Radio frequency vertical transition structure

Abstract

The invention discloses a radio frequency vertical transition structure, and relates to the technical field of electronic components. In three stacked structures from top to bottom formed by multiple layers of stacked aluminum nitride ceramic circuit substrates, a microstrip line is arranged on the first stacked structure, a strip line is clamped in the second stacked structure, and a central vertical via hole and surrounding quasi-coaxial metal through holes are formed in the first stacked structure and the second stacked structure. A vertical interconnection center conductor is arranged in the center vertical via hole, the microstrip line and the strip line are connected through the vertical interconnection center conductor, a microstrip line-vertical transition-strip line conversion structure is formed, a conical air cavity is formed in the position, corresponding to the vertical transition part, of the third stacking structure, and the conical air cavity and the vertical transition part form a resonance effect; and ultra-low loss of vertical interconnection can be realized.

Description

Technical Field

[0001] The invention relates to the technical field of electronic components, and in particular to a radio frequency vertical transition structure. Background Art

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

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

[0004] However, the current RF vertical transition structure has a large insertion loss. Summary of the invention

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

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

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

[0008] A multi-layer stacked aluminum nitride ceramic circuit substrate forms a first stacking structure, a second stacking structure and a third stacking structure from top to bottom;

[0009] A microstrip line, the head end of which is arranged at the edge of the surface layer of the first stacking structure, and the end of which is located in the middle area of ​​the surface layer of the first stacking structure; a central vertical via hole is arranged at the end of the microstrip line in the first stacking structure and the second stacking structure, a plurality of quasi-coaxial metal through holes are arranged around the central vertical via hole, a vertical interconnection center conductor is arranged in the central vertical via hole, and a quasi-coaxial metal column is arranged in the quasi-coaxial metal through hole;

[0010] A microstrip line equivalent grounding metal layer is arranged between the first stacking structure and the second stacking structure;

[0011] The stripline is sandwiched in the second stacking structure and connected to the microstrip line through a vertically interconnected central conductor to form a microstrip line-vertical transition-stripline conversion structure;

[0012] The stripline equivalent grounding metal layer is arranged between the second stacking structure and the third stacking structure;

[0013] The conical air cavity is arranged in the third stacking structure and is located below the vertical transition portion. The conical air cavity is used to form a resonance effect with the vertical transition portion to reduce insertion loss.

[0014] Optionally, the aluminum nitride ceramic circuit substrate adopts 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 6 layers of aluminum nitride ceramic circuit substrates, the microstrip line corresponds to 2 layers of aluminum nitride ceramic circuit substrates, the vertical transition part and the strip line correspond to 4 layers of aluminum nitride ceramic circuit substrates; and the tapered air cavity corresponds to 9 layers of aluminum nitride ceramic circuit substrates.

[0016] Optionally, the microstrip line equivalent grounding metal layer is provided with an opening in a vertical transition portion.

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

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

[0019] Optionally, the stripline equivalent ground metal layer is provided with a window in a vertical transition portion.

[0020] Optionally, the conical air cavity is a three-level cavity structure, including 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 depths of the three are the same.

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

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

[0023] At least one of the above technical solutions adopted in the embodiments of the present invention can achieve the following beneficial effects:

[0024] The present invention forms three stacked structures from top to bottom by multi-layer stacked aluminum nitride ceramic circuit substrates, wherein a microstrip line is arranged on the first stacked structure, a strip line is sandwiched in the second stacked structure, a central vertical via hole and surrounding quasi-coaxial metal through holes are arranged on the first stacked structure and the second stacked structure, a vertical interconnection center conductor is arranged in the central vertical via hole, the microstrip line and the strip line are connected by the vertical interconnection center conductor, and a conversion structure of microstrip line-vertical transition-strip line is formed, and a conical air cavity is arranged at the third stacked structure corresponding to the vertical transition part, so that the conical air cavity and the vertical transition part form a resonance effect, thereby realizing ultra-low loss of vertical interconnection. BRIEF DESCRIPTION OF THE DRAWINGS

[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 a vertical transition overall structure of a tapered air cavity of an aluminum nitride ceramic provided by the present invention;

[0027] Figure 2 A schematic diagram of 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 A schematic side view of an integral radio frequency vertical transition structure provided by the present invention;

[0029] Figure 4 A schematic diagram of the radio frequency transmission characteristics of a radio frequency vertical transition structure provided by the present invention. DETAILED DESCRIPTION

