Tutorials: Hideo Hosono
Amorphous Oxide Semiconductors
The Fermi level can be controlled in semiconductors via impurity doping or by applying an electric field. Amorphous materials have distinct advantages over their crystalline counterparts in terms of processability and homogeneity, i.e., ease of fabrication of large-sized homogenous thin films at low temperatures. Amorphous materials with good controllability of Fermi level would be highly beneficial for large-area electronics, optoelectronics, and flexible applications. These advantages are the major driving force for researching amorphous semiconductors. However, controlling the Fermi level in amorphous semiconductors is impossible because of high-density carrier traps arising from structural randomness. An exception is hydrogenated amorphous silicon (a-Si:H), which is widely used as solar cells and thin-film transistors for liquid crystal displays (LCD). However, band conduction has not been attained in a-Si:H. Thus, the mobility of a-Si:H remains at ~1 cm2/Vs, which is less than that of polycrystalline Si by two orders of magnitude.
Transparent amorphous oxide semiconductor (TAOS) is a novel class of amorphous semiconductors characterized by its ionic bonding nature. In addition to high optical transparency to visible light, its mobility is greater than that of a-Si:H by one order of magnitude and can be fabricated using conventional DC sputtering at low temperatures. Presently, thin-film transistors with a channel layer of In–Ga–Zn–O (IGZO) are used to drive pixels of high-definition and energy-saving LCDs in smartphones, tablets, PC monitors, and large-sized organic LED TVs and are being studied for several more applications in X-ray imagers and memories.
Although materials science and device physics of TAOS have rapidly advanced in the last decade, the understanding of science and technology is incomplete due to the short research history and the difference in chemical bonding between oxides and covalent-type semiconductors. Consequently, conventional processing used for a-Si:H has caused serious degradation of the resulting devices, such as plasma treatment involving hydrogen. TAOS is the only semiconducting material which can be fabricated by heating the precursor in the ambient atmosphere. Solution-derived processing has been extensively studied for using this unique feature toward flexible electronics.
In this lecture I introduce the fundamental of TAOS and their TFT applications along with a novel class of AOS.
Reference: Hideo Hosono and Hideya Kumomi（Edited）Amorphous Oxide Semiconductors: IGZO and Related Materials for Display and Memory (Wiley 2022)
Tutorial (8:00-9:00, 23rd Aug, Zhongda Lecture Hall (中大报告厅))
Tokyo Institute of Technology
SE-1, 4259 Nagatsuta, Midori, Yokohama 226-8503, Japan
National Institute for Materials Science
1-1 Namiki, Tsukuba, Ibaraki, 305-0044 JAPAN
Hideo Hosono received a Ph.D. in Applied Chemistry from Tokyo Metropolitan University in 1982, and became a professor of Tokyo Institute of Technology in 1999 via associate prof. of Nagoya Institute of Technology and Institute for Molecular Science. He is now an honorary and institute professor (the funding director of materials research center for element strategy, MCES) of Tokyo Tech and a group leader (a distinguished fellow) at The International Center for Materials Nanoarchitectonics (MANA) of National Institute for Materials Science (NIMS).
His research focus is creation of novel electronic materials. The representative achievements are material designing of transparent amorphous oxide semiconductors such as IGZO and their TFT applications for flat panel displays, creation of stable electrides and their application to catalysts for ammonia synthesis, and discovery of high-Tc iron-based superconductors.
He is a recipient of various honors including the Japan Prize, von Hippel Prize (MRS) and J.McGroddy Prize (APS), Jan Raychman Prize (SID), Imperial Prize, Japan Academy Prize, Thomson Reuter Citation Laureate, and a foreign fellow of the Royal Society.
WELCOME TO CHINA TO ATTEND THE ICANS
23-26 August, Nanjing, China
Connect with us: