Imager Pixel Reset Diode for Compact Fill Factor
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Solution Overview
Problem
Conventional CMOS imager pixels require additional area for a separate reset transistor, which increases pixel cell size and complexity, and there is a need to minimize transistor count to enhance pixel density and fill factor.
Innovation Solution
The use of a reset diode within the imager pixel to reset the floating diffusion region, eliminating the need for a separate reset transistor and allowing for a more compact design that increases the fill factor of the charge accumulation region.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a separate reset transistor is used to reset the floating diffusion region, then the reset function is achieved, but the pixel cell size increases and device complexity increases
Solution Approach 1:
The patent extracts the reset function from the transistor family and implements it using a dedicated reset diode structure. This separation allows the reset operation to be performed independently without requiring a full transistor, thereby reducing the overall device complexity while maintaining the essential reset capability for the floating diffusion region.
Solution Approach 2:
The reset diode acts as an intermediary element between the floating diffusion region and the reset signal. Instead of using a transistor that would require gate control and additional connections, the diode provides a simplified path for resetting the floating diffusion region, reducing the number of required components and interconnections.
2Reliability
If a separate reset transistor is used, then the reset function is achieved, but the pixel density decreases due to increased pixel cell size
Solution Approach 1:
By extracting the reset function from the transistor implementation and using a dedicated reset diode, the patent significantly reduces the area required for the reset circuitry within each pixel. This area reduction directly increases the number of pixels that can be packed into a given sensor area, thereby improving pixel density.
3Reliability
If a separate reset transistor is used, then the reset function is achieved, but the fill factor of the charge accumulation region decreases
Solution Approach 1:
The patent extracts the reset functionality from the main pixel transistor structure and implements it using a separate, more compact reset diode. This extraction reduces the area occupied by reset circuitry within the pixel, thereby increasing the fill factor - the proportion of the pixel area dedicated to the light-sensitive charge accumulation region.
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 approach reduces noise during the reset operation and increases the proportion of the charge accumulation region within the imager pixel, leading to improved pixel density and simplified fabrication, while maintaining effective charge transfer and signal conversion.
Implementation Method 1
When incident light strikes the photodiode 12, electron/hole pairs are generated in the p-n junction of the photodiode 12
Implementation Method 2
The reset transistor 28 selectively resets the collection or floating diffusion region 18 to a predetermined voltage by coupling a voltage Vdd to the collection or floating diffusion region 18 during a reset period
Data Source
AI summary
An imager pixel and imaging device and system including an imager pixel for discharging a floating diffusion region are described. The imager pixel includes a photoconversion regions floating diffusion region, and a reset diode. A reset diode is coupled to the floating diffusion region and, when activated, discharges accumulated and collected charge from the photoconversion and the floating diffusion regions. Following successive accumulation, transfer and collection processes, the reset diode again discharges residual accumulated and collected charge from the photoconversion and the floating diffusion regions.