A radio frequency vertical transition structure

Abstract

This invention discloses a radio frequency vertical transition structure, relating to the field of electronic component technology. The invention comprises three stacked structures formed from top to bottom on a multilayered aluminum nitride ceramic circuit substrate. A microstrip line is disposed on the first stacked structure, and a stripline is sandwiched in the second stacked structure. A central vertical via and surrounding quasi-coaxial metal vias are disposed on both the first and second stacked structures. A vertical interconnect center conductor is disposed within the central vertical via, connecting the microstrip line and the stripline, forming a microstrip line-vertical transition-stripline conversion structure. A conical air cavity is disposed at the vertical transition portion of the third stacked structure, creating a resonant effect between the conical air cavity and the vertical transition portion, thereby achieving ultra-low loss in the vertical interconnect.

Description

Technical Field

[0001] This invention relates to the field of electronic components technology, and in particular to a radio frequency vertical transition structure. Background Technology

[0002] Currently, with the widespread application of wireless communication systems and radar systems in the millimeter-wave band, miniaturization of microwave and millimeter-wave systems has become a trend, and their main three-dimensional stacked structure adopts a radio frequency vertical transition structure.

[0003] In the prior art, in order to improve heat dissipation performance, traditional radio frequency vertical transition structure materials are generally selected from low-temperature co-fired ceramics (LTCC) and high-temperature co-fired ceramics (HTCC), and some use aluminum nitride ceramics to form radio frequency vertical transition structures.

[0004] However, current RF vertical transition structures have relatively high insertion losses. Summary of the Invention

[0005] The present invention provides a radio frequency vertical transition structure to partially solve the problems existing in the prior art.

[0006] The present invention adopts the following technical solution:

[0007] This invention provides a radio frequency vertical transition structure, comprising:

[0008] A multilayer stacked aluminum nitride ceramic circuit board forms a first stacked structure, a second stacked structure, and a third stacked structure from top to bottom;

[0009] The microstrip line has its first end located on the edge of the surface layer of the first stacked structure and its end located in the middle region of the surface layer of the first stacked structure. A central vertical via is provided at the end of the microstrip line in the first stacked structure and the second stacked structure. Multiple quasi-coaxial metal vias are provided around the central vertical via. A vertical interconnecting central conductor is provided in the central vertical via, and a quasi-coaxial metal pillar is provided in the quasi-coaxial metal via.

[0010] A microstrip line equivalent ground metal layer is disposed between the first stacked structure and the second stacked structure;

[0011] The stripline, sandwiched in the second stacked structure, is connected to the microstrip line through a vertical interconnect center conductor, forming a microstrip line-vertical transition-stripline conversion structure.

[0012] An equivalent grounding metal layer for the stripline is disposed between the second and third stacked structures;

[0013] A conical air cavity is disposed in the third stack structure and located below the vertical transition section. The conical air cavity is used to form a resonant effect with the vertical transition section to reduce insertion loss.

[0014] Optionally, the aluminum nitride ceramic circuit board uses an aluminum nitride ceramic substrate with a dielectric constant of 8.25, a single layer thickness of 0.1 mm, and a total of 15 layers.

[0015] Optionally, the transition structure corresponds to a 6-layer aluminum nitride ceramic circuit board, the microstrip line corresponds to a 2-layer aluminum nitride ceramic circuit board, the vertical transition portion and the strip line correspond to a 4-layer aluminum nitride ceramic circuit board, and the conical air cavity corresponds to a 9-layer aluminum nitride ceramic circuit board.

[0016] Optionally, the microstrip line equivalent ground metal layer has an opening at the vertical transition portion.

[0017] Optionally, the distance between the bottom of the vertical transition portion and the conical air cavity is two layers of aluminum nitride ceramic circuit board.

[0018] Optionally, the overall height of the conical air cavity is 0.5 times the transmission wavelength.

[0019] Optionally, the stripline equivalent grounding metal layer has a window at the vertical transition section.

[0020] Optionally, the conical air cavity has a three-stage cavity structure, comprising a first cavity, a second cavity, and a third cavity from bottom to top; the diameter of the first cavity is larger than that of the second cavity, the diameter of the second cavity is larger than that of the third cavity, and the three cavities have the same depth.

[0021] Optionally, the diameter of the third cavity is 0.6 to 0.8 times the opening diameter of the equivalent grounding metal layer of the strip.

