A crystal oscillator and an atomic clock

Abstract

This application provides a crystal oscillator and an atomic clock, relating to the field of oscillator technology. The crystal oscillator includes a package cavity, a crystal, a temperature sensor, and a cantilever beam assembly. The crystal, temperature sensor, and cantilever beam assembly are disposed within the housing of the package cavity, which is a vacuum-sealed structure. The crystal and temperature sensor are mounted on the cantilever beam assembly and are electrically connected to the package cavity through different connection points, with the temperature sensor surrounding the crystal. The cantilever beam assembly includes a heating module. When the temperature sensor detects that the temperature in the area where the crystal is located is lower than a preset temperature threshold, the heating module heats the crystal. This eliminates the energy loss of the crystal's high-frequency vibration due to air damping, improves the Q value, and enhances the phase noise suppression capability. It also achieves precise temperature control of the area where the crystal is located, improves thermal response speed and temperature control accuracy, and solves the problem of poor stability in existing crystal oscillators.

Description

Technical Field

[0001] This application relates to the field of oscillator technology, and more particularly to a crystal oscillator and an atomic clock. Background Technology

[0002] As a core frequency control element, crystal oscillators are widely used in fields such as satellite navigation and quantum communication. Crystal oscillators and atomic clocks can provide a stable reference frequency source, ensuring the timing synchronization and signal accuracy of equipment.

[0003] However, the high-frequency vibration of a crystal is affected by air damping, leading to energy loss and limiting the Q value, a key parameter for resonator performance. This weakens the phase noise suppression capability, with a typical phase noise value of only -120dBc / Hz@1kHz. In fields with high signal accuracy requirements, such as communication and radar, this can easily cause signal distortion and increased bit error rate. Furthermore, existing crystal oscillators typically require heating multiple components with different thermal characteristics, such as the crystal, circuit board, and housing, resulting in slow thermal response and insufficient temperature control accuracy. This leads to poor frequency and phase stability of the crystal oscillator, making it difficult to meet timing synchronization requirements in high-precision scenarios such as communication and navigation.

[0004] It is evident that existing crystal oscillators suffer from poor stability. Summary of the Invention

[0005] This application provides a crystal oscillator and an atomic clock to solve the problem of poor stability of crystal oscillators in the prior art.

[0006] This application provides a crystal oscillator, including a package cavity, a crystal, a temperature sensor, and a cantilever beam assembly. The crystal, the temperature sensor, and the cantilever beam assembly are disposed in the accommodating cavity of the package cavity. The package cavity is a vacuum-sealed structure. The crystal and the temperature sensor are disposed on the cantilever beam assembly. The crystal and the temperature sensor are electrically connected to the package cavity through different connection points of the cantilever beam assembly, and the temperature sensor is arranged around the crystal.

[0007] The cantilever beam assembly includes a heating module, which heats the crystal when the temperature sensor detects that the temperature in the area where the crystal is located is less than a preset temperature threshold.

[0008] Optionally, the cantilever beam assembly further includes a cantilever beam support and a thin film layer. The cantilever beam support is adapted to the accommodating cavity. The thin film layer is disposed on the top surface of the cantilever beam support. The heating module is disposed in the interlayer of the thin film layer. The thin film layer integrates metal traces. The crystal and the temperature sensor are disposed on the thin film layer, and the crystal and the temperature sensor are electrically connected to different connection points of the encapsulation cavity through the metal traces.

[0009] Optionally, the projection of the crystal onto the thin film layer is located in the region where the heating module is located.

[0010] Optionally, the heating module is a concentric ring structure formed by a heating wire.

[0011] Optionally, the film layer is a polyimide film.

[0012] Optionally, the temperature sensor is a negative temperature coefficient (NTC) resistor.

[0013] Optionally, the encapsulation cavity includes a cover plate and a base, the cover plate and the base cooperate to form the receiving cavity, and a sealing coating is provided at the contact position between the cover plate and the base.

[0014] Optionally, a getter is provided on the side of the cover plate facing the receiving cavity.

[0015] Optionally, the encapsulation cavity is made of a metal-ceramic composite material, and the vacuum degree of the encapsulation cavity is less than or equal to 10. -1 Pa.

