TFT Source Electrode Barrier Metal Structure for Contact Resistance
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Solution Overview
Problem
The existing methods for forming poly-Si TFTs in display devices result in increased contact resistance due to Al atom migration and oxidation, affecting the emission efficiency of organic EL devices and operation speed of liquid crystal display devices.
Innovation Solution
A source electrode is formed with a three-layer structure comprising a lower barrier metal layer, an Al alloy, and a cap metal, where the barrier metal is divided into two layers to prevent oxidation and reduce contact resistance by maintaining the Al alloy in a non-oxidized state.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a barrier metal layer is formed by sputtering to prevent Al atom migration, then the barrier effect is improved, but the contact resistance increases due to oxidation of the barrier metal
Solution Approach 1:
The barrier metal layer is divided into two distinct layers: a lower barrier metal layer (first layer) that provides the barrier effect against Al atom migration, and an upper barrier metal layer (second layer) that protects the lower layer from oxidation. This segmentation allows each layer to perform its specific function independently, resolving the contradiction between barrier effect and contact resistance.
Solution Approach 2:
The upper barrier metal layer acts as an intermediary protective layer between the lower barrier metal layer and the Al alloy layer. It prevents oxygen from reaching and oxidizing the lower barrier metal layer, thereby maintaining low contact resistance while preserving the barrier effect of the lower layer.
2Reliability
If the barrier metal is subjected to heat treatment to increase density and improve barrier effect, then the barrier effect is improved, but oxidation of the barrier metal occurs increasing contact resistance
Solution Approach 1:
The lower barrier metal layer is subjected to heat treatment before forming the upper barrier metal layer. This preliminary heat treatment increases the density and barrier effect of the lower layer while it is still protected from oxidation by the subsequent upper layer that will be formed. The upper layer is then formed to protect the already-treated lower layer during subsequent processing steps.
3Reliability
If Al alloy is used for source electrode to decrease resistance, then electrical conductivity is improved, but Al atom migration and oxidation occur increasing contact resistance
Solution Approach 1:
The barrier metal layers serve as intermediary layers between the Al alloy source electrode and the semiconductor layer. These intermediary layers prevent direct contact between Al atoms and the semiconductor layer, blocking Al atom migration while maintaining the low electrical resistance properties of the Al alloy.
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 configuration decreases contact resistance, suppressing the rise of driving voltage and enhancing emission efficiency in organic EL devices and increasing operation speed in liquid crystal display devices.
Implementation Method 1
a lower barrier metal layer, an Al alloy, and a cap metal, where the barrier metal is divided into two layers to prevent oxidation and reduce contact resistance
Implementation Method 2
While the barrier metal is formed by sputtering, the barrier metal in the state as sputtered has no sufficient barrier effect for Al
Data Source
AI summary
An organic EL display device includes scanning lines, video signal lines, and pixels, each including a TFT having a semiconductor layer and an organic EL layer located between a lower electrode and an upper electrode. A source electrode connecting the semiconductor layer and the lower electrode is formed of three layers including a barrier metal, an Al-containing metal, and a cap metal. The barrier metal is formed of a first layer in contact with the semiconductor layer and a second layer in contact with the Al-containing metal. Each of the first layer, the second layer, and the cap metal is formed of a metal comprising a high melting point metal, and an amount of oxygen in the first layer is larger than an amount of oxygen in the second layer.