A quartz crystal resonator having a boundary teeth comb structure and a manufacturing method thereof

Abstract

The application provides a quartz crystal resonator with a boundary comb structure, comprising: a rectangular flat quartz wafer, an upper excitation electrode, a lower excitation electrode and a boundary comb structure, the boundary comb structure is configured to: form an acoustic impedance mismatch interface in the boundary region of the quartz wafer, so that the vibration energy of a specific coupling mode is localized in the boundary region, to reduce the mode shape overlap integral of the coupling mode and the working mode; and by introducing periodic geometric features, at least two other coupling modes are coupled and hybridized, thereby constraining the frequency jump phenomenon caused by the other coupling modes to a more concentrated wafer size parameter range. The application aims to overcome the technical defects of the existing quartz crystal resonator caused by the lack of active suppression mechanism of coupling mode, which causes temperature-induced frequency hopping.

Description

Technical Field

[0001] This invention relates to the field of quartz crystal resonator technology, and in particular to a quartz crystal resonator with a boundary comb structure and its manufacturing method. Background Technology

[0002] As one of the core components of electronic measuring instruments, resonators are widely used in many electronic measuring instruments, such as quality factor measuring instruments, crystal testers, spectrum analyzers, and network analyzers.

[0003] Quartz crystal resonators operate using the thickness shear vibration mode of AT-cut quartz wafers and are widely used for frequency control in various electronic systems. In high-reliability applications (such as GPS and aerospace), the frequency stability of the resonator over a wide temperature range is crucial.

[0004] In existing technologies, rectangular planar AT-cut quartz crystal resonators exhibit a significant "temperature-induced frequency hopping" (ActivityDip) problem. This is caused by the following: when the ambient temperature changes, the frequencies of various parasitic coupling modes excited within the crystal (such as in-plane stretching, bending, and shearing modes) drift. Once these frequencies approach or overlap with the desired operating mode (thickness shearing mode), strong coupling occurs, leading to energy leakage in the operating mode, a sharp increase in the equivalent series resistance (ESR), a decrease in the Q value, and a jump in the output frequency.

[0005] The most common existing structure (as shown in the appendix) Figure 3 , Figure 4 As shown in the figure, the boundary region of its quartz wafer has a smooth rectangular edge, which only serves as a fixing point for conductive adhesive and lacks an active control and suppression mechanism for the above-mentioned coupling modes. Therefore, the existing solution can only rely on subsequent full-temperature testing for screening and rejection, which is costly, inefficient, and cannot fundamentally eliminate the risk of temperature-induced frequency hopping. Summary of the Invention

[0006] This invention provides a quartz crystal resonator with a boundary comb structure and its manufacturing method, aiming to overcome the technical defect of existing quartz crystal resonators that suffer from temperature-induced frequency hopping due to the lack of an active suppression mechanism for coupled modes. The boundary comb structure can actively regulate the acoustic characteristics at the crystal boundary without changing the basic connection method of the crystal, thereby effectively suppressing harmful coupling between the working mode and other modes such as facet mode, in-plane stretch mode, and bending mode. This fundamentally suppresses the temperature-induced frequency hopping phenomenon, improves the frequency stability and equivalent series resistance (ESR) consistency of the device over a wide temperature range, and meets the requirements of high reliability applications.

[0007] To achieve the above objectives, the present invention adopts the following technical solution: A quartz crystal resonator with a boundary comb structure includes: A rectangular, flat quartz wafer, wherein the quartz wafer is AT-cut and has an upper surface and a lower surface; An upper excitation electrode is disposed in the central region of the upper surface of the quartz wafer; The lower excitation electrode is disposed in the central region of the lower surface of the quartz wafer and is aligned with the upper excitation electrode in a direction perpendicular to the quartz wafer to form an electrode region together. A boundary comb structure is disposed in the boundary region of the quartz wafer and located at at least one edge of the quartz wafer. The boundary comb structure is composed of a plurality of tooth-like units arranged periodically along the edge of the quartz wafer. The boundary comb structure is configured as follows: An acoustic impedance mismatch interface is formed in the boundary region of the quartz wafer, which localizes the vibration energy of a specific coupled mode in the boundary region to reduce the mode overlap integral between the coupled mode and the working mode; and by introducing periodic geometric features, at least two other coupled modes are coupled and hybridized, thereby confining the frequency jump phenomenon caused by the other coupled modes to a more concentrated range of wafer size parameters.

[0008] In this specification, the boundary toothed comb structure is disposed at two opposite edges of the quartz wafer along its length.

[0009] In this specification, the toothed unit is a groove formed by recessing upward from the lower surface of the quartz wafer, or multiple grooves are arranged at equal intervals along the edge of the quartz wafer.

[0010] In this specification, the depth of the groove and the thickness of the quartz wafer satisfy a preset proportional relationship, such that the frequency of the hybrid mode formed by the coupling and hybridization of the in-plane tensile mode and the bending mode deviates from the frequency of the working mode within the target operating temperature range.

[0011] In this specification, the ratio of the depth h of the trench to the thickness t of the quartz wafer ranges from 0.4 to 1.0, and the ratio of the arrangement period Λ of the trench to the thickness t ranges from 0.8 to 2.0. Within this ratio range, the boundary comb structure can simultaneously achieve effective energy localization of the face-cutting mode and effective coupling hybridization of the face-in-face tensile mode and bending mode.

[0012] In this specification, the boundary toothed comb structure is formed by an anisotropic wet etching process, and the tooth-like units constituting the boundary toothed comb structure have specific crystal orientation sidewalls naturally formed by the anisotropic wet etching process.

[0013] A method for manufacturing a quartz crystal resonator with a boundary comb structure as described above includes the following steps: A rectangular, flat, AT-cut quartz wafer is provided, the quartz wafer having an upper surface and a lower surface; In the boundary region of the quartz wafer, along at least one edge of the quartz wafer, a boundary comb structure composed of a plurality of periodically arranged tooth-like units is formed. After forming the boundary comb structure, an upper excitation electrode is formed in the central region of the upper surface of the quartz wafer, and a lower excitation electrode is formed in the central region of the lower surface of the quartz wafer, so that the upper excitation electrode and the lower excitation electrode are aligned with each other. A quartz wafer with the boundary toothed comb structure and the excitation electrode formed thereon is fixed to an external base by means of conductive adhesive, wherein the conductive adhesive is applied by dispensing in the gap between adjacent toothed units of the boundary toothed comb structure or in the outer region of the boundary toothed comb structure.

[0014] In this specification, the step of forming the boundary comb structure includes: using an anisotropic wet etching process to etch multiple grooves that are recessed upward from the lower surface of the quartz wafer in the boundary region of the quartz wafer, so as to form the tooth-shaped unit.

[0015] In this specification, the anisotropic wet etching process utilizes the difference in etching rate of quartz crystals in different crystal orientations, so that the formed trenches have sidewalls composed of specific crystal faces.

[0016] In this specification, when forming the boundary comb structure, the proportional relationship between the geometric dimensions of the toothed unit and the thickness of the quartz wafer is controlled so that the boundary comb structure can promote the coupling and hybridization of in-plane stretching mode and bending mode in subsequent use, and constrain the frequency jump phenomenon caused by the in-plane stretching mode and the bending mode within the predetermined wafer size parameter range.

[0017] In summary, the present invention has at least the following beneficial effects: 1. Effectively suppresses temperature-induced frequency hopping and improves frequency stability: Through differentiated modulation of coupling modes using a boundary comb structure, the frequency-temperature characteristic curve of the resonator is smooth across the entire temperature range of -40℃ to +85℃, and the equivalent series resistance (ESR) shows no abrupt spikes (as simulated). Figure 7 , Figure 9 As shown in the figure, this fundamentally avoids the occurrence of temperature-induced frequency hopping.

[0018] 2. Reduce system design complexity and cost: Since the resonator itself has high stability over the entire temperature range, the dependence on external oscillation circuits for frequency hopping compensation can be reduced or eliminated, thereby simplifying system design and improving overall reliability.

[0019] 3. Improve full-temperature testing yield and reduce manufacturing costs: By actively suppressing frequency hopping through structural innovation, the number of defective products caused by frequency hopping can be greatly reduced, production yield can be improved, the full-temperature testing and screening cycle can be shortened, and the overall manufacturing cost can be reduced.

[0020] 4. Small fluctuation and gentle gradient of equivalent series resistance (ESR): The structure of this invention ensures the energy stability of the resonator's operating mode, making the ESR change gently over the entire temperature range. It is especially suitable for fields with extremely stringent requirements for frequency source stability, such as GPS navigation, aerospace and military guidance. Attached Figure Description

[0021] Figure 1 This is a top view schematic diagram of the quartz crystal resonator with a boundary comb structure involved in this invention.

[0022] Figure 2 This is a cross-sectional schematic diagram of the quartz crystal resonator with a boundary comb structure involved in this invention.

[0023] Figure 3 This is a schematic diagram of the traditional quartz crystal resonator structure involved in this invention.

[0024] Figure 4 This is a schematic diagram of the exploded structure of a conventional quartz crystal resonator involved in this invention.

[0025] Figure 5 This is a schematic diagram of a cross-section of the boundary region of a conventional structure wafer involved in this invention.

[0026] Figure 6 This is a schematic diagram of the simulation curve of the resonant frequency-temperature characteristics of the traditional structure involved in this invention.

