A high robustness MEMS resonator on silicon based on dual piezoelectric thin film driving

Abstract

This invention discloses a silicon-based MEMS resonator driven by dual piezoelectric thin films, belonging to the field of MEMS resonator technology. It includes an upper electrode, an upper piezoelectric thin film, a single-crystal silicon, a lower piezoelectric thin film, and a lower electrode arranged sequentially from top to bottom. The interfaces between the upper piezoelectric thin film and the single-crystal silicon, and between the lower piezoelectric thin film and the single-crystal silicon, are grounded. The upper and lower electrodes are respectively subjected to voltage excitations of opposite phases. This invention effectively suppresses the coupled vibration behavior of the length stretching mode and bending mode in existing MEMS resonator technologies through structural symmetry and quasi-symmetry of the driving modes, thereby effectively improving the admittance robustness of the silicon-based MEMS resonator and avoiding degradation of its admittance performance due to improper device design.

Description

Technical Field

[0001] This invention relates to the field of silicon piezoelectric thin-film MEMS resonators, and more specifically, to a highly robust silicon-based MEMS resonator driven by dual piezoelectric thin films. Background Technology

[0002] With the development of radio frequency communication and high-performance sensing technologies, piezoelectric microelectromechanical systems (MEMS) resonators based on silicon-based processes, especially piezoelectric thin-film resonators on silicon, have become an important means of realizing frequency control and filtering devices due to their high frequency, small size, easy integration, and good electromechanical coupling performance. In practical applications, these resonators are typically designed to operate in an in-plane tensile mode and achieve energy conversion through electromechanical coupling.

[0003] However, due to the asymmetry in the thickness direction and the finite-size boundary effects, silicon-based MEMS resonators generally suffer from the problem of in-plane tensile and bending mode coupling vibration. This causes the actual mode shape to deviate from the ideal single-mode distribution and results in acoustic energy dispersion, leading to a deterioration in the admittance response under the target vibration mode. This limits their application in scenarios with high frequency stability requirements, such as low-noise oscillators and narrowband filters. Therefore, how to optimize the resonator structure to suppress modal coupling and thus enhance the admittance response has become an urgent problem to be solved in current silicon-based MEMS resonator technology.

[0004] Currently, structural optimization of silicon-based MEMS resonators focuses on reducing anchoring losses. Optimization strategies include reconstructing the resonator profile and adding a vibration-damping outer frame structure to the resonator support beam, thereby improving the admittance response of silicon-based MEMS resonators by reducing anchoring losses. Reference document 202410983001.6 proposes a microelectro-acoustic resonator that combines a butterfly and drum-shaped resonator to localize more energy within the resonator, thus enhancing the resonator's quality factor and admittance response. However, this approach also increases the complexity of the original resonator structure. In actual micro / nano fabrication, due to limitations such as thin film deposition errors and etching uniformity, deviations between the fabricated structural dimensions and the design values ​​are inevitable. This is especially true for delicate structures such as the concave regions of the butterfly profile and the semi-elliptical boundaries of the drum shape; any minute geometric shift can cause the actual admittance response to deviate from expectations. The existing optimization methods do not address the inherent modal coupling vibration problem in silicon-based MEMS, and still struggle to solve problems such as low modal purity, energy dispersion, and deterioration of admittance response caused by modal coupling.

[0005] Existing technologies either focus on anchor point loss suppression and out-of-plane bending elimination, or on the purity excitation of specific waveguide modes, but neither addresses nor solves the core problem of in-plane length-stretching and bending mode coupling in silicon-based MEMS resonators. This coupling problem is widespread and severely impairs the admittance performance and robustness of devices, becoming a key bottleneck limiting their high-performance applications. Therefore, how to effectively suppress in-plane mode coupling and improve the robustness of admittance response is a technical problem that urgently needs to be solved in this field. Summary of the Invention

[0006] To address the technical problems mentioned above, this invention provides a silicon-based MEMS resonator driven by dual piezoelectric thin films. By using symmetrical and quasi-symmetrical vibration modes, the modal coupling behavior in the resonator is effectively suppressed, thereby achieving high robust device admittance performance. Furthermore, the designed resonator does not increase the complexity and design difficulty of its original structure.

[0007] This invention provides a silicon-based MEMS resonator driven by dual piezoelectric thin films. The resonator includes a single-crystal silicon, an upper piezoelectric thin film, a lower piezoelectric thin film, an upper electrode, and a lower electrode. The thickness parameters of the upper and lower piezoelectric thin films and the electrodes are not required to be exactly the same.

[0008] The interface between the upper and lower piezoelectric films and the single-crystal silicon of the silicon-based MEMS resonator driven by dual piezoelectric films needs to be grounded, while the upper and lower electrodes need to be excited by voltages of opposite phase to ensure that the upper and lower piezoelectric films are excited by the piezoelectric coefficient to produce length-tension vibration modes of the same phase.