[0016] This application also provides an atomic clock, including the crystal oscillator described above.

[0017] In this embodiment, the crystal, temperature sensor, and cantilever beam assembly are housed within the encapsulation cavity, which employs a vacuum encapsulation structure. This eliminates energy loss due to air damping during high-frequency crystal vibration, improving the Q value and enhancing phase noise suppression. Furthermore, the cantilever beam assembly provides mechanical vibration damping and thermal isolation, improving the crystal's shock resistance and reducing the impact of external temperature fluctuations. The temperature sensor, positioned around the crystal and integrated with the heating module of the cantilever beam assembly, enables precise temperature control of the crystal's region. Compared to traditional overall heating methods, this significantly improves thermal response speed and temperature control accuracy, solves the problem of poor stability in existing crystal oscillators, and meets the timing synchronization requirements of high-precision applications. Attached Figure Description

[0018] To more clearly illustrate the technical solutions of the embodiments of this application, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0019] Figure 1 This is a schematic diagram of the structure of the crystal oscillator provided in the embodiments of this application;

[0020] Figure 2 This is a phase noise curve of a common crystal oscillator;

[0021] Figure 3 A phase noise curve of a crystal oscillator provided in an embodiment of this application;

[0022] Figure 4 This is a schematic diagram of the structure of an atomic clock provided in an embodiment of this application. Detailed Implementation

[0023] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0024] The terms "first," "second," etc., used in the embodiments of this application are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. Furthermore, the terms "comprising" and "having," and any variations thereof, are intended to cover non-exclusive inclusion. For example, a process, method, system, product, or device that includes a series of steps or units is not necessarily limited to those steps or units explicitly listed, but may include other steps or units not explicitly listed or inherent to these processes, methods, products, or devices.

[0025] like Figure 1 As shown, this application embodiment provides a crystal oscillator. The crystal oscillator 1 includes a package cavity 10, a crystal 20, a temperature sensor 30, and a cantilever beam assembly 40. The crystal 20, the temperature sensor 30, and the cantilever beam assembly 40 are disposed in the accommodating cavity of the package cavity 10. The package cavity 10 is a vacuum-sealed structure. The crystal 20 and the temperature sensor 30 are disposed on the cantilever beam assembly 40. The crystal 20 and the temperature sensor 30 are electrically connected to the package cavity 10 through different connection points of the cantilever beam assembly 40, and the temperature sensor 30 is arranged around the crystal 20.

[0026] The cantilever beam assembly 40 includes a heating module 401, which heats the crystal 20 when the temperature sensor 30 detects that the temperature in the area where the crystal 20 is located is less than a preset temperature threshold.

[0027] The crystal oscillator 1 provided in this application embodiment houses a crystal 20, a temperature sensor 30, and a cantilever beam assembly 40 within a housing cavity of a packaging cavity 10. The packaging cavity 10 employs a vacuum-sealed structure to eliminate energy loss due to air damping on the high-frequency vibrations of the crystal 20, thereby improving the Q value and enhancing phase noise suppression capabilities. Furthermore, the cantilever beam assembly 40 provides mechanical vibration damping and thermal isolation, improving the crystal 20's shock resistance and reducing the impact of external temperature fluctuations on the crystal 20. The temperature sensor 30 is positioned around the crystal 20, working in conjunction with the heating module 401 of the cantilever beam assembly 40 to achieve precise temperature control of the area where the crystal 20 is located. Compared to traditional overall heating methods, this significantly improves thermal response speed and temperature control accuracy, solves the problem of poor stability in existing crystal oscillators, and meets the timing synchronization requirements of high-precision scenarios.

[0028] The crystal 20 and temperature sensor 30 are electrically connected to the encapsulation cavity 10 through different connection points of the cantilever beam assembly 40. Different connection points can correspond to different external control circuits or modules, realizing independent signal transmission. This ensures that the oscillation signal generated by the crystal 20 can be stably transmitted to the frequency output device, while the temperature signal collected by the temperature sensor 30 is accurately transmitted to the temperature control device, avoiding mutual interference between signals and ensuring the accuracy of signal transmission. Furthermore, the oscillation function and temperature control function of the crystal oscillator 1 are relatively independent, which facilitates precise control and monitoring by external devices, thereby improving the stability and reliability of the entire crystal oscillator 1 and meeting the needs of efficient collaborative work of different functional modules.

