Back-Illuminated CMOS Image Sensor Memory Unit Light Shielding
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Solution Overview
Problem
In back-illuminated CMOS image sensors operating in global shutter mode, it is challenging to completely shield memory units from light without using light blocking films, which increases the size of the solid-state imaging device.
Innovation Solution
A solid-state imaging device design featuring a semiconductor substrate with a photoelectric conversion film on the first surface and a transfer path unit extending from the charge accumulation layer to the second surface, utilizing a material with a great light blocking effect to prevent light from reaching the memory unit, eliminating the need for light blocking films and reducing device size.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If a light blocking film is formed to shield the memory unit from light, then the memory unit is protected from light interference, but the thickness of the solid-state imaging device becomes greater
Solution Approach 1:
The patent extracts the light-blocking function from a separate dedicated film and integrates it into the photoelectric conversion film itself. The photoelectric conversion film is designed to perform both photoelectric conversion and light blocking for the memory unit, eliminating the need for an additional light blocking film and thereby reducing device thickness.
Solution Approach 2:
The photoelectric conversion film is given multiple functions: it performs photoelectric conversion of incident light and simultaneously blocks light from reaching the memory unit. This multi-functional design eliminates the need for separate light blocking structures, reducing overall device thickness while maintaining protective functionality.
2Productivity
If two vertical transistors are used to increase frame rate, then the frame rate increases, but the area efficiency becomes lower
Solution Approach 1:
The patent extracts the charge transfer function from vertical transistor structures and implements it through a different mechanism involving charge accumulation units and transfer paths through the substrate. This alternative approach achieves the same functional result (charge transfer for global shutter operation) without requiring additional transistors, thereby maintaining area efficiency while supporting high frame rates.
Solution Approach 2:
The patent replaces the mechanical/electronic system of vertical transistors with a charge transfer mechanism that utilizes the substrate structure and electric field control. This substitution achieves charge transfer functionality without the area penalty of additional transistor structures.
3Reliability
If the charge accumulation unit is saturated and charge release path is formed in power supply or adjacent pixels, then charge overflow is handled, but the saturation charge amount changes or area efficiency drops
Solution Approach 1:
The patent introduces a dedicated charge release path that extends through the substrate to a charge release unit on the opposite surface. This intermediary structure provides a direct route for charge overflow without requiring modifications to power supply structures or sharing with adjacent pixels, maintaining both reliability and area efficiency.
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 design allows for a smaller size of the solid-state imaging device while maintaining high frame rates and preventing decreases in image quality due to charge overflow and saturation charge amount variations.
Implementation Method 1
a photoelectric conversion film that performs photoelectric conversion of light emitted from a first surface side of the semiconductor substrate
Implementation Method 2
the photoelectric conversion film is formed by stacking a layer on the first surface of the semiconductor substrate, the layer being formed with a material having a great light blocking effect
Data Source
AI summary
The present disclosure relates to a solid-state imaging device that can be made smaller in size, a method of manufacturing the solid-state imaging device, and an electronic apparatus.The solid-state imaging device includes a photoelectric conversion film that performs photoelectric conversion of light emitted from the back surface side of the semiconductor substrate. Also, in each pixel, a charge accumulation layer is formed to be in contact with the photoelectric conversion film on the back surface of the semiconductor substrate, a transfer path unit is formed to extend from the charge accumulation layer to a point near the front surface of the semiconductor substrate, and a memory unit is disposed near the back surface side of the semiconductor substrate, with a charge transfer gate being interposed between the memory unit and the transfer path unit. Then, the photoelectric conversion film is formed by stacking a layer formed with a material having a great light blocking effect on the back surface of the semiconductor substrate. The present technology can be applied to back-illuminated CMOS image sensors in global shutter mode.