[0022] Optionally, the RF vertical transition structure further includes: a frequency tuning unit embedded in the microstrip line, spaced at a preset distance from the central vertical via, wherein the microstrip line and the frequency tuning unit form a surface metal structure.

[0023] The at least one technical solution adopted in the embodiment of the present invention can achieve the following beneficial effects:

[0024] This invention utilizes three stacked structures formed from top to bottom on a multilayer stacked aluminum nitride ceramic circuit substrate. A microstrip line is disposed on the first stacked structure, and a stripline is sandwiched in the second stacked structure. A central vertical via and surrounding quasi-coaxial metal vias are disposed on both the first and second stacked structures. A vertical interconnect center conductor is disposed within the central vertical via, connecting the microstrip line and the stripline to form a microstrip line-vertical transition-stripline conversion structure. A conical air cavity is disposed at the vertical transition portion of the third stacked structure, creating a resonant effect between the conical air cavity and the vertical transition portion, thus achieving ultra-low loss in vertical interconnection. Attached Figure Description

[0025] The drawings described herein are used to provide a further understanding of the present invention and constitute a part of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation of the present invention. In the drawings:

[0026] Figure 1 A three-dimensional schematic diagram of the overall structure of a cone-shaped air cavity vertical transition of aluminum nitride ceramic provided by the present invention;

[0027] Figure 2 A schematic diagram illustrating the matching relationship between a surface microstrip line, a frequency tuning unit, and a quasi-coaxial structure provided by the present invention;

[0028] Figure 3 This is a side view schematic diagram of an integral radio frequency vertical transition structure provided by the present invention;

[0029] Figure 4 This is a schematic diagram of the radio frequency transmission characteristics of a radio frequency vertical transition structure provided by the present invention. Detailed Implementation

[0030] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below in conjunction with specific embodiments and corresponding drawings. Obviously, the described embodiments are only a part of the embodiments of this invention, and not all of them. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0031] The technical solutions provided by various embodiments of the present invention are described in detail below with reference to the accompanying drawings.

[0032] Currently, the insertion loss problem of conventional RF vertical transition structures is particularly prominent in the millimeter-wave band, becoming a major limitation on the performance of RF 3D stacking. Furthermore, according to the wavelength theory of the millimeter-wave band, the component size is often small, especially after 3D stacking, where the size becomes even more limited, making heat dissipation a major challenge. Aluminum nitride ceramics possess excellent heat dissipation performance, making it crucial to solve the problem of low insertion loss vertical transitions within aluminum nitride ceramic substrates. Traditional RF vertical transition structure materials generally select low-temperature co-fired ceramics (LTCC) and high-temperature co-fired ceramics (HTCC), with some using aluminum nitride ceramics. However, the insertion loss of the RF vertical transition structure on the circuit board is relatively high.

[0033] Figure 1 This is a three-dimensional schematic diagram of the overall structure of a cone-shaped air cavity with vertical transition of aluminum nitride ceramic provided by the present invention. Figure 2 This is a schematic diagram illustrating the matching relationship between a surface microstrip line, a frequency tuning unit, and a quasi-coaxial structure, as provided by the present invention. Figure 3 This is a side view schematic diagram of an overall radio frequency vertical transition structure provided by the present invention.

[0034] Depend on Figures 1-3 As can be seen, the radio frequency vertical transition structure in this invention may include a microstrip line 1, a quasi-coaxial metal via 3, a central vertical via 4, a surface metal structure 5 formed by the microstrip line 1 and the frequency tuning unit 2, a vertical interconnect center conductor 6, a stripline 7, a microstrip line equivalent ground metal layer 8, a stripline line equivalent ground metal layer 9, a first stacked structure 10, a second stacked structure 11, a third stacked structure 12, and a conical air cavity 13.

[0035] Among them, the multilayer stacked aluminum nitride ceramic circuit substrate forms a first stacked structure 10, a second stacked structure 11 and a third stacked structure 12 from top to bottom.

[0036] The microstrip line 1 has its first end located on the edge of the surface layer of the first stacked structure 10, and its last end located in the middle region of the surface layer of the first stacked structure 10.

[0037] In the first and second stacked structures, a central vertical via 4 is provided at the end of the microstrip line 1. A plurality of quasi-coaxial metal vias 3 are provided around the central vertical via 4. A vertical interconnecting central conductor 6 is provided in the central vertical via 4, and a quasi-coaxial metal pillar is provided in the quasi-coaxial metal via 3.

