Double-cavity integrated MEMS atomic clock and preparation method thereof

Abstract

The invention provides a double-cavity integrated MEMS atomic clock and a preparation method thereof, and belongs to the technical field of micro electro mechanical systems and precise timing. According to the invention, the photonic crystal regulation and control layer is provided with the cavities in array arrangement, the cross sections of the cavities are cross-shaped, the cavities have orthogonal symmetry and dual-band band gap characteristics, and meanwhile, the fluorescence signal intensity is improved through a surface plasma resonance effect, so that the optical efficiency is improved; the cross-shaped structure has symmetrical thermal expansion distribution and low thermal stress deviation, so that the thermal mechanical stability is improved; the waveguide wire is coupled with the cavities arranged in the array in the photonic crystal regulation and control layer through the coplanar waveguide to form a composite resonant cavity, and the slow light effect of the cavities arranged in the array in the photonic crystal regulation and control layer is utilized to prolong the interaction time of atoms and microwaves, so that the thermal mechanical stability is improved; the coplanar waveguide layer is provided with the conductive adhesive, so that effective transmission of microwave signals can be realized, and the optical efficiency is further improved.

Description

Technical Field

[0001] This invention belongs to the field of microelectromechanical systems (MEMS) and precision timing technology, specifically relating to a dual-cavity integrated MEMS atomic clock and its fabrication method. Background Technology

[0002] With the rapid development of technologies such as satellite navigation and quantum communication, the demand for miniaturized, low-power atomic clocks is becoming increasingly urgent. Traditional atomic clocks rely on bulky vacuum tubes and discrete optical systems, making it difficult to meet the integration requirements of portable devices. In recent years, atomic clocks based on MEMS technology have significantly reduced size and power consumption through the integration of silicon-based gas cells and micro resonant cavities, but their performance is still limited by two bottlenecks: 1. Low optical efficiency: Existing MEMS atomic clocks rely on external lenses and filters for laser control, leading to difficulties in optical path alignment and high scattering losses (typical loss rate >30%). Currently, to improve optical efficiency, photonic crystals are generally used, which have a circular aperture array structure. This can only optimize a single function (such as laser collimation) and cannot simultaneously solve the problems of fluorescence signal collection and background noise suppression. 2. Insufficient thermomechanical stability: During the heating process of the micro gas chamber in the circular aperture array structure of traditional photonic crystals (which usually needs to be maintained at 80℃±1℃), radial stress concentration occurs due to the mismatch of thermal expansion coefficients, which easily causes thermal deformation of the packaging structure, resulting in microwave resonant cavity frequency drift (typical value >0.5Hz / ℃).

[0003] Therefore, how to improve MEMS atomic clocks to enhance their optical efficiency and thermomechanical stability has become a pressing technical challenge in this field. Summary of the Invention

[0004] The purpose of this invention is to provide a dual-cavity integrated MEMS atomic clock and its fabrication method. The dual-cavity integrated MEMS atomic clock provided by this invention possesses high optical efficiency and excellent thermomechanical stability.

[0005] To achieve the above-mentioned objectives, the present invention provides the following technical solution: This invention provides a dual-cavity integrated MEMS atomic clock, comprising a photonic crystal control layer, a silicon substrate, a temperature control module, a glass substrate, and a coplanar waveguide layer stacked from top to bottom; The photonic crystal control layer is provided with an array of cavities; the cavities open onto the upper surface of the photonic crystal control layer; the cross-section of the cavities is cross-shaped. The silicon substrate is provided with a first through hole penetrating the upper and lower surfaces; the first through holes are arranged in an array. The two ends of the first through hole are sealed by the photonic crystal control layer and the glass substrate to form a sealed cavity; the sealed cavity is filled with atomic vapor and buffer gas; The coplanar waveguide layer includes a waveguide and a conductive adhesive; the waveguide has a second through hole penetrating the upper and lower surfaces; the conductive adhesive fills the second through hole.

[0006] Preferably, the photonic crystal control layer is made of at least one of borosilicate glass, aluminate glass, and quartz glass, and the coefficient of thermal expansion of the material is 3.0~4.5ppm / ℃.

[0007] Preferably, the thickness of the photonic crystal modulation layer is 0.2~1.0 mm.

[0008] Preferably, the cross arm of the cavity is 100~110nm long, 90~110nm wide, and 195~205nm deep. The distance between two adjacent cavities is 355~365nm, measured from the center of the cross arm. The cavities are arranged in a matrix.

[0009] Preferably, the cross-section of the first through hole is circular, the diameter of the first through hole is 2.5~5.0mm, and the center distance between two adjacent first through holes is 500~1500μm; the thickness of the silicon substrate is 0.3~1.0mm.

[0010] Preferably, the thickness of the glass substrate is 0.2~1.0 mm.

[0011] Preferably, the air pressure of the sealed cavity is 5~20 kPa.

[0012] Preferably, the width of the waveguide is 30~100μm.

[0013] Preferably, the cross-section of the second through hole is circular, and the diameter of the circle is 20~100μm.

[0014] The present invention also provides a method for fabricating the dual-cavity integrated MEMS atomic clock described above, comprising the following steps: An array of cavities is fabricated on the upper surface of the photonic crystal control layer to obtain the photonic crystal control layer; A first through-hole array is fabricated on a silicon substrate, and then anodic bonding is performed for the first time with the photonic crystal control layer to obtain a first intermediate. A temperature control module is fabricated on a glass substrate; Solid alkali metal is injected into the first through hole in the first intermediate, and then a buffer gas is filled in. Subsequently, a second anodic bonding is performed with a glass substrate equipped with a temperature control module to obtain a second intermediate. A coplanar waveguide layer is fabricated on the second intermediate to obtain a dual-cavity integrated MEMS atomic clock.

