High current integrated circuit based transformers

Abstract

An integrated circuit transformer (150) is formed with: a primary winding (91) located at least in a first winding layer having a first thickness; a secondary winding (92) located at least in the first winding layer and having a first center point at a first side of the transformer and two secondary ends at a second, opposite side of the transformer; and a first center tap feed line (81) located in an upper metal layer along an axis of symmetry of the transformer, the upper metal layer having a second thickness at least equal to the first thickness of the first winding layer, wherein the first center tap feed line has a direct electrical connection to the first center point in the secondary winding.

Description

Technical Field

[0001] The present invention generally relates to integrated circuit inductive devices. In one aspect, the present invention relates to integrated circuit transformer devices and methods of making and / or operating the same. Background Art

[0002] Advances in integrated circuit technology that provide thick top metal back-end layers have enabled the fabrication of high-quality inductive components (e.g., spiral inductors, transformers, and microstrip lines) capable of operating at GHz frequencies suitable for high-performance, low-cost, high-band applications such as automotive radar sensors. Specifically, 28nm node CMOS process technology that forms multiple metal conductor layers (including copper layers of increasing thickness capped by one or more thick aluminum back-end metal layers) can be used to fabricate integrated circuit transformers with two inductively coupled windings that provide the ability to transform impedance levels and provide galvanic isolation for high-frequency signals, which is attractive for inter-stage impedance matching in differential power amplifier stages of new 78GHz automotive radar products. Using existing methods, integrated circuit transformers can form two interleaved metal coils in one or more of the thickest upper layers, each comprising an integer number of approximately circular turns. This can be advantageous because the top metal layer in integrated circuit process technology has the greatest thickness and, therefore, the lowest resistivity, and is therefore the layer most suitable for transformer windings, which typically carry the highest currents. However, in such scaled-down process technologies, the reduction in maximum supply voltage also requires an increase in drain current to maintain the same RF output power level from the transformer circuit, thereby increasing the current load on other parts of the transformer circuit, which can reduce the circuit's lifespan through electromigration damage that accumulates over time. There are also integrated circuit transformer designs that use coils of the same type and diameter formed in different metal layers and connected in parallel, but these designs reduce coil series resistance at the expense of increased inter-coil capacitance. Additionally, there are existing inductor designs that interleave coil windings to maximize the inductive coupling factor (K) and, therefore, gain, and also add a third coil, where only the third coil has a center tap point configured to couple to a voltage source. However, existing designs do not describe how to design and connect the coil center points. As can be seen from the foregoing, the design, manufacture, and use of existing integrated circuit transformers are extremely difficult at a practical level due to the challenges of balancing the competing considerations of size, cost, high-frequency performance, reliability, and preventing parasitic loop inductance from the supply voltage conductor. Summary of the Invention

[0003] According to one aspect of the present invention, there is provided an integrated circuit transformer, comprising:

[0004] a primary winding located in at least a first winding layer having a first thickness, the primary winding having two primary ends at a first side of the transformer;

[0005] a secondary winding located at least in the first winding layer, the secondary winding having a first center point at the first side of the transformer and two secondary ends at second, laterally opposite sides of the transformer; and

[0006] a first center tap feed line located in an upper metal layer along an axis of symmetry of the transformer, the upper metal layer having a second thickness at least equal to the first thickness of the first winding layer, wherein the first center tap feed line has a direct electrical connection to the first center point in the secondary winding.

[0007] According to one or more embodiments, the integrated circuit transformer further includes a substrate and a patterned ground shield located between the first winding layer and the substrate to electrically shield the primary winding and the secondary winding from the substrate.

[0008] According to one or more embodiments, the integrated circuit transformer further includes a second center tap feed line, which is located in a lower metal layer between the patterned ground shield and the first winding layer along the symmetry axis of the transformer, wherein the second center tap feed line has a direct electrical connection to a second center point in the primary winding and has a thickness that is less than the second thickness of the upper metal layer.

[0009] According to one or more embodiments, the first center-tap feed line is located in a first upper metallic copper layer, which is located below a second adjacent upper metallic copper layer including the first winding layer, wherein the first upper metallic copper layer and the second adjacent upper metallic copper layer have substantially the same thickness.

[0010] According to one or more embodiments, the first center tap feed line is located in a first upper conductive metal layer, which is located above a second upper conductive metal layer including the first winding layer, wherein the first upper conductive metal layer is at least as thick as the second upper conductive metal layer.

[0011] According to one or more embodiments, the first center-tap feed line includes a plurality of lower conductive metal layers directly electrically connected to each other, the plurality of lower conductive metal layers being located below an upper conductive metal layer including the first winding layer, wherein the plurality of lower conductive metal layers have a combined thickness at least as thick as the upper conductive metal layer.

[0012] According to one or more embodiments, the primary winding and the secondary winding are concentric.

[0013] According to one or more embodiments, the primary winding and the secondary winding are both located in the first winding layer and the adjacent last metal layer, and each has a different winding radius.

[0014] According to one or more embodiments, the primary winding and the secondary winding form a 1×1 transformer in two relatively thick metal interconnect layers.

[0015] According to one or more embodiments, the primary winding and the secondary winding form an N×M transformer in two relatively thick metal interconnect layers.

[0016] According to one or more embodiments, the two primary ends of the primary winding are connected to gate terminals G+, G− of an output amplifier, and wherein the two secondary ends of the secondary winding are connected to drain terminals D+, D− of an input amplifier.

[0017] According to one or more embodiments, further included are patterned power supply voltage wiring tracks formed in the upper metal layer to be symmetrically arranged about the symmetry axis, wherein the patterned power supply voltage wiring tracks are laterally spaced apart from the primary winding and the secondary winding by a minimum spacing distance, the minimum spacing distance being selected to prevent RF currents induced in the patterned power supply voltage wiring tracks from adversely affecting transformer performance.

[0018] According to a second aspect of the present invention, there is provided an electronic circuit comprising:

[0019] a first power amplifier including a first output drain terminal and a second output drain terminal;

[0020] a second power amplifier comprising a first input gate terminal and a second input gate terminal; and

[0021] an integrated circuit transformer connected between the first power amplifier and the second power amplifier, the integrated circuit transformer comprising:

[0022] a primary gate winding located in at least a first relatively thick upper metal interconnect layer, the primary gate winding having a gate center point at a first side of the integrated circuit transformer and two primary ends at a second, opposite side of the integrated circuit transformer, the two primary ends connected to the first and second input gate terminals of the second power amplifier,

[0023] a secondary drain winding located in at least the first relatively thick upper metal interconnect layer, the secondary drain winding having a drain center point at the second opposite side of the integrated circuit transformer and two secondary ends at the first side of the integrated circuit transformer, the two secondary ends connected to the first output drain terminal and the second output drain terminal of the first power amplifier, and

[0024] a first center tap feed line located in a second relatively thick upper metal interconnect layer along an axis of symmetry of the integrated circuit transformer, the second relatively thick upper metal interconnect layer being at least as thick as the first relatively thick upper metal interconnect layer, wherein the first center tap feed line is directly electrically connected to the drain center point of the secondary drain winding.

[0025] According to one or more embodiments, the integrated circuit transformer further includes a patterned supply voltage wiring track formed in the second relatively thick upper metal interconnect layer to be symmetrically arranged about the symmetry axis, wherein the patterned supply voltage wiring track is laterally spaced apart from the primary gate winding by a minimum spacing distance, the minimum spacing distance being selected to prevent the primary gate winding from inducing RF current in the patterned supply voltage wiring track that adversely affects transformer performance.

[0026] According to one or more embodiments, the first center tap feed line is located in a first upper metal copper layer, which is located below a second adjacent upper metal copper layer forming the primary gate winding and the secondary drain winding, wherein the first upper metal copper layer and the second adjacent upper metal copper layer have substantially the same thickness.

[0027] According to one or more embodiments, the first center tap feed line is located in a first upper conductive metal layer, which is located above a second upper conductive metal layer forming the primary gate winding and the secondary drain winding, wherein the first upper conductive metal layer is at least as thick as the second upper conductive metal layer.

[0028] According to one or more embodiments, the first center-tap feed line includes a plurality of lower conductive metal layers directly electrically connected to each other, the plurality of lower conductive metal layers being located below an upper conductive metal layer forming the primary gate winding and the secondary drain winding, wherein the plurality of lower conductive metal layers have a combined thickness at least as thick as the upper conductive metal layer.

[0029] According to one or more embodiments, the primary gate winding and the secondary drain winding are concentrically shaped windings having different winding radii to form a 1×1 transformer in two relatively thick metal interconnect layers.

[0030] According to one or more embodiments, the primary gate winding and the secondary drain winding are concentrically shaped windings having different winding radii to form an N×M transformer in two relatively thick metal interconnect layers.

[0031] According to a third aspect of the present invention, there is provided a transformer, comprising:

[0032] at least one primary turn formed in an upper metal interconnect layer having a first local power line thickness and symmetrically positioned along an axis of symmetry of the transformer;

[0033] at least one secondary turn formed in the upper metal interconnect layer and symmetrically positioned along the axis of symmetry of the transformer; and

[0034] a first center-tapped feed line located in an upper metal interconnect layer along the axis of symmetry of the transformer, the upper metal interconnect layer being at least as thick as the first local power line, wherein the first center-tapped feed line is directly electrically connected to a drain center point of the at least one secondary turn. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] The present invention may be understood, and many of its objects, features, and advantages attained, when the following detailed description is considered in conjunction with the accompanying drawings, in which:

[0036] Figure 1 Depicted are circuit diagrams of a basic CMOS inverter and a transformer-coupled RF-CMOS differential amplifier.

[0037] Figure 2 A perspective view of an integrated circuit transformer is depicted.

[0038] Figure 3 Depicted is a simplified cross-sectional side view of a conductive metal layer that may be used to fabricate an integrated circuit transformer according to a first selected embodiment of the present disclosure.