[0009] On the one hand, when the thickness parameters of the upper piezoelectric film and the upper electrode are the same as those of the lower piezoelectric film and the lower electrode, the overall resonator is a thickness-oriented symmetrical structure. In this case, the length-stretching mode and the bending mode of the resonator are naturally decoupled. That is, after being excited by voltage, the resonator will only resonate in the length-stretching mode, without exhibiting the inherent vibrational behavior of coupled length-stretching and bending modes in existing single-piezoelectric film-driven silicon-on-MEMS resonators. Therefore, the vibrational energy of the dual-piezoelectric film-driven silicon-on-MEMS resonator is entirely concentrated in the length-stretching mode, and its admittance performance is significantly higher than that of existing MEMS resonators.

[0010] On the other hand, due to limitations in actual manufacturing processes, the thickness parameters of the upper and lower piezoelectric films and electrodes in a silicon-on-thin-film resonator driven by dual piezoelectric films may exhibit manufacturing deviations. This means the overall resonator structure no longer possesses thickness symmetry, and in this case, the length-stretching mode and bending mode in the resonator are still coupled. However, since the upper and lower piezoelectric films vibrate in the same phase under the driving voltage in the length-stretching mode, this quasi-symmetrical stretching vibration effectively counteracts the vibration deformation of the bending mode, thereby achieving mode coupling suppression and ultimately realizing the high robust admittance performance of the silicon-on-MEMS resonator under mode coupling.

[0011] The beneficial effects of this invention are as follows: This invention discloses a silicon-based MEMS resonator driven by dual piezoelectric thin films. By achieving structural symmetry and quasi-symmetry of the driving modes, it effectively suppresses the coupled vibration behavior of the length stretching mode and bending mode in existing MEMS resonator technologies, thereby effectively improving the robustness of the admittance performance of the silicon-based MEMS resonator and avoiding the reduction of its admittance performance due to improper device design. Attached Figure Description

[0012] Figure 1 This is a schematic diagram of the structure of the present invention; Figure 2 yes Figure 1 Cross-sectional view along the AA direction; Figure 3 This is a spectrum diagram of the silicon-based MEMS resonator driven by dual piezoelectric thin films in this invention; Figure 4 This is a spectrum diagram of an existing MEMS resonator on silicon; Figure 5 yes Figure 3 Vibration deformation diagrams of points A and B in the middle; Figure 6 yes Figure 4 Vibration deformation diagrams of points A1 and B1 in the middle; Figure 7 This is the admittance response diagram of the silicon-based MEMS resonator driven by dual piezoelectric thin films in this invention; Figure 8 This is the admittance response diagram of an existing single piezoelectric thin film driven MEMS resonator on silicon; Figure 9 This is a comparison of the admittance response of the silicon-based MEMS resonator driven by dual piezoelectric thin films in this invention under different thicknesses of the upper and lower piezoelectric thin films.

[0013] In the figure: 1-upper electrode, 2-upper piezoelectric film, 3-single crystal silicon, 4-lower piezoelectric film, 5-lower electrode. Detailed Implementation

[0014] The exemplary embodiments of this disclosure are described below with reference to the accompanying drawings, including various details of the embodiments to aid understanding, and should be considered merely exemplary. Therefore, those skilled in the art will recognize that various changes and modifications can be made to the embodiments described herein without departing from the scope and spirit of this disclosure. Similarly, for clarity and brevity, descriptions of well-known functions and structures are omitted in the following description.

[0015] Please see Figure 1-2This invention discloses a robust silicon-based MEMS resonator driven by dual piezoelectric thin films, comprising an upper electrode 1, an upper piezoelectric thin film 2, a single-crystal silicon 3, a lower piezoelectric thin film 4, and a lower electrode 5 arranged sequentially from top to bottom. The interfaces between the upper piezoelectric thin film 2 and the single-crystal silicon 3, and between the lower piezoelectric thin film 4 and the single-crystal silicon 3, are grounded. The upper electrode 1 and the lower electrode 5 are respectively subjected to voltage excitations with opposite phases.

[0016] When the thickness parameters of the "upper piezoelectric film 2, upper electrode 1" and the "lower piezoelectric film 4, lower electrode 5" are the same, the resonator is a symmetrical structure in the thickness direction. The length stretching mode and bending mode of the resonator are naturally decoupled. That is, after the resonator is excited by voltage, it only resonates in the length stretching mode.

[0017] When the thickness parameters of the upper piezoelectric film 2 and the upper electrode 1 are different from those of the lower piezoelectric film 4 and the lower electrode 5, the length stretching mode and the bending mode of the resonator are coupled. The upper and lower piezoelectric films vibrate in the same phase under the driving voltage, achieving the mode coupling suppression effect and realizing the high robust admittance performance of the silicon-based MEMS resonator under mode coupling.

[0018] Please see Figure 3-6 When the upper and lower piezoelectric films and electrodes of a silicon-based MEMS resonator driven by dual piezoelectric films have the same thickness parameter, the relationship between the resonant frequency of the first-order length-stretch mode of the resonator and the length-to-thickness ratio of the structure (i.e., the spectrum diagram) obtained from COMSOL finite element software simulation is as follows: Figure 3 As shown, the spectrum of an existing single piezoelectric thin film driven MEMS resonator on silicon is as follows. Figure 4 As shown.

