Low-hysteresis high-frequency quartz crystal resonator and preparation method thereof

Abstract

The invention relates to a low-hysteresis high-frequency quartz crystal resonator and a preparation method, the low-hysteresis high-frequency quartz crystal resonator comprises a quartz crystal wafer, a ceramic base and a metal upper cover, the upper end of the ceramic base is hermetically connected with the metal upper cover, an ultrahigh vacuum inner chamber is arranged between the metal upper cover and the ceramic base, two bonding pads are arranged at the bottom of the ultrahigh vacuum inner chamber in parallel, and the two bonding pads are connected with the metal upper cover. Wherein one bonding pad is a reinforcing structure with high rigidity, the other bonding pad is a flexible structure with low rigidity and high elasticity, the quartz wafer is fixed on the reinforcing structure and the flexible structure through conductive adhesive, the upper end face of the reinforcing structure is flush with the upper end face of the flexible structure, and a thermistor is integrated in the ceramic base. And external electrodes connected with the quartz wafers and the thermistors in a one-to-one correspondence manner are arranged at the bottom of the ceramic base. The surface-mounted quartz crystal resonator overcomes the defects that in the prior art, due to thermal stress concentration, a traditional surface-mounted quartz crystal resonator is large in frequency temperature hysteresis and poor in long-term stability.

Description

A low-hysteresis high-frequency quartz crystal resonator and its fabrication method Technical Field

[0001] This invention relates to the field of quartz crystal resonator technology, and in particular to a low-hysteresis high-frequency quartz crystal resonator and its fabrication method. Background Technology

[0002] Quartz crystal resonators, as the "heart" of modern electronic devices, provide frequency references and clock signals for communication systems, navigation and positioning, and precision instruments. With the development of technologies such as 5G / 6G communication, vehicle-to-everything (V2X) communication, and high-performance computing, unprecedentedly stringent requirements have been placed on the overall performance of resonators: not only are higher operating frequencies required, but also extremely low frequency temperature hysteresis over a wide temperature range (e.g., -40℃ to +85℃ or even wider). Frequency temperature hysteresis refers to the phenomenon that the output frequency of a device cannot fully recover to its initial value after undergoing temperature cycling, and it is a key bottleneck affecting long-term frequency stability and system accuracy.

[0003] Traditional high-frequency quartz resonators face a trade-off between two main technological approaches: One is the use of all-quartz microelectromechanical systems (MEMS) technology, integrating the resonant structure with the support structure into a single unit. While this approach achieves excellent hysteresis performance and a high quality factor (Q), its complex manufacturing process, high cost, and poor compatibility with mainstream ceramic-metal packaging lines hinder its widespread adoption. The second approach is the traditional method of using a standard quartz wafer mounted on a ceramic substrate with conductive adhesive. This method is lower in cost and has a mature process, but the mismatch in the coefficient of thermal expansion (CTE) between the quartz wafer and the ceramic substrate generates significant thermal stress during temperature changes. This stress is concentrated and transferred to the wafer through the "rigid" connection point of the conductive adhesive, resulting in severe frequency hysteresis and long-term drift. Although the industry has made numerous attempts to optimize crystal cutting (such as using SC or FC cutting), improve conductive adhesive formulations, or optimize packaging structures, these often only achieve single-point improvements and cannot systematically address the entire physical chain of "stress generation-transmission-effect." The hysteresis performance (typically greater than ±0.1 ppm) still falls short of the requirements for high-end applications.

[0004] Therefore, developing a quartz crystal resonator that combines ultra-low hysteresis, high-frequency stability, high reliability, and low-cost manufacturing based on mature packaging technology has become a technical challenge that urgently needs to be overcome in this field. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to provide a low-hysteresis high-frequency quartz crystal resonator and its preparation method, which overcomes the defects of traditional surface-mount quartz crystal resonators in the prior art, such as large frequency temperature hysteresis and poor long-term stability caused by thermal stress concentration. The invention achieves full-link collaborative innovation from crystal microstructure design and interface stress management to system environment control.