[0015] This invention provides a dual-cavity integrated MEMS atomic clock, comprising, from top to bottom, a photonic crystal control layer, a silicon substrate, a temperature control module, a glass substrate, and a coplanar waveguide layer; the photonic crystal control layer has arrayed cavities; the cavities open onto the upper surface of the photonic crystal control layer; the cross-section of the cavities is cross-shaped; the silicon substrate has a first through-hole penetrating both the upper and lower surfaces; the first through-hole is arrayed; the two ends of the first through-hole are sealed by the photonic crystal control layer and the glass substrate to form a sealed cavity; the sealed cavity is filled with atomic vapor and a buffer gas; the coplanar waveguide layer includes waveguides and conductive adhesive; the waveguides have a second through-hole penetrating both the upper and lower surfaces; the conductive adhesive fills the second through-hole. This invention features an array of cavities arranged on a photonic crystal control layer. These cavities have a cross-shaped cross-section, exhibiting orthogonal symmetry and dual-band bandgap characteristics. Simultaneously, the surface plasmon resonance effect enhances the fluorescence signal intensity, thereby improving optical efficiency. The cross-shaped structure provides symmetrical thermal expansion distribution and low thermal stress deviation (<5MPa), reducing thermal deformation during subsequent packaging and significantly minimizing the frequency drift of the microwave resonant cavity (to 0.05Hz / ℃), thus improving thermomechanical stability. The two ends of the first via connect the photonic crystal control layer and the glass substrate. The plate is sealed to form an atomic gas chamber. A temperature control module is installed on the glass substrate to achieve precise temperature control of the atomic gas chamber. The waveguide is coupled to the array of cavities in the photonic crystal control layer through the coplanar waveguide to form a composite resonant cavity. The slow light effect of the array of cavities in the photonic crystal control layer is used to extend the interaction time between atoms and microwaves, which can improve the stability of the output frequency and thus improve the thermomechanical stability. Conductive adhesive is set in the coplanar waveguide layer, which can realize the effective transmission of microwave signals and avoid signal interference, thereby further improving optical efficiency. Attached Figure Description

[0016] Figure 1 This is a schematic diagram of the structure of the dual-cavity integrated MEMS atomic clock provided by the present invention; Figure 2 This is a schematic diagram of the structure of each layer of the dual-cavity integrated MEMS atomic clock provided by the present invention; Figure 3 This is a schematic diagram of the front view structure of the dual-cavity integrated MEMS atomic clock provided by the present invention; Figure 4 The shape of the waveguide in Examples 1-3; Figure 5 The fluorescence signal intensity data are for the dual-cavity integrated MEMS atomic clocks prepared in Examples 1-3 and the MEMS atomic clock prepared in Comparative Example 1. Figure 6 The frequency stability data are for the dual-cavity integrated MEMS atomic clock prepared in Example 1. Figure 7 Environmental adaptability data for the dual-cavity integrated MEMS atomic clocks prepared in Examples 1-3 and the MEMS atomic clock prepared in Comparative Example 1; Figure 8 The waveguide optical speed data are for the photonic crystal of the dual-cavity integrated MEMS atomic clock prepared in Example 1 and the MEMS atomic clock prepared in Comparative Example 1. Figure 9 The data are CPT resonance signals of the dual-cavity integrated MEMS atomic clocks prepared in Examples 1-3 and the MEMS atomic clock prepared in Comparative Example 1. Detailed Implementation

[0017] This invention provides a dual-cavity integrated MEMS atomic clock, comprising a photonic crystal control layer, a silicon substrate, a temperature control module, a glass substrate, and a coplanar waveguide layer stacked from top to bottom; The photonic crystal control layer is provided with an array of cavities; the cavities open onto the upper surface of the photonic crystal control layer; the cross-section of the cavities is cross-shaped. The silicon substrate is provided with a first through hole penetrating the upper and lower surfaces; the first through holes are arranged in an array. The two ends of the first through hole are sealed by the photonic crystal control layer and the glass substrate to form a sealed cavity; the sealed cavity is filled with atomic vapor and buffer gas; The coplanar waveguide layer includes a waveguide and a conductive adhesive; the waveguide has a second through hole penetrating the upper and lower surfaces; the conductive adhesive fills the second through hole.

[0018] The present invention does not impose any special restrictions on the source of materials for each component in the dual-cavity integrated MEMS atomic clock; commercially available products known to those skilled in the art can be used.

[0019] like Figure 1 As shown, in this invention, the dual-cavity integrated MEMS atomic clock includes a photonic crystal control layer; the photonic crystal control layer is provided with an array of cavities; the cavities open onto the upper surface of the photonic crystal control layer; the cross-section of the cavities is cross-shaped. This invention provides an array of cavities on the photonic crystal control layer. These cavities have a cross-shaped cross-section, exhibiting orthogonal symmetry and dual-band bandgap characteristics. Simultaneously, through surface plasmon resonance, the fluorescence signal intensity is improved, thereby enhancing optical efficiency. The cross-shaped structure has a symmetrical thermal expansion distribution, resulting in low thermal stress deviation (<5MPa), reducing the degree of thermal deformation during subsequent packaging, thus significantly reducing the frequency drift of the microwave resonant cavity and improving thermomechanical stability.

[0020] like Figure 1As shown, in one embodiment of the present invention, the photonic crystal control layer is cylindrical. The present invention does not impose a specific limitation on the diameter of the photonic crystal control layer; it can be adjusted according to actual needs.

[0021] In this invention, the length of the cross arm of the cavity is preferably 100-110 nm, and the width of the cross arm is preferably 90-110 nm; the depth of the cavity is preferably 195-205 nm; the distance between two adjacent cavities, measured from the center of the cross arm, is preferably 355-365 nm; and the cavities are arranged in a matrix. As one embodiment, the length of the cross arm of the cavity can be 101 nm, 102 nm, 103 nm, 104 nm, 105 nm, 106 nm, 107 nm, 108 nm, or 109 nm; the width of the cross arm can be 95 nm, 100 nm, or 105 nm; the depth of the cavity can be 198 nm, 200 nm, or 203 nm; and the distance between two adjacent cavities, measured from the center of the cross arm, can be 358 nm, 360 nm, or 363 nm. By limiting the size of the cavity within the aforementioned range, this invention enables the cavity to form a cross-shaped microstructure array with a subwavelength period, which can simultaneously achieve collimation and focusing of 780nm pump laser, achieve bandgap filtering of 6.8GHz microwave frequency band, and enhance the intensity of atomic fluorescence signal by more than 8 times through local surface plasmon resonance.

[0022] In this invention, the photonic crystal modulation layer is preferably made of at least one of borosilicate glass, aluminate glass, and quartz glass; the coefficient of thermal expansion of the material is preferably 3.0~4.5 ppm / ℃. By limiting the coefficient of thermal expansion of the material to the above range, this invention enables it to work synergistically with the cross-shaped structure, thereby ensuring overall stability and performance.

