Signal transmission structure and molecular clock

Abstract

The invention provides a signal transmission structure and a molecular clock, and relates to the technical field of electromagnetic wave conduction. The signal transmission structure comprises a filtering structure, a waveguide and an airtight cavity; the filtering structure comprises a plurality of filtering layers, and a connecting window corresponding to a waveguide interface of the waveguide is arranged in the filtering structure; target gas corresponding to the molecular clock is arranged in the airtight cavity, the waveguide is arranged in the airtight cavity, and a waveguide interface extends out of the airtight cavity; and the waveguide interface is connected with the connection window in parallel to the layer number overlapping direction of the filtering structure in the layer number overlapping direction. The molecular clock comprises a transmitting chip, a receiving chip and a signal transmission structure, the transmitting chip is used for transmitting an electromagnetic wave signal to the signal transmission structure; the signal transmission structure is used for transmitting the electromagnetic wave signal; the receiving chip is used for receiving the electromagnetic wave signal transmitted by the signal transmission structure. Through vertical connection of the waveguide and the filtering structure, the area required by connection is reduced, so that the size and difficulty of connection are reduced, and the overall airtightness is optimized.

Description

Technical Field

[0001] The present application relates to the field of electromagnetic wave conduction technology, and in particular to a signal transmission structure and a molecular clock. Background Art

[0002] Molecular clocks mainly use molecules to absorb or emit photons and resonate by matching the energy difference between their vibrational energy levels or rotational energy levels with electromagnetic waves of a specific frequency. This specific frequency is the inherent frequency of molecular energy level transitions and is very stable, which can be used as a time reference. Therefore, molecular clocks need to use electromagnetic waves in the terahertz band to resonate with molecules.

[0003] In order to improve the accuracy of molecular clocks, the gas stored in the chip-level molecular clock package has high requirements for airtightness. In the transmission structure of molecular clocks, traditional substrate-integrated waveguide technology combines the advantages of rectangular waveguides and microstrip transmission lines, and can realize high-performance millimeter-wave planar circuits. However, the serious impedance mismatch at the radiation aperture leads to a very narrow bandwidth and poor radiation performance. In addition, the electromagnetic waves of existing substrate-integrated waveguides are mainly transmitted in the horizontal direction, requiring a larger connection area, which increases the difficulty of packaging and is not conducive to airtight packaging. The airtight waveguide window of the box-type window requires the addition of a circular waveguide for impedance matching, which is large in size and not conducive to processing and integration. In the case of miniaturization, the airtightness is also poor, which cannot meet the current high-airtightness transmission requirements of molecular clocks. Summary of the Invention

[0004] In view of this, an object of the embodiments of the present application is to provide a signal transmission structure and a molecular clock to improve the problem of poor airtightness of the transmission structure existing in the prior art.

[0005] In order to solve the above problems, in a first aspect, an embodiment of the present application provides a signal transmission structure, wherein the signal transmission structure includes: a filtering structure, a waveguide, and an airtight cavity; Wherein, the filtering structure comprises multiple filter layers, and a connection window corresponding to the waveguide interface of the waveguide is provided in the filtering structure; A target gas corresponding to a molecular clock is provided in the airtight cavity, the waveguide is provided in the airtight cavity, and the waveguide interface extends outside the airtight cavity; In the stacking direction of the layers of the filtering structure, the waveguide interface is connected to the connection window in parallel with the stacking direction of the layers.

[0006] In the above implementation process, the waveguide is set in a sealed airtight cavity to transmit electromagnetic wave signals based on the target gas set in the airtight cavity. In order to achieve a better signal filtering effect, the filter structure is set as a multi-layer structure including multiple filter layers. In the stacking direction of the multiple filter layers, the waveguide is connected to the filter structure parallel to the stacking direction of the layers, that is, the waveguide is connected to the filter structure perpendicular to the plane of the filter layer of the filter structure. This effectively reduces the size of the connection area between the waveguide and the filter structure, thereby reducing the difficulty of connecting the waveguide and the filter structure and the overall volume of the signal transmission structure, optimizing the airtightness of signal transmission between the waveguide and the filter structure, and meeting the current high airtightness transmission requirements of molecular clocks.

[0007] Optionally, the number of layers of the filter structure is determined based on simulation results of the vibration frequency and signal bandwidth of the target gas; The resonant frequency of the filtering structure is a frequency range including the vibration frequency.

[0008] In the above implementation process, the influence of the target gas's vibration frequency on signal transmission efficiency during signal transmission is taken into account. Therefore, the number of filter layers in the filter structure can be determined based on the simulation results of the target gas's vibration frequency and signal bandwidth. Setting an appropriate number of filter layers ensures that the filter structure has better signal transmission performance, and the signal has a higher bandwidth after passing through the filter structure, effectively improving signal transmission efficiency. Furthermore, the resonant frequency of the filter structure can be within a frequency range that includes the vibration frequency, so that the frequency of the filter structure and the target gas overlap, allowing the filter structure to properly transmit the signal transmitted within the waveguide, thereby improving the reliability of the filter structure's signal transmission.

[0009] Optionally, the thickness of each filter layer is determined based on the resonant frequency; The filter layers have a thickness-symmetrical structure based on the intermediate layer.

