Nikkei Electronics Asia -- March 2008
Pins & Vias
New Materials Power Nanoscale Manufacturing

Feb 26, 2008 20:36 Nikkei Electronics Asia

Coupled with new manufacturing methods, next-generation device, packaging and substrate materials are being developed to meet the technical challenges of fabricating and assembling nanoscale ICs. These advanced materials include nanoparticles, fabricated or self-assembled nanostructures such as carbon nanotubes (CNT) and semiconductor or metallic nanowires, as well as composites containing at least one nanoscale component.
CNTs may be used in various parts of both active and passive devices as well as packages, for added strength, improved thermal conductivity, and reduced weight, as well as providing higher-speed conductors. Although multi-walled CNTs are also being developed, semiconducting single-walled CNTs with diameters of around 1nm are thought by many to be major candidates for replacing silicon as a semiconductor in nanoelectronics.

Recently, researchers at Purdue University's Birck Nanotechnology Center devised a method for growing densely-packed CNTs on chips in order to enhance heatflow at critical points where chips connect to heatsinks. The method - using microwave plasma chemical vapor deposition - outperforms conventional thermal interface materials, and does not require a clean-room environment, making it a potentially low-cost approach.

Materials aside from carbon are also being examined, such as graphene, and even silicon continues to hold promise in some areas. Graphene is theoretically capable of scaling down much further than silicon, to circuits only a few atoms across, in part because of its extreme strength and stability. Its conductive properties work differently from other conductors: electrons move at the same high speeds, regardless of their energy. Those high speeds mean that graphene-based transistors could theoretically switch faster than silicon-based transistors.

Other Developments
A nanocrystalline metal/polymer hybrid technology is being developed by DuPont in conjunction with Morph Technologies Inc, Integran Technologies Inc, and PowerMetal Technologies. The MetaFuse nanometal/polymer hybrid process will be used for manufacturing electronic components with the strength and stiffness of metal and the design flexibility and light weight of high-performance thermoplastics.

Because of the central function that silicon plays in semiconductors and electronics, it remains the material of choice for at least some researchers, including those at the Institute for the Structure of Matter, and the Institute of Atmospheric Sciences & Climate, both in Italy, and those at the Center for Research on Condensed Matter & Nanoscience in France. In January, scientists from these institutions created silicon nanowires that are atomically perfect: that is, their crystalline structure is free of imperfections down to the single-atom level, which is not true of typical, bulk silicon. Each nanowire in the array is an excellent conductor, and the array is also highly parallel.

Piezoelectric nanowires, which generate energy when stretched or bent, may hold promise for use in highly sensitive vibration sensors and foot-powered radio tags. Although these have been fabricated from gallium nitride and zinc oxide, the low piezoelectric charge constant of these materials - 3pC/N and 12pC/N, respectively - makes the process inefficient. Last fall, a team of researchers at the University of Illinois, Urbana-Champaign made piezoelectric nanowires from barium titanate. Although the process is currently more complex and difficult to control, the charge constant is vastly improved at 85pC/N.

Also last fall, researchers at the University of Pennsylvania demonstrated lithography-free, self-assembled nanowire memories made of germanium antimony telluride, a commercial alloy that is also a phase-change material. The devices switch between a high-resistance amorphous phase and a low-resistance crystalline phase. The research team said the memories can theoretically store data for 100,000 years, requiring only 0.7mW for operation, and that data can be written and erased at speeds of less than 50ns.

by Ann R. Thryft

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