bonded, which can specifically include fusion bonding the first monocrystalline silicon layer 11 of the first wafer 1 and the piezoelectric material layer 3 of the second wafer 2. Through fusion bonding, atomic-level diffusion bonding can be achieved at the interface between the first monocrystalline silicon layer 11 and the piezoelectric material layer 3 to form a high-strength bonding interface, which can withstand thermal stress in subsequent high-temperature processes and long-term operation of the resonator. Moreover, fusion bonding is an intermediate layer-free bonding, which completely avoids failure problems caused by aging and peeling of the intermediate layer. Direct bonding of the monocrystalline silicon layer and the piezoelectric material layer 3 can avoid the problem of thermal expansion mismatch at the interface, improve the overall thermal stability of the resonator, and improve the electromechanical coupling efficiency and the quality factor Q.

[0043] In one example, the first monocrystalline silicon layer 11 can also have a piezoelectric material layer 3, i.e., the first wafer 1 at least includes the first monocrystalline silicon layer 11 and the piezoelectric material layer 3 on the first monocrystalline silicon layer 11, thereby constructing a double-sided piezoelectric layer structure of the resonator. Bonding the first wafer 1 and the second wafer 2 can specifically include fusion bonding the piezoelectric material layer 3 on the first monocrystalline silicon layer 11 and the piezoelectric material layer 3 on the second monocrystalline silicon layer 21, i.e., piezoelectric-piezoelectric interface bonding. Thereby, a symmetrical piezoelectric driving structure can be formed, which is helpful to the symmetry and stability of the resonant mode, and can increase the electric-acoustic energy conversion efficiency. Compared with a single-layer piezoelectric structure, the electromechanical coupling coefficient is higher, and the symmetrical piezoelectric material layer 3 design makes the stress distribution uniform, reduces the warping of the resonator body and energy leakage, and further improves the quality factor (Q value).

[0044] In one example, the first single crystal silicon layer 11 and the second single crystal silicon layer 21 are subjected to high doping treatment. For example, the first single crystal silicon layer 11 is subjected to P doping treatment by depositing a layer of PSG on the surface of the first single crystal silicon layer 11 through chemical vapor deposition (e.g. PECVD), and then annealing at a high temperature of 1000°C. The PSG can be removed by etching or wet etching.

[0045] In one example, the first single crystal silicon layer 11 and the second single crystal silicon layer 21 are subjected to high doping treatment. For example, the first single crystal silicon layer 11 is subjected to P doping treatment by depositing a layer of PSG on the surface of the first single crystal silicon layer 11 through chemical vapor deposition (e.g. PECVD), and then annealing at a high temperature of 1000°C. The PSG can be removed by etching or wet etching.

[0046] In one example, the first single crystal silicon layer 11 and the second single crystal silicon layer 21 are subjected to high doping treatment. For example, the first single crystal silicon layer 11 is subjected to P doping treatment by depositing a layer of PSG on the surface of the first single crystal silicon layer 11 through chemical vapor deposition (e.g. PECVD), and then annealing at a high temperature of 1000°C. The PSG can be removed by etching or wet etching.

[0047] It should be noted that, based on the process design of the formation of the laminated structure 4, the first single crystal silicon layer 11 has a reverse polarity parabolic TCF, and the inherent parabolic TCF of the piezoelectric material layer 3 is offset by the reverse polarity parabolic TCF of the first single crystal silicon layer 11, the first-order and second-order TCFs of which are within the expected range (-40℃-85℃) and the net TCF is less than 50ppm, thereby ensuring that the MEMS resonator has high temperature stability, and the crystal defects of the first single crystal silicon layer 11 and the second single crystal silicon layer 21 are few, and the mechanical loss is low. After bonding with the piezoelectric material layer 3, the vibration energy loss can be significantly reduced, and the MEMS resonator has a high quality factor.

[0048] It can be understood that TCF refers to the temperature frequency characteristic coefficient (Temperature Coefficient of Frequency), also known as the temperature compensation coefficient, which is a characteristic parameter used to describe the change of the resonator frequency with temperature. Generally, the TCF coefficient is expressed in ppm / ℃, which means that for every increase or decrease of 1 degree Celsius in temperature, the resonator frequency changes by a corresponding proportion.

