CMOS Image Sensor Dual Charge Accumulation Global Shutter
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing solid-state imaging devices with global shutter function suffer from reduced saturation charge amount and image quality due to the need for additional components, leading to inferior dynamic range and increased noise, especially in low light conditions, and are prone to image distortions when capturing moving subjects.
Innovation Solution
A CMOS image sensor design incorporating two charge accumulation sections, where an embedded MOS capacitor serves as the first charge accumulation section and a capacitor with higher capacitance per unit area as the second, allowing for simultaneous exposure of all pixels with improved saturation charge capacity and reduced noise.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If an embedded MOS capacitor is added as a photocharge accumulation section to realize global shutter, then the simultaneity of exposure is improved, but the area of the photodiode is reduced and saturation charge amount is reduced
Solution Approach 1:
The charge accumulation function is segmented into two separate sections: the photodiode for photoelectric conversion and the embedded MOS capacitor for charge storage. This segmentation allows the photodiode to maintain its area for adequate photocharge generation while the capacitor provides the necessary storage capacity for global shutter operation, resolving the contradiction between simultaneity of exposure and saturation charge amount.
2Quantity of substance
If a capacitor with higher capacitance value per unit area is used as charge accumulation section, then the saturation charge amount is improved, but leakage current increases and image quality deteriorates
Solution Approach 1:
The patent applies different capacitor structures to different spatial locations and functional requirements. The embedded MOS capacitor is positioned and designed with specific characteristics suitable for its role in charge accumulation, while the photodiode maintains its own optimized structure. This local optimization allows achieving adequate saturation charge amount while controlling leakage current through proper structural design and material selection in each region.
3Reliability
If additional transistors are added in the unit pixel to realize global exposure, then the global shutter function is improved, but the dynamic range is reduced
Solution Approach 1:
The embedded MOS capacitor serves multiple functions: it acts as the charge accumulation section for global shutter operation, provides overflow path for excess photocharges, and enables dual-capacitor configuration for extended dynamic range. This multi-functionality reduces the need for separate dedicated components that would consume additional pixel area, thereby preserving dynamic range while achieving global shutter capability.
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 the dynamic range and image quality by increasing the total capacitance value while minimizing the impact of leakage currents and dark current issues, enabling high-quality imaging of moving subjects with reduced distortions.
Implementation Method 1
a photodiode being a photoelectric conversion section
Implementation Method 2
an embedded MOS capacitor, for example, is provided as a region to accumulate photocharges
Data Source
AI summary
A solid-state imaging device includes a photoelectric conversion section configured to generate photocharges and a transfer gate that transfers the photocharges to a semiconductor region. A method for driving a unit pixel includes a step of accumulating photocharges in a photoelectric conversion section and a step of accumulating the photocharges in a semiconductor region. A method of forming a solid-state imaging device includes implanting ions into a well layer through an opening in a mask, implanting additional ions into the well layer through an opening in another mask, and implanting other ions into the well layer through an opening in yet another mask. An electronic device includes the solid-state imaging device.