[0039] Figure 4 Depicted is a simplified cross-sectional side view of a conductive metal layer that may be used to fabricate an integrated circuit transformer according to a second selected embodiment of the present disclosure.

[0040] Figure 5 Depicted is a simplified cross-sectional side view of a conductive metal layer that may be used to fabricate an integrated circuit transformer in accordance with a third selected embodiment of the present disclosure.

[0041] Figure 6 Depicted are plan or top views of a patterned first metal layer for forming an integrated circuit transformer, according to selected embodiments of the present disclosure.

[0042] Figure 7Depicts a patterned second metal layer in an integrated circuit transformer above Figure 6 Level floor plan.

[0043] Figure 8 Depicts the patterned third metal layer in an integrated circuit transformer above Figure 7 Level floor plan.

[0044] Figure 9 Depicts a patterned fourth metal layer in an integrated circuit transformer above Figure 8 Level floor plan.

[0045] Figure 10 Depicts a patterned fifth metal layer in an integrated circuit transformer above Figure 9 Level floor plan.

[0046] Figure 11 Depicted is a simplified cross-sectional side view of the center point of an outer gate coil in an integrated circuit transformer according to selected embodiments of the present disclosure.

[0047] Figure 12 Depicted is a simplified cross-sectional side view of the center point of an inner drain coil in an integrated circuit transformer according to selected embodiments of the present disclosure.

[0048] Figure 13 Depicted is a simplified cross-sectional side view of the center point of an outer drain coil in an integrated circuit transformer according to selected embodiments of the present disclosure.

[0049] Figure 14 Depicted is a simplified cross-sectional side view of the center point of an inner gate coil in an integrated circuit transformer according to selected embodiments of the present disclosure.

[0050] Figure 15 Depicted is a perspective view of an integrated circuit transformer according to selected embodiments of the present disclosure.

[0051] Figure 16 Depicted are plan views of patterned metal layers in an integrated circuit transformer according to selected embodiments of the present disclosure, wherein a drain voltage supply conductor is spaced apart from the transformer.

[0052] Figure 17 A two-stage, three-transformer differential amplifier is depicted in accordance with selected embodiments of the present disclosure.

[0053] Figure 18 Depicted are plan views of patterned metal layers in a 2x1 integrated circuit transformer according to selected embodiments of the present disclosure.

[0054] Figure 19 Depicts Figure 18 A perspective view of an integrated circuit transformer is shown in FIG. DETAILED DESCRIPTION

[0055] A high-current integrated circuit-based transformer device for configuring a transformer with two coupled inductive windings, and associated methods of operation and manufacturing, is described. One or more coils or winding center points in an integrated circuit inductor are protected from high DC current loads by forming two coupled coils in an upper metal / conductor layer and also by forming at least one coil center point feed line in a thick upper metal / conductor layer to contact from two opposing sides along the transformer's axis of symmetry. By forming the coil center point feed lines with metal / conductor layers of equal width and thickness on each side of the coil center point, DC current is evenly distributed between the two feed lines, thereby reducing the DC current density in each feed line. In selected embodiments, the integrated circuit-based transformer device is formed to include: a primary transformer coil winding (having end points and a transformer center point) located in one or more thick upper metal conductor layers; a secondary transformer coil winding (having end points and a transformer center point) located in one or more thick upper metal conductor layers; and at least a first center-tap conductor feed line formed in one of the thick upper metal conductor layers (or in a plurality of thinner upper metal conductor layers) and connected to the first transformer coil center point. When referring to "primary" and "secondary" windings, the primary winding is the winding with the highest inductance. When referring to "gate" and "drain" windings, the drain winding is the winding connected to carry high DC current during circuit operation. It should be noted that the drain winding can be either a primary winding or a secondary winding. By forming the first center-tap conductor feeder(s) to have a combined thickness similar to the upper metal conductor layers used for the transformer coil windings, and by positioning the center-tap conductor feeders on either side of the first transformer coil center point, the DC current passing through the first transformer coil center point is distributed among the first center-tap conductor feeder(s) such that the DC current density in each feeder is sufficiently low that neither feeder becomes a bottleneck relative to the electromigration damage design rule. Additionally, a second center-tap conductor feeder extending in a lower metal level is used to contact the second transformer coil center point. By forming the center-tap conductor feeders to the two transformer coil center points in different metal layers, they can both be routed along the transformer's axis of symmetry without imposing any restrictions on the sides that can reach the coil center points.

[0056] In order to provide additional details for improving the understanding of selected embodiments of the present invention, reference is now made to Figure 1 , Figure 1A circuit diagram of a basic CMOS inverter 10 and a transformer-coupled RF-CMOS differential amplifier 11 is depicted. In CMOS inverter 10, a first pair of PMOS and NMOS transistors, M1 and M2, are connected in series between Vdd and Vss to receive input voltage V1. A shared node, V2, has a parasitic capacitance, Cp, which is provided as an input to a second pair of PMOS and NMOS transistors, M3 and M4, which are connected in series between Vdd and Vss to generate the inverter output, Vout. In digital CMOS circuit 10, current consumption arises from the charging and discharging of the MOS transistor gate and drain junctions and interconnect capacitances. Therefore, the resulting power consumption is proportional to the circuit's operating frequency. While the trend toward smaller feature sizes, smaller parasitic capacitances, and lower operating voltages has helped reduce this power consumption, unavoidable parasitic capacitances limit the practical clock frequency of current digital circuits to approximately 3 GHz. In digital CMOS inverter 10, current is lost when loading and unloading the circuit's parasitic capacitance, Cp. In order to enable efficient electronic circuits to operate at significantly higher frequencies, it is necessary to recover the energy entering the parasitic capacitances via inductive circuit elements.

[0057] To this end, integrated circuit-based transformers can be used to recycle energy in a very area-efficient manner. Specifically, an RF-CMOS differential amplifier 11 is depicted, comprising a first pair of NMOS transistors M11, M12, whose drain nodes are connected to a first inductor L1 to receive an input voltage V1 across the gates of transistors M11, M12, wherein the first inductor L1 has a center point connected to Vdd, and wherein the shared source node of transistors M11, M12 is connected to Vss. Additionally, a second pair of NMOS transistors M13, M14 is provided with their gate nodes connected across a second inductor L2 to generate a voltage V2, wherein the second inductor L2 has a center point connected to Vg, and wherein the shared source node of transistors M13, M14 is also connected to Vss. Instead of losing current during loading and unloading of circuit capacitance CP, the transformer-coupled RF-CMOS differential amplifier 11 is able to recycle current using inductive elements L1, L2. Although full (100%) energy recovery is only possible at a single operating frequency, a suitable design will typically target about 90% energy recovery to ensure that the circuit can be used over a sufficiently large frequency range. As will be appreciated, those skilled in the art of RF circuit design will understand how to use electromagnetic and circuit simulation techniques to accurately tune the coupling coil diameter or inductance value to optimize performance in a given application at a given frequency.

[0058] In order to provide additional details for improving the understanding of selected embodiments of the present invention, reference is now made to Figure 2 , Figure 2 A perspective view of an integrated circuit transformer 20 is depicted. As depicted, the IC transformer 20 includes an outer primary winding 21 located in a winding layer and having two primary gate terminals G+, G- on a first side of the transformer. Additionally, the IC transformer 20 includes an inner secondary winding 22 located in the winding layer and having two secondary terminals on a second, opposite side of the transformer for connection to secondary drain terminals D+, D- via underlying conductors 23A, 23B. Although not shown, the center point of the inner secondary winding 22 can be connected to a supply voltage Vdd via a center tap connection 24 formed in an underlying conductor layer. Because center tap connections do not carry RF current, they are not conventionally considered to affect RF performance and, therefore, have not been designed in existing solutions to withstand the high DC drive currents found in high-power (50 mW) high-frequency (78 GHz) amplifier stages, where these transformers are attractive for impedance matching and energy efficiency.

[0059] To address these design challenges and other limitations from conventional integrated circuit transformer solutions, reference is now made to Figures 3 to 5 , Figures 3 to 5Simplified cross-sectional side views of conductive metal layers (e.g., M1-M9) that can be used to fabricate an integrated circuit transformer according to selected embodiments of the present disclosure are shown. In each of the described example embodiments, the transformer is configured with a back-end conductive or metal layer of a semiconductor manufacturing process that can form a first plurality of thin copper layers on a substrate, such as by sequentially depositing six (6) thin copper layers M1-M6 of a first predetermined thickness (e.g., 85 nm) intended for short-distance circuit connections in the integrated circuit. Additionally, a second plurality of relatively thick copper layers can be formed on the first plurality of thin copper layers and separated from each other by interlayer dielectric (ILD) layers (such as by depositing two (2) thick copper layers M7-M8 of a second predetermined thickness (e.g., 850 nm) intended for long-distance circuit connections and local power lines in the integrated circuit). Finally, a final or top conductive layer can be formed on the second plurality of thick copper layers, such as by depositing a thick aluminum layer M9 of a third predetermined thickness (e.g., 2800 nm) intended for global power lines and bond pads. Although not shown, the conductive metal layers M1-M9 are separated from each other by interlayer dielectric (ILD) layers and connected where necessary by conductive via structures that penetrate the ILD layers to electrically connect adjacent conductive metal layers. In addition, the shape and size of each conductive metal layer M1-M9 can be patterned to adjust the parameters of each integrated circuit, thereby forming a transformer with individually tunable inductance values ​​for the primary and secondary coils in the top thick metal layer having concentrically shaped but patterned conductive metal layers with different radii. As will be understood, for illustrative purposes, the sizes and spacings of the various conductive metal layers may be exaggerated and not drawn to scale.

