Global-Shutter CMOS Sensor Charge-Holding Layout for Higher Sensitivity
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Solution Overview
Problem
In global-shutter type CMOS image sensors, the limited area for both photodiodes and memory sections due to their shared substrate constraints the improvement of sensitivity, as direct charge movement from the photodiode to the memory section can lead to blooming and reduced saturation signal amounts.
Innovation Solution
A solid-state imaging device with a semiconductor substrate featuring a photoelectric conversion section, a charge holding section, and an n-type semiconductor region, where charges are transferred via the n-type region to the charge holding section, and a separation film is used to prevent direct movement between the photodiode and memory section, enhancing sensitivity by increasing the potential barrier without aggravating blooming.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of stationary object
If the photodiode and memory section are provided on the same plane of the substrate, then the area for providing both components is limited, but this configuration allows for simpler structure and manufacturing
Solution Approach 1:
The patent transitions from a planar two-dimensional layout to a three-dimensional stacked configuration. The photodiode is formed in a first region of the substrate, and the memory section is formed in a second region at a different depth level (stacked above or below), utilizing the vertical dimension to increase the effective area for both components without increasing the planar footprint.
Solution Approach 2:
The substrate is divided into distinct regions at different depth levels. The photodiode is segmented into a first region, and the memory section is segmented into a second region, allowing independent optimization of each component's area and performance while maintaining a compact overall structure.
2Device complexity
If charges are transferred directly from the photodiode to the memory section, then the transfer path is simple, but this causes blooming and reduces saturation signal amounts
Solution Approach 1:
An n-type semiconductor region is introduced as an intermediary between the photodiode and the memory section. This intermediate region serves as a buffer that receives charges from the photodiode and transfers them to the memory section, preventing direct charge movement that causes blooming while maintaining efficient charge transfer functionality.
Solution Approach 2:
The n-type semiconductor region is specifically positioned in the charge transfer path between the photodiode and memory section. This localized modification creates a potential barrier only where needed to prevent blooming, while other regions maintain their original charge transfer characteristics, thus improving reliability without excessive complexity.
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 improves the saturation signal amounts and sensitivity of the imaging device by reducing direct charge movement and allowing for higher potential barriers without increasing blooming, thus enabling more effective charge transfer and improved imaging performance.
Implementation Method 1
a photoelectric conversion section formed to be embedded in the semiconductor substrate
Data Source
AI summary
A solid-state imaging device of an embodiment of the present disclosure includes a semiconductor substrate having one surface and another surface opposed to the one surface, a photoelectric conversion section formed to be embedded in the semiconductor substrate, a charge holding section provided in the one surface of the semiconductor substrate while being stacked on the photoelectric conversion section, an n-type semiconductor region provided in the one surface of the semiconductor substrate, and a charge-voltage conversion section provided in the one surface of the semiconductor substrate. A charge generated in the photoelectric conversion section is transferred via the n-type semiconductor region to the charge holding section.