Solid-State Image Sensor Pixel Structure for 940 Nm NIR Absorption
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Solution Overview
Problem
Conventional solid-state imaging devices have low quantum efficiency for near infrared light, particularly at 940 nm, due to the Si substrate's low absorption, leading to reduced image quality and increased color mixture between pixels when attempting to increase absorption depth.
Innovation Solution
Incorporating a light scattering structure between the photodiode and microlens, with a refractive index lower than the surrounding materials, to increase the optical path length and absorption of near infrared light, while stabilizing the Si substrate surface with insulating films and a light shielding layer to prevent dark current and image quality degradation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the depth of photodiode is increased to increase quantum efficiency for near infrared light, then absorption of incident light is improved, but color mixture with adjacent pixels increases
Solution Approach 1:
The patent introduces a light scattering structure that changes the light propagation from a straight path to a scattered path with multiple directions, effectively increasing the optical path length in the depth dimension without increasing the physical depth of the photodiode. This allows achieving sufficient absorption while maintaining pixel isolation.
Solution Approach 2:
The light scattering structure acts as an intermediary between the microlens and the photodiode, modifying the light path by scattering it to increase the optical path length. This mediator enables the photodiode to absorb more light without needing to increase its depth, thereby preventing color mixture with adjacent pixels.
2Measurement precision
If the Si substrate surface is processed directly to increase light absorption, then quantum efficiency is improved, but interface level destabilization occurs causing dark current increase
Solution Approach 1:
The patent introduces a light scattering structure as an intermediary layer between the microlens and the photodiode. This structure increases light absorption through scattering while maintaining the stability of the Si substrate surface, thereby preventing dark current increase and interface level destabilization.
3Measurement precision
If inverted pyramid structures are formed on Si substrate to increase optical path length, then light absorption is improved, but incidence angle characteristics become irregular causing shading and moire
Solution Approach 1:
The light scattering structure provides localized light scattering properties without imposing a regular periodic pattern on the entire substrate surface. This local scattering approach increases optical path length while maintaining uniform incidence angle characteristics across different regions, preventing shading and moire effects.
Solution Approach 2:
The light scattering structure uses asymmetric scattering centers that scatter light in multiple directions rather than following a regular periodic pattern. This asymmetric design increases optical path length while avoiding the regularity that causes shading and moire, thereby maintaining good incidence angle characteristics.
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 approach enhances quantum efficiency without compromising image quality, reducing shading and moire effects, and improving sensitivity to near infrared light while maintaining high image quality.
Implementation Method 1
at least one light scattering structure provided between the light receiving portion and the microlens
Implementation Method 2
A microlens is formed for each of the pixels in order to condense light
Implementation Method 3
a photodiode (PD) is formed for each of pixels formed to be arrayed in a two-dimensional matrix on a substrate. A microlens is formed for each of the pixels in order to condense light
Data Source
AI summary
A solid-state imaging device includes a plurality of pixels arrayed in a two-dimensional matrix on a substrate. Each of the pixels includes a light receiving potion that performs photoelectric conversion, a microlens that condenses light to the light receiving potion, and at least one light scattering structure provided between the light receiving potion and the microlens.