[0029] Optionally, the cantilever beam assembly 40 further includes a cantilever beam support 403 and a thin film layer 402. The cantilever beam support 403 is adapted to the accommodating cavity. The thin film layer 402 is disposed on the top surface of the cantilever beam support 403. The heating module 401 is disposed in the interlayer of the thin film layer 402. The thin film layer 402 integrates metal traces. The crystal 20 and the temperature sensor 30 are disposed on the thin film layer 402, and the crystal 20 and the temperature sensor 30 are electrically connected to different connection points of the encapsulation cavity 10 through the metal traces.

[0030] In this embodiment, the cantilever beam support 403 serves as the basic support set within the encapsulation cavity 10. Adapted to the cavity, the cantilever beam support 403 provides stable support for the heating module 401, thin film layer 402, crystal 20, and temperature sensor 30 mounted on it. The heating module 401 enables precise localized heating of the area where the crystal 20 is located. By placing the heating module 401 within the thin film layer 402, the excellent thermal insulation properties of the thin film layer 402 effectively reduce heat loss and maintain the stability of the crystal 20's operating temperature. Simultaneously, the integrated metal traces within the thin film layer 402 create independent electrical connection channels, allowing the crystal 20 and temperature sensor 30 to connect to corresponding control circuits or modules outside the encapsulation cavity 10 through different connection points. This not only ensures independent transmission and precise control of the oscillation and temperature signals, avoiding signal interference, but also achieves low parasitic parameter electrical connections through optimized wiring layout, reducing signal transmission loss and further improving the stability and reliability of signal transmission. Combined with the mechanical support and shock absorption function of the cantilever beam bracket 403, the overall performance of the crystal oscillator 1 is comprehensively improved.

[0031] Optionally, the projection of the crystal 20 onto the thin film layer 402 is located in the region where the heating module 401 is located.

[0032] In this embodiment, the projection of the crystal 20 onto the thin film layer 402 is located in the area where the heating module 401 is located, ensuring that the heat generated by the heating module 401 can be applied to the crystal 20 accurately and efficiently. This minimizes heat transfer loss and delay, allowing the crystal 20 to quickly reach and maintain its optimal operating temperature. Simultaneously, it avoids localized overheating or uneven heating caused by misalignment of the heating area. Combined with real-time monitoring by the temperature sensor 30, precise closed-loop control of the crystal temperature is achieved, thereby effectively improving the frequency stability and overall performance of the crystal oscillator.

[0033] Optionally, the thin film layer 402 is a polyimide film.

[0034] In this embodiment, a polyimide (PI) film can be used as the film layer 402. The PI film has the characteristics of high temperature resistance (can withstand high temperatures above 200°C for a long time), excellent electrical insulation, high mechanical strength and good flexibility. It can support the crystal 20 and temperature sensor 30, ensure the structural stability of the cantilever beam assembly 40, and can work with the heating module 401 in the interlayer to reduce heat loss and maintain the stable operating temperature of the crystal 20. At the same time, the good insulation performance of the PI film helps the integrated metal traces to achieve low parasitic parameter electrical connection, reduce signal transmission loss, avoid interference, and comprehensively improve the performance and reliability of the crystal oscillator.

[0035] In one example, the heating module 401 can be a gold thin-film heater, or a platinum thin-film heater with a thickness of 5μm to 10μm integrated in a PI film, enabling rapid heat conduction; the resistance value of the gold thin-film heater is precisely controlled at 50Ω±0.5Ω, ensuring that the heater heats up quickly at a suitable power, and facilitating circuit design and precise adjustment of the temperature control system; in this way, the crystal oscillator 1 can quickly reach and stably maintain the preset operating temperature, effectively improving the overall temperature control response speed and accuracy.

[0036] In another example, the heating module 401 may be a concentric ring structure formed by a heating wire.

