Image Sensor Transfer Structure Without Etched Vertical Gates
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Solution Overview
Problem
Vertical transfer gates in image sensors introduce surface imperfections due to etching, leading to white pixel and other deleterious effects, and require a tradeoff between blooming and white pixel control.
Innovation Solution
A transfer structure with a vertical channel structure formed by implanted and doped PN junctions, eliminating the need for etched trenches and allowing for deeper photodiode placement without surface defects, using planar transfer gates and doped regions to regulate charge carrier movement.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If vertical transfer gates are formed by etching column-shaped recesses, then charge carrier transfer capability is improved, but surface imperfections are introduced causing white pixel effects
Solution Approach 1:
The patent removes the etched column-shaped recess structure entirely and replaces it with a planar transfer gate configuration. This extraction of the problematic vertical etching structure eliminates the source of surface imperfections while maintaining charge transfer functionality through an alternative planar geometry with doped regions.
Solution Approach 2:
Instead of creating vertical structures by etching downward into the substrate, the patent inverts the approach by using a planar gate structure with doped semiconductor regions that extend vertically. The charge transfer path is inverted from a vertical channel in a trench to a horizontal planar channel with vertical doping profiles.
2Area of stationary object
If vertical transfer gates with etched trenches are used, then pixel layout area is reduced, but manufacturing complexity increases due to multiple surface treatments
Solution Approach 1:
The patent extracts and removes the complex multi-step etching and surface treatment process for vertical trenches, replacing it with a simpler planar gate fabrication process that uses standard doping and deposition techniques without requiring deep trench formation or multiple surface passivation steps.
3Reliability
If gate control voltage is increased to prevent blooming, then blooming control is improved, but white pixel effects are exacerbated
Solution Approach 1:
The patent applies different doping concentrations and types in specific local regions around the planar transfer gate. Heavily doped regions are positioned to enhance charge transfer efficiency and prevent blooming, while lightly doped or intrinsic regions are positioned to minimize surface effect impacts, allowing independent optimization of these conflicting requirements.
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 solution reduces surface defects, minimizes white pixel effects, and enhances full well capacity while maintaining control over blooming and charge transfer efficiency.
Implementation Method 1
A transfer structure with a vertical channel structure formed by implanted and doped PN junctions
Implementation Method 2
using planar transfer gates and doped regions to regulate charge carrier movement
Implementation Method 3
a photodiode configured to photogenerate and accumulate charge carriers in response to amount of incident light absorbed
Data Source
AI summary
Pixels, such as for image sensors and electronic devices, include a photodiode formed in a semiconductor substrate, a floating diffusion, and a transfer structure selectively coupling the photodiode to the floating diffusion. The transfer structure includes a transfer gate formed on the semiconductor substrate, and a vertical channel structure including spaced apart first doped regions formed in the semiconductor substrate between the transfer gate and the photodiode. Each spaced apart first doped region is doped at a first dopant concentration with a first-type dopant. The spaced apart first doped regions are formed in a second doped region doped at a second dopant concentration with a second-type dopant of a different conductive type.