[0030] In order to make the purpose, technical solution and advantages of the present invention clearer, the technical solution of the present invention will be clearly and completely described below in conjunction with the specific embodiments of the present invention and the corresponding drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

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

[0032] At present, the insertion loss problem of ordinary RF vertical transition structure in the millimeter wave frequency band is particularly prominent, and has become a major limitation of RF three-dimensional stacking performance. In addition, according to the wavelength theory of the millimeter wave frequency band, its component size is often small, especially after three-dimensional stacking, its size is more limited, and its heat dissipation problem has also become a major contradiction. Aluminum nitride ceramics have very excellent heat dissipation performance, so it is particularly important to solve the low insertion loss vertical transition problem in aluminum nitride ceramic substrates. Traditional RF vertical transition structure materials generally choose low temperature co-fired ceramics (Low Temperature Co-fired Ceramic, LTCC) and high temperature co-fired ceramics (High Temperature Co-fired Ceramic, HTCC), and some use aluminum nitride ceramics. The insertion loss of the circuit substrate RF vertical transition structure is relatively large.

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

[0034] Depend on Figure 1 to Figure 3 It can be seen that the RF vertical transition structure in the present invention may include a microstrip line 1, a quasi-coaxial metal through hole 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 interconnected central conductor 6, a strip line 7, a microstrip line equivalent grounding metal layer 8, a strip line equivalent grounding metal layer 9, a first stacking structure 10, a second stacking structure 11, a third stacking structure 12 and a tapered air cavity 13.

[0035] The multi-layer stacked aluminum nitride ceramic circuit substrate forms a first stacking structure 10 , a second stacking structure 11 and a third stacking structure 12 from top to bottom.

[0036] The microstrip line 1 has its head end arranged at the edge of the surface layer of the first stacked structure 10 , and its tail end located in the middle area of ​​the surface layer of the first stacked structure 10 .

[0037] In the first stacking structure and the second stacking structure, a central vertical via 4 is arranged at the end of the microstrip line 1, a plurality of quasi-coaxial metal through holes 3 are arranged around the central vertical via 4, a vertical interconnected central conductor 6 is arranged in the central vertical via 4, and a quasi-coaxial metal column is arranged in the quasi-coaxial metal through hole 3.

[0038] Furthermore, in one or more embodiments of the present invention, the RF vertical transition structure in the present invention may also include a frequency tuning unit 2, which is arranged on the microstrip line 1 and is spaced 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] The microstrip line equivalent grounding metal layer 8 is arranged between the first stacking structure 10 and the second stacking structure 11 .

[0040] The stripline 7 is sandwiched in the second stacking structure 11 and connected to the microstrip line 1 through the vertical interconnection center conductor 6 to form a conversion structure of microstrip line-vertical transition-stripline.

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

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

[0043] The present invention forms three stacked structures from top to bottom by multi-layer stacked aluminum nitride ceramic circuit substrates, wherein a microstrip line is arranged on the first stacked structure, a strip line is sandwiched in the second stacked structure, a central vertical via hole and surrounding quasi-coaxial metal through holes are arranged on the first stacked structure and the second stacked structure, a vertical interconnection center conductor is arranged in the central vertical via hole, the microstrip line and the strip line are connected by the vertical interconnection center conductor, and a conversion structure of microstrip line-vertical transition-strip line is formed, and a conical air cavity is arranged at the third stacked structure corresponding to the vertical transition part, so that the conical air cavity and the vertical transition part form a resonance effect, thereby realizing ultra-low loss of vertical interconnection.

[0044] The present invention innovatively adopts 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. At the same time, the conical structure is convenient for lamination and sintering, which can greatly improve the long-term reliability of the resonant cavity. Its resonant air structure reduces the dielectric loss of the transition structure and thus reduces the insertion loss of the transition structure. The present invention can be extended to higher frequencies, so that the high-temperature ceramic transition structure can cover the Ka band to the V band. In the Ka band, especially in narrowband point frequency applications, the insertion loss of this transmission structure is only 0.18dB, which can improve the insertion loss of the traditional vertical interconnection structure by more than 0.4dB.