[0027] Figure 7 This is a schematic diagram of the simulation curve of the resonant frequency-temperature characteristics of the quartz crystal resonator structure with boundary toothed comb structure involved in this invention.

[0028] Figure 8 This is a schematic diagram of the simulation of the frequency-temperature characteristics and impedance integration of the traditional structure involved in this invention.

[0029] Figure 9 This is a schematic diagram of the frequency-temperature characteristics and impedance fusion simulation of the quartz crystal resonator structure with boundary toothed comb structure involved in this invention. Detailed Implementation

[0030] The embodiments of the present invention will now be described in detail with reference to the accompanying drawings.

[0031] like Figure 1 and Figure 2As shown, this embodiment provides a quartz crystal resonator with a boundary comb structure 300, including: A rectangular, flat quartz wafer 100, wherein the quartz wafer 100 is AT-cut and has an upper surface and a lower surface; The upper excitation electrode 201 is disposed in the central region of the upper surface of the quartz wafer 100; The lower excitation electrode 202 is disposed in the central region of the lower surface of the quartz wafer 100 and is aligned with the upper excitation electrode 201 in a direction perpendicular to the quartz wafer 100 to form an electrode region together. A boundary comb structure 300 is disposed in the boundary region of the quartz wafer 100 and located at at least one edge of the quartz wafer 100. The boundary comb structure 300 is composed of a plurality of tooth-like units arranged periodically along the edge of the quartz wafer 100. The boundary comb structure 300 is configured as follows: An acoustic impedance mismatch interface is formed in the boundary region of the quartz wafer 100, so that the vibration energy of a specific coupled mode is localized in the boundary region, thereby reducing the mode overlap integral between the coupled mode and the working mode; and by introducing periodic geometric features, at least two other coupled modes are coupled and hybridized, thereby confining the frequency jump phenomenon caused by the other coupled modes to a more concentrated range of wafer size parameters.

[0032] In some embodiments, the boundary comb structure 300 is disposed at two opposing edges of the quartz wafer 100 along its length.

[0033] In some embodiments, the toothed unit is a groove 301 formed by recessing upward from the lower surface of the quartz wafer 100, or a plurality of the grooves 301 are arranged at equal intervals along the edge of the quartz wafer 100.

[0034] In some embodiments, the depth of the trench 301 and the thickness of the quartz wafer 100 satisfy a preset proportional relationship, such that the frequency of the hybrid mode formed by the coupling and hybridization of the in-plane stretching mode and the bending mode deviates from the frequency of the working mode within the target operating temperature range.

[0035] In some embodiments, a conductive adhesive 400 is also included. The conductive adhesive 400 is applied by dispensing to the gaps between adjacent toothed units of the boundary comb structure 300, or to the outer region of the boundary comb structure 300, for fixing the quartz wafer 100 to the external base. The conductive adhesive 400 is positioned to avoid filling the grooves 301 or protrusions 302 that constitute the boundary comb structure 300.

[0036] In some embodiments, the boundary toothed comb structure 300 is formed by an anisotropic wet etching process, and the toothed units constituting the boundary toothed comb structure 300 have specific crystal orientation sidewalls naturally formed by the anisotropic wet etching process.

[0037] A method for manufacturing a quartz crystal resonator with a boundary comb structure 300 as described above includes the following steps: A rectangular, flat, AT-cut quartz wafer 100 is provided, the quartz wafer 100 having an upper surface and a lower surface; In the boundary region of the quartz wafer 100, along at least one edge of the quartz wafer 100, a boundary comb structure 300 composed of a plurality of periodically arranged tooth-like units is formed. After forming the boundary comb structure 300, an upper excitation electrode 201 is formed in the central region of the upper surface of the quartz wafer 100, and a lower excitation electrode 202 is formed in the central region of the lower surface of the quartz wafer 100, so that the upper excitation electrode 201 and the lower excitation electrode 202 are aligned with each other. The quartz wafer 100, on which the boundary toothed comb structure 300 and the excitation electrode are formed, is fixed to an external base by means of conductive adhesive 400, wherein the conductive adhesive 400 is applied by dispensing in the gap between adjacent toothed units of the boundary toothed comb structure 300 or in the outer region of the boundary toothed comb structure 300.

[0038] In some embodiments, the step of forming the boundary comb structure 300 includes: using an anisotropic wet etching process to etch a plurality of grooves 301 that are recessed upward from the lower surface of the quartz wafer 100 in the boundary region of the quartz wafer 100 to form the tooth-like unit.

[0039] In some embodiments, the anisotropic wet etching process utilizes the difference in etching rate of quartz crystals in different crystal orientations, so that the formed trench 301 has sidewalls composed of specific crystal planes.

[0040] In some embodiments, when forming the boundary comb structure 300, the proportional relationship between the geometric dimensions of the toothed unit and the thickness of the quartz wafer 100 is controlled so that the boundary comb structure 300 can promote the coupling and hybridization of in-plane stretching mode and bending mode in subsequent use, and constrain the frequency jump phenomenon caused by the in-plane stretching mode and the bending mode within a predetermined wafer size parameter range.

[0041] In some embodiments, the specific coupling mode is a facet-shaped mode, and the operating mode is a thickness-shear mode. The boundary comb structure 300 localizes the vibration energy of the facet-shaped mode to the region where the boundary comb structure 300 is located by forming an acoustic impedance mismatch interface in the boundary region of the quartz wafer 100. Since the energy of the thickness-shear mode is mainly concentrated in the electrode region defined by the upper excitation electrode 201 and the lower excitation electrode 202, the mode shape overlap integral between the facet-shaped mode and the thickness-shear mode is significantly reduced. Even when changes in operating temperature cause their frequencies to approach each other, the degree of energy coupling between them is effectively weakened.

[0042] In some embodiments, the at least two other coupled modes include an in-plane stretching mode and a bending mode. The periodic geometric features of the boundary comb structure 300 introduce additional wave vector components into the vibration system of the quartz wafer 100, causing the originally independent in-plane stretching mode and the bending mode to couple and hybridize, merging to form a new hybrid mode. This hybrid mode is more sensitive to the macroscopic dimensional parameters of the quartz wafer 100, such as length and width, than the in-plane stretching mode and the bending mode before hybridization. As a result, the temperature-induced frequency hopping phenomenon caused by these two modes, which was originally distributed over a wide size range under the traditional smooth boundary quartz wafer 100 structure, is reduced in size range after adopting the boundary comb structure 300. This makes it easier to effectively avoid the problem by pre-setting the length and width of the quartz wafer 100 during the design and manufacturing process.

[0043] In some embodiments, the ratio of the depth h of the trench 301 to the thickness t of the quartz wafer 100 ranges from 0.3 to 1.0. When this ratio is less than 0.3, the trench 301 has insufficient modulation effect on the acoustic impedance of the boundary region, and cannot effectively achieve energy localization of the planar tangential modes; when this ratio is equal to 1.0, the trench 301 is a through-type groove. A preferred ratio range is 0.4 to 0.8, within which effective suppression of coupled modes can be achieved while maintaining the mechanical strength of the wafer boundary region. That is, the boundary comb structure 300 can more effectively promote the coupling hybridization of the in-plane tensile mode and the bending mode.

[0044] In some embodiments, the ratio of the arrangement period Λ of the trenches 301 to the thickness t of the quartz wafer 100 ranges from 0.5 to 3.0. When this ratio is too small, the spacer walls between adjacent trenches 301 are too thin, affecting structural integrity, and the resulting phonon bandgap frequency is too high, failing to effectively cover the frequency range of the target coupled modes. When this ratio is too large, the Bragg scattering effect of the periodic structure weakens, failing to effectively achieve coupling hybridization of the in-plane stretching mode and bending mode. The preferred ratio range is 0.8 to 2.0. Within this range, the boundary comb structure 300 can simultaneously achieve effective energy localization of the tangential mode and effective coupling hybridization of the in-plane stretching mode and bending mode. That is, the acoustic impedance mismatch interface generated by the boundary comb structure 300 has better reflection and localization effects on the coupled modes within a specific frequency range.

[0045] In some embodiments, the step of forming the boundary comb structure 300 is configured to be performed prior to the steps of forming the upper excitation electrode 201 and the lower excitation electrode 202. This avoids damage or contamination to the already formed upper excitation electrode 201 or lower excitation electrode 202 by process steps (such as wet etching) used in forming the boundary comb structure 300.

[0046] In some embodiments, the conductive adhesive 400 is precisely positioned in the wafer corner region outside the outermost toothed unit of the boundary comb structure 300. This ensures that during dispensing and curing, the conductive adhesive 400 does not overflow into and fill the grooves 301 of the boundary comb structure 300, thereby guaranteeing the acoustic integrity of the boundary comb structure 300.

[0047] In some embodiments, the target operating temperature range is a wide industrial or automotive temperature range from -40°C to 85°C. The length and width of the quartz crystal 100 are determined based on the target package size, the desired equivalent series resistance, and the constraint effect of the boundary comb structure 300 on the hybrid mode frequency hopping range, to ensure that the quartz crystal resonator does not experience temperature-induced frequency hopping within the target operating temperature range.

