Pixel Formation Method for Blooming Reduction
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Solution Overview
Problem
Camera pixels with vertical transfer gates are vulnerable to blooming, a phenomenon where excess photoelectrons from saturated pixels are collected by adjacent pixels, degrading image quality due to increased distance between the photodiode and floating diffusion regions.
Innovation Solution
A pixel design featuring a semiconductor substrate with a trench structure and a floating diffusion region extending beyond the trench depth, allowing excess photoelectrons to tunnel directly to the nearest floating diffusion region, preventing blooming, and including a dielectric layer to reduce junction capacitance and enhance charge transfer.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If the distance between the photodiode and floating diffusion region is increased to reduce blooming, then blooming is reduced, but pixel sensitivity decreases and image quality deteriorates
Solution Approach 1:
The patent transitions from a horizontal arrangement of photodiode and floating diffusion region to a vertical arrangement extending in the depth direction. The photodiode region is positioned at a first depth and the floating diffusion region at a second depth greater than the first depth, creating a vertical separation that reduces blooming while maintaining electrical connectivity through the transfer gate. This dimensional change allows excess photoelectrons to be contained more effectively without compromising pixel sensitivity.
Solution Approach 2:
The patent embeds the floating diffusion region within the pixel structure at a deeper level, with the transfer gate positioned between the photodiode and floating diffusion regions. The transfer gate acts as an intermediate structure that controls charge transfer while the vertical nesting of regions reduces the lateral distance for electron collection, thereby reducing blooming effects while preserving sensitivity.
2Quantity of substance
If pixel size is decreased to increase pixel density, then pixel density increases, but the distance between photodiode and floating diffusion region increases causing blooming
Solution Approach 1:
By arranging the photodiode and floating diffusion region vertically at different depths rather than horizontally adjacent to each other, the patent enables smaller pixel footprints while maintaining adequate separation between regions. The vertical stacking allows pixel density to increase without proportionally increasing the distance between photodiode and floating diffusion region, thus preventing blooming even at high pixel densities.
Solution Approach 2:
The patent creates different spatial zones within the pixel: the photodiode region at a shallower depth for efficient light absorption, the transfer gate region in between for controlled charge transfer, and the floating diffusion region at greater depth for charge collection. This localized spatial differentiation optimizes each region's function while maintaining compact pixel dimensions that support high pixel density without blooming.
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
The design effectively reduces blooming and increases pixel sensitivity by optimizing the trench and floating diffusion region geometry, improving image quality and conversion gain.
Implementation Method 1
allowing excess photoelectrons to tunnel directly to the nearest floating diffusion region
Implementation Method 2
including a dielectric layer to reduce junction capacitance and enhance charge transfer
Implementation Method 3
Light reaching the photodiode region generates photoelectrons
Data Source
AI summary
A method for forming a pixel includes forming, in a semiconductor substrate, a wide trench having an upper depth with respect to a planar top surface of the semiconductor substrate. The method also includes ion-implanting a floating-diffusion region between the planar top surface and a junction depth in the semiconductor substrate. In a cross-sectional plane perpendicular to the planar top surface, the floating-diffusion region has (i) an upper width between the planar top surface and the upper depth, and (ii) between the upper depth and the junction depth, a lower width that exceeds the upper width. Part of the floating-diffusion region is beneath the wide trench and between the upper depth and the junction depth.