Reducing Crosstalk in MOS Image Sensors with Deep Well Design
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Summary
Problems
MOS image sensors experience crosstalk between pixels due to optical and electrical interference, leading to image distortion, reduced resolution, and blooming, particularly in color sensors, which affects image quality.
Innovation solutions
An image sensor design featuring a substrate with an active pixel sensor region, a first conductivity-type deep well electrically connected to a positive voltage, and a guard ring surrounding the pixel array, which reduces electrical crosstalk by draining negative charges away from adjacent pixels.
TRIZ Analysis
Specific contradictions:
General conflict description:
Principle concept:
If photodiodes are arranged closely to increase pixel density, then productivity and resolution are improved, but electrical crosstalk between adjacent pixels increases
Why choose this principle:
A deep well structure with opposite conductivity type is introduced between adjacent photodiodes of the same conductivity type. This deep well acts as an intermediary barrier that repels minority carriers (electrons in P-type photodiodes, holes in N-type photodiodes) generated by incident light, preventing them from migrating to adjacent pixels and causing electrical crosstalk, while allowing the photodiodes to be closely spaced for high pixel density.
Principle concept:
If deep well structures are added to reduce crosstalk, then image quality is improved, but device complexity and manufacturing difficulty increase
Why choose this principle:
The deep well structure is merged with the existing photodiode formation process. The deep well and photodiodes are created using the same ion implantation and thermal diffusion steps, integrating the crosstalk reduction function into the standard CMOS image sensor fabrication process without requiring separate manufacturing stages, thereby limiting the increase in device complexity.
Application Domain
Data Source
AI summary:
An image sensor design featuring a substrate with an active pixel sensor region, a first conductivity-type deep well electrically connected to a positive voltage, and a guard ring surrounding the pixel array, which reduces electrical crosstalk by draining negative charges away from adjacent pixels.
Abstract
An image sensor includes a substrate having an active pixel sensor region defined therein, a plurality of first conductivity type photodiodes formed in the active pixel sensor region and a first conductivity-type first deep well formed in the active pixel sensor region in a location which does not include the plurality of the first conductivity-type photodiodes. Moreover, the first deep well is electrically connected to a positive voltage.