[0060] Now turn Figure 3, shows a simplified cross-sectional side view 30 of conductive metal layers M1-M9 that can be used to fabricate an integrated circuit transformer according to a first selected embodiment of the present disclosure. For example, the conductive metal layers M1-M9 can be formed on a substrate and gate conductor (not shown) as levels 301-309 forming wiring layers. In an example embodiment, the six metal wiring layers M1-M6 formed at levels 301-306 can be referred to as local metal wiring layers and have a thickness thin enough to allow even dense areas of small standard FET devices to be interconnected. Above the thin metal wiring layers M1-M6, relatively thick metal wiring layers M7-M8 formed at levels 307-308 can be referred to as global metal wiring layers. Finally, a relatively thick metal wiring layer M9 formed at level 309 is formed as the top or last metal wiring layer(s). The thin metal wiring layers 301-306 have a thickness less than the thickness of the global metal wiring layers 307-308, and the top or last metal wiring layer is the thickest metal wiring layer. According to example embodiments, a ratio of thicknesses of the thin metal layer, the relatively thick metal layer, and the thick metal wiring layer is 1:2:8 to 1:10:32. Figure 3 In FIG, the primary coil is implemented in a top aluminum layer M9309A with a primary crossover layer 315 and a last (or crossover) copper layer M8308A with a primary crossover layer 313, which can be patterned into a first coil shape and connected by a conductive via structure between conductive metal layers M8 and M9. In a similar manner, the secondary coil is implemented in a top (or crossover) aluminum layer M9309B with a secondary crossover layer 316 and a last (or crossover) copper layer M8308B with a secondary crossover layer 314, which can be patterned into a second coil shape and connected by a conductive via structure between conductive metal layers M8 and M9. The smaller the lateral spacing between the primary and secondary coils, the stronger their inductive coupling. For a 1×1 turn transformer, the aluminum secondary coil will crossover with the copper primary coil near the center point of the primary coil. Aside from the crossover regions, both the primary and secondary coils reside in conductive metal layers M8308 and M9309. For multi-turn transformers, more crossovers are required, which can also be implemented in the top two metal layers. Separate metal layers are required because the crossover and connection to the center point of the coil must occur along the transformer's axis of symmetry.

[0061] exist Figure 3In the cross-sectional side view 30 shown in FIG, a first thin metal wiring layer M1 301 can be used to form a ground shield layer 310 to protect the integrated circuit transformer from substrate noise. In one or more of the remaining thin metal wiring layers M2-M6 302-306, a second wiring is formed that is connected to a second center tap 311. In applications where the DC current density requirements of the second center tap are not important, a single thin metal wiring layer (e.g., M6 306) may be sufficient, but additional thin metal wiring layers (e.g., M2-M5) can be added from the second center tap 311A. Since the wiring connected to the first center tap 312 needs to carry the same DC current as the relatively thick metal wiring layer M8 of the coil itself, the first center tap feed line 312 is formed in a relatively thick metal wiring layer M7, which has a thickness and current carrying capacity similar to the relatively thick metal wiring layer M8 of the coil layer. Reference Figures 6 to 12 The layout and fabrication of integrated circuit transformers will be better understood, Figures 6 to 10 A plan view of an alternative metal conductor layer of an integrated circuit transformer is shown, and Figures 11 to 12 A cross-sectional side view showing the levels of metal conductor layers of an integrated circuit transformer is shown.

[0062] Now turn Figure 4 , shows a simplified cross-sectional side view 40 of conductive metal layers M1-M8 that can be used to fabricate an integrated circuit transformer according to a second selected embodiment of the present disclosure. In the example embodiment, there is no top aluminum conductive layer, and the integrated circuit transformer is formed in a first plurality (e.g., 6) of local metal wiring layers M1-M6 formed in layers 401-406 with a first predetermined thickness, and a second plurality (e.g., 2) of relatively thick global metal wiring layers M7-M8 formed in layers 407-408. Although not drawn to scale, the thickness of the thin metal wiring layers 401-406 is less than the thickness of the global metal wiring layers 407-408, such that the ratio of the thickness of the thin metal wiring layer (e.g., 401) to the thickness of the relatively thick global metal wiring layer (e.g., 407) is 1:2 to 1:10. In Figure 4, the primary coil is implemented in a top (or crossover) copper layer M8408A having a primary crossover layer 415, and in a copper layer M8407A having a lower (or crossover layer) having a primary through-link layer 413, wherein the primary through-link layer 413 can be patterned into a first coil shape and connected by a conductive via structure between conductive metal layers M7 and M8. Additionally, the secondary coil is implemented in a top (or crossover) copper layer M8408B having a secondary crossover layer 416, and in a copper layer M7407B having a lower (or crossover layer) having a secondary through-link layer 414, wherein the secondary through-link layer 414 can be patterned into a second coil shape and connected by a conductive via structure between conductive metal layers M7 and M8. The inductive coupling effect K of the lateral spacing between the primary and secondary coils and the use of the lower metal layer to provide a crossover connection at the center point of the (one or more) coils is similar to that of FIG. Figure 3 402. The example described in . Since the wiring connected to the first center tap 412 needs to carry the same DC current as the relatively thick metal wiring layer M7 used for the coil itself, the first center tap feed line 412 is formed with a combination of thin metal wiring layers M3-M6403-406, which are connected together by conductive via structures (not shown) to provide an effective thickness with a current carrying capacity comparable to the relatively thick metal wiring layer M7 used for the coil layer. In one or more of the remaining thin metal wiring layers (e.g., M2402), a second wiring is formed that is connected to the second center tap 411. In addition, the first thin metal wiring layer M1401 can be used to form a ground shield layer 410 for protecting the integrated circuit transformer from substrate noise.

[0063] Now turn Figure 5 , shows a simplified cross-sectional side view 50 of conductive metal layers M1-M9 that can be used to fabricate an integrated circuit transformer according to a third selected embodiment of the present disclosure. In an exemplary embodiment, the integrated circuit transformer is formed in a plurality of conductive metal layers M1-M9 501-509, including a first plurality (e.g., 6) of local metal wiring layers M1-M6 formed at levels 501-506 with a first predetermined thickness, a second plurality (e.g., 2) of relatively thick global metal wiring layers M7-M8 formed at levels 507-508, and one or more relatively thick topmost metal wiring layers M9 formed at level 509. Again, the conductive metal layers M1-M9 501-509 have different thicknesses that are not drawn to scale. In Figure 5, the primary coil is implemented in a top (or crossover) copper layer M8508A having a primary crossover layer 515, and in a copper layer M7507A having a lower (or crossover layer) having a primary through-link layer 513, wherein the primary through-link layer 513 can be patterned into a first coil shape and connected by a conductive via structure between conductive metal layers M7 and M8. Additionally, the secondary coil is implemented in a top (or crossover) copper layer M8508B having a secondary crossover layer 516, and in a copper layer M7507B having a lower (or crossover layer) having a secondary through-link layer 514, wherein the secondary through-link layer 514 can be patterned into a second coil shape and connected by a conductive via structure between conductive metal layers M7 and M8. Similarly, the inductive coupling effect K of the lateral spacing between the primary and secondary coils and the use of the lower metal layer to provide a crossover connection at the center point of the (one or more) coils is similar to that of FIG. Figure 3 , . Since the wiring connected to the first center tap 512 needs to carry the same DC current as the relatively thick metal wiring layers M7, M8 of the coil, the first center tap feed line 512 is formed in a relatively thick aluminum layer 509, which has a current carrying capacity comparable to the relatively thick metal wiring layers M7, M8 of the coil layer. In one or more thin metal wiring layers M2-M6502-506, a second wiring connected to the second center tap 511 is formed. In applications where the DC current density requirements of the second center tap are not important, a single thin metal wiring layer (e.g., M6506) may be sufficient, but additional thin metal wiring layers (e.g., M2-M5) may be added from the second center tap 511. In addition, the first thin metal wiring layer M1501 can be used to form a ground shield layer 510 for protecting the integrated circuit transformer from substrate noise.

[0064] As will be appreciated, the patterning and etching process techniques used to form the coil features prevent the coil width and spacing from being much smaller than the thickness of the coil metal layer. Therefore, if a coil with a width less than 4 μm and a spacing less than 2 μm is to be manufactured, the aluminum layer M9 should not be used to form the coil (e.g., Figure 3 Instead, the transformer coil should be realized in two thick copper layers M7 and M8 (as shown in FIG. Figures 4 and 5 In this case, the first center tap connection should be formed on a thick aluminum metal layer M9 (such as Figure 5 ) or a thin copper metal layer (as shown in Figure 4 ), where the layers (e.g., M3-M6) can be connected together in parallel to effectively form a larger wiring width that compensates for the insufficient thickness of the individual thin layers. Similarly, a second center tap can be formed by connecting two or more thin copper metal layers in parallel.

[0065] In order to provide additional details for improving the understanding of selected embodiments of the present invention, reference is now made to Figures 6 to 10 , which shows example features in different metal layers, starting from the lowest metal layer M1 ( Figure 6 ) and continues to the top metal layer M9 ( Figure 10 ). As will be appreciated, each metal layer feature in a given layer can be fabricated using any suitable back-end process, such as depositing a conductive metal layer on a planarized dielectric layer, planarizing the deposited conductive metal layer, and then patterning and etching the conductive metal layer to define the desired features in each metal layer. Thus, an integrated circuit transformer can be formed with metal layers M1-M9 formed by sequentially depositing, planarizing, patterning, and etching any suitable conductive material (e.g., aluminum, copper, tantalum, tungsten, tantalum nitride, tungsten nitride, titanium, titanium nitride, etc., and combinations thereof) on an underlying ILD layer that separates each metal layer from the underlying metal layer(s) so as to be electrically disconnected from each other. As will be appreciated, each constituent conductor layer in the interconnect stack can be formed to a predetermined final thickness using chemical vapor deposition (CVD), plasma-enhanced chemical vapor deposition (PECVD), physical vapor deposition (PVD), atomic layer deposition (ALD), focused ion beam (FIB) deposition, electron beam induced deposition (EBID), micro-CVD, laser focused deposition, laser focused atomic deposition, or any other suitable deposition or localized deposition technique, or any combination thereof. Where appropriate, the plan view includes an indication of one or more conductive via structures used to connect between the different metal layers. While the specific arrangement, configuration, and connections of the different conductive interconnect layers are not critical, as is known to those skilled in the art, each conductive interconnect layer can be configured within a constituent ILD layer using a damascene process, wherein the conductive layer is deposited within an opening formed in the constituent ILD layer and then polished or etched back to be planar with the constituent ILD layer. Of course, other more conventional interconnect fabrication techniques, such as photoresist masking and plasma etching, can be used to configure the different conductive interconnect layers.

