Global-Shutter Pixel Recess Structure for Crosstalk Blocking
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Solution Overview
Problem
Global-shutter image sensors are susceptible to parasitic crosstalk due to stray light reaching the pixel's storage node, which distorts the resulting pixel values and affects image quality.
Innovation Solution
The design includes a semiconductor substrate with recessed regions and a photodiode region having specific dopant concentrations and structures, along with a dielectric and conductive fill, to prevent stray light from reaching the storage node, utilizing recessed regions and a protrusion to block parasitic light and enhance charge transfer.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a global-shutter image sensor uses a conventional flat pixel structure, then the device complexity is low, but parasitic crosstalk occurs due to stray light reaching the storage node during integration period
Solution Approach 1:
The pixel structure is segmented by introducing two recessed regions (first and second recessed regions) that divide the path between the photodiode region and storage node. These recessed regions create physical separation zones that block stray light from reaching the storage node during the integration period, thereby reducing parasitic crosstalk while maintaining global-shutter functionality.
Solution Approach 2:
The invention transitions from a conventional two-dimensional flat pixel structure to a three-dimensional structure by etching recessed regions into the semiconductor substrate. This vertical dimensionality change creates depth-based light blocking without significantly increasing lateral footprint, effectively preventing parasitic crosstalk while preserving pixel array density.
2Productivity
If the photodiode region uses uniform dopant concentration, then the manufacturing process is simple, but charge transfer efficiency to the storage node is insufficient
Solution Approach 1:
The photodiode region employs non-uniform dopant concentration with a first doped section having higher dopant concentration near the storage node interface and a second doped section with lower dopant concentration toward the front surface. This local variation in doping concentration optimizes charge transfer efficiency at critical interfaces while reducing noise in other regions, achieving enhanced productivity without excessive manufacturing complexity.
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 configuration effectively reduces parasitic crosstalk, improving image quality by preventing stray light from affecting the storage node and ensuring accurate pixel value generation.
Implementation Method 1
each pixel produces photo-generated charge in response to illumination incident thereon
Implementation Method 2
During integration period, light that reaches a pixel's storage node, or immediate surroundings, generates charges that change the amount of photo-generated charge at the storage node
Data Source
AI summary
A global-shutter pixel includes a semiconductor substrate that has a storage node and a photodiode region. A front surface of the substrate has a first recessed region between the photodiode region and the storage node in a first direction parallel to the front surface, and a second recessed region between the first recessed region and the storage node in the first direction. The first and second recessed regions extend into the substrate to a respective first recess-depth and a second recess-depth that exceeds the first recess-depth. The photodiode region includes (i) a first doped-section spanning a depth-range and having a first dopant concentration, and (ii) a second doped-section between the front surface and the first doped-section and having a second dopant concentration that is less than the first dopant concentration. The first doped-section includes a protrusion that extends at least partially beneath the first recessed region in the first direction.