Thin Film Transistor with Local Crystallinity Control
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Solution Overview
Problem
Existing thin film transistors face challenges in balancing low OFF current with maintaining mobility in the channel section between the source and drain electrodes, as structures with polycrystalline silicon layers enhance mobility but increase OFF current, while amorphous silicon layers lower resistance but reduce mobility.
Innovation Solution
A thin film transistor design featuring a silicon semiconductor layer with a crystalline region, including a channel region of lower crystallinity than the surrounding regions, and an insulating protection layer to control laser light absorption and crystallization, resulting in a microcrystalline channel region and polycrystalline source and drain regions, which reduces OFF current while preserving mobility.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If a polycrystalline silicon layer is used in the channel section, then mobility is enhanced, but OFF current increases
Solution Approach 1:
The patent applies local quality by creating different crystalline structures in different regions of the silicon semiconductor layer. The channel region maintains lower crystallinity (microcrystalline or amorphous) to suppress OFF current, while the source and drain regions have higher crystallinity (polycrystalline) to enhance mobility and reduce contact resistance. This spatial differentiation of material properties resolves the contradiction between low OFF current and high mobility.
2Object-generated harmful factors
If an amorphous silicon layer is left in the channel section, then OFF current is lowered, but mobility decreases
Solution Approach 1:
The patent resolves this contradiction by implementing local quality differentiation: the channel region uses amorphous or microcrystalline silicon to maintain low OFF current, while the source and drain regions use polycrystalline silicon to provide high mobility. This allows the system to benefit from both material types in their respective optimal locations without the trade-offs of using a single material throughout.
Solution Approach 2:
The patent employs composite materials by combining different crystalline phases of silicon within the same semiconductor layer. The silicon semiconductor layer comprises a mixture of amorphous/microcrystalline regions (for low OFF current) and polycrystalline regions (for high mobility), creating a composite structure that achieves both low OFF current and high mobility simultaneously.
3Speed
If laser annealing is applied to the entire channel section, then mobility is improved, but OFF current increases
Solution Approach 1:
The patent applies local quality by using the insulating protection layer as a mask during laser annealing. The laser irradiation selectively crystallizes the source and drain regions while leaving the channel region in an amorphous or microcrystalline state. This selective local treatment achieves high mobility in contact regions without increasing OFF current in the channel, resolving the contradiction.
Solution Approach 2:
The insulating protection layer serves as an intermediary element that enables selective laser annealing. By positioning this layer over the channel region, it prevents laser energy from crystallizing the channel silicon while allowing crystallization in exposed source and drain regions. This intermediary structure resolves the contradiction between improving mobility and suppressing OFF current.
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 effectively lowers OFF current while minimizing the decrease in mobility, ensuring sufficient performance for applications like liquid crystal display panels, with the channel section's microcrystalline silicon region and polycrystalline regions effectively managing resistance and conductivity.
Implementation Method 1
irradiating the semiconductor film with laser light from above the insulating protection layer to crystallize the semiconductor film
Implementation Method 2
made polycrystalline by laser annealing technique
Implementation Method 3
to crystallize the semiconductor film so that, in a region overlapping the gate electrode
Data Source
AI summary
A thin film transistor according to an embodiment of the present invention includes: a gate electrode supported by a substrate; a gate insulating layer covering the gate electrode; a silicon semiconductor layer being provided on the gate insulating layer and having a crystalline silicon region, the crystalline silicon region including a first region, a second region, and a channel region located between the first region and the second region, such that the channel region, the first region, and the second region overlap the gate electrode via the gate insulating layer; an insulating protection layer disposed on the silicon semiconductor layer so as to cover the channel region and allow the first region and the second region to be exposed; a source electrode electrically connected to the first region; and a drain electrode electrically connected to the second region. The channel region is lower in crystallinity than the first region and the second region.