Biology Reference
In-Depth Information
While amorphous silicon TFT suffers from low electronic
performance, it is very flexible in application and manufacturing.
One important advantage is that amorphous Si can be deposited
at temperatures as low as 75
◦
C. This makes it possible for the
device to be made not only on glass, but also on plastics. In
addition, amorphous silicon can be deposited over very large
areasbyplasma-enhancedchemicalvapordeposition(PECVD)with
standard industrial equipments. Both features make mass-scale
production of amorphous silicon TFT-based devices relatively easy
and economic. The main application for amorphous silicon TFT is
on liquid crystal displays (LCDs), in which each pixel is individually
driven by a TFT transistor.
Polycrystalline silicon is a material consisting of multiple small
siliconcrystalswithsizesrangingfromnanometerstomicrometers,
widely used as a gate material of FET and interconnection in
integrated circuits. Depending on the size of the crystals or
grains, the electron mobility in polycrystalline silicon lies between
that of amorphous and crystalline silicon, ranging from 10 to
100cm
2
V
−
1
s
−
1
,andprovidingdeviceperformancegoodenoughfor
electroniccircuits.Itwastheabilitytofabricateintegrateddrivecir-
cuits[13]thatstimulatedtheinitialinterestinpolycrystallinesilicon
for active matrix displays. The technology, now well developed, has
been for long time applied in LCD displays for projectors and is now
beingusedformobilephones.Poly-SiTFTshavealsobeenemployed
to make static random-access memories (SRAMs) and operational
amplifiers.
The fabrication of a polycrystalline silicon film can be achieved
through various CVD methods or crystallization of amorphous
silicon. But these processes require high temperatures of at least
300
◦
C, making the deposition only possible on glass but not
plastic. A relatively new technique called laser recrystallization has
been devised to crystallize a precursor amorphous silicon film by
localized heating without damaging the plastic substrate. A transfer
process has also been developed to fabricate poly-Si TFT circuits on
plastic substrates [14].
In recent years, organic or polymer semiconductor materials
have been intensively researched to make TFTs. These organic
TFTs can be manufactured with very low cost using much simpler
