12-07-2013, 03:51 PM
THIN FILM TRANSISTOR
INTRODUCTION
A thin film transistor comprises :
a semiconductor layer
a gate insulating layer
a gate electrode
The semiconductor layer is typically a polysilicon layer whose electron mobility is 100 times higher than that of an amorphous silicon layer. Thin film transistors are used as switching devices in flat display panels such as organic light emitting diodes (OLEDs) or liquid crystal displays (LCDs).
Types:-
IPS - in-plane switching
MVA - multi-domain vertical alignment
PVA - patterned vertical alignment
CPA - Continuous Pinwheel Alignment
WORKING:
A voltage applied at the gate controls the flow of electrons (resistance) from the source to the drain; a positive gate voltage attracts electrons to the bottom surface of the semiconductor layer and creates a conduction channel. When a voltage difference is applied between the two connector wires, electrons enter at one end (the source) and exit at the other (the drain), resulting in a current along the channel.
MANUFACTURE:
Manufacture
TFTs can be made using a wide variety of semiconductor materials. A common material is silicon. The characteristics of a silicon based TFT depend on the crystalline state. That is, the semiconductor layer can be either amorphous silicon, microcrystalline silicon, or it can be polysilicon.
Other materials which have been used as semiconductors in TFTs include compound semiconductors such as cadmium selenide and metal oxides such as Zinc Oxide. TFT's have also been made using organic materials.
By using transparent semiconductors and transparent electrodes, such as indium tin oxide (ITO), some TFT devices can be made completely transparent.