Solid-State Imaging Device Floating Diffusion Readout Gate Design
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Solution Overview
Problem
In MOS solid-state imaging devices, it is challenging to read out signal charge from photodiodes located far from the readout gate electrode, leading to residual images due to long readout distances, which requires high readout gate voltages or reduced saturated signal charge to prevent charge loss.
Innovation Solution
A solid-state imaging device design where the readout gate electrode completely or partially surrounds the floating diffusion element in a ring or quadrangular shape, reducing the readout distance and allowing signal charge to be read out from the periphery, thereby minimizing residual images and enabling lower readout voltages.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If photodiodes are disposed to face each other with floating diffusion element therebetween in conventional linear arrangement, then device structure is simple, but readout distance becomes long causing residual images
Solution Approach 1:
The patent transitions from a conventional linear arrangement where photodiodes are positioned on opposite sides of the floating diffusion element to a two-dimensional planar arrangement where photodiodes are disposed adjacently. This dimensional change allows the readout gate electrode to effectively modulate potential across the floating diffusion element, enabling complete signal charge readout while maintaining structural simplicity.
2Reliability
If readout gate voltage is increased to read out signal charge from distant photodiodes, then signal charge readout is improved, but power consumption increases
Solution Approach 1:
The patent changes the spatial arrangement parameter of photodiodes from a distant linear configuration to an adjacent two-dimensional configuration. This parameter change reduces the effective readout distance, allowing signal charge to be read out at lower readout gate voltages, thereby reducing power consumption while maintaining readout completeness.
3Measurement precision
If photodiode area is increased to improve sensitivity, then photoelectric conversion efficiency is improved, but readout distance increases causing residual images
Solution Approach 1:
The patent employs a two-dimensional planar arrangement where photodiodes are disposed adjacently rather than linearly. This allows photodiodes to occupy larger area for improved sensitivity while the readout gate electrode positioned between them in the planar configuration maintains effective potential modulation, enabling complete signal charge readout without residual images.
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 design allows for efficient signal charge readout from the periphery of the readout gate electrode to the floating diffusion element, reducing residual images and enabling deeper potential wells for increased sensitivity and lower power consumption.
Implementation Method 1
Each pixel is composed of a photodiode, which functions as a photoelectric conversion element
Data Source
AI summary
A solid-state imaging device that includes at least one pixel. The pixel includes a photodiode, a floating diffusion element in a region of the photodiode and a read out gate electrode at least partially surrounding the floating diffusion element in plan view.