A high coupling coefficient on-chip transformer with a sandwich-like structure
By employing a sandwich-like three-dimensional spiral secondary coil design in the on-chip transformer, the problems of low coupling coefficient and large area are solved, realizing an on-chip transformer with high coupling coefficient and small area, which is suitable for radio frequency integrated circuits.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- HANGZHOU DIANZI UNIV
- Filing Date
- 2026-04-01
- Publication Date
- 2026-05-29
Smart Images
Figure CN122117614A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of integrated circuit technology, and in particular to a high-coupling-coefficient on-chip transformer with a sandwich-like structure using multi-layer metal stacking, suitable for signal conversion in radio frequency front-end circuits, such as the conversion between single-ended signals and differential signals. Background Technology
[0002] On-chip transformers are key passive components in radio frequency integrated circuits. They are widely used in circuits such as power amplifiers, low-noise amplifiers, mixers, and voltage-controlled oscillators to achieve impedance matching, signal coupling, and single-ended to differential signal conversion.
[0003] Existing on-chip transformers mostly employ a design with two single-layer planar coils coupled together. The primary and secondary coils are spaced apart by different metal layers along the axial direction, resulting in a low coupling coefficient and significant energy transfer losses. In applications requiring high impedance conversion ratios, the ratio of inductance between the primary and secondary coils used in the impedance transformation transformer is large. Traditional on-chip transformer structures struggle to simultaneously achieve a large inductance ratio and a high coupling coefficient. Furthermore, the on-chip integrated spiral inductor in traditional structures occupies a large area, leading to high manufacturing costs.
[0004] Chinese patent application CN104103636A discloses a structure that splits the primary and secondary coils into multiple parallel sub-coils using an annular dividing slot, aiming to reduce skin effect and proximity effect. However, in this scheme, the primary and secondary coils are basically on the same plane or have the same structure, resulting in low magnetic flux coupling efficiency in the vertical direction. Another prior art, such as CN102522402A, reduces substrate loss by placing a substrate shielding layer under the transformer, but does not improve the coupling coefficient between the primary and secondary coils.
[0005] With the continuous increase in wireless communication frequencies, the demand for on-chip transformers with high inductance ratios, high coupling coefficients, and small area is becoming increasingly urgent. Traditional planar or two-layer structures cannot simultaneously meet the requirements of high coupling coefficients and small layout area. Summary of the Invention
[0006] The present invention aims to provide a sandwich-like structure high coupling coefficient on-chip transformer to solve the technical problems of low coupling coefficient and large layout area of existing on-chip transformers.
[0007] To achieve the above objectives, the present invention provides a sandwich-like structure high coupling coefficient on-chip transformer, comprising: at least three metal layers, namely a first metal layer, a second metal layer, and a third metal layer; a primary coil disposed on the second metal layer, having a number of turns N of 1; and a secondary coil in a three-dimensional spiral shape, having a number of turns M≥2, and distributed on the first metal layer, the second metal layer, and the third metal layer; the secondary coil surrounds the primary coil in the vertical direction to form a sandwich-like structure; the first terminal and the second terminal of the secondary coil are both disposed on the outermost winding of the first metal layer; and the first terminal and the second terminal of the primary coil are both disposed on the outermost winding of the second metal layer.
[0008] Furthermore, the windings of the secondary coil are sequentially electrically connected between the first metal layer, the second metal layer, and the third metal layer through through-holes, forming a continuous three-dimensional spiral path. Specifically: the first metal layer includes a first metal wire and a second metal wire; the second metal layer includes a first metal wire and a second metal wire; the third metal layer includes a first metal wire; the first metal wire is wound once, and one end of the first metal wire is electrically connected to one end of the first metal wire in the second metal layer through a first through-hole; the second... The first metal wire of the three metal layers is wound once; the other end of the first metal wire of the second metal layer is electrically connected to one end of the first metal wire of the third metal layer through the second through hole; the other end of the first metal wire of the third metal layer is electrically connected to one end of the second metal wire of the second metal layer through the third through hole; the other end of the second metal wire of the second metal layer is electrically connected to one end of the second metal wire of the first metal layer through the fourth through hole; the second metal layer is also provided with a third metal wire, which is wound once, and is the primary coil. The third metal wire is insulated from the first metal wire of the second metal layer and the second metal wire of the second metal layer.
