Pixel Sensor Refraction Structures for Large-Angle Light Capture
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
CMOS image sensors face reduced quantum efficiency and increased optical crosstalk at large incident angles due to light reflection off the top surface of the substrate, which hinders their performance, especially in cameras operating at small f-numbers.
Innovation Solution
Incorporating a main deep trench isolation (DTI) structure surrounding the photodiode and sub-DTI structures filled with oxide material within the perimeter of the main DTI structure to refract and absorb incident light at various angles, reducing reflections and enhancing light penetration into the substrate.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If light enters the pixel sensor at large incident angles, then the aperture diameter increases allowing more light collection, but light reflection off the top surface of the substrate increases reducing quantum efficiency
Solution Approach 1:
The substrate top surface is segmented into multiple regions: flat regions for normal incidence light and angled regions for oblique incidence light. This segmentation allows different surface orientations to optimize light capture for different incident angles, reducing reflection losses while maintaining high quantum efficiency across varying light entry angles
Solution Approach 2:
Different regions of the substrate surface are given different local qualities - flat surfaces in central areas and angled surfaces at peripheral areas. This local quality variation enables the substrate to simultaneously optimize for both normal and oblique light incidence, improving quantum efficiency for large incident angles without compromising overall light collection capability
2Use of energy by moving object
If the substrate is designed to capture light at large incident angles, then low-light performance improves, but optical crosstalk between adjacent pixels increases
Solution Approach 1:
The substrate is segmented with individual angled regions positioned above each photodiode, creating isolated light capture zones. This segmentation prevents light captured at large angles from one pixel from spilling into adjacent pixels, reducing optical crosstalk while maintaining improved low-light performance through enhanced oblique light capture
Solution Approach 2:
The angled substrate regions act as intermediaries that redirect oblique light rays onto the photodiodes. These angled surfaces serve as optical mediators that capture light at large incident angles and redirect it precisely onto the corresponding photodiode, preventing crosstalk while improving low-light sensitivity
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 configuration increases quantum efficiency at large incident angles, reduces optical crosstalk, and improves low-light performance in CMOS image sensors.
Implementation Method 1
one or more refraction structures above the photodiode and within a perimeter of the DTI structure in the substrate
Data Source
AI summary
A pixel sensor may include a main deep trench isolation (DTI) structure and one or more sub-DTI structures in a substrate of the pixel sensor to increase the quantum efficiency of the pixel sensor at large incident angles. The one or more sub-DTI structures may be located within the perimeter of the main DTI structure and above a photodiode. The one or more sub-DTI structures may be configured to provide a path of travel for incident light into the photodiode from large incident angles in that the one or more sub-DTI structures may be filled with an oxide material to increase light penetration into the one or more sub-DTI structures. This may reduce reflections at a top surface of the substrate, thereby permitting incident light to refract into the substrate and toward the photodiode.