[0023] In one embodiment, the coefficient of thermal expansion of the material may be 3.2ppm / ℃, 3.4ppm / ℃, 3.6ppm / ℃, 3.8ppm / ℃, 4.0ppm / ℃, 4.2ppm / ℃, or 4.4ppm / ℃.

[0024] In this invention, the thickness of the photonic crystal control layer is preferably 0.2~1.0 mm. As one embodiment, the thickness of the photonic crystal control layer can be 0.3 mm, 0.4 mm, 0.5 mm, 0.6 mm, 0.7 mm, 0.8 mm, or 0.9 mm. Limiting the thickness of the photonic crystal control layer to the above range ensures that the photonic crystal control layer has sufficient mechanical strength and thermal stability, while also adapting to different process requirements.

[0025] The photonic crystal modulation layer of this invention features a dual-band bandgap design, achieving collimation (divergence angle < ±1°) for 780nm lasers and suppressing background noise (transmittance < 0.1%) for 1550nm.

[0026] like Figure 1 As shown, in this invention, the dual-cavity integrated MEMS atomic clock includes a silicon substrate disposed on the lower surface of the photonic crystal control layer; the silicon substrate is provided with a first through hole penetrating the upper and lower surfaces; the first through hole is arranged in an array.

[0027] like Figure 1 As shown, in one embodiment of the present invention, the first through holes are arranged in a matrix.

[0028] like Figure 1 As shown, the cross-section of the first through hole is circular.

[0029] like Figure 1 As shown, in one embodiment of the present invention, the silicon substrate is cylindrical. The present invention does not impose a specific limitation on the diameter of the silicon substrate, as long as it is the same as the diameter of the photonic crystal modulation layer.

[0030] In this invention, the diameter of the first through-hole is preferably 2.5~5.0 mm, and the center distance between two adjacent first through-holes is preferably 500~1500 μm; the thickness of the silicon substrate is preferably 0.3~1.0 mm. By limiting the diameter of the first through-hole, the center distance between two adjacent first through-holes, and the thickness of the silicon substrate within the above ranges, this invention ensures that the sealed cavity maintains good airtightness, optical performance, and stability, making it suitable for different manufacturing processes and application requirements.

[0031] In one embodiment, the diameter of the first through hole can be 3.0 mm, 3.5 mm, 4.0 mm, or 4.5 mm; the center distance between two adjacent first through holes can be 600 μm, 700 μm, 800 μm, 900 μm, 1000 μm, 1100 μm, 1200 μm, 1300 μm, or 1400 μm; and the thickness of the silicon substrate can be 0.4 mm, 0.5 mm, 0.6 mm, 0.7 mm, 0.8 mm, or 0.9 mm.

[0032] In this invention, the sidewall roughness of the first through-hole is preferably <10 nm. This invention ensures the interaction efficiency between photons and atoms by limiting the sidewall roughness of the first through-hole to the above range.

[0033] In this invention, a temperature control module is provided on the glass substrate. This temperature control module on the glass substrate enables precise control of the temperature of the atomic gas chamber.

[0034] The present invention does not impose any special limitations on the setting method of the temperature control module; any operation familiar to those skilled in the art can be used.

[0035] In one embodiment of the present invention, the temperature control module is a polycrystalline silicon linear resistance temperature sensor. The present invention uses a polycrystalline silicon linear resistance temperature sensor (resistance 500Ω, sensitivity 0.385Ω / ℃) in the temperature control module to ensure accurate temperature control within the atomic gas chamber; and it can monitor the temperature within the atomic gas chamber in real time, ensuring stable operation of the atomic gas chamber within the set temperature range.

[0036] In this invention, the polycrystalline silicon linear resistance temperature sensor is preferably disposed on the upper surface of a glass substrate; the pattern of the heating wire in the polycrystalline silicon linear resistance temperature sensor is preferably a zigzag shape; and the thickness of the polycrystalline silicon linear resistance temperature sensor is preferably 0.1~1.0 μm. By limiting the thickness of the polycrystalline silicon linear resistance temperature sensor within the above range, this invention ensures that the polycrystalline silicon linear resistance temperature sensor has sufficient heating capacity and stability, while not affecting the overall structure and thermal conductivity of the device.

[0037] In one embodiment, the thickness of the polycrystalline silicon linear resistance temperature sensor can be 0.2μm, 0.3μm, 0.4μm, 0.5μm, 0.6μm, 0.7μm, 0.8μm or 0.9μm.

[0038] The present invention does not have any special limitation on the specific material of the polycrystalline silicon linear resistance temperature sensor; a polycrystalline silicon linear resistance temperature sensor known to those skilled in the art can be used.

[0039] like Figure 1 As shown, in this invention, the dual-cavity integrated MEMS atomic clock includes a glass substrate disposed on the lower surface of the silicon substrate. In this invention, the glass substrate is used to seal the first through-hole.

[0040] The present invention does not have any special limitation on the specific material of the glass substrate; any glass substrate well known to those skilled in the art can be used.

[0041] like Figure 1 As shown, in one embodiment of the present invention, the glass substrate is cylindrical. The present invention does not impose a specific limitation on the diameter of the glass substrate, as long as it is the same as the diameter of the photonic crystal modulation layer.

[0042] In this invention, the thickness of the glass substrate is preferably 0.2 to 1.0 mm. As one embodiment, the thickness of the glass substrate can be 0.3 mm, 0.4 mm, 0.5 mm, 0.6 mm, 0.7 mm, 0.8 mm, or 0.9 mm. Limiting the thickness of the glass substrate within the above range ensures sealing requirements and overall structural strength, guaranteeing good optical properties and mechanical stability.

[0043] like Figure 1 As shown, in this invention, the two ends of the first through-hole are sealed by the photonic crystal control layer and the glass substrate to form a sealed cavity. In this invention, the two ends of the first through-hole are sealed by the photonic crystal control layer and the glass substrate, forming a sealed cavity that is an atomic gas chamber.

[0044] In this invention, the sealed cavity is filled with atomic vapor and a buffer gas; the gas pressure of the sealed cavity is preferably 5~20 kPa. As one embodiment, the gas pressure of the sealed cavity can be 10 kPa or 15 kPa. Limiting the gas pressure of the sealed cavity within the above range ensures that the density of the atomic vapor, gas diffusion, and the interaction effect of the photonic crystal structure are optimized.

