Single Crystal Thin Film Transistors
Original Publication Date: 1993-Aug-01
Included in the Prior Art Database: 2005-Mar-20
Doany, F: AUTHOR [+4]
Disclosed is a method for locating polysilicon grains in a polysilicon sheet covering an insulator so that a single grain covers the position of each device in a flat display panel display.
CrystalThin Film Transistors
a method for locating polysilicon grains in a
polysilicon sheet covering an insulator so that a single grain covers
the position of each device in a flat display panel display.
amorphous silicon used for typical active display
Thin Film Transistors (TFT) has too low a mobility for the displays
to be made as large or as fast as desired. Polysilicon has a higher
mobility than amorphous silicon. However, ordinarily when it is
attempted to produce TFT devices in polysilicon film, the presence of
grain boundaries in the active region of the devices leads to leakage
current that is undesirable. If, for example, TFT devices are to be
made with 3 micron lithography in a polysilicon film of submicron
thickness, polysilicon grains at least 10 microns diameter are needed
positioned so that no grain boundaries occur in the active regions of
annealing of polysilicon and amorphous silicon has been
carried out for a decade now. Such laser annealing is successful for
use with solar cells to produce very thin layers with high dopant
concentration. Large grain polysilicon can be made by melting fine
grain polysilicon on SiO&sub2.. However, in large grain polysilicon
on SiO&sub2. made by conventional melting, the location of each
grain is random.
polysilicon in which a grain is located at a
desired position can be made by projecting a laser beam onto the
surface of polysilicon on SiO&sub2. so that there is less energy in
the small region where the polysilicon grain is wanted. Everywhere
else has essentially uniform i...