[0049] In one example, the first single crystal silicon layer 11, the piezoelectric material layer 3, and the second single crystal silicon layer 21 form a symmetric laminated structure. If the resonator structure has asymmetry, refer to Figure 5 If the resonator body 10 and the connecting beam 20 are asymmetric with respect to the X direction in the figure, then greater energy loss is likely to occur at the resonator anchor 30 connection, which will cause the resonator quality factor to be poor. Therefore, laser ablation means can be used to adjust the structures of the resonator to eliminate the asymmetry, thereby ensuring the quality factor of the resonator.

[0050] In one possible implementation of the present application, refer to Figure 6 The formation of the first wafer 1 includes: A first silicon-on-insulator wafer is provided, which at least includes a first silicon layer 101, and a groove 102 is formed on the first silicon layer 101; A second silicon-on-insulator wafer is provided, which includes a first single crystal silicon layer 11, and a first dielectric layer 103 on the first single crystal silicon layer 11; The side of the first silicon layer 101 with the groove 102 and the first dielectric layer 103 are bonded to form a first silicon-on-insulator (C-SOI) wafer 1, and the groove 102 forms a cavity 104 in the first wafer 1.

[0051] The cavity 104 provides a pre-space for the suspension of the resonator body 10 to facilitate the release of the resonator body 10, and the first silicon layer 101 serves as a support base structure. It can be understood that, due to the thin thickness of the single crystal silicon in the resonator body 10, the first silicon layer 101 provides support for subsequent bonding, etching and other processes to improve process reliability, and of course also serves as a support layer for the resonator.

[0052] Preferably, the groove 102 is formed on the first silicon layer 101, which can specifically include: depositing an intermediate dielectric layer 101a on the first silicon layer 101, forming a photoresist mask 101b on the intermediate dielectric layer 101a, and the photoresist mask 101b has a photoetching pattern exposing the groove 102, then etching the first silicon-on-insulator wafer to form the groove 102 on the first silicon layer 101, and then removing the photoresist mask 101b and the intermediate dielectric layer 101a.

[0053] Optionally, the intermediate dielectric layer 101a includes a silicon dioxide layer.

[0054] Preferably, during the formation of the first wafer 1, the first single crystal silicon layer 11 can be optionally subjected to high-doping treatment. Specifically, a layer of phosphorus-silicon glass 11a is deposited on the surface of the first single crystal silicon layer 11 by chemical vapor deposition (such as PECVD), and then high-temperature annealing at 1000°C is performed to complete P-doping of the first single crystal silicon layer 11. After that, the phosphorus-silicon glass layer 11a can be removed by etching or wet etching. It can be understood that, during the formation of the second wafer 2, the second single crystal silicon layer 21 can also be optionally subjected to high-doping treatment, and the high-doping treatment process is the same as above.

[0055] In a possible implementation of the present application, referring to Figure 7 , the forming of the second wafer 2 includes: providing a third silicon-on-insulator wafer including at least a second silicon layer 201, a second dielectric layer 202 and a second single crystal silicon layer 21 formed in sequence on the second silicon layer 201; and depositing an aluminum nitride layer on the second single crystal silicon layer 21 to form the piezoelectric material layer 3.

[0056] That is, the forming material of the piezoelectric material layer 3 includes aluminum nitride (AlN), which has excellent piezoelectric properties, good thermal conductivity, chemical stability and good compatibility with the silicon substrate, and the c-axis preferred orientation structure can provide a higher piezoelectric response on a specific crystal surface.

[0057] Of course, the forming material of the piezoelectric material layer 3 of the embodiment of the present application is not limited to this, and can also include but is not limited to zinc oxide, lead zirconate titanate, lithium niobate, gallium nitride, indium nitride, scandium aluminum nitride or quartz, etc.

[0058] Preferably, based on the forming process of the first wafer 1 and the second wafer 2, after the first wafer 1 and the second wafer 2 are bonded, further comprising: etching and removing the second silicon layer 201 and the second dielectric layer 202.

