Buried Source Follower Gate Layout for Lower RTS Noise
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Solution Overview
Problem
Current image sensors face challenges in reducing random telegraph signal (RTS) noise, which affects the performance and reliability of image capture.
Innovation Solution
The design includes a source follower transistor with a buried portion that protrudes below the body portion into the substrate, positioned closer to the drain region than the source region, optimizing the distance and depth of the recess region to enhance the effective channel length and reduce noise.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the source follower gate pattern is designed with a buried portion protruding into the substrate, then the RTS noise property is improved, but the device complexity increases
Solution Approach 1:
The source follower gate pattern is extended from a two-dimensional planar structure into the third dimension by adding a buried portion that protrudes below the body portion into the substrate. This vertical extension creates a three-dimensional gate structure that increases the effective channel length and improves RTS noise properties without requiring additional planar space.
Solution Approach 2:
The gate pattern is divided into two distinct segments: a body portion that remains on the substrate surface and a buried portion that extends into the substrate. This segmentation allows each portion to serve specific functions - the body portion for standard gate control and the buried portion for noise reduction - while maintaining manufacturing feasibility through separate formation processes.
2Reliability
If the buried portion is positioned closer to the drain region, then the RTS noise property is improved, but the manufacturing precision requirements increase
Solution Approach 1:
The design specifies a quantitative parameter range for the buried portion position, defining it as being located between 0.1 to 0.5 times the gate length from the first side surface. This parameterization transforms the qualitative requirement of 'closer to drain' into a measurable and controllable manufacturing specification, enabling precise control of the noise reduction effect while maintaining fabrication feasibility.
3Reliability
If the effective channel length is increased through the buried portion, then the RTS noise property is improved, but the area of the active region increases
Solution Approach 1:
The effective channel length is extended by utilizing the vertical dimension through the buried portion that protrudes into the substrate. This approach increases the channel length without proportionally increasing the planar area of the active region, as the additional channel length is achieved through depth rather than surface expansion, thereby improving noise properties with minimal area penalty.
Data Source
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AI summary
An image sensor includes a substrate including an active region with source and drain regions, a source follower gate pattern on the active region, the drain and source regions being adjacent to first and second side surfaces of the source follower gate pattern, respectively, and a gate insulating layer between the active region and the source follower gate pattern. An upper portion of the active region includes a recess region, and the source follower gate pattern includes a body portion on the active region and a buried portion provided in the recess region and protruding below the body portion. A distance between the first and second side surfaces is a first length, and a distance between a center of the buried portion and the first side surface is a second length. The second length is greater than or equal to 0.1 times the first length and is less than 0.5 times the first length.