Gradient Index Microlens Waveguide Solid-State Image Sensor
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Solution Overview
Problem
Conventional solid-state image sensors face issues with low light-collecting efficiency for oblique incident light due to increased light-collection loss and color-mixing within the waveguide path, particularly as the angle of incidence increases, leading to reduced sensitivity.
Innovation Solution
The implementation of a solid-state image sensor configuration featuring gradient index microlenses with effective refractive index distributions and optical waveguide regions made of high-refractive index materials, including metal oxides with dispersed metallic inclusion particles, which reduce light propagation loss and color-mixing by optimizing the refractive index distribution and wavelength absorption characteristics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of moving object
If the cell size is reduced to achieve miniaturization, then the pixel density increases, but the light-collecting efficiency deteriorates due to increased distance from the on-chip lens to the photodiode
Solution Approach 1:
An optical waveguide region is introduced as an intermediary component between the on-chip lens and the photodiode. This waveguide region has a higher refraction index than the surrounding interlayer insulation film, creating a refraction index difference that enables total internal reflection. The waveguide region acts as a mediator to guide light from the lens to the photodiode, solving the light-collection problem caused by miniaturization.
Solution Approach 2:
The refraction index parameter is changed by introducing a material with higher refraction index for the optical waveguide region compared to the interlayer insulation film. This parameter change creates the conditions for total internal reflection and enables effective light guidance in the miniaturized pixel structure.
2Adaptability or versatility
If the angle of incident light increases for oblique incident light, then the field of view expands, but light-collection loss and color-mixing increase within the waveguide path
Solution Approach 1:
The optical waveguide region serves as an intermediary that maintains total internal reflection even for oblique incident light. By controlling the refraction index difference between the waveguide region and surrounding medium, the system can handle a wider range of incidence angles while preventing light leakage and color-mixing.
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 enhances light-collecting efficiency and sensitivity by minimizing light-collection loss and color-mixing across various incidence angles, effectively improving the performance of solid-state image sensors.
Implementation Method 1
the total reflection condition is given as θ−1 (n2/n1). However, when θ becomes big, the previous expression can no longer be satisfied
Implementation Method 2
each of the light-collecting elements is a gradient index microlens having an effective refractive index distribution
Implementation Method 3
Photoelectric conversion regions (photodiodes) 102 are formed in the surface of an Si substrate 101
Data Source
AI summary
A solid-state image sensor having a configuration which reduces increases in light-collection loss and light mixing due to an increase in the angle of light entering into a waveguide path during oblique incidence and which is effective for sensitivity improvement includes: an Si substrate; unit-pixels arranged on the Si substrate; a wiring layer formed on the unit-pixels; optical waveguide regions each formed on a photoelectric conversion region included in a corresponding one of the unit-pixels, and penetrating the wiring layer; and light-collecting elements each formed above a corresponding one of the optical waveguide regions, wherein each of the light-collecting elements is a gradient index microlens having an effective refractive index distribution.