Amplifying Transistor Low Concentration Region RTS Noise Reduction
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Solution Overview
Problem
As solid state imaging devices reduce in size, Random Telegraph Signal (RTS) noise increases due to a decrease in the number of carriers in amplifying transistors, leading to deteriorated Signal-to-Noise (S/N) characteristics, and existing methods to mitigate this noise, such as buried channel structures, can result in leakage and reduced breakdown voltage.
Innovation Solution
Forming a low concentration impurity region with an impurity concentration lower than the well region in the channel area of the amplifying transistor, achieved through ion implantation, to increase the number of carriers and reduce the influence of carrier traps at the gate insulating film interface, without forming a buried channel layer.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the size of pixel cells including amplifying transistors is reduced to increase pixel density, then the number of pixels increases, but the number of carriers in the amplifying transistor decreases causing RTS noise to increase and S/N characteristics to deteriorate
Solution Approach 1:
The patent applies local quality by creating a low concentration impurity region specifically in the channel area of the amplifying transistor, while maintaining the well region structure. This localized modification of impurity concentration in the channel region increases the number of carriers without affecting the overall transistor size, thereby reducing RTS noise while preserving high pixel density
Solution Approach 2:
The patent changes the impurity concentration parameter in the channel region by forming a low concentration impurity region with impurity concentration lower than the well region. This parameter change increases the number of carriers N in the channel, which directly reduces RTS noise according to the relationship RTS noise ∝ 1/N², while maintaining the reduced transistor size for high pixel density
2Reliability
If a buried channel structure is formed to increase the number of carriers and reduce RTS noise, then the RTS noise characteristic improves, but the breakdown voltage in the isolation region is reduced and leakage is likely to occur
Solution Approach 1:
The patent applies local quality by creating a low concentration impurity region specifically in the channel area of the amplifying transistor, while maintaining the well region structure. This localized modification of impurity concentration in the channel region increases the number of carriers without affecting the overall transistor size, thereby reducing RTS noise while preserving high pixel density
Solution Approach 2:
The patent segments the impurity distribution into two distinct regions: a well region with higher impurity concentration and a low concentration impurity region in the channel area with lower impurity concentration. This segmentation allows the channel region to have optimized carrier concentration for reduced RTS noise, while the well region maintains adequate breakdown voltage, preventing the leakage issues associated with uniform buried channel structures
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 and improves the S/N characteristic of the circuit, enabling the manufacture of high-sensitive solid state imaging devices with reduced leakage and increased yield, even when amplifying transistors are isolated by STI regions during size reduction.
Implementation Method 1
implanting a second conductivity type impurity by ion implantation to reduce an impurity concentration in a top surface portion of the semiconductor layer serving as a channel region of the amplifying transistor
Implementation Method 2
signal charges generated by photoelectric conversion by the photodiode
Data Source
AI summary
A solid state imaging device includes a transfer transistor for transferring signal charges generated by photoelectric conversion to a floating diffusion layer, a reset transistor for resetting a potential of the floating diffusion layer, and an amplifying transistor for outputting a signal corresponding to the potential of the floating diffusion layer. A low concentration impurity region having an impurity concentration lower than that of the first conductivity type semiconductor region is formed in part of a surface portion of the first conductivity type semiconductor region which is located below a gate electrode of the amplifying transistor and serves as a well region of the amplifying transistor.