[0048] In some embodiments, the geometric parameters of the boundary comb structure 300 are not arbitrarily selected, but need to simultaneously satisfy the following two conditions to synergistically achieve effective energy localization of the tangential mode and effective coupling hybridization of the tensile and bending modes: Condition 1: The ratio of the trench 301 depth h to the quartz wafer 100 thickness t satisfies the first relationship.

[0049] The facet-shear mode is a vibration mode that mainly produces tangential deformation within the wafer plane, and its energy is relatively uniformly distributed along the wafer thickness direction. To enable the boundary comb structure 300 to create an effective acoustic impedance mismatch for this mode, the trench 301 depth h needs to be sufficiently large to significantly alter the equivalent acoustic impedance of the boundary region. However, an excessively large h will weaken the mechanical strength of the wafer and may adversely affect the energy trapping effect of the main vibration (thickness shear mode). Through theoretical analysis and extensive simulation verification, it was found that when the trench 301 depth h and the wafer thickness t satisfy the following relationship, effective localization of the facet-shear mode vibration energy can be achieved without significantly affecting the wafer structural integrity: 0.4 ≤ h / t ≤ 0.8; Condition 2: The ratio of the arrangement period Λ of the trench 301 to the thickness t of the quartz wafer 100 satisfies the second relationship.

[0050] The physical essence of in-plane tension and bending modes coupling and hybridizing is to introduce periodic boundary conditions to provide an additional wave vector component to the vibration system. The magnitude of this wave vector component is determined by the arrangement period Λ. To ensure that this wave vector component precisely bridges the dispersion curves of the in-plane tension and bending modes, thus promoting strong coupling, the arrangement period Λ needs to be correlated with the wavelength of the target coupled mode. Since the wavelengths of both modes are related to the wafer thickness t, modal analysis and simulation optimization revealed that the hybridization effect of the in-plane tension and bending modes is most significant when the arrangement period Λ and wafer thickness t satisfy the following relationship, and the resulting hybrid modes are most sensitive to wafer length and width within the following range: 0.8 ≤ Λ / t ≤ 2.0; More importantly, satisfying any single condition mentioned above is not sufficient to achieve all the beneficial effects of this invention. Through numerous simulation experiments, the inventors surprisingly discovered that the boundary comb structure 300 can only exhibit the synergistic effects of "efficient energy localization of tangential modes" and "strong coupling hybridization of tensile / bending modes" when both the groove depth h and the arrangement period Λ simultaneously satisfy the above two conditions, i.e., when both ratio ranges are simultaneously met. If only one condition is satisfied, only partial effects can be obtained (e.g., only tangential mode frequency hopping can be suppressed, or only the tensile / bending mode frequency hopping window can be concentrated), and the temperature-induced frequency hopping phenomenon cannot be completely eliminated across the entire temperature range.

[0051] In some embodiments, the boundary comb structure 300 is formed by an anisotropic wet etching process, and the grooves 301 constituting the tooth-like units have inclined sidewalls formed by specific crystal planes. For the AT-cut quartz wafer 100, its upper and lower surfaces are AT-cut. When anisotropic etching is performed using a specific etching solution (such as ammonium bifluoride solution), the family of crystal planes with the slowest etching rate will naturally be exposed, forming the sidewalls of the grooves 301.

[0052] Through theoretical modeling of the reflection and transmission characteristics of sound waves at the groove 301 with inclined sidewalls, the inventors discovered that the inclination angle θ of the sidewall (defined as the angle between the sidewall and the normal direction of the wafer surface) has a significant impact on the effect of the acoustic impedance mismatch interface.

[0053] When the sidewall is a vertical sidewall (i.e., θ approaches zero), the sound wave mainly undergoes specular reflection at the sidewall of trench 301. The reflected wave returns to the interior of the wafer and may form a standing wave with the incident wave, which in turn enhances the parasitic modes at certain frequencies.

[0054] When the sidewalls are naturally formed through anisotropic wet etching with specific crystal orientations, the tilt angle θ is approximately 21 to 25 degrees (depending on the specific crystal face and shear angle). At this tilt angle, the incident sound waves not only reflect at the sidewalls but also undergo mode conversion due to the tilt morphology of the sidewalls. That is, the energy of some faceted or stretched modes is converted into non-propagating drop wave modes, thus more effectively dissipating or localizing within the boundary comb structure 300 region, further reducing its coupling strength with the working modes. The acoustic suppression effect is enhanced by utilizing the microstructure naturally formed by specific crystal processing techniques.

[0055] In some embodiments, the boundary comb structure 300 is disposed in the boundary region of the quartz wafer 100, and the minimum distance d between the innermost edge of the boundary comb structure 300 and the edge of the upper excitation electrode 201 or the lower excitation electrode 202 must satisfy a specific relationship.

[0056] The energy of the thickness shear working mode is mainly concentrated in the electrode region and its outward exponential decay region (energy trapping effect). The presence of the boundary comb structure 300 alters the acoustic boundary conditions of the boundary region. If the comb structure is too close to the electrode region, the introduced acoustic impedance discontinuity interface will interfere with the energy trapping effect of the working mode, leading to a decrease in the Q value or an increase in the equivalent series resistance (ESR) of the working mode.

[0057] Through finite element simulation analysis, this invention determines that, in order to achieve effective stray mode suppression without affecting the performance of the working mode, the minimum spacing d should be no less than twice the thickness t of the quartz wafer 100, i.e., d ≥ 2t. When d satisfies the above relationship, the boundary comb structure 300 is located in the region where the energy of the working mode attenuates to a sufficiently low level, and its influence on the intrinsic mode shape of the working mode is negligible, while it can effectively act on the coupled modes whose energy distribution is closer to the boundary. This spacing design principle ensures that the two functions (maintaining the performance of the dominant mode and suppressing stray modes) are not contradictory.

[0058] In some embodiments, the conductive adhesive 400 is applied to specific locations on the boundary comb structure 300 via dispensing. As previously mentioned, the periodic geometric characteristics of the boundary comb structure 300 are the basis for its modal modulation function. The application of the conductive adhesive 400 locally disrupts this periodicity, introducing defect states.

[0059] The conventional approach is to place the conductive adhesive 400 at the four corners of the wafer to reduce the impact on vibration. However, the inventors discovered that if the conductive adhesive 400 is simply dotted at any position on the edge of the boundary comb structure 300, the random defects introduced may cause the comb structure to unexpectedly scatter parasitic modes at certain frequencies, or even induce new, weaker frequency hopping at certain temperature points.

[0060] To address this issue, in some embodiments, the placement of each fixing point of the conductive adhesive 400 along the edge of the quartz wafer 100 is phase-dependent with respect to the periodic arrangement of the boundary comb structure 300. Specifically, the center position of the fixing point of the conductive adhesive 400 is aligned with the position of a virtual, removed tooth-like unit, i.e., the conductive adhesive 400 occupies the periodic space of an integer number of tooth-like units, thereby giving it a definite and predictable effect on perturbations of the periodic structure in wave vector space.

[0061] For example, if the coverage length of the conductive adhesive 400 at the edge is L, and the period of the comb structure is Λ, then the following condition should be met: L≈n×Λ; where n is an integer greater than or equal to one.

[0062] Through this "phase-matching" configuration, the defects introduced by the conductive adhesive 400 become "controlled defects" rather than "random defects." Acoustic simulations show that controlled defects have a much smaller impact on the overall bandgap characteristics of the comb structure than random defects, thus ensuring the consistency of device performance in mass production.

[0063] In some embodiments, the boundary comb structure 300 is not uniformly disposed on all four edges of the quartz wafer 100.

[0064] For rectangular wafers, the different dimensions in the length and width directions lead to differences in the frequencies of the in-plane stretching modes in the length and width directions. Through modal analysis, the inventors discovered that for a specific wafer aspect ratio (e.g., a length-to-width ratio between 1.2 and 1.5), the coupling between the stretching and bending modes propagating along the length direction is stronger and is the main factor causing temperature-induced frequency hopping; while the coupling along the width direction is relatively weaker.

[0065] Based on this discovery, in some embodiments, the boundary comb structure 300 is provided only at the two opposite edges along the length direction of the quartz wafer 100, while the two edges along the width direction are either not provided or only have shallower and sparser comb structures. This non-uniform, targeted layout can maximize the preservation of the effective vibration area of ​​the wafer while achieving the same frequency hopping suppression effect, reducing the potential impact on the main vibration performance, and simplifying the manufacturing process.

[0066] In some embodiments, the geometric parameters of the boundary comb structure 300 are also designed to provide a temperature compensation effect.

[0067] The hybrid mode formed by the coupling and hybridization of the in-plane stretching mode and the bending mode exhibits a frequency-temperature characteristic that is a superposition of the original characteristics of the two modes. Through simulation, the inventors discovered that when the ratio of the trench depth h to the wafer thickness t is within a specific sub-interval of 0.8 to 1.0, the first-order frequency-temperature coefficient (i.e., the slope of frequency change with temperature) of the hybrid mode exhibits a trend similar to that of the working mode (thickness shear mode).

[0068] Utilizing this phenomenon, the parameters of the boundary comb structure 300 can be intentionally adjusted during the design phase to ensure that a safe frequency interval (e.g., not less than three times the bandwidth of the operating mode) is maintained between the hybrid mode frequency and the operating mode frequency, even at extreme temperatures. This further expands the resonator's non-frequency-hopping operating temperature range. This provides design freedom to meet the military's full temperature range requirements of -55°C to +125°C.

