Pixel-Array Substrate with Metal Annulus for Optical Cross-Talk Reduction
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Solution Overview
Problem
Camera image sensors experience optical cross-talk due to light propagating through microlenses and color filters at high incident angles, leading to image artifacts.
Innovation Solution
A pixel-array substrate is designed with a semiconductor substrate, a buffer layer, and a metal annulus, where the buffer layer has a thin region above photodiode regions and a thick annulus region surrounding trenches, with the metal annulus covering the thick buffer-layer region to prevent optical cross-talk.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional pixel array structure is used, then the device complexity is low, but optical cross-talk occurs causing image artifacts
Solution Approach 1:
The buffer layer is segmented into different thickness regions: a first thickness region above photodiode regions and a second thickness region in annular regions between adjacent photodiode regions. This segmentation allows the structure to simultaneously maintain low optical cross-talk over photodiodes and permit high-angle light transmission in inter-pixel regions, resolving the contradiction between image quality and structural simplicity.
Solution Approach 2:
The buffer layer exhibits local quality variations with different thicknesses in different spatial locations. The first thickness region provides optical isolation where needed, while the second thickness region allows light propagation paths for high-angle incident light to reach adjacent photodiodes, thus improving image quality without requiring complete structural redesign.
2Reliability
If the buffer layer thickness is uniformly increased to block cross-talk, then optical cross-talk is reduced, but light propagation at high incident angles is also blocked
Solution Approach 1:
The buffer layer is designed with non-uniform thickness: thicker regions above photodiode regions provide optical isolation to prevent cross-talk, while thinner annular regions between photodiode regions maintain light propagation capability for high-angle incident light. This local differentiation resolves the contradiction between optical isolation and light propagation adaptability.
Solution Approach 2:
The buffer layer is divided into functionally distinct segments: first buffer layer regions with greater thickness for isolation and second buffer layer regions with lesser thickness for light transmission. This segmentation enables simultaneous achievement of optical cross-talk reduction and high-angle light acceptance.
3Adaptability or versatility
If a thinned buffer layer is used to allow high-angle light propagation, then light propagation is improved, but optical cross-talk increases
Solution Approach 1:
The buffer layer is segmented into first thickness regions (thinner) above photodiode regions that allow high-angle light propagation, and second thickness regions (thicker) in annular regions between photodiode regions that provide optical isolation. This spatial segmentation resolves the contradiction between light propagation and optical isolation.
Solution Approach 2:
The solution moves from a uniform one-dimensional thickness parameter to a two-dimensional thickness distribution map, where thickness varies laterally across the pixel array. This dimensional change enables simultaneous optimization of light propagation (over photodiodes) and optical isolation (between photodiodes).
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 solution effectively reduces optical cross-talk by blocking light that would otherwise reach unintended photodiode regions, improving image quality by minimizing artifacts.
Implementation Method 1
The metal annulus is on the buffer layer and covers the thick buffer-layer region... effectively reduces optical cross-talk by blocking light that would otherwise reach unintended photodiode regions
Data Source
AI summary
A pixel-array substrate includes a semiconductor substrate, a buffer layer, and a metal annulus. The semiconductor substrate includes a first-photodiode region. A back surface of the semiconductor substrate forms a trench surrounding the first-photodiode region in a cross-sectional plane parallel to a first back-surface region of the back surface above the first-photodiode region. The buffer layer is on the back surface and has (i) a thin buffer-layer region located above the first-photodiode region and (ii) a thick buffer-layer region forming an annulus above the trench in a plane parallel to the cross-sectional plane. The metal annulus is on the buffer layer and covers the thick buffer-layer region.