Semiconductor Pixel Circuit Using Oxide Transistors for Low-Light Imaging
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Solution Overview
Problem
Solid-state imaging devices with CMOS sensors face challenges in achieving improved dynamic range and image quality, especially under low light conditions, due to limited photodiode size and high power consumption, leading to distorted images and short operation times in portable devices.
Innovation Solution
The implementation of a semiconductor device with a pixel structure using transistors with extremely low off-state current density, specifically oxide semiconductors, allows for electrical connectivity between pixels to enhance charge accumulation and reduce leakage, enabling improved dynamic range and image quality without extending exposure time.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If exposure time is extended to improve dynamic range under low light conditions, then the amount of light accumulated increases, but image distortion occurs due to object or device movement
Solution Approach 1:
The patent connects photodiodes from multiple rows (n-th row and (n+1)-th row) through a shared first transistor, merging their charge accumulation regions. This allows the device to accumulate light from multiple rows simultaneously without extending exposure time, thereby improving dynamic range while preventing image distortion caused by movement during extended exposure.
2Volume of moving object
If photodiode region is reduced to decrease device size, then device portability improves, but light accumulation capability deteriorates
Solution Approach 1:
The patent extends the charge accumulation capability into the vertical dimension by connecting photodiodes from multiple rows through the first transistor. This allows the device to maintain compact horizontal dimensions while accumulating light from multiple rows vertically, effectively increasing light accumulation capability without increasing device footprint.
3Ease of manufacture
If conventional transistors are used in pixel circuits, then manufacturing simplicity is maintained, but power consumption increases
Solution Approach 1:
The patent changes the electrical parameters of the transistor by using an oxide semiconductor material, which has fundamentally different properties from conventional semiconductors. This material change enables extremely low off-state current while maintaining compatibility with existing CMOS manufacturing processes, thus reducing power consumption without sacrificing manufacturing simplicity.
4Use of energy by moving object
If oxide semiconductor transistors are used to reduce off-state current, then power consumption decreases, but device complexity increases
Solution Approach 1:
The oxide semiconductor transistor serves multiple functions: it acts as a switching element, a charge accumulation element, and a low-leakage element simultaneously. The first transistor connects multiple photodiodes while the second transistor controls charge transfer, and both benefit from the oxide semiconductor's inherently low off-state current, eliminating the need for additional leakage prevention circuits.
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 solution enhances the dynamic range and image quality of solid-state imaging devices, particularly under low light conditions, while reducing power consumption and preventing image distortion, thus improving performance in portable electronic devices.
Implementation Method 1
a photodiode passing current having a value determined by an intensity of light entering the photodiode
Data Source
AI summary
The semiconductor device includes a plurality of pixels arranged in rows and columns, and first transistors fewer than the number of the plurality of pixels. The plurality of pixels each includes a photodiode and an amplifier circuit. The amplifier circuit holds the accumulated charge and includes at least a second transistor electrically connected to a cathode of the photodiode. The cathode of the photodiode in the pixel in an n-th row and the cathode of the photodiode in the pixel in an (n+1)-th row are electrically connected to the first transistor. The number n is a natural number. The pixel in the n-th row and the pixel in the (n+1)-th row are in an identical column.