[0066] Now refer to Figure 6, depicts a plan or top view 60 of a patterned first metal layer M1 for forming an integrated circuit transformer according to selected embodiments of the present disclosure. In the depicted example, the first metal layer M1 can be formed into a patterned ground shield by patterning and etching the bottommost thin metal wiring layer M1 to define a center shield track 61 electrically connected to a ground or reference voltage Vsh and a plurality of parallel metal tracks 62. Specifically, the center shield track 61 is defined and positioned to be aligned with the transformer symmetry axis and electrically connected to the plurality of parallel metal tracks 62, which are oriented vertically to extend from the transformer symmetry axis. By forming the patterned ground shields 61, 62 as the lowest thin copper layer M1, the vertical distance between the transformer coil (formed in the upper conductive metal layer) and the patterned ground shield is as large as possible.

[0067] As disclosed herein, integrated circuit transformers can benefit from including a ground shield, such as patterned ground shields 61, 62. The term "patterned" may refer to a ground shield 62 comprising a series of discontinuous parallel conductive strips, oriented transversely to the mirror symmetry plane along a central shield track 61 in the example depicted. That is, the conductive strips 62 may be close to each other but not touching. Such ground shields 61, 62 can reduce capacitive coupling to the substrate during transformer operation. Capacitive coupling in this manner can result in signal power loss due to unfavorable substrate conductivity. While a transverse orientation is considered most effective, it should be understood that other orientations of the ground shield strips can be used, which can achieve the advantages provided by the ground shield. As will be appreciated, the width and spacing of the ground shield strips can be selected to approximate the thickness of the ground shield metal to minimize signal power loss due to current loops induced in the shield strips by the transformer's magnetic field during inductor / transformer operation, as would be the case with current induced in the transformer's secondary winding.

[0068] When manufacturing inductors or transformers in integrated circuit processes, the distance between the coil windings and the substrate is typically a few microns. In some processes, such as those using GaAs substrates, the substrate can be isolated. If the substrate is silicon, as in other IC processes, it is semiconducting. The magnetic field present during inductor / transformer operation can induce current loops in the semiconductor substrate, just as current is induced in the secondary winding of a transformer. In systems where the distance between the windings and the substrate is on the order of a few microns, capacitive coupling with the substrate can occur, inducing unwanted charge and current in the (non-fully isolated) substrate. The (induced) capacitance between the two ends of the transformer winding can degrade transformer performance and cause parasitic losses due to the induced current. These parasitic losses from capacitive coupling can be mitigated by using a high substrate resistivity or an isolating substrate; however, this can be difficult to achieve in most silicon-based RFIC processes, where the substrate resistivity is high enough (>10 ohm-cm) to negligibly reduce signal power losses due to eddy currents, but not high enough to prevent capacitive losses. This is why a patterned ground shield is included. Embodiments of the present invention can address these issues by including a patterned lower metal layer between the substrate layer and the winding layer. By patterning the lower metal layer to include a series of discontinuous conductive metal strips as the ground shield layers 61, 62, the inductance of the circular loops in the shield layer is greatly reduced, and transformer performance can be enhanced. Such strips in the ground shield can be manufactured in IC processes with small widths, for example, on the order of one micron.

[0069] Now refer to Figure 7 , depicting the patterned second metal layer M6 and conductive via V6 in the integrated circuit transformer Figure 6FIG70 is a plan or top view of a layer above the layer shown in FIG70 . In the depicted example, no transformer features are present in the intermediate thin copper layers M2-M5. As depicted, the second metal layer M6 can be formed into first tracks 71, 72 for connecting to the center point of the gate transformer coil by patterning and etching the topmost thin metal wiring layer M6 to define a center track 71 electrically connected to the gate voltage Vg and a first through-hole contact plate 72. Specifically, the center track 71 is defined and positioned to align with the transformer symmetry axis and electrically connected to the first through-hole contact plate 72, which is positioned to align with and electrically connected to the (subsequently formed) first center point of the gate transformer coil. To enable electrical connection to the (subsequently formed) first center point of the gate transformer coil, one or more conductive via structures 73a-d are formed on the second metal layer M6 to extend from the first through-hole contact plate 72 using any suitable interconnection process. For example, a planarized ILD layer can be formed on the second metal layer M6, then selectively patterned and etched to define openings in the ILD layer that expose the via contact plate 72. One or more conductive layers can then be deposited into the defined openings and then polished or planarized to form one or more conductive via structures 73a-d in the ILD layer. By routing patterned first tracks 71, 72 along the transformer's axis of symmetry for connection to the center point of the gate coil, it will be at a virtual RF ground during differential operation. Thus, the track can serve as a gate bias voltage Vg connection.

[0070] Now refer to Figure 8 , depicting the patterned third metal layer M7 and conductive via V7 in the integrated circuit transformer Figure 780. As depicted, the third metal layer M7 can form a power supply voltage routing track 81 for connecting to the center point of the drain transformer coil by patterning and etching the first relatively thick metal routing layer M7 to define first and second feed conductors 81A and 81B, a second through-hole contact plate 81G, and power supply voltage routing tracks 81C-81F that are electrically connected to route the power supply voltage Vdd to the first and second feed conductors 81A and 81B and the second through-hole contact plate 81G. In addition, the patterned third metal layer M7 defines one or more third through-hole contact plates 82 and 83 that are electrically connected to the underlying first through-hole contact plate 72 using conductive via structures 73a-d and are not electrically connected to the power supply voltage routing track 81. Specifically, first and second feed conductors 81A, 81B are defined and positioned to align with the transformer axis of symmetry and electrically connect to a second through-hole contact plate 81G, which is positioned to align with and electrically connect to the (subsequently formed) second center point of the drain transformer coil. To enable electrical connection to the (subsequently formed) second center point of the drain transformer coil, one or more conductive via structures V8 are formed on the third metal layer M7 using any suitable interconnection process. For example, one or more conductive via structures (e.g., 87e, 87f) are formed to electrically contact through-hole contact plate 81G. Similarly, one or more conductive via structures (e.g., 87a-87d) are formed across third through-hole contact plates 82, 83 using any suitable interconnection process to enable electrical connection to the (subsequently formed) first center point of the gate transformer coil. By routing the supply voltage routing tracks 81 along or symmetrically relative to the transformer axis of symmetry to connect to the center point of the drain coil, they will be at a virtual RF ground during differential operation. Therefore, these tracks can be used as drain bias voltage connections.

[0071] Now refer to Figure 9 , depicting the patterned fourth metal layer M8 and conductive via V8 in the integrated circuit transformer Figure 890 is a plan view or top view at a level above the level of the circuit. As depicted, the fourth metal layer M8 can be formed as the lower primary / gate and secondary / drain coil windings 91 and 92 by patterning and etching the second relatively thick metal wiring layer M8. As formed, the lower primary / gate coil winding 91 includes a first center point 95 at one end and a pair of gate terminals 91A and 91B at opposite ends for connecting to the negative gate G and positive gate G+ of the next amplifier stage. Similarly, the lower secondary / drain coil winding 92 is formed with a second center point 96 at one end and a pair of terminals 92A and 92B at opposite ends for connecting to the positive drain D+ and negative drain D+ of the previous amplifier stage. To enable connection to the previous stage, the patterned fourth metal layer M8 also includes separately defined through-hole contact plates 93 and 94, which electrically connect the positive drain and negative drain of the previous amplifier stage. As formed, via contact plates 93 and 94 are not electrically connected to other layers of the integrated circuit transformer. However, a first center point 95 of lower primary / gate coil winding 91 is electrically connected to the gate voltage Vg on underlying first rails 71 and 72 via conductive via structures 87a-87d and third via contact plates 82 and 83. Similarly, a second center point 96 of lower secondary / drain coil winding 92 is electrically connected to the drain voltage Vdd on underlying power supply voltage routing track 81 via conductive via structures 87e-87f and second via contact plate 81G. Specifically, lower primary / gate coil 91 and lower secondary / drain coil 92 are formed as concentric windings in the second, relatively thick metal layer M8, each with a different radius. Therefore, the end terminals 92A and 92B of lower secondary / drain winding 92 are arranged on different layers to make electrical contact with the D+ and D- terminals of terminal pair 93 and 94, avoiding contact with primary / gate winding 91. To achieve electrical connections with other layers, one or more conductive via structures V8 are formed across the fourth metal layer M8 using any suitable interconnection process. For example, one or more conductive via structures (e.g., 97a-97d) are formed to electrically contact the via contact plates 93, 94. Similarly, a first set of conductive via structures (e.g., 98a-98d) are formed on the lower primary / gate winding 91, and a second set of conductive via structures (e.g., 99a-99f) are formed on the lower primary / gate and secondary / drain coil windings 91, 92 of the lower secondary / drain winding 92 using any suitable interconnection process.

