CMOS Image Sensor Channel Stop Region RTS Noise Reduction
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Solution Overview
Problem
CMOS image sensors face significant random telegraph signal (RTS) noise due to charge trap/de-trap in shallow trench isolation (STI) edges, which reduces sensitivity and is difficult to mitigate without increasing transistor size.
Innovation Solution
The semiconductor device minimizes STI edges by incorporating a channel stop region with a different conductivity type, reducing RTS noise by hindering current flow in edge regions and increasing voltage threshold, thus reducing noise without enlarging the transistor.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If shallow trench isolation (STI) is used for transistor isolation, then device integration is enabled, but RTS noise increases due to charge trap/de-trap at STI edges
Solution Approach 1:
The patent applies local quality by creating a channel stop region with different conductivity type (opposite to the channel region) at specific locations adjacent to the STI structure. This localized modification of electrical properties eliminates charge trap/de-trap effects at the STI edge without requiring removal of the STI isolation structure itself, thus maintaining device integration while reducing RTS noise
Solution Approach 2:
The patent converts the harmful STI edge structure into a beneficial configuration by introducing a channel stop region with opposite conductivity type. This transformation changes the electrical behavior at the STI interface, turning the previously harmful charge trap region into a controlled channel termination that prevents carrier accumulation and reduces RTS noise
2Object-generated harmful factors
If transistor size is increased to reduce RTS noise, then noise reduction is achieved, but device area increases
Solution Approach 1:
The patent applies parameter changes by modifying the conductivity type parameter of the channel stop region (making it opposite to the channel region). This parameter change fundamentally alters the electrical characteristics at the channel-STI interface, enabling RTS noise reduction through electrical field control rather than geometric scaling, thus avoiding increased transistor area
3Object-generated harmful factors
If channel stop region with opposite conductivity type is introduced, then RTS noise is reduced by hindering current flow in edge regions, but device complexity increases
Solution Approach 1:
The patent applies segmentation by dividing the channel region into distinct segments: the main channel region and the channel stop region with opposite conductivity type. This segmentation creates clear functional zones where the channel stop region acts as a barrier to carrier flow at the STI interface, enabling precise control of current flow paths and reduction of RTS noise through spatial separation of functional regions
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 approach effectively reduces RTS noise in CMOS image sensors, enhancing sensitivity without the need for larger transistors, thereby improving image sensor performance.
Implementation Method 1
a first channel stop region on a first side of the first channel region, the first channel stop region having a second conductivity type that is different from the first conductivity type
Data Source
AI summary
A semiconductor device includes a light-receiving element which outputs electric charges in response to incident light, and a drive transistor which is gated by an output of the light-receiving element to generate a source-drain current in proportion to the incident light, wherein the drive transistor include a first gate electrode, a first channel region which is disposed under the first gate electrode, first source-drain regions which are disposed at respective ends of the first channel region and that have a first conductivity type, and a first channel stop region which is disposed on a side of the first channel region, and that separates the light-receiving element and the first channel region, the first channel stop region having a second conductivity type that is different from the first conductivity type.