Solid-State Imaging Element With Buried Light Shielding Film
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Solution Overview
Problem
In CMOS image sensors using the global shutter system, the thickness of the photoelectric conversion film with light shielding properties needs to be reduced to minimize chip size and processing complexity while maintaining effective light shielding, which is challenging due to the requirement for a thickness of at least 1 μm and the need for a stacked structure with memory units and transistors.
Innovation Solution
A solid-state imaging element with a photodiode and a photoelectric conversion film stacked on the light incident side, where a light shielding film is buried within the photoelectric conversion film, using an inorganic compound semiconductor like CIGS, allowing for reduced thickness and effective light shielding by positioning the memory unit below the light shielding film.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the thickness of the photoelectric conversion film is increased to improve light shielding properties, then light shielding effectiveness is improved, but chip size and processing complexity increase
Solution Approach 1:
The light shielding film is embedded within the photoelectric conversion film structure, with the light shielding film forming a region inside the photoelectric conversion film. This nested configuration allows the light shielding function to be integrated within the existing photoelectric conversion layer, achieving effective light shielding without increasing the overall chip area.
Solution Approach 2:
Instead of increasing thickness in the vertical dimension, the invention implements light shielding by creating a laterally extended light shielding region within the photoelectric conversion film plane. The light shielding film extends in the horizontal direction to shield the memory unit, transitioning from a thickness-based solution to a planar configuration that maintains thin film profiles.
2Reliability
If the thickness of the photoelectric conversion film is increased to improve light shielding properties, then light shielding effectiveness is improved, but processing complexity and film formation load increase
Solution Approach 1:
The light shielding film and photoelectric conversion film are formed as integrated structures through a unified manufacturing process. The light shielding film is embedded within the photoelectric conversion film formation process, combining what would otherwise be separate processing steps into a single integrated operation, thereby reducing overall processing complexity.
Solution Approach 2:
The light shielding film is formed within the photoelectric conversion film structure during the same processing sequence, nesting the light shielding function within the photoelectric conversion layer formation. This integrated approach eliminates the need for separate thick film formation and associated complex processing steps.
3Area of stationary object
If a stacked structure with memory unit and transistors is implemented, then chip area is reduced, but light shielding becomes more challenging
Solution Approach 1:
The light shielding film is embedded within the photoelectric conversion film, with the light shielding region positioned to overlay and shield the memory unit in the stacked configuration. This nested arrangement enables effective light shielding of the memory unit while maintaining the compact stacked structure, as the light shielding function is integrated into the photoelectric conversion layer rather than requiring additional external shielding structures.
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 solution enables a thinner photoelectric conversion film with improved light shielding properties, reducing the semiconductor chip size and processing complexity, while maintaining effective light shielding and global shuttering functionality.
Implementation Method 1
a photoelectric conversion film that can have a reduced thickness
Implementation Method 2
a light shielding film having light shielding properties needs to be formed to shield the memory unit from light
Data Source
AI summary
In pixels that are two-dimensionally arranged in a matrix fashion in the pixel array unit of a solid-state imaging element, a photoelectric conversion film having a light shielding film buried therein is formed and stacked on the light incident side of the photodiode. The present technique can be applied to a CMOS image sensor compatible with the global shutter system, for example.