[0010] In the above implementation process, the thickness of each filter layer can be determined according to the actual resonant frequency of the filter structure, so as to transmit signals of multiple frequencies within the signal passband range of the resonant frequency. In addition, multiple filter layers can be set to a structure with symmetrical thickness based on the intermediate layer, using symmetry to minimize arithmetic requirements and generate regionally effective filters to achieve corresponding signal processing functions, further improving the reliability of signal transmission within the filter structure and reducing the adverse conditions of abnormal signal transmission.

[0011] Optionally, each filter layer includes: a dielectric layer, a metal hole and a metal layer; In the stacking direction of the layers, the metal layer is arranged on the top and bottom of the dielectric layer, and the metal layer is sealed and connected to the dielectric layer; The dielectric layer has a plurality of through holes whose central axes are parallel to the stacking direction of the layers, and the through holes are filled with metal to form the metal holes; Wherein, the material of the dielectric layer includes alumina ceramics, quartz or silicon.

[0012] In the above implementation process, the filter layer may include a dielectric layer, metal holes, and a metal layer. In the direction of the stacking of the layers, the metal layer is arranged at the top and bottom of the dielectric layer. The metal layer and the metal holes work together to limit the transmission of electromagnetic wave signals in the filter structure. In addition, the metal layer is sealed with the dielectric layer. The dielectric layer has multiple through holes whose central axes are parallel to the stacking direction of the layers, and the through holes are filled with metal to form metal holes. The edge sealing and solid metal hole structure ensure the airtightness of the filter structure, thereby improving the airtightness of the entire signal transmission structure. The material of the dielectric layer is set to be a highly airtight and high-temperature resistant material such as alumina ceramic, quartz, or silicon to further optimize the airtightness of the filter structure.

[0013] Optionally, in the stacking direction of the layers, the metal holes between two adjacent filter layers are in a staggered structure.

[0014] In the above implementation process, considering the metal holes set on the dielectric layer, even if metal is used to fill the holes to form solid holes, there is still a risk of air leakage due to the gaps between the materials. Therefore, in order to further optimize the airtightness of the filter structure with multiple filter layers, the metal holes between the two adjacent filter layers can be designed as a staggered structure in the stacking direction of the layers, so that the metal holes of the current filter layer can be sealed at the top and bottom through the two adjacent filter layers, thereby reducing the risk of air leakage caused by the metal holes of the multiple filter layers being in the same position in the stacking direction of the layers.

[0015] Optionally, the connection window does not have the metal hole and the metal layer; An equivalent filtering structure is provided in the connection window; the equivalent filtering structure is provided based on the E-surface and H-surface of the resonant cavity.

[0016] In the above implementation, the connection window does not have metal holes or metal layer structures to allow the signal to pass through the connection window. Considering that the gaps between metal holes are limited by the difficulty of processing, the gaps between the metal holes in the multi-layer filter layer will cause corresponding losses. The filtering structure cannot be completely equivalent to a waveguide, resulting in a narrow bandwidth. The gaps between the metal holes will also cause resonance effects. Therefore, a corresponding equivalent filtering structure can be set in the connection window to broaden the bandwidth and reduce the resonance effects through the equivalent filtering structure.

[0017] Optionally, a coupling structure is provided in an inner layer of the plurality of filter layers and in a peripheral area surrounding the connection window; The coupling structure includes a blank area obtained by hollowing out the metal layer; In the stacking direction of the layers, the coupling structure does not overlap with the metal holes in two adjacent filter layers; The structural parameters of the coupling structure are determined based on the simulation results of the signal bandwidth; wherein the structural parameters include: the number, arrangement layers and area size of the coupling structure.

[0018] In the above implementation process, considering that the bandwidth of the multi-layer filter layer is relatively narrow, in the inner layer of the multi-layer filter layer, a blank area in which the metal layer is hollowed out can be set in the surrounding area surrounding the connection window as a coupling structure, and in the stacking direction of the layers, the coupling structure and the metal holes in the two adjacent filter layers do not have an overlapping area to reduce the risk of air leakage. The structural parameters of the coupling structure are determined according to the simulation results of the signal bandwidth, so as to optimize some resonance points through the coupling structure and broaden the bandwidth of the filter structure, thereby further improving the signal transmission efficiency.

[0019] Optionally, the waveguide includes: the waveguide interface and a waveguide body; the waveguide interface includes a first interface and a second interface; The waveguide body is disposed in the airtight cavity, the waveguide body is connected to the first interface, the first interface is welded to the first end of the connection window, and the second interface is welded to the second end of the connection window; The non-connection end of the second interface away from the connection window is aligned with the receiving area of ​​the external receiving chip; The waveguide length between the waveguide body and the first interface is determined based on the vibration frequency of the target gas.

[0020] In the above implementation process, the waveguide includes a waveguide interface and a waveguide body. The waveguide structure includes a first interface welded to the first end of the connection window and a second interface welded to the second end of the connection window. The first interface is connected to the waveguide body disposed within the airtight cavity, and the second interface is located away from the non-connected end of the connection window and aligned with the receiving area of ​​an external receiving chip. The electromagnetic wave signal is transmitted to the external receiving chip through the transmission path of the waveguide body, the first interface, the filtering structure, and the second interface. In addition, the overall waveguide length of the waveguide body and the first interface is determined based on the vibration frequency of the target gas disposed within the airtight cavity, so that a suitable waveguide length is designed to achieve good signal transmission efficiency and received power.

