Photodiode Cathode Lateral Doping Profile Engineering
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Solution Overview
Problem
The challenge in active pixel sensors is to improve the trade-off between pixel well capacity and depletion voltage, as scaling down pixel size reduces well capacity while increasing doping increases depletion voltage, contradicting the requirement for full well depletion and noise suppression.
Innovation Solution
The method involves defining and implanting a photodiode cathode region with a higher dopant concentration at the edges and corners, and counter-doping the central region to achieve a better balance between well capacity and depletion voltage, utilizing lateral doping profile engineering.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If pixel area is increased to improve well capacity, then well capacity is improved, but device density decreases and die size increases
Solution Approach 1:
The patent applies lateral doping profile engineering to create non-uniform doping concentrations across the pixel area. By concentrating dopants at edges and corners with higher density, the patent achieves improved well capacity in specific regions without increasing the overall pixel area, thus resolving the contradiction between well capacity and device density
2Quantity of substance
If doping concentration is increased to improve well capacity, then well capacity is improved, but depletion voltage increases
Solution Approach 1:
The patent implements spatially varying doping concentrations where edge and corner regions have higher doping levels to increase well capacity, while the central region maintains lower doping levels to control depletion voltage. This local differentiation resolves the contradiction by optimizing doping distribution rather than uniformly increasing it
Solution Approach 2:
The patent transitions from uniform one-dimensional doping profiles to two-dimensional lateral doping profiles. By engineering doping concentrations in the lateral dimension (across the pixel surface) rather than only in the vertical dimension, the patent achieves improved well capacity while maintaining depletion voltage control through the lateral doping profile engineering process
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 enhances well capacity by up to 30% or more while maintaining or reducing depletion voltage, thereby improving the dynamic range and sensitivity of image sensors.
Implementation Method 1
defining and implanting an edge region of the photodiode cathode regions with a photodiode cathode edge implant dose of a dopant species
Implementation Method 2
defining and implanting a region of the photodiode away from the edges of the photodiode cathode region with a counterdoping implant dose of a dopant species
Data Source
AI summary
A method for forming a photodiode cathode in an integrated circuit imager includes defining and implanting a photodiode cathode region with a photodiode cathode implant dose of a dopant species and defining and implanting an edge region of the photodiode cathode region with a photodiode cathode edge implant dose of a dopant species to form a region of higher impurity concentration than the photodiode cathode impurity concentration.