Near-Infrared Absorber Structure for Optical Black Pixel Isolation
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Solution Overview
Problem
Conventional image sensors face challenges in effectively canceling out dark current offsets due to near-infrared and infrared light leakage, which increases the size of the sensor and reduces the maximal frame rate, especially in applications capturing both near-IR/IR and visible light.
Innovation Solution
Incorporating a near-infrared absorber with a higher absorption coefficient than silicon, such as germanium, between the active and optical black pixel regions, and optionally using a deep trench isolator to absorb or reflect photons, thereby reducing light leakage and maintaining a smaller optical black dummy region.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If the optical black dummy pixel region is enlarged to block near-infrared light leakage, then light leakage into optical black pixels is reduced, but sensor size increases
Solution Approach 1:
A near-infrared absorber layer is introduced as an intermediary component between the active pixel region and the optical black pixel region. This layer specifically absorbs near-infrared light wavelengths, preventing them from reaching the optical black pixels and causing false signals, while allowing the optical black dummy pixel region to remain compact without compromising its light-blocking function.
Solution Approach 2:
The near-infrared absorber is selectively positioned only in the regions where near-infrared light leakage is problematic (between active and optical black pixel regions), rather than uniformly treating the entire sensor. This localized approach blocks harmful near-IR light where needed while maintaining the compact design of the optical black dummy pixel region.
2Object-affected harmful factors
If the optical black dummy pixel region is enlarged to block near-infrared light leakage, then light leakage into optical black pixels is reduced, but maximal frame rate decreases
Solution Approach 1:
The near-infrared absorber acts as a mediator that enables the optical black dummy pixel region to remain small while still effectively blocking near-infrared light. This allows the sensor to maintain high frame rates by reducing the time required for charge transfer and readout operations, while simultaneously preventing near-IR light leakage that would otherwise require a larger dummy region.
3Object-affected harmful factors
If a near-infrared absorber is added between active and optical black pixel regions, then near-infrared light leakage is reduced, but device complexity increases
Solution Approach 1:
The near-infrared absorber changes the optical absorption parameters of the sensor structure by introducing a material with high near-infrared absorption coefficient. This material layer is integrated into the existing sensor architecture, modifying the optical properties without fundamentally changing the structural complexity or requiring complete redesign of the pixel array.
4Device complexity
If conventional silicon is used without near-infrared absorber, then device complexity is low, but near-infrared light leakage increases
Solution Approach 1:
The sensor employs a composite structure combining conventional silicon-based active pixels with a specialized near-infrared absorber material layer. This composite approach leverages the well-established silicon photodetector technology for visible light detection while adding a targeted near-IR absorbing layer to prevent light leakage, achieving both simplicity and 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 near-IR light leakage into optical black pixels, allowing for a smaller sensor size and higher frame rates while maintaining accurate dark current cancellation.
Implementation Method 1
a near-infrared absorber positioned between the active pixel region and the optical black pixel region, the near-infrared absorber comprising a material having a higher near-infrared absorption coefficient than that of silicon
Data Source
AI summary
An example imaging sensor comprises a bulk silicon substrate and a pixel array. The pixel array comprises an active pixel region including an active pixel subarray, an optical black pixel region including an optical black pixel subarray, and an optical black dummy pixel region including an optical black dummy pixel subarray, the optical black dummy pixel region positioned between the active pixel region and the optical black pixel region. A near-infrared absorber is positioned between the active pixel region and the optical black pixel region, the near-infrared absorber comprising a material having a higher near-infrared absorption coefficient than that of silicon.