[0038] Furthermore, in one or more embodiments of the present invention, the radio frequency vertical transition structure of the present invention may further include a frequency tuning unit 2, which is disposed on the microstrip line 1 and spaced at a preset distance from the central vertical via 4. The microstrip line 1 and the frequency tuning unit 2 form a surface metal structure 5 for adjusting the operating frequency.

[0039] A microstrip line equivalent ground metal layer 8 is disposed between the first stacked structure 10 and the second stacked structure 11.

[0040] The stripline 7 is sandwiched in the second stacked structure 11 and is connected to the microstrip line 1 through the vertical interconnect center conductor 6, forming a microstrip line-vertical transition-stripline conversion structure.

[0041] The stripline equivalent grounding metal layer 9 is disposed between the second stack structure 11 and the third stack structure 12.

[0042] A conical air cavity 13 is disposed in the third stacked structure 12 and located below the vertical transition portion. The conical air cavity 13 is used to form a resonant effect with the vertical transition portion to reduce insertion loss.

[0043] This invention utilizes three stacked structures formed from top to bottom on a multilayer stacked aluminum nitride ceramic circuit substrate. A microstrip line is disposed on the first stacked structure, and a stripline is sandwiched in the second stacked structure. A central vertical via and surrounding quasi-coaxial metal vias are disposed on both the first and second stacked structures. A vertical interconnect center conductor is disposed within the central vertical via, connecting the microstrip line and the stripline to form a microstrip line-vertical transition-stripline conversion structure. A conical air cavity is disposed at the vertical transition portion of the third stacked structure, creating a resonant effect between the conical air cavity and the vertical transition portion, thus achieving ultra-low loss in vertical interconnection.

[0044] This invention innovatively employs a conical resonant cavity transition transmission structure. The size of the conical resonant cavity is closely related to the transmission frequency of the RF vertical transition structure. Simultaneously, the conical structure facilitates lamination and sintering, significantly improving the long-term reliability of the resonant cavity. Its resonant air structure reduces dielectric losses in the transition structure, thereby lowering its insertion loss. This invention can be extended to higher frequencies, enabling high-temperature ceramic transition structures to cover the Ka-band to V-band. In the Ka-band, especially in narrowband point-frequency applications, this transmission structure exhibits an insertion loss of only 0.18 dB, which is more than 0.4 dB better than the insertion loss of traditional vertical interconnect structures.

[0045] Furthermore, in one or more embodiments of the present invention, the aluminum nitride ceramic circuit board may use an aluminum nitride ceramic substrate with a dielectric constant of 8.25, a single layer thickness of 0.1 mm, and a total of 15 layers, with a total thickness of 1.5 mm. Specifically, the transition structure uses a total of 6 layers of aluminum nitride ceramic, the microstrip line 1 corresponds to 2 layers of aluminum nitride ceramic substrate with a thickness of 0.2 mm, the vertical transition portion and the strip line 7 correspond to 4 layers of aluminum nitride ceramic substrate with a thickness of 0.4 mm, and the conical air cavity 13 corresponds to 9 layers of aluminum nitride ceramic substrate with a thickness of 0.9 mm.

[0046] Furthermore, in one or more embodiments of the present invention, during the microstrip line to vertical transition, a vertical interconnect center conductor 6 and a frequency tuning unit 2 need to be loaded. The frequency tuning unit 2 has a certain electromagnetic field coupling relationship with the microstrip line ground (GND) 8 aperture diameter and the vertical interconnect center conductor 6. That is, the microstrip line equivalent ground metal layer 8 has an aperture in the vertical transition section, and the aperture diameter can be set based on the size of the frequency tuning unit 2 and the diameter of the vertical interconnect center conductor 6. The quasi-coaxial equivalent diameter and the size of the frequency tuning unit need to be considered comprehensively. The radius of the quasi-coaxial metal via 3 and the microstrip line GND metal layer 8 aperture have a certain electromagnetic field compatibility relationship; the diameter of the quasi-coaxial metal via 3 can be approximately 0.9-0.95 times the size of the microstrip line GND metal layer 8 aperture.

[0047] Furthermore, in one or more embodiments of the present invention, the distance between the bottom of the vertical transition portion and the conical air cavity 13 is positively correlated with the insertion loss.

