Nanowire Assembly

Tech Forecast

Half a century ago, Intel co-founder Gordon Moore made a bold prediction: the number of transistors in an integrated circuit would just about double every two years. This statement about computing power — now known as Moore’s Law — held true for decades and still guides thinking and planning in the semiconductor industry. Whereas early computer chips held around 2,000 transistors, today’s chips can hold billions.

The frontiers of miniaturization keep extending further.

Prototypes of new nanoscale materials with novel and useful properties are now coming on the scene. The implications for a broad range of industrial sectors — not just computing — are tremendous. Still, to realize the promise of these new technologies, it’s essential to develop cost-effective means to integrate nanoscale materials into working devices.

Today, the question is: How can manufacturers overcome challenges of cost, quality, and yield to assemble nanoscale materials at scale?

Nanowires — structures that are just a few billionths of a meter in diameter but can be thousands or millions of times longer — are slowly starting to migrate from laboratories to the marketplace. At the nanoscale, materials can display radically new traits, including higher melting points, extreme conductivity, and optical transparency.

Electronics are just the beginning. In additional to ever-smaller transistors for computing, nanowires have emerging applications in energy, optics, defense, healthcare, and environmental management.

Figure1: Atomically precise nanowires assembly. Image courtesy of SLAC National Accelerator Laboratory. Potential applications of nanowire technologies include gas sensors with 30 times the sensitivity, batteries with substantially increased capacity, and super-capacitor electrodes with improved energy, power density, and cycling performance.

Across diverse sectors, new opportunities include:

Electronics: Nanowires made from iron and nickel alloy could create new, incredibly dense memory devices. Silver nanowires, embedded in a polymer, could make conductive layers that can flex, without damaging the conductor. And sensors using zinc oxide nanowire detection elements could make it possible to reliably detect a range of chemical vapors.
Energy: Silicon nanowires have potential to increase optical absorption and collection efficiency in solar cells.
Medicine: Nanowires enable new sensing capabilities that can help with the diagnosis and monitoring of diseases as well as the discovery and screening of new drug molecules.
Environment: Silver chloride nanowires could someday be used as a catalyst to decompose organic molecules in polluted water. Electrified filters made from silver nanowires may create new capacity to kill bacteria in water. There are also a range of possible applications for nanowires in absorbing pollution from oil spills.
Figure 2: Schematic illustration and SEM of fabricated silicon nanowire sensors. Image courtesy of Jen Research Group at University of Washington.

It’s now possible to produce individual nanowires with near-atomic precision, resulting in repeatable processes and predictability in terms of chemical composition, size, and structure. Simple nanowire assemblies — unorganized mats of overlapping nanowires — are starting to reach the market. Manufactured using “roll-to-roll” techniques, these new products already have applications including transparent electrodes for touch panel displays and high-conductivity components for advanced vehicle batteries.

Still, to realize the promise of nanowires, new fabrication and assembly advances are necessary.

Genuine mass-production of nanowires is not yet possible, and it’s still extremely difficult to usefully arrange nanowires once they’re built. The current technical challenges include alignment, assembly, bonding, and patterning — as well as integration of nanowires into useful devices and components. While opto-electronic applications of nanowires have extraordinary potential, it’s not yet feasible to integrate nanowires into traditional semiconductors with the required low rate of defects.

Questions of cost and yield will determine whether nanowire technologies can take hold in the market. While manufacturers have a crucial role to play in identifying how to cost-effectively assemble nanoscale materials and integrate them into functional devices, federal agencies and research universities can also play a role. The United States has invested in nanowire fabrication and assembly through a range of agencies, including the Department of Energy (opto-electronics and lasers), Department of Defense (chemical detection), National Science Foundation (materials research), and a range of other federal players through the Small Business Innovation Research program.

Solutions are emerging. A team at Harvard and MIT recently tested a new nanocombing assembly technique with potential to significantly reduce nanowire defects. A team at Penn State has developed an approach to nanowire patterning using standing surface acoustic waves — bringing high degrees of versatility, tunability, and efficiency to the fabrication of large-scale nanowire arrays. Other researchers are making progress in understanding how nanowires can improve device performance in targeted applications like sensing.

Moore’s Law pointed at some crucial truths: Miniaturization has massive implications for technology, and its forward march is essentially unstoppable. With sustained investments in new manufacturing techniques, nanoscale materials can transform diverse fields in untold ways. Even beyond electronics, the movement toward unprecedented miniaturization continues.


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