Transfer Gate Electrode Depth Layout for Low-Noise Image Sensors
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Solution Overview
Problem
Current image sensors face challenges in achieving improved reliability and efficiency in charge transfer due to interfacial defects and fixed pattern noise, which affect the operational performance and reliability of image sensing devices.
Innovation Solution
The image sensor design incorporates a transfer gate electrode with first to third extensions extending into the substrate, where the first depth is greater than the second and third depths, and the second and third extensions are closer to the floating diffusion area, reducing the probability of interfacial defects and improving charge transfer efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional transfer gate electrode structure is used, then the device complexity is low, but the charge transfer efficiency is insufficient and interfacial defects occur
Solution Approach 1:
The transfer gate electrode is divided into multiple segments (first transfer gate electrode and second transfer gate electrode) with different extension depths into the substrate. The first extension has a first depth, while the second extension has a second depth greater than the first depth, allowing each segment to perform specialized functions in charge transfer
Solution Approach 2:
Different portions of the transfer gate electrode structure are given different properties through varying extension depths. The deeper second extension targets specific regions to reduce interfacial defects and fixed pattern noise, while the first extension handles general charge transfer, creating local quality variations to optimize overall performance
2Reliability
If the transfer gate electrode extensions are made deeper into the substrate, then interfacial defects are reduced, but the manufacturing precision requirements increase
Solution Approach 1:
Instead of uniformly increasing the depth of all transfer gate extensions, the invention applies partial action by having only the second extension extend deeper than the first extension. This selective approach reduces manufacturing precision requirements compared to uniformly deep extensions, while still achieving the benefit of reduced interfacial defects in critical areas
3Reliability
If the transfer gate electrode structure is optimized for charge transfer, then fixed pattern noise is reduced, but the device complexity increases
Solution Approach 1:
The transfer gate electrode structure employs asymmetry by having extensions with different depths (first depth vs. second depth) rather than uniform depths. This asymmetric configuration specifically targets fixed pattern noise reduction while maintaining a relatively simple overall structure that does not require complex multi-layer arrangements
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 enhances the transfer efficiency of electric charges and reduces fixed pattern noise, leading to improved operational performance and reliability of the image sensor.
Implementation Method 1
each pixel of the plurality of pixels including a photoelectric conversion area in the substrate
Data Source
AI summary
An image sensor includes a substrate including first and second surfaces opposite to each other in a first direction; pixels each including a photoelectric conversion area in the substrate; and a transfer gate electrode overlapping the photoelectric conversion area of one pixel of the plurality of pixels in the first direction. The substrate contains impurities of a first conductivity type. The photoelectric conversion area contains impurities of a different second conductivity type. The transfer gate electrode includes first, second and third extensions extending from the first surface into the substrate and having respective a first, second, and third depths. The first depth is larger than each of the second and third depths. A bottom surface of the first extension is in the photoelectric conversion area. Each of the bottom surfaces of the second and third extensions is spaced apart from the photoelectric conversion area in the first direction.