[0037] In this example, the heating module 401 is configured as a concentric ring structure formed by a heating wire. When current flows through the heating wire, the current directions on adjacent rings are opposite. According to Ampere's law, the magnetic fields generated by the reverse currents cancel each other out, reducing the equivalent inductance of the heating wire, lowering parasitic capacitance, and effectively suppressing high-frequency oscillations, thereby reducing electromagnetic interference generated when energized. This improves the electromagnetic compatibility of the crystal oscillator, enabling it to maintain stable operation in complex electromagnetic environments, making it particularly suitable for high-precision applications such as satellite navigation and quantum communication that are sensitive to electromagnetic interference.

[0038] In addition, the crystal 20 is placed at the center of the ring, ensuring that the heat generated by the heating wire can be radiated evenly to the crystal along the circumference, effectively avoiding thermal stress and temperature control deviation caused by local temperature differences. Furthermore, the concentric ring structure maximizes the laying of the heating wire in a limited space, ensuring heating efficiency while facilitating integration with the thin film layer 402. In conjunction with the temperature control system, the output power can be precisely adjusted to achieve stable control of the crystal temperature, thereby improving the stability and reliability of the crystal oscillator.

[0039] Optionally, the encapsulation cavity 10 is made of a metal-ceramic composite material, and the vacuum degree of the encapsulation cavity is less than or equal to 10. -1 Pa.

[0040] In this embodiment, the encapsulation cavity 10 can be made of a metal-ceramic composite material, and the vacuum level is controlled to be less than or equal to 10. -1 The vacuum level was optimized to achieve both mechanical properties and a suitable vacuum environment. The metal-ceramic composite material combines the high toughness of metals with the high hardness, corrosion resistance, and strong insulation properties of ceramics, ensuring the structural safety of internal components such as the crystal 20 and temperature sensor 30, and effectively isolating them from external electromagnetic interference. The vacuum level was controlled at less than or equal to 10 Pa. -1Pa can weaken the influence of air damping on the high-frequency vibration of the crystal, reduce energy loss (steady-state power consumption ≤ 0.5W (at 10MHz output)), improve the quality factor Q of the crystal, thereby enhancing the phase noise suppression capability, and enabling the crystal oscillator to maintain excellent frequency stability and reliability in complex application scenarios.

[0041] Optionally, the temperature sensor 30 is a negative temperature coefficient NTC resistor.

[0042] In this embodiment, a negative temperature coefficient (NTC) resistor is used as the temperature sensor 30. Utilizing the non-linear decrease in resistance of the NTC resistor with increasing temperature, temperature changes in the area where the crystal 20 is located can be accurately monitored. Specifically, the NTC resistor has advantages such as fast response speed (millisecond level), high temperature measurement accuracy (±0.01℃), small size, and easy integration. It can be tightly arranged around the crystal to provide real-time feedback on the crystal surface temperature. After circuit compensation using the NTC resistor characteristics, it can form a precise closed-loop control with the heating module 401. Heating is quickly initiated when the temperature in the area where the crystal 20 is located is below a preset threshold, and the heating power is dynamically adjusted according to the resistance value change, ensuring that the crystal always operates within a stable temperature range (temperature control accuracy ±0.01℃ (24-hour drift)), effectively improving the frequency stability and environmental adaptability of the crystal oscillator 1.

[0043] This design can employ three NTC resistors surrounding the crystal 20. These resistors collect temperature data in real-time at different locations around the crystal 20, and the average temperature at these three points eliminates localized thermal deviations. Each NTC resistor can be 1.0mm × 0.5mm × 0.3mm in size, achieving miniaturization and allowing for a tight fit between the resistors and the crystal 20, thus shortening the thermal response time. When any NTC resistor detects a temperature deviation from a preset value, the temperature control circuit immediately adjusts the heating power to reduce the temperature gradient at different locations within the crystal 20 area, improving frequency stability. This design is suitable for high-precision oscillation scenarios with stringent temperature uniformity requirements.

[0044] Furthermore, it can be used with a 1ms sampling period digital proportional-integral-derivative (PID) control algorithm to achieve high-frequency and precise temperature control of the crystal 20. The digital PID algorithm improves the temperature control accuracy to ±0.01℃ by rapidly responding to deviations with the proportional term, eliminating static errors with the integral term, and suppressing temperature overshoot with the derivative term. Combined with the nonlinear characteristics compensation of the NTC, it shortens the temperature adjustment response time to less than 50ms, effectively suppressing the influence of ambient temperature fluctuations on the crystal frequency. It is suitable for precision oscillation applications with stringent temperature stability requirements.

