Enlarged Waveguide Extending Into Buried Insulator Layer
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Solution Overview
Problem
Propagation losses in nitride waveguides are high, and enlarging waveguides to reduce these losses impacts interconnect layers, leading to increased contact resistance and preventing optical coupling between silicon and nitride waveguides in photonic integrated circuits (PICs).
Innovation Solution
A semiconductor-on-insulator (SOI) substrate with an enlarged waveguide that extends into a buried insulator layer, allowing for vertical enlargement without increasing the inter-level dielectric (ILD) layer thickness, enabling optical side-coupling between silicon and nitride waveguides.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If waveguides are enlarged to reduce propagation losses, then propagation losses are reduced, but the inter-level dielectric (ILD) layer thickness must be increased, which increases contact resistance and negatively impacts PIC performance
Solution Approach 1:
The waveguide structure transitions from a planar configuration to a three-dimensional configuration by extending vertically into the buried insulator layer. This dimensional change allows the waveguide to achieve larger effective area for reduced propagation losses without increasing the lateral footprint or requiring thicker ILD layers, thereby avoiding increased contact resistance.
Solution Approach 2:
The enlarged waveguide structure is nested within the existing ILD layer thickness constraints by utilizing the vertical space into the buried insulator layer. The waveguide core is positioned such that its lower surface extends into the buried insulator while the upper surface remains within the ILD layer, effectively nesting the enlarged structure within the existing layer architecture.
2Loss of energy
If waveguides are enlarged to reduce propagation losses, then propagation losses are reduced, but optical coupling between silicon waveguides and nitride waveguides in different layers becomes impossible
Solution Approach 1:
The waveguide structure enables vertical optical coupling by extending into the buried insulator layer, creating three-dimensional overlap between waveguides in different layers. This dimensional extension allows optical fields from silicon waveguides in one layer to couple with nitride waveguides in another layer through the enlarged interaction volume, achieving inter-layer optical coupling that was previously impossible with planar structures.
Solution Approach 2:
The waveguide structure implements local quality enhancement by concentrating the optical field interaction in the vertical region where the lower surface extends into the buried insulator layer. This localized field enhancement in the critical coupling region enables efficient optical coupling between different material systems (silicon and nitride) while maintaining low propagation losses in the waveguide sections.
3Loss of energy
If vertically enlarged waveguides are implemented, then propagation losses are reduced, but the thickness of inter-level dielectric (ILD) layer must be increased, which increases the length of vertical interconnects
Solution Approach 1:
The waveguide enlargement is achieved by utilizing the vertical dimension into the buried insulator layer rather than increasing the ILD layer thickness. This dimensional strategy allows the waveguide to achieve larger effective area for reduced propagation losses while maintaining the original ILD thickness and interconnect lengths, avoiding the penalty of increased vertical interconnect length.
Solution Approach 2:
The waveguide structure is segmented into distinct regions: the lower surface extending into the buried insulator layer for enlargement, the upper surface remaining within the ILD layer for interconnect compatibility, and the lateral dimensions for optical confinement. This segmentation allows the waveguide to achieve enlargement benefits in one region while maintaining compatibility with existing interconnect structures in other regions.
Data Source
AI summary
Structures and methods implement an enlarged waveguide. The structure may include a semiconductor-on-insulator (SOI) substrate including a semiconductor-on-insulator (SOI) layer over a buried insulator layer over a semiconductor substrate. An inter-level dielectric (ILD) layer is over the SOI substrate. A first waveguide has a lower surface extending at least partially into the buried insulator layer, which allows vertical enlargement of the waveguide, without increasing the thickness of the ILD layer or increasing the length of interconnects to other devices. The enlarged waveguide may include nitride, and can be implemented with other conventional silicon and nitride waveguides.