|
While breakthroughs in Science and Technology are often brought about by the discovery of new materials, it is not easy to create truly new materials. Dr.Hideo Hosono has opened new avenues in materials science by creating a series of novel electro-functional materials based on his own materials design concept and approach. His most representative research achievements are discovery of iron pnictide high Tc superconductors and creation of transparent amorphous oxide semiconductors with high electron mobility and their application to high performance thin film transistors (TFTs). Each of them is featured by large impact on worldwide research trend and/or industry as exemplified by application of oxide TFTs to the backplane for state-of-the art high resolution displays.
1. Discovery of Iron-based high Temperature superconductors : breakthrough since high temperature cuprates
Since it is prerequisite for the emergence of superconductivity emerges that electrons form a pair (called Copper Pair) transiently, it is believed that long range magnetic ordering is incompatible with superconductivity. Iron with a large magnetic moment was widely believed to be the most harmful for emergence of superconductivity.
Dr.Hosono discovered LaFeAsO1-xFx with Tc = 26K in the course of exploration for magnetic semiconductors in layered 3d transition metal oxypnictides which started from transparent p-type semiconductors. This discovery was reported in a communication ofJ.Am.Chem.Soc. in early 2008 and followed by a paper reporting Tc-raise to 43K under a high pressure of 2GPa (Nature in May 2008). This Tc recorded the highest except high Tc cuprates exceeding the value (39K) of MgB2. These reports gave a large impact on research community, breaking a widely accepted consensus that the presence of CuO2 plane is indispensable for the emergence of high Tc. Superconductivity research was rekindled since discovery of high Tc cuprates in late 1980s and urgent international symposia and special sessions at various conferences have been held. As a consequence, more than 6,000 printed papers on this subject have been published until 2013. It has been clarified that there is a vast family of parent materials and unique superconducting properties such as high critical magnetic field and robustness to impurities originate from its multi-orbital nature. Iron-based superconductor is now ranked as " a rich vein in superconductors since the discovery cuprates". The JACS communication in 2008 became the most cited paper among all the papers published in 2008 and discovery of iron-based superconductor was chosen as a breakthrough of year 2008 by Science Magazine.
Dr. Hosono has been got several outstanding achievements in research for their applications as well. Successful fabrication of epitaxial thin films, Josephson Junction, superconducting quantum interference device, and determination of critical grain boundary angle to keep high critical current density for iron-based superconductors were achieved for the first time by his group. He is leading the research front since the first discovery of the first superconductors.
2. Invention of high mobility thin film transistors using transparent amorphous oxide semiconductors for retina display applications
Thin film transistor (TFT) is a heart of flat panel displays and controls the display performance. Amorphous hydrogenated silicon (a-Si:H), which was invented by W.Spear and P.LeComber in 1975, has been exclusively used as a channel semiconductor in TFTs to liquid panel displays (LCDs) but is almost impossible to drive high resolution LCDs and organic LEDs due to its low field effect mobility. Thus, new semiconductor materials to meet this need are strongly demanding. Dr. Hosono published a material design concept of amorphous oxide semiconductors(TAOS) with high electron mobility in 1996 based on a consideration about chemical bonding on oxides. Subsequently, he fabricated high field effect transparent TFT using epitaxial thin film of homologous crystal InGaO3(ZnO)5, demonstrating a hidden potential of oxide semiconductors as a TFT channel layer (Science 2003). Subsequently, Dr.Hosono reported the high performance and flexible TFTs utilizing amorphous In-Ga-Zn-O (IGZO), a member of TAOS, inNature of 2004. IGZO-TFTs have mobility of 10-20 cm2/Vs, which is larger by an order of magnitude than that of a-Si:H, can be easily fabricated by conventional sputtering process at low temperatures, and show high transparency for visible radiation. This report attracted much attention of display companies and relevant researchers, and triggered extensive research in fundamental science and display application. New sessions on oxide semiconductors and oxide TFTs were established in the international conference on amorphous semiconductor in 2005 and in SID (largest academic society in the information displays) annual meeting in 2006, respectively, and now both have grown to the focused subjects. He has been leading the fundamental research on IGZO-TFTs such as elucidation of electronic transport and electronic structure by publishing more than 60 papers and the Nature paper in 2004, cited more than 1,500 times, is taken as the door-opening literature of this field. IGZO-TFTs were adopted as the backplane to drive the high precision and low power assumption displays and mass production started from 2012 by a domestic display company and are scheduled by foreign companies in 2013.
In summary, Dr.Hideo Hosono cultivated new frontiers in the fields of superconductor and semiconductor, each of which is a major subject of condensed matter physics or applied physics, with his own material sense and approach endorsed by deep understanding solid state chemistry. These achievements are highly evaluated worldwide. Accordingly, it was approved that his achievements merit the Chemical Society of Japan (CSJ) Award.
|
