Oxide Semiconductor Pixel Circuit for CMOS Image Sensor Noise Reduction
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Solution Overview
Problem
As semiconductor devices miniaturize, manufacturing transistors for CMOS image sensors becomes increasingly difficult, leading to variations in electrical characteristics and noise in imaging data, making it challenging to achieve high-quality imaging with low power consumption, high-speed operation, and low noise.
Innovation Solution
The proposed imaging device incorporates a pixel circuit with a specific configuration of transistors and capacitors, including oxide semiconductors with In, Zn, and M (where M is Al, Ti, Ga, Sn, Y, Zr, La, Ce, Nd, or Hf), and a photoelectric conversion element using selenium, to correct threshold voltage variations and improve imaging performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of moving object
If transistor miniaturization is pursued to increase pixel density, then device integration and resolution are improved, but manufacturing precision deteriorates due to increased process difficulty and electrical characteristic variation
Solution Approach 1:
The patent changes the material parameter from conventional silicon to oxide semiconductor, which fundamentally alters the electrical characteristics to achieve extremely low off-state current. This material parameter change enables transistors to maintain uniform electrical characteristics even at miniaturized dimensions, resolving the contradiction between pixel density and manufacturing precision
Solution Approach 2:
The patent employs a composite transistor structure combining oxide semiconductor channel layer with silicon-based source and drain regions. This composite material approach leverages the low leakage current property of oxide semiconductors while maintaining compatibility with existing silicon fabrication processes, enabling high-density pixels with uniform electrical characteristics
2Ease of manufacture
If conventional silicon transistors are used in pixel circuits, then manufacturing process compatibility is maintained, but power consumption increases due to higher off-state current
Solution Approach 1:
The patent changes the off-state current parameter by using oxide semiconductor material instead of silicon, achieving extremely low off-state current levels. This material substitution maintains compatibility with existing CMOS fabrication processes while dramatically reducing power consumption in the pixel circuit
Solution Approach 2:
The patent applies oxide semiconductor material specifically to the channel formation region where low off-state current is most critical, while using conventional silicon for source and drain regions. This localized material optimization reduces power consumption at the critical interface without requiring complete process overhaul
3Area of moving object
If transistor size is reduced to increase pixel count, then resolution is improved, but noise increases due to electrical characteristic variation
Solution Approach 1:
The patent changes the electrical parameter regime by using oxide semiconductors which exhibit extremely low off-state current and reduced threshold voltage variation. This parameter change enables miniaturized transistors to maintain low noise performance, allowing high pixel counts without proportionally increasing imaging noise
Solution Approach 2:
The patent uses a standardized oxide semiconductor transistor design that can be replicated across all pixels in the array. This copying approach ensures uniform electrical characteristics and consistent noise performance across all miniaturized pixels, enabling high resolution with controlled noise
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 enables high-quality imaging data with reduced noise, low power consumption, high sensitivity, wide dynamic range, and high resolution, while maintaining reliability and cost-effectiveness.
Implementation Method 1
a photoelectric conversion element using selenium
Data Source
AI summary
An imaging device capable of obtaining high-quality imaging data is provided. The imaging device can correct variation in the threshold voltage of amplifier transistors included in pixel circuits. The amplifier transistor includes two gates facing each other with a channel formation region provided therebetween. The amplifier transistor operates in such a manner that one of the gates holds a potential for correcting variation in the threshold voltage and the other thereof is supplied with a potential corresponding to imaging data.