[0072] Now refer to Figure 10 , depicting the patterned fifth metal layer M9 in an integrated circuit transformer Figure 9100 at a level above the level of the transformer. As depicted, the fifth metal layer M9 can be formed into an upper primary / gate coil winding 101 and a secondary / drain coil winding 102 by patterning and etching the topmost relatively thick metal wiring layer M9. As depicted, the upper primary / gate coil winding 101 includes a first curved top metal winding layer 111 and a second curved top metal winding layer 112, the second curved top metal winding layer 112 being formed in the fifth metal layer M9 to be symmetrically arranged about the symmetry axis of the transformer, having a first center point 105 at one end, and a pair of gate terminals 111A, 112A at opposite ends for connection to a negative gate G- and a positive gate G+ of the next amplifier stage. Similarly, upper secondary / drain coil winding 102 includes a concentric circular top metal winding layer 113 formed in the fifth metal layer M9 to be symmetrically positioned about the transformer's axis of symmetry, having a second center point 106 at one end and a pair of ends 113A, 113B at opposite ends for connection to the positive drain D+ and negative drain D- of the preceding amplifier stage. Ideally, the shape and positioning of upper primary / gate coil winding 101 and secondary / drain coil winding 102 substantially correspond to the shape and positioning of lower primary / gate coil winding 91 and secondary / drain coil winding 92. As shown, transformer coil 101, having a larger diameter, intersects transformer coil 102, having a smaller diameter, at end pair 113A, 113B, such that first center point 105 of transformer coil 101 is contacted from the lower metal layer. Thus, a first center point 105 of the primary / gate coil winding 101 is physically located in the lower primary / gate coil 91, where the primary / gate coil is electrically connected to the gate voltage Vg on the underlying first rails 71, 72 via conductive via structures 87a-87d and third via contact plates 82, 83. Similarly, a second center point 106 at the upper secondary / drain coil winding 102 is electrically connected to the drain voltage Vdd on the underlying supply voltage routing track 81 via conductive via structures 99a-99f, the lower drain coil 92, conductive via structures 87e-87f, and second via contact plate 81G. Additional crossovers are used in transformers where the coils have multiple turns to increase their inductance. And to maximize inductive coupling, the turns belonging to the primary and secondary coils should be alternated accordingly. In cases where crossovers are not required, the two transformer coils can be located in the two highest metal layers (e.g., M8, M9).

[0073] As mentioned above, the long wiring used to connect to the center point of the coil is sensitive to electromigration damage when the current density is too high. Those skilled in the art will understand that electromigration is the effect of the atoms of the copper or aluminum interconnect being slowly displaced by the steady flow of electrons. As the displacement along the wiring causes a buildup of metal atoms at the ends of the wire, this can cause the wire to break at the opposite end. For low electron current densities, the atoms can diffuse back to their original positions before damage accumulates. In addition, AC current can be ignored in electromigration assessments. However, DC current may accumulate electromigration damage when the circuit is operating. Since the effect is most significant for the first center point conductor to the drain winding, the layers of the first feed conductor and the second feed conductor should have a specified minimum width dimension to ensure that the integrated circuit transformer does not exceed the safe current density limit. As an example, the following table lists the sheet resistance and EM safety reference current of the metal layers of the transformer example:

[0074] thickness Metal Atomic mass <![CDATA[R sheet Oh]]> <![CDATA[I max mA / μm]]> <![CDATA[I max mA / μm 2 ]]> 85nm copper 63 0.24 0.94 10.5 850nm copper 63 0.023 8.14 9.58 2800nm aluminum 27 0.01 5.21 1.86

[0075] As seen above, aluminum's lower atomic mass means its safe current density (ImaxmA / μm²) is significantly lower than copper. Therefore, despite being thicker (2800nm), aluminum wire can carry less current than a thinner (850nm) copper wire of the same width. At the same time, when a transformer coil has thick copper and aluminum tracks in parallel, approximately 70% of the current will flow in the aluminum track because the current is distributed between them based on their relative resistances. Therefore, in the end, a single thick copper track and an aluminum track in parallel can potentially have approximately the same safe current level.

[0076] In order to improve the understanding of selected embodiments of the present invention, reference is now made to Figure 10 , Figure 10 The key dimensions of the metal layers of the transformer 100 are depicted, including a first width dimension W1 of the width of the drain terminal (e.g., 113A), a second width dimension W2 of the width of the secondary coil winding (e.g., 113), a third width dimension W3 of the width of the feed conductors (e.g., 81A, 81B), and a fourth width dimension W4 of the width of the power supply voltage wiring tracks (e.g., 81C-81F). Figure 3 For example, an integrated circuit transformer is formed with 85nm copper layers M1-M6, 850nm copper layers M7-M8, and 2800nm ​​aluminum layer M9. The minimum track widths W1-W4 required to provide a total safe reference drain current of up to 100mA are listed in the following table:

[0077] size Current Metal Wmin W1 50mA Al 9.6μm W2 50mA Al||Cu 6.7μm W3 50mA Cu 6.2μm W4 25mA Cu 3.1μm

[0078] With these example widths, all metal tracks of the transformer layout are equally robust to electromigration damage.

[0079] To ensure that current can be conducted from one metal layer to another, the current is distributed to a sufficient number of conductive via structures. Typically, a 3×3 μm via structure interconnecting the aluminum and copper layers can each carry 12 mA. Therefore, the number of via structures shown in the figure can work. The 0.36×0.36 μm via structures interconnecting the two thick copper layers M7 and M8 can each carry 3 mA, but they can be placed at a much higher density, so they can also work. As will be understood, other size values ​​and arrangements can be used to achieve the desired electrical interconnection.

[0080] In order to provide additional details for improving the understanding of selected embodiments of the present invention, reference is now made to Figure 11 , Figure 11 Depicted through Figure 10 A simplified cross-sectional side view 110 of a first center point 105 of an outer or primary / gate coil in an integrated circuit transformer is shown in FIG. Figure 11 ” perspective view. As will be understood, for purposes of illustration, the sizes and spacing of the various conductive metal layers may be exaggerated and not drawn to scale. In the depicted view 110, the ground shield layer 62 is formed in the first thin copper layer M1. Additionally, a through-hole contact plate 72 is formed in the second thin metal layer M6 and is connected to the outer gate winding layer 91 (formed in the second thick copper layer M8) and the outer gate winding layers 111, 112 (formed in the thick aluminum layer M9) using conductive interconnect structures (e.g., 73a-d, 82-83, 87a-d, 98a-d) formed in the intermediate layers. Finally, the feed conductor 81A is formed in the first thick copper layer M7 and is connected to the inner drain winding layer 113 using conductive interconnect structures (not shown). Collectively, the conductive layers 72, 82, 81A, 83 and their conductive vias 73a-d, 87a-d form an underlying interconnect structure 121 for connecting the through-hole contact plate 72 to the gate winding.

[0081] In a similar way, Figure 12 Depicted through Figure 10 A simplified cross-sectional side view 120 of a second center point 106 of an inner or secondary / drain coil in an integrated circuit transformer is shown, as indicated by the marking “ Figure 12” perspective view. Again, for illustrative purposes, the sizes and spacing of the various conductive metal layers may be exaggerated and not drawn to scale. In the depicted view 120, the ground shield layer 62 is formed in the first thin copper layer M1. Additionally, a second through-hole contact plate 81G positioned between the feed conductors 81A, 81B is formed in the first thick copper layer M7 and is connected to the inner drain winding layer 92 (formed in the second thick copper layer M8) and the inner drain winding layer 113 (formed in the thick aluminum layer M9) using conductive interconnect structures (e.g., 87e-f, 99a-d) formed in the intermediate layers. Finally, the center track 71 is formed in the second thin metal layer M6 and is connected to the outer gate winding layer (not shown) using conductive interconnect structures (not shown). Collectively, the conductive layer 81G and the conductive vias 87e-f form an underlying interconnect structure 122 for connecting the feed conductors 81A, 81B to the drain winding.

[0082] exist Figure 11 The gate coil center tap is located at the center of the lower primary / gate coil winding 91 and is Figure 12 In FIG, the drain coil center tap is located at the center of the secondary / drain coil winding layer 92, 113. Since the connection to the outer gate coil does not carry any DC current, it can be formed with a very narrow conductor layer (such as a thin (e.g., 85nm) copper layer) that forms the through-hole contact plate 72 ( Figure 11 ) and center track 71( Figure 12 ). In contrast, the wiring connected to the inner drain coil must carry the average drain current and should therefore be formed with a solid conductor layer having at least approximately the same width and thickness as the transformer coil, such as forming the feed conductors 81A, 81B ( Figure 11 ) and a second through-hole contact plate 81G ( Figure 12 ).

[0083] As will be appreciated, there will be situations where the center point connections to the coils must be swapped, such as when the outer or primary coil in an integrated circuit transformer is connected to the drain node carrying DC current, and the inner or secondary coil is connected to the gate node carrying AC current. Figure 13 and Figure 14 As shown in Figure 13 and Figure 14 A cross section through the center tap points of the gate and drain coils connected to the outer drain coil and inner gate coil, respectively, is shown. Specifically, Figure 13A simplified cross-sectional side view 130 through a first center point of an outer or primary / drain winding in an integrated circuit transformer is depicted in accordance with selected embodiments of the present disclosure. In the depicted view 130, the ground shield layer 62 is formed in a first thin copper layer M1. Additionally, the underlying interconnect structure 122 (similar to Figure 12 ) is formed in the second thin metal layer M6 and the first thick copper layer M7, and is used to connect the feed conductors 81A, 81B (formed in the first thick copper layer M7) to the outer drain winding layer conductors 91 (formed in the second thick copper layer M8) and 111, 112 (formed in the top aluminum layer M9) through the conductive via structures 98a-d.

[0084] in addition, Figure 14 A simplified cross-sectional side view 140 of a second center point of an inner or secondary / gate coil in an integrated circuit transformer according to selected embodiments of the present disclosure is depicted. In the depicted view 140, the underlying interconnect structure 121 (similar to Figure 11 ) is formed in the second thin metal layer M6 and the first thick copper layer M7, and is used to connect the through-hole contact plate 72 to the inner gate winding layer 92 (formed in the second thick copper layer M8) and the gate winding layer 113 (formed in the thick aluminum layer M9).

