| 초록 |
Oxide thin film transistors (TFTs) have attracted much attention because they can be applied to flexible and large scale electronic devices in next generation display fields. Especially, TFTs using semiconductor layer of Indium Gallium Zinc Oxide (IGZO) are widely used in mass-production. However, these TFTs don’t have enough field-effect mobility and reliable features despite their outstanding off current levels and threshold voltages. Herein, we have demonstrated the improved metal oxide TFTs with double-stacked oxide semiconductor (OS) layer composed of channel layer at the bottom and buffer layer at the top. These TFTs show excellent electrical performance such as high average field-effect mobility (~80 cm2/V·s), on-current near zero, high on-off current ratio (~109), and good stability in positive-bias-test (PBT) and negative-bias-test (NBT). The channel layer increases the field-effect mobility, and the buffer layer increases on-off ratio by lowering the off current. We have explained in more detail why this improvement took place. For TFTs using single semiconductor layer, two areas exist: gate-bias-induced area (GBIA) and electrode-bias-induced area (EBIA). These areas entirely depend on the gate bias, the source-drain bias, the thickness of the semiconductor, the conductivity of the semiconductor, the capacitance of the gate insulator, and etc. The trends of interaction between BGIA and EBIA were demonstrated by modulation the thickness of the semiconductor as well as their conduction mechanism. For TFTs using dual-stacked semiconductor layer, new areas are generated in the interface of the channel layer and the buffer layer, respectively: band-offset-induced area (BOIA) and BOIA-induced area (BIA). When two semiconductor layers are connected, the band offset is formed. As a result, electrons are confined in curved conduction band due to band offset on the interface side of the semiconductors, resulting in the forming of the semi-charge accumulation region, BOIA, at the bottom of the bulk semiconductor layer. If BOIA overlaps with EBIA, it induces BIA that plays a similar role as electrodes at the top of the channel layer, which affects GBIA consequently. The conduction mechanism has been demonstrated in relation to the properties mentioned above. Our findings highlight that the metal oxide TFTs with high performance can be yielded through double-stacked semiconductor at low annealing temperatures, and hold great promise for widespread industrial applications. |
