Solid-State Image Pickup Optical Waveguide Light Leakage Prevention
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Solution Overview
Problem
In solid-state image pickup apparatuses, light leakage occurs between pixels due to gaps between optical waveguides and light shielding portions, leading to reduced SN ratio of pixel signals.
Innovation Solution
A solid-state image pickup apparatus is designed with an optical waveguide and a light reflecting layer having a refractive index lower than the waveguide, positioned at the boundary between the waveguide and a second insulating layer, where the angle between the light reflecting layer and the second insulating layer is less than 90 degrees, effectively suppressing light leakage between adjacent pixels.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If a light shielding portion is formed between the inner lens and optical waveguide to prevent light mixture, then light leakage to adjacent pixels is reduced, but light that passes through the inner lens still leaks into adjacent pixels via the connection member or insulator
Solution Approach 1:
A light reflecting layer is introduced as an intermediary component between the optical waveguide and the second insulating layer. This reflective layer acts as a mediator to redirect light that would otherwise leak into adjacent pixels, reflecting it back toward the optical waveguide or absorbing it, thereby preventing cross-pixel contamination while maintaining the light shielding function.
Solution Approach 2:
The refractive index parameter of the light reflecting layer is specifically designed to be lower than that of the optical waveguide. This parameter change creates a refractive index contrast that enables effective light reflection at the interface, preventing light leakage without requiring additional complex structures.
2Illumination intensity
If an optical waveguide with high refractive index is formed to guide light to photoelectric converter, then light collection efficiency is improved, but light leaks out to adjacent pixels through regions between waveguide and light shielding portion
Solution Approach 1:
The light that would normally leak out from the optical waveguide into adjacent pixels is converted into a beneficial effect by the light reflecting layer. This layer reflects the stray light back toward the optical waveguide or directs it to the intended photoelectric converter, transforming potential harmful leakage into additional useful light signal.
Solution Approach 2:
By controlling the refractive index of the light reflecting layer to be lower than the optical waveguide, the patent creates optimal optical conditions for light reflection. This parameter optimization ensures that light collection efficiency is maximized while preventing cross-pixel interference.
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 increases the amount of light received by photoelectric converters, enhancing the SN ratio of pixel signals by preventing light leakage and improving light collection efficiency.
Implementation Method 1
a light reflecting layer, which is formed at a boundary between the optical waveguide and the second insulating layer, and has a refractive index that is lower than a refractive index of the optical waveguide
Implementation Method 2
an optical waveguide configured to guide incident light to a photoelectric converter of a pixel in order to increase the amount of light that enters the photoelectric converter
Implementation Method 3
a photoelectric converter configured to photoelectrically convert the incident light
Data Source
AI summary
Provided are a solid-state image pickup apparatus which includes: a semiconductor substrate having a plurality of photoelectric converters; a first and a second insulating layers formed on the semiconductor substrate; an optical waveguide formed above each of the plurality of photoelectric converters and in an opening portion of the first and the second insulating layers, and has a refractive index higher than a refractive index of the first insulating layer; and a light reflecting layer formed at a boundary between the optical waveguide and the second insulating layer, and has a refractive index lower than a refractive index of the optical waveguide, where the following expression is satisfied: α<90°, where a represents an angle formed by a boundary surface between the light reflecting layer and the second insulating layer with respect to a boundary surface between the first insulating layer and the second insulating layer.