Imaging Sensor NIR Absorber Layout for Dark Current Control
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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 a larger optical black dummy pixel region is used to absorb near-infrared light, then light leakage is reduced, but the sensor die size increases
Solution Approach 1:
The patent applies local quality by introducing a near-infrared absorber material with specific optical properties only in the optical black pixel region, while the rest of the sensor maintains standard silicon substrate properties. This localized material substitution allows targeted near-infrared absorption without requiring the entire sensor to be redesigned, thus reducing light leakage in critical areas while maintaining overall compact dimensions.
Solution Approach 2:
The patent employs composite materials by combining the standard silicon substrate with a near-infrared absorber material that has higher near-infrared absorption coefficient. This composite structure enables the sensor to simultaneously maintain good visible light response from the silicon while adding enhanced near-infrared absorption capability through the specialized material layer in the optical black region.
2Ease of manufacture
If the sensor area is reduced to lower manufacturing costs, then manufacturing cost decreases, but near-infrared absorption becomes insufficient
Solution Approach 1:
The patent applies local quality by introducing a near-infrared absorber material with specific optical properties only in the optical black pixel region, while the rest of the sensor maintains standard silicon substrate properties. This localized material substitution allows targeted near-infrared absorption without requiring the entire sensor to be redesigned, thus reducing light leakage in critical areas while maintaining overall compact dimensions.
Solution Approach 2:
The patent employs composite materials by combining the standard silicon substrate with a near-infrared absorber material that has higher near-infrared absorption coefficient. This composite structure enables the sensor to simultaneously maintain good visible light response from the silicon while adding enhanced near-infrared absorption capability through the specialized material layer in the optical black region.
3Ease of manufacture
If silicon substrate is used for near-infrared absorption, then manufacturing is simplified, but absorption coefficient is insufficient leading to increased dark current
Solution Approach 1:
The patent applies local quality by introducing a near-infrared absorber material with specific optical properties only in the optical black pixel region, while the rest of the sensor maintains standard silicon substrate properties. This localized material substitution allows targeted near-infrared absorption without requiring the entire sensor to be redesigned, thus reducing light leakage in critical areas while maintaining overall compact dimensions.
Solution Approach 2:
The patent applies the extraction principle by separating the near-infrared absorption function from the general light-sensitive pixel regions. The near-infrared absorber is extracted and placed specifically in the optical black pixel region, which is not used for image capture anyway. This extraction allows the main imaging pixels to remain simple silicon-based structures while the specialized absorption function is handled by a dedicated material in the optical black region, reducing dark current in active pixels.
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.