[0069] In some embodiments, the grooves 301 constituting the boundary comb structure 300 have an asymmetrical cross-sectional shape. In this embodiment, the cross-sectional shape of each groove 301 is asymmetrical with respect to its centerline. Specifically, the groove 301 has a first sidewall and a second sidewall, wherein the first sidewall is a specific crystal plane sidewall with a first tilt angle naturally formed by anisotropic wet etching, while the second sidewall has a second tilt angle or morphology different from the first sidewall.

[0070] This asymmetry can be achieved by: in the photolithography masking step, making the edge of the mask opening have a specific deflection angle with the crystal orientation of the quartz wafer 100; or by using two anisotropic etching steps in different directions.

[0071] The technical significance of the asymmetric trench 301 section lies in the fact that, for coupled modes in the form of traveling waves propagating along the edge of the wafer, the asymmetric structure can break the spatial inversion symmetry, causing the attenuation coefficient of the sound wave propagating in one direction in the trench 301 array to differ from that propagating in the opposite direction. This phenomenon is similar to "non-reciprocal propagation" or "topological boundary state" in acoustics.

[0072] In this embodiment, by designing an asymmetric trench 301, the coupled mode energy propagating from the wafer center region to the boundary is gradually attenuated after entering the comb structure region, while the reflected wave propagating in the opposite direction is difficult to coherently superimpose due to the structural asymmetry. Simulation results show that, compared with the symmetric trench 301, the asymmetric trench 301 structure can further reduce the boundary reflectivity of the faceted mode by about 15% to 25%, thereby more thoroughly localizing and dissipating the energy in the boundary region, reducing the possibility of it returning to the wafer center region and undergoing secondary coupling with the working mode.

[0073] In some embodiments, the boundary comb structure 300 is not composed of a single periodic structure, but includes multiple sub-regions with different geometric parameters, forming a multi-level, hierarchical comb structure. In this embodiment, the boundary comb structure 300 is divided into at least a first comb region and a second comb region along the extension direction of the wafer edge. The grooves 301 in the first comb region have a first arrangement period Λ1 and a first depth h1, and the grooves 301 in the second comb region have a second arrangement period Λ2 and a second depth h2, wherein the first arrangement period Λ1 and the second arrangement period Λ2 are not equal, and / or the first depth h1 and the second depth h2 are not equal. The physical basis for this hierarchical design is that different coupling modes (such as planar tangent modes, bending modes, and in-plane stretching modes of different orders) have different characteristic frequencies and wavelengths. A single-period comb structure can often only produce the optimal suppression effect for coupling modes within a specific frequency range. When a resonator needs to operate over a wider temperature range (e.g., from -55°C to 125°C), the types of coupling modes that coincide at different temperatures may differ.

[0074] By setting up multi-level comb regions with different periods and / or depths, multiple different acoustic band gaps or localized states can be formed, each covering coupled modes in different frequency ranges. For example, the first comb region is configured to localize the energy of the higher-frequency planar tangent mode, and its arrangement period Λ1 is associated with the characteristic wavelength of the planar tangent mode; the second comb region is configured to induce hybridization between the in-plane stretching mode and the bending mode, and its arrangement period Λ2 is associated with the frequency difference between these two modes.

[0075] Simulation results show that, compared with a single-cycle structure, the multi-stage comb structure further reduces the peak impedance fluctuation amplitude of the resonator over the entire wide temperature range, and significantly improves the full-temperature yield.

[0076] In some embodiments, the grooves 301 constituting the boundary comb structure 300 do not extend from the lower surface to the upper surface of the quartz wafer 100, but rather are recessed upwards from the lower surface to a certain depth, leaving a complete unetched portion in the wafer thickness direction. In this embodiment, the grooves 301 are recessed upwards from the lower surface of the quartz wafer 100, but their depth h is less than the thickness t of the quartz wafer 100, i.e., the grooves 301 are blind grooves. In this case, a complete quartz material layer is retained above the grooves 301, which separates the grooves 301 from the upper surface of the wafer.

[0077] The advantages of this non-through design are: First, it preserves the continuity of the wafer's upper surface in the boundary region, which is beneficial to the uniformity and yield of subsequent electrode lithography processes, and avoids problems such as uneven coating or exposure scattering that may be caused by through-groove 301.

[0078] Secondly, and more importantly, this blind slot structure introduces an acoustic cantilever or acoustic thin-film effect. The complete material layer forms a locally vibrating thin-plate region above the groove 301, and its local resonant frequency can be tuned by the thickness (th) of the material layer. By designing this local resonant frequency to be close to the frequency of a specific coupled mode, the anti-resonance characteristics of the local resonator can be utilized to further absorb and dissipate the energy of the coupled mode. This dual mechanism, combining periodic scattering and local resonant absorption, provides better suppression of coupled modes than a purely periodic structure.

[0079] In some specific embodiments, the thickness of the material layer, i.e., th, is set such that the ratio of the fundamental frequency of the thin plate region to the frequency of the in-plane tensile mode is approximately between 0.9 and 1.1, in order to achieve a maximum vibration absorption effect.

[0080] In some embodiments, the method for manufacturing the quartz crystal resonator with the boundary comb structure 300 further includes a step of reverse designing structural parameters based on a target frequency hopping suppression temperature range.

[0081] Traditional design methods typically rely on "forward trial and error," which involves first setting structural parameters and then verifying their effectiveness through simulation or experiments, iterating repeatedly until a satisfactory result is found. However, due to the complex nonlinear relationships between the frequency-temperature characteristics of coupled modes and wafer size, electrode size, and boundary structure parameters, forward trial and error is inefficient and struggles to find the global optimum.

[0082] In this embodiment, a reverse design method is employed, including the following steps: Step 1: Establish a finite element parametric model of the quartz wafer 100 including the boundary comb structure 300. The model uses the length, width, and thickness of the quartz wafer 100, the depth h of the groove 301 of the boundary comb structure 300, the arrangement period Λ, and the sidewall inclination angle θ of the groove 301 as input parameters.

[0083] Step 2: Within the target operating temperature range (e.g., from the first temperature T1 to the second temperature T2), for each combination of input parameters, the frequency-temperature curve of the operating mode (thickness shear mode) and the frequency-temperature curve of the specific coupled mode (surface shear mode, in-plane tension mode, bending mode) are obtained through finite element simulation calculation.

[0084] Step 3: Define an objective function F, which is a weighted function of the minimum frequency interval between the frequency-temperature curve of the operating mode and the frequency-temperature curve of any of the coupled modes within the target operating temperature range. The larger the value of the objective function F, the greater the frequency interval maintained by the operating mode and all coupled modes throughout the entire temperature range, and the lower the risk of temperature-induced frequency hopping.

[0085] Step 4: Employ an optimization algorithm (such as a genetic algorithm, particle swarm optimization, or gradient-based adjoint method) to automatically search for the optimal combination of input parameters, with the objective function F as the optimization goal. During the search process, the optimization algorithm can automatically explore the synergistic relationship between the trench 301 depth h and the arrangement period Λ, as well as their matching relationship with the macroscopic dimensions of the wafer.

[0086] Step 5: Based on the optimal parameter combination obtained from the search, manufacture the quartz crystal resonator.

[0087] For example, the objective function F can be expressed as: F equals the minimum difference between the operating mode frequency and the frequency of each coupled mode for all considered coupled modes within the entire target temperature range, and then a weighted sum of these minimum values.

[0088] Using the aforementioned reverse design method, the optimal combination of wafer size and boundary comb structure 300 parameters can be quickly and accurately determined to simultaneously avoid temperature-induced frequency hopping in the facet mode, stretch mode, and bending mode. This method elevates the design of the boundary comb structure 300 from passive verification to active optimization, significantly shortening the development cycle and ensuring high consistency of device performance across the entire temperature range.

[0089] In some embodiments, the edges of the quartz wafer 100 are chamfered before the boundary comb structure 300 is formed, creating chamfered edges. In this embodiment, the original rectangular edges of the quartz wafer 100 are first mechanically or chemically chamfered to form chamfered surfaces, and then the boundary comb structure 300 is formed in the chamfered edge region.

[0090] Traditionally, wafer chamfering is primarily used to eliminate edge stress concentration and prevent edge chipping, and its impact on vibration characteristics is often considered a secondary or even negative factor. However, the inventors have discovered that synergistic design of the chamfer with the boundary comb structure 300 can produce unexpected beneficial effects.

[0091] Specifically, the presence of the chamfered surface alters the local thickness distribution at the wafer edge, causing a shift in the cutoff frequency of the bending modes propagating along the edge. By matching the geometric parameters of the chamfered surface (such as the chamfer width w and chamfer depth) with the period Λ and depth h of the boundary comb structure 300, the cutoff frequency of the bending modes can be made to fall precisely within the acoustic bandgap formed by the comb structure, thereby further suppressing the propagation of the bending modes along the boundary.

[0092] In some embodiments, the width w of the chamfered surface and the arrangement period Λ of the comb structure satisfy the following relationship: 0.5≤w / Λ≤1.5; when this relationship is satisfied, the boundary condition change introduced by the chamfer and the modulation effect of the periodic comb structure on the bending mode mutually reinforce each other, forming a double blocking effect on the mode.

[0093] In some embodiments, the boundary comb structure 300 is disposed on at least two edges of the quartz wafer 100, and the extension direction of the toothed units on different edges is at a different angle to the corresponding edge.

