Symmetrical Stacked Transformer for RF On-Chip Integration
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Solution Overview
Problem
Existing integrated transformers for RF applications at millimeter-wave frequencies are limited by the need for multiple metal layers to achieve sufficient inductance, making them large and difficult to implement in on-chip designs, especially when trying to create structures with two turns or more.
Innovation Solution
A symmetrical transformer structure using four identical basic elements in two conductive planes, with each element providing half the turns of each coil, allowing for magnetic coupling and easy connection of terminals on opposite sides, enabling a compact design with improved electrical and geometrical symmetry.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If the number of turns or area is increased to increase inductance, then the inductance increases, but the transformer area increases
Solution Approach 1:
The patent transitions from planar windings to three-dimensional stacked windings across multiple conductive layers. The primary coil uses first and second conductive layers while the secondary coil uses third and fourth conductive layers, with vertical interconnections via vias. This dimensional change allows the magnetic flux to couple through the vertical dimension (dielectric layers) rather than requiring larger planar area, thereby increasing inductance without proportionally increasing the transformer footprint.
2Speed
If the number of layers is increased to increase the number of turns, then the inductance increases, but the device complexity increases
Solution Approach 1:
The transformer is segmented into functionally independent coil structures: the primary coil is formed by conductive paths on the first and second conductive layers, while the secondary coil is formed by conductive paths on the third and fourth conductive layers. Each coil is further segmented into multiple turns within its respective layers. This segmentation allows each layer to be optimized for its specific function and simplifies the overall design and manufacturing process compared to a monolithic multi-layer structure.
3Manufacturing precision
If a symmetrical stacked structure is used to improve electrical symmetry, then the phase balance improves, but the manufacturing complexity increases
Solution Approach 1:
While the overall transformer structure is symmetrical, the patent employs asymmetrical routing of conductive paths within each layer to achieve the desired number of turns and optimize magnetic coupling. The conductive paths are configured to create the specific winding patterns needed for the primary and secondary coils, with vias positioned asymmetrically to connect layers. This controlled asymmetry within a symmetrical framework allows optimization of electrical performance while maintaining manufacturability.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This configuration simplifies the layout, enhances symmetry, and allows for easier adaptation to increase the number of turns, resulting in a more efficient and compact transformer with better electrical properties, suitable for on-chip integration in RF circuits.
Implementation Method 1
the primary and secondary coils being electrically isolated from each other and being arranged so that magnetic coupling takes place between them
Data Source
AI summary
One aspect of the invention relates to a symmetrical transformer with a stacked coil structure comprising two coils each having at least two turns. The coils are located in two conductive planes. The structure includes four identical basic elements, each basic element providing a conductive path for part of the coils. The terminals of the transformer are located at opposite sites of the structure so that the structure can be easily connected in a chain. The invention also relates to a semiconductor device comprising such a structure.