Thin Film Transistor Devices with Different Electrical Characteristics
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Solution Overview
Problem
The existing low-temperature polysilicon (LTPS) fabrication process for active-matrix organic light-emitting diode (AMOLED) displays struggles to produce thin film transistors (TFTs) with different electrical characteristics in peripheral and pixel regions, leading to mura defects due to non-uniform laser output energy affecting driving current.
Innovation Solution
A method involving a substrate with distinct regions for forming TFTs using different crystallization processes, where non-laser crystallization is used for driving TFTs in the pixel region and laser crystallization for switching TFTs and peripheral circuits, allowing for varying grain sizes and electrical characteristics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a single LTPS fabrication process is used for all TFTs, then the manufacturing process is simple and integrated, but TFTs in different regions cannot achieve different electrical characteristics
Solution Approach 1:
The substrate is divided into different regions (first region for driving TFTs, second region for switching TFTs) that undergo different crystallization processes. This segmentation allows each region to achieve tailored electrical characteristics while maintaining an integrated manufacturing approach.
Solution Approach 2:
Different crystallization methods are applied to different regions: non-laser crystallization for driving TFTs in the first region to achieve high sub-threshold swing and low threshold voltage, and laser crystallization for switching TFTs in the second region to achieve high carrier mobility. This local differentiation enables optimized electrical characteristics for each functional requirement.
2Reliability
If high power laser crystallization is used for all TFTs, then carrier mobility is high and manufacturing is easier, but non-uniform laser output energy causes mura defects
Solution Approach 1:
The problematic laser crystallization step is extracted and removed from the driving TFT region. Only the switching TFT region undergoes laser crystallization, while driving TFTs use non-laser crystallization methods. This eliminates the source of non-uniformity and mura defects in the driving TFTs while preserving the manufacturing advantages of laser crystallization where applicable.
3Duration of action of stationary object
If driving TFTs require high sub-threshold swing and low threshold voltage, then gray scale and OLED lifespan are improved, but carrier mobility decreases compared to switching TFTs
Solution Approach 1:
Different crystallization characteristics are applied locally to different TFT types. Driving TFTs in the first region use non-laser crystallization to achieve high sub-threshold swing and low threshold voltage for extended OLED lifespan and improved gray scale. Switching TFTs in the second region use laser crystallization to achieve high carrier mobility for fast response speeds. Each region is optimized for its specific functional requirements.
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 prevents mura defects and maintains high performance by ensuring different electrical characteristics for driving and switching TFTs, enhancing OLED lifespan and display quality.
Implementation Method 1
the active layers of TFTs are formed by a high power laser crystallization process
Implementation Method 2
laser crystallization for switching TFTs and peripheral circuits
Data Source
AI summary
A system for displaying images. The system includes a thin film transistor (TFT) device including a first insulating layer covering a first region and a second region of a substrate. A first polysilicon active layer is disposed in the first region and between the substrate and the first insulating layer. A second polysilicon active layer is disposed on the first insulating layer in the second region. A polysilicon gate layer is disposed above the first polysilicon active layer. A second insulating layer covers the polysilicon gate layer and the second polysilicon active layer. A metal gate layer is disposed above the second polysilicon active layer. A method for fabricating the system for displaying images including the TFT device is also disclosed.