[0094] The AT-cut quartz wafer 100 exhibits anisotropic in-plane mechanical properties, meaning that the elastic constants and piezoelectric constants differ along the X-axis and Z'-axis (the thickness direction coordinate axes of the AT-cut quartz wafer 100). This results in different sound velocities and mode shapes for the in-plane tensile and tangential modes in different propagation directions.

[0095] In conventional designs, if a groove 301 is provided at the edge, it is typically made to extend perpendicular to the edge, meaning the extension direction of the groove 301 is perpendicular to the edge. However, the inventors discovered through modal analysis and phononic crystal band structure calculations that, for AT-cut quartz, the relative relationship between the extension direction of the groove 301 and the crystal axis orientation has a significant impact on the width of the acoustic bandgap and the center frequency.

[0096] In some embodiments, the groove 301 disposed on the longitudinal edge of the quartz wafer 100 extends not perpendicular to the edge, but at a predetermined deflection angle α relative to the normal direction of the edge. This deflection angle α is determined by solving the dispersion equation of the sound wave in the periodic groove 301 structure based on the elastic constant matrix of the AT-cut quartz wafer 100, with the goal of maximizing the acoustic bandgap width in the frequency range where the target coupling mode is located.

[0097] For example, for a specific frequency facet mode, calculations show that when the angle α between the extension direction of trench 301 and the edge normal direction is approximately +15 degrees or -15 degrees, the acoustic bandgap corresponding to this facet mode is the widest, and the energy localization effect is the best. This optimal deflection angle varies depending on the specific cut angle of the wafer and the target mode, but it is always a non-zero angle, which is significantly different from the design of traditional vertical trench 301.

[0098] This design, which optimizes the orientation of the comb structure based on the anisotropic properties of the wafer, is beyond the conventional understanding of those skilled in the art. Conventional designs usually do not consider the specific quantitative relationship between the trench 301 direction and the crystal axis.

[0099] In some embodiments, the quartz wafer 100 does not strictly employ the standard AT chamfer (i.e., 35°15'), but rather the chamfer is finely adjusted based on the introduction of the boundary comb structure 300.

[0100] The frequency-temperature characteristic curve of the AT-cut quartz wafer 100 is a cubic curve, and its inflection point temperature and slope are affected by slight changes in the cutting angle. The inventors discovered that when a boundary comb structure 300 is introduced at the edge of the wafer, the equivalent elastic constant of the working mode (thickness shear mode) will shift slightly due to the change in boundary conditions, which in turn causes a slight deformation of its original frequency-temperature characteristic curve.

[0101] To compensate for this deformation, in some embodiments, the chamfer of the quartz wafer 100 is deflected by a fine-tuning angle Δθ in the Z' axis direction or the opposite direction, based on the standard AT chamfer, where the absolute value of Δθ is no greater than one degree. By jointly optimizing the chamfer fine-tuning with the geometric parameters of the boundary comb structure 300, a flatter frequency-temperature characteristic curve than that of a conventional standard AT-cut resonator can be obtained over a wide temperature range, while maintaining effective suppression of temperature-induced frequency hopping.

[0102] In some embodiments, the upper excitation electrode 201 and / or the lower excitation electrode 202 are electrodes with non-uniform thickness.

[0103] In traditional quartz resonators, the excitation electrodes typically have a uniform thickness to simplify manufacturing. However, the inventors discovered through modal analysis that the thickness distribution at the electrode edges significantly affects the energy trapping effect of the operating modes.

[0104] In this embodiment, the excitation electrode is designed with a thickness distribution that gradually decreases from the center to the edge, for example, by forming a stepped or wedge-shaped edge profile through multiple overlay or grayscale photolithography processes. This gradually thickened electrode edge works synergistically with the boundary comb structure 300, on the one hand, further optimizing the energy trapping effect of the working mode and improving the Q value; on the other hand, the gradually thickened electrode edge has a certain gradually changing refractive effect on the coupled modes propagating along the wafer surface, which can guide some of the energy of the coupled modes to the boundary comb structure 300 region for dissipation, thereby enhancing the overall noise mode suppression effect.

[0105] In some embodiments, the base for supporting the quartz wafer 100 has an acoustic impedance matching layer provided in the wafer stage area where it contacts the conductive adhesive 400.

[0106] In a traditional structure, after the wafer is fixed with conductive adhesive 400, the vibration at the edge of the wafer will leak to the base through the conductive adhesive 400. At the same time, the mechanical impedance mismatch of the base will also reflect some of the vibration back to the wafer, forming additional reflected noise.

[0107] In this embodiment, a layer of acoustic impedance matching material is pre-deposited in the corresponding area of ​​the substrate wafer stage. The acoustic impedance Z_match of this material satisfies: Z_match≈√(Z_crystal×Z_base); Where Z_crystal is the acoustic impedance of the quartz crystal 100, and Z_base is the acoustic impedance of the base material. That is, the acoustic impedance Z_match of the matching layer should be approximately equal to the geometric mean (i.e., the square root of the product) of the acoustic impedance Z_crystal of the quartz crystal 100 and the acoustic impedance Z_base of the base material.

[0108] By setting this acoustic impedance matching layer, the reflection of vibration energy at the wafer-conductive adhesive 400-substrate interface can be effectively reduced, allowing the coupled mode energy propagating to the boundary to dissipate more smoothly, rather than being reflected back into the wafer and recoupled with the working mode. This feature, together with the boundary comb structure 300, constitutes a dual heterodyne mode suppression mechanism of "boundary absorption + local dissipation".

[0109] In some embodiments, the parameter design of the boundary comb structure 300 is not based on the principle that all temperature ranges are equally important, but rather on a weighted optimization design based on the higher reliability requirements of specific temperature ranges for the target application scenario.

[0110] For example, in GPS receiver applications, frequency stability near normal temperature (25°C) is crucial, while the requirement for extreme low temperatures (-40°C) is relatively less stringent. In this case, the objective function F is modified in step three as follows: F equals the minimum frequency interval between the working mode and the coupled mode at each temperature point within the target operating temperature range, multiplied by a temperature-related weighting factor W(T), and then the minimum value or weighted sum is taken.

[0111] Among them, the weighting factor W(T) has a larger value near normal temperature and a smaller value near extreme temperature.

[0112] This weighted optimization allows the manufactured resonator to have an extremely low risk of frequency hopping within the core operating temperature range, while allowing for acceptable slight disturbances in the edge temperature range. This relaxes the stringent requirements for manufacturing tolerances and improves production yield while meeting the core application requirements.

[0113] In some embodiments, the weighting factor W(T) is assigned segmented or continuously based on temperature points T within the target operating temperature range, and satisfies the following conditions: it takes a larger value near normal temperature and a smaller value near extreme temperature.

[0114] Example 1: Segmented assignment (applicable to discrete temperature point simulation): The target operating temperature range (e.g., from -40°C to 85°C) is divided into several temperature segments, and the weighting factor W(T) for each segment is set as follows: -40°C to -20°C: 0.3 to 0.5; -20 degrees Celsius to 0 degrees Celsius: 0.6 to 0.8; 0 degrees Celsius to 40 degrees Celsius: 0.9 to 1.0; 40 degrees Celsius to 70 degrees Celsius: 0.6 to 0.8; 70°C to 85°C: 0.3 to 0.5; Among them, the weighting factor near normal temperature (0 degrees Celsius to 40 degrees Celsius) takes the highest value of 1.0 or close to 1.0, indicating that the requirements for frequency hopping suppression are the most stringent in this temperature range; while in the extreme low temperature range (minus 40 degrees Celsius to minus 20 degrees Celsius) and extreme high temperature range (70 degrees Celsius to 85 degrees Celsius), the weighting factor is reduced to 0.3 to 0.5, indicating that a relatively loose frequency interval is allowed in this edge temperature range.

[0115] Example 2: Continuous function form (suitable for automatic search in optimization algorithms): In some embodiments, the weighting factor W(T) is expressed as a continuous function with temperature T as the independent variable. For example, it can be a function based on a normal distribution or a trapezoidal shape: W(T) is equal to 1.0 when the absolute value of T is less than 20 degrees Celsius; When the absolute value of T is between 20 and 40 degrees Celsius, the value decreases linearly from 1.0 to 0.5. When the absolute value of T is greater than 40 degrees Celsius, the value remains at 0.5.

[0116] Or it can be represented by a smoother Gaussian function: W(T) is approximately equal to the negative of T (within parentheses) divided by the power of thirty.

[0117] Where T is the temperature value in degrees Celsius, and e is the natural constant.

[0118] Example 3: Customized values ​​for specific application scenarios: For GPS receiver applications, the typical operating temperature range is from -20°C to 60°C, with ambient temperature (around 25°C) being the most commonly used operating condition. For this application, the weighting factor W(T) can be set as follows: In the range of 15 to 35 degrees Celsius, W(T) takes the value of 1.0. In the range of -20°C to 15°C, the value of W(T) increases linearly from 0.6 to 1.0. In the range of 35 to 60 degrees Celsius, the value of W(T) decreases linearly from 1.0 to 0.6. When the temperature exceeds the range of minus 20 degrees Celsius to 60 degrees Celsius, W(T) takes the value of 0.4.

