Vertical Gate Pixel Transistor Layout for RTS Noise Reduction
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Solution Overview
Problem
As CMOS image sensors have miniaturized, pixel transistors have become finer, leading to increased noise such as RTS noise due to impurity fluctuations in the channel region.
Innovation Solution
A solid-state imaging device is designed with a photoelectric conversion unit, transfer unit, charge storage unit, amplifying transistor, and isolation portion, where the amplifying transistor has a gate electrode with two vertical gate electrode portions and an insulating layer overlapping a part of the isolation portion to suppress impurity entry into the channel region, and the isolation portion surrounds the photoelectric conversion unit with first and second isolation portions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If pixel transistors are miniaturized to increase integration density, then productivity and device compactness improve, but noise increases due to impurity fluctuations in the channel region
Solution Approach 1:
The channel region is segmented into multiple regions with different impurity concentrations. The channel formation region has a first impurity concentration while the source/drain regions have a second impurity concentration, creating distinct zones that reduce noise while maintaining high integration density
Solution Approach 2:
Different regions of the transistor are given different local properties: the channel formation region is designed with specific impurity characteristics to reduce noise, while source and drain regions have different impurity concentrations optimized for their respective functions, allowing high integration density without compromising signal quality
2Area of stationary object
If pixel transistors are miniaturized, then device area decreases, but manufacturing precision becomes more difficult to maintain
Solution Approach 1:
The transistor structure is divided into distinct regions (channel formation region, source region, drain region) that can be independently controlled during manufacturing. This segmentation allows precise control of impurity concentrations in each region even at miniaturized dimensions, maintaining manufacturing precision while reducing pixel area
Solution Approach 2:
The invention controls multiple parameters including impurity concentration, region depth, and lateral dimensions to achieve the desired transistor characteristics at miniaturized scales. By adjusting these parameters independently in different regions, manufacturing precision is maintained despite reduced pixel area
3Speed
If impurity concentration in the channel region is increased to improve transistor performance, then switching speed improves, but noise increases due to impurity fluctuations
Solution Approach 1:
The transistor is segmented such that the channel formation region maintains lower impurity concentration to reduce RTS noise, while source and drain regions have higher impurity concentrations to ensure rapid charge injection and extraction, achieving fast switching speed without increasing channel noise
Solution Approach 2:
Different regions are assigned different impurity concentrations optimized for their specific functions: the channel region has controlled impurity levels to minimize noise while maintaining adequate conductivity for fast switching, and source/drain regions have higher impurity concentrations to enable rapid charge transfer
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 reduces noise such as RTS noise by preventing impurity entry into the channel region, allowing the amplifying transistor to be formed as a fully depletion type, thereby enhancing signal amplification and image quality.
Implementation Method 1
a photoelectric conversion unit that generates charge corresponding to an amount of received light
Data Source
AI summary
Noise is reduced. A solid-state imaging device includes a photoelectric conversion unit that generates charge corresponding to an amount of received light, a transfer unit that transfers the charge generated by the photoelectric conversion unit, a charge storage unit that stores the charge transferred by the transfer unit, an amplifying transistor that amplifies a signal corresponding to the charge stored in the charge storage unit, and an isolation portion that isolates the photoelectric conversion unit, the amplifying transistor has a gate electrode including two vertical gate electrode portions provided in a depth-wise direction from a first surface of a semiconductor layer to sandwich a channel region therebetween, the isolation portion includes at least a first isolation portion provided in a first groove provided in the depth-wise direction from the first surface, and an insulating layer provided on a side of one of the two vertical gate electrode portions opposite to the channel region is provided to overlap at least a part of the first isolation portion when viewed in the depth-wise direction.