Silicon Optical Modulator Vertical PN Diode Structure
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Solution Overview
Problem
Conventional silicon-based optical modulators face challenges such as high optical loss, complex fabrication processes, and low modulation efficiency due to waveguide implantation-induced absorption loss, complicated doping schemes, and small overlap between optical fields and free carrier regions.
Innovation Solution
A method for forming a silicon-based optical modulator using a vertical PN diode structure, which simplifies the fabrication process and enhances interaction between the optical field and free carriers, involving implantation of dopants to create overlapping regions within a ridge waveguide, allowing for high-speed and low-power operation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If waveguide implantation is used to form optical modulators, then modulation speed can be improved, but optical loss increases due to implantation-induced absorption loss
Solution Approach 1:
The patent extracts the doping function from the waveguide formation process. Instead of implanting dopants directly into the waveguide region (which causes absorption loss), the dopants are implanted into separate regions that adjoin the waveguide. This separates the optical confinement function (waveguide) from the electrical modulation function (doped regions), eliminating implantation-induced absorption loss while maintaining modulation capability.
2Speed
If multiple implantations with different energy levels and dosages are used to fabricate high-speed modulators, then modulation speed improves, but fabrication complexity increases
Solution Approach 1:
The patent segments the doping process into two separate implantation steps targeting different regions: first dopants are implanted into a first region, then second dopants are implanted into a second region that overlaps with the first. This segmentation allows each implantation to use optimized, simpler parameters rather than requiring multiple complex implantations with varying energies and dosages, reducing fabrication complexity while achieving high-speed modulation.
3Productivity
If the overlap between optical field and free carrier changing region is increased, then modulation efficiency improves, but device structure becomes more complicated
Solution Approach 1:
The patent transitions from traditional lateral overlap geometry to a vertical stacking arrangement where the first and second doped regions are positioned above/below each other in the vertical dimension, with the waveguide running through both regions. This dimensional change enables sufficient overlap between the optical field (confined in the waveguide) and free carrier regions without requiring complex lateral structuring, thereby improving modulation efficiency while maintaining structural simplicity.
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 vertical PN diode structure achieves modulation speeds greater than 40 GHz with a low modulation efficiency of 1.66 V·cm at 3.5 V DC bias, reducing operational power and simplifying the fabrication process while maintaining high performance.
Implementation Method 1
implanting dopants of a first conductivity type into the substrate to form a first doped region, implanting dopants of a second conductivity type into the substrate to form a second doped region
Implementation Method 2
relatively high optical loss due to the waveguide implantation induced absorption loss
Data Source
AI summary
According to embodiments of the present invention, a method for forming an optical modulator is provided. The method includes providing a substrate, implanting dopants of a first conductivity type into the substrate to form a first doped region, implanting dopants of a second conductivity type into the substrate to form a second doped region, wherein a portion of the second doped region is formed over and overlaps with a portion of the first doped region to form a junction between the respective portions of the first doped region and the second doped region, and wherein a remaining portion of the second doped region is located outside of the junction, and forming a ridge waveguide, wherein the ridge waveguide overlaps with at least a part of the junction.