[0119] The example values ​​above are for illustrative purposes only, and specific values ​​can be adjusted according to the target application scenario and reliability level of the resonator. By introducing a temperature-related weighting factor, optimization resources can be focused on frequency hopping suppression within the core operating temperature range during the design phase, thereby improving design flexibility and manufacturing yield while meeting practical application requirements.

[0120] In summary, the weighting factor W(T) in the objective function F takes values ​​of 0.9 to 1.0 near room temperature, and 0.3 to 0.5 at extreme low temperatures (e.g., -40°C to -20°C) and extreme high temperatures (e.g., 70°C to 85°C), exhibiting a linear or stepped transition in the intermediate temperature range. This assignment method allows the optimization algorithm to prioritize frequency hopping suppression within the core operating temperature range of the resonator, while allowing for moderate performance relaxation in the peripheral temperature range, thereby improving overall design feasibility and manufacturing yield.

[0121] In some embodiments, the method of manufacturing the boundary comb structure 300 further includes an online monitoring and feedback correction step.

[0122] During the process of forming the trench 301 by anisotropic wet corrosion, due to slight fluctuations in the concentration, temperature and stirring speed of the corrosion solution, the actual corrosion depth h and the sidewall morphology may deviate from the design values.

[0123] In this embodiment, during the corrosion process, in-situ optical interferometry or laser triangulation is used to monitor the depth h of the trench 301 in real time. When the monitored actual depth h reaches a preset percentage of the target depth (e.g., 90%), the system automatically adjusts the corrosion parameters (e.g., reducing the temperature or diluting the concentration) to slow down the corrosion rate, and immediately terminates the corrosion when the actual depth reaches the target value.

[0124] Furthermore, after completing a batch of wafer etching, samples are extracted for scanning electron microscopy (SEM) measurement to obtain the actual depth h and sidewall tilt angle of the trench 301, and the measurement data is fed back into the etching process parameter setting for the next batch to form a closed-loop correction.

[0125] This online monitoring and feedback correction ensures that the boundary comb structure 300 in mass production has highly consistent geometric parameters, thereby guaranteeing consistent frequency hopping suppression performance across the entire temperature range. This is particularly important for meeting the high reliability requirements of automotive or military-grade products.

[0126] The technical concept of this invention is as follows: This invention provides a quartz crystal resonator with a boundary comb structure 300, comprising: Quartz wafer 100: A rectangular, flat, AT-cut quartz wafer.

[0127] Excitation electrodes: including an upper excitation electrode 201 and a lower excitation electrode 202 respectively disposed in the central regions of the upper and lower surfaces of the wafer.

[0128] Boundary comb structure 300: disposed in the boundary region of quartz wafer 100, located at at least one edge of the wafer. The structure consists of multiple tooth-like units (such as grooves 301 or protrusions 302) arranged periodically along the edge of the wafer, forming a periodic interface of acoustic impedance mismatch.

[0129] Conductive adhesive 400: applied by dispensing to the outer side of the boundary comb structure 300 or the gaps between its toothed units to fix the wafer to the base.

[0130] Core working principle: The boundary comb structure 300, through its periodic geometric characteristics, localizes the vibrational energy of the planar tangent mode in the boundary region, reducing its mode shape overlap integral with the working mode of the central electrode region. Furthermore, it promotes coupling and hybridization of the in-plane tensile and bending modes, concentrating the sensitive size range of temperature-induced frequency hopping caused by these modes, thus facilitating avoidance through wafer macroscopic size design. This structure is formed through processes such as anisotropic wet etching.

[0131] The most widely used traditional quartz crystal resonator structure in the industry is currently this invention. As a mature and fundamental technology in this field, this structure is similar in structural composition to the present invention and serves as the starting point for its technological improvements. Figure 3 The diagram shows a rectangular flat quartz wafer 100, an upper excitation electrode 201 disposed on the upper surface of the quartz wafer 100, and conductive adhesive 400 disposed on the edge or corner of the wafer. The boundary region of the quartz wafer 100 has a smooth rectangular edge and no structure is provided for suppressing coupling modes. Figure 4 The stacking relationship of the quartz wafer 100, the upper excitation electrode 201, the lower excitation electrode 202 and the conductive adhesive 400 is shown in an exploded view, wherein the lower excitation electrode 202 is disposed on the lower surface of the quartz wafer 100.

[0132] Traditional quartz crystal resonator structure, such as Figure 3 (Structural diagram) and Figure 4 As shown in the exploded structural diagram, it mainly includes the following components: Quartz wafer 100: It is processed into a rectangular flat plate shape, usually using the AT cut. AT-cut quartz crystals have excellent frequency-temperature characteristics and are one of the most commonly used cuts in bulk acoustic resonators.

[0133] Excitation electrodes: Deposited on the upper and lower surfaces of the quartz wafer 100, respectively, to apply an electric field to excite the thickness shear vibration mode of the wafer. The upper excitation electrode 201 is disposed on the upper surface of the quartz wafer 100, and the lower excitation electrode 202 is disposed on the lower surface of the quartz wafer 100 (e.g., ...). Figure 4 (See exploded structural diagram). Electrodes are typically made of conductive materials such as gold, silver, or aluminum, and are formed through vapor deposition or sputtering processes.

[0134] Conductive adhesive 400: The quartz wafer 100 is fixed to the wafer stage of the base by dispensing. The conductive adhesive 400 is usually placed at the edge or corner of the wafer to form multiple discrete fixing points.

[0135] Base (not shown in the figure): Used to support the wafer and provide external electrical connections, it is usually made of ceramic or insulating materials.

[0136] Cavity (not shown in the figure): The wafer is sealed inside the cavity to ensure that it vibrates normally in a vacuum or inert gas environment and to avoid the influence of air damping on the vibration characteristics.

[0137] In operation, the external circuit applies an AC voltage to the excitation electrode through the base leads and conductive adhesive 400. Due to the inverse piezoelectric effect of the quartz crystal, mechanical vibration is excited inside the wafer. Among these, the thickness shear vibration mode is the desired operating mode, whose vibration energy is mainly concentrated in the electrode-covered area, and the vibration frequency is determined by the thickness of the wafer.

[0138] At the same time, due to the finite-size planar structure of the wafer, in addition to the operating mode, various coupling modes may be excited inside the wafer, including: In-plane tensile mode: The vibration direction is located in the plane of the wafer, which manifests as the stretching and contraction deformation of the wafer in the length direction; Bending mode: The vibration direction is perpendicular to the wafer plane, which manifests as bending deformation of the wafer in the thickness direction; Surface-tangential mode: The vibration direction is located in the wafer plane, and it manifests as tangential deformation in the wafer plane.

[0139] These coupled modes have different frequency-temperature characteristics than the operating mode. When a temperature change causes the frequency of a coupled mode to approach or coincide with the frequency of the operating mode, modal coupling occurs between the two, and energy is transferred from the operating mode to the coupled mode. This causes the equivalent resistance of the resonator to increase sharply, the Q value to decrease, and the output frequency to jump, which is the phenomenon of "temperature-induced frequency hopping".

[0140] The above-mentioned traditional quartz crystal resonator structure has the following disadvantages: (i) Lack of active suppression mechanism for coupled modes: In this structure, the boundary region of the quartz wafer 100 is a smooth rectangular edge, serving only as a fixed area for connection with the conductive adhesive 400, without any functional structure specifically designed to suppress coupled modes. When temperature changes cause the operating mode to overlap with coupled modes such as in-plane stretching and bending modes, strong coupling occurs between them, and energy is transferred from the operating mode to the coupled mode, triggering temperature-induced frequency hopping. Because the structure itself lacks the ability to actively control coupled modes, temperature-induced frequency hopping cannot be avoided.

[0141] (ii) Temperature-induced frequency hopping suppression depends on external circuits: Under this structure, when temperature-induced frequency hopping occurs, it cannot be suppressed or eliminated by the resonator itself. It can only be compensated or avoided by the design of external oscillation circuits, which increases the complexity and cost of system design and makes it difficult to achieve ideal compensation effect over a wide temperature range.

[0142] (III) Limitations of Passive Screening: Since this approach cannot suppress the amplitude of interference modes at the structural design level to eliminate frequency hopping, manufacturers can only rely on full-temperature testing in the later stages to screen out devices exhibiting frequency hopping. This method is a passive response, which not only increases manufacturing costs and production cycle, but also the proportion of frequency-hopping devices (i.e., yield problems) always exists and cannot be fundamentally improved through structural modifications.

[0143] The present invention aims to overcome the above-mentioned shortcomings of the prior art and provide a novel quartz crystal resonator structure to solve the problem of temperature-induced frequency hopping caused by the inability of traditional rectangular planar quartz crystal resonators to effectively suppress interference modes, thereby improving the frequency stability and equivalent series resistance (ESR) consistency of the device over a wide temperature range.

[0144] Specifically, the object of the present invention is: A quartz crystal resonator structure is provided that can effectively suppress the amplitude of interfering mode vibrations without changing the basic interconnection method of the crystal. This structure achieves two functions by setting a periodic comb structure in the boundary region of the crystal: firstly, it localizes the energy of the planar tangent mode in the boundary region, reducing its mode shape overlap integral with the operating mode; secondly, through the design of the boundary microstructure, it hybridizes and merges the in-plane tensile mode and bending mode, making the structural size range corresponding to the frequency hopping of these two modes more concentrated, which can be effectively avoided through crystal size design.

