Stacked Image Sensor Photodiodes Resolve Cross-Talk
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Solution Overview
Problem
Conventional substrate-stacked image sensors experience cross-talk phenomena and reduced quantum efficiency due to narrow pixel sizes and light absorption issues, leading to signal loss and inefficient light conversion.
Innovation Solution
A dual detection function is achieved by forming a first photodiode on one substrate and a second photodiode on another, with both photodiodes electrically coupled to form a complete photodiode pixel, allowing for improved light absorption and reduced cross-talk through strategic positioning and alignment.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If pixel size is reduced to increase resolution, then imaging resolution is improved, but cross-talk between adjacent pixels increases and quantum efficiency decreases
Solution Approach 1:
The patent transitions from a two-dimensional planar pixel structure to a three-dimensional stacked structure with multiple photodiodes at different depths. This vertical dimensionality change allows light to be detected at multiple depths simultaneously, improving resolution while maintaining quantum efficiency by capturing light that would otherwise be lost due to absorption or cross-talk in conventional single-layer structures.
Solution Approach 2:
The pixel structure is segmented into multiple photodiodes stacked vertically at different depths. Each photodiode segment detects light at its specific depth, with upper photodiodes detecting light absorbed less and lower photodiodes detecting residual light. This segmentation resolves the contradiction by distributing light detection across multiple segments, reducing cross-talk between adjacent pixels while maintaining high quantum efficiency through cumulative detection.
2Measurement precision
If pixel size is reduced to increase resolution, then imaging resolution is improved, but signal loss due to cross-talk increases
Solution Approach 1:
By adding the vertical dimension with stacked photodiodes at different depths, the patent creates depth-resolved detection channels. This allows the system to distinguish between light originating from different depths, thereby reducing cross-talk between adjacent pixels and minimizing signal loss while maintaining high imaging resolution.
Solution Approach 2:
The pixel is segmented into multiple vertically stacked photodiodes, each responsible for detecting light at its specific depth. This segmentation isolates the detection function across multiple segments, reducing interference and cross-talk between adjacent pixels while preserving signal integrity through cumulative detection across segments.
3Device complexity
If conventional single photodiode structure is used, then device complexity is low, but quantum efficiency is insufficient due to light absorption limitations
Solution Approach 1:
The single photodiode is segmented into multiple stacked photodiodes at different depths. Each photodiode segment captures light that has not been fully absorbed by upper layers, thereby improving overall quantum efficiency. The segmentation approach maintains relatively simple individual photodiode structures while achieving enhanced performance through their stacked arrangement.
Solution Approach 2:
Multiple photodiodes are nested vertically one above another in a stacked configuration. The upper photodiodes detect light first, and lower photodiodes detect residual light that passes through or is scattered by upper layers. This nesting arrangement improves quantum efficiency by utilizing the same detection volume multiple times at different depths without significantly increasing lateral device 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 enhances quantum efficiency by ensuring most blue, green, and red light is absorbed by the first photodiode, with residual light absorbed by the second photodiode, minimizing waste and enabling effective dual detection for high-resolution imaging.
Implementation Method 1
most blue, green, and red light is absorbed by the first photodiode
Implementation Method 2
first photodiode disposed on a first substrate, a second photodiode disposed on a second substrate, and the first photodiode and the second photodiode coupled to one another to form a complete photodiode
Implementation Method 3
residual light absorbed by the second photodiode
Implementation Method 4
second photodiode disposed on a second substrate, and the first photodiode and the second photodiode coupled to one another
Data Source
AI summary
The present invention relates to an image sensor in which substrates are stacked, wherein a substrate-stacked image sensor according to the present invention is configured such that a first photodiode is formed on a first substrate, a second photodiode is formed on a second substrate, the two substrates are aligned with and bonded to each other to electrically couple the two photodiodes to each other, thereby forming a complete photodiode within one pixel.