High electron mobility oxide TFT capable of driving 8K OLED TV screens

Published on August 9, 2024, at 15:30                EE Times Japan

A research group from Japan Hokkaido University has jointly developed an "oxide thin-film transistor" with an electron mobility of 78cm2/Vs and excellent stability with Kochi University of Technology. It will be possible to drive the screens of next-generation 8K OLED TVs.

The surface of the active layer thin film is covered with a protective film, greatly improving stability

In August 2024, a research group including Assistant Professor Yusaku Kyo and Professor Hiromichi Ota of the Research Institute for Electronic Science, Hokkaido University, in collaboration with Professor Mamoru Furuta of the School of Science and Technology, Kochi University of Technology, announced that they have developed an "oxide thin-film transistor" with an electron mobility of 78cm2/Vs and excellent stability. It will be possible to drive the screens of next-generation 8K OLED TVs.

Current 4K OLED TVs use oxide-IGZO thin-film transistors (a-IGZO TFTs) to drive the screens. The electron mobility of this transistor is about 5 to 10 cm2/Vs. However, to drive the screen of a next-generation 8K OLED TV, an oxide thin-film transistor with an electron mobility of 70 cm2/Vs or more is required.

Assistant Professor Mago and his team developed a TFT with an electron mobility of 140 cm2/Vs 2022, using a thin film of indium oxide (In2O3) for the active layer. However, it was not put to practical use because its stability (reliability) was extremely poor due to the adsorption and desorption of gas molecules in the air.

This time, the research group decided to cover the surface of the thin active layer with a protective film to prevent gas from being adsorbed in the air. The experimental results showed that TFTs with protective films of yttrium oxide and erbium oxide exhibited extremely high stability. Moreover, the electron mobility was 78 cm2/Vs, and the characteristics did not change even when a voltage of ±20V was applied for 1.5 hours, remaining stable.

On the other hand, stability did not improve in TFTs that used hafnium oxide or aluminum oxide as protective films. When the atomic arrangement was observed using an electron microscope, it was found that indium oxide and yttrium oxide were tightly bonded at the atomic level (heteroepitaxial growth). In contrast, it was confirmed that in TFTs whose stability did not improve, the interface between the indium oxide and the protective film was amorphous.