Solid-State Imaging Pixel Transistor Isolation
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Solution Overview
Problem
In solid-state imaging devices, leakage currents from pixel transistors introduce noise, degrading the signal-to-noise ratio and sensitivity due to direct connection of signal transmission lines to the silicon substrate, leading to mixed colors and reduced light absorption efficiency.
Innovation Solution
A solid-state imaging device with a semiconductor region featuring unit pixels including a photoelectric converter, an amplifier transistor, and a reset transistor, isolated by an impurity diffusion layer, and peripheral transistors isolated by an insulating film, reducing leakage currents through a specific manufacturing process involving gate insulating films and source/drain regions with varying impurity concentrations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a transmission line is directly connected to the pn junction in the silicon substrate, then the device complexity is reduced, but leakage currents from the floating diffusion increase and become noise
Solution Approach 1:
An isolation region made of intrinsic or lightly-doped semiconductor material is introduced between the transmission line and the floating diffusion. This intermediary region blocks the leakage currents from the floating diffusion while allowing the signal transmission to proceed, thus solving the problem without significantly increasing device complexity.
2Object-affected harmful factors
If the thickness of photo diodes is reduced to prevent mixed colors, then mixed colors are reduced, but light absorption efficiency degrades
Solution Approach 1:
The invention transitions from a single-layer photo diode structure to a multilayer structure where photoelectric conversion films are stacked on a semiconductor substrate. This dimensional change allows light absorption to occur in multiple layers, maintaining high absorption efficiency while keeping each individual photoelectric conversion layer thin enough to prevent mixed colors.
3Object-generated harmful factors
If pixel transistors are isolated by an insulating film, then leakage currents are reduced, but the manufacturing process becomes more complex
Solution Approach 1:
Instead of using a uniform insulating film isolation method throughout the device, the invention applies isolation regions with specific doping characteristics (intrinsic or lightly-doped) only in the critical areas where leakage currents occur. This localized approach reduces leakage currents while minimizing the impact on the overall manufacturing process complexity.
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
The solution effectively reduces leakage currents in pixel transistors, enhancing the signal-to-noise ratio and sensitivity by minimizing noise and thermal noise, while maintaining miniaturization and operational characteristics.
Implementation Method 1
The transistors of the unit pixels in the semiconductor region are isolated by an impurity diffusion layer
Implementation Method 2
Each of the unit pixels includes a photoelectric converter formed above the semiconductor region
Data Source
AI summary
Each unit pixel includes a photoelectric converter formed above a semiconductor region, an amplifier transistor formed in the semiconductor region, and including a gate electrode connected to the photoelectric converter, a reset transistor configured to reset a potential of the gate electrode, and an isolation region formed in the semiconductor region between the amplifier transistor and the reset transistor to electrically isolate the amplifier transistor from the reset transistor. The amplifier transistor includes a source/drain region. The source/drain region has a single source/drain structure.