X-Ray Imaging TFT Gate Control to Prevent Threshold Shift
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Solution Overview
Problem
Existing X-ray imaging devices using normally-off thin film transistors face threshold shift issues due to the application of gate voltages, which are not addressed by the configuration in devices with normally-on transistors.
Innovation Solution
The X-ray imaging device incorporates a control circuit to manage the connection and disconnection of gate lines and voltage lines with switches, ensuring the gate electrodes of thin film transistors are in a floating state or grounded during periods without X-ray emission to prevent threshold shift.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a normally-off thin film transistor is used in the X-ray imaging device, then the device can operate with lower leakage current and improved signal accuracy, but threshold shift occurs due to hole fixation at the transistor interface when gate voltage is applied
Solution Approach 1:
The control circuit applies a preliminary action by setting the gate voltage to a first voltage level (different from the normal operating voltage) during a predetermined period before X-ray imaging. This preliminary voltage application prevents hole fixation at the transistor interface by maintaining the transistor in a specific state, thereby preventing threshold shift before the actual imaging operation begins.
Solution Approach 2:
The control circuit implements periodic action by applying different voltage levels to the gate electrode at different time periods: a first voltage during a predetermined period before imaging, and a second voltage (normal operating voltage) during the imaging period. This periodic voltage switching prevents threshold shift while maintaining normal transistor operation during imaging.
2Measurement precision
If gate voltage is continuously applied to the thin film transistor during imaging, then the transistor remains in conduction state for accurate signal reading, but threshold shift occurs due to prolonged hole fixation at the interface
Solution Approach 1:
The control circuit applies a preliminary action by setting the gate voltage to a first voltage level during a predetermined period before imaging. This preliminary state preparation prevents hole fixation before imaging begins, allowing the transistor to be in the optimal conduction state during imaging without suffering from threshold shift.
Solution Approach 2:
The control circuit implements dynamics by dynamically switching the gate voltage between different levels based on the operational phase: a first voltage during the pre-imaging period to prevent threshold shift, and a second voltage during imaging to ensure proper conduction. This dynamic voltage adjustment optimizes both threshold shift prevention and signal reading accuracy.
3Stability of the object's composition
If the gate line is continuously connected to the voltage supply, then the thin film transistor maintains stable operation, but threshold shift occurs due to continuous voltage application causing hole fixation
Solution Approach 1:
The control circuit implements dynamics by making the gate line connection dynamic rather than static. The gate line is connected to a first voltage during a predetermined period before imaging to prevent threshold shift, and then connected to a second voltage during imaging to ensure stable transistor operation. This dynamic connection strategy maintains operational stability while preventing threshold shift.
Solution Approach 2:
The control circuit applies periodic action by switching the gate line connection between different voltage sources at different time periods. During the pre-imaging period, the gate line connects to the first voltage to prevent hole fixation. During imaging, it connects to the second voltage for stable operation. This periodic switching maintains stability while preventing threshold shift.
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 effectively reduces threshold shift in normally-off thin film transistors by preventing hole fixation at the transistor interface, allowing for recovery of the threshold value.
Implementation Method 1
a scintillator configured to convert X-rays emitted from an X-ray source into light
Implementation Method 2
a photoelectric conversion element configured to convert light from the scintillator into an electric signal
Data Source
AI summary
An X-ray imaging device includes a normally-off TFT, a gate line, a gate drive circuit including an output line, a switch connected between the gate line and the output line, and a control circuit. The control circuit operates the switch to switch from a state in which the gate line and the output line are connected to each other to a state in which the gate line and the output line are disconnected from each other in at least part of a period during which X-rays are not emitted from the X-ray source.