Multi-Branch Transistor for Image Sensor Floating Diffusion Reset
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Solution Overview
Problem
Conventional transistors with two source/drain terminals in image sensors limit design and layout optimization, leading to trade-offs between fill factor, conversion gain, and gate area, particularly when multiple reset transistors are used, which can increase floating diffusion active area and reduce image sensor performance.
Innovation Solution
The use of multi-branch transistors with more than two source/drain terminals and a unique gate structure that allows for efficient sharing of readout circuitry among pixels, reducing the floating diffusion active area and improving conversion gain without compromising fill factor.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of stationary object
If multiple reset transistors are used, then the floating diffusion active area increases, but the conversion gain deteriorates
Solution Approach 1:
The reset transistor is divided into multiple branches, each with its own source/drain terminal connected to different floating diffusion regions. This segmentation allows the transistor to reset multiple floating diffusion areas simultaneously without requiring multiple separate transistors, thereby preventing conversion gain deterioration while still covering the needed floating diffusion active area.
Solution Approach 2:
The multi-branch transistor structure serves multiple functions: it can reset multiple floating diffusion regions simultaneously, maintain low conversion gain across all regions, and share a single gate control structure. This multi-functionality eliminates the need for separate reset transistors for each floating diffusion region.
2Area of stationary object
If multiple reset transistors are used, then the fill factor is reduced, but the floating diffusion active area increases
Solution Approach 1:
Multiple reset transistor functions are merged into a single multi-branch transistor structure. By combining multiple source/drain terminals and their associated floating diffusion regions under one gate, the design achieves the coverage of multiple transistors while using only one physical transistor instance, thereby preserving the fill factor while increasing the effective floating diffusion active area.
Solution Approach 2:
The multi-branch transistor acts as a universal reset element that can service multiple floating diffusion regions simultaneously. This multi-functional design eliminates the need for multiple separate transistors, each occupying space that would otherwise be available for photodiode area, thus maintaining a high fill factor while still providing reset capability across the entire floating diffusion active area.
3Device complexity
If conventional transistors with two source/drain terminals are used, then the design is simple, but the layout optimization is limited
Solution Approach 1:
The transistor structure is segmented into multiple branches with multiple source/drain terminals, allowing flexible connection to different floating diffusion regions. This segmentation provides layout versatility while maintaining a relatively simple transistor architecture that can be integrated into existing image sensor designs.
Solution Approach 2:
The transistor design extends from a conventional two-terminal configuration to a multi-terminal configuration by adding spatial dimensions to the source/drain connections. This dimensional expansion allows the same transistor structure to serve multiple floating diffusion regions in different spatial locations, greatly enhancing layout optimization capabilities.
Data Source
AI summary
Various embodiments of the present technology may comprise a method and device for a multi-branch transistor for use in an image sensor. The device may comprise an active region, wherein the active region comprises three doped regions. At least two of the three doped region may be floating diffusion active regions, wherein each floating diffusion active region is connected to a single photosensitive element or multiple photosensitive elements. The device may comprise a multi-branch channel region defined by the area underlying a gate region and substantially surrounded by the doped regions.