[0045] The present invention does not impose any special limitation on the ratio of atomic vapor and buffer gas; it can be adjusted according to actual needs.

[0046] In this invention, the atomic vapor is preferably rubidium (Rb) atomic vapor, sodium (Na) atomic vapor, potassium (K) atomic vapor, cesium (Cs) atomic vapor, hydrogen (H) atomic vapor, or deuterium (D) atomic vapor. In this invention, the density of the rubidium atomic vapor is 5 × 10⁻⁶. 10 atoms / cm 3 Sodium atoms in sodium vapor have a low evaporation temperature and can be effectively used in precision measurement fields such as atomic clocks and laser frequency standards; potassium atoms in atomic clocks have high frequency stability and strong adaptability to environmental conditions; cesium atoms in cesium vapor are widely used in high-precision atomic clocks, with good long-term stability and high-precision time measurement capabilities; hydrogen or deuterium atoms in hydrogen or deuterium vapor can be used as working media in some high-precision measurements, especially suitable for applications in low-temperature environments.

[0047] In this invention, the buffer gas is preferably a helium-argon mixed buffer gas; the volume ratio of helium to argon in the helium-argon mixed buffer gas is preferably (2~6):1. As one embodiment, the volume ratio of helium to argon can be 3:1, 4:1, or 5:1. Limiting the volume ratio of helium to argon within the above range ensures good interaction and optical properties between the gas medium and the atomic gas chamber.

[0048] In this invention, the dual-cavity integrated MEMS atomic clock includes a coplanar waveguide layer disposed on the lower surface of the glass substrate; the coplanar waveguide layer includes waveguides and conductive adhesive; the waveguides are provided with a second through-hole penetrating both the upper and lower surfaces; the conductive adhesive fills the second through-hole. In this invention, the waveguides are coupled with cavities arranged in an array in the photonic crystal control layer to form a composite resonant cavity. The slow-light effect of the arrayed cavities in the photonic crystal control layer extends the interaction time between atoms and microwaves, improving the stability of the output frequency and thus enhancing thermomechanical stability. The conductive adhesive in the coplanar waveguide layer enables effective transmission of microwave signals, avoiding signal interference and further improving optical efficiency.

[0049] In this invention, the thickness of the coplanar waveguide layer is preferably 0.5~1.5 μm. As one embodiment, the thickness of the coplanar waveguide layer can be 1.0 μm.

[0050] In this invention, the width of the waveguide is preferably 30-100 μm. As one embodiment, the width of the waveguide can be 40 μm, 50 μm, 60 μm, 70 μm, 80 μm, or 90 μm. Limiting the waveguide width to the above range allows for impedance matching to 50 Ω, ensuring efficient microwave signal transmission and minimal reflection loss.

[0051] In this invention, the spacing between adjacent waveguides is preferably 10-30 μm. As one embodiment, the spacing between adjacent waveguides can be 15 μm, 20 μm, or 25 μm. Limiting the spacing between adjacent waveguides to the above range ensures impedance matching.

[0052] In this invention, the waveguide is preferably made of copper. The use of copper as the primary conductive material ensures effective signal transmission after the second via is provided.

[0053] The present invention does not impose any special limitations on the shape of the waveguide; it can be adjusted according to actual needs.

[0054] In one implementation, the waveguide pattern can be a parallel arrangement of straight waveguides, and can be designed as a straight or curved waveguide depending on the actual application requirements.

[0055] In this invention, the conductive adhesive is preferably silver paste, gold paste, or carbon paste. In this invention, the conductive adhesive enables low-loss transmission of microwave signals from the lower waveguide to the upper layer; the conductive adhesive possesses good conductivity, adhesion, and thermal stability. Specifically, silver paste has excellent conductivity and is suitable for high-frequency signal transmission; gold paste provides high conductivity and excellent mechanical properties, making it suitable for high-precision applications; and carbon paste is suitable for low-cost applications and has good conductivity and stability.

[0056] In this invention, the cross-section of the second via is preferably circular; the diameter of the circle is preferably 20-100 μm. As one embodiment, the diameter of the circle can be 30 μm, 40 μm, 50 μm, 60 μm, 70 μm, 80 μm, or 90 μm. This invention does not impose a specific limitation on the number of the second vias; it is determined based on the area of ​​the waveguide layer and the required number of vertical interconnect paths.

[0057] In one implementation, each waveguide connection point in the waveguide layer preferably has 1 to 4 second vias. This invention, by providing 1 to 4 second vias at each waveguide connection point, ensures effective signal transmission and avoids signal interference.

[0058] In this invention, the waveguide in the coplanar waveguide layer is a microwave cavity structure, and a composite resonant cavity (Q value > 10000) is formed by coupling the coplanar waveguide with the array of cavities in the photonic crystal control layer.

[0059] The dual-cavity integrated MEMS atomic clock provided by this invention adopts an optical-microwave synergistic resonance mechanism. Laser pumping: A 780nm laser is collimated by a photonic crystal and then vertically incident into the gas chamber. Through the coherent population trapping (CPT) effect, the atoms are excited to a coherent superposition state of the hyperfine energy levels (F=1 and F=2) of the ground state. Microwave driving: A 6.834GHz microwave signal is coupled to the photonic crystal through a coplanar waveguide. The slow light effect of the photonic crystal extends the atom-microwave interaction time to 1.5ms, and the Rabi oscillation amplitude is increased by 30%, resulting in a high-precision and low-power miniature atomic clock.

[0060] The dual-cavity integrated MEMS atomic clock provided by this invention adopts a three-layer vertical stacked architecture: the photonic crystal control layer forms an orthogonal cross-shaped photonic crystal array on its surface through nanoimprinting and reactive ion etching processes, achieving collimation and focusing of 780nm laser (divergence angle <1°) and suppression of 1550nm background noise (transmittance <0.1%); the atomic gas chamber layer constructs a sealed cavity through silicon-glass anodic bonding process, which is filled with atomic vapor and buffer gas, and a polycrystalline silicon linear resistance temperature sensor (accuracy ±0.05℃) is integrated on the glass substrate to maintain the gas chamber temperature at 80℃±0.1℃; the waveguide in the lower coplanar waveguide layer couples with the photonic crystal to form a composite resonant cavity (Q value >10000), and integrates a piezoelectric ceramic driver (displacement accuracy 0.1nm) to achieve ±10MHz frequency tuning.

