Mode-Switched CMOS Image Sensor With Dual Floating Diffusions
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Solution Overview
Problem
High-definition applications face challenges in securing enough space to provide two floating diffusions in solid-state imaging devices, making it difficult to achieve both high sensitivity and a high dynamic range.
Innovation Solution
A solid-state imaging device with a mode-switching switch section that couples and decouples signal paths to a photoelectric conversion section, using amplification transistors on different substrates to expand dynamic range while maintaining sensitivity, and forming amplification transistors in a substrate different from the photoelectric conversion section to secure space for floating diffusions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If two floating diffusions are provided to achieve both high sensitivity and high dynamic range, then sensitivity and dynamic range are improved, but device area increases making it difficult to secure enough space in high-definition applications
Solution Approach 1:
The patent transitions from a planar layout to a three-dimensional stacked architecture, placing the photoelectric conversion section on a first substrate and the readout circuit containing floating diffusions and amplification transistors on a second substrate stacked above it. This vertical arrangement allows both high-definition pixel arrays and dual floating diffusion structures to coexist without increasing lateral device area.
Solution Approach 2:
The device is divided into functionally independent sections: the photoelectric conversion section on the first substrate and the readout circuit on the second substrate. This segmentation allows each section to be optimized independently, enabling the photoelectric conversion section to maintain high-definition resolution while the readout circuit accommodates the dual floating diffusion structure for extended dynamic range.
2Device complexity
If amplification transistors are integrated on the same substrate as the photoelectric conversion section, then device complexity is reduced, but space for floating diffusions becomes insufficient in high-definition applications
Solution Approach 1:
The patent resolves the space constraint by moving amplification transistors and floating diffusions to a second substrate stacked vertically above the first substrate containing the photoelectric conversion section. This three-dimensional integration maintains functional connectivity while providing sufficient lateral space on each substrate for high-definition pixel arrays.
3Area of stationary object
If a single floating diffusion is used, then device area is minimized, but the dynamic range cannot be extended
Solution Approach 1:
The patent implements a dual floating diffusion structure on the second substrate, with first and second floating diffusions that can be selectively coupled to the photoelectric conversion section. This vertical stacking enables extended dynamic range through multiple signal paths without increasing the lateral footprint of the device.
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
Enables both high sensitivity and a high dynamic range in high-definition applications by selectively using amplification transistors and securing space for floating diffusions, reducing noise through silicide electrodes in the readout circuit.
Implementation Method 1
a CMOS (complementary MOS) image sensor that reads charges accumulated in a photodiode, which is a photoelectric conversion element
Data Source
AI summary
A solid-state imaging device according to an embodiment of the present disclosure includes a mode-switching switch section that, in a first mode, electrically couples a first signal path to a photoelectric conversion section and electrically decouples a second signal path from the photoelectric conversion section, and that, in a second mode, electrically couples both of the first signal path and the second signal path to the photoelectric conversion section. At least the photoelectric conversion section is formed in a first substrate, and at least a second amplification transistor is formed in a second substrate, among the first substrate and the second substrate stacked on each other.