Electrostatic discharge effects in thin film transistors

Although amorphous silicon thin film transistors (α-Si:H TFT’s) have a very low electron mobility and pronounced instabilities of their electrical characteristics, they are still very useful and they have found their place in the semiconductors industry, as they possess some very good properties: they can be deposited under low temperature and over a large area, and they are very cheap. It is proved from practice that electrostatic discharge (ESD) is one of the most important issues in thin film electronics. It jeopardizes reliable operation of thin film transistors, firstly during the manufacturing process in the cleanroom, and also in some cases during their operation. Having a large on-resistance, α-Si:H TFT’s are very difficult from the point of ESD protection, as it is difficult to sink the current. Another difficulty for the ESD protection is that they are also built on an insulation substrate. Finally, the testing methods and the design rules that are already developed for the silicon integrated circuits are not applicable on the amorphous silicon TFT’s. Therefore an original design has to be created in order to protect TFT circuits from the electrostatic discharge.