Image Sensor Gate Biasing for Dark Current Reduction
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Solution Overview
Problem
Dark current, which degrades image quality by accumulating at semiconductor-dielectric interfaces in image sensors, particularly at adjacent gates, is not effectively eliminated by existing technologies, including pinned photodiodes.
Innovation Solution
The method involves biasing the gate to accumulate majority carriers at the semiconductor-dielectric interface during integration, creating a potential profile that drains away dark current from the photogeneration diffusion, and using a potential barrier or gradient to separate dark current from signal charge, ensuring it does not contribute to the image signal.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If electrons accumulate at semiconductor-dielectric interface during integration, then charge collection is enabled, but undesirable dark current degrades image quality
Solution Approach 1:
The patent segments the charge collection process by spatially separating signal charge and dark current through potential barriers. The pinned photodiode structure creates distinct potential wells: one for collecting signal charge from the photosensitive area and another configuration for repelling or draining dark current electrons generated at the semiconductor-dielectric interface, preventing their migration into the photosensitive area.
Solution Approach 2:
The patent converts the harmful effect of dark current generation at the semiconductor-dielectric interface into a beneficial separation mechanism. By applying specific potentials to adjacent gates, the potential barrier not only prevents dark current migration but also enhances the collection efficiency of signal charge in the photosensitive area, turning the interface into a selective filter rather than a source of degradation.
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 substantially eliminates dark current adjacent to gates and other structures, improving image sensor performance by keeping dark charge separate from signal charge, thereby enhancing image quality.
Implementation Method 1
the gate is held at a voltage which will accumulate majority carriers at a semiconductor-dielectric interface during integration for the photosensitive area
Implementation Method 2
accumulate majority carriers at a semiconductor-dielectric interface
Implementation Method 3
the potential profile under the adjoining gate is created so that dark current related to the gate is drained away from the photogeneration diffusion
Implementation Method 4
a photosensitive area for receiving incident light which is converted into a charge
Data Source
AI summary
A method for lowering dark current in an image sensor pixel, the method includes the steps of providing a photosensitive area for receiving incident light which is converted into a charge; providing a gate for transferring charge from the photosensitive area; wherein the gate is held at a voltage which will accumulate majority carriers at a semiconductor-dielectric interface during integration for the photosensitive area. Alternatively, a potential profile can be provided under the gate to drain the dark current away from the photogeneration diffusion.