Rib Waveguide PN Junction Self-Aligned Fabrication
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Solution Overview
Problem
Existing silicon electro-optic devices for high-speed optical modulators have complex fabrication processes that are not CMOS compatible, limiting their practicality for mass production and device yield, despite improvements in data transmission rate and VπLπ efficiency.
Innovation Solution
An electro-optic device with a layer of light-carrying material and a rib waveguide featuring a pn junction formed by doped regions extending into the rib, allowing for a self-aligned fabrication process and increased surface area of the pn junction for enhanced efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If complex fabrication processes are used to improve data transmission rate and VπLπ efficiency, then device performance is improved, but manufacturing complexity increases and device yield decreases
Solution Approach 1:
The patent merges the waveguide structure formation and pn junction creation into a single rib formation step. The pn junction is formed by doping regions that extend into the rib structure, combining what would traditionally be separate fabrication processes into one integrated operation, thereby reducing overall process complexity while maintaining device performance
Solution Approach 2:
The patent transitions from planar doping to three-dimensional doping by having doped regions extend vertically into the rib structure. This dimensional change allows the pn junction to be formed within the rib itself rather than requiring separate lateral junction formation steps, simplifying the fabrication process while improving device efficiency through increased junction surface area
2Reliability
If complex fabrication processes are used to improve data transmission rate and VπLπ efficiency, then device performance is improved, but ease of manufacture deteriorates
Solution Approach 1:
The patent combines waveguide rib formation and pn junction creation into a single fabrication step, making the process more suitable for mass production. The doped regions are formed to extend into the rib structure during the same process that defines the rib geometry, eliminating the need for subsequent complex alignment and doping steps
Solution Approach 2:
The rib structure itself serves as the template for pn junction formation. The doped regions automatically align with the rib geometry because they are formed in the same step, making the structure self-defining and eliminating the need for external alignment references or multiple patterning steps
3Reliability
If complex fabrication processes are used to improve data transmission rate and VπLπ efficiency, then device performance is improved, but device yield decreases
Solution Approach 1:
The patent merges multiple critical structure formations into one process step, reducing the number of opportunities for defects and misalignments. By forming the rib and pn junction simultaneously, the patent eliminates alignment errors and process variations that would otherwise accumulate across multiple steps, thereby improving device yield
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 self-aligned fabrication process increases device yield and efficiency, achieving high electro-optic bandwidths above 50 GHz, with preliminary results showing approximately 32 GHz for a 910 microns long device, while simplifying the production process.
Implementation Method 1
The plasma dispersion effect uses changes in the free-carrier concentration to cause modulation of the light passing through the device
Implementation Method 2
Carrier depletion can be based upon a PN junction diode in the waveguide. Reverse biasing the diode causes carriers to be swept out of part or all of the waveguide region, again resulting in a change in refractive index
Implementation Method 3
a rib, projecting from the layer of light-carrying material, for guiding optical signals propagating through the device
Data Source
AI summary
An electro-optic device, comprising a layer of light-carrying material; and a rib, projecting from the layer of light-carrying material, for guiding optical signals propagating through the device. The layer of light-carrying material comprises a first doped region of a first type extending into the rib, and a second doped region of a second, different type extending into the rib such that a pn junction is formed within the rib. The pn junction extends substantially parallel to at least two contiguous faces of the rib, resulting in a more efficient device. In addition, a self-aligned fabrication process can be used in order to simplify the fabrication process and increase reliability and yield.