Oxide Semiconductor Pixel Transistors for Distortion-Free Global Shutter
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Solution Overview
Problem
Conventional CMOS image sensors with global shutter systems face challenges in suppressing charge leakage, leading to image distortion and high off-state current issues, particularly when capturing fast-moving objects, due to the prolonged charge holding period and high off-state current of transistors.
Innovation Solution
The use of a semiconductor device with a pixel circuit structure that includes a photodiode, signal charge accumulation portion, and transistors, where at least one transistor includes an oxide semiconductor with extremely low off-state current, allowing for simultaneous charge accumulation and read operations across all pixels, reducing charge leakage and image distortion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If a global shutter system is used in a CMOS sensor, then image distortion is prevented, but charge leakage occurs due to high off-state current
Solution Approach 1:
The patent changes the material parameter of the transistor channel from conventional silicon to oxide semiconductor, which fundamentally alters the off-state current characteristic. This material substitution reduces the off-state current by several orders of magnitude, enabling the global shutter system to function without significant charge leakage while maintaining image quality stability.
2Ease of manufacture
If conventional transistors are used in CMOS sensors, then manufacturing is simpler, but off-state current is high causing charge leakage
Solution Approach 1:
The patent changes the semiconductor material parameter from silicon to oxide semiconductor in the transistor channel. This material parameter change achieves extremely low off-state current (10^-15 A/μm or less) while being compatible with standard CMOS manufacturing processes, thus improving charge holding capability without significantly complicating manufacturing.
3Measurement precision
If the charge accumulation period is extended to capture moving objects, then image quality improves, but charge leakage increases
Solution Approach 1:
The patent changes the transistor material to oxide semiconductor, which fundamentally alters the leakage parameter. This enables extended charge accumulation periods (e.g., 100 μs or more) without significant charge loss, as the off-state current is reduced by several orders of magnitude compared to conventional transistors.
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 enables the suppression of charge leakage and maintains image quality without distortion, even when capturing fast-moving objects, by utilizing transistors with low off-state current, thereby enhancing the performance of CMOS image sensors with global shutter systems.
Implementation Method 1
each of the plurality of pixels includes a photodiode
Implementation Method 2
A channel formation region in at least one or more of the plurality of transistors includes an oxide semiconductor
Data Source
AI summary
In a CMOS image sensor in which a plurality of pixels is arranged in a matrix, a transistor in which a channel formation region includes an oxide semiconductor is used for each of a charge accumulation control transistor and a reset transistor which are in a pixel portion. After a reset operation of the signal charge accumulation portion is performed in all the pixels arranged in the matrix, a charge accumulation operation by the photodiode is performed in all the pixels, and a read operation of a signal from the pixel is performed per row. Accordingly, an image can be taken without a distortion.