Polycrystalline Silicon TFT Channel Orientation for OLED Flicker Reduction
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Solution Overview
Problem
The display quality of OLED display devices is compromised due to variations in the properties and uniformity of thin-film transistors (TFTs) caused by differing grain growth directions of polycrystalline silicon, leading to issues like flicker and reduced performance.
Innovation Solution
The use of a sequential lateral solidification (SLS) method to form polycrystalline silicon layers in TFTs, where the switching TFTs have channels parallel to grain growth directions for optimal properties and driving TFTs have channels perpendicular to grain growth directions for uniformity, along with a metallic bent conduction line to maintain signal integrity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If polycrystalline silicon layers are formed using conventional crystallization methods, then manufacturing process is simpler, but TFT properties show large variations due to random grain growth directions
Solution Approach 1:
The patent applies preliminary action by forming a crystalline seed layer before the main polycrystalline silicon layer. This seed layer with controlled crystal orientation guides the subsequent grain growth, ensuring that grains grow in predetermined directions rather than randomly. This preliminary structural preparation resolves the contradiction by establishing reliable grain orientation early in the process.
Solution Approach 2:
The patent changes physical parameters during crystallization, specifically controlling temperature gradients and laser beam parameters to influence grain growth direction. By adjusting these parameters, the patent achieves controlled grain orientation that improves TFT uniformity while managing process complexity through parameter optimization rather than fundamental process changes.
2Manufacturing precision
If grain growth direction is not controlled, then manufacturing is easier, but display quality deteriorates due to flicker and non-uniformity
Solution Approach 1:
The patent introduces a crystalline seed layer as an intermediary between the substrate and the polycrystalline silicon layer. This seed layer acts as a mediator that transmits controlled crystal orientation to the growing grains, enabling precise grain direction control without directly complicating the main manufacturing process. The intermediary layer simplifies the control mechanism while achieving high manufacturing precision.
3Reliability
If switching TFT and driving TFT have same grain orientation, then manufacturing is simpler, but switching TFT cannot achieve optimal properties and driving TFT cannot achieve uniformity
Solution Approach 1:
The patent applies local quality by assigning different channel orientations to different TFT types within the same device. Switching TFTs have channels oriented parallel to grain growth direction for optimal switching performance, while driving TFTs have channels oriented perpendicular to grain growth direction for uniformity. This localized differentiation resolves the contradiction by optimizing each TFT type for its specific function rather than using a uniform orientation.
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 approach enhances the device properties of switching TFTs and achieves uniformity in driving TFTs, preventing flicker and improving overall display quality by ensuring consistent signal transmission and resistance uniformity.
Implementation Method 1
The step of crystallizing the amorphous silicon may be performed by various crystallization methods such as a crystallization method using a heat or a crystallization method using a laser beam
Implementation Method 2
a sequential lateral solidification (SLS) method using a laser beam has become of interest. The SLS method takes advantage of the fact that grains of polycrystalline silicon grow laterally from the phase boundary between liquid silicon and solid silicon
Data Source
AI summary
An organic light emitting diode display device includes: a switching thin film transistor in a pixel region, the switching thin film transistor including a switching semiconductor layer of polycrystalline silicon; a driving thin film transistor connected to the switching thin film transistor, the driving thin film transistor including a driving semiconductor layer of polycrystalline silicon layer; and a light emitting diode connected to the driving thin film transistor, wherein a direction of a channel of the switching thin film transistor is parallel to a first direction, and a direction of a channel of the driving thin film transistor is perpendicular to the first direction.