Back-illuminated Global-shutter Image Sensor Optical Insulation
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Solution Overview
Problem
Front-illuminated global-shutter image sensors face challenges in integration within three-dimensional structures due to the need for an opaque storage area to minimize noise, which complicates optical insulation and increases the risk of optical crosstalk.
Innovation Solution
A back-illuminated global-shutter image sensor is integrated into a three-dimensional structure, utilizing capacitive insulation trenches and protection screens to ensure optical insulation of the storage area, with passive or active protectors that prevent back illumination and facilitate charge transfer, while also serving as light guides for infrared radiation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If front-illuminated global-shutter image sensor is used, then optical insulation of storage area is required to minimize noise, but device complexity and manufacturing difficulty increase due to the need for opaque storage area in three-dimensional integrated structures
Solution Approach 1:
The patent inverts the illumination direction from front-illuminated to back-illuminated architecture. By illuminating the sensor from the back, the storage area can remain transparent while still achieving effective optical insulation through the protective structure extending from the back surface, thereby simplifying integration in three-dimensional structures without compromising noise minimization
Solution Approach 2:
The patent introduces a vertical dimension by extending the protective structure (capacitive insulation trenches and protection screens) from the back surface into the substrate. This three-dimensional approach provides optical insulation without requiring the storage area to be opaque, allowing light to pass through the photosensitive area while blocking stray light from reaching the storage area directly
2Reliability
If opaque storage area is used to minimize noise, then optical insulation is improved, but optical crosstalk risk increases in three-dimensional integrated structures
Solution Approach 1:
The patent segments the pixel structure into distinct functional areas (photosensitive area, storage area, readout area) separated by protective structures. The capacitive insulation trenches and protection screens create physical and optical separation between adjacent pixels and between different areas within a pixel, preventing optical crosstalk while maintaining effective optical insulation of the storage area
Solution Approach 2:
The patent introduces intermediate protective structures (capacitive insulation trenches filled with insulating material and protection screens) that act as mediators between the photosensitive area and the storage area. These intermediate structures block stray light and prevent direct optical paths that could cause crosstalk, while still allowing the storage area to remain transparent for efficient charge collection
3Ease of manufacture
If back-illuminated architecture is used, then integration in three-dimensional structures is facilitated, but protection against back illumination of storage area becomes necessary
Solution Approach 1:
The patent implements protective structures (capacitive insulation trenches and protection screens) that are formed during the manufacturing process before final device assembly. These structures are preliminarily positioned to extend from the back surface into the substrate, pre-establishing the optical insulation barriers needed to prevent back illumination noise while maintaining the simplified back-illuminated architecture for easy integration
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 effectively reduces optical crosstalk and noise, enabling clearer image capture by protecting the storage area from back illumination and allowing for efficient charge transfer, while maintaining the benefits of global-shutter operation in three-dimensional integrated structures.
Implementation Method 1
protection means or a protector extending at least partly into the substrate from its back and configured to ensure that the storage area is protected against back illumination
Implementation Method 2
capacitive insulation trenches which extend from the back into the elongation of the at least first and second insulated vertical electrodes
Implementation Method 3
the protectors may also serve as light guides, notably for infrared radiation
Data Source
AI summary
A global shutter image sensor of a back-illuminated type includes a semiconductor substrate and pixels. Each pixel includes a photosensitive area, a storage area, a readout area and areas for transferring charges between these different areas. The image sensor includes, for each pixel, a protector extending at least partly into the substrate from the back of the substrate to ensure that the storage area is protected against back illumination.