Distributed Index Lens for Wide-Angle Light Collection
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Solution Overview
Problem
Conventional solid-state imaging devices experience a decrease in light-collecting efficiency at wide incident angles due to the interception of oblique light by Al interconnections, leading to reduced sensitivity, especially in pixels near the edge, making it difficult to apply them in optical systems with short focal lengths and limiting further pixel size reduction.
Innovation Solution
A distributed index lens is developed with a discretized refractive index distribution across an area roughly half the width of the incident light's wavelength, combining light-collecting characteristics of both distributed index and film thickness distribution lenses, allowing for high light-collecting efficiency without the limitations of conventional microlens processing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If a conventional microlens is used, then light-collecting efficiency is relatively high for incident angles around 20°, but light-collecting efficiency declines suddenly for incident angles more than 20°
Solution Approach 1:
The microlens is divided into multiple zones (first zone, second zone, third zone) with different refractive indices. This segmentation allows each zone to handle different incident angle ranges, enabling the lens to maintain high light-collecting efficiency across a wide angular range rather than declining suddenly at 20°.
Solution Approach 2:
Different zones of the microlens are assigned different refractive indices tailored to their specific functional requirements. The first zone (central region) has a higher refractive index for capturing near-normal incident light, while the second and third zones have progressively lower refractive indices for capturing oblique incident light, optimizing performance at each location.
2Quantity of substance
If the pixel size is reduced to increase pixel density, then high pixel density is achieved, but light-collecting efficiency further declines due to increased incident angles at edge pixels
Solution Approach 1:
The microlens is divided into multiple zones (first zone, second zone, third zone) with different refractive indices. This segmentation allows each zone to handle different incident angle ranges, enabling the lens to maintain high light-collecting efficiency across a wide angular range rather than declining suddenly at 20°.
Solution Approach 2:
The refractive index parameter is varied across different zones of the microlens to optimize light collection at different incident angles. By changing the refractive index from the first zone to the third zone, the lens adapts to different angular ranges, maintaining efficiency even when pixel size is reduced and edge pixels experience higher incident angles.
3Illumination intensity
If electric wiring parts are shrunk to improve light-collecting efficiency at edge pixels, then light path obstruction is reduced, but manufacturing complexity increases and further shrinking becomes impossible
Solution Approach 1:
A transparent resin layer is introduced as an intermediary medium between the microlens and the Al interconnection. This resin layer fills the space and allows oblique light to pass through without being blocked by the interconnection structure, effectively solving the light path obstruction problem without requiring further shrinking of the wiring parts.
Solution Approach 2:
The refractive index parameter is varied across different zones of the microlens to optimize light collection at different incident angles. By changing the refractive index from the first zone to the third zone, the lens adapts to different angular ranges, maintaining efficiency even when pixel size is reduced and edge pixels experience higher incident angles.
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
The distributed index lens maintains high light-collecting efficiency across a wide range of incident angles, improving sensitivity and enabling the use in optical systems with short focal lengths, while allowing for easier and more accurate manufacturing processes.
Implementation Method 1
a light-collecting device (distributed index lens) having a discretized refractive index distribution in an area with about a half of width of a wavelength of incident light in size
Data Source
AI summary
The present invention provides a solid-state imaging apparatus and the like which is able to support an optical system whose incident angle is wide. Each pixel is 2.25 μm square in size, and includes a distributed index lens (1), a color filter (for example, for green) (2), an Al interconnections (3), a signal transmitting unit (4), a planarized layer (5), a light-receiving device (Si photodiodes) (6), and an Si substrate (7). The two-stage concentric circle structure of the distributed index lens is formed by SiO2 (n=2) with the film thickness 1.2 μm (“grey color”), the film thickness 0.8 μm (“dots pattern”) and the film thickness of 0 μm (“without pattern: white color”), and the medium surrounding the distributed index lens (1)is air (n=1).