Oxide Semiconductor Transistor Gate Bias for Light Stability
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Solution Overview
Problem
Transistors using oxide semiconductors experience unstable electric characteristics due to light irradiation, leading to variations in photocurrent and threshold voltage, which affect display quality.
Innovation Solution
Applying a positive voltage to the gate electrode of the transistor for a duration of at least 100 μsec, either during or after light irradiation, helps stabilize the electric characteristics by bringing them back to their pre-irradiation state, using a driving circuit and optical sensor to detect light conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a transistor including an oxide semiconductor is used, then high electron mobility and low off-state current are achieved, but the electric characteristics become unstable under light irradiation
Solution Approach 1:
A positive voltage is applied to the gate electrode before light irradiation occurs (or immediately upon detection) to prevent threshold voltage shift. The optical sensor detects light conditions in advance, and the driving circuit proactively applies the positive voltage to maintain stable electric characteristics before degradation occurs.
Solution Approach 2:
An optical sensor continuously monitors light irradiation conditions and provides feedback to a driving circuit. When light is detected, the driving circuit automatically applies a positive voltage to the gate electrode to compensate for threshold voltage shifts, creating a closed-loop control system that maintains stable electric characteristics under varying light conditions.
2Reliability
If a positive voltage is applied to the gate electrode to stabilize threshold voltage, then electric characteristic stability improves, but additional circuit complexity is required
Solution Approach 1:
The transistor structure itself provides the solution by utilizing the gate electrode for dual purposes: normal transistor control and threshold voltage stabilization. By applying positive voltage to the existing gate electrode (which overlaps the oxide semiconductor layer with gate insulating layer), the system stabilizes electric characteristics without requiring separate stabilization structures, thereby minimizing additional complexity.
3Reliability
If the positive voltage application duration is extended, then threshold voltage recovery is more complete, but power consumption increases
Solution Approach 1:
Instead of continuous voltage application, the system uses periodic or pulsed voltage application triggered by light detection. The optical sensor detects light irradiation events, and the driving circuit applies positive voltage in discrete pulses (at least 100 μsec duration) only when needed, thereby achieving complete threshold voltage recovery while minimizing overall power consumption through event-driven operation.
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 method effectively minimizes variations in electric characteristics and maintains display quality by resetting the threshold voltage and photocurrent to their pre-irradiation levels, enhancing the reliability of oxide semiconductor transistors.
Implementation Method 1
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Data Source
AI summary
When a positive bias voltage is applied to a gate electrode of a transistor including an oxide semiconductor for longer than or equal to 10 msec, electric characteristics of the transistor, which have varied due to the light irradiation, can be brought to the state which is substantially the same as the state before the light irradiation. Note that a positive bias voltage is applied to the gate electrode of the transistor at an appropriate timing with reference to the amount of incident light received by the transistor. Accordingly, a display device in which a reduction in display quality is suppressed even when light irradiation is performed can be realized.