[0085] In order to provide additional details for improving the understanding of selected embodiments of the present invention, reference is now made to Figure 15 , Figure 15 Depicted by reference Figures 6 to 10 A perspective view 150 of an integrated circuit transformer fabricated by the process is shown. Figure 15 The dimensions of the individual features in the Figures 6 to 10, but perspective view 160 shows the underlying patterned ground shields 61, 62 formed in the first local metal wiring layer. In one or more upper local metal wiring layers, a first patterned track 71 is formed for connecting to the center point 105 of the gate transformer coil across a first via contact pad (not shown). In a first thick global metal wiring layer, a patterned supply voltage routing track 81 is formed for connecting to the center point of the drain transformer coil on the thick global metal wiring layer to define a feed conductor along the transformer's axis of symmetry and along the periphery (not shown) for routing the supply voltage Vdd to the center point of the drain transformer coil 106. In a second thick global metal wiring layer, a patterned lower gate coil 91 and a concentric inner lower drain coil 92 are formed to be symmetrically positioned about the transformer's axis of symmetry. As shown, the patterned lower gate coil 91 includes a first center point 105 at one end of the patterned lower gate coil 91 and a pair of drain terminals 91A, 91B at opposite ends for connecting to the negative gate G− and positive gate G+ of the next amplifier stage. Similarly, the lower drain winding 92 includes a concentric circular top metal winding layer having a second center point 106 at one end and a pair of ends 92A and 92B at the other end for connection to the positive drain D+ and negative drain D- of the previous amplifier stage. Furthermore, in the topmost, thickest metal wiring layer, patterned upper gate coils 111 and 112 and a concentric inner upper drain coil 113 are formed to be symmetrically arranged about the transformer's axis of symmetry and connected to the underlying patterned lower gate coil 91 and concentric inner lower drain coil 92.

[0086] As disclosed herein, supplying voltage at the center point of the inner drain coil from several sides using power supply voltage routing tracks formed in a first relatively thick (copper) conductor layer (e.g., M7) results in a current loop. To illustrate the current loop, reference is now made to Figure 16 , Figure 16A plan view 160 of patterned metal layers 161-164 in an integrated circuit transformer is depicted, wherein drain voltage supply conductors 162A-F supply voltage Vdd to a drain center point 165. In this case, an RF current flowing clockwise from D+ terminal 164E to D- terminal 164F will induce opposing RF currents i1-i4 in drain voltage supply conductors 162C-162F. To prevent the induced current from adversely affecting transformer performance, the integrated circuit transformer can be designed to ensure that the parasitic loop inductance L is sufficiently large and the mutual inductance M to the drain winding is sufficiently small. In most cases, a ratio L / M > 10 is sufficient. To achieve this result, at least the vertical drain voltage supply conductors 162C-162F can be spaced apart from the transformer by a lateral spacing distance D1 that is approximately 1 / 10 to 1 / 4 of the transformer's outer diameter. Furthermore, the horizontal drain voltage supply conductors can also be spaced apart from the transformer by a minimum vertical spacing distance D2 that is approximately half to twice the transformer's outer diameter. And because the Vdd voltage supply conductors 162A, 162B extending along the transformer's axis of symmetry are at the virtual ground for the differential signal, it is beneficial to position the MOS devices of the output and input stages close to the Vdd voltage supply conductors 162A, 162B and symmetrically with respect to the transformer's axis of symmetry. As disclosed herein, using the Vdd voltage supply conductors 162A, 162B in a thick copper layer as a ground reference for both sides of the transformer is beneficial because it has a lower resistance than the center strip (e.g., center shield track 61) in a thin copper patterned ground shield.

[0087] As disclosed herein, integrated circuit transformers can be deployed in a variety of configurations and circuit arrangements and are particularly attractive for inter-stage impedance matching and energy efficiency in differential power amplifier stages, where the transformers can withstand the high DC drive currents present in high power (50 mW) high frequency (78 GHz) amplifier stages. To provide example circuit arrangements, reference is now made to Figure 17 , Figure 17 A two-stage, three-transformer differential amplifier 170 is depicted in accordance with selected embodiments of the present disclosure. For illustrative purposes, the circuitry for supplying gate bias is not shown. Furthermore, decoupling and tuning capacitors are not shown. Furthermore, the transformer coil sizes are shown as being equal for all three stages, but they may have different diameters, widths, and spacings.

[0088] As depicted, the differential amplifier 170 includes a first-stage input transformer 171 connected to receive differential input signals Vin+ and Vin- at input terminals of an inner coil 171a to inductively couple with an outer coil 171b to produce output signals G+ and G- at output terminals of (one or more) outer coils 171b 1-2. Because the first-stage input transformer 171 does not require a tap at the center point of the inner coil 171a, no feed conductor is required, but the first-stage input transformer 171 does include an underlying patterned ground shield (connected to Vsh) and a first rail for connecting the center points of the outer coils (connected to Vg).

[0089] Differential amplifier 170 also includes a second-stage transformer 172, which is connected to receive differential input drain signals D+ and D- at the input terminals of inner coil 172A to inductively couple with outer coil(s) 172b, thereby generating output signals G+ and G- at the output terminals of outer coils 172b1-2. As depicted, differential input drain signals D+ and D- are generated by NFET transistors M1 and M2, which are respectively gated by output signals G+ and G- from first-stage input transformer 171 to connect power supply voltage Vss to input terminals D+ and D- of inner coil 172A. Although not visible, second-stage transformer 172 does include an underlying patterned ground shield (connected to Vsh) and a first rail for connecting the center point of the outer coil (connected to Vg). In addition, since the second stage transformer 172 includes a tap at the center point of the inner coil 172a, there is also a center feed conductor 172c formed in a relatively thick copper layer for connecting the drain coil center point to the power supply voltage Vdd.

[0090] Finally, differential amplifier 170 includes a third-stage transformer 173 connected to receive differential input drain signals D+ and D- at the input terminals of inner coil 173A for inductive coupling with outer coil(s) 173b to generate output signals Vout- and Vout+ at the output terminals of outer coils 173b1-2. As depicted, the differential input drain signals D+ and D- of third-stage transformer 173 are generated by NFET transistors M3 and M4, which are respectively gated by output signals G+ and G- from second-stage transformer 172 to connect the power supply voltage Vss to the input terminals D+ and D- of inner coil 173A. Although not visible, third-stage transformer 173 also includes an underlying patterned ground shield (connected to Vsh) and a first rail for connecting the center point of the outer coil (connected to Vg). In addition, third-stage transformer 173 includes a tap at the center point of inner coil 173a, which is connected to a center feed conductor 173c formed in a relatively thick copper layer for connecting the drain coil center point to the power supply voltage Vdd. As depicted, at least the Vss and Vdd leads of third-stage transformer 173 are wider than the Vss and Vdd leads of second-stage transformer 172 because the power, and therefore the drive current, in the second stage will be greater.

[0091] As disclosed herein, selected embodiments of integrated circuit transformer devices can be formed into multi-turn transformers in which multiple crossovers are formed in the top metal layer. To provide additional details for improving understanding of selected embodiments of the present invention, reference is now made to Figure 18 , Figure 18A plan view 180 of patterned metal layers 181-188 and conductive via structures 189, 193 used to form a 2×1 integrated circuit transformer is depicted. In plan view 180, visible portions of the patterned metal layers 181-188 are shown along with the location of the conductive via structure 189 and the drain center tap via 193. From this perspective, it should be understood that the metal interconnects M1-M9 are sequentially deposited, patterned, and etched on an intermediate interlayer dielectric (ILD) layer using any suitable back-end process that includes the ability to form conductive via structures between different metal interconnect layers to establish the desired electrical connections. For example, a first, relatively thin metal interconnect layer M1 can be patterned to form a ground shield (not shown) in the lowest metal interconnect layer on a bottom or bottom passivation layer or dielectric layer. After forming one or more intermediate ILD layers ILD1-5 and metal interconnect layers (e.g., M2-M5), a second, relatively thin metal interconnect layer M6 can be patterned to form a gate center tap (CT) bar 182 extending along the transformer's axis of symmetry and including a through-hole contact pad for making an electrical connection across a subsequently formed gate center tap via V6 (not shown) to connect to the gate center tap 192. After forming the intermediate ILD layer ILD6 and any desired interconnect via structures V6, a first, relatively thick metal interconnect layer M7 can be patterned to form a drain center tap bar 183 extending along the transformer's axis of symmetry and including a through-hole contact pad for making an electrical connection across a subsequently formed drain center tap via V7 193 to connect to the drain center tap 191.

[0092] After forming the intermediate ILD layer ILD7 and any desired interconnect via structures V7, a second relatively thick metal interconnect layer M8 can be patterned to form concentric primary gate windings 185A-B on the inner and outer sides of the generally circular secondary drain winding 184. To provide a through-path for the primary and secondary windings, the secondary drain winding 184A and drain winding end 184B in the relatively thick metal interconnect layer M8 can be formed as a circular metal winding layer having one or more gaps or openings through which the primary gate winding 185B can extend. In the same manner, the concentric primary gate windings 185A, 185B in the relatively thick metal interconnect layer M8 can be formed as a pair of circular-shaped metal winding layers having one or more gaps or openings through which the secondary drain winding 184A can extend, thereby allowing the concentric primary gate windings 185A, 185b to be formed on both sides of the secondary drain winding 184A.

