“Our radically different approach of directly contacting nanostructures via nanosoldering is simple and relies on cheap, well-established technologies: optical microscopy and micromanipulation. We realized that we could produce sub 100 nm solder spikes, used to contact nanostructures, by a simple technique. Much as a glass-blower can pull out very thin filaments from molten glass, we were able to pull out very narrow solder spikes from a molten indium bead. By regulating the extraction speed and temperature gradient, the end of this spike had a radius of curvature as small as 50 nm. None of this is expensive to implement.”
The Berkeley researchers are confident that their soldering technique is a highly attractive alternative for industry in fabrication processes where nanostructures need to be electrically contacted. Their process is not only simple, it also is only a fraction of the cost of state-of-the-art e-beam systems. All that is needed for nano-soldering is a good optical microscope and a micromanipulator – two instruments that can be bought for about $10,000. Compare that to a $4+ million EBL system, and consider that the lithography equipment supplied to the semiconductor industry runs an annual $5-8 billion, the potentially substantial cost savings for industry become obvious.
Girit is convinced that the soldering process could be totally automated for mass production. “A similar technique, called wirebonding, already exists to ‘solder’ to much larger structures” he says. “While this technique cannot be used to contact