Conversion Gain Capacitor for Image Sensor Sensitivity
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Solution Overview
Problem
Image sensing devices face challenges in adjusting sensitivity to achieve high-quality images in varying illumination environments, as existing technologies struggle to optimize conversion gain effectively.
Innovation Solution
The implementation of a conversion gain capacitor that electrically couples first and second conversion gain transistors, allowing for adjustable capacitance to enhance sensitivity, comprising conductive lines with specific shapes and configurations to support high-quality image capture in both high and low illumination conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a single floating diffusion is used for charge storage, then the device structure is simple, but the sensitivity cannot be adjusted for varying illumination environments
Solution Approach 1:
The patent merges multiple floating diffusions (first and second floating diffusions from adjacent pixel groups) into a single shared floating diffusion region. This combined structure functions as a unified charge storage node with increased total capacitance, enabling sensitivity adjustment without requiring a completely separate capacitor structure. The merging approach maintains structural simplicity while achieving the desired adaptability.
Solution Approach 2:
The shared floating diffusion serves multiple functions: it acts as the charge storage node for multiple pixel groups simultaneously, provides adjustable capacitance through the conversion gain capacitor, and maintains compatibility with existing pixel architectures. This multi-functionality allows sensitivity adjustment across varying illumination environments without adding dedicated separate structures for each function.
2Adaptability or versatility
If a conversion gain capacitor is added to adjust sensitivity, then sensitivity adjustment capability improves, but device area increases
Solution Approach 1:
The conversion gain capacitor is implemented by nesting the second floating diffusion within or adjacent to the first floating diffusion structure. This nested arrangement allows the capacitor to share physical space with the existing pixel structures, minimizing the additional area required. The capacitor utilizes the same vertical column space and overlaps with existing conductive lines and transistor structures.
Solution Approach 2:
The patent utilizes the vertical dimension and overlapping layouts to accommodate the conversion gain capacitor. Instead of expanding the capacitor horizontally across the pixel array, the structure is arranged vertically with overlapping conductive lines and diffusions in different layers. This dimensional approach allows sensitivity adjustment functionality without proportionally increasing the horizontal pixel array area.
3Device complexity
If multiple pixel groups share a common floating diffusion, then device complexity is reduced, but charge transfer precision between pixel groups decreases
Solution Approach 1:
The conversion gain capacitor acts as an intermediary element between the multiple pixel groups sharing the common floating diffusion. By providing a controlled capacitance interface, it mediates the charge transfer process, ensuring precise charge accumulation and transfer from each pixel group to the shared node. The capacitor's controlled capacitance value (0.5 fF to 5 fF) maintains charge transfer precision despite the shared structure.
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 solution enables the image sensing device to achieve high-quality images by dynamically adjusting sensitivity, providing a capacitance greater than a single floating diffusion, effectively handling both high and low illumination environments.
Implementation Method 1
a conversion gain capacitor structured to electrically couple the first conversion gain transistor to the second conversion gain transistor to provide a capacitance to the first and second image sensing pixels
Implementation Method 2
a first pixel group including a plurality of first image sensing pixels structured to convert light into electrical charges
Data Source
AI summary
Image sensing devices are disclosed. An image sensing device includes a first pixel group including a plurality of first image sensing pixels to convert light into electrical charges and a first conversion gain transistor coupled to the plurality of first image sensing pixels, a second pixel group including a plurality of second image sensing pixels to convert light into electrical charges and a second conversion gain transistor coupled to the plurality of second image sensing pixels, the second pixel group disposed adjacent to the first pixel group, and a conversion gain capacitor to electrically couple the first conversion gain transistor to the second conversion gain transistor to provide a capacitance to the first and second image sensing pixels. The conversion gain capacitor comprises a first conductive line to include a region having a ring type shape and a second conductive line disposed adjacent to the first conductive line.