Thin Film Transistor Gate Electrode Thickness for Stable Crystallization
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Solution Overview
Problem
The formation of unstable crystal growth regions in polycrystalline silicon semiconductor layers during the crystallization process for thin film transistors, leading to deteriorated driving characteristics and reliability in display devices.
Innovation Solution
A thin film transistor with a polycrystalline silicon semiconductor layer formed using sequential lateral solidification (SLS) with specific gate electrode and gate insulating layer thicknesses, and primary grain boundary distances to prevent unstable crystal growth, ensuring stable crystallization.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a laser beam is irradiated on the a-Si layer to crystallize it into a poly-Si layer, then the semiconductor layer can be formed with higher electron mobility, but heat flows toward the gate electrode causing insufficient crystal growth and unstable crystal growth regions
Solution Approach 1:
A buffer layer is introduced between the gate electrode and the a-Si layer to act as a thermal barrier. This intermediary layer prevents excessive heat from the laser beam from flowing into the gate electrode during the crystallization process, thereby eliminating unstable crystal growth regions while maintaining the desired electron mobility in the poly-Si layer.
Solution Approach 2:
The thickness of the gate electrode is controlled within a specific range (500-1500 Å) to optimize the balance between electrical performance and thermal management. By adjusting this parameter, the gate electrode can withstand the thermal load during laser irradiation without causing insufficient crystal growth, thus resolving the contradiction between achieving high electron mobility and preventing heat-induced crystal growth instability.
2Reliability
If the gate electrode thickness is increased to improve electrical performance, then current control capability is enhanced, but heat flow during crystallization increases causing unstable crystal growth regions
Solution Approach 1:
The gate electrode thickness is optimized to a specific range (500-1500 Å) that simultaneously satisfies electrical performance requirements and thermal management needs. This parameter optimization ensures adequate current control capability while limiting heat absorption during laser irradiation, thereby preventing unstable crystal growth regions and improving overall device reliability.
Solution Approach 2:
The buffer layer serves as a thermal intermediary that decouples the thermal relationship between the gate electrode and the a-Si layer. This allows the gate electrode to be designed with sufficient thickness for electrical performance without directly experiencing the full thermal load during crystallization, thus eliminating the harmful heat flow effect.
3Reliability
If the gate insulating layer thickness is increased to improve electrical isolation, then leakage current is reduced, but the distance for heat dissipation increases causing insufficient crystal growth
Solution Approach 1:
The gate insulating layer thickness is optimized to a specific range that provides adequate electrical isolation while maintaining sufficient thermal coupling for crystal growth. By controlling this parameter, the design achieves low leakage current through improved electrical isolation while ensuring that heat from the laser beam can still effectively reach the a-Si layer for complete crystallization.
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 prevents the formation of unstable crystal growth regions, enhancing the reliability and driving characteristics of thin film transistors by maintaining the gate electrode thickness between 500 Å to 1500 Å and the gate insulating layer thickness between 1600 Å to 2500 Å, and optimizing the distance between primary grain boundaries to 2.75 μm to 3 μm.
Implementation Method 1
the heat source of a laser beam, which is irradiated on the a-Si layer, may cause heat to flow toward the gate electrode
Implementation Method 2
crystallizing the a-Si layer into a poly-Si layer using a crystallization process, e.g., solid phase crystallization (SPC), rapid thermal annealing (RTA), metal-induced crystallization (MIC), metal-induced lateral crystallization (MILC), excimer laser annealing (ELA), or sequential lateral solidification (SLS)
Implementation Method 3
the heat source of a laser beam, which is irradiated on the a-Si layer
Data Source
AI summary
A thin film transistor, a display device including the same, and a method of manufacturing the display device, the thin film transistor including a substrate; a gate electrode on the substrate; a gate insulating layer on the gate electrode; a semiconductor layer on the gate insulating layer; and source/drain electrodes electrically connected with the semiconductor layer, wherein the gate electrode has a thickness of about 500 Å to about 1500 Å and the gate insulating layer has a thickness of about 1600 Å to about 2500 Å.