[0059] Therefore, in the process of bonding the first wafer 1 and the second wafer 2, the first single crystal silicon layer 11 of the first wafer 1 can be considered to be fusion bonded with the piezoelectric material layer 3 of the second wafer 2, thereby forming the laminated structure 4, so as to facilitate subsequent patterning of the laminated structure 4, and deep reactive ion etching is adopted to realize high aspect ratio structure separation, so as to accurately construct the three-dimensional structure features of the MEMS resonator, that is, the resonator body 10, the connecting beam 20 and the anchor 30.

[0060] In a possible implementation of the present application, the deep reactive ion etching of the laminated structure 4 comprises: a. Referring to Figure 8 , the region of the top of the laminated structure 4 corresponding to the resonator body 10 is identified as a target region M, and the region other than the target region M is a peripheral region N.

[0061] That is, through region division, the deep reactive ion etching of the laminated structure 4 is targeted, which facilitates the patterning of the etching process to realize the division of functional structures and peripheral support structures in subsequent processes.

[0062] b. Referring to Figure 8 , a second isolation groove 5b connected to the piezoelectric material layer 3 is formed on the second single crystal silicon layer 21 in the target region M by the first mask 401.

[0063] In this step, the first mask 401 has a photoetching pattern exposing the second isolation groove 5b, and the second isolation groove 5b connected to the piezoelectric material layer 3 can be formed by etching the photoetching pattern.

[0064] Then, the second isolation groove 5b can be considered to divide the second single crystal silicon layer 21 into two parts, that is, the second isolation groove 5b plays the role of an electrical isolation groove to prevent electrode crosstalk and isolate the sensing electrode and the driving electrode formed on the second single crystal silicon layer 21 subsequently.

[0065] And, after the second isolation groove 5b is formed, the first mask 401 is removed.

[0066] c. Referring to Figure 9 , a ground electrode hole 6a connected to the first dielectric layer 103 by the second single crystal silicon layer 21 is formed in the peripheral region N by the second mask 402.

[0067] In this step, the second mask 402 has a photolithography pattern that exposes the ground electrode hole 6 a , and the ground electrode hole 6 a connected to the first dielectric layer 103 can be formed by etching the photolithography pattern.

[0068] The ground electrode holes 6 a may be symmetrically distributed relative to the target area M in the peripheral area N.

[0069] Then, after the ground electrode hole 6 a is formed, the second mask 402 is removed.

[0070] d. Reference Figure 10 , electrode material is deposited on the top of the stacked structure 4 through the third mask 403, a ground electrode 6 is formed on the ground electrode hole 6a, and a driving electrode 71 and a sensing electrode 72 are formed on both sides of the second isolation groove 5b in the target area M.

[0071] In this step, the third mask 403 has a deposition pattern exposing the ground electrode hole 6a, and the third mask 403 has a deposition pattern exposing the driving electrode 71 and the sensing electrode 72. By depositing the electrode material of this deposition pattern, the ground electrode 6, the driving electrode 71 and the sensing electrode 72 are formed.

[0072] And after forming the ground electrode 6 , the driving electrode 71 and the sensing electrode 72 , the third mask 403 is removed.

[0073] The driving electrodes 71 and the sensing electrodes 72 are located in the target area M and may be symmetrically distributed relative to the second isolation trench 5 b.

[0074] The design of the ground electrode 6 in the peripheral region N can effectively reduce the parasitic capacitance effect, suppress electromagnetic interference and signal crosstalk, and thus improve the quality factor of the resonator and enhance its reliability.

[0075] Preferably, the electrode material includes polysilicon and metal Ge, that is, the ground electrode 6 includes a polysilicon layer 601 and a metal layer 602 , and the metal layer 602 is relatively located on top of the polysilicon layer 601 .

[0076] Furthermore, the deposition structures of the driving electrode 71 and the sensing electrode 72 are the same as those of the ground electrode 6 , and both include a polysilicon layer and a metal layer.

[0077] e. Reference Figure 11 A first release hole 81 and a second release hole 91 are formed on the stacked structure 4 through a fourth mask 404. The first release hole 81 is connected to the first silicon layer 101 by the second single crystal silicon layer 21, and the second release hole 91 is connected to the cavity 104 by the second single crystal silicon layer 21, so as to release the area of ​​the resonator body 10 and form the resonator body 10, the connecting beam 20 and the anchor 30.