[0093] After forming the middle ILD layer ILD8 and any desired interconnect via structures V8, the upper relatively thick metal interconnect layer M9 can be patterned to form concentric primary gate windings 187A-B on the inner and outer sides of the generally circular secondary drain winding 186. As formed, the shapes and positions of the primary gate windings 187A-B and the secondary drain winding 186 substantially conform to the shapes and positions of the underlying primary gate windings 185A-B and the secondary drain winding 184A. To provide a crossover path for the primary and secondary windings, the secondary drain winding 186 and the drain winding end 188A in the upper relatively thick metal interconnect layer M9 can be formed as a circular metal winding layer having one or more gaps or openings through which the primary gate winding 187A can extend. In the same manner, the concentric primary gate windings 187A, 187B in the upper relatively thick metal interconnect layer M9 can be formed as a pair of circular-shaped metal winding layers having one or more gaps or openings, and the secondary drain winding 186 can extend through the gaps or openings, thereby allowing the concentric primary gate windings 187A, 187b to be formed on both sides of the secondary drain winding 186.

[0094] By patterning and positioning concentric primary gate windings 185 and 187 to surround the inner and outer sides of secondary drain windings 184 and 186, a 2×1 transformer is formed with an axis of symmetry extending along the drain center tap strip 183. By defining the winding diameter and width to allow for a plurality of conductive via structures 189, defined layers in the second relatively thick metal interconnect layer M8 and the upper relatively thick metal interconnect layer M9 electrically connect to form the primary gate winding and the secondary drain winding. Furthermore, the symmetry and positioning of the layers 185 and 187 used to form the primary gate winding creates a gate center tap point 192 that is aligned to electrically connect to the M6 ​​gate center tap strip 182. Similarly, the symmetry and positioning of the layers 184 and 186 used to form the primary drain winding creates a drain center tap point 191 that is aligned to electrically connect to the M7 drain center tap strip 183.

[0095] In order to provide additional details for improving the understanding of selected embodiments of the present invention, reference is now made to Figure 19 , Figure 19 Depicts Figure 18190 . As depicted, a lower patterned ground shield 181 is formed in a first, relatively thin, local metal wiring interconnect layer M1. In one or more upper, relatively thin local metal interconnect layers M2-M6, a first patterned gate center tap strip 182 is formed along the transformer's axis of symmetry, with a first via contact pad (not shown) for connecting to the center tap points 192 of subsequently formed gate transformer coil windings 185, 187. In a first, thicker, global metal interconnect layer M7, a second patterned drain center tap strip 183 is formed along the transformer's axis of symmetry, with a second via contact pad (not shown) for connecting to the center tap points 191 of subsequently formed drain transformer coil windings 184, 186. In a second, thicker, global metal wiring interconnect layer M8, a patterned lower drain coil 184 and concentric lower gate coils 185A, 185B are formed to be symmetrically positioned about the transformer's axis of symmetry. As shown, the patterned lower drain coil segment 184 forms a generally circular loop and includes a pair of drain terminals 188A, 188B at one end of the patterned lower drain coil and a drain center tap point 191 at the opposite end for connection to the patterned drain center tap strip 183. Similarly, the patterned lower gate coil segments 185A, 185B include concentric circularly shaped metal winding layers with a pair of gate terminals 188C, 188D at one end of the patterned lower gate coil and a gate center tap point 192 at the opposite end for connection to the patterned gate center tap strip 182. And in the topmost, thickest metal wiring interconnect layer M9, the patterned upper drain coil 186 and concentric inner and outer upper gate coils 187A, 187B are formed to be symmetrically disposed about the transformer's axis of symmetry and connected to the underlying patterned lower drain coil 184 and concentric lower gate coils 185A, 185B. As shown, the first patterned lower gate coil segments 185A, 187A are wound around one exterior side of the patterned lower drain coil segment 184 and also around an interior side of the patterned lower drain coil segment 184, with substantially equidistant spacing between the opposing sides. Additionally, the second patterned lower gate coil segments 185B, 187B are wound around the opposing exterior sides of the patterned lower drain coil segment 184, with substantially equidistant spacing between the opposing sides.

[0096] exist Figures 18 and 19In the example integrated circuit transformer embodiment depicted in FIG, a 2×1 transformer can be formed in the two uppermost metal interconnect layers M8, M9 by using the thick global metal wiring interconnect layer M8 as the through winding layers 184, 185B and the thickest metal wiring interconnect layer M9 as the crossover winding layers 186C, 187C. However, it should be understood that the crossover can be configured in different ways. For example, a 45 degree angled winding track can be used to achieve the following. Figure 19 The crossover is shown in FIG, but other crossover angles may be used. In addition, it will be appreciated that the winding track length required for the crossover limits the inner diameter of the transformer. Therefore, Figure 19 An example is shown where the inner diameter (across the primary gate winding layers) is only slightly larger than the winding track lengths 187C, 186C consumed by the crossing. Of course, for a 1×1 turn transformer, the angled crossing winding tracks can be avoided, in which case the inner diameter can be made even smaller. Even when the number of turns is only 1 or 2, having a small inner diameter is important for the low inductance values ​​required for 78 GHz radar circuits.

[0097] At much lower frequencies, it may be desirable to achieve much larger inductance values ​​while maintaining a relatively small transformer diameter. In this case, a 2×2, 3×2, or even N×M turn transformer may be desirable, with a structure similar to Figure 19 , but with crossed winding tracks at other locations.

[0098] As disclosed herein, several design options are possible for constructing and using transformers. First, in a stacked transformer, the desired inductive coupling can be achieved by using the same width and diameter for the primary and secondary windings and forming them in different metal (winding) layers. Alternatively, in a transverse transformer, the desired inductive coupling can be achieved by using different diameters for the primary and secondary windings and forming them in the same metal (winding) layer. Thus, the mutual inductance can be increased by increasing the number of primary and secondary windings. Since the winding tracks must be able to cross each other so that the different primary and secondary windings can be connected in series, at least two metal (winding) layers are required to ensure that the desired connection can be formed between the transformer windings. In other embodiments, where the transformer windings are implemented in only a single metal, the capacitance between the nested windings can be reduced. When only two metal (winding) layers of sufficient thickness are available to produce a high-performance transformer, the use of a stacked layout is limited to symmetrical designs with the same number of primary and secondary turns, which can provide a unit impedance transformation ratio. The lateral architecture is more flexible in this respect and enables the fabrication of transformers with different turns ratios, combining the balun function with the impedance transformation function using only two metal layers.

[0099] An integrated transformer according to the present disclosure can be built in a standard IC processing flow, where multiple interconnect metal layers are added in the back-end processing after the transistors, diodes and resistors are manufactured in the substrate. Typically, the ground shield is made by patterning polysilicon or a first metal (ground shield) interconnect layer. The wires for connecting to the center point of the gate coil can be made in a subsequent relatively thin metal layer, and the wires for connecting to the center point of the drain coil can be made in a subsequent relatively thick metal layer, such as a first copper layer for long-distance circuit connections and local power lines. The primary and secondary windings and their crossings can then be formed in a third and fourth metal layers (winding layers), which can include a second copper layer for long-distance circuit connections and local power lines and a topmost aluminum layer for global power lines and bonding pads. Where necessary, the different metal layers can be interconnected with vias.

[0100] It should now be understood that an integrated circuit transformer and methods of manufacturing and operating the same are provided herein. As disclosed, the integrated circuit transformer includes a primary winding, a secondary winding, and a first center tap feed line. The primary winding is located in at least a first winding layer having a first thickness and has two primary ends at a first side of the transformer. The secondary winding is located in at least the first winding layer and has a first center point at the first side of the transformer and two secondary ends at an opposite second side of the transformer. In selected embodiments, the primary winding and the secondary winding are concentric. In other embodiments, the primary winding and the secondary winding are both located in the first winding layer and the adjacent last metal layer and each has a different winding radius. The first center tap feed line is located in an upper metal layer along the symmetry axis of the transformer, the upper metal layer having a second thickness at least equal to the first thickness of the first winding layer, and has a direct electrical connection to the first center point in the secondary winding. In selected embodiments, the first center tap feed line is formed in a first upper copper layer, the first upper copper layer being located below a second adjacent upper copper layer comprising the first winding layer, wherein the first upper copper layer and the second adjacent upper copper layer have substantially the same thickness. In other embodiments, the first center tap feed line is formed in a first upper conductive metal layer being located above a second upper conductive metal layer comprising the first winding layer, wherein the first upper conductive metal layer is at least as thick as the second upper conductive metal layer. In other embodiments, the first center tap feed line is formed in a plurality of lower conductive metal layers that are directly electrically connected to one another, the plurality of lower conductive metal layers being located below the upper conductive metal layer comprising the first winding layer, wherein the plurality of lower conductive metal layers have a combined thickness that is at least as thick as the upper conductive metal layer. The integrated circuit transformer may further include a substrate and a patterned ground shield layer, the patterned ground shield layer being located between the first winding layer and the substrate. In addition, the integrated circuit transformer can have a second center-tap feed line, which is located in a lower metal layer between the patterned ground shield layer and the first winding layer along the symmetry axis of the transformer, wherein the second center-tap feed line has a direct electrical connection to a second center point in the primary winding and has a thickness that is less than the second thickness of the upper metal layer. In selected embodiments, the primary and secondary windings of the integrated circuit transformer form a 1×1 transformer in two upper, relatively thick metal interconnect layers. In other embodiments, the primary and secondary windings of the integrated circuit transformer form a 2×1 transformer in two upper, relatively thick metal interconnect layers. In selected embodiments, the two primary ends of the primary winding are connected to the gate terminals G+, G- of the output amplifier, and the two secondary ends of the secondary winding are connected to the drain terminals D+, D- of the input amplifier.Additionally, the integrated circuit transformer may include patterned power supply voltage wiring tracks formed in an upper metal layer to be symmetrically arranged about an axis of symmetry, wherein the patterned power supply voltage wiring tracks are laterally spaced apart from the primary winding and the secondary winding by a minimum spacing distance selected to prevent RF currents induced in the patterned power supply voltage wiring tracks from adversely affecting transformer performance.