[0045] Optionally, crystal 20 can be a high-Q crystal, and crystal 20 is suspended and supported by a PI film.

[0046] In this embodiment, the crystal 20 can be subjected to stress-compensated cutting (SC) to improve the stability of the crystal 20 during operation, in conjunction with its inherent high Q value (Q value ≥ 2 × 10⁻⁶). 6 The PI film suspension support structure utilizes the high flexibility and low thermal conductivity (≤0.1W / m·K) of polyimide material to suspend and fix the crystal, isolating it from external mechanical vibration transmission and reducing heat conduction loss.

[0047] Optionally, the encapsulation cavity 10 includes a cover plate 101 and a base 102, the cover plate 101 and the base 102 cooperate to form the receiving cavity, and a sealing coating is provided at the contact position between the cover plate 101 and the base 102.

[0048] In this embodiment, the metal-ceramic cover plate 101 and the base 102 can be precision machined to form a micro-nano-level bonding surface at the contact point between the cover plate 101 and the base 102, and a sealing coating (such as gold-tin alloy solder or glass glaze sealant) is applied. After high-temperature sintering, the interfacial gaps are filled to form a continuous and dense sealing ring, which improves the vacuum degree of the encapsulation cavity 10 and ensures that it remains ≤10°C under drastic environmental changes. -1 The high vacuum of Pa provides a long-term stable working environment for the internal crystal 20, improving the oscillator's anti-aging performance and reliability.

[0049] Optionally, a getter 50 is provided on the side of the cover plate 101 facing the accommodating cavity.

[0050] In this embodiment, a getter 50 is provided on the side of the cover plate 101 facing the cavity. The getter 50 adsorbs trace amounts of residual gas molecules (such as water vapor and nitrogen gas left over from the manufacturing process) inside the cavity, continuously maintaining the high vacuum level of the cavity. The getter 50 can be an active metal alloy such as barium or zirconium, which can chemically react or physically adsorb with the gas in a vacuum environment, further improving the vacuum level of the encapsulated cavity 10. This effectively avoids the damping effect of residual gas molecules on the high-frequency vibration of the crystal, continuously ensuring the high Q value characteristics of the crystal, and suppressing the vacuum level decay caused by the desorption of gas molecules at high temperatures. This allows the crystal oscillator to maintain excellent frequency stability and phase noise performance during long-term operation.

[0051] like Figure 2 and Figure 3 As shown, Figure 2 This is a phase noise curve for a common crystal oscillator. Figure 3The diagram shows the phase noise of a crystal oscillator provided in this embodiment. The phase noise of a typical crystal oscillator is -120 dBc / Hz @1kHz. The crystal oscillator 1 provided in this embodiment eliminates air damping, optimizing the phase noise to -150 dBc / Hz @1kHz (a 20 dB improvement over a typical crystal oscillator).

[0052] like Figure 4 As shown in the embodiment of this application, an atomic clock is also provided. The atomic clock includes a chip atomic clock housing 2, a physical optical path system 3, a control circuit system 4, and a crystal oscillator 1. The crystal oscillator 1, the physical optical path system 3, and the control circuit system 4 are all disposed in the cavity of the chip atomic clock housing 2. The crystal oscillator 1 is disposed on the control circuit system 4. The physical optical path system 3 can also be disposed on the control circuit system 4. The crystal oscillator 1 is electrically connected to the control circuit system 4 through the encapsulation cavity 10.

[0053] In this embodiment, a vacuum-encapsulated crystal oscillator 1 is used as a high-stability reference source to eliminate energy loss from air damping during high-frequency vibration of the crystal 20, improve the Q value and enhance phase noise suppression capability, and achieve precise temperature control of the region where the crystal 20 is located, significantly improving thermal response speed and temperature control accuracy. This provides a low-noise reference for the coherent population trapping (CPT) frequency-locked loop. The frequency-locked loop based on all-digital phase-locked loop (ADPLL) technology corrects the crystal oscillator frequency in real time through digital processing algorithms, improving short-term stability to 10. -11 The power consumption is reduced significantly by combining low-power application-specific integrated circuit (ASIC) chips with a vacuum insulation structure. Furthermore, while maintaining miniaturization and low power consumption, it outperforms traditional temperature-compensated crystal oscillators (TCXOs) in phase noise and stability performance, enabling the atomic clock to meet the high-precision time and frequency requirements of scenarios such as satellite navigation enhancement, deep space exploration time and frequency references, and 5G base station synchronization.