[0019] contrast Figure 3 and Figure 4 The trend of the mid-spectrum curve shows that... Figure 3 The spectral curves of the medium-length stretching mode and the bending mode intersect, while Figure 4 The spectral curves of the stretching mode and the bending mode do not intersect, which indicates that the stretching mode and the bending mode are decoupled in the dual piezoelectric thin film driven MEMS resonator on silicon, while the stretching mode and the bending mode are coupled in the existing single piezoelectric thin film driven MEMS resonator on silicon.

[0020] Figure 5 Given Figure 3 Vibration deformation diagrams of points A and B in the middle. Figure 6 Given Figure 4 Vibration deformation diagrams of points A1 and B1 in the middle; At the same time, by comparison Figure 5 and Figure 6 The vibration deformation diagram shows that Figure 5The mode at 12.972 MHz is a pure length-stretching mode, while the mode at 12.96 MHz is a pure bending mode; these two modes are decoupled from each other. Figure 6 The two vibration modes are a length stretching mode and a bending mode coupled together. Therefore, the dual piezoelectric driven silicon-based thin-film resonator proposed in this invention can achieve mutual decoupling between the length stretching mode and the bending mode when the thickness of the upper and lower piezoelectric films and electrodes is the same.

[0021] Furthermore, the admittance response performance of silicon-based thin-film resonators driven by dual piezoelectric thin films and single piezoelectric thin films is compared, such as... Figure 7-8 As shown.

[0022] Figure 7 The admittance response diagram of a silicon-based thin-film resonator driven by dual piezoelectric sensors is presented. Figure 8 The admittance response diagrams of existing silicon-based thin-film resonators are presented; from Figure 7 As can be seen, because the silicon-based MEMS resonator driven by dual piezoelectric thin films can achieve complete decoupling between the length-stretching mode and the bending mode, its admittance response peak at the resonant frequency exceeds 100 s⁻¹. In contrast, from... Figure 8 As can be seen, for existing single-piezoelectric thin-film driven MEMS resonators on silicon, due to the coupling between their length extension mode and bending mode, their admittance response peak is less than 25 s. Therefore, the dual-piezoelectric thin-film driven MEMS resonator on silicon proposed in this invention significantly outperforms existing MEMS resonators on silicon in terms of admittance response performance.

[0023] On the other hand, in the actual fabrication of MEMS resonators on silicon, manufacturing deviations in the thickness of the upper and lower piezoelectric films and electrodes are inevitable. Therefore, this invention further demonstrates the robustness of the admittance performance of MEMS resonators on silicon driven by quasi-symmetric piezoelectricity, such as... Figure 9 As shown.

[0024] from Figure 9 As can be seen, although the thicknesses of the upper and lower piezoelectric films are no longer the same, meaning the overall resonator is no longer symmetrical about the thickness direction, the silicon-based thin-film resonator driven by dual piezoelectrics still exhibits the coupling of the length stretch mode and the bending mode. However, due to the in-phase dual piezoelectric drive, the bending mode deformation is effectively suppressed by the quasi-symmetrical length stretch vibration. Therefore, the admittance response performance of the overall resonator is not reduced, meaning the admittance response of the resonator has high robustness, which significantly improves the fault tolerance of the design parameters of the silicon-based thin-film resonator.

[0025] The specific embodiments described above do not constitute a limitation on the scope of protection of this disclosure. Those skilled in the art should understand that various modifications, combinations, sub-combinations, and substitutions can be made according to design requirements and other factors. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of this disclosure should be included within the scope of protection of this disclosure.

Claims

1. A robust silicon-based MEMS resonator driven by dual piezoelectric thin films, characterized in that: It includes an upper electrode, an upper piezoelectric thin film, a single crystal silicon, a lower piezoelectric thin film, and a lower electrode arranged sequentially from top to bottom. The interfaces between the upper piezoelectric thin film and the single crystal silicon, and between the lower piezoelectric thin film and the single crystal silicon, are grounded. The upper electrode and the lower electrode are respectively subjected to voltage excitations of opposite phases.

2. The robust silicon-based MEMS resonator driven by dual piezoelectric thin films according to claim 1, characterized in that, When the thickness parameters of the "upper piezoelectric film and upper electrode" and the "lower piezoelectric film and lower electrode" are the same, the resonator is a thickness-oriented symmetrical structure. The length stretching mode and bending mode of the resonator are naturally decoupled. That is, after being excited by voltage, the resonator only resonates in the length stretching mode.

3. The highly robust silicon-based MEMS resonator driven by dual piezoelectric thin films according to claim 1, characterized in that, When the thickness parameters of the "upper piezoelectric film and upper electrode" are different from those of the "lower piezoelectric film and lower electrode", the length stretching mode and bending mode of the resonator are coupled. The upper and lower piezoelectric films vibrate in the same phase under the driving voltage, achieving the mode coupling suppression effect and realizing the high robust admittance performance of the silicon-based MEMS resonator under mode coupling.

Images