Optical Modulator Gate Layout With Regrown Silicon for Lower Loss
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Solution Overview
Problem
The performance of optical modulators with a polycrystalline silicon region is negatively affected by parasitic resistances and optical signal losses due to doping levels and grain boundaries, which hinder mobility of free carriers.
Innovation Solution
The introduction of a regrown silicon region epitaxially formed over a polycrystalline silicon region, reducing resistances and grain size to enhance bandwidth by removing part of the polycrystalline silicon and regrowing a silicon layer.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If higher doping levels are used in the polycrystalline silicon region, then parasitic resistance is reduced, but optical signal losses increase
Solution Approach 1:
The gate region is divided into two distinct segments: a polycrystalline silicon region and a regrown silicon region. The polycrystalline region provides high doping levels for low parasitic resistance, while the regrown silicon region with lower doping maintains optical performance, thus resolving the contradiction between reducing parasitic resistance and preventing optical signal losses.
Solution Approach 2:
Different regions of the gate are assigned different doping levels and material properties tailored to their specific functions. The polycrystalline silicon region is heavily doped to minimize parasitic resistance, while the regrown silicon region is lightly doped to preserve optical signal transmission, allowing each local area to optimize its performance for its intended purpose.
2Area of stationary object
If more polycrystalline silicon material is present in the active region, then device area is reduced, but parasitic resistance and optical losses increase
Solution Approach 1:
The gate is segmented into polycrystalline silicon and regrown silicon regions, allowing the active region to be minimized in area while the polycrystalline silicon is concentrated in contact regions where it provides low parasitic resistance without interfering with optical performance in the active modulation area.
Solution Approach 2:
Heavily doped polycrystalline silicon is localized to the contact and access regions where low parasitic resistance is critical, while the active modulation region uses regrown silicon with optimal optical properties. This local differentiation allows small device area while maintaining low parasitic resistance and minimal optical losses.
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 approach reduces parasitic resistances and increases available bandwidth by minimizing the polycrystalline silicon material in the active region, thereby improving the operational characteristics of the optical modulator.
Implementation Method 1
a regrown silicon region epitaxially formed over a polycrystalline silicon region
Data Source
AI summary
Embodiments provide for an optical modulator that includes a first silicon region, a polycrystalline silicon region; a gate oxide region joining the first silicon region to a first side of the polycrystalline region; and a second silicon region formed on a second side of the polycrystalline silicon region opposite to the first side, thereby defining an active region of an optical modulator between the first silicon region, the polycrystalline region, the gate oxide region, and the second silicon region. The polycrystalline silicon region may be between 0 and 60 nanometers thick, and may be formed or patterned to the desired thickness. The second silicon region may be epitaxially grown from the polycrystalline silicon region and patterned into a desired cross sectional shape separately from or in combination with the polycrystalline silicon region.