[0021] Optionally, the waveguide body is bent; The waveguide body is provided with a step structure, chamfers and air holes; The air hole is used to transmit the target gas in the airtight cavity to the inside of the waveguide.

[0022] In the above implementation process, considering that the waveguide may be long, in order to reduce the space occupied by the waveguide, the waveguide body can be configured as a curved structure. This curved waveguide can reduce the overall volume of the signal transmission structure and meet various integrated and miniaturized usage requirements. In addition, in order to allow the target gas set in the airtight cavity to normally enter the waveguide, corresponding air holes can be provided on the waveguide body to transmit the target gas in the airtight cavity to the interior of the waveguide, thereby transmitting the signal based on the target gas within the waveguide. In addition, considering that the curved structure of the waveguide body will cause local reflection at the bending change, corresponding step structures and chamfers can be provided to reduce reflection.

[0023] In a second aspect, an embodiment of the present application provides a molecular clock, comprising: a transmitting chip, a receiving chip, and the signal transmission structure described in any one of the first aspects above; The transmitting chip is used to transmit electromagnetic wave signals to the signal transmission structure; The signal transmission structure is used to transmit the electromagnetic wave signal; The receiving chip is used to receive the electromagnetic wave signal transmitted by the signal transmission structure.

[0024] In the above implementation process, a signal transmission structure with a small volume and high airtightness can be set up in the molecular clock, so that the electromagnetic wave signal sent by the transmitting chip can be transmitted to the receiving chip based on the signal transmission structure, and the receiving chip can analyze and process the received signal based on the signal, thereby effectively improving the stability and accuracy of the molecular clock.

[0025] In summary, the embodiments of the present application provide a signal transmission structure and a molecular clock. Through the vertical connection structure between the waveguide and the filtering structure, the size of the connection area between the waveguide and the filtering structure is effectively reduced, thereby reducing the difficulty of connecting the waveguide and the filtering structure and the overall volume of the signal transmission structure, and optimizing the airtightness of signal transmission between the waveguide and the filtering structure, thereby meeting the current high airtightness transmission requirements of the molecular clock. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the following is a brief introduction to the drawings required for use in the embodiments of the present application. It should be understood that the following drawings only show certain embodiments of the present application and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other relevant drawings can be obtained based on these drawings without creative work.

[0027] Figure 1 A schematic diagram of a signal transmission structure provided in an embodiment of the present application; Figure 2 A schematic structural diagram of a filter layer provided in an embodiment of the present application; Figure 3 A schematic structural diagram of another filter layer provided in an embodiment of the present application; Figure 4 A schematic diagram of another signal transmission structure provided in an embodiment of the present application; Figure 5 A schematic structural diagram of a waveguide body provided in an embodiment of the present application.

[0028] Icon: 100-filtering structure; 200-waveguide; 300-airtight cavity; A-layer stacking direction; 110-filtering layer; 210-waveguide interface; 120-connection window; 111-dielectric layer; 112-metal hole; 113-metal layer; 114-coupling structure; 211-first interface; 212-second interface; 220-waveguide body; 221-air hole; 222-step structure; 223-chamfer. DETAILED DESCRIPTION

[0029] The following will be combined with the drawings in the embodiments of the present application to clearly and completely describe the technical solutions in the embodiments of the present application. Obviously, the embodiments described are only part of the embodiments of the present application, not all of them. Based on the embodiments of the present application, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the embodiments of the present application.

[0030] In the prior art, chip-scale molecular clocks primarily consist of a transmitter chip, a receiver chip, a crystal oscillator frequency source, a transmission structure, and a control circuit. The transmitter chip emits terahertz waves, which are absorbed by the gas within the transmission structure. The absorption peak is detected by the receiver chip, and the inherent frequency of the molecular energy level transition is the absorption peak. Therefore, to ensure the stability and accuracy of chip-scale molecular clocks, the gas stored within the chip-scale molecular clock package must be highly airtight. Conventional substrate-integrated waveguide technology combines the advantages of rectangular waveguides and microstrip transmission lines, enabling high-performance millimeter-wave planar circuits. However, severe impedance mismatch at the radiation aperture results in a narrow bandwidth and poor radiation performance. Furthermore, existing substrate-integrated waveguides primarily transmit electromagnetic waves horizontally, requiring a large connection area, increasing packaging complexity and hindering hermetic packaging. Furthermore, the box-shaped window-type airtight waveguide window requires the addition of a circular waveguide for impedance matching, which is bulky and difficult to process and integrate. Even with miniaturization, airtightness is poor, failing to meet the current requirements for high-airtightness transmission of molecular clocks.

[0031] In order to solve the above problems, the embodiments of the present application provide a signal transmission structure and a molecular clock. Through the vertical connection structure between the waveguide and the filtering structure, the size of the connection area between the waveguide and the filtering structure is effectively reduced, thereby reducing the difficulty of connecting the waveguide and the filtering structure and the overall volume of the signal transmission structure, and optimizing the airtightness of signal transmission between the waveguide and the filtering structure, thereby meeting the current high airtightness transmission requirements of the molecular clock.

[0032] See also Figure 1 , Figure 1 This is a structural schematic diagram of a signal transmission structure provided in an embodiment of the present application. The signal transmission structure may include: a filtering structure 100, a waveguide 200 and an airtight cavity 300.

[0033] The filter structure 100 includes a plurality of filter layers 110 , and a connection window 120 corresponding to the waveguide interface 210 of the waveguide 200 is provided in the filter structure 100 .

