TFT Second Semiconductor Layer Buffer Reduces Off-Current
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Solution Overview
Problem
Thin-film transistors (TFTs) used in active-matrix organic electroluminescence displays face issues with high off-current and variation between on-current and off-current due to direct contact between the ohmic contact layer and crystallized silicon film, leading to electric field concentration and performance deterioration.
Innovation Solution
A TFT structure is developed with a substrate, gate electrode, gate insulation film, first and second semiconductor layers, and ohmic contact layers, where the second semiconductor layer has varying thicknesses to act as a buffer and reduce electric field concentration, and the ohmic contact layers are formed on the second semiconductor layer to separate the source and drain electrodes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If the ohmic contact layer is directly formed on the crystallized silicon film, then the manufacturing process is simplified, but the electric field concentrates between the layers causing increased off-current
Solution Approach 1:
An insulation film is introduced as an intermediary layer between the ohmic contact layer and the crystallized silicon film. This mediator prevents direct contact, thereby eliminating electric field concentration and reducing off-current while maintaining manufacturing feasibility.
Solution Approach 2:
A protective film is formed over the crystallized silicon film to serve as a buffer during processing. This protective intermediary shields the channel layer from damage when the ohmic contact layer is processed, preventing characteristic deterioration.
2Power
If the crystallized silicon film is used for the TFT channel layer, then the on-current is increased, but the channel layer becomes damaged during ohmic contact layer processing
Solution Approach 1:
A protective film is formed beforehand over the crystallized silicon film to cushion and protect it from damage during subsequent processing of the ohmic contact layer. This pre-protective measure prevents characteristic deterioration while maintaining the high on-current benefits of crystallized silicon.
3Ease of manufacture
If the amorphous silicon film is used as the channel layer, then the manufacturing process is simpler, but the mobility is low resulting in low on-current
Solution Approach 1:
The amorphous silicon film is subjected to laser beam heating to induce crystallization, transforming it from amorphous to crystalline phase. This phase transition increases carrier mobility and on-current while maintaining compatibility with existing manufacturing processes.
Data Source
AI summary
A TFT includes a supporting substrate, a gate electrode formed on the supporting substrate, a gate insulation film formed on the substrate so as to cover the gate electrode, a first semiconductor layer formed across from the gate electrode with respect to the gate insulation film, a second semiconductor layer formed on the first semiconductor layer, and having a first thickness and a second thickness which is greater than the first thickness, an ohmic contact layer formed on the second semiconductor layer, and a source electrode and a drain electrode formed on the ohmic contact layer, spacing apart with each other.