[0009] Furthermore, the second metal layer is also provided with a third metal wire, which is wound once to form a primary coil. The third metal wire is insulated from the first metal wire and the second metal wire of the second metal layer.
[0010] Furthermore, it also includes a fourth metal layer, to which the secondary coil extends to increase the number of turns of the secondary coil.
[0011] Furthermore, the secondary coil has 6 turns, and the primary coil has 1 turn; the first metal layer includes a first metal wire, a second metal wire, and a third metal wire; the second metal layer includes a first metal wire, a second metal wire, a third metal wire, a fourth metal wire, a fifth metal wire, and a sixth metal wire; the third metal layer includes a first metal wire, a second metal wire, and a third metal wire; the fourth metal layer includes a first metal wire; the primary coil is disposed on the second metal layer, is composed of the fourth metal wire and the fifth metal wire of the second metal layer connected in parallel, and is wound with one turn; the three-dimensional helical path of the secondary coil includes: the first metal wire of the first metal layer is wound... One turn, connected to the first metal wire of the second metal layer through the first through hole; the first metal wire of the second metal layer is connected to the first metal wire of the third metal layer through the second through hole; the first metal wire of the third metal layer is wound with two turns and connected to the second metal wire of the second metal layer through the fourth through hole; the second metal wire of the second metal layer is connected to the second metal wire of the first metal layer through the fifth through hole; the second metal wire of the first metal layer is wound with two turns and connected to the third metal wire of the second metal layer through the sixth through hole; the third metal wire of the second metal layer is connected to the second metal wire of the third metal layer through the seventh through hole; the second metal wire of the third metal layer is wound with one turn and connected to the first metal wire of the fourth metal layer through the third through hole; the first metal wire of the fourth metal layer is connected to the third metal wire of the first metal layer through the eighth through hole, the third metal wire of the third metal layer, the ninth through hole, the sixth metal wire of the second metal layer, and the tenth through hole.
[0012] Furthermore, the metal wires of the primary coil and the secondary coil are wound in a shape that is square, octagonal, or circular.
[0013] Furthermore, the metal wires of the first metal layer and the second metal layer are wound at intervals.
[0014] Furthermore, the metal wires in the same layer of the secondary coil are insulated from each other, and the metal wires of the primary coil and the secondary coil are insulated from each other in the intermediate metal layer.
[0015] Furthermore, the on-chip transformer is integrated into a standard CMOS process.
[0016] Compared with the prior art, the present invention has the following beneficial effects: 1. Significantly improved coupling coefficient: By placing the primary coil in the middle layer (M2) and distributing the secondary coils in the bottom layer (M1) and top layer (M3) to form a three-dimensional spiral structure, the primary coil is "sandwiched" in the middle by the secondary coil in the vertical direction, which greatly enhances the electromagnetic field coupling between the primary and secondary coils and effectively improves the coupling coefficient k.
[0017] 2. Reduced layout area: By using vertical three-dimensional spiral traces, a smaller chip area is occupied compared to planar structures with the same number of turns, thus improving integration density.
[0018] 3. High flexibility: The number of turns of the secondary coil can be adjusted by extending to more metal layers (such as M4) to adapt to the application requirements of different impedance transformation ratios. Attached Figure Description
[0019] Figure 1 This is an exploded three-dimensional schematic diagram of the structure of Embodiment 1 of the present invention.
[0020] Figure 2 This is a three-dimensional schematic diagram of the structure of Embodiment 1 of the present invention.
[0021] Figure 3 This is another three-dimensional schematic diagram of the structure of Embodiment 1 of the present invention.
[0022] Figure 4 This is a side view of the structure of Embodiment 1 of the present invention.
[0023] Figure 5 This is a planar and three-dimensional exploded view of Embodiment 2 of the present invention when M=6.
[0024] Figure 6 This is a three-dimensional schematic diagram of the secondary coil when M=6 in Embodiment 2 of the present invention.
[0025] Figure 7 This is a three-dimensional schematic diagram of the primary coil when M=6 in Embodiment 2 of the present invention.
[0026] Figure 8 This is a side view of Embodiment 2 of the present invention when M=6. Detailed Implementation
[0027] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be described in detail below with reference to the accompanying drawings and specific embodiments.