[0034] It should be noted that the multilayer filter layer 110 in the filtering structure 100 can be a SIW (Substrate Integrated Waveguide) structure, which is a hybrid planar waveguide structure that combines the low-loss characteristics of traditional metal waveguides and the planar integration advantages of microstrip lines / coplanar waveguides. It simulates the electromagnetic boundaries of traditional waveguides by periodically arranging metallized through holes (or gaps) on the dielectric substrate, and can be equivalent to a rectangular waveguide, which can limit the propagation of electromagnetic wave signals therein, and the propagation characteristics are similar to those of rectangular metal waveguides.

[0035] For example, the number of layers of the multi-layer filter layer 110 can be selected and adjusted according to actual needs. Figure 1 Only one feasible embodiment of the filter structure 100 including five filter layers 110 is shown, and structures with other numbers of filter layers 110 are not described in detail.

[0036] Optionally, the shape and size of the connection window 120 provided on the filtering structure 100 may correspond to the shape and size of the waveguide interface 210 , so as to realize a complete and uniform signal transmission channel through the waveguide 200 and the connection window 120 .

[0037] It should be noted that the airtight cavity 300 is a sealed cavity, which can be formed by a boxed structure made of metal or other materials. The target gas corresponding to the molecular clock is set in the airtight cavity 300. The target gas can be a variety of different types of gases set according to actual needs, such as carbonyl sulfide (OCS), ammonia (NH3), carbon monoxide (CO), and other gases. The waveguide 200 is arranged in the airtight cavity 300 to transmit electromagnetic wave signals based on the target gas set in the airtight cavity 300. The waveguide interface 210 extends outside the airtight cavity 300. In the layer stacking direction A of the filtering structure 100, the waveguide interface 210 is connected to the connection window 120 parallel to the layer stacking direction A, that is, the waveguide 200 is connected to the filtering structure 100 perpendicular to the plane of the filter layer 110 of the filtering structure 100, effectively reducing the size of the connection area between the waveguide 200 and the filtering structure 100, thereby reducing the difficulty of connecting the waveguide 200 and the filtering structure 100 and the overall volume of the signal transmission structure, optimizing the airtightness of signal transmission between the waveguide 200 and the filtering structure 100, and meeting the current high airtightness transmission requirements of molecular clocks.

[0038] For example, the waveguide 200 for transmitting signals may be configured as various types of rectangular waveguides.

[0039] It should be noted that the edges of the multi-layer filter layers 110 in the filter structure 100 for transmitting signals can be connected by sealing welding, and the two connecting planes of the filter structure 100 are sealed by setting a metal layer 113, etc., so that a more airtight area is formed inside the filter structure 100, thereby improving the overall airtightness of the signal transmission structure.

[0040] Optionally, considering the influence of the vibration frequency of the target gas on the signal transmission efficiency during signal transmission, the number of layers of the filtering structure 100 is determined based on the simulation results of the vibration frequency of the target gas and the signal bandwidth, that is, the number of filtering layers 110 of the filtering structure 100 can be determined according to the simulation results of the vibration frequency of the target gas and the signal bandwidth, so as to set an appropriate number of filtering layers 110 to make the signal transmission performance of the filtering structure 100 better, and the signal has a higher bandwidth after passing through the filtering structure 100, thereby effectively improving the transmission efficiency of the signal.

[0041] It should be noted that the resonant frequency of the filter structure 100 is a frequency range that includes the vibration frequency, so that the frequency of the filter structure 100 and the target gas have an overlapping part, so that the filter structure 100 can normally transmit the signal transmitted in the waveguide 200, thereby improving the reliability of the filter structure 100 in transmitting the signal.

[0042] For example, taking the target gas as carbon sulfide gas, the vibration frequency of its molecules is 231 GHz, therefore, the resonant frequency of the filter structure 100 can be set to 211 GHz-251 GHz so that the resonant frequency can include the vibration frequency. The simulation results of the signal bandwidth may include the simulation results of the scattering parameters. The scattering parameters describe the relationship between the incident wave and the reflected wave of the linear network at different ports, and may include S11 and S21. S11 is the reflection coefficient of the filter structure 100, and S21 is the forward transmission coefficient between the filter structure 100 and the waveguide 200. S11 and S21 can be limited according to actual needs. For example, S11 is less than or equal to -10 dB, and S21 is greater than or equal to -5 dB, so that the filter structure 100 has a wider bandwidth and achieves better passband performance. Taking into account the relationship between the number of layers (i.e., order) of the filter layer 110 of the filter structure 100 and its performance, the higher the number of layers, the stronger the out-of-band suppression effect but the narrower the bandwidth. Therefore, based on the actual resonant frequency and the bandwidth of the simulation results, the resonant frequency can be used as the center frequency of the filter structure 100, and S11 less than or equal to -10dB and S21 greater than or equal to -5dB can be used as the passband width of the filter structure 100. Combined with the actual type of the filter structure 100 (such as a low-pass type), the normalized frequency and attenuation requirements of the filter structure 100, the order table of the filter design manual is queried to determine the number of layers of the filter structure 100. For example, the filter structure 100 includes 5 filter layers 110.

