Global Shutter Imaging Pixel Circuit With Shared Transistors
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Solution Overview
Problem
Current imaging devices face challenges in achieving high-resolution, low-noise, and high-speed imaging with a global shutter system while minimizing transistor count and wiring complexity, especially under low illuminance conditions and varying temperatures.
Innovation Solution
The design incorporates a circuit structure where transistors and wiring can be used in common across multiple pixels, utilizing oxide semiconductors with low off-state current for efficient charge retention and photoelectric conversion elements like selenium for enhanced sensitivity, enabling high-resolution imaging with a global shutter system.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a global shutter system is implemented, then imaging distortion is eliminated and all pixels capture data simultaneously, but the data retention time increases and requires dedicated charge retention portions for each pixel, increasing device complexity
Solution Approach 1:
The patent makes the reset transistor (43) serve multiple functions: it resets both the photoelectric conversion element (PD) and the charge retention portion (node AN) simultaneously, eliminating the need for separate reset transistors. Additionally, the transistor (45) connected to the floating diffusion (FD) is shared across multiple pixels, allowing one transistor to perform charge transfer for several pixels, thereby reducing overall transistor count while maintaining global shutter functionality
Solution Approach 2:
The patent combines the reset function for both the photoelectric conversion element and the charge retention portion into a single reset transistor (43). This merging of functions reduces the number of required transistors per pixel while ensuring that both components are properly reset for the global shutter operation, thus simplifying the circuit structure without compromising imaging accuracy
2Manufacturing precision
If the pixel area is reduced to achieve high resolution, then more pixels can be densely arranged, but the number of transistors and wiring complexity increases
Solution Approach 1:
The patent makes transistor (45) connected to the floating diffusion (FD) serve multiple pixels simultaneously. This single transistor handles charge transfer for multiple pixels, reducing the per-pixel transistor count and allowing smaller pixel areas to be packed densely without proportionally increasing total transistor numbers, thus enabling high resolution with controlled complexity
Solution Approach 2:
The patent extracts the charge transfer function from individual pixel circuits and consolidates it into a shared transistor (45) that operates at the floating diffusion level. This extraction allows the photoelectric conversion elements to be miniaturized for high-resolution packing while the shared transistor handles the charge management for multiple pixels, decoupling pixel density from transistor count
3Reliability
If oxide semiconductors are used for charge retention, then off-state current is reduced and charge retention is improved, but manufacturing precision requirements increase
Solution Approach 1:
The patent changes the material parameter of the semiconductor layer from conventional materials to oxide semiconductors, which inherently provide lower off-state current and better charge retention. This material parameter change improves reliability while the patent addresses manufacturing precision by incorporating specific structural features like the insulating layer interface design and controlled deposition processes to ensure consistent oxide semiconductor quality across the device
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 allows for high-resolution, low-noise imaging with reduced transistor count and wiring complexity, enabling high-speed operation and reliability across a wide temperature range, including low illuminance conditions.
Implementation Method 1
photoelectric conversion elements like selenium for enhanced sensitivity
Implementation Method 2
utilizing oxide semiconductors with low off-state current for efficient charge retention
Data Source
AI summary
An imaging device that has a structure where a transistor is used in common by a plurality of pixels and is capable of imaging with a global shutter system is provided. A transistor that resets the potential of a charge detection portion, a transistor that outputs a signal corresponding to the potential of the charge detection portion, and a transistor that selects a pixel are used in common by the plurality of pixels. A transistor is provided between a power supply line and a photoelectric conversion element. Exposure is performed by turning on the transistor. Imaging data is retained in a charge retention portion by turning off the transistor.