[0028] This invention discloses a high-coupling-coefficient on-chip transformer with a sandwich-like structure, comprising three metal layers (top, middle, and bottom). The primary coil is disposed in the middle metal layer, and the secondary coil, arranged in a three-dimensional spiral, is distributed across the top, middle, and bottom layers, sandwiching the primary coil in the middle to form a sandwich-like structure. The primary coil has N turns (N=1), and the secondary coil has M turns (M≥2), with the turns ratio N:M adjustable to suit different applications. The secondary coil windings can be connected in parallel to reduce resistance losses. This layout enhances the electromagnetic field coupling between the primary and secondary coils, effectively increasing the coupling coefficient k; simultaneously, the downward-pointing vertical three-dimensional spiral design improves space utilization, effectively reducing the transformer's layout area.
[0029] The manufacturing process of this invention is compatible with standard CMOS processes, which helps to reduce costs.
[0030] Example 1 (see Figures 1 to 4 ) This embodiment provides a sandwich-like structure high-coupling-coefficient on-chip transformer, implemented using standard CMOS technology, employing three layers of metal wiring: a first metal layer M1 (top layer), a second metal layer M2 (middle layer), and a third metal layer M3 (bottom layer). The metal wires of both the primary and secondary coils are wound in a square, octagonal, or circular pattern.
[0031] Primary coil: Located on the second metal layer M2, with 1 turn N. The first terminal A11 and the second terminal B11 of the primary coil are both located on the outermost winding of the second metal layer M2.
[0032] Secondary coil: A top-down three-dimensional spiral structure is formed using a first metal layer M1, a second metal layer M2, and a third metal layer M3. In this embodiment, the secondary coil has 2 turns M.
[0033] The first metal layer M1 includes a first metal line 11 and a second metal line 12; the second metal layer M2 includes a first metal line 21 and a second metal line 22; the third metal layer M3 includes a first metal line 31.
[0034] The specific connection method of the secondary coil (e.g.) Figure 3 Figure 4 (as shown) The first metal wire 11 of the first metal layer is wound once (i.e., one turn), and one end of the first metal wire 11 of the first metal layer is electrically connected to one end of the first metal wire 21 of the second metal layer through the first through hole V11.
[0035] The third metal layer has one loop (i.e., one turn) of the first metal wire 31. The other end of the first metal line 21 of the second metal layer is electrically connected to one end of the first metal line 31 of the third metal layer through the second through hole V21; the other end of the first metal line 31 of the third metal layer is electrically connected to one end of the second metal line 22 of the second metal layer through the third through hole V31.
[0036] The other end of the second metal line 22 of the second metal layer is electrically connected to one end of the second metal line 12 of the first metal layer through the fourth through hole V22.
[0037] The second metal layer is also provided with a third metal wire 23. The third metal wire 23 is wound once, which is the primary coil. The third metal wire 23 is insulated from the first metal wire 21 and the second metal wire 22 of the second metal layer to avoid short circuit.
[0038] Through the above connections, the secondary coil forms a complete three-dimensional spiral path from the top layer → middle layer → bottom layer → middle layer → top layer. The first terminal A12 and the second terminal B12 of the secondary coil are both located on the outermost turn of the top layer (first metal layer M1).
[0039] With the above structure, the primary coil is surrounded in the vertical direction by the top and bottom parts of the secondary coil, forming a "sandwich-like" structure, which significantly enhances the magnetic flux coupling between the primary and secondary coils.
[0040] Example 2 (see Figures 5 to 8 ) The difference between this embodiment and Embodiment 1 is that the secondary coil has more turns (M=6), and in order to lead out the metal wire, it is further extended to a fourth metal layer (M4).
[0041] like Figure 8 As shown, the secondary coil uses four metal wiring layers: the first metal layer M1, the second metal layer M2, the third metal layer M3, and the fourth metal layer M4, to form a more complex three-dimensional spiral path, thus realizing a 6-turn coil.
[0042] Primary coil: Located on the second metal layer M2, with 1 turn. The first terminal A11 and the second terminal B11 of the primary coil are both located on the outermost winding of the second metal layer M2.
[0043] Secondary coil: It adopts a top-down three-dimensional spiral structure formed by the first metal layer M1, the second metal layer M2, the third metal layer M3, and the fourth metal layer M4.
[0044] The first metal layer M1 includes a first metal line 11, a second metal line 12, and a third metal line 13; the second metal layer M2 includes a first metal line 21, a second metal line 22, a third metal line 23, a fourth metal line 24, a fifth metal line 25, and a sixth metal line 26; the third metal layer M3 includes a first metal line 31, a second metal line 32, and a third metal line 33; and the fourth metal layer M4 includes a first metal line 41.