[0048] The RF vertical transition structure is converted to a stripline structure. A conical air resonant cavity is designed at the bottom layer of the vertical transition. The resonant cavity has an overall conical shape, and the entire cavity resonates with the vertical transition section to achieve low insertion loss. The distance between the bottom of the vertical transition structure and the resonant cavity needs to be designed according to electromagnetic field relationships; the closer the distance, the lower the insertion loss. However, the long-term reliability of the air cavity must be considered. Therefore, the distance between the bottom of the vertical transition section and the conical air cavity 13 can be two layers of aluminum nitride ceramic circuit board. The overall height of the conical air cavity 13 can be approximately half the transmission wavelength.

[0049] Furthermore, in one or more embodiments of the present invention, the microstrip line equivalent ground metal layer 8 has a window at the vertical transition portion. The diameter of this window can be set based on the size of the frequency tuning unit 2 and the diameter of the vertical interconnect center conductor 6. The window size is directly related to the radius of the quasi-vertical interconnect center conductor 6 and the size of the frequency tuning unit. In the present invention, the diameter of the opening size of the microstrip line equivalent ground metal layer 8 can be 0.7 mm. Grounding structures are required both above and below the stripline. A window needs to be designed at the junction of the stripline and the vertical transition. The size of the metal window is directly related to the resonant air cavity and the vertical transition equivalent metal pillar. In the present invention, the diameter of the window of the stripline equivalent ground metal layer 9 can be 0.9 mm.

[0050] Furthermore, in one or more embodiments of the present invention, the conical air cavity 13 may be a three-stage cavity structure, comprising a first cavity, a second cavity, and a third cavity from bottom to top. The diameter of the first cavity is larger than that of the second cavity, the diameter of the second cavity is larger than that of the third cavity, and all three cavities have the same depth. The diameter of the third cavity may be set based on the opening size of the stripline equivalent grounding metal layer 9. Specifically, the diameter of the third cavity may be 0.6 to 0.8 times the opening diameter of the stripline equivalent grounding metal layer 9.

[0051] Furthermore, in one or more embodiments of the present invention, the width of the microstrip line 1 and the width and length of the tuning unit 2 can be set. The microstrip line width can be 0.23 mm, the tuning unit line width can be 0.3 mm, and the length can be 0.35 mm. The distance between the frequency tuning unit 2 and the vertical via 4 can be 0.12 mm. The equivalent radius of the quasi-coaxial metal via 3 can be 0.65 mm. The diameter of the center vertical via can be 0.12 mm. This dimension is directly related to the operating frequency; in the Ka band, this dimension is 0.1 mm-0.15 mm.

[0052] The design includes the stripline width 7 and the ceramic dielectric thickness 11. The stripline width 7 can be 0.12 mm, and the dielectric layer thickness can be 0.4 mm. The stripline width and ceramic dielectric layer thickness are calculated based on the characteristic impedance. A pad needs to be added to the transition section of the vertical via for reliability matching. The pad diameter for the stripline transition section can be 0.2 mm. The microstrip line GND metal layer 8 opening is designed, with an opening diameter of 0.7 mm. Its opening size has a certain proportional relationship with the structural radius of the quasi-coaxial metal via 3. The stripline equivalent grounding metal layer 9 opening size is designed, with a diameter of 0.9 mm. Its size has a proportional relationship with the diameter of the third air cavity, as listed above.

[0053] Furthermore, a conical air cavity with a depth of 13 and a stepped distribution is designed. The depth of the conical air cavity is 12 times the thickness of 6 ceramic layers, which is 0.6 mm. The conical air cavity is designed with a gradually changing diameter and depth, which are directly related to the operating frequency. Generally, its depth is at least 1 / 5 of the wavelength of the operating frequency, typically 1 / 5 to 1 / 2. The conical air cavity can be configured with more stepped structures, which can improve the Q value of the vertical transition circuit. Considering engineering factors, in one or more embodiments, the stepped structure can be configured as a three-step structure with diameters of 1 mm, 0.8 mm, and 0.6 mm, and each with a depth of 0.2 mm.

[0054] Figure 4 This is a schematic diagram of the radio frequency transmission characteristics of a radio frequency vertical transition structure provided by the present invention. Figure 4 The figure shows the S-parameter index curves of the transition structure of this invention. The horizontal axis represents frequency, ranging from 26 GHz to 40 GHz, and the vertical axis represents dB values, ranging from 0 dB to -35 dB. The curve labeled dB(S(2,1)) is the insertion loss curve, with an insertion loss of only 0.17 dB at the labeled point. The curve labeled dB(S(1,1)) is the return loss curve, with a minimum return loss of 24.9 dB at the labeled point.

