Thin Film Transistor Drain Electrode Surrounding Source for LTPS Reliability
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Thin film transistors (TFTs) using low temperature poly-silicon (LTPS) crystallized by the solid phase crystallization (SPC) method exhibit poor output current characteristics and reliability due to the current kink effect, which affects the image quality and durability in organic light emitting display devices.
Innovation Solution
A TFT design with a drain electrode formed to surround at least three surfaces of the source electrode, incorporating a protection layer and an ohmic contact layer, and using a gate insulating layer and active layer to improve electric field distribution and reduce contamination, enhancing the reliability and stability of the TFT.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If LTPS is crystallized using the SPC method, then manufacturing cost and process simplicity are improved, but output current characteristics and reliability deteriorate due to the current kink effect
Solution Approach 1:
The patent applies local quality by forming a protection layer selectively over specific regions of the active layer, particularly at the drain electrode interface where the current kink effect occurs. This localized protection modifies the electric field distribution only in the critical region, allowing the SPC method to be used for manufacturing while mitigating the reliability issues in the problematic area.
Solution Approach 2:
The protection layer acts as an intermediary between the drain electrode and the active layer. It mediates the electric field interaction, preventing direct high-field stress on the active layer that causes the current kink effect, thereby improving reliability without changing the fundamental SPC crystallization process.
2Reliability
If the drain electrode is formed to surround the source electrode, then electric field distribution is improved and reliability is enhanced, but device complexity increases
Solution Approach 1:
The patent merges the drain electrode structure with the protection layer formation process. The protection layer is formed to extend over the surrounding drain electrode structure, combining the electrical function of the drain with the protective function in a single integrated structure, thereby reducing overall device complexity.
Solution Approach 2:
The patent transitions from a planar electrode structure to a three-dimensional surrounding structure where the drain electrode wraps around the source electrode. This dimensional change improves electric field distribution and reliability by creating a more uniform field, while the integration with the protection layer formation keeps the manufacturing process manageable.
3Reliability
If a protection layer is formed to overlap the source and drain electrodes, then contamination is reduced and reliability is improved, but manufacturing precision requirements increase
Solution Approach 1:
The protection layer is formed preliminarily over the active layer and electrodes before subsequent processing steps. This preliminary protection prevents contamination during manufacturing, and the layer is designed with sufficient overlap margins that accommodate normal manufacturing tolerances, reducing the stringency of precision 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
The TFT achieves stable output current characteristics in the saturation region and improved reliability, maintaining constant drain current and reducing the impact of gate bias stress, thereby enhancing the image quality and longevity of organic light emitting display devices.
Implementation Method 1
an ohmic contact layer contacting and formed between the active layer and the drain electrode
Implementation Method 2
the active layer is formed of low temperature poly-silicon (LTPS) crystallized using a solid phase crystallization (SPC) method
Data Source
AI summary
A thin film transistor (TFT) and an organic light emitting display device having the same are disclosed. In one embodiment, a TFT includes a gate electrode formed on a substrate. A gate insulating layer is formed on the substrate having the gate electrode. An active layer is formed on the gate insulating layer. A source electrode is formed over the active layer. A drain electrode is formed to substantially surround at least three surfaces of the source electrode on the active layer.