[0045] like Figure 6As shown, the first metal wire 11 of the first metal layer is wound one turn. One end of the first metal wire 11 of the first metal layer is electrically connected to one end of the first metal wire 21 of the second metal layer through the first through-hole V11. The other end of the first metal wire 21 of the second metal layer is electrically connected to one end of the first metal wire 31 of the third metal layer through the second through-hole V21. The first metal wire 31 of the third metal layer is wound two turns. The other end of the first metal wire 31 of the third metal layer is electrically connected to one end of the second metal wire 22 of the second metal layer through the fourth through-hole V22. The other end of the second metal wire 22 of the second metal layer is electrically connected to one end of the second metal wire 12 of the first metal layer through the fifth through-hole V12. The second metal wire 12 of the first metal layer is wound two turns. The other end of the second metal wire 12 in the first metal layer is electrically connected to one end of the third metal wire 23 in the second metal layer through the sixth through-hole V13. The other end of the third metal wire 23 in the second metal layer is electrically connected to one end of the second metal wire 32 in the third metal layer through the seventh through-hole V23. The second metal wire 32 in the third metal layer is wound one turn. The other end of the second metal wire 32 in the third metal layer is electrically connected to one end of the first metal wire 41 in the fourth metal layer through the third through-hole V31. The other end of the first metal wire 41 in the fourth metal layer is electrically connected to one end of the third metal wire 13 in the first metal layer through the eighth through-hole V32, the third metal wire 33 in the third metal layer, the ninth through-hole V24, the sixth metal wire 26 in the second metal layer, and the tenth through-hole V14. The fourth metal wire 24 and the fifth metal wire 25 in the second metal layer are radially arranged, which are the primary coils. The fourth metal wire 24 and the fifth metal wire 25 in the second metal layer are connected in parallel to form one turn. The metal wires in the same layer are insulated from each other.
[0046] The first terminal A12 and the second terminal B12 of the secondary coil are both located on the outermost turn of the top layer M1 winding.
[0047] like Figure 5 As shown, the metal wires of the first metal layer M1 and the second metal layer M2 are wound at intervals on the top surface, which improves compactness while maintaining the spacing between the metal layers in the same layer.
[0048] This embodiment is suitable for applications requiring a large inductance ratio (high impedance transformation ratio) while maintaining a high coupling coefficient.
[0049] The on-chip transformer structure provided by this invention is fully compatible with standard CMOS processes, requires no additional process steps, and can be widely used in various radio frequency integrated circuits, demonstrating significant industrial applicability.
[0050] It is understood that the present invention has been described through some embodiments, and those skilled in the art will recognize that various changes or equivalent substitutions can be made to these features and embodiments without departing from the spirit and scope of the invention. Furthermore, under the teachings of the present invention, these features and embodiments can be modified to adapt to specific situations and materials without departing from the spirit and scope of the invention. Therefore, the present invention is not limited to the specific embodiments disclosed herein, and all embodiments falling within the scope of the claims of this application are within the protection scope of the present invention.
Claims
1. A sandwich-like structure high coupling coefficient on-chip transformer, characterized in that, include: The system comprises at least three metal layers: a first metal layer (M1), a second metal layer (M2), and a third metal layer (M3); a primary coil disposed on the second metal layer (M2) with a turn count N of 1; and a secondary coil, which is a three-dimensional spiral with a turn count M ≥ 2, distributed on the first metal layer (M1), the second metal layer (M2), and the third metal layer (M3); the secondary coil surrounds the primary coil in the vertical direction, forming a sandwich-like structure; the first terminal (A12) and the second terminal (B12) of the secondary coil are both disposed on the outermost winding of the first metal layer (M1); and the first terminal (A11) and the second terminal (B11) of the primary coil are both disposed on the outermost winding of the second metal layer (M2).