[0078] In the step, the fourth mask 404 has a photoetching pattern exposing the first release hole 81 and the second release hole 91, so that the first release hole 81 connected to the first silicon layer 101 and the second release hole 91 connected to the cavity 104 can be formed by etching the photoetching pattern.

[0079] The second release hole 91 is located in the target area M and can be symmetrically distributed relative to the second isolation groove 5b, and the first release hole 81 can be located in the peripheral area N close to the target area M or at the junction of the target area M and the peripheral area N, so as to release the resonator body 10 corresponding to the target area M.

[0080] After the first release hole 81 and the second release hole 91 are formed, the fourth mask 404 is removed.

[0081] Preferably, after the first release hole 81 and the second release hole 91 are formed on the laminated structure 4 through the fourth mask 404, the method further comprises: introducing an acid etching gas into the second release hole 91 to remove the first dielectric layer 103 in the cavity 104, thereby ensuring the structure effect of the resonator body 10 being suspended.

[0082] The first dielectric layer 103 and the second dielectric layer 202 can be a silicon dioxide layer.

[0083] Optionally, the acid etching gas is a hydrofluoric acid gas.

[0084] It can be understood that the first release hole 81 does not represent that the structures on both sides of the corresponding first release hole 81 in the first silicon layer 101 are completely separated, and the first release hole 81 has a connecting structure not connected to the driving electrode 71 and the sensing electrode 72, and the second release hole 91 is the same, for example, the second release hole 91 has a connecting beam 20 connected to the resonator body 10.

[0085] The application further discloses a MEMS resonator prepared by the MEMS resonator composite preparation method of any one of the above-mentioned embodiments.

[0086] The MEMS resonator comprises a resonator body 10, a connecting beam 20 and an anchor 30.

[0087] In the specific implementation process, the resonator body 10 is suspended, and the resonator body 10 is connected to the anchor 30 through the connecting beam 20, wherein the resonator body 10 is a laminated structure 4 formed by bonding the first wafer 1 and the second wafer 2, and the laminated structure 4 at least comprises a first single crystal silicon layer 11, a piezoelectric material layer 3 and a second single crystal silicon layer 21, which are sequentially laminated.

[0088] In a possible implementation of the present application, the second monocrystalline silicon layer 21 is provided with a first isolation groove 5a connected to the piezoelectric material layer 3, the first isolation groove 5a divides a part of the second monocrystalline silicon layer 21 into a driving electrode, and divides another part of the second monocrystalline silicon layer 21 into a sensing electrode.

[0089] For other working principles and processes of the MEMS resonator of the present embodiment, refer to the foregoing description of the MEMS resonator composite preparation method of the present embodiment, which will not be repeated here.

[0090] The MEMS resonator and the composite preparation method thereof provided in the present application are described in detail above, and the principles and implementation manners of the present application are described by applying specific examples. It should be noted that the description of each embodiment in the present application has its own focus, and the parts not described or recorded in a certain embodiment can be referred to the relevant description of other embodiments.

[0091] The above is only the preferred embodiment of the present application, and does not limit the patent scope of the present application, and each technical feature of the technical solution of the present application can be combined arbitrarily. In order to make the description simple, each technical feature in the above embodiments is not described all possible combinations, and any equivalent structure or equivalent flow conversion made by using the content of the present application specification and drawings, or directly or indirectly applied in other related technical fields, as long as the combination of these technical features does not exist contradiction, are also included in the patent protection scope of the present application.

Claims

1. A method for preparing a MEMS resonator, characterized in that: include: forming a first wafer, wherein the first wafer includes at least a first single crystal silicon layer; forming a second wafer, wherein the second wafer comprises at least a second single crystal silicon layer and a piezoelectric material layer located on the second single crystal silicon layer; Bonding the first wafer and the second wafer to form a stacked structure comprising at least the first single crystal silicon layer, the piezoelectric material layer, and the second single crystal silicon layer, and performing a high-doping treatment on the first single crystal silicon layer and the second single crystal silicon layer before or after the bonding; The stacked structure is subjected to deep reactive ion etching to form a resonator body, a connecting beam and an anchoring piece. The resonator body is suspended in the air, and the resonator body is connected to the anchoring piece via the connecting beam.