[0043] It should be noted that in the stacking direction A, the thickness of each filter layer 110 is determined based on the resonant frequency, and the multiple filter layers 110 have a thickness-symmetrical structure based on the intermediate layer. The thickness of each filter layer 110 can be determined based on the actual resonant frequency of the filter structure 100 to transmit signals of multiple frequencies within the signal passband range of the resonant frequency. In addition, the multiple filter layers 110 can be arranged to have a thickness-symmetrical structure based on the intermediate layer, using symmetry to minimize arithmetic requirements and generate regionally efficient filters to implement corresponding signal processing functions. For example, when a signal cannot be transmitted normally in a certain filter layer 110, it can be retransmitted in a symmetrical layer with the same thickness as the filter layer 110, further improving the reliability of signal transmission within the filter structure 100 and reducing the adverse conditions of abnormal signal transmission.

[0044] For example, taking a filter structure 100 comprising five filter layers 110, the thickness of the middle layer, i.e., the third layer, can be set to be the thickest, the first and fifth layers can be the same thickness and the thinnest, and the second and fourth layers can be the same thickness and intermediate. Alternatively, various other structures can be configured, with the middle layer being the thinnest and the edge layers being the thickest. Therefore, the multi-layer filter layer 110 can include three filter layers 110 of varying thicknesses, each corresponding to a different sub-resonant frequency, but each thickness encompassing the vibration frequency of a target gas. For example, the sub-resonant frequency of the third filter layer 110 can be 211 GHz to 251 GHz, the sub-resonant frequencies of the second and fourth layers can be 221 GHz to 241 GHz, and the sub-resonant frequencies of the first and second layers can be 226 GHz to 236 GHz. This allows for transmission and processing of signals at different resonance points during actual use. Even if a signal corresponding to the fifth frequency is not properly processed by the fifth filter layer 110, it can be reprocessed by the first filter layer 110, corresponding to the thickness of the fifth filter layer 110. This effectively improves the reliability of signal processing by the filter structure 100.

[0045] Optionally, see Figure 2 , Figure 2 This is a schematic diagram of the structure of a filter layer provided in an embodiment of the present application. Each filter layer 110 may include a dielectric layer 111, metal holes 112, and a metal layer 113. In the stacking direction A, the metal layers 113 are disposed at the top and bottom of the dielectric layer 111. The metal layers 113 are sealed to the dielectric layer 111 to achieve a sealing function for the filter structure 100 in the planar direction. The dielectric layer 111 includes multiple through-holes whose central axes are parallel to the stacking direction A. The through-holes are filled with metal to form the metal holes 112. The filter layer 110 may include a dielectric layer 111, a metal hole 112 and a metal layer 113. In the layer stacking direction A, the metal layer 113 is arranged at the top and bottom of the dielectric layer 111. The metal layer 113 and the metal hole 112 work together to limit the transmission of electromagnetic wave signals in the filter structure 100. In addition, the metal layer 113 is sealed and connected to the dielectric layer 111. The dielectric layer 111 has multiple through holes whose central axes are parallel to the layer stacking direction A, and the through holes are filled with metal to form metal holes 112, so as to ensure the airtightness of the filter structure 100 through the edge sealing and the structure of the solid metal hole 112, thereby improving the overall airtightness of the signal transmission structure.

[0046] Optionally, the dielectric layer 111 is the corresponding dielectric material substrate, the metal layer 113 is the corresponding metal substrate, and the metal filling the through hole and the metal layer 113 can be made of the same metal material. For example, considering the conductivity, processing cost and high-frequency performance requirements, copper, silver, aluminum, tungsten, gold and other materials can be selected as the materials of the metal layer 113 and the metal hole 112, and the metal hole 112 can be set by filling with metal slurry.

[0047] Optionally, considering that the gaps between the multiple metal holes 112 will cause the loss of electromagnetic wave signals, theoretically, the smaller the gaps between the metal holes 112, the smaller the loss. However, considering the actual processing difficulty, a smaller gap that meets the processing requirements can be selected to design the positions of the multiple metal holes 112.

[0048] It should be noted that the material of the dielectric layer 111 may include highly airtight and high-temperature resistant materials such as alumina ceramics, quartz or silicon. Taking alumina ceramics as an example, its airtightness can reach 1E-11Pa·m³ / s to reduce the adverse situation of air leakage caused by poor airtightness of the material, and the high-temperature resistance of the material can meet the use requirements of various high-temperature scenarios.

[0049] Optionally, even if the metal holes 112 provided on the dielectric layer 111 are filled with metal to form solid holes, there is still a risk of air leakage due to the gaps between the materials. Therefore, to further optimize the airtightness of the filter structure 100 having multiple filter layers 110, the metal holes 112 between two adjacent filter layers 110 are staggered in the stacking direction A. The metal holes 112 of the filter layer 110 can be sealed at the top and bottom of the two adjacent filter layers 110, thereby reducing the risk of air leakage caused by the metal holes 112 of the multiple filter layers 110 being in the same position in the stacking direction A.

[0050] For example, adjacent filter layers 110 are isolated by the metal layer 113. The top of the first filter layer 110 can be sealed based on the metal layer 113. The top of the second filter layer 110 can be sealed based on the metal layer 113 between the first and second filter layers 110. The bottom of the second filter layer 110 can be sealed based on the metal layer 113 between the second and third filter layers 110. In addition, the area on the first filter layer 110 is divided into the area of ​​the metal hole 112 as a. Taking the non-metal hole 112 area b as an example, the metal holes 112 of the second filter layer 110 can all be set in the b area, so that the metal holes 112 in the two adjacent filter layers 110 have no overlapping areas in the layer stacking direction A, thereby reducing the risk of air leakage. Moreover, in the third filter layer 110 and the first filter layer 110, since the second filter layer 110 has been set for isolation, the metal holes 112 of the third filter layer 110 can also be set in the a area, or in other areas other than the b area.