2. The sandwich-like high-coupling-coefficient on-chip transformer according to claim 1, characterized in that, The windings of the secondary coil are sequentially electrically connected through through-holes between the first metal layer (M1), the second metal layer (M2), and the third metal layer (M3) to form a continuous three-dimensional spiral path. Specifically, the first metal layer (M1) includes a first metal wire (11) and a second metal wire (12); the second metal layer (M2) includes a first metal wire (21) and a second metal wire (22); the third metal layer (M3) includes a first metal wire (31); the first metal wire (11) of the first metal layer is wound once, and one end of the first metal wire (11) is electrically connected to one end of the first metal wire (21) of the second metal layer through a first through-hole (V11); the third metal layer... The first metal wire (31) is wound once; the other end of the first metal wire (21) of the second metal layer is electrically connected to one end of the first metal wire (31) of the third metal layer through the second through hole (V21); the other end of the first metal wire (31) of the third metal layer is electrically connected to one end of the second metal wire (22) of the second metal layer through the third through hole (V31); the other end of the second metal wire (22) of the second metal layer is electrically connected to one end of the second metal wire (12) of the first metal layer through the fourth through hole (V22); the second metal layer is also provided with a third metal wire (23), which is wound once and is the primary coil. The third metal wire (23) is insulated from the first metal wire (21) and the second metal wire (22) of the second metal layer.
3. The on-chip transformer with a high coupling coefficient and a sandwich-like structure according to claim 2, characterized in that, The second metal layer (M2) is also provided with a third metal wire (23). The third metal wire (23) is wound once, which is the primary coil. The third metal wire (23) is insulated from the first metal wire (21) of the second metal layer and the second metal wire (22) of the second metal layer.
4. The sandwich-like high-coupling-coefficient on-chip transformer according to claim 1, characterized in that, It also includes a fourth metal layer (M4), to which the secondary coil is further extended to increase the number of turns of the secondary coil.
5. The sandwich-like high-coupling-coefficient on-chip transformer according to claim 4, characterized in that, The secondary coil has 6 turns, and the primary coil has 1 turn; the first metal layer (M1) includes a first metal wire (11), a second metal wire (12), and a third metal wire (13); the second metal layer (M2) includes a first metal wire (21), a second metal wire (22), a third metal wire (23), a fourth metal wire (24), a fifth metal wire (25), and a sixth metal wire (26); the third metal layer (M3) The third metal layer (M2) includes a first metal wire (31), a second metal wire (32), and a third metal wire (33); the fourth metal layer (M4) includes a first metal wire (41); the primary coil is disposed on the second metal layer (M2), and is composed of a fourth metal wire (24) and a fifth metal wire (25) of the second metal layer connected in parallel, and is wound with one turn; the three-dimensional spiral path of the secondary coil includes: the first metal wire (11) of the first metal layer is wound with one turn, and is connected to the second metal layer through a first through hole (V11). The first metal wire (21) of the second metal layer is connected; the first metal wire (21) of the second metal layer is connected to the first metal wire (31) of the third metal layer through the second through hole (V21); the first metal wire (31) of the third metal layer is wound with two turns and connected to the second metal wire (22) of the second metal layer through the fourth through hole (V22); the second metal wire (22) of the second metal layer is connected to the second metal wire (12) of the first metal layer through the fifth through hole (V12); the second metal wire (12) of the first metal layer is wound with two turns and connected to the third metal wire (21) of the second metal layer through the sixth through hole (V13). 23) Connection; the third metal wire (23) of the second metal layer is connected to the second metal wire (32) of the third metal layer through the seventh through hole (V23); the second metal wire (32) of the third metal layer is wound with one turn and connected to the first metal wire (41) of the fourth metal layer through the third through hole (V31); the first metal wire (41) of the fourth metal layer is connected to the third metal wire (13) of the first metal layer through the eighth through hole (V32), the third metal wire (33) of the third metal layer, the ninth through hole (V24), the sixth metal wire (26) of the second metal layer, and the tenth through hole (V14).
6. The sandwich-like high-coupling-coefficient on-chip transformer according to claim 1, characterized in that, The metal wires of the primary coil and the secondary coil are wound in a shape that is square, octagonal, or circular.
7. The sandwich-like high-coupling-coefficient on-chip transformer according to claim 1, characterized in that, The metal wires of the first metal layer (M1) and the second metal layer (M2) are wound at intervals.
8. The sandwich-like high-coupling-coefficient on-chip transformer according to claim 1, characterized in that, The metal wires in the same layer of the secondary coil are insulated from each other, and the metal wires of the primary coil and the secondary coil are insulated from each other in the intermediate metal layer (M2).
9. The sandwich-like high-coupling-coefficient on-chip transformer according to claim 1, characterized in that, The on-chip transformer is integrated in a standard CMOS process.