Stacked Image Sensor Floating Diffusion Layout for Dual Conversion Gain
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Solution Overview
Problem
Current image sensors face challenges in enhancing image quality, particularly in balancing low light quantity and high light quantity performance, due to limitations in the design of floating diffusion regions and conversion gain mechanisms.
Innovation Solution
The image sensor design incorporates a through electrode structure that penetrates through substrates, connecting floating diffusion regions and landing pads, allowing for adjustable capacitance through a double conversion gain transistor, which improves image quality by optimizing performance in varying light conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a conventional floating diffusion region design is used, then the structure is simple, but the image quality and sensitivity are limited
Solution Approach 1:
The image sensor is divided into multiple substrates (first substrate with photodiode, second substrate with floating diffusion region) connected through through-electrodes. This segmentation allows each substrate to be optimized independently for its specific function while achieving superior overall image quality through the stacked architecture.
Solution Approach 2:
The patent transitions from a planar single-substrate design to a three-dimensional stacked architecture with through-electrodes penetrating vertically through multiple substrates. This dimensional change enables improved light sensitivity and image quality by separating photodetection and signal processing functions across different vertical layers.
2Quantity of substance
If the floating diffusion region size is increased to improve full well capacity, then high light performance improves, but low light sensitivity deteriorates
Solution Approach 1:
By separating the photodiode (light detection) and floating diffusion region (signal storage) into different substrates connected via through-electrodes, the design allows the photodiode area to be maximized for sensitivity while the floating diffusion region can be optimized for full well capacity, resolving the trade-off between low light and high light performance.
Solution Approach 2:
The through-electrodes act as intermediaries connecting the photodiode on the first substrate to the floating diffusion region on the second substrate. This intermediary connection enables efficient charge transfer while allowing independent optimization of the photodetection area and signal storage capacity.
3Reliability
If through electrodes are used to connect substrates, then electrical connection is achieved, but parasitic capacitance increases
Solution Approach 1:
The through-electrodes are designed with thin film structures and minimal cross-sectional area to reduce parasitic capacitance while maintaining reliable electrical connection. The electrodes penetrate through the substrates with optimized dimensions to minimize capacitive effects on the signal.
Solution Approach 2:
The design optimizes the physical parameters of the through-electrodes (dimensions, material, spacing) to minimize parasitic capacitance. By carefully controlling the electrode geometry and electrical characteristics, reliable connection is achieved while energy loss from parasitic capacitance is minimized.
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 design enhances image quality by selectively switching between low light and high light performance modes, improving sensitivity and full well capacity, thereby addressing the limitations of existing image sensors.
Implementation Method 1
Each of the pixels includes a photodiode (PD). The PD converts incident light into an electrical signal.
Data Source
AI summary
Provided is an image sensor including a first substrate including a first surface to which light is incident and a second surface opposite the first surface, a second substrate facing the second surface of the first substrate, a wiring layer between the first substrate and the second substrate and including an insulating layer and a conductive structure in the insulating layer, a first floating diffusion region provided in the first substrate, a first through electrode penetrating through the second substrate and electrically connected to the first floating diffusion region through the conductive structure, a second floating diffusion region provided in the second substrate, and a landing pad arranged on a bottom surface of the second substrate and electrically connected to the second floating diffusion region, wherein a bottom surface of the first through electrode may be in contact with the landing pad.