Imaging Device Pixel Circuit With Dual Capacitors And OS Transistors
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Current imaging devices struggle to capture high-quality images in both bright and dark environments with a dynamic range equivalent to human vision, and there is a need for a compact imaging device with improved image quality and reduced leakage current.
Innovation Solution
The implementation of a pixel structure with two capacitors, a large and a small capacitor, where charge is accumulated only in the small capacitor in dark environments and in both capacitors in bright environments, utilizing oxide semiconductor transistors to prevent saturation and enhance dynamic range, along with silicon transistors connected to a photodiode on a silicon substrate for improved signal-to-noise ratio.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a single capacitor is used in the pixel circuit, then the device complexity is low, but the dynamic range is limited and saturation occurs in bright environments
Solution Approach 1:
The pixel circuit is divided into two separate capacitor units: a first capacitor connected to the photoelectric conversion element for accumulating charge in dark environments, and a second capacitor connected to the first capacitor for accumulating overflow charge in bright environments. This segmentation allows each capacitor to serve a specific function, enabling the circuit to handle both low-light and high-light conditions without saturation while maintaining manageable complexity through modular design.
2Reliability
If oxide semiconductor transistors are used to reduce leakage current, then the dynamic range is widened, but the manufacturing precision requirements increase
Solution Approach 1:
The invention employs oxide semiconductor materials (such as In-Ga-Zn-O) for the transistor active layers, which inherently provide extremely low off-state current characteristics. This material selection achieves high reliability with leakage currents of 1×10^-21 A or less, while the standardized manufacturing processes for oxide semiconductor transistors help manage the precision requirements through established fabrication techniques.
3Measurement precision
If two capacitors are provided in one pixel to widen dynamic range, then the imaging quality in both dark and bright environments is improved, but the area of the pixel increases
Solution Approach 1:
The first and second capacitors are merged into a unified capacitor structure where the second capacitor is connected to the first capacitor. This combined structure allows charge to be accumulated in the first capacitor during dark environments and overflow charge to be accumulated in the second capacitor during bright environments, achieving wide dynamic range and high image quality while optimizing the overall pixel area through integrated design.
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 allows for high-quality image capture across a wide illuminance range without saturation, improving the signal-to-noise ratio and reducing image deterioration due to leakage current, enabling imaging devices to perform similarly to human vision in both bright and dark conditions.
Implementation Method 1
two silicon transistors are connected to a photodiode formed to be embedded in a silicon substrate
Data Source
AI summary
An imaging device capable of taking an image in both a dark environment and a bright environment in a light amount range equivalent to or greater than that of human vision is desired. A wide dynamic range and high image quality are achieved. In order to obtain an image with a widened dynamic range, two capacitors, a large capacitor and a small capacitor, are provided in one pixel. The large capacitor is formed to be interposed between a transistor for controlling the amount of charge overflowed from the small capacitor and a transistor for resetting accumulated charge, and OS transistors are used as these two transistors. The OS transistor has extremely low off-state current characteristics, and thus can widen the dynamic range of imaging.