[0061] The atomic clock of this invention is based on the highly efficient synergistic effect of light, microwave, and atoms. It utilizes the slow-light effect of cavities arranged in an array within the photonic crystal control layer to extend the interaction time between atoms and microwaves to 1.5 times that of conventional structures, achieving an output frequency stability of 3 × 10⁻⁶. -13 @On the order of 1 hour; The atomic clock of this invention provides an atomic clock solution that combines millimeter-level miniaturization and ultra-high stability for scenarios such as 5G communication base stations and deep space probes, solving problems such as low optical efficiency, poor thermal stability and complex manufacturing process in the prior art.

[0062] The present invention also provides a method for fabricating the dual-cavity integrated MEMS atomic clock described above, comprising the following steps: An array of cavities is fabricated on the upper surface of the photonic crystal control layer to obtain the photonic crystal control layer; A first through-hole array is fabricated on a silicon substrate, and then anodic bonding is performed for the first time with the photonic crystal control layer to obtain a first intermediate. A temperature control module is fabricated on a glass substrate; Solid alkali metal is injected into the first through hole in the first intermediate, and then a buffer gas is filled in. Subsequently, a second anodic bonding is performed with a glass substrate equipped with a temperature control module to obtain a second intermediate. A coplanar waveguide layer is fabricated on the second intermediate to obtain a dual-cavity integrated MEMS atomic clock.

[0063] The present invention prepares cavities arranged in an array on the upper surface of a photonic crystal control layer to obtain a photonic crystal control layer.

[0064] The present invention does not have any special limitations on the operation of preparing the array of cavities on the upper surface of the photonic crystal control layer; any operation known to those skilled in the art can be used.

[0065] As one implementation method, the present invention can use nanoimprinting and reactive ion etching processes to prepare arrayed cavities. Specifically, the operation can be as follows: spin-coating a 300nm thick UV-curable adhesive onto the upper surface of the photonic crystal control layer, imprinting using a cross-shaped array silicon template, peeling off after UV curing, and then transferring the pattern to the photonic crystal control layer using reactive ion etching (CF4 and O2 volume ratio of 4:1, 100W) for 5 minutes, with a depth error of <5nm.

[0066] The present invention prepares an array of first through-holes on a silicon substrate, and then performs a first anodic bonding with the photonic crystal control layer to obtain a first intermediate.

[0067] In this invention, the silicon substrate is preferably polished on both sides before use. This invention does not impose any particular limitations on the double-sided polishing operation; any operation well-known to those skilled in the art can be used.

[0068] In this invention, the first via is preferably fabricated on the silicon substrate using a deep reactive ion etching (DRIE) process.

[0069] The present invention does not have any special limitations on the operation of the first anodic bonding, and any operation known to those skilled in the art can be used.

[0070] This invention fabricates a temperature control module on a glass substrate.

[0071] The present invention does not impose any special limitations on the operation of preparing the temperature control module; any operation known to those skilled in the art can be used.

[0072] After obtaining the first intermediate, the present invention injects solid alkali metal into the first through hole in the first intermediate, then fills it with buffer gas, and then performs a second anodic bonding with a glass substrate equipped with a temperature control module to obtain the second intermediate. A coplanar waveguide layer is then fabricated on the second intermediate to obtain a dual-cavity integrated MEMS atomic clock.

[0073] The present invention does not have any special limitations on the operation of injecting solid alkali metal into the first through hole in the first intermediate, filling it with buffer gas, and then performing a second anodic bonding with a glass substrate equipped with a temperature control module. Any operation known to those skilled in the art can be used.

[0074] The present invention does not impose any special limitations on the operation of preparing the coplanar waveguide layer on the second intermediate, and any operation known to those skilled in the art can be used.

[0075] As one implementation, the operation of preparing a coplanar waveguide layer on the second intermediate can be to deposit a coating using a sputtering process, then perform photolithography to obtain a waveguide, then perform laser drilling to prepare a second through hole, and then fill it with conductive adhesive.

[0076] The preparation method provided by this invention is simple.

[0077] In terms of manufacturing process, this invention uses nanoimprint lithography to replace traditional electron beam lithography, significantly improving mass production feasibility and device lifespan; in addition, the three-dimensional heterogeneous integration design reduces the atomic clock volume to 5×5×1mm. 3 In summary, this invention systematically overcomes the technical barriers of precision, reliability, and cost in MEMS atomic clocks through innovative photonic crystal functions and synergistic optimization of multi-physics fields, providing a disruptive solution for the large-scale application of high-precision spatiotemporal reference technology.

[0078] The technical solutions of this invention will be clearly and completely described below with reference to the embodiments thereof. Obviously, the described embodiments are only a part of the embodiments of this invention, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0079] Schematic diagrams of the dual-cavity integrated MEMS atomic clocks prepared in Examples 1-3 are shown below. Figures 1-4 As shown, Figure 1 This is a schematic diagram of the structure of the dual-cavity integrated MEMS atomic clock provided by the present invention; Figure 2 This is a schematic diagram of the structure of each layer of the dual-cavity integrated MEMS atomic clock provided by the present invention; Figure 3 This is a schematic diagram of the front view structure of the dual-cavity integrated MEMS atomic clock provided by the present invention; Figure 4 The shape of the waveguide is shown in Examples 1-3.

