High-performance TFT Using Oxide Materials

The realization a large sheet-type display to present ultrahigh-definition video such as 8K Super Hi-Vision (8K) will require a higher speed thin-film transistor (TFT) to control organic light-emitting diode (OLED) devices. The Science & Technology Research Laboratories (STRL) has been researching high-performance TFT technology based on oxide materials for 8K sheet-type displays. Oxide TFTs are promising candidates for driving devices in large-screen OLED displays because they can provide the high mobility (a measure of how easily an electron moves in a particular material) necessary to drive OLED devices and are adaptable to large-area fabrication. The oxide semi-conductor IGZO (In-Ga-Zn-O)^*1 has been under research and development at numerous institutions, and work has already begun on practical OLED displays based on IGZO-TFTs. On the other hand, making an 8K sheet-type display a reality will necessitate further improvements in mobility, low-temperature technology for forming devices on heat-sensitive plastic substrates, and flexibility so that driving remains stable even when the device is bent.

STRL has been developing high-mobility oxide semi-conductors and corresponding device structures, along with low-temperature forming technology for plastic substrates and devices using highly flexible materials. We fabricated a TFT with approximately three times the mobility of IGZO through application of ITZO (In-Sn(Tin)-Zn-O)^*2 with an optimized constituting element ratio and a flexible organic passivation layer. A prototype backplane^*3 was also fabricated for a flexible OLED display. We have found that ITZO is at least as reliable as IGZO in long-period driving applications, and thus, it seems to be a promising material for practical 8K sheet-type displays.

Our work will continue on high-performance TFT manufacturing technology with the goal of making sheet-type displays.