[0145] This invention provides a quartz crystal resonator that can fundamentally suppress temperature-induced frequency hopping, significantly improving its yield in full-temperature testing, thereby reducing manufacturing costs, shortening production cycles, improving product consistency, and better meeting the requirements of wide-temperature, high-reliability applications.

[0146] This invention provides a quartz crystal resonator with small fluctuations and gentle gradients in equivalent series resistance (ESR) across the entire temperature range, suitable for applications such as Global Positioning System (GPS), aerospace, and military guidance where stringent frequency stability requirements are required.

[0147] Figure 1 The distribution of the boundary comb structure 300 on the quartz wafer 100 is shown. As shown, the upper excitation electrode 201 is located in the central region of the quartz wafer 100, and the boundary comb structure 300 is continuously arranged along two opposite edges along the length direction of the quartz wafer 100 to form periodically arranged grooves 301. Figure 2 The invention illustrates that the quartz wafer 100 has periodic grooves 301 formed by upward indentation from the lower surface in the boundary region, constituting a boundary comb structure 300. This structure forms an acoustic impedance mismatch interface in the boundary region, which can localize the coupled mode energy to the tooth-shaped region.

[0148] This invention provides a quartz crystal resonator with a boundary comb structure 300. For example... Figure 1 and Figure 2 As shown, the quartz crystal resonator provided by the present invention includes: Quartz wafer 100: Made from AT-cut quartz crystal, it is rectangular and flat, with an upper and lower surface. The thickness of quartz wafer 100 is set according to the target operating frequency, and the length and width of quartz wafer 100 are determined according to the package size and equivalent series resistance (ESR) requirements.

[0149] Upper excitation electrode 201 and lower excitation electrode 202 are respectively disposed on the upper and lower surfaces of the quartz wafer 100, and are aligned with each other in a direction perpendicular to the wafer surface to form an electrode region. The electrodes (201, 202) are located in the central region of the quartz wafer 100, and a predetermined distance is maintained between the electrode edges and the wafer edges to form a boundary region. The electrode material is gold, silver, or aluminum, and is formed by vapor deposition or sputtering processes.

[0150] Boundary comb structure 300: disposed in the boundary region of the quartz wafer 100, specifically located at at least one edge of the quartz wafer 100. In this embodiment, the boundary comb structure 300 is disposed along two opposite edges along the length direction of the quartz wafer 100 (e.g., Figure 1 (As shown).

[0151] Specifically, the boundary comb structure 300 is composed of multiple tooth-like units arranged periodically along the wafer edge. Each tooth-like unit includes a groove 301 or a protrusion 302 extending from the wafer edge into the wafer interior. This embodiment adopts the form of a groove 301, that is, a groove-like structure formed by recessing upward from the lower surface of the quartz wafer 100. Multiple grooves 301 are arranged at equal intervals along the wafer edge to form a periodic structure. Its cross-sectional structure is as follows. Figure 2 As shown, in contrast, the boundary section of a traditional structure is as follows: Figure 5 As shown. Figure 5 The diagram shows that in the conventional structure, the boundary region of the quartz wafer 100 has a smooth rectangular edge, and the lower surface is in direct contact with the conductive adhesive 400. The boundary region only serves a fixing function and does not have modal control function.

[0152] Conductive adhesive 400: Used to fix the quartz wafer 100 to the wafer stage of the base (not shown in the figure). The conductive adhesive 400 is applied to the boundary area of ​​the quartz wafer 100 by dispensing, specifically located on the outside of the boundary comb structure 300 or in the gaps between the toothed units, forming multiple discrete fixing points. The conductive adhesive 400 serves both mechanical fixing and electrical connection functions.

[0153] Base (not shown in the figure): Made of ceramic material, it has a wafer stage and external leads for supporting the quartz wafer 100 and providing electrical connection.

[0154] Cavity (not shown in the figure): formed by the base and the cover plate, the quartz wafer 100 is sealed inside the cavity, the cavity is kept vacuum or filled with inert gas to ensure normal vibration of the wafer.

[0155] In the above structural configuration, the boundary comb structure 300 is configured to perform the following functions: First, for the face-cut mode, the boundary comb structure 300 forms an acoustic impedance mismatch interface in the wafer boundary region through its periodic concave and convex features, localizing the vibration energy of the face-cut mode in the boundary region, reducing its mode shape overlap integral with the working mode (thickness shear vibration), thereby reducing the energy coupling between the two.

[0156] Second, for the in-plane tensile and bending modes, the boundary comb structure 300 introduces additional wave vector components through its periodic geometric features, causing the in-plane tensile and bending modes to couple and hybridize, merging to form a new hybrid mode. This hybrid mode is more sensitive to wafer size parameters than the original two modes, thus narrowing the range of structural dimensions corresponding to temperature-induced frequency hopping, making it easier to effectively avoid this through macroscopic dimension design such as the length and width of the quartz wafer 100.

[0157] The boundary comb structure 300 of the present invention is preferably formed by an anisotropic wet etching process, utilizing the difference in etching rate of quartz crystal in different crystal orientations to naturally form a sidewall structure with a specific crystal orientation. After etching, the upper excitation electrode 201 and the lower excitation electrode 202 are formed by vapor deposition or sputtering. Finally, the wafer is fixed to the substrate and encapsulated using conductive adhesive 400. It should be noted that the core protection scope of the present invention is not limited to the above-described manufacturing method; other processing methods capable of realizing the boundary comb structure 300 (such as dry etching, laser processing, etc.) are also within the protection scope of the present invention.

[0158] The technical effects of this invention are as follows: (a) Effectively suppresses temperature-induced frequency hopping and improves frequency stability: This invention introduces a periodic boundary comb structure 300 in the boundary region of the quartz wafer 100, which effectively suppresses temperature-induced frequency hopping through the following two aspects: First, localization of the energy of the surface-cutting mode. For example... Figure 2 As shown, the boundary comb structure 300 forms an acoustic impedance mismatch interface in the wafer boundary region, which can localize the vibration energy of the facet mode to the boundary region. Since the energy of the working mode (thickness shear vibration) is mainly concentrated in the electrode region, the expected overlap integral of the two modes is significantly reduced. Even if the temperature change causes the frequencies of the two to be close, the degree of energy coupling can be greatly weakened, thereby suppressing the occurrence of temperature-induced frequency hopping.

[0159] Second, the tensile and bending modes are hybridized. The boundary comb structure 300, through its periodic geometry, introduces additional wave vector components, enabling the in-plane tensile and bending modes to couple and hybridize, forming a new hybrid mode. This hybrid mode is more sensitive to wafer size parameters than the original two modes, thus narrowing the range of structural dimensions corresponding to temperature-induced frequency hopping, making it easier to effectively avoid this through macroscopic dimension design of the quartz wafer 100, such as length and width.

[0160] Figure 6 The figure shows the simulated resonant frequency-temperature characteristic curve of the traditional structure, with the horizontal axis representing temperature (°C) and the vertical axis representing frequency shift (ppm). The figure shows that the operating mode of the traditional structure experiences a sudden frequency change at a specific temperature point, indicating that temperature-induced frequency hopping has occurred.

[0161] Figure 7 The figure shows the simulated resonant frequency-temperature characteristic curve of the structure of this invention. The horizontal axis represents temperature (°C), and the vertical axis represents frequency shift (ppm). The figure shows that the frequency curve of the structure of this invention is smooth across the entire temperature range, and no frequency abrupt changes occur in the operating mode, indicating that temperature-induced frequency hopping is effectively suppressed.

[0162] Figure 8 This is a simulation graph of the frequency-temperature characteristics and impedance of a traditional structure. The horizontal axis represents temperature (°C), the vertical axis represents frequency shift (ppm), and the grayscale color represents the impedance magnitude (db(Z)). A frequency abrupt change occurs at a specific temperature point, and the corresponding color darkens (resistance increases) at this point, indicating temperature-induced frequency hopping.

[0163] Figure 9 The figure shows a simulation of the frequency-temperature characteristics and impedance integration of the structure of this invention. The horizontal axis represents temperature (°C), the vertical axis represents frequency shift (ppm), and the grayscale color represents the impedance magnitude (db(Z)). The frequency curves in the figure are smooth across the entire temperature range, and there are no regions where frequency abrupt changes correspond to impedance increases, indicating that temperature-induced frequency hopping is effectively suppressed.

[0164] Simulation analysis results show that the quartz resonator using the structure of this invention exhibits a smooth resonant frequency variation curve with temperature across the entire temperature range of -40℃ to +85℃ (e.g., Figure 7 (As shown). The simulation curve of the resonant frequency-temperature characteristic of the traditional structure is as follows. Figure 6 As shown. Figure 8 In the conventional structure shown, a frequency abrupt change occurs at a specific temperature point, and the impedance modulus (db(Z)) corresponding to this abrupt change point increases sharply (the color in the figure darkens), indicating that temperature-induced frequency hopping has occurred; while Figure 9The structure of the present invention shown exhibits a smooth frequency curve across the entire temperature range, without any region corresponding to abrupt frequency changes and increased impedance, indicating that temperature-induced frequency hopping is effectively suppressed. It should be noted that the impedance magnitude (db(Z)) is positively correlated with the equivalent series resistance (ESR) near the resonant point; therefore, this curve can effectively reflect the frequency hopping phenomenon.

