APD Pixel Isolation Structure for Low Crosstalk and Dark Current
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Avalanche photodiodes (APDs) face issues with crosstalk and dark count rate (DCR) due to light emission in high-electric-field regions and dark current generation at interfaces, which affect their sensitivity and accuracy.
Innovation Solution
The implementation of a sensor design with a hole accumulation region and an isolation region that penetrates through the substrate, along with an electron accumulation region, to reduce crosstalk and suppress DCR by isolating pixels and trapping electrons, thereby enhancing photon detection efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If an isolation region is formed between pixels to reduce crosstalk, then crosstalk is reduced, but dark current is generated at the interface between the insulating film and silicon
Solution Approach 1:
A hole accumulation region is introduced as an intermediary layer between the isolation region and the well region. This hole accumulation region acts as a mediator that prevents dark current generation at the insulating film-silicon interface while maintaining the crosstalk isolation function. The accumulated holes create a positive charge layer that repels electrons, blocking the dark current path without compromising the electrical isolation between adjacent pixels.
Solution Approach 2:
The hole accumulation region is specifically positioned only where needed - at the interface between the isolation region and the well region. This localized structure provides dark current suppression exactly where the harmful effect occurs, without affecting other regions of the pixel. The regional differentiation allows the isolation region to maintain its crosstalk-reducing function while the hole accumulation region provides targeted dark current blocking.
2Reliability
If a high-electric-field region is created for carrier multiplication, then sensitivity is enhanced, but light emission causes photons to be incident on neighboring pixels
Solution Approach 1:
The pixel structure is segmented into distinct functional regions: a well region for carrier generation, an isolation region for electrical separation, and a hole accumulation region for dark current suppression. This segmentation allows the high-electric-field multiplication region to operate at full sensitivity while the isolation region physically separates it from neighboring pixels, preventing photon crosstalk. The segmented structure enables each region to optimize its specific function without interfering with others.
3Object-affected harmful factors
If physical isolation between pixels is implemented using an insulating film, then crosstalk is reduced, but dark current is generated at the interface
Solution Approach 1:
The hole accumulation region serves as an intermediary between the insulating film and the silicon substrate. This intermediary layer prevents the direct contact that causes dark current generation at the insulating film-silicon interface, while still allowing the insulating film to perform its crosstalk isolation function. The accumulated holes create a potential barrier that blocks electron flow, preventing dark current without compromising the isolation effectiveness.
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 effectively reduces crosstalk and DCR, improving the sensitivity and accuracy of APDs by isolating neighboring pixels and enhancing photon detection efficiency.
Implementation Method 1
an avalanche photodiode to convert incident light into electric charge
Implementation Method 2
a hole accumulation region between the isolation region and the well region
Implementation Method 3
carriers generated by photoelectric conversion are multiplied in a high-electric-field PN junction region
Data Source
AI summary
A sensor includes a first substrate including at least a first pixel. The first pixel includes an avalanche photodiode to convert incident light into electric charge and includes an anode and a cathode. The cathode is in a well region of the first substrate. The first pixel includes an isolation region that isolates the well region from at least a second pixel that is adjacent to the first pixel. The first pixel includes a hole accumulation region between the isolation region and the well region. The hole accumulation region is electrically connected to the anode.