[0051] Optionally, in order to enable the signal to be transmitted normally through the filtering structure 100, the shape of the connection window 120 can be set based on the waveguide interface 210. For example, when the waveguide interface 210 is a rectangular shape of c×d, the connection window 120 is also set to a rectangular shape of c×d. The connection window 120 can also be set to other shapes larger than c×d or smaller than c×d. The specific size of the connection window 120 can be designed according to the actual filtering function requirements of the filtering structure 100.

[0052] It should be noted that the connection window 120 does not include the metal hole 112 and the metal layer 113, so that the signal can pass through the connection window 120 normally. In addition, considering that the gap between the metal holes 112 is limited by the difficulty of processing, the gap between the metal holes 112 in the multi-layer filter layer 110 will cause corresponding losses. The filter structure 100 cannot be completely equivalent to the waveguide 200, resulting in a narrow bandwidth. The gap between the metal holes 112 will also cause resonance. Therefore, an equivalent filter structure 100 can be provided in the connection window 120. The equivalent filter structure 100 can be a metal surface structure provided based on the E-plane and H-plane of the resonant cavity within the filter structure 100. The E-plane is the plane where the electric field intensity vector (E) lies, and the H-plane is the plane where the magnetic field intensity vector (H) lies, and the E-plane and the H-plane are perpendicular. Based on the simulation results of the signal bandwidth, metal surface structures of corresponding size and shape can be selected and provided on the E-plane and H-plane of the resonant cavity to enable the filter structure 100 to have a wider signal bandwidth. A corresponding equivalent filtering structure 100 may be provided in the connection window 120 , so as to broaden the bandwidth and reduce the resonance effect through the equivalent filtering structure 100 .

[0053] For example, the area of ​​the metal surface inserted in the E-plane or H-plane can be smaller than the size of the waveguide interface 210. Since the connection window 120 has a multi-layer structure, the multi-layer windows can also be set to different sizes to achieve a filtering effect through the joint action of the multi-layer windows.

[0054] Optionally, see Figure 3 , Figure 3 This is a schematic diagram of the structure of another filter layer provided in an embodiment of the present application. Considering that the higher the number of layers in the filter structure 100, the narrower the bandwidth, a coupling structure 114 may be provided in the area surrounding the connection window 120 in the inner layer of the multi-layer filter layer 110. The coupling structure 114 may include a blank area hollowed out from the metal layer 113. Furthermore, in the stacking direction A, the coupling structure 114 does not overlap with the metal holes 112 in two adjacent filter layers 110, thereby reducing the risk of air leakage in the stacking direction A caused by the overlap of the coupling structure 114 and the metal holes 112.

[0055] It should be noted that the structural parameters of the coupling structure 114 can be determined based on the simulation results of the signal bandwidth, wherein the structural parameters may include: the number, setting layer and area size of the coupling structure 114. For example, the coupling structure 114 can be set to a circular ring shape, and the number of circular rings, the area of ​​the ring band and the specific situation of whether it is set in a certain filter layer 110 or certain filter layers 110 can be determined according to the simulation results of the signal bandwidth so that the filtering structure 100 has a wider signal bandwidth. Figure 3 Only one feasible embodiment of arranging 10 annular coupling structures 114 around the connection window 120 is shown, and other numbers and shapes of coupling structures 114 are not described in detail.

[0056] For example, to meet high airtightness requirements, a low-loss, high-dielectric-constant alumina ceramic can be selected to form the substrate of the filter layer 110. The resonant cavity of the rectangular waveguide 200 is constructed through vias in the alumina ceramic and the metal layer 113. A connection window 120 is opened in the metal layer 113 to serve as a coupling port. Transmission loss and reflection are inevitable in the filter structure 100. The specific resonant cavity length and Q factor (quality factor) can be determined through simulation based on the mode and resonant frequency of the filter structure 100. Once the resonant cavity length and Q factor are determined, they are incorporated into the filter structure 100. Although smaller spacing between metal holes 112 in the resonant cavity improves transmission and reflection, considering the actual manufacturing difficulty and to ensure greater transmission in the multi-layer filter layer 110, it is recommended to select an appropriate diameter and spacing for the metal holes 112, and to enlarge the resonant cavity at the center corresponding to the waveguide interface 210. The gaps between the outer metal holes 112 can also be reduced, multiple rows of metal holes 112 can be added to form a periodic structure, an electromagnetic bandgap structure can be constructed to suppress the propagation of electromagnetic wave signals, and the window size of the connection window 120 of the metal layer 113 on the resonant cavity can be set to achieve the filtering function.