[0055] This invention has frequency extension applicability, and the relationship between the corresponding frequency wavelength and the size of the conical air resonator is given in the text. This invention can solve the heat dissipation problem of higher integration three-dimensional interconnected millimeter-wave components. The structure of this invention can be extended to other transition structures involving microstrip lines-vertical transitions-strip lines, such as low-temperature ceramics.

[0056] It should also be noted that the terms "comprising," "including," or any other variations thereof in this invention are intended to cover non-exclusive inclusion, that is, in addition to the elements listed in this invention, other elements not expressly listed may also be included.

[0057] The various embodiments in this invention are described in a progressive manner. For the same or similar parts between the various embodiments, please refer to each other. Each embodiment focuses on describing the differences from other embodiments.

[0058] The above description is merely an embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principle of the present invention should be included within the scope of the claims of the present invention.

Claims

1. A radio frequency vertical transition structure, characterized in that, include: A multilayer stacked aluminum nitride ceramic circuit substrate forms a first stacked structure (10), a second stacked structure (11), and a third stacked structure (12) from top to bottom; The microstrip line (1) has its first end located on the edge of the surface layer of the first stacked structure (10) and its end located in the middle region of the surface layer of the first stacked structure (10). In the first stacked structure and the second stacked structure, a central vertical via (4) is provided at the end of the microstrip line (1), and a plurality of quasi-coaxial metal vias (3) are provided around the central vertical via (4). A vertical interconnecting central conductor (6) is provided in the central vertical via, and a quasi-coaxial metal pillar is provided in the quasi-coaxial metal via (3). A microstrip line equivalent ground metal layer (8) is disposed between the first stacked structure (10) and the second stacked structure (11); A stripline (7) is sandwiched in the second stacked structure (11) and connected to the microstrip line (1) through a vertical interconnect center conductor (6) to form a microstrip line-vertical transition-stripline conversion structure; the vertical interconnect center conductor (6) and its surrounding part are the vertical transition part; A stripline equivalent grounding metal layer (9) is disposed between the second stacked structure (11) and the third stacked structure (12); A conical air cavity (13) is disposed in the third stacked structure (12) and located below the vertical transition section. The conical air cavity (13) is used to form a resonant effect with the vertical transition section to reduce insertion loss.

2. The radio frequency vertical transition structure as described in claim 1, characterized in that, The aluminum nitride ceramic circuit board uses an aluminum nitride ceramic substrate with a dielectric constant of 8.25, a single layer thickness of 0.1 mm, and a total of 15 layers.

3. The radio frequency vertical transition structure as described in claim 2, characterized in that, The transition structure corresponds to a 6-layer aluminum nitride ceramic circuit board, the microstrip line (1) corresponds to a 2-layer aluminum nitride ceramic circuit board, the vertical transition portion and the strip line (7) correspond to a 4-layer aluminum nitride ceramic circuit board; the conical air cavity (13) corresponds to a 9-layer aluminum nitride ceramic circuit board.

4. The radio frequency vertical transition structure as described in claim 1, characterized in that, The microstrip line equivalent ground metal layer (8) has an opening in the vertical transition section.

5. The radio frequency vertical transition structure as described in claim 1, characterized in that, The distance between the bottom of the vertical transition section and the conical air cavity (13) is two layers of aluminum nitride ceramic circuit board.

6. The radio frequency vertical transition structure as described in claim 1, characterized in that, The overall height of the conical air cavity (13) is 0.5 times the transmission wavelength.

7. The radio frequency vertical transition structure as described in claim 1, characterized in that, The strip equivalent grounding metal layer (9) has a window at the vertical transition section.

8. The radio frequency vertical transition structure as described in claim 7, characterized in that, The conical air cavity (13) is a three-level cavity structure, consisting of a first cavity, a second cavity, and a third cavity from bottom to top; the diameter of the first cavity is larger than that of the second cavity, the diameter of the second cavity is larger than that of the third cavity, and the three cavities have the same depth.

9. The radio frequency vertical transition structure as described in claim 8, characterized in that, The diameter of the third cavity is 0.6 to 0.8 times the opening diameter of the strip equivalent grounding metal layer (9).

10. The radio frequency vertical transition structure as described in claim 8, characterized in that, The radio frequency vertical transition structure further includes: a frequency tuning unit (2), embedded on the microstrip line (1), spaced at a preset distance from the central vertical via (4), and the microstrip line (1) and the frequency tuning unit (2) form a surface metal structure (5).

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