Stacked Pixel Architecture for 100% Fill Factor Image Sensors
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Solution Overview
Problem
Conventional image sensors have a limited fill factor due to the allocation of both photodiodes and transistors within the same active region, leading to reduced light capture efficiency and increased noise, with existing solutions like microlenses increasing production costs and causing cross-talk effects.
Innovation Solution
The implementation of a pixel architecture with two patterned semiconductor layers, where the top layer is dedicated to photodiodes with a 100% fill factor and the bottom layer contains transistors for signal detection, amplification, and transmission, separated by an interlayer insulating layer with metal interconnections.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If photodiodes and transistors are allocated within the same active region, then the device complexity is reduced, but the fill factor is limited and light capture efficiency is reduced
Solution Approach 1:
The pixel structure is segmented into two separate semiconductor layers: a first semiconductor layer containing photodiodes for light detection, and a second semiconductor layer containing transistors for signal processing. This segmentation allows each layer to be optimized independently, achieving 100% fill factor in the first layer while maintaining necessary transistor functionality in the second layer.
Solution Approach 2:
The invention transitions from a planar two-dimensional layout to a three-dimensional stacked architecture. By vertically stacking the first semiconductor layer with photodiodes and the second semiconductor layer with transistors, separated by an interlayer insulating layer, the design maximizes the light-sensitive area in the horizontal plane while accommodating signal processing components in the vertical dimension.
2Extent of automation
If transistors are included in the active region, then signal processing is integrated, but noise increases and light capture efficiency decreases
Solution Approach 1:
The pixel is divided into distinct functional zones across two layers: the first semiconductor layer is dedicated exclusively to photodiodes for light capture, while the second semiconductor layer houses transistors for signal processing. This spatial segmentation isolates noise-generating transistor operations from the sensitive photodiode region, reducing electromagnetic interference and noise while maintaining integrated signal processing capability.
3Area of moving object
If microlenses are added to increase fill factor, then light capture efficiency improves, but production costs increase and cross-talk effects occur
Solution Approach 1:
Instead of adding microlenses as a post-processing solution, the invention preliminarily designs the pixel structure with 100% fill factor by separating photodiodes and transistors into different semiconductor layers. This preliminary structural optimization eliminates the need for additional microlens components and their associated alignment and fabrication processes, reducing production complexity and cost while avoiding cross-talk issues.
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 light capture efficiency, reduces noise, and eliminates cross-talk, allowing for improved image quality and dynamic range without increasing production costs, as the fill factor is maximized and the transistors do not affect the photodiode area.
Implementation Method 1
Each pixel includes a photodiode for generating signal charges in response to photons (i.e., light) incident thereon
Data Source
AI summary
An image sensor having pixels that include two patterned semiconductor layers. The top patterned semiconductor layer contains the photoelectric elements of pixels having substantially 100% fill-factor. The bottom patterned semiconductor layer contains transistors for detecting, resetting, amplifying and transmitting signals charges received from the photoelectric elements. The top and bottom patterned semiconductor layers may be separated from each other by an interlayer insulating layer that may include metal interconnections for conducting signals between devices formed in the patterned semiconductor layers and from external devices.