[0057] Optionally, see Figure 4 , Figure 4 A structural diagram of another signal transmission structure provided in an embodiment of the present application. Among them, the waveguide 200 may include: a waveguide interface 210 and a waveguide body 220. Considering the image of the waveguide interface 210 being connected to both ends of the filter structure 100, the waveguide interface 210 may include a first interface 211 and a second interface 212. The waveguide body 220 is arranged in the airtight cavity 300, the waveguide body 220 is connected to the first interface 211, the first interface 211 is welded to the first end of the connection window 120, and the second interface 212 is welded to the second end of the connection window 120. The second interface 212 is aligned with the receiving area of ​​the external receiving chip away from the non-connection end of the connection window 120, and the waveguide length of the waveguide body 220 and the first interface 211 is determined based on the vibration frequency of the target gas. The electromagnetic wave signal can be transmitted to the external receiving chip through the transmission path of the waveguide body 220, the first interface 211, the filter structure 100, and the second interface 212. Furthermore, the overall waveguide length of the waveguide body 220 and the first interface 211 is determined based on the vibration frequency of the target gas disposed in the airtight cavity 300 , so as to design a suitable waveguide length to achieve better signal transmission efficiency and receiving power.

[0058] Optionally, the number of waveguide interfaces 210 can be set according to actual transmission requirements.

[0059] For example, since the vibration and rotation modes in molecules are fixed and have high frequency stability and accuracy, in order to obtain the vibration frequency of the molecule, it is necessary to make the resonant frequency of the waveguide 200 correspond to the molecular area. Taking the target gas as carbon sulfide gas, the vibration frequency of its molecules is 231GHz. In order to make the resonant frequency of the gas chamber in the waveguide 200 correspond to the molecular area, the WR4 and WR3 rectangular waveguides can be selected, both of which can meet the requirements. The decay constant of the mode is known as: ; in, is the waveguide wall surface resistance, is the size of the waveguide wide side, b is the size of the waveguide narrow side, , is the wave number in the filling medium, is the intrinsic impedance of the medium filling the waveguide. Therefore, a larger WR4 waveguide can be selected to minimize attenuation. After the waveguide 200 is filled with gas, it is sealed and connected to the filter structure 100 via the waveguide interface 210, forming a sealed structure and a sealed encapsulated gas chamber. The volume of the WR4 waveguide cavity is related to the gas properties. In the gas chamber, the received signal power varies according to the gas absorption intensity and can be expressed as: ; in, is the reflected signal power, is the peak absorption coefficient at the center of the spectral line, is the path loss coefficient, and L is the length of the air chamber. In order to maximize the received signal power, Derivative, its first-order derivative has only one zero-crossing point and is monotonically decreasing, that is, the extreme value of the first-order derivative is where the received signal power is maximum. The detailed calculation is as follows: ; ; ; ; ; ; For example, the OCS gas 2.0544 , waveguide loss About 0.2677dB / cm( ), we can get L as 14cm.

[0060] Although the vibration frequency of the molecule during resonance is close to the resonant frequency of the waveguide 200, they are not strictly equal. The lasing oscillation frequency (here the laser is a gas laser) is related to both, but is not strictly equal to them. To determine this frequency, in principle, a method similar to that of classical radio oscillation frequency can be used, that is, the phase shift equation between the signal fed back from the oscillator and the input signal is solved to satisfy the phase condition for oscillation (the phase shift in one round trip is The oscillation frequency is obtained by taking the signal frequency (integer multiples of ) of the waveguide 200 cavity into account. When the resonant frequency of the waveguide 200 cavity is inconsistent with the frequency of the molecular absorption line, the oscillation frequency of the other system is only affected by a pulling effect. The degree of pulling is determined by the frequency detuning between the two systems and the ratio of their Q values. In a highly stable frequency standard, the frequency stability of both the molecular absorption line and the cavity is crucial. Therefore, considering factors such as molecular absorption, terahertz wave attenuation, frequency shift, and short stability, a waveguide length of 140.325 mm is selected to eliminate frequency shift and optimize short stability, thereby minimizing signal attenuation and reflection, and improving signal transmission efficiency and quality.

[0061] Optionally, see Figure 5 , Figure 5 A schematic diagram of the structure of a waveguide body provided in an embodiment of the present application, wherein, considering that the waveguide may be long, in order to reduce the size of the space occupied by the waveguide 200, the waveguide body 220 may be bent, for example Figure 5 The various curved structures shown, such as the meandering structure, spiral structure, serpentine structure, and overlapping structures of meandering, spiral, and serpentine structures, can reduce the overall volume of the signal transmission structure through the curved waveguide structure, meeting various integration and miniaturization requirements.

[0062] It should be noted that in order to allow the target gas set in the airtight cavity 300 to normally enter the waveguide 200, the waveguide body 220 can be provided with air holes 221. The number, size, shape, and location of the air holes 221 can be set according to actual needs. For example, three circular air holes can be set on a side of the waveguide body 220 to transmit the target gas in the airtight cavity 300 to the interior of the waveguide 200, thereby transmitting the signal based on the target gas within the waveguide 200. In addition, considering the curved structure of the waveguide body 220, local reflection will occur at the bending change. Therefore, corresponding step structures 222 and chamfers 223 can be provided. The step structure 222 can be provided at the beginning of the waveguide 200, and the chamfer 223 can be provided at the bend. The number of steps in the step structure 222 and the angle of the chamfer 223 can be set according to the actual size of the airtight cavity 300 to reduce reflection.

[0063] An embodiment of the present application further provides a molecular clock, which may include: a transmitting chip, a receiving chip, and the signal transmission structure described in any of the above embodiments.

