* Question
What types of silicon-based TFTs are classified according to the crystallinity of silicon?
* Answer
Silicon-based Thin-Film Transistors (TFTs) can be classified according to the crystallinity of the silicon used in the active layer, which significantly affects their electrical performance, manufacturing cost, and suitability for various applications. There are three main types:
1. Amorphous Silicon (a-Si) TFTs
Structure: Non-crystalline (disordered) silicon.
Properties:
Low electron mobility (~0.5–1 cm²/V·s).
Inexpensive and easy to fabricate at low temperatures.
Suitable for large-area substrates like glass or plastic.
Applications:
Widely used in LCD panels, such as those in calculators, TVs, and monitors.
Best for displays with moderate refresh rates.
2. Polycrystalline Silicon (poly-Si or p-Si) TFTs
Structure: Composed of multiple small silicon crystals (grains).
Properties:
Higher mobility (~50–200 cm²/V·s) compared to a-Si.
Can support integration of drivers directly on the panel (System-on-Glass).
Higher fabrication complexity and cost.
Applications:
High-resolution and high-performance displays (e.g., smartphones, OLED displays).
Used in active-matrix OLED (AMOLED) and microdisplays.
3. Single-Crystalline or Monocrystalline Silicon TFTs
Structure: A single, continuous crystal of silicon (usually transferred from a wafer).
Properties:
Very high electron mobility (hundreds to thousands of cm²/V·s).
Excellent for high-speed electronics.
Expensive and technically demanding fabrication.
Applications:
Advanced electronics, such as flexible electronics, wearables, and high-speed logic circuits.
Summary Table
Type | Crystallinity | Mobility | Cost | Application |
Amorphous Silicon (a-Si) | Non-crystalline | Low (~1) | Low | LCDs, large-area displays |
Polycrystalline (p-Si) | Multi-crystalline | Medium (~50–200) | Medium-High | AMOLED, mobile devices |
Single-Crystalline | Monocrystalline | High (>>200) | High | High-speed/flexible circuits |
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