[0101] In another embodiment, an electronic circuit and methods for manufacturing and operating the same are provided herein. As disclosed, the electronic circuit includes a first power amplifier having a first output drain terminal and a second output drain terminal, and a second power amplifier having a first input gate terminal and a second input gate terminal. The electronic circuit also includes an integrated circuit transformer connected between the first power amplifier and the second power amplifier. As formed, the integrated circuit transformer includes a primary gate winding, a secondary drain winding, and a center-tapped feed line. The primary gate winding is located at least in a first, relatively thick, upper metal interconnect layer and has a gate center point on a first side of the integrated circuit transformer and two primary terminals on an opposite second side of the integrated circuit transformer, the two primary terminals being connected to the first and second input gate terminals of the second power amplifier. The secondary drain winding is located at least in the first, relatively thick, upper metal interconnect layer and has a drain center point on a second, opposite side of the integrated circuit transformer and two secondary terminals on the first side of the integrated circuit transformer, the two secondary terminals being connected to the first and second output drain terminals of the first power amplifier. A first center-tapped feed line is located in a second, relatively thick upper metal interconnect layer along an axis of symmetry of the integrated circuit transformer, the second relatively thick upper metal interconnect layer being at least as thick as the first relatively thick upper metal interconnect layer, wherein the first center-tapped feed line is directly electrically connected to the drain center point of the secondary drain winding. In selected embodiments, the first center-tapped feed line is formed in a first upper copper metal layer located below a second adjacent upper copper metal layer forming the primary gate winding and the secondary drain winding, wherein the first upper copper metal layer and the second adjacent upper copper metal layer have substantially the same thickness. In other embodiments, the first center-tapped feed line is formed in a first upper conductive metal layer located above a second upper conductive metal layer forming the primary gate winding and the secondary drain winding, wherein the first upper conductive metal layer is at least as thick as the second upper conductive metal layer. In other embodiments, the first center-tap feed line is formed in a plurality of lower conductive metal layers that are directly electrically connected to one another, the plurality of lower conductive metal layers being located below an upper conductive metal layer forming the primary gate winding and the secondary drain winding, wherein the plurality of lower conductive metal layers have a combined thickness at least as thick as the upper conductive metal layer. The electronic circuit may further include patterned power supply voltage routing tracks formed in a second, relatively thick upper metal interconnect layer to be symmetrically arranged about an axis of symmetry, wherein the patterned power supply voltage routing tracks are laterally spaced from the primary gate winding by a minimum spacing distance selected to prevent the primary gate winding from inducing RF currents in the patterned power supply voltage routing tracks that could adversely affect transformer performance. In selected embodiments, the primary gate winding and the secondary drain winding are concentric windings having different winding radii to form a 1×1 transformer in the two upper, relatively thick metal interconnect layers.In other embodiments, the primary gate winding and the secondary drain winding are concentrically shaped windings with different winding radii to form a 2x1 transformer in two relatively thick metal interconnect layers.

[0102] In yet another form, a transformer and methods for manufacturing and operating the same are provided. As disclosed, the transformer circuit includes at least one primary turn formed in an upper metal interconnect layer having a first local power line thickness and symmetrically disposed along a symmetry axis of the transformer. The transformer also includes at least one secondary turn formed in the upper metal interconnect layer and symmetrically disposed along the symmetry axis of the transformer. Additionally, the transformer includes a first center-tapped feed line located in the upper metal interconnect layer along the symmetry axis of the transformer, the upper metal interconnect layer being at least as thick as the first local power line thickness, wherein the first center-tapped feed line is directly electrically connected to a drain center point of the at least one secondary turn. In selected embodiments, the at least one primary turn is formed as a gate winding having a single outer circular segment formed in a lower layer and two semicircular segments formed in an upper layer, the two semicircular segments being aligned with the single outer circular segment and electrically connected across a conductive via structure through the single semicircular segment formed in the lower layer. In addition, the at least one secondary turn is formed as a drain winding having a single concentric inner circular segment formed in a lower layer and electrically connected to a single circular segment formed in an upper layer, the single circular segment being aligned with the single concentric inner circular segment layer. In other embodiments, the at least one primary turn is formed as a gate winding using multiple segments, the multiple segments being concentrically located on both the inside and outside of the at least one secondary winding (which is the drain winding). In such embodiments, the at least one secondary turn is formed as a drain winding having a first circular segment formed in a lower layer, the first circular segment being electrically connected to an aligned second circular segment formed in an upper layer. In addition, the gate winding includes a first semicircular winding segment formed in a lower layer, the first semicircular winding segment being electrically connected to an aligned first semicircular winding segment formed in an upper layer, wherein the first semicircular winding segment is located at a uniform distance from a first outer half of the first circular segment. In addition, the gate winding includes a second winding segment formed in the lower layer, which is electrically connected to the aligned first segment formed in the upper layer, wherein the first segment is located at a uniform distance from the second outer half of the first circular segment and is also located at a uniform distance from the inner half of the first circular segment.

[0103] While the exemplary embodiments described herein are directed to integrated circuit-based transformer devices and associated manufacturing methods, wherein metal layers having widths and / or thicknesses similar to those used to form the transformer coils are used to contact the center point of the transformer coils from two opposing sides along the transformer's axis of symmetry, the present invention is not necessarily limited to exemplary embodiments illustrating the inventive aspects of the present invention applicable to various integrated circuit transformer devices. Accordingly, the particular embodiments disclosed above are merely illustrative and should not be construed as limiting the invention, as the invention may be modified and practiced in different but equivalent manners apparent to those skilled in the art having the benefit of the teachings herein. Therefore, the foregoing description is not intended to limit the invention to the particular forms set forth, but, on the contrary, is intended to cover such alternatives, modifications, and equivalents as may be included within the spirit and scope of the invention as defined by the appended claims, such that those skilled in the art will understand that they may make various changes, substitutions, and alterations without departing from the spirit and scope of the invention in its broadest form.

[0104] Benefits, other advantages, and solutions to problems have been described above with respect to specific embodiments. However, benefits, advantages, solutions to problems, and any (one or more) elements that may cause any benefit, advantage, or solution to appear or become more significant should not be construed as key, required, or essential features or elements of any or all of the claims. As used herein, the terms "comprises," "comprising," or any other variations thereof are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that includes a list of elements includes not only those elements, but may also include other elements not expressly listed or inherent to those processes, methods, articles, or apparatus.

[0105] Although the described exemplary embodiments disclosed herein focus on single-wire turn inductor structures formed in two metal layers, the present invention is not necessarily limited to the exemplary embodiments shown herein and may be applied to protect any integrated circuit inductor formed in one or more metal layers. Therefore, the particular embodiments disclosed above are merely illustrative and should not be construed as limiting the invention, as the invention may be modified and practiced in different but equivalent manners apparent to those skilled in the art having the benefit of the teachings herein. Therefore, the foregoing description is not intended to limit the invention to the particular forms set forth, but, on the contrary, is intended to cover such alternatives, modifications and equivalents as may be included within the spirit and scope of the invention as defined by the appended claims, so that those skilled in the art will understand that they can make various changes, substitutions and alterations without departing from the spirit and scope of the invention in its broadest form.

[0106] Benefits, other advantages, and solutions to problems have been described above with respect to specific embodiments. However, benefits, advantages, solutions to problems, and any (one or more) elements that may cause any benefit, advantage, or solution to appear or become more significant should not be construed as key, required, or essential features or elements of any or all of the claims. As used herein, the terms "comprises," "comprising," or any other variations thereof are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that includes a list of elements includes not only those elements, but may also include other elements not expressly listed or inherent to those processes, methods, articles, or apparatus.

Claims

1. An integrated circuit transformer, characterized in that: include: a primary winding located at least in a first winding layer having a first thickness, the primary winding having two primary ends at a first side of the transformer; a secondary winding located at least in the first winding layer, the secondary winding having a first center point at the first side of the transformer and two secondary ends at second, laterally opposite sides of the transformer; as well as a first center-tapped feed line located in an upper metal layer along an axis of symmetry of the transformer, the upper metal layer having a second thickness at least equal to the first thickness of the first winding layer, wherein the first center-tapped feed line has a direct electrical connection to the first center point in the secondary winding; a substrate and a patterned ground shield positioned between the first winding layer and the substrate to electrically shield the primary winding and the secondary winding from the substrate; and a second center tap feed line located in a lower metal layer between the patterned ground shield and the first winding layer along the axis of symmetry of the transformer, wherein the second center tap feed line has a direct electrical connection to a second center point in the primary winding and has a thickness less than the second thickness of the upper metal layer.

2. The integrated circuit transformer according to claim 1, wherein: The first center-tap feed line is located in a first upper metallic copper layer located below a second adjacent upper metallic copper layer including the first winding layer, wherein the first upper metallic copper layer and the second adjacent upper metallic copper layer have substantially the same thickness.

3. The integrated circuit transformer according to claim 1, wherein: The first center tap feed line is located in a first upper conductive metal layer located above a second upper conductive metal layer including the first winding layer, wherein the first upper conductive metal layer is at least as thick as the second upper conductive metal layer.

4. The integrated circuit transformer according to claim 1, wherein: The first center-tap feed line includes a plurality of lower conductive metal layers directly electrically connected to each other, the plurality of lower conductive metal layers being located below an upper conductive metal layer including the first winding layer, wherein the plurality of lower conductive metal layers have a combined thickness at least as thick as the upper conductive metal layer.

5. The integrated circuit transformer according to claim 1, wherein: The primary winding and the secondary winding are concentric.

6. The integrated circuit transformer according to claim 1, wherein: The primary winding and the secondary winding are both located in the first winding layer and the adjacent last metal layer, and each has a different winding radius.

7. An electronic circuit, characterized in that include: An integrated circuit transformer according to any preceding claim, wherein the electronic circuit comprises: a first power amplifier including a first output drain terminal and a second output drain terminal; A second power amplifier includes a first input gate terminal and a second input gate terminal; and wherein the integrated circuit transformer is connected between the first power amplifier and the second power amplifier.

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