[0080] Example 1 A dual-cavity integrated MEMS atomic clock consists of a photonic crystal control layer, a silicon substrate, a temperature control module, a glass substrate, and a coplanar waveguide layer stacked from top to bottom; The photonic crystal control layer is provided with an array of cavities; the cavities open onto the upper surface of the photonic crystal control layer; the cross-section of the cavities is cross-shaped. The photonic crystal modulation layer is cylindrical; The cross arm of the cavity is 100nm long, 110nm wide, and 195nm deep; the distance between two adjacent cavities is 365nm, measured from the center of the cross arm. The cavities are arranged in a matrix; The photonic crystal modulation layer is made of borosilicate glass with a thermal expansion coefficient of 3.2 ppm / ℃. The thickness of the photonic crystal modulation layer is 0.4 mm; The silicon substrate is provided with a first through hole penetrating the upper and lower surfaces; the first through holes are arranged in an array. The first through holes are arranged in a matrix; The cross-section of the first through hole is circular; The silicon substrate is cylindrical; The diameter of the first through hole is 2.5 mm, and the center distance between two adjacent first through holes is 1500 μm; the thickness of the silicon substrate is 0.3 mm. The sidewall roughness of the first through hole is <10nm; The temperature control module is a polycrystalline silicon linear resistance temperature sensor; The thickness of the polycrystalline silicon linear resistance temperature sensor is 0.2 μm; The glass substrate is cylindrical and made of BF33 glass; The thickness of the glass substrate is 0.4 mm; The two ends of the first through hole are sealed by the photonic crystal control layer and the glass substrate to form a sealed cavity; The sealed cavity is filled with atomic vapor and buffer gas; the gas pressure in the sealed cavity is 10 kPa. The atomic vapor is rubidium atomic vapor; The buffer gas is a helium-argon mixed buffer gas; the volume ratio of helium to argon in the helium-argon mixed buffer gas is 4:1; The coplanar waveguide layer is composed of waveguides and conductive adhesive; the waveguides are provided with second through holes penetrating the upper and lower surfaces; the conductive adhesive fills the second through holes; The thickness of the coplanar waveguide layer is 1.0 μm; The width of the waveguide is 30 μm; the spacing between adjacent waveguides is 30 μm; The waveguide is made of copper; The conductive adhesive is silver paste; The cross-section of the second through hole is circular; the diameter of the circle is 20 μm; Each waveguide connection point in the waveguide layer is provided with one second through hole; The fabrication method of the dual-cavity integrated MEMS atomic clock is as follows: A 300 nm thick UV-curable adhesive was spin-coated onto the upper surface of the photonic crystal control layer. The pattern was then imprinted using a cross-shaped array of silicon templates, cured under UV light, and then peeled off. The pattern was then transferred to the photonic crystal control layer by reactive ion etching for 5 min at a CF4:1 volume ratio and an energy of 100 W. The first vias are fabricated on a double-sided polished silicon substrate using deep reactive ion etching, and then anodic bonding is performed with the photonic crystal control layer to obtain the first intermediate; wherein the voltage of the first anodic bonding is 800V, the temperature is 400℃, and the pressure is 10kN. A temperature control module is fabricated on a glass substrate; Solid alkali metal is injected into the first through hole in the first intermediate, and then a buffer gas is filled in. Subsequently, a second anodic bonding is performed with a glass substrate equipped with a temperature control module to obtain the second intermediate. The voltage of the second anodic bonding is 800V, the temperature is 400℃, and the pressure is 10kN. A coating is deposited on the second intermediate using a sputtering process, followed by photolithography to obtain a waveguide. Then, a second through-hole is prepared by laser drilling, and finally, conductive adhesive is filled to obtain a dual-cavity integrated MEMS atomic clock.

[0081] Example 2 A dual-cavity integrated MEMS atomic clock consists of a photonic crystal control layer, a silicon substrate, a temperature control module, a glass substrate, and a coplanar waveguide layer stacked from top to bottom; The photonic crystal control layer is provided with an array of cavities; the cavities open onto the upper surface of the photonic crystal control layer; the cross-section of the cavities is cross-shaped. The photonic crystal modulation layer is cylindrical; The cross arm of the cavity is 105nm long, 100nm wide, and 200nm deep; the distance between two adjacent cavities is 360nm, measured from the center of the cross arm. The cavities are arranged in a matrix; The photonic crystal modulation layer is made of borosilicate glass with a thermal expansion coefficient of 3.2 ppm / ℃. The thickness of the photonic crystal modulation layer is 0.5 mm; The silicon substrate is provided with a first through hole penetrating the upper and lower surfaces; the first through holes are arranged in an array. The first through holes are arranged in a matrix; The cross-section of the first through hole is circular; The silicon substrate is cylindrical; The diameter of the first through hole is 4.0 mm, and the center distance between two adjacent first through holes is 1000 μm; the thickness of the silicon substrate is 0.6 mm; The sidewall roughness of the first through hole is <10nm; The temperature control module is a polycrystalline silicon linear resistance temperature sensor; The thickness of the polycrystalline silicon linear resistance temperature sensor is 0.5 μm; The glass substrate is cylindrical and made of BF33 glass; The thickness of the glass substrate is 0.6 mm; The two ends of the first through hole are sealed by the photonic crystal control layer and the glass substrate to form a sealed cavity; The sealed cavity is filled with atomic vapor and buffer gas; the gas pressure in the sealed cavity is 10 kPa. The atomic vapor is rubidium atomic vapor; The buffer gas is a helium-argon mixed buffer gas; the volume ratio of helium to argon in the helium-argon mixed buffer gas is 4:1; The coplanar waveguide layer is composed of waveguides and conductive adhesive; the waveguides are provided with second through holes penetrating the upper and lower surfaces; the conductive adhesive fills the second through holes; The thickness of the coplanar waveguide layer is 1.0 μm; The width of the waveguide is 65 μm; the spacing between adjacent waveguides is 20 μm; The waveguide is made of copper; The conductive adhesive is silver paste; The second through hole has a circular cross-section; the diameter of the circle is 60 μm; Each waveguide connection point in the waveguide layer is provided with three second through holes; The fabrication method of the dual-cavity integrated MEMS atomic clock is as follows: A 300 nm thick UV-curable adhesive was spin-coated onto the upper surface of the photonic crystal control layer. The pattern was then imprinted using a cross-shaped array of silicon templates, cured under UV light, and then peeled off. The pattern was then transferred to the photonic crystal control layer by reactive ion etching for 5 min at a CF4:1 volume ratio and an energy of 100 W. The first vias are fabricated on a double-sided polished silicon substrate using deep reactive ion etching, and then anodic bonding is performed with the photonic crystal control layer to obtain the first intermediate; wherein the voltage of the first anodic bonding is 800V, the temperature is 400℃, and the pressure is 10kN. A temperature control module is fabricated on a glass substrate; Solid alkali metal is injected into the first through hole in the first intermediate, and then a buffer gas is filled in. Subsequently, a second anodic bonding is performed with a glass substrate equipped with a temperature control module to obtain the second intermediate. The voltage of the second anodic bonding is 800V, the temperature is 400℃, and the pressure is 10kN. A coating is deposited on the second intermediate using a sputtering process, followed by photolithography to obtain a waveguide. Then, a second through-hole is prepared by laser drilling, and finally, conductive adhesive is filled to obtain a dual-cavity integrated MEMS atomic clock.

