Image Sensor Pixel Isolation for WDR Blooming Control
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Solution Overview
Problem
Existing CMOS image sensors with wide dynamic range (WDR) and LED flicker mitigation (LFM) capabilities face challenges with blooming phenomena between photodiodes of different sensitivity, leading to image distortion.
Innovation Solution
The image sensor incorporates a substrate with first and second photodiodes of different sensitivities, along with an isolation structure that completely penetrates the substrate vertically, electrically isolating the photodiodes and preventing blooming.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If multiple photodiodes with different sensitivity are used to achieve wide dynamic range, then the dynamic range is improved, but blooming phenomenon occurs between photodiodes causing image distortion
Solution Approach 1:
The pixel is divided into multiple photodiodes with different sensitivity levels (first photodiode with first sensitivity, second photodiode with second sensitivity) to capture different illuminance ranges, enabling wide dynamic range imaging while maintaining separation between sensitivity zones
Solution Approach 2:
An isolation structure is introduced as an intermediary element between photodiodes of different sensitivity. This isolation structure prevents photocharge overflow from high-illuminance photodiodes to adjacent low-illuminance photodiodes, thereby eliminating blooming phenomenon while preserving the benefits of multiple sensitivity levels
2Area of stationary object
If photodiodes are placed adjacent to each other for compact design, then device area is reduced, but photocharges overflow between adjacent photodiodes causing blooming
Solution Approach 1:
The pixel area is segmented into distinct regions with different photodiodes (first region with first photodiode, second region with second photodiode), allowing compact arrangement while maintaining electrical separation through the isolation structure to prevent photocharge overflow
Solution Approach 2:
The isolation structure serves as a physical and electrical intermediary between adjacent photodiodes, blocking the path of photocharge overflow while allowing the photodiodes to remain in close proximity for compact pixel design
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 reduces blooming and enhances the signal-to-noise ratio (SNR), enabling a wider WDR and improved image quality by preventing the overflow of photocharges between photodiodes.
Implementation Method 1
a first photodiode located in a first region of the substrate and generating photocharges from light incident on the first region of the first surface, a second photodiode located in a second region of the substrate and generating photocharges from light incident on the second region of the first surface
Data Source
AI summary
An image sensor includes a substrate including a first surface and a second surface facing the first surface, a first photodiode located in a first region of the substrate and generating photocharges from light incident on the first region, a second photodiode located in a second region of the substrate and generating photocharges from light incident on the second region, and an isolation structure defining the first region in which the first photodiode is located and the second region in which the second photodiode is located, and extending between the first photodiode and the second photodiode. An area of the second region is smaller than an area of the first region, a first end of the isolation structure is coplanar with the second surface, and the isolation structure extends in a vertical direction from the second surface of the substrate toward the first surface of the substrate.