Increasing microintegration of electronic devices in recent years has resulted in the development of a number of competing technologies for manufacturing nanometer-scale materials (one nanometer (nm) equals one-millionth of a millimeter). Future development of components used in electronic circuits and quantum components are to require ultra-fine processing in the range of 100nm or below.
The degree of precision in photolithography, the primary wire processing technique in use today, is currently limited to wavelengths of visible light, making it very difficult to process materials at the scale of hundreds of nanometers and smaller. However, carbon nanotubes with diameters of several nanometers, recently the subject of extensive research and development, exhibit very good electricity-conducting properties; therefore, they are expected to be utilized as material for wiring in future electronic devices. Like carbon nanotubes, highly conductive metal nanowires (wires with diameters in the nanometer scale) are also expected to be used in wiring material applications. However, while there have been reports of various methods to synthesize nanowires of highly conductive metals such as silver and copper, their aspect ratios (the ratio of the length to the diameter of the wire) are insufficient to practical applications to the wire in future devices. The technology for creating conductive nanowires with high aspect ratio is one elemental process technology that will be indispensable to the manufacture of next-generation ultra large-scale circuits.
This research resulted from discoveries made during development of antibacterial agents for use in sea water, and now is continuing as a budding research subject at AIST.
Yoji Makita, chief research scientist at AIST’s Institute for Marine Resources and Environment, has developed a method of synthesizing nanowires by irradiating a parent substance containing silver ions with an electron beam, allowing metallic silver nanowires with diameters on the scale of several nanometers to several tens of nanometers to be created easily. With the silver nanowire aspect ratios of 2000 and higher now being achieved, this method has been used to synthesize the world’s longest silver nanowire. Furthermore, this technique can also be used to synthesize nanowires of copper and other metals. A joint patent covering the results of this research was disclosed.
Silver features the best electricity-conducting properties of all metals, and the silver nanowires of the present research may therefore exhibit high electrical conductivity. It is anticipated that these materials will be utilized as wiring in the rapid miniaturization of ultra large-scale circuits and quantum components taking place recently, as well as for electron field emission sources in FEDs (field emission displays).