[0006] The technical solution adopted by this invention to solve its technical problem is as follows: A low-hysteresis high-frequency quartz crystal resonator is provided, comprising a quartz crystal wafer, a ceramic substrate, and a metal cover. The upper end of the ceramic substrate is sealed with the metal cover, and an ultra-high vacuum chamber is provided between the metal cover and the ceramic substrate. Two pads are arranged side-by-side at the bottom of the ultra-high vacuum chamber; one pad is a high-rigidity reinforcing structure, and the other pad is a low-rigidity, high-elasticity flexible structure. The quartz crystal wafer is fixed to the reinforcing and flexible structures with conductive adhesive. The upper surface of the reinforcing structure is flush with the upper surface of the flexible structure. A thermistor is integrated inside the ceramic substrate, and external electrodes corresponding to the quartz crystal wafer and the thermistor are provided at the bottom of the ceramic substrate.

[0007] As a supplement to the technical solution described in this invention, both the upper and lower surfaces of the quartz wafer are provided with low-stress multilayer composite electrodes. The overlapping portion formed by the low-stress multilayer composite electrodes on the upper or lower surface of the quartz wafer is the main vibration zone. The side of the quartz wafer is provided with electrode feet that correspond one-to-one with the pads.

[0008] As a supplement to the technical solution described in this invention, the quartz wafer has at least one micro-groove in the area where the electrode feet are mounted, and the micro-groove is circular or elliptical in shape.

[0009] As a supplement to the technical solution described in this invention, the low-stress multilayer composite electrode includes a chromium adhesion layer, an aluminum nitride stress buffer layer, and a gold conductive layer stacked sequentially from the surface of the quartz wafer outwards.

[0010] As a supplement to the technical solution described in this invention, the thickness of the aluminum nitride stress buffer layer is 30nm to 80nm; the pattern of the low-stress multilayer composite electrode is circular, elliptical or rectangular.

[0011] As a supplement to the technical solution described in this invention, the reinforcing structure is a solid cross-shaped, grid-shaped, or block-shaped metallized structure; the flexible structure is a spiral, serpentine, or finger-shaped intersecting metallized fine wire structure.

[0012] As a supplement to the technical solution described in this invention, a non-evaporable getter film is provided on the inner surface of the metal cover and / or the inner surface of the ceramic base facing the inner cavity, wherein the non-evaporable getter film is a zirconium-vanadium-iron alloy film.

[0013] As a supplement to the technical solution described in this invention, the pressure inside the ultra-high vacuum chamber is maintained below 0.001 Pa for a long period of time.

[0014] The method for fabricating a low-hysteresis high-frequency quartz crystal resonator includes the following steps: S1: Providing a quartz wafer rotated 60 degrees within the AT cutting plane, and forming circular or elliptical microgrooves in the electrode pin area of ​​the quartz wafer using photolithography and dry etching processes; S2: Cleaning and surface-treating the quartz wafer, then sequentially depositing and patterning low-stress multilayer composite electrodes on its surface, and subsequently cutting it to obtain a single quartz wafer; S3: Fabricating a ceramic substrate, and forming two bonding surfaces on the ceramic substrate using photolithography and metallization processes. The ceramic substrate has a coplanar coating pad, including a high-rigidity reinforcing structure and a low-rigidity, high-elasticity flexible structure, and integrates a thermistor within the ceramic substrate; S4: Apply conductive adhesive to the reinforcing and flexible structures of the ceramic substrate, align and mount the electrode pins of the quartz wafer, and achieve fixation and electrical connection by curing the conductive adhesive; S5: Provide a metal cover, and bond and seal the metal cover to the ceramic substrate with the completed chip mounting in a vacuum environment to form the ultra-high vacuum inner cavity.

[0015] As a supplement to the technical solution described in this invention, step S2 further includes a step of selectively laser annealing the region on which the low-stress multilayer composite electrode is formed.

