Solid-State Image Sensor High Refractive Index Aperture Filling
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Solution Overview
Problem
As solid-state image sensors are miniaturized to achieve higher pixel density, the aperture widths in the light-blocking film become smaller than the wavelength of visible light, leading to decreased transmittance of longer wavelength light, such as red light, and reduced sensitivity due to difficulty in condensing light through small apertures, especially for near-infrared light and red wavelengths.
Innovation Solution
Incorporating a high refractive index layer within the aperture of the light-blocking film, made of materials like titanium oxide or tantalum oxide, which increases the refractive index and allows longer wavelengths to pass through by effectively shortening the wavelength of light that can be transmitted, even when the aperture width is smaller than the original wavelength, and optionally forming the high refractive index layer into a convex lens shape to enhance light condensation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the aperture width is decreased to increase pixel density, then the pixel density is improved, but the transmittance of longer wavelength light deteriorates
Solution Approach 1:
The patent changes the refractive index parameter of the material filling the aperture from a low value (air, n=1.0) to a high value (titanium oxide, n=2.5). This parameter change allows the aperture to transmit longer wavelength light effectively even when the aperture width is reduced, thus maintaining reliability while improving productivity.
Solution Approach 2:
The patent fills the entire aperture region with a homogeneous high refractive index material (titanium oxide), ensuring uniform optical properties across the aperture. This homogeneous filling eliminates wavelength-dependent transmission variations and maintains consistent performance for all visible light wavelengths.
2Productivity
If the aperture width is decreased to increase pixel density, then the pixel density is improved, but the sensitivity deteriorates
Solution Approach 1:
By changing the refractive index parameter from 1.0 to 2.5, the optical path length within the aperture is effectively increased. This allows more light to be directed into the photodiode even through smaller apertures, maintaining sensitivity while enabling higher pixel density.
Solution Approach 2:
The high refractive index material acts as an optical intermediary that redirects and concentrates light entering the aperture toward the photodiode. This intermediary material ensures efficient light coupling even when the aperture size is reduced, thereby maintaining sensitivity.
3Ease of manufacture
If a low refractive index material is used to fill the aperture, then the manufacturing is simplified, but the light condensation ability deteriorates
Solution Approach 1:
The patent selects titanium oxide as the filling material specifically for its high refractive index (n=2.5). This parameter selection directly improves light condensation ability by increasing the refractive index contrast at the aperture boundaries, thereby enhancing light redirection efficiency.
Solution Approach 2:
The patent employs a composite structure where titanium oxide particles or film are integrated into the aperture region. This composite approach combines the light-condensing properties of high refractive index titanium oxide with the structural integrity of the surrounding low refractive index materials, achieving both manufacturing feasibility and superior optical performance.
4Productivity
If the aperture width is decreased, then the pixel density is improved, but the light diffusion increases
Solution Approach 1:
By increasing the refractive index parameter to 2.5, the patent reduces the angular spread of light passing through the aperture. The high refractive index material confines light more effectively, reducing diffusion and maintaining directed light paths even in smaller apertures.
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 significantly improves the sensitivity of the image sensor by allowing longer wavelengths to pass through smaller apertures, maintaining sensitivity even with finer light-receiving cells and increased pixel density, while also reducing light diffusion and inconsistency among cells.
Implementation Method 1
Incorporating a high refractive index layer within the aperture of the light-blocking film, made of materials like titanium oxide or tantalum oxide, which increases the refractive index and allows longer wavelengths to pass through by effectively shortening the wavelength of light that can be transmitted
Implementation Method 2
there is a suggested method of condensing light using total reflection at boundaries between high refractive index materials and low refractive index materials by positioning, in apertures of a light-blocking film, the high refractive index materials and the low refractive index materials so that the low refractive index materials surround the high refractive index materials
Data Source
AI summary
An object of the present invention is to provide a small solid-state image sensor which realizes significant improvement in sensitivity. The solid-state image sensor of the present invention includes a semiconductor substrate in which photoelectric conversion units are formed, a light-blocking film which is formed above the semiconductor substrate and has apertures formed so as to be positioned above respective photoelectric conversion units, and a high refractive index layer formed in the apertures. Here, each aperture has a smaller aperture width than a maximum wavelength in a wavelength of light in a vacuum converted from a wavelength of the light entering the photoelectric conversion unit through the apertures, and the high refractive index is made of a high refractive index material having a refractive index which allows transmission of light having the maximum wavelength through the aperture.