Over a decade, amorphous oxide semiconductors (AOSs) have been significantly developed. And, they are already employed in flat panel displays (FPDs), including LCDs and OLED displays. However, a longstanding issue such as bias-stress, illumination stress, e.g. NBS, NBIS, PBS, is not yet fully resolved. While, transparent or flexible electronics, recently, attract much attention for next generation. To realize practical transparent or flexible electronics, stability of conventional AOSs should be improved much than now. For instabilities of AOSs, many phenomenalistic cases have been reported, but their origins and mechanisms have not been theoretically elucidated. But, it is clear that all instabilities result from external factors such as illumination, hydrogen diffusion, humidity and electrical bias. Thus, it can be said that the material with less sensitivities to a variety of external factors exhibits higher stability.

We recently demonstrated a highly photo-stable TFT consisting of an ultra-wide bandgap AOS (UWB-AOS) based on a-GaO_x [1-3]. The UWB-AOS has a low sensitivity against visible light due to its very wide optical bandgap of ~4.0 eV. However, a wider bandgap AOSs tend to have low mobility or difficulty in doping electrons. As shown in Fig. 1, the AOSs comprising the cations of relatively large principle quantum number have a relatively high mobility of >20 cm²/Vs. However, they have a narrow band gap (E_g) of ~2.5 eV. Therefore, a widening the E_g by decreasing only the valence band maximum (VBM) level would be the best approach to obtain high-performance UWB-AOSs.

Details, including the relation between electronic structures and stabilities, will be presented at the conference.

References

[1] J. Kim el al., SID Symposium Digest of Technical Papers 47 (2016) 951.

[2] J. Kim et al., NPG Asia Materials 9.3 (2017) e359.

[3] J. Kim et al., Active-Matrix Flatpanel Displays and Devices (AM-FPD), 2017 24th International Workshop on. IEEE, 2017.