Deep Trench Isolation for Image Sensor Black Level Stability
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Solution Overview
Problem
Image sensors face light-leakage issues that distort black levels due to incident light reflection, refraction, and diffusion, affecting image quality, especially at high intensities.
Innovation Solution
The implementation of a light-leakage prevention structure in image sensors, featuring deep trenches and buried wells with specific doping and metal coatings, blocks leakage light and diffusion carriers, stabilizing black levels by forming a vertical and horizontal structure around the active region.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If additional pixels are added to measure black levels, then black level measurement capability is improved, but light leakage from the active region distorts the black levels
Solution Approach 1:
The patent segments the semiconductor substrate into distinct regions: active region for light sensing, optical-black region for black level measurement, and deep trenches as isolating structures. This spatial segmentation prevents light leakage from the active region to the optical-black region, ensuring accurate black level measurement while maintaining separate functional zones.
Solution Approach 2:
The deep trench acts as an intermediary structure between the active region and optical-black region. Filled with dielectric material and optionally metal coating, the trench serves as a light-blocking barrier that prevents direct light paths and carrier diffusion, thereby protecting the black level measurement pixels from light leakage while allowing the regions to remain functionally connected through the substrate.
2Power
If the image sensor operates at high light intensity, then photo charge generation is improved, but light leakage and diffusion increase affecting black levels
Solution Approach 1:
The patent extracts the harmful diffusion carriers from reaching the optical-black region by introducing deep trenches filled with dielectric material. These trenches act as extraction barriers that remove the light leakage and diffusion paths, allowing high-intensity operation for improved photo charge generation while preventing the associated harmful effects from contaminating the black level measurement.
3Stability of the object's composition
If deep trenches are formed to block light leakage, then black level stability is improved, but device complexity increases
Solution Approach 1:
The patent addresses light leakage prevention by transitioning from two-dimensional surface-level shielding to three-dimensional deep trench structures extending vertically through the substrate. This dimensional approach effectively blocks light leakage paths and carrier diffusion in the vertical dimension, achieving superior black level stability while the trenches can be integrated into existing pixel architectures with minimal lateral space occupation.
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 solution effectively prevents light leakage and diffusion carriers from reaching the black level measurement pixels, thereby stabilizing black levels and improving image quality across varying light intensities.
Implementation Method 1
a portion of the incident light may arrive at the additional pixels through reflection, refraction and diffraction
Implementation Method 2
a portion of the incident light may arrive at the additional pixels through reflection, refraction and diffraction
Implementation Method 3
photo carriers generated by the incident light may be diffused to the additional pixels to affect the black levels
Implementation Method 4
A metal coating layer may be formed on an inner surface of the deep trench
Data Source
AI summary
An image sensor includes first pixels, second pixels and a deep trench. The first pixels are formed in an active region of a semiconductor substrate, and configured to measure photo-charges corresponding to incident light. The second pixels are formed in an optical-black region of the semiconductor substrate, and are configured to measure black levels. The deep trench is formed vertically in a boundary region of the optical-black region, where the boundary region is adjacent to the active region, and configured to block leakage light and diffusion carriers from the active region.