Imaging Device Gate Insulator for X-ray Stability
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Medical imaging devices using flat panel detectors face issues with stability under X-ray irradiation, leading to increased power consumption and reduced reliability, as well as decreased electrical characteristics and resolution, due to defect states generated in semiconductor or insulating materials within the pixel circuits.
Innovation Solution
An imaging device utilizing an oxide semiconductor in the pixel circuits with a gate insulating film comprising a silicon nitride film and an ultrathin silicon oxide film, which reduces defect states and minimizes changes in threshold voltage, thereby enhancing stability and reducing power consumption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a semiconductor material or insulating material is used in the pixel circuits of a flat panel detector, then the device can convert X-rays to electrical signals, but defect states are generated under X-ray irradiation causing changes in electrical characteristics and reduced reliability
Solution Approach 1:
A scintillator layer is introduced as an intermediary between the X-ray source and the pixel circuit. The scintillator converts X-rays to visible light, which then activates the photodiode. This mediator protects the semiconductor materials in the pixel circuit from direct X-ray irradiation, preventing defect state generation while maintaining the X-ray detection function.
Solution Approach 2:
The direct conversion system (where X-rays directly generate electrical signals in semiconductor materials) is replaced with an indirect conversion system. The scintillator converts X-rays to light, and the photodiode converts light to electrical signals. This substitution eliminates the harmful interaction between X-rays and semiconductor materials while preserving the detection capability.
2Measurement precision
If the pixel circuits are irradiated with X-rays, then X-ray detection is achieved, but power consumption increases and electrical characteristics degrade
Solution Approach 1:
The scintillator acts as a mediator that converts high-energy X-rays into visible light photons. This energy transformation allows the photodiode to detect the signal with lower energy requirements, reducing power consumption while maintaining detection precision. The scintillator efficiently transfers energy from X-rays to light without significant loss.
3Manufacturing precision
If conventional semiconductor materials are used in the pixel circuits, then the device can be manufactured with current technology, but the electrical characteristics change under radiation exposure reducing resolution
Solution Approach 1:
The scintillator layer serves as a protective intermediary that shields the semiconductor materials from direct X-ray exposure. This allows conventional semiconductor manufacturing processes to be used while achieving radiation resistance, as the semiconductor materials only encounter visible light from the scintillator rather than direct X-ray irradiation.
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
The solution provides a highly stable imaging device with improved electrical characteristics, reduced power consumption, and high resolution, capable of taking images with low radiation doses while maintaining reliability.
Implementation Method 1
In the indirect conversion system, X-rays are converted to visible light with a scintillator and the light is converted to electrical charges by a photodiode
Implementation Method 2
the light is converted to electrical charges by a photodiode
Data Source
AI summary
An imaging device that is highly stable to irradiation with radial rays such as X-rays and can inhibit a decrease in electrical characteristics is provided. The imaging device takes an image with radial rays such as X-rays and includes pixel circuits arranged in a matrix and a scintillator overlapping the pixel circuits. The pixel circuits each includes a switching transistor with an extremely small off-state current and a light-receiving element which is configured to convert the radial rays to electrical charges. A gate insulating film of the switching transistor has a stacked structure including a silicon nitride film with a thickness of 100 nm to 400 nm and a silicon oxide film or a silicon oxynitride film with a thickness of 5 nm to 20 nm.