Microcrystalline Silicon TFT Active Layer via Hydrogen Plasma
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Solution Overview
Problem
Amorphous silicon thin film transistors (TFTs) used in LCDs have low mobility, serious threshold voltage drift, and instability, making them unsuitable for current-driving AMOLEDs, and microcrystalline silicon TFTs face carrier mobility and response speed issues due to incubation layers and defects in the channel region.
Innovation Solution
A thin film transistor structure with a microcrystalline silicon active layer formed by treating amorphous silicon thin films with hydrogen plasma in a layer-by-layer manner, combined with a successive deposition process for the upper portion, to reduce crystal boundaries and defects, enhancing carrier mobility and response speed.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If PECVD process is used to prepare microcrystalline silicon active layer, then good stability and high uniformity are achieved, but incubation layer with crystal boundaries and defects appears in channel region, decreasing carrier mobility and response speed
Solution Approach 1:
The active layer is divided into multiple thin amorphous silicon layers (first amorphous silicon layer and second amorphous silicon layer) with an interface between them. Hydrogen plasma treatment is applied at the interface to selectively reduce defects where crystal boundaries typically form, while maintaining the segmented structure that prevents extensive incubation layer formation throughout the entire active layer.
Solution Approach 2:
The patent changes the physical and chemical parameters of the silicon layers by applying hydrogen plasma treatment at specific conditions (temperature, pressure, gas flow rate) to the interface region. This treatment modifies the hydrogen concentration and bonding structure at the interface, reducing defect density and improving carrier mobility without converting the entire layer to microcrystalline silicon.
2Ease of manufacture
If a-Si TFT is used in LCD industry, then ease of manufacture is maintained, but low mobility, serious threshold voltage drift and bad stability occur
Solution Approach 1:
The patent applies different properties to different regions of the active layer. The interface region between the first and second amorphous silicon layers receives hydrogen plasma treatment to improve local quality and reduce defects, while the bulk regions maintain their amorphous structure. This localized improvement enhances overall device stability without requiring complete structural redesign.
Solution Approach 2:
The active layer is constructed as a composite structure combining multiple amorphous silicon layers with treated and untreated regions. The interface region has modified properties due to hydrogen plasma treatment, creating a composite material system that leverages the ease of manufacture of amorphous silicon while adding local defect reduction capabilities.
3Productivity
If microcrystalline silicon is used for big size display panel, then good stability and low process costs are achieved, but incubation layer causes crystal boundaries and defects, resulting in low on/off response speed
Solution Approach 1:
The patent extracts or removes the harmful incubation layer formation by preventing the PECVD process from creating microcrystalline silicon in the channel region. Instead of allowing incubation layer to form and then dealing with its effects, the segmented amorphous silicon structure with interface treatment prevents extensive crystal boundary formation, effectively taking out the source of response speed degradation.
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 solution significantly increases carrier mobility and on/off response speed, reduces power consumption, and improves stability, making the thin film transistor more suitable for display applications like AMOLEDs.
Implementation Method 1
the active layer lower portion is microcrystalline silicon obtained by using hydrogen plasma to treat at least two layers of amorphous silicon thin film prepared in a layer-by-layer manner
Implementation Method 2
treating amorphous silicon thin films with hydrogen plasma in a layer-by-layer manner, combined with a successive deposition process for the upper portion, to reduce crystal boundaries and defects
Implementation Method 3
The solution significantly increases carrier mobility and on/off response speed
Data Source
AI summary
One or more embodiments of the disclosed technology provide a thin film transistor, an array substrate and a method for preparing the same. The thin film transistor comprises a base substrate, and a gate electrode, a gate insulating layer, an active layer, an ohmic contact layer, a source electrode, a drain electrode and a passivation layer prepared on the base substrate in this order. The active layer is formed of microcrystalline silicon, and the active layer comprises an active layer lower portion and an active layer upper portion, and the active layer lower portion is microcrystalline silicon obtained by using hydrogen plasma to treat at least two layers of amorphous silicon thin film prepared in a layer-by-layer manner.