In 1985, Noboru Kimizuka of the National Institute for Research in Inorganic Materials, Japan had pioneered the idea of polycrystalline indium-gallium-zinc oxide (IGZO) ceramics, with the general chemical formula (InGaO3)m(ZnO)n (m, n = natural number; hereafter referred to as IGZO-mn). Little would he have thought that its curious electrical properties would bring the electronics industry to license thin-film transistors (TFTs) made from these metal oxides for various devices, including touchable displays. However, this did not come easy. In fact, even today, many of the characteristics of pure IGZO crystals remain unknown owing to their difficult extraction procedure. Then what makes them tantalizing?
When you shine light on metals, the free conducting electrons resonate or vibrate with external light (electromagnetic waves). Thus, the light wave is shielded, and as a result, light is not transmitted but is reflected. This is why metals are not generally transparent despite being good reflectors and conductors. In contrast, semiconductors with a large band gap, such as IGZO, can absorb and transmit light even in the visible light range. In general, the large band gap implies that these types of materials are insulators. Injecting carriers, using oxygen defects, into a semiconductor material with a large band gap can yield a material that is both transparent and conductive.
Transparent - Semiconductors - Use - Devices - One
Thus, being both transparent and conductive makes these semiconductors suitable for use in optoelectronic devices, much like the one you're reading this on! Furthermore, IGZO-based transistors have added advantages such as high electron mobility, good uniformity over a large area, and low processing temperature, which make it possible to achieve unparalleled energy-efficient high resolution. Within this IGZO-1n family, polycrystalline IGZO-11 (i.e. InGaZnO4) exhibits the highest conductivity and the largest optical band gap. In addition, von Neumann-type computers, or simply digital computers, require "on-off state" electrical circuits as the basic building blocks,...
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