Honeycomb Pixel Layout to Preserve CMOS Photodiode Area
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
In miniaturized CMOS image sensors, the photodiode regions are reduced due to boron penetration and electric field effects at the corners of square-shaped pixels, leading to a decrease in pixel efficiency, especially when hexagonal pixels are not adequately considered for photodiode region formation.
Innovation Solution
A light-receiving element with a pixel array forming a honeycomb structure, where each pixel has a regular hexagonal shape with an inter-pixel separation part and a pinning region of opposite conductivity type, reducing the area overlap of p-type semiconductor regions and minimizing the decrease in n-type semiconductor regions, thus enhancing photodiode efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If pixels are miniaturized to increase pixel density, then the number of pixels per unit area increases, but the photodiode region area decreases due to boron penetration and electric field effects at corner portions
Solution Approach 1:
The patent applies asymmetry by changing the pixel shape from square to regular hexagonal. This geometric transformation eliminates the right-angled corners that cause concentrated boron penetration and electric field effects, distributing these effects more evenly along the pixel periphery and thereby preserving photodiode region area while maintaining high pixel density
Solution Approach 2:
The patent employs curvature by replacing the sharp right-angle corners of square pixels with obtuse-angled hexagonal corners. This curvature modification reduces the concentration of electric fields and boron penetration at corner portions, preventing excessive reduction of the photodiode region while enabling miniaturization for increased pixel density
2Reliability
If a p-type pinning region is formed at the trench side surface to insulate and separate pixels, then pixel separation is improved, but the photodiode region is reduced due to boron penetration and electric field effects at corner portions
Solution Approach 1:
The regular hexagonal pixel shape with obtuse-angled corners creates a more uniform distribution of the p-type pinning region along the pixel periphery. This asymmetry in geometry prevents concentrated boron penetration and electric field effects at corner portions, maintaining effective pixel separation while preserving photodiode region area
Solution Approach 2:
The patent applies local quality by forming the p-type pinning region specifically at the trench side surfaces adjacent to the photodiode region, while the obtuse-angled hexagonal geometry ensures that corner portions do not experience excessive boron penetration. This localized approach maintains pixel separation functionality while minimizing photodiode region reduction
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 honeycomb structure increases pixel density and improves light condensation, reducing dark current and enhancing signal charge generation in miniaturized pixels, particularly by forming obtuse angles at corner intersections which minimizes the reduction in photodiode area.
Implementation Method 1
a photoelectric conversion region of a first conductivity type, the photoelectric conversion region photoelectrically converting the light incident
Data Source
AI summary
Provided is a light-receiving element capable of reducing a decrease in a photodiode region of a pixel. The light-receiving element includes a pixel array unit in which a plurality of pixels is disposed in an array, the pixels being capable of generating an electrical signal according to light incident from outside. Each of the plurality of pixels includes a photoelectric conversion region of a first conductivity type, the photoelectric conversion region photoelectrically converting the light incident, an inter-pixel separation part that defines an outer edge shape of the pixels, and insulates and separates adjacent pixels, and a pinning region of a second conductivity type, the pinning region being formed between the photoelectric conversion region and a sidewall of the inter-pixel separation part. The plurality of pixels is disposed in an array so as to form a honeycomb structure in which corner parts where a plurality of sides intersects are obtuse angles in plan view.