Ring-Shaped Gate Image Sensor Pixels for Dynamic Range
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Solution Overview
Problem
Conventional image sensors suffer from low dynamic range and high noise, particularly in scenes with both bright and dark portions, leading to overexposure and underexposure artifacts, as well as a lower-than-desired signal-to-noise ratio.
Innovation Solution
The implementation of imaging pixels with dual conversion gain transistors and overflow capacitors, along with a common ring-shaped gate for dual conversion gain and overflow transistors, allows for charge overflow and storage, enabling improved dynamic range and reduced noise through dual conversion gain modes and noise reduction mechanisms.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional image sensors are used, then device complexity is low, but dynamic range is limited and noise is high
Solution Approach 1:
The pixel is segmented into multiple functional regions: a photodiode for charge generation, a first transistor for initial charge transfer, a second transistor for overflow charge transfer, and an overflow capacitor for storing excess charge. This segmentation allows the system to handle both low-light and high-light scenarios effectively, improving dynamic range while managing complexity through functional specialization.
Solution Approach 2:
The overflow capacitor is nested within the pixel structure, and the ring-shaped gate is integrated to control multiple transistors simultaneously. This nesting approach allows compact arrangement of components, enabling improved functionality without proportionally increasing the overall pixel area and complexity.
2Measurement precision
If conventional image sensors are used, then manufacturing is simple, but signal-to-noise ratio is low
Solution Approach 1:
Multiple control functions are merged into a single ring-shaped gate that simultaneously controls the first transistor, second transistor, and overflow transistor. This merging reduces the total number of separate gate structures, simplifying the fabrication process while enabling complex charge management operations that improve signal-to-noise ratio through dual conversion gain modes.
3Reliability
If dual conversion gain transistors and overflow capacitors are added, then dynamic range is improved, but device complexity increases
Solution Approach 1:
The ring-shaped gate serves multiple functions: it controls the first transistor for normal charge transfer, controls the second transistor for overflow charge transfer, and can be configured to control the overflow transistor. This multi-functionality allows the system to achieve improved dynamic range through dual conversion gain modes without proportionally increasing the number of independent control structures, thereby managing device complexity.
4Reliability
If conventional pixels are used, then area per pixel is small, but noise reduction capability is insufficient
Solution Approach 1:
The ring-shaped gate extends in the lateral dimension, surrounding and controlling multiple transistor gates simultaneously. This dimensional approach allows a single gate structure to control charge transfer across multiple pathways, enabling effective noise reduction through dual conversion gain modes without proportionally increasing the pixel area, as the ring structure efficiently utilizes the available space.
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 reduces noise in image sensors, resulting in improved image quality by allowing charge overflow and storage, thereby addressing the limitations of conventional systems.
Implementation Method 1
Each pixel may include a photosensor such as a photodiode that receives incident photons (light) and converts the photons into electrical charges.
Data Source
AI summary
An image sensor may include a plurality of imaging pixels with high dynamic range. Each imaging pixel may have a photodiode, a floating diffusion region, and a transfer transistor configured to transfer charge from the photodiode to the floating diffusion region. Each imaging pixel may also include an overflow capacitor and an overflow transistor interposed between the photodiode and the overflow capacitor. A dual conversion gain transistor may be interposed between the overflow capacitor and the floating diffusion region. To reduce noise associated with operation of the pixel, a ring-shaped conductive layer may form a gate for both the overflow transistor and the dual conversion gain transistor. This common gate may be set to an intermediate level during integration to allow charge to overflow past the overflow transistor to the overflow capacitor. The common gate may also be used to assert the dual conversion gain transistor.