Solid-State Imaging Device Planarization Film Refractive Index
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Solution Overview
Problem
Existing solid-state imaging devices face challenges in enhancing light sensitivity due to the decrease in photodiode area with increasing pixels, leading to reduced aperture ratio and difficulty in reducing device size and thickness while maintaining microlens functionality and reliability.
Innovation Solution
A solid-state imaging device structure featuring a light receiving element chip with a planarization film of a transparent member with a lower refractive index covering microlenses, and a transparent protective film made of inorganic material on the back surface, allowing for thicker planarization without stressing the microlenses and enabling easy dust removal without degrading functionality.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If a microlens is formed to increase light collection efficiency, then light sensitivity is improved, but the thickness of photoresist required (2-3 μm) increases the space area and reduces the effective aperture ratio
Solution Approach 1:
The patent changes the refractive index parameter of the planarization film material to be lower than that of the microlens. This parameter change allows the microlens to maintain its light-focusing function while the planarization film can be made thicker without compromising the effective aperture ratio, thus resolving the contradiction between light sensitivity and effective aperture ratio.
2Strength
If a hard transparent protective layer is provided to cover the microlens, then mechanical strength is improved, but the microlens functionality is degraded due to stress and difficulty in dust removal
Solution Approach 1:
The patent changes the refractive index parameter of the planarization film to be lower than the microlens, creating an optical gradient that maintains microlens functionality. This allows the film to be thick enough for dust removal while the lower refractive index prevents stress-induced functional degradation.
Solution Approach 2:
The planarization film acts as an intermediary layer between the microlens and the external environment. It provides mechanical protection and facilitates dust removal while its specific refractive index properties ensure it does not degrade the microlens optical function, serving as a mediator that balances protection and functionality.
3Measurement precision
If the pixel area is reduced to increase the number of pixels, then resolution is improved, but the photodiode area decreases leading to reduced light collection efficiency
Solution Approach 1:
The patent changes the refractive index parameter of the planarization film material to be lower than the microlens, which allows for optimized light focusing in smaller pixels. This parameter change enables the microlens to effectively concentrate light onto the reduced photodiode area, maintaining light collection efficiency even as pixel size decreases for higher resolution.
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 structure enhances light sensitivity, maintains microlens functionality, and allows for a compact, reliable camera module with reduced size and thickness, improving environmental resistance and ease of fabrication while eliminating the need for ceramic packaging.
Implementation Method 1
a planarization film which is formed over the principal plane of the light receiving element chip to cover the microlens and planarize unevenness of the microlens and which is made of a transparent member having a lower refractive index than the microlens
Data Source
AI summary
An optical device includes a light receiving element chip having: an active region formed on a principal plane of a substrate and made by arranging a plurality of light receiving pixels; a circuit region disposed around an outer circumference of the active region; a penetrating conductor provided to penetrate the substrate in the thickness direction of the substrate; and an external connection terminal provided on a back surface of the substrate facing the principal plane thereof and connected to the penetrating conductor. The optical device further includes a microlens, a planarization film, and a transparent protective film formed on the planarization film.