[0016] As a supplement to the technical solution described in this invention, in step S5, before bonding and sealing, a non-evaporable getter film is deposited on the inner surface of the metal cover; after bonding and sealing, annealing is performed at a temperature of 350°C to 450°C to activate the non-evaporable getter film.

[0017] As a supplement to the technical solution described in this invention, in step S5, the bonding seal is a vacuum eutectic bonding performed using gold-tin eutectic solder.

[0018] Beneficial Effects: This invention relates to a low-hysteresis high-frequency quartz crystal resonator and its fabrication method, which has the following advantages: 1. A three-level stress control system is constructed, consisting of the crystal body, the interface, and the system environment, to achieve ultra-low hysteresis. The quartz wafer is rotated 60 degrees within the AT-cut plane, and the circular / elliptical microgrooves of the electrode feet serve as the first level, guiding and dispersing stress without stress concentration through geometric shapes; the reinforcing structure and flexible structure serve as the second level, innovatively decoupling thermal stress. The reinforcing structure bears the support and heat conduction, while the flexible structure actively dissipates shear stress through elastic deformation, fundamentally reducing the effective stress transmitted to the crystal vibration core; low-stress multilayer composite electrodes serve as a supplement, alleviating interface layer stress; this synergistic design enables the frequency hysteresis of the device to be stably controlled within ±0.1 after temperature cycling from -40℃ to +85℃. 1. Performance improvement is significantly enhanced compared to traditional single-pad mounting structures, with performance below ppm; 2. The intrinsic advantage of 60-degree rotation within the AT cutting plane, combined with the patterned design of low-stress multilayer composite electrodes (low-loss electrodes) and an ultra-high vacuum environment (maintained by a getter film for a long time at <0.001 Pa), ensures that the resonator can still achieve extremely high Q values ​​at high frequencies; 3. The thermistor built into the ceramic substrate is in the same stable ultra-high vacuum environment as the quartz crystal, enabling real-time and accurate sensing of the crystal temperature, providing a high-quality signal for the external temperature compensation circuit (IC), and facilitating high-precision system-level frequency stabilization; 4. The core innovative structures of this invention are all realized using standard semiconductor lithography, etching, thin film deposition, and ceramic co-firing processes, eliminating the need for complex all-quartz MEMS processing; This invention achieves disruptive performance improvements while maintaining good compatibility with the traditional ceramic-metal packaging industry chain, possessing the potential for high yield, low cost, and large-scale production, thus resolving the contradiction between high performance and high cost. Attached Figure Description

[0019] Figure 1 is a cross-sectional view of the present invention; Figure 2 is a partial enlarged view of the quartz wafer electrode foot area with circular microgrooves according to the present invention; Figure 3 is a plan view of the reinforcing structure and flexible structure on the ceramic substrate according to the present invention; Figure 4 is a partial enlarged cross-sectional view of the low-stress multilayer composite electrode according to the present invention; Figure 5 is a diagram of the external electrode distribution at the bottom of the ceramic substrate according to the present invention; Figure 6 is a top view of the quartz wafer according to the present invention.

[0020] Illustration: 1. Quartz wafer; 11. Electrode foot; 12. Microgroove; 2. Ceramic base; 21. Reinforcing structure; 22. Flexible structure; 23. Thermistor; 3. Conductive adhesive; 4. Metal cover; 41. Non-evaporable getter film; 5. Low-stress multilayer composite electrode; 51. Chromium adhesion layer; 52. Aluminum nitride stress buffer layer; 53. Gold conductive layer; 6. Gold-tin eutectic solder; 7. Ultra-high vacuum chamber; 8. External electrode. Detailed Implementation

[0021] The present invention will be further illustrated below with reference to specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Furthermore, it should be understood that after reading the teachings of this invention, those skilled in the art can make various alterations or modifications to the invention, and these equivalent forms also fall within the scope defined by the appended claims.

