Imaging Panel Bias Wiring for X-ray TFT Stability
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Solution Overview
Problem
X-ray imaging systems using indirect conversion schemes face instability in thin film transistors due to exposure to scintillation light, leading to deterioration and reduced operational reliability.
Innovation Solution
Incorporating a bias wiring line that overlaps the gate electrode and semiconductor active layer, applying a reverse bias voltage to shield the semiconductor active layer from light and function as a second gate electrode, and using an oxide semiconductor with specific compositions like InGaZnO for enhanced performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a bias wiring line is added to apply reverse bias voltage to the photoelectric conversion element, then the operation stability of thin film transistors is improved, but the device complexity increases
Solution Approach 1:
The bias wiring line is designed to serve dual purposes: it applies reverse bias voltage to the photoelectric conversion element while simultaneously functioning as a back gate electrode for the thin film transistor. This multi-functionality resolves the contradiction by improving transistor stability without adding separate dedicated structures, thus avoiding increased device complexity.
Solution Approach 2:
The patent merges the bias wiring line for the photoelectric conversion element with the back gate electrode of the thin film transistor into a single integrated structure. This consolidation achieves the same functional效果 as separate components would provide, thereby stabilizing transistor operation while preventing an increase in overall device complexity.
2Productivity
If the transistor size is reduced to achieve smaller pixel pitch, then the productivity and resolution are improved, but the leakage current increases
Solution Approach 1:
The bias wiring line applies reverse bias voltage to the photoelectric conversion element in advance, creating a potential barrier that prevents carrier generation and leakage current before it can occur. This preliminary anti-action allows transistors to be miniaturized for smaller pixel pitch while maintaining low leakage current levels, thus resolving the contradiction between productivity and energy loss.
3Loss of energy
If the reverse bias voltage is applied to the photoelectric conversion element, then the leakage current is reduced, but the manufacturing precision requirements increase
Solution Approach 1:
The bias wiring line simultaneously serves as the back gate electrode, meaning the same structural element fulfills multiple functions. This eliminates the need for separate alignment between dedicated bias wiring and gate electrodes, thereby reducing manufacturing precision requirements while still achieving leakage current reduction through reverse bias voltage application.
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 stabilizes the operation of thin film transistors, reduces leakage current, and enables higher resolution images by increasing ON current and minimizing OFF current, allowing for smaller transistor sizes and reduced pixel pitch.
Implementation Method 1
a photoelectric conversion element connecting to the thin film transistor and receiving the scintillation light
Implementation Method 2
a bias wiring line connecting to the photoelectric conversion element and applying a reverse bias voltage to the photoelectric conversion element
Implementation Method 3
a scintillator converts incident X-rays into scintillation light
Data Source
AI summary
An aim of the present invention is to make it possible to achieve stable operation of thin film transistors in an imaging panel of an X-ray imaging system that uses an indirect conversion scheme. An imaging panel includes a substrate, thin film transistor, photoelectric conversion element, and bias wiring line. The thin film transistor is formed on the substrate. The photoelectric conversion element is connected to the thin film transistor and irradiated by scintillation light. The bias wiring line is connected to the photoelectric conversion element and applies a reverse bias voltage to the photoelectric conversion element. The thin film transistor includes a semiconductor active layer and a gate electrode. The gate electrode is formed between the substrate and semiconductor active layer. The bias wiring line includes a portion that overlaps the gate electrode and semiconductor active layer as seen from the radiation direction of the scintillation light.