3D Stacked Image Sensor Pixel Architecture for Dynamic Range
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Solution Overview
Problem
Sub-micron pixels in digital imaging systems face challenges such as reduced sensing speeds, degraded resolution, and limited dynamic range due to smaller sizes, leading to inferior image quality and signal-to-noise ratio, particularly in mobile devices where the dynamic range of CMOS sensors is insufficient to capture natural outdoor scenes effectively.
Innovation Solution
The implementation of 3D stacked, vertically integrated pixel architectures with shared pixel configurations, including four transistor 4-shared, 8-shared, or 16-shared pixel designs, that utilize additional storage capacitors and specific transistor arrangements to enhance full well capacity, signal-to-noise ratio, and dynamic range, while maintaining high resolution and color fidelity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If pixel size is reduced to increase megapixel count and enable smaller sensor areas, then device compactness is improved, but sensing speed and sensitivity are degraded
Solution Approach 1:
The patent transitions from a planar pixel layout to a three-dimensional stacked architecture, separating the photodetector layer from the readout circuitry layer. This vertical stacking enables compact sensor area while maintaining sufficient charge handling capacity and sensing speed by utilizing the third dimension (depth) rather than reducing pixel footprint in the horizontal plane.
Solution Approach 2:
The pixel structure is segmented into distinct functional layers: a photodetector layer for light sensing and charge generation, and a separate readout circuitry layer for signal processing. This segmentation allows each layer to be optimized independently, enabling small pixel size while maintaining sensing performance through specialized layer design.
2Measurement precision
If pixel size is reduced to increase megapixel count, then resolution is improved, but color fidelity is degraded
Solution Approach 1:
Multiple photodetectors (e.g., red, green, blue color filters with underlying photodetectors) are merged into a single pixel unit, sharing common readout circuitry. This merging enables high resolution through pixel density while maintaining color fidelity through the combined spectral response of multiple photodetectors within each pixel unit.
Solution Approach 2:
The shared readout circuitry serves multiple photodetectors simultaneously, providing multi-functional capability. This universal circuit design reduces the area required per pixel, allowing smaller pixel sizes for high resolution while maintaining color accuracy through the coordinated operation of multiple photodetectors.
3Volume of moving object
If pixel size is reduced, then dynamic range is limited, but device compactness is improved
Solution Approach 1:
A transfer gate acts as an intermediary mechanism between the photodetector and the readout circuitry, enabling controlled charge transfer. This intermediary structure allows efficient charge handling in small pixels by precisely managing the flow of photocharges, thereby extending dynamic range through optimized charge transfer timing and control.
Solution Approach 2:
The three-dimensional stacked architecture provides additional vertical space for charge storage and transfer mechanisms, enabling extended dynamic range in compact pixels. The depth dimension allows for larger effective full-well capacity without increasing the horizontal pixel footprint, maintaining device compactness.
4Volume of moving object
If pixel size is reduced, then signal-to-noise ratio is degraded, but device compactness is improved
Solution Approach 1:
The readout circuitry is extracted from the photodetector layer and placed in a separate layer. This extraction reduces the area occupied by non-sensitive circuit elements within each pixel, increasing the light-sensitive area ratio and improving signal-to-noise ratio while maintaining device compactness through vertical integration.
Solution Approach 2:
By moving readout circuitry to a separate vertical layer, the patent increases the effective light-sensitive area in the horizontal plane. This dimensional reorganization improves signal-to-noise ratio by maximizing photon collection area while keeping the overall device footprint compact through three-dimensional stacking.
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 approach enables low-noise and high-gain readouts, increased dynamic range, and improved color fidelity, effectively addressing the limitations of sub-micron pixels by enhancing light absorption and charge handling capabilities, resulting in superior image quality and performance in compact imaging devices.
Implementation Method 1
a photodiode and a transfer gate... configured to convert light into a charge
Data Source
Figure 1A
Figure 1B~1C
Figure 2
AI summary
Certain aspects relate to imaging systems and methods for manufacturing imaging systems and image sensors. The imaging system includes a pixel array including a plurality of pixels, the pixels configured to generate a charge when exposed to light and disposed on a first layer. The imaging system further includes a plurality of pixel circuits for reading light integrated in the pixels coupled thereto, each of the plurality of pixel circuits comprising one or more transistors shared between a subset of the plurality of the pixels, the one or more transistors disposed on a second layer different than the first layer. The imaging system further includes a plurality of floating diffusion nodes configured to couple each of the plurality of pixels to the plurality of pixel circuits.