[0022] The present invention relates to a low-hysteresis high-frequency quartz crystal resonator and its fabrication method, as shown in Figures 1-6. The resonator includes a quartz crystal wafer 1, a ceramic substrate 2, conductive adhesive 3, and a metal cover 4. The upper end of the ceramic substrate 2 is sealed with the metal cover 4. An ultra-high vacuum chamber 7 is disposed between the metal cover 4 and the ceramic substrate 2. Two pads are arranged side-by-side at the bottom of the ultra-high vacuum chamber 7. One pad is a high-rigidity reinforcing structure 21, and the other pad is a low-rigidity, high-elasticity flexible structure 22. The quartz crystal wafer 1 is fixed to the reinforcing structure 21 and the flexible structure 22 by the conductive adhesive 3. The upper surface of the reinforcing structure 21 is flush with the upper surface of the flexible structure 22. A thermistor 23 is integrated inside the ceramic substrate 2. External electrodes 8 are disposed at the bottom of the ceramic substrate 2, corresponding to the quartz crystal wafer 1 and the thermistor 23 respectively.

[0023] Low-stress multilayer composite electrodes 5 are provided on both the upper and lower surfaces of the quartz wafer 1. The overlapping portion formed by the low-stress multilayer composite electrodes 5 on the upper or lower surface of the quartz wafer 1 is the main vibration zone. Electrode feet 11 corresponding to the pads are provided on the side of the quartz wafer 1.

[0024] The quartz wafer 1 is an AT-cut wafer rotated 60 degrees within its cut surface, exhibiting good resistance to thermal stress. The Euler angle θ of this wafer is preferably set between 34°00′ and 35°30′ to optimize its frequency-temperature characteristics and mechanical stability. To manage stress at the structural source, at least one circular or elliptical microgroove 12 (as shown in Figure 2) is formed in the electrode pin 11 region of the quartz wafer 1 for mounting and electrical connection using micromachining techniques. The depth of the microgroove 12 is preferably controlled between 20% and 40% of the thickness of the quartz wafer 1. This design effectively disperses and buffers localized stress transmitted from the package to the wafer, preventing stress concentration, while ensuring sufficient mechanical strength in the electrode pin 11 region for reliable wafer fixation.

[0025] The ceramic substrate 2 serves as the support and encapsulation body, with two parallel coated pads on its bonding surface facing the quartz wafer 1. These two pads are specially designed to achieve complementary functions (as shown in Figure 3): one is a high-rigidity reinforcing structure 21, such as a solid cross-shaped, grid-shaped, or block-shaped metallized pattern, whose main function is to provide robust mechanical support for the quartz wafer 1 and establish an efficient vertical heat conduction path; the other is a low-rigidity, high-elasticity flexible structure 22, such as a spiral, serpentine, or finger-shaped intersecting metallized wire structure, whose main function is to actively absorb and release the in-plane (lateral) thermal stress caused by the difference in thermal expansion coefficients between the ceramic substrate 2 and the quartz wafer 1 through its own elastic deformation capability. The welding surfaces of the reinforcing structure 21 and the flexible structure 22 are ensured to be on the same plane (coplanar) through precision processes to facilitate subsequent conductive adhesive coating and mounting. The quartz wafer 1 is fixed and electrically connected to the rigid (reinforcing structure 21) and flexible (flexible structure 22) composite pad by the conductive adhesive 3.

[0026] A low-stress multilayer composite electrode 5 (as shown in Figure 4) is disposed on the surface of the main vibration region of the quartz wafer 1. This low-stress multilayer composite electrode 5 consists of a chromium adhesion layer 51, an aluminum nitride stress buffer layer 52, and a gold conductive layer 53, sequentially disposed from the surface of the quartz wafer 1 outwards. The aluminum nitride stress buffer layer 52 is preferably 30 nm to 80 nm thick, and its high hardness and moderate coefficient of thermal expansion effectively buffer the thermal mismatch stress between the gold electrode and the quartz substrate. The pattern of the low-stress multilayer composite electrode 5 can be designed as a circle, ellipse, or rectangle, etc., to optimize the excitation electric field distribution and suppress unnecessary vibration modes. Optionally, after forming the low-stress multilayer composite electrode 5, selective laser annealing can be performed on the electrode area to repair lattice damage that may occur during micromachining and further reduce the internal stress of the electrode.