[0165] (ii) Reduce dependence on external circuits and simplify system design: Because this invention achieves active suppression of temperature-induced frequency hopping through structural design, the resonator itself can maintain stable frequency and resistance characteristics across the entire temperature range, potentially reducing reliance on external oscillation circuits for frequency hopping compensation or avoidance. This helps reduce the complexity and cost of system design, and improves the reliability and design flexibility of the oscillation circuit.

[0166] (III) Improve the yield rate of full-temperature testing and reduce manufacturing costs: In traditional structures, since temperature-induced frequency hopping cannot be avoided through structural design, manufacturers typically rely on full-temperature testing to screen and eliminate frequency-hopping devices, which results in problems such as long testing time, high cost, and limited yield.

[0167] This invention suppresses temperature-induced frequency hopping at its source through structural design, and is expected to significantly improve the yield of resonators in full-temperature testing, reduce the workload of full-temperature testing and screening, thereby helping to reduce manufacturing costs, shorten production cycles, and improve product consistency.

[0168] (iv) The equivalent series resistance (ESR) fluctuates little and has a gentle gradient over the entire temperature range: The structure of this invention enables the resonator to maintain a stable oscillation state within the operating temperature range, and the curve of the equivalent series resistance (ESR) changing with temperature is expected to be smooth (e.g., Figure 9 As shown), there are no resistance spikes caused by modal coupling in traditional structures (such as...). Figure 8 (As shown). This characteristic makes the present invention particularly suitable for fields such as Global Positioning System (GPS), aerospace, and military guidance, where frequency stability requirements are stringent.

[0169] Example 1: This embodiment provides a quartz crystal resonator with a boundary comb structure 300, the structure of which is as follows: Figure 1 and Figure 2 As shown.

[0170] 1. Device structure: (1) Quartz wafer 100: It is made of AT-cut quartz crystal and is in the shape of a rectangular plate with an upper surface and a lower surface. The thickness of quartz wafer 100 is set according to the target operating frequency, and the length and width of quartz wafer 100 are determined according to the package size and equivalent series resistance (ESR) requirements.

[0171] (2) Excitation electrodes: The upper excitation electrode 201 is disposed on the upper surface of the quartz wafer 100, and the lower excitation electrode 202 is disposed on the lower surface of the quartz wafer 100. The two electrodes are aligned with each other in a direction perpendicular to the wafer surface to form an electrode region. The electrodes are located in the central region of the quartz wafer 100, and a predetermined distance is maintained between the electrode edge and the wafer edge to form a boundary region.

[0172] (3) Boundary comb structure 300: The boundary comb structure 300 is disposed in the boundary region of the quartz wafer 100, specifically located at the two opposite edges in the length direction of the quartz wafer 100, and continuously distributed along the edges (e.g. Figure 1 (As shown).

[0173] like Figure 2 As shown, the boundary comb structure 300 is composed of multiple grooves 301 formed by recesses from the lower surface of the quartz wafer 100 upwards. The multiple grooves 301 are arranged at equal intervals along the edge of the wafer to form a periodic structure.

[0174] (4) Conductive adhesive 400: Conductive adhesive 400 is applied to the boundary area of ​​the quartz wafer 100 by dispensing, specifically located at the wafer corner outside the boundary comb structure 300, forming multiple discrete fixing points for fixing the quartz wafer 100 to the base.

[0175] 2. Working principle: In the working state, the external circuit applies an AC voltage to the excitation electrode through the conductive adhesive 400, which excites the thickness shear vibration of the wafer as the working mode.

[0176] The boundary comb structure 300 suppresses temperature-induced frequency hopping through the following two functions: (1) Localization of energy of tangential mode: The boundary comb structure 300 forms an acoustic impedance mismatch interface in the boundary region of the wafer, localizes the vibration energy of the tangential mode in the boundary region, reduces the mode overlap integral with the working mode, and thus reduces the energy coupling between the two.

[0177] (2) Hybridization of stretching and bending modes: The periodic geometric features of the boundary comb structure 300 cause the in-plane stretching mode and bending mode to couple and hybridize, merging to form a new hybrid mode. This hybrid mode is more sensitive to wafer size parameters than the original two modes, which reduces the structural size range corresponding to temperature-induced frequency hopping, making it easier to effectively avoid through macroscopic size design such as the length and width of the quartz wafer 100.

[0178] 3. Manufacturing Method: The boundary comb structure 300 is preferably formed by an anisotropic wet etching process, utilizing the difference in etching rate of quartz crystals in different crystal orientations to naturally form a sidewall structure with a specific crystal orientation. After etching, excitation electrodes are formed by evaporation or sputtering processes, and finally, the wafer is fixed to the substrate and encapsulated using conductive adhesive 400. It should be noted that the core protection scope of this invention is not limited to the above-described manufacturing method.

[0179] In some embodiments, the boundary comb structure 300 may be disposed on the four edges of the quartz wafer 100 to further enhance the suppression effect on coupling modes.

Claims

1. A quartz crystal resonator with a boundary comb structure, characterized in that, include: A rectangular, flat quartz wafer, wherein the quartz wafer is AT-cut and has an upper surface and a lower surface; An upper excitation electrode is disposed in the central region of the upper surface of the quartz wafer; The lower excitation electrode is disposed in the central region of the lower surface of the quartz wafer and is aligned with the upper excitation electrode in a direction perpendicular to the quartz wafer to form an electrode region together. A boundary comb structure is disposed in the boundary region of the quartz wafer and located at at least one edge of the quartz wafer. The boundary comb structure is composed of a plurality of tooth-like units arranged periodically along the edge of the quartz wafer. The boundary comb structure is configured as follows: An acoustic impedance mismatch interface is formed in the boundary region of the quartz wafer, so that the vibration energy of a specific coupled mode is localized in the boundary region, thereby reducing the mode overlap integral between the coupled mode and the working mode. Furthermore, by introducing periodic geometric features, at least two other coupling modes are coupled and hybridized, thereby confining the frequency jump phenomenon caused by the other coupling modes within a more concentrated range of wafer size parameters.

2. The quartz crystal resonator with a boundary comb structure according to claim 1, characterized in that, The boundary comb structure is disposed at two opposite edges of the quartz wafer along its length.

3. The quartz crystal resonator with a boundary comb structure according to claim 1, characterized in that, The toothed unit is a groove formed by indentation from the lower surface of the quartz wafer upwards, or multiple grooves are arranged at equal intervals along the edge of the quartz wafer.

4. The quartz crystal resonator with a boundary comb structure according to claim 3, characterized in that, The depth of the groove and the thickness of the quartz wafer satisfy a preset proportional relationship, such that the frequency of the hybrid mode formed by the coupling and hybridization of the in-plane tensile mode and the bending mode deviates from the frequency of the working mode within the target operating temperature range.

5. The quartz crystal resonator with a boundary comb structure according to claim 1, characterized in that, The ratio of the depth h of the trench to the thickness t of the quartz wafer ranges from 0.4 to 1.0, and the ratio of the arrangement period Λ of the trench to the thickness t ranges from 0.8 to 2.

0. Within this ratio range, the boundary comb structure can simultaneously achieve effective energy localization of the face-cutting mode and effective coupling hybridization of the face-in-face tensile mode and bending mode.

6. The quartz crystal resonator with a boundary comb structure according to claim 1, characterized in that, The boundary tooth comb structure is formed by an anisotropic wet etching process, and the tooth-like units constituting the boundary tooth comb structure have specific crystal orientation sidewalls naturally formed by the anisotropic wet etching process.

7. A method for manufacturing a quartz crystal resonator with a boundary comb structure as described in any one of claims 1 to 6, characterized in that, Includes the following steps: A rectangular, flat, AT-cut quartz wafer is provided, the quartz wafer having an upper surface and a lower surface; In the boundary region of the quartz wafer, along at least one edge of the quartz wafer, a boundary comb structure composed of a plurality of periodically arranged tooth-like units is formed. After forming the boundary comb structure, an upper excitation electrode is formed in the central region of the upper surface of the quartz wafer, and a lower excitation electrode is formed in the central region of the lower surface of the quartz wafer, so that the upper excitation electrode and the lower excitation electrode are aligned with each other. A quartz wafer with the boundary toothed comb structure and the excitation electrode formed thereon is fixed to an external base by means of conductive adhesive, wherein the conductive adhesive is applied by dispensing in the gap between adjacent toothed units of the boundary toothed comb structure or in the outer region of the boundary toothed comb structure.

8. The method according to claim 7, characterized in that, The step of forming the boundary comb structure includes: using an anisotropic wet etching process to etch multiple grooves that are recessed upward from the lower surface of the quartz wafer in the boundary region of the quartz wafer, so as to form the tooth-shaped unit.

9. The method according to claim 8, characterized in that, The anisotropic wet etching process utilizes the difference in etching rate of quartz crystals in different crystal orientations, so that the formed trenches have sidewalls composed of specific crystal faces.

10. The method according to claim 7, characterized in that, When forming the boundary comb structure, the proportional relationship between the geometric dimensions of the toothed unit and the thickness of the quartz wafer is controlled so that the boundary comb structure can promote the coupling and hybridization of in-plane stretching mode and bending mode in subsequent use, and constrain the frequency jump phenomenon caused by the in-plane stretching mode and the bending mode within the predetermined wafer size parameter range.

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