Multi-branch Transistor Layout for Image Sensor Reset Circuit
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Solution Overview
Problem
In image sensor design, multiple reset transistors required due to design constraints occupy larger chip areas, reducing photodiode area and fill factor, and can increase the active area of the floating diffusion region, adversely affecting conversion gain.
Innovation Solution
A multi-branch transistor layout for the reset transistor with more than two source/drain terminals and a multi-branch channel is used to reduce the overall area utilized by the floating diffusion active regions, improving layout efficiency and conversion gain.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If multiple reset transistors are used due to design constraints, then the reset function is ensured, but the chip area increases and photodiode area decreases
Solution Approach 1:
The patent merges multiple reset transistors into a single multi-branch transistor structure where multiple source/drain terminals share a common gate and channel. This consolidation maintains the reset functionality for multiple photodiodes while reducing the total transistor area and increasing photodiode area.
Solution Approach 2:
The multi-branch transistor serves multiple functions simultaneously - it acts as a reset transistor for multiple photodiodes through its multiple source/drain terminals, while sharing a common gate control. This multi-functionality eliminates the need for separate transistors for each photodiode.
2Reliability
If multiple reset transistors are used, then the reset function is ensured, but the fill factor decreases
Solution Approach 1:
By combining multiple reset transistors into one multi-branch transistor with shared gate and channel structures, the patent reduces the overall area occupied by reset circuitry, thereby increasing the fill factor while maintaining reset functionality for all photodiodes.
3Reliability
If other designs and placement of the reset transistor are used, then the reset function is achieved, but the active area of the floating diffusion region increases
Solution Approach 1:
The multi-branch transistor structure concentrates the reset functionality in a localized area with optimized source/drain terminal placements that minimize the spread of the floating diffusion region, maintaining compact geometry while achieving the reset function.
4Reliability
If the active area of the floating diffusion region increases, then the reset function is achieved, but the conversion gain is adversely affected
Solution Approach 1:
The patent merges multiple reset operations into a single multi-branch transistor structure that maintains compact floating diffusion regions, thereby preserving conversion gain while achieving the reset function for multiple photodiodes simultaneously.
Data Source
AI summary
Various embodiments of the present technology may comprise a method and device for a multi-source/drain transistor for use in an image sensor. The device may comprise an active region, wherein the active region comprises three doped regions. Two of the three doped region may be floating diffusion active regions, wherein each floating diffusion active region is connected to a photosensitive element. The device may comprise a multi-branch channel defined by the area underlying a gate region and substantially surrounded by the doped regions. During operation the electron path may form an “L” shape within the channel.