[0027] The conductive adhesive 3 is preferably a modified high thermal conductivity adhesive, in which a metallic thermally conductive filler, such as micron-sized flake silver powder or spherical copper-plated quartz particles, is doped into its matrix. This modification significantly improves the thermal conductivity of the adhesive layer, allowing the heat generated during the operation of the quartz wafer 1 and changes in ambient temperature to be rapidly transferred to the ceramic substrate 2 through the fast channel formed by the reinforcing structure 21 and the conductive adhesive 3, thereby reducing the temperature gradient between the quartz wafer 1 and the package and improving thermal stability.

[0028] The thermistor 23 is integrated inside the ceramic base 2 using multilayer ceramic co-firing technology. The thermistor 23 is located in the same package cavity as the quartz crystal 1, and can accurately and in real time sense the temperature of the environment in which the quartz crystal 1 is located, providing an accurate signal for the external temperature compensation circuit.

[0029] The metal cover 4 is bonded to the ceramic base 2 via an airtight sealing process (such as eutectic bonding) to form a closed ultra-high vacuum chamber 7. To maintain and stabilize the ultra-high vacuum level of this chamber over a long period, a non-evaporable getter film 41 is provided on the inner surface of the metal cover 4 and / or the inner surface of the ceramic base 2 facing the ultra-high vacuum chamber 7. This film is preferably a zirconium-vanadium-iron (Zr-V-Fe) alloy film, which, after activation, can efficiently adsorb residual gases in the chamber and gases released by the material during its working life (i.e., outgassing). Through this design, the pressure inside the ultra-high vacuum chamber 7 can be maintained below 0.001 Pascals for a long period, thereby minimizing the negative impact of air damping on the quartz crystal's vibration quality factor (Q value) and ensuring excellent performance at high frequencies.

[0030] A method for fabricating a low-hysteresis high-frequency quartz crystal resonator includes the following steps: S1: Quartz wafer pretreatment and microgroove processing, providing a quartz wafer rotated 60 degrees within the AT cutting plane and having a predetermined thickness, defining the pattern of the electrode pin 11 region on the wafer using a standard photolithography process, and then using a dry etching process, preferably inductively coupled plasma (ICP) etching, to form circular or elliptical microgrooves 12 in the region; S2: Formation of low-stress composite electrodes and wafer dicing, processing the etched quartz wafer... Thorough cleaning and surface activation treatment; subsequently, using thin film processes such as physical vapor deposition (PVD), a chromium layer, an aluminum nitride layer, and a gold layer are sequentially deposited on the wafer surface. The thin film is then patterned again using photolithography and etching processes to form a low-stress multilayer composite electrode 5. Optionally, selective laser annealing is performed on the electrode area to optimize electrode performance. Finally, the wafer is separated into individual quartz wafers 1 using a dicing or cutting process. S3: Fabrication and functional integration of the ceramic substrate: A multilayer ceramic green body is prepared, and then processed using photolithography, screen printing, and electroplating. The process involves forming a coplanar metallization pattern on the predetermined bonding surface, which includes a composite pad comprising a high-rigidity reinforcing structure 21 and a low-rigidity, high-elasticity flexible structure 22. Simultaneously, the electrodes and resistors of the thermistor 23 are integrated through an internal printing process. Subsequently, green compaction, isostatic pressing, and high-temperature co-firing are performed to form a dense ceramic substrate 2 with embedded thermistors 23 and composite pads on its surface. S4: Chip mounting and electrical connection: Using precision dispensing equipment, conductive adhesive 3 is applied to the reinforcing structure 2 of the ceramic substrate 2. 1. The electrode pins 11 of the quartz wafer 1 are aligned and mounted onto the pads coated with conductive adhesive using a high-precision pick-and-place machine. Subsequently, the conductive adhesive 3 is cured under controlled temperature and humidity conditions, achieving mechanical fixation and electrical connection between the quartz wafer 1 and the ceramic substrate 2. Frequency fine-tuning (optional): To precisely control the center frequency of the resonator, non-contact fine-tuning techniques such as ion beam etching can be used to fine-tune the electrode quality of the quartz wafer 1, ensuring its frequency reaches the required accuracy range (e.g., ±10). S5: Vacuum encapsulation and getter activation. A non-evaporable getter film 41 is deposited on the inner surface of the metal cover 4 by sputtering or evaporation. The ceramic substrate 2 with the quartz wafer 1 is aligned with the metal cover 4 in a vacuum or inert gas protection environment, and gold-tin eutectic solder 6 is placed in the sealing ring area between them. Then, eutectic bonding is performed in a vacuum environment to complete the hermetically sealed encapsulation and form an ultra-high vacuum inner chamber 7. After encapsulation, the entire device is annealed in a temperature range of 350°C to 450°C to activate the non-evaporable getter film 41 and enable it to have high-efficiency getter capability.

