Oxide TFT Display Circuit Layout for Threshold Drift Control
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Solution Overview
Problem
Transistors using oxide semiconductor layers in display devices face reliability issues due to changes in threshold voltage over time, particularly when formed in bottom gate or dual gate structures, leading to thermal degradation and display unevenness.
Innovation Solution
The display device employs a dual gate structure for the writing transistor and a bottom gate structure for the driving transistor, with varying thicknesses of gate insulating films to optimize switching characteristics and current control, using oxide semiconductors with impurity areas to stabilize the transistors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a bottom gate or dual gate structure is used for transistors with oxide semiconductor layers, then the transistors can be formed in the display device, but threshold voltage changes over time leading to thermal degradation and display unevenness
Solution Approach 1:
The patent changes the gate structure parameter from bottom gate/dual gate to top gate configuration. This parameter change resolves the threshold voltage instability issue by positioning the gate electrode above the oxide semiconductor layer, preventing the thermal degradation and display unevenness that occur with bottom gate or dual gate structures.
2Use of energy by moving object
If oxide semiconductor layers are used in transistors, then low off-leakage current and low-frequency driving are achieved, but threshold voltage changes over time causing thermal degradation
Solution Approach 1:
The patent changes the gate structure parameter to top gate configuration while maintaining oxide semiconductor layers. This resolves the contradiction by achieving both low power consumption (through oxide semiconductors) and high reliability (through top gate structure that prevents threshold voltage drift and thermal degradation).
3Ease of operation
If dual gate structure is used for writing transistor and bottom gate for driving transistor, then switching characteristics and current control are optimized, but thermal degradation and display unevenness occur
Solution Approach 1:
The patent changes the gate structure parameter for the driving transistor from bottom gate to top gate configuration. This maintains good current control while eliminating thermal degradation and display unevenness. The writing transistor can retain dual gate structure for optimized switching characteristics.
Data Source
AI summary
A display device including a substrate, a light-emitting element, a first transistor, and a second transistor, the first transistor including the first gate electrode on the substrate; a first insulating film on the first gate electrode, a first oxide semiconductor on the first insulating film, and having an area overlapping the first gate electrode, a second insulating film on the first oxide semiconductor, and a first conductive layer on the second insulating film, the second transistor including the first insulating film on the substrate, a second oxide semiconductor on the first insulating film, a second insulating film on the first oxide semiconductor and the second oxide semiconductor, and having a thickness smaller than a thickness of the first insulating film, a second gate electrode on the second insulating film, and having an area overlapping the second oxide semiconductor.