Suppression of Interface and Bulk Defects in a-IGZO Thin Film Transistors with Improved Carrier Mobility
Date Issued
2012
Date
2012
Author(s)
Lin, Huang-Kai
Abstract
Metal oxides, due to its high mobility (>10cm2/V‧s), become a promising channel material in thin-film-transistors (TFTs), which is expected to provide large current to drive larger sized displays and organic light emitting diodes (OLEDs).
To achieve the goal, many efforts have been made by several groups to improve the TFTs’ properties. Among the researches, subthreshold swing (SS) is the main parameter to benchmark the TFT’s performance. According to the transport mechanism of the TFTs, mobile carriers flow through the channel just beneath the dielectric. The interface and bulk defects there would somehow trap carrier causing larger SS and lower drift mobility. Therefore, the quality of channel close to the channel/dielectric interface is the most important factor to affect the characteristics of TFTs.
In the thesis, a new approach, hybrid structure, is applied in gate dielectric layer and channel layer separately. For dielectric layer application, HfO2/SiO2 composition is adopted. With high-κ material, HfO2, gate voltage can induce stronger electrical field to increase its ability to control the carrier. For the channel layer application, channel is composed of a-IGZO layers grown in two steps with varied annealing condition. These two layers show different conductivity and carrier concentration. By using the method to combine them together, the advantages of each channel can be kept, which can achieve more than 170mV/decade decrease of SS and more than 50% increased mobility.
After improving TFT’s characteristics, some circuit applications are conducted to verify the dynamic performance of the TFT device. The outcome of the circuits and devices are quite consistent with each other. However, it is found that threshold voltage plays a rather important role when operating complicated circuit, which would affect whether the logic gate circuit can function in a correct manner. Furthermore, TFTs are applied to be a novel bio-sensor, which can sense small net charge variation.
Subjects
a-IGZO
TFT
hybrid structure
subthreshold swing
Type
thesis
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