THESIS
2013
xx, 161 pages : illustrations ; 30 cm
Abstract
A new structure (dubbed bridged-grain, or BG for short) for thin-film transistors (TFTs),
exhibiting the benefits but not the drawbacks of both the short-channel and multi-junction
effects, is proposed and demonstrated. A series of short channels is formed through selective
doping of the channel using a grating-shaped layer as a mask. This grating can be formed
simply using a low-cost nanoimprinting process. All characteristics such as threshold voltage
(V
th), pseudo subthreshold slope (SS), on-off current ratio and field-effect mobility are
improved. The physics of this device structure is studied in detail. The fabrication process is
optimized for small grain low temperature polycrystalline silicon (LTPS) TFTs, including
those based on solid phase crystallization (SPC) and met...[
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A new structure (dubbed bridged-grain, or BG for short) for thin-film transistors (TFTs),
exhibiting the benefits but not the drawbacks of both the short-channel and multi-junction
effects, is proposed and demonstrated. A series of short channels is formed through selective
doping of the channel using a grating-shaped layer as a mask. This grating can be formed
simply using a low-cost nanoimprinting process. All characteristics such as threshold voltage
(V
th), pseudo subthreshold slope (SS), on-off current ratio and field-effect mobility are
improved. The physics of this device structure is studied in detail. The fabrication process is
optimized for small grain low temperature polycrystalline silicon (LTPS) TFTs, including
those based on solid phase crystallization (SPC) and metal induced crystallization (MIC). A
prototype of 4-inch active matrix organic light emitting diode (OLED) display adopting BG
MIC TFTs is demonstrated, showing the potential for mass production and commercialization
of BG-TFT based active matrix displays.
Application of high-κ dielectrics in LTPS TFTs can greatly reduce the V
th and sharpen
the SS. However, the leakage current due to the high drain electric field is much more serious
than in those using SiO
2 as gate dielectrics. The combined application of high- κ dielectrics
and BG in LTPS TFTs is explored. It is considered as an optimal combination for realization
of high performance small grain TFTs with good uniformity, which is highly desirable for
driving high resolution displays including those based on OLED.
To simplify the fabrication process, a new device structure is designed, making use of the
anisotropic conductivity of BG lines. In the new design, the shape of the active island is
modified so that the current flows along the BG lines in the source/drain region. As a result,
one implantation step is saved, and the measurements of the fabricated devices show no
problems in source/drain contact.
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