[0082] Example 3 A dual-cavity integrated MEMS atomic clock consists of a photonic crystal control layer, a silicon substrate, a temperature control module, a glass substrate, and a coplanar waveguide layer stacked from top to bottom; The photonic crystal control layer is provided with an array of cavities; the cavities open onto the upper surface of the photonic crystal control layer; the cross-section of the cavities is cross-shaped. The photonic crystal modulation layer is cylindrical; The cross arm of the cavity is 110nm long, 90nm wide, and 205nm deep; the distance between two adjacent cavities is 355nm, measured from the center of the cross arm. The cavities are arranged in a matrix; The photonic crystal modulation layer is made of borosilicate glass with a thermal expansion coefficient of 3.2 ppm / ℃. The thickness of the photonic crystal modulation layer is 1.0 mm; The silicon substrate is provided with a first through hole penetrating the upper and lower surfaces; the first through holes are arranged in an array. The first through holes are arranged in a matrix; The cross-section of the first through hole is circular; The silicon substrate is cylindrical; The diameter of the first through hole is 5.0 mm, and the center distance between two adjacent first through holes is 500 μm; the thickness of the silicon substrate is 1.0 mm. The sidewall roughness of the first through hole is <10nm; The temperature control module is a polycrystalline silicon linear resistance temperature sensor; The thickness of the polycrystalline silicon linear resistance temperature sensor is 1.0 μm; The glass substrate is cylindrical and made of BF33 glass; The thickness of the glass substrate is 1.0 mm; The two ends of the first through hole are sealed by the photonic crystal control layer and the glass substrate to form a sealed cavity; The sealed cavity is filled with atomic vapor and buffer gas; the gas pressure in the sealed cavity is 10 kPa. The atomic vapor is rubidium atomic vapor; The buffer gas is a helium-argon mixed buffer gas; the volume ratio of helium to argon in the helium-argon mixed buffer gas is 4:1; The coplanar waveguide layer is composed of waveguides and conductive adhesive; the waveguides are provided with second through holes penetrating the upper and lower surfaces; the conductive adhesive fills the second through holes; The thickness of the coplanar waveguide layer is 1.0 μm; The width of the waveguide is 100 μm; the spacing between adjacent waveguides is 10 μm; The waveguide is made of copper; The conductive adhesive is silver paste; The cross-section of the second through hole is circular; the diameter of the circle is 100 μm; Each waveguide connection point in the waveguide layer is provided with four second through holes; The fabrication method of the dual-cavity integrated MEMS atomic clock is as follows: A 300 nm thick UV-curable adhesive was spin-coated onto the upper surface of the photonic crystal control layer. The pattern was then imprinted using a cross-shaped array of silicon templates, cured under UV light, and then peeled off. The pattern was then transferred to the photonic crystal control layer by reactive ion etching for 5 min at a CF4:1 volume ratio and an energy of 100 W. The first vias are fabricated on a double-sided polished silicon substrate using deep reactive ion etching, and then anodic bonding is performed with the photonic crystal control layer to obtain the first intermediate; wherein the voltage of the first anodic bonding is 800V, the temperature is 400℃, and the pressure is 10kN. A temperature control module is fabricated on a glass substrate; Solid alkali metal is injected into the first through hole in the first intermediate, and then a buffer gas is filled in. Subsequently, a second anodic bonding is performed with a glass substrate equipped with a temperature control module to obtain the second intermediate. The voltage of the second anodic bonding is 800V, the temperature is 400℃, and the pressure is 10kN. A coating is deposited on the second intermediate using a sputtering process, followed by photolithography to obtain a waveguide. Then, a second through-hole is prepared by laser drilling, and finally, conductive adhesive is filled to obtain a dual-cavity integrated MEMS atomic clock.

[0083] Comparative Example 1 MEMS atomic clocks: a typical structure with no photonic crystals and a single-cavity atomic gas cell (i.e., the existing conventional structure). The performance of the dual-cavity integrated MEMS atomic clocks prepared in Examples 1-3 and the MEMS atomic clock prepared in Comparative Example 1 were tested. The test methods and standards are as follows: 1. Fluorescence signal intensity test: The fluorescence signal emitted by the 780nm laser was detected using a spectrometer (Ando AQ6317C spectrometer). The intensity of the fluorescence signal was connected to the signal detector via an optical fiber. During the test, the ambient temperature was kept stable at 25℃±0.5℃ and the humidity was controlled at 40%.

[0084] Figure 5 The fluorescence signal intensity data are for the dual-cavity integrated MEMS atomic clocks prepared in Examples 1-3 and the MEMS atomic clock prepared in Comparative Example 1.

[0085] from Figure 5 As can be seen, the fluorescence signal intensity of the dual-cavity integrated MEMS atomic clock of this invention is increased by 8 times, and the signal-to-noise ratio (SNR) reaches 25dB.

[0086] 2. Frequency stability test: Frequency stability was tested using an Agilent 53230A frequency meter. During the 1-hour stability test, frequency drift was monitored using a temperature stabilization control system (maintained at 80℃ ± 0.1℃).

[0087] During the testing process, standard frequency stability testing methods (such as phase noise measurement and short-term stability measurement) were used.

[0088] Figure 6 The frequency stability data are for the dual-cavity integrated MEMS atomic clock prepared in Example 1.

[0089] from Figure 6 It can be seen that the frequency stability of the dual-cavity integrated MEMS atomic clock of this invention is 3×10⁻⁶. -13 @1 hour.

[0090] 3. Power consumption test: The power consumption of the dual-cavity integrated MEMS atomic clock under normal operating conditions was measured using a power meter (Keysight N6705B power analyzer).

[0091] In different working modes (active state, standby state), record the power consumption value to verify that the power consumption is always below 50mW.

[0092] 4. Package volume test: The package volume was precisely measured using a coordinate measuring machine (Zeiss Contura G2) to verify that the miniature atomic clock package volume is 5×5×1mm. 3 .

[0093] 5. Environmental adaptability test: The atomic clock was subjected to stability and reliability tests under different temperature (-20~85℃) and humidity (40% RH) conditions to ensure its normal operation in extreme environments.