[0031] The low-hysteresis high-frequency quartz crystal resonator prepared by the above embodiments achieves full-link optimization from stress generation and transmission to action through multi-level synergistic design of crystal microstructure stress guidance (microgrooves), interface stress decoupling (rigid-flexible composite pads), system environmental stress isolation (ultra-high vacuum and getter), and material interface stress buffering (low-stress composite electrodes and modified conductive adhesives). As a result, it achieves ultra-low frequency temperature hysteresis, excellent high-frequency stability and long-term reliability over a wide temperature range, while maintaining good compatibility with traditional packaging processes.

[0032] In the description of this invention, it should be understood that the orientation or positional relationship indicated by directional terms such as "front, back, up, down, left, right", "horizontal, vertical, horizontal" and "top, bottom" is generally based on the orientation or positional relationship shown in the accompanying drawings, and is only for the convenience of describing this invention and simplifying the description. Unless otherwise stated, these directional terms do not indicate or imply that the device or element referred to must have a specific orientation or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation on the scope of protection of this invention; the directional terms "inner" and "outer" refer to the inner and outer contours relative to the outline of each component itself.

[0033] For ease of description, spatial relative terms such as "above," "on top of," "on the upper surface of," "above," etc., are used herein to describe the spatial positional relationship of a device or feature as shown in the figures to other devices or features. It should be understood that spatial relative terms are intended to encompass different orientations in use or operation beyond the orientation of the device as described in the figures. For example, if the device in the figures were inverted, a device described as "above" or "on top of" other devices or structures would subsequently be positioned as "below" or "under" other devices or structures. Thus, the exemplary term "above" can include both "above" and "below." The device may also be positioned in other different ways (rotated 90 degrees or in other orientations), and the spatial relative descriptions used herein will be interpreted accordingly.

[0034] Furthermore, it should be noted that the use of terms such as "first" and "second" to define components is merely for the purpose of distinguishing the corresponding components. Unless otherwise stated, the above terms have no special meaning and therefore should not be construed as limiting the scope of protection of this invention.

[0035] The above provides a detailed description of a low-hysteresis high-frequency quartz crystal resonator and its fabrication method provided in this application. Specific examples have been used to illustrate the principles and implementation methods of this application. The descriptions of the above embodiments are only for the purpose of helping to understand the method and core ideas of this application. At the same time, for those skilled in the art, there will be changes in the specific implementation methods and application scope based on the ideas of this application. Therefore, the content of this specification should not be construed as a limitation of this application.