[0064] The transmitting chip transmits electromagnetic wave signals to the signal transmission structure, which transmits the electromagnetic wave signals. The receiving chip receives the electromagnetic wave signals transmitted by the signal transmission structure. A compact and airtight signal transmission structure can be installed within the molecular clock to transmit the electromagnetic wave signals from the transmitting chip to the receiving chip. The receiving chip then analyzes and processes the received signals, effectively improving the stability and accuracy of the molecular clock.

[0065] For example, the transmitting chip may be a CMOS spectrum transmitting chip, and correspondingly, the receiving chip may be a CMOS spectrum receiving chip, etc. The electromagnetic wave signal may be a terahertz frequency band signal or other types of signals.

[0066] In addition, the various parts in the various embodiments of the present application can be integrated together to form an independent part, or each part can exist separately, or two or more parts can be integrated to form an independent part.

[0067] The foregoing is merely an embodiment of the present application and is not intended to limit the scope of protection of the present application. Various modifications and variations are possible for those skilled in the art. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present application shall be included within the scope of protection of the present application. It should be noted that similar reference numerals and letters represent similar items in the following figures. Therefore, once an item is defined in one figure, it does not need to be further defined or explained in subsequent figures.

[0068] The above is only a specific implementation method of the present application, but the scope of protection of the present application is not limited thereto. Any technician familiar with this technical field can easily think of changes or replacements within the technical scope disclosed in this application, which should be covered by the scope of protection of the present application.

[0069] It should be noted that, in this document, relational terms such as first and second, etc., are used only to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any actual relationship or order between these entities or operations. Moreover, the terms "include", "comprises", or any other variants thereof are intended to cover non-exclusive inclusion, so that a process, article, or device comprising a series of elements includes not only those elements, but also other elements not explicitly listed, or elements inherent to such process, article, or device. In the absence of further limitations, the elements defined by the statement "includes..." do not exclude the presence of other identical elements in the process, article, or device comprising the elements.

Claims

1. A signal transmission structure, characterized in that: The signal transmission structure includes: a filtering structure, a waveguide and an airtight cavity; Wherein, the filtering structure comprises multiple filter layers, and a connection window corresponding to the waveguide interface of the waveguide is provided in the filtering structure; A target gas corresponding to a molecular clock is provided in the airtight cavity, the waveguide is provided in the airtight cavity, and the waveguide interface extends outside the airtight cavity; In the stacking direction of the layers of the filtering structure, the waveguide interface is connected to the connection window in parallel with the stacking direction of the layers.

2. The signal transmission structure according to claim 1, characterized in that: in, The number of layers of the filter structure is determined based on simulation results of the vibration frequency and signal bandwidth of the target gas; The resonant frequency of the filtering structure is a frequency range including the vibration frequency.

3. The signal transmission structure according to claim 2, characterized in that: in, The thickness of each filter layer is determined based on the resonant frequency; The filter layers have a thickness-symmetrical structure based on the intermediate layer.

4. The signal transmission structure according to claim 1, wherein: in, Each filter layer includes: a dielectric layer, a metal hole and a metal layer; In the stacking direction of the layers, the metal layer is arranged on the top and bottom of the dielectric layer, and the metal layer is sealed and connected to the dielectric layer; The dielectric layer has a plurality of through holes whose central axes are parallel to the stacking direction of the layers, and the through holes are filled with metal to form the metal holes; Wherein, the material of the dielectric layer includes alumina ceramics, quartz or silicon.

5. The signal transmission structure according to claim 4, characterized in that: in, In the stacking direction of the layers, the metal holes between two adjacent filter layers are in a staggered structure.

6. The signal transmission structure according to claim 4, characterized in that: in, The connection window does not have the metal hole and the metal layer; An equivalent filtering structure is provided in the connection window; the equivalent filtering structure is provided based on the E-surface and H-surface of the resonant cavity.

7. The signal transmission structure according to claim 4, characterized in that: in, In the inner layer of the multi-layer filter layer, a coupling structure is provided in the peripheral area surrounding the connection window; The coupling structure includes a blank area obtained by hollowing out the metal layer; In the stacking direction of the layers, the coupling structure does not overlap with the metal holes in two adjacent filter layers; The structural parameters of the coupling structure are determined based on the simulation results of the signal bandwidth; wherein the structural parameters include: the number, arrangement layers and area size of the coupling structure.

8. The signal transmission structure according to any one of claims 1 to 7, characterized in that: in, The waveguide includes: the waveguide interface and the waveguide body; the waveguide interface includes a first interface and a second interface; The waveguide body is disposed in the airtight cavity, the waveguide body is connected to the first interface, the first interface is welded to the first end of the connection window, and the second interface is welded to the second end of the connection window; The non-connection end of the second interface away from the connection window is aligned with the receiving area of ​​the external receiving chip; The waveguide length between the waveguide body and the first interface is determined based on the vibration frequency of the target gas.

9. The signal transmission structure according to claim 8, characterized in that: in, The waveguide body is bent; The waveguide body is provided with a step structure, chamfers and air holes; The air hole is used to transmit the target gas in the airtight cavity to the inside of the waveguide.

10. A molecular clock, characterized in that The molecular clock comprises: a transmitting chip, a receiving chip and a signal transmission structure according to any one of claims 1 to 9; The transmitting chip is used to transmit electromagnetic wave signals to the signal transmission structure; The signal transmission structure is used to transmit the electromagnetic wave signal; The receiving chip is used to receive the electromagnetic wave signal transmitted by the signal transmission structure.

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