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

[0046] In addition, in one or more embodiments of the present invention, when the microstrip line is converted to a vertical transition, it is necessary to load the vertical interconnection center conductor 6 and the frequency tuning unit 2, and there is a certain electromagnetic field coupling relationship between the frequency tuning unit 2 and the microstrip line ground (GND) 8 opening diameter and the vertical interconnection center conductor 6. That is, the microstrip line equivalent grounding metal layer 8 is provided with an opening in the vertical transition part, and the opening diameter can be set based on the size of the frequency tuning unit 2 and the diameter of the vertical interconnection center conductor 6. The quasi-coaxial equivalent diameter and the size of the frequency tuning unit need to be comprehensively considered. There is a certain electromagnetic field adaptation relationship between the radius of the quasi-coaxial metal through hole 3 and the opening of the microstrip line GND metal layer 8, and the diameter of the quasi-coaxial metal through hole 3 can be approximately 0.9-0.95 times the opening of the microstrip line GND metal layer 8.

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

[0048] The RF vertical transition structure is converted into a stripline structure, and a conical air resonant cavity is designed at the bottom of the vertical transition. The resonant cavity is in a conical shape as a whole, and the entire cavity forms a resonance effect with the vertical conversion part to achieve a low insertion loss function. At the same time, the distance between the bottom of the vertical conversion structure and the resonant cavity needs to be designed according to the electromagnetic field relationship. The closer the distance, the lower the insertion loss. However, the long-term reliability of the air cavity needs to be considered. Therefore, the distance between the bottom of the vertical transition part and the conical air cavity 13 can be two layers of aluminum nitride ceramic circuit substrates. The overall height of the conical air cavity 13 can be about 1 / 2 times the transmission wavelength.

[0049] Furthermore, in one or more embodiments of the present invention, the microstrip line equivalent grounding metal layer 8 is provided with a window in the vertical transition portion, and the diameter of the window can be set based on the size of the frequency tuning unit 2 and the diameter of the vertical interconnection center conductor 6. The window size is directly related to the radius of the quasi-vertical interconnection 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 grounding metal layer 8 can be 0.7mm. The stripline requires a grounding structure both above and below, and a window needs to be designed at the junction of the stripline and the vertical conversion. The metal window size is directly related to the resonant air cavity and the vertical conversion equivalent metal column. In the present invention, the window diameter of the stripline equivalent grounding metal layer 9 can be 0.9mm.

[0050] In addition, in one or more embodiments of the present invention, the conical air cavity 13 may be a three-level cavity structure, including a first cavity, a second cavity, and a third cavity from bottom to top. Among them, 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 depths of the three are the same. The diameter of the third cavity can be set based on the window size of the stripline equivalent grounding metal layer 9. Specifically, the diameter of the third cavity can be 0.6 to 0.8 times the diameter of the window 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 width of the microstrip line can be 0.23 mm, the width of the tuning unit line 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 through hole 3 can be 0.65 mm. The diameter of the central vertical via can be 0.12 mm, which is directly related to the operating frequency. In the Ka band, this dimension is 0.1 mm-0.15 mm.

[0052] And design the stripline width 7 and the ceramic dielectric thickness 11. The stripline 7 width can be 0.12mm, and the dielectric layer thickness can be 0.4mm. The stripline width and the ceramic dielectric layer thickness are calculated according to the characteristic impedance. A pad needs to be added to the transition section of the vertical through hole for reliability matching, and the pad diameter of the stripline transition part can be 0.2mm. Design the microstrip line GND metal layer 8 opening, and its opening diameter can be 0.7mm. There is a certain proportional relationship between its opening size and the radius of the quasi-coaxial metal through hole 3 structure. Design the stripline equivalent grounding metal layer 9 opening size, and its diameter can be 0.9mm. There is a proportional relationship between its size and the diameter of the third air cavity, which has been listed above.

[0053] And the depth and step distribution of the conical air cavity 13 are designed. The depth of the conical air cavity is 0.6 mm, which is the thickness of 6 layers of ceramic 12. The conical air cavity is designed to have a gradual diameter and depth, and this gradual diameter and depth are directly related to the operating frequency. Generally, its depth is at least 1 / 5 of the wavelength of the operating frequency, generally 1 / 5-1 / 2. The conical air cavity can be set to more step structures, and its step structure can improve the Q value of the vertical transition circuit. Considering engineering factors, the step structure can be set to three steps in one or more embodiments, and its diameters are 1 mm, 0.8 mm, and 0.6 mm, respectively, and their depths are 0.2 mm, respectively.