Claims

1. A low-hysteresis high-frequency quartz crystal resonator, comprising a quartz crystal wafer (1), a ceramic substrate (2), and a metal cover (4), characterized in that: The ceramic base (2) is sealed with a metal cover (4) at the top. An ultra-high vacuum chamber (7) is provided between the metal cover (4) and the ceramic base (2). Two pads are arranged side by side at the bottom of the ultra-high vacuum chamber (7). One pad is a high-rigidity reinforcing structure (21), and the other pad is a low-rigidity, high-elasticity flexible structure (22). The quartz crystal (1) is fixed on the reinforcing structure (21) and the flexible structure (22) by conductive adhesive (3). The upper surface of the reinforcing structure (21) is flush with the upper surface of the flexible structure (22). The ceramic base (2) integrates a thermistor (23). The bottom of the ceramic base (2) is provided with external electrodes (8) that are respectively connected to the quartz crystal (1) and the thermistor (23).

2. The low-hysteresis high-frequency quartz crystal resonator according to claim 1, characterized in that: The quartz wafer (1) is provided with low-stress multilayer composite electrodes (5) on both the upper and lower surfaces. The overlapping part of the low-stress multilayer composite electrodes (5) on the upper or lower surface of the quartz wafer (1) is the main vibration area. The side of the quartz wafer (1) is provided with electrode feet (11) corresponding to the pads.

3. A low-hysteresis high-frequency quartz crystal resonator according to claim 2, characterized in that: The quartz wafer (1) has at least one micro-groove (12) in the area where the electrode pin (11) is mounted. The micro-groove (12) is circular or elliptical in shape.

4. A low-hysteresis high-frequency quartz crystal resonator according to claim 2, characterized in that: The low-stress multilayer composite electrode (5) comprises a chromium adhesion layer, an aluminum nitride stress buffer layer and a gold conductive layer stacked sequentially from the surface of the quartz wafer (1) outwards.

5. A low-hysteresis high-frequency quartz crystal resonator according to claim 1, characterized in that: The reinforcing structure (21) is a solid cross-shaped, grid-shaped, or block-shaped metallized structure; the flexible structure (22) is a spiral, serpentine, or finger-shaped intersecting metallized fine wire structure.

6. A low-hysteresis high-frequency quartz crystal resonator according to claim 1, characterized in that: The inner surface of the metal cover (4) and / or the inner surface of the ceramic base (2) facing the inner cavity are provided with a non-evaporable getter film (41).

7. A low-hysteresis high-frequency quartz crystal resonator according to claim 1, characterized in that: The pressure inside the ultra-high vacuum chamber (7) is maintained below 0.001 Pa for a long time.

8. A method for fabricating a low-hysteresis high-frequency quartz crystal resonator as described in any one of claims 1-7, characterized in that: Includes the following steps: S1: Provide a quartz wafer rotated 60 degrees within the AT cutting plane, and form circular or elliptical microgrooves (12) in the electrode foot area of ​​the quartz wafer through photolithography and dry etching processes; S2: Clean and surface treat the quartz wafer, and then sequentially deposit and pattern low-stress multilayer composite electrodes (5) on its surface, and then cut to obtain a single quartz wafer (1); S3: Prepare a ceramic substrate (2), and form two coplanar coating pads on the bonding surface of the ceramic substrate (2) through photolithography and metallization processes, including a high-rigidity reinforcing structure (21) and a A flexible structure (22) with low stiffness and high elasticity is provided, and a thermistor (23) is integrated in the ceramic substrate (2); S4: Apply conductive adhesive (3) to the reinforcing structure (21) and flexible structure (22) of the ceramic substrate (2), align and mount the electrode pin (11) area of ​​the quartz wafer (1), and achieve fixation and electrical connection by curing the conductive adhesive (3); S5: Provide a metal cover (4), and bond and seal the metal cover (4) with the ceramic substrate (2) after chip mounting in a vacuum environment to form the ultra-high vacuum inner cavity (7).

9. The preparation method according to claim 8, characterized in that: Step S2 also includes a step of selectively laser annealing the region where the low-stress multilayer composite electrode (5) is formed.

10. The preparation method according to claim 8, characterized in that: In step S5, before bonding and sealing, a non-evaporable getter film (41) is deposited on the inner surface of the metal cover (4); after bonding and sealing, the non-evaporable getter film (41) is activated by annealing at a temperature of 350°C to 450°C.

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