[0054] It should be noted that, in this document, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes that element. Furthermore, it should be noted that the scope of the methods and apparatuses in the embodiments of this application is not limited to performing functions in the order discussed, but may also include performing functions substantially simultaneously or in the reverse order, depending on the functions involved. For example, the described methods may be performed in a different order than described, and various steps may be added, omitted, or combined. Additionally, features described with reference to certain examples may be combined in other examples.

[0055] Through the above description of the embodiments, those skilled in the art can clearly understand that the methods of the above embodiments can be implemented by means of software plus necessary general-purpose hardware platforms. Of course, they can also be implemented by hardware, but in many cases the former is a better implementation method. Based on this understanding, the technical solution of this application, in essence, or the part that contributes to the prior art, can be embodied in the form of a software product. This computer software product is stored in a storage medium (such as ROM / RAM, magnetic disk, optical disk) and includes several instructions to cause a terminal (which may be a mobile phone, computer, server, air conditioner, or network device, etc.) to execute the methods described in the various embodiments of this application.

[0056] The embodiments of this application have been described above with reference to the accompanying drawings. However, this application is not limited to the specific embodiments described above. The specific embodiments described above are merely illustrative and not restrictive. Those skilled in the art can make many other forms under the guidance of this application without departing from the spirit and scope of the claims, and all of these forms are within the protection scope of this application.

Claims

1. A crystal oscillator, characterized in that, The device includes a packaging cavity, a crystal, a temperature sensor, and a cantilever beam assembly. The crystal, the temperature sensor, and the cantilever beam assembly are disposed in the receiving cavity of the packaging cavity. The packaging cavity is a vacuum-sealed structure. The crystal and the temperature sensor are disposed on the cantilever beam assembly. The crystal and the temperature sensor are electrically connected to the packaging cavity through different connection points of the cantilever beam assembly, and the temperature sensor is arranged around the crystal. The cantilever beam assembly includes a heating module, which heats the crystal when the temperature sensor detects that the temperature in the area where the crystal is located is less than a preset temperature threshold. The cantilever beam assembly further includes a cantilever beam support and a thin film layer. The cantilever beam support is adapted to the accommodating cavity. The thin film layer is disposed on the top surface of the cantilever beam support. The heating module is disposed in the interlayer of the thin film layer. The thin film layer has good thermal insulation performance. The thin film layer integrates metal traces. The crystal and the temperature sensor are disposed on the thin film layer, and the crystal and the temperature sensor are electrically connected to different connection points of the encapsulation cavity through the metal traces.

2. The crystal oscillator according to claim 1, characterized in that, The projection of the crystal onto the thin film layer is located in the region where the heating module is located.

3. The crystal oscillator according to claim 1, characterized in that, The heating module is a concentric ring structure formed by a heating wire.

4. The crystal oscillator according to claim 1, characterized in that, The thin film layer is a polyimide film.

5. The crystal oscillator according to claim 1, characterized in that, The temperature sensor is a negative temperature coefficient NTC resistor.

6. The crystal oscillator according to any one of claims 1 to 5, characterized in that, The encapsulation cavity includes a cover plate and a base, the cover plate and the base cooperate to form the receiving cavity, and a sealing coating is provided at the contact position between the cover plate and the base.

7. The crystal oscillator according to claim 6, characterized in that, A getter is provided on the side of the cover plate facing the accommodating cavity.

8. The crystal oscillator according to any one of claims 1 to 5, characterized in that, The encapsulation cavity is made of a metal-ceramic composite material, and the vacuum degree of the encapsulation cavity is less than or equal to 10. -1 Pa.

9. An atomic clock, characterized in that, Includes a crystal oscillator as described in any one of claims 1 to 8.

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