CMOS Image Sensor Global Shutter for Charge Holding and 3D Imaging
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Solution Overview
Problem
The increase in channel width of transistors in solid-state imaging devices leads to higher off-state current, deteriorating the holding of accumulated charge and affecting the quality and duration of imaging, while also increasing power consumption.
Innovation Solution
A driving method for semiconductor devices that includes specific circuits and transistors to manage light exposure and charge accumulation, using a global shutter method to concurrently perform reset and accumulation operations across all pixels, and reading data sequentially, with the option to perform three-dimensional imaging by calculating distance based on light intensity variations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If the channel width of transistors is increased to improve charge transfer efficiency, then the transfer efficiency is improved, but the off-state current increases leading to deterioration in holding characteristics of accumulated charge
Solution Approach 1:
The pixel circuit is divided into multiple transistor components with distinct functions. Specifically, the charge transfer transistor has its gate divided into multiple electrode regions (first gate electrode and second gate electrode) that can be independently controlled. This segmentation allows optimized control of charge transfer while maintaining proper charge holding characteristics through coordinated gate voltage application.
Solution Approach 2:
Different regions of the transistor gate are assigned different voltage levels to achieve local optimization. The first gate electrode and second gate electrode are driven with different potentials during charge transfer operations, enabling precise control of charge flow in specific regions while maintaining stable holding characteristics in other regions.
2Manufacturing precision
If the channel width of transistors is increased to improve charge transfer efficiency, then the transfer efficiency is improved, but the power consumption increases
Solution Approach 1:
The transistor gate structure employs dynamic voltage control where different gate electrode regions receive different potentials during operation. This dynamic control enables efficient charge transfer when needed while allowing power reduction during charge holding phases, thus optimizing the balance between transfer efficiency and power consumption.
Solution Approach 2:
The multi-electrode gate structure enables periodic switching between charge transfer mode and charge holding mode with optimized voltage patterns. During transfer periods, specific gate potentials enable efficient charge movement; during holding periods, adjusted potentials minimize leakage and power consumption while maintaining charge integrity.
3Manufacturing precision
If the channel width of transistors is increased to improve charge transfer efficiency, then the transfer efficiency is improved, but the imaging duration is extended
Solution Approach 1:
The pixel circuit performs preliminary charge accumulation in the photodiode during the exposure period, with the multi-electrode gate structure pre-configured to enable rapid charge transfer immediately after exposure. This preliminary action allows the actual transfer operation to be completed quickly, reducing the total imaging duration while maintaining high transfer efficiency.
Solution Approach 2:
The dynamic voltage control of multiple gate electrodes enables the charge transfer operation to be completed in a optimized time window. By applying specific voltage patterns during different phases of the imaging cycle, the system achieves rapid charge transfer when required while minimizing the overall imaging duration through efficient timing of transfer operations.
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 high-quality, high-definition imaging with reduced power consumption and short imaging duration, while allowing for both two-dimensional and three-dimensional imaging capabilities with improved reliability.
Implementation Method 1
A photosensor using an amplification function of a metal oxide semiconductor (MOS) transistor, called a complementary metal oxide semiconductor (CMOS) sensor
Data Source
AI summary
A driving method of a semiconductor device that takes three-dimensional images with short duration is provided. In a first step, a light source starts to emit light, and first potential corresponding to the total amount of light received by a first photoelectric conversion element and a second photoelectric conversion element is written to a first charge accumulation region. In a second step, the light source stops emitting light and second potential corresponding to the total amount of light received by the first photoelectric conversion element and the second photoelectric conversion element is written to a second charge accumulation region. In a third step, first data corresponding to the potential written to the first charge accumulation region is read. In a fourth step, second data corresponding to the potential written to the second charge accumulation region is read.