On-Chip Transformer With Through-Substrate Windings
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Solution Overview
Problem
Existing on-chip transformer topologies face challenges such as unequal winding lengths, high insertion loss, asymmetry in electrical response, and limited frequency response due to parasitic capacitance and thin metal layers, which affect the transformer's coupling coefficient and efficiency.
Innovation Solution
A transformer design where windings pass through a substrate, providing large cross-sectional areas and enhanced electromagnetic coupling, with metal connectors passing through trenches to ensure high coupling coefficients and low insertion loss, and a method involving anisotropic etching and metal deposition processes to manufacture this configuration.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If windings are implemented using conventional on-chip topologies (Shibata or Finlay architectures), then the transformer can be integrated on substrate, but the coupling coefficient is limited (0.75-0.9) and insertion loss is high due to thin metal layers and unequal winding lengths
Solution Approach 1:
The patent transitions from planar on-chip windings to three-dimensional windings that pass through the substrate thickness. The windings are formed by metal connectors extending through the substrate from top to bottom surfaces, creating a vertical dimension that increases the effective cross-sectional area and reduces resistance while improving coupling between primary and secondary windings
Solution Approach 2:
The patent changes the geometric parameters of the windings by increasing the cross-sectional area through substrate penetration. The metal connectors have larger effective area compared to thin film windings, and the winding length through the substrate provides better magnetic coupling, directly improving the coupling coefficient and reducing insertion loss
2Area of stationary object
If Finlay stacked architecture is used to achieve low area and high coupling coefficient, then area is reduced and coupling is improved, but asymmetry in electrical response occurs due to different metal layer resistances and high insertion loss from thin intermediate metal layers
Solution Approach 1:
The patent uses vertical penetration through the substrate to create windings that are symmetric in their interaction with the substrate. Both primary and secondary windings pass through the same substrate thickness, ensuring equal electrical path lengths and symmetric electrical response, eliminating the asymmetry problem of stacked architectures
Solution Approach 2:
The patent applies uniform substrate penetration to both primary and secondary windings, ensuring that both windings experience identical electrical characteristics through the substrate. This local uniformity in winding implementation through the substrate ensures symmetric electrical response and equal coupling to the substrate
3Reliability
If upper winding is electrically shielded from substrate by lower winding, then substrate coupling is reduced, but parasitic capacitance to substrate differs for each winding causing frequency response limitations
Solution Approach 1:
The patent positions both primary and secondary windings to pass through the substrate, placing them on equal footing regarding substrate coupling. This vertical arrangement eliminates the shielding effect where one winding blocks substrate coupling to another, as both windings have direct access to the substrate through their respective paths
4Loss of energy
If metal connectors pass through substrate with large cross-sectional area, then resistance is reduced and coupling is improved, but manufacturing complexity increases due to trench formation and multi-layer metal deposition
Solution Approach 1:
The patent divides the metal connector formation into separate stages: first forming trenches through the substrate, then filling with metal material, and finally adding metal capping layers. This segmentation of the manufacturing process makes the complex task of creating through-substrate connectors manageable and compatible with standard semiconductor fabrication techniques
Solution Approach 2:
The patent introduces trenches as intermediary structures that facilitate the formation of metal connectors through the substrate. The trenches provide defined pathways that guide metal deposition and ensure proper alignment, simplifying the manufacturing process compared to direct through-substrate metal formation
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
The design achieves a high coupling coefficient and low insertion loss, making it suitable for both high and low frequency applications, while being easy to design and manufacture, thus overcoming the limitations of previous topologies.
Implementation Method 1
The two windings therefore have a large cross-sectional area, reducing their resistance, and present a large electromagnetic coupling area to each other via the metal connectors passing through the substrate.
Implementation Method 2
The first and second trenches may be made using an anisotropic etching process.
Implementation Method 3
Typically, metal is deposited within the trenches using a vapour deposition processor by electrolytic growth.
Data Source
AI summary
A transformer comprising primary and secondary windings is disclosed. Each winding has first and second metal capping layers coupled together electrically in parallel by a metal connector passing through a substrate lying between the first and second metal capping layers.