2. The method for preparing a MEMS resonator according to claim 1, wherein: The first wafer at least includes a first single crystal silicon layer and a piezoelectric material layer formed on the first single crystal silicon layer.

3. The method for preparing a MEMS resonator according to claim 1, wherein: The forming of the first wafer comprises: Providing a first silicon-on-insulator wafer, wherein the first silicon-on-insulator wafer includes at least a first silicon layer, and forming a groove in the first silicon layer; Providing a second silicon-on-insulator wafer, wherein the second silicon-on-insulator wafer includes the first single crystal silicon layer and a first dielectric layer on the first single crystal silicon layer; The side of the first silicon layer having the groove is bonded to the first dielectric layer to form the first silicon-on-insulator type wafer, and the groove forms a cavity in the first wafer.

4. The method for preparing a MEMS resonator according to claim 3, wherein: The forming of the second wafer comprises: Providing a third silicon-on-insulator wafer, the third silicon-on-insulator wafer comprising at least a second silicon layer, and sequentially forming a second dielectric layer and a second single crystal silicon layer on the second silicon layer; An aluminum nitride layer is deposited on the second single crystal silicon layer to form the piezoelectric material layer.

5. The method for preparing a MEMS resonator according to claim 4, wherein: After bonding the first wafer and the second wafer, the method further includes: The second silicon layer and the second dielectric layer are removed by etching.

6. The method for preparing a MEMS resonator according to claim 2, wherein: Bonding the first wafer and the second wafer includes: performing melt bonding on the first single crystal silicon layer of the first wafer and the piezoelectric material layer of the second wafer; or, The piezoelectric material layer on the first single crystal silicon layer and the piezoelectric material layer on the second single crystal silicon layer are melt-bonded.

7. The method for preparing a MEMS resonator according to claim 1, wherein: The performing deep reactive ion etching on the stacked structure comprises: A first isolation trench is formed on the second single crystal silicon layer of the second wafer, wherein the first isolation trench divides a portion of the second single crystal silicon layer into a driving electrode and divides another portion of the second single crystal silicon layer into a sensing electrode.

8. The method for preparing a MEMS resonator according to claim 5, wherein: The performing deep reactive ion etching on the stacked structure comprises: Identify a region of the top of the stacked structure corresponding to the resonator body as a target region, and a region other than the target region as a peripheral region; forming a second isolation trench on the second single crystal silicon layer in the target area through a first mask, wherein the second isolation trench is connected to the piezoelectric material layer; forming a ground electrode hole in the peripheral area through a second mask, wherein the ground electrode hole is connected to the first dielectric layer through the second single crystal silicon layer; depositing an electrode material on top of the stacked structure through a third mask to form a ground electrode on the ground electrode hole, and forming a driving electrode and a sensing electrode on both sides of the second isolation trench in the target area; A first release hole and a second release hole are formed on the stacked structure through a fourth mask, wherein the first release hole is connected to the first silicon layer by the second single crystal silicon layer, and the second release hole is connected to the cavity by the second single crystal silicon layer, so as to release the area of ​​the resonator body and form the resonator body, the connecting beam and the anchor.

9. The method for preparing a MEMS resonator according to claim 8, wherein: After forming the first release hole and the second release hole on the stacked structure through the fourth mask, the method further includes: Acid etching gas is introduced into the second release hole to remove the first dielectric layer in the cavity.

10. A MEMS resonator manufactured by the MEMS resonator manufacturing method according to any one of claims 1 to 9, characterized in that: include: A resonator body, a connecting beam and an anchoring piece, wherein the resonator body is suspended in the air, and the resonator body is connected to the anchoring piece via the connecting beam; The resonator body is a stacked structure formed by bonding a first wafer and a second wafer. The stacked structure includes at least a first single crystal silicon layer, a piezoelectric material layer and a second single crystal silicon layer. The first single crystal silicon layer, the piezoelectric material layer and the second single crystal silicon layer are stacked in sequence.

Images