[0094] Figure 7 The environmental adaptability data are for the dual-cavity integrated MEMS atomic clocks prepared in Examples 1-3 and the MEMS atomic clock prepared in Comparative Example 1.

[0095] from Figure 7As can be seen, the dual-cavity integrated MEMS atomic clock of this invention achieves performance stability in a wide temperature range environment through a cross-shaped photonic crystal symmetrical thermal expansion design and a high-precision temperature control module integrated on a glass substrate: the temperature adaptability covers -20~85℃, solving the problem of "high temperature signal attenuation and low temperature response lag" caused by thermal stress concentration in traditional structures; the core performance still maintains a peak retention rate of more than 80%, and the environmental robustness is significantly better than that of traditional MEMS atomic clocks, making it suitable for complex environments such as outdoor deployment of 5G base stations and deep space probes.

[0096] Figure 8 The waveguide optical speed data are for the photonic crystal of the dual-cavity integrated MEMS atomic clock prepared in Example 1 and the MEMS atomic clock prepared in Comparative Example 1.

[0097] from Figure 8 As can be seen, the dual-cavity integrated MEMS atomic clock of this invention achieves a significant slow-light effect. Its core value lies in the following: the propagation speed of photons in the photonic crystal waveguide is reduced to 1 / 3 to 1 / 2 of that in a normal waveguide, directly extending the interaction time between atoms and microwaves to more than 1.5 ms; the slow-light effect improves the response efficiency of atoms to microwave signals, increasing the Rabi oscillation amplitude by more than 30%, laying the foundation for the high contrast and high stability of the subsequent CPT resonance signal; compared with traditional atomic clocks without slow-light design, the photonic crystal waveguide of this invention further reduces optical loss and avoids the problem of "atoms escaping before fully interacting" caused by the rapid propagation of photons.

[0098] Figure 9 The data are CPT resonance signals of the dual-cavity integrated MEMS atomic clocks prepared in Examples 1-3 and the MEMS atomic clock prepared in Comparative Example 1.

[0099] from Figure 9 It can be seen that the CPT resonance signal performance of the dual-cavity integrated MEMS atomic clock of the present invention is significantly improved. The high contrast indicates that the intensity ratio of the CPT signal to light absorption is higher, and the signal recognition and anti-noise capability are stronger. The narrow linewidth, which directly reflects the core indicator of the frequency stability of the atomic clock, shows that the narrower the linewidth, the lower the frequency uncertainty, confirming that it has reached the level of a high-precision atomic clock. The resonance peaks of Examples 1 to 3 have high symmetry and no obvious shift or distortion, indicating that the microwave signal transmission is stable and the temperature control is accurate, further verifying the synergistic optimization effect of thermomechanical stability and optical efficiency of the present invention.

[0100] Experimental verification shows that the miniature atomic clock of this invention has excellent performance in terms of fluorescence signal intensity, frequency stability, power consumption and size, and ensures its applicability in satellite navigation timing and 5G base station synchronization scenarios, combining high precision and miniaturization characteristics.

[0101] As can be seen from the above embodiments, the dual-cavity integrated MEMS atomic clock provided by the present invention has high optical efficiency and excellent thermomechanical stability.

[0102] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A dual-cavity integrated MEMS atomic clock, comprising a photonic crystal control layer, a silicon substrate, a temperature control module, a glass substrate, and a coplanar waveguide layer stacked from top to bottom; The photonic crystal control layer is provided with an array of cavities; the cavities open onto the upper surface of the photonic crystal control layer; the cross-section of the cavities is cross-shaped. The silicon substrate is provided with a first through hole penetrating the upper and lower surfaces; the first through holes are arranged in an array. The two ends of the first through hole are sealed by the photonic crystal control layer and the glass substrate to form a sealed cavity; the sealed cavity is filled with atomic vapor and buffer gas; The coplanar waveguide layer includes a waveguide and a conductive adhesive; the waveguide has a second through hole penetrating the upper and lower surfaces; the conductive adhesive fills the second through hole.

2. The dual-cavity integrated MEMS atomic clock according to claim 1, characterized in that, The photonic crystal control layer is made of at least one of borosilicate glass, aluminate glass and quartz glass, and the coefficient of thermal expansion of the material is 3.0~4.5ppm / ℃.

3. The dual-cavity integrated MEMS atomic clock according to claim 1, characterized in that, The thickness of the photonic crystal modulation layer is 0.2~1.0 mm.

4. The dual-cavity integrated MEMS atomic clock according to claim 1, characterized in that, The cross arm of the cavity is 100~110nm long, 90~110nm wide, and 195~205nm deep. The distance between two adjacent cavities is 355~365nm from the center of the cross arm. The cavities are arranged in a matrix.

5. The dual-cavity integrated MEMS atomic clock according to claim 1, characterized in that, The first through hole has a circular cross-section and a diameter of 2.5~5.0mm. The center distance between two adjacent first through holes is 500~1500μm. The thickness of the silicon substrate is 0.3~1.0mm.

6. The dual-cavity integrated MEMS atomic clock according to claim 1, characterized in that, The thickness of the glass substrate is 0.2~1.0 mm.

7. The dual-cavity integrated MEMS atomic clock according to claim 1, characterized in that, The air pressure in the sealed cavity is 5~20 kPa.

8. The dual-cavity integrated MEMS atomic clock according to claim 1, characterized in that, The width of the waveguide is 30~100μm.

9. The dual-cavity integrated MEMS atomic clock according to claim 1, characterized in that, The cross-section of the second through hole is circular, and the diameter of the circle is 20~100μm.

10. A method for fabricating the dual-cavity integrated MEMS atomic clock according to any one of claims 1 to 9, comprising the following steps: An array of cavities is fabricated on the upper surface of the photonic crystal control layer to obtain the photonic crystal control layer; A first through-hole array is fabricated on a silicon substrate, and then anodic bonding is performed for the first time with the photonic crystal control layer to obtain a first intermediate. A temperature control module is fabricated on a glass substrate; Solid alkali metal is injected into the first through hole in the first intermediate, and then a buffer gas is filled in. Subsequently, a second anodic bonding is performed with a glass substrate equipped with a temperature control module to obtain a second intermediate. A coplanar waveguide layer is fabricated on the second intermediate to obtain a dual-cavity integrated MEMS atomic clock.

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