[0054] Figure 4 A schematic diagram of the radio frequency transmission characteristics of a radio frequency vertical transition structure provided by the present invention. Figure 4 The S parameter index curve of the transition structure of the present invention is given in the figure. The horizontal axis in the figure is the frequency, ranging from 26GHz-40GHz, and the vertical axis is the dB value, ranging from 0dB to -35dB. The curve marked as dB(S(2,1)) is the insertion loss curve, and the insertion loss at the marked point is only 0.17dB. The curve marked as dB(S(1,1)) is the return loss curve, and the minimum return loss at the marked point is 24.9dB.

[0055] The invention has frequency expansion applicability, and the relationship between the corresponding frequency wavelength and the size of the conical air resonant cavity is given in the article. The invention can solve the heat dissipation problem of three-dimensional interconnected millimeter wave components with higher integration. The structure of the invention can be extended and applied to other transition structures involving microstrip line-vertical transition-strip line, such as low-temperature ceramics.

[0056] It should also be noted that the terms “comprises”, “includes” or any other variations thereof in the present invention are intended to cover non-exclusive inclusion, that is, in addition to the elements listed in the present invention, other elements not explicitly listed may also be included.

[0057] The various embodiments of the present invention are described in a progressive manner, and the same or similar parts between the various embodiments can be referred to each other, and each embodiment focuses on the differences from other embodiments.

[0058] The above description is only an embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent substitution, improvement, etc. made within the spirit and principle of the present invention should be included in the scope of the claims of the present invention.

Claims

1. A radio frequency vertical transition structure, characterized in that: include: A multi-layer stacked aluminum nitride ceramic circuit substrate forms a first stacking structure (10), a second stacking structure (11) and a third stacking structure (12) from top to bottom; A microstrip line (1), the head end of which is arranged at an edge of a surface layer of the first stacked structure (10), and the tail end is located in a middle area of ​​the surface layer of the first stacked structure (10); A central vertical via hole (4) is provided at the end of the microstrip line (1) in the first stacking structure and the second stacking structure, a plurality of quasi-coaxial metal through holes (3) are provided around the central vertical via hole (4), a vertical interconnected central conductor (6) is provided in the central vertical via hole, and a quasi-coaxial metal column is provided in the quasi-coaxial metal through hole (3); A microstrip line equivalent grounding metal layer (8) is arranged between the first stacking structure (10) and the second stacking structure (11); The stripline (7) is sandwiched in the second stacking structure (11) and connected to the microstrip line (1) via a vertically interconnected central conductor (6) to form a microstrip line-vertical transition-stripline conversion structure; The stripline equivalent grounding metal layer (9) is arranged between the second stacking structure (11) and the third stacking structure (12); The tapered air cavity (13) is arranged in the third stacked structure (12) and is located below the vertical transition portion. The tapered air cavity (13) is used to form a resonance effect with the vertical transition portion to reduce insertion loss.

2. The radio frequency vertical transition structure according to claim 1, characterized in that: The aluminum nitride ceramic circuit substrate adopts 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 according to claim 2, characterized in that: The transition structure corresponds to 6 layers of aluminum nitride ceramic circuit substrates, the microstrip line (1) corresponds to 2 layers of aluminum nitride ceramic circuit substrates, the vertical transition part and the strip line (7) correspond to 4 layers of aluminum nitride ceramic circuit substrates; and the tapered air cavity (13) corresponds to 9 layers of aluminum nitride ceramic circuit substrates.

4. The radio frequency vertical transition structure according to claim 1, characterized in that: The microstrip line equivalent grounding metal layer (8) is provided with an opening in a vertical transition portion.

5. The radio frequency vertical transition structure according to claim 1, characterized in that: The distance between the bottom of the vertical transition portion and the conical air cavity (13) is two layers of aluminum nitride ceramic circuit substrates.

6. The radio frequency vertical transition structure according to 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 according to claim 1, characterized in that: The stripline equivalent grounding metal layer (9) is provided with a window at a vertical transition portion.

8. The radio frequency vertical transition structure according to claim 7, characterized in that: The conical air cavity (13) is a three-level 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 have the same depth.

9. The radio frequency vertical transition structure according to claim 8, characterized in that: The diameter of the third cavity is 0.6 to 0.8 times the diameter of the window of the stripline equivalent grounding metal layer (9).

10. The radio frequency vertical transition structure according to claim 8, characterized in that: The radio frequency vertical transition structure further comprises: a frequency tuning unit (2), embedded in the microstrip line (1) and spaced apart from the central vertical via hole (4) by a preset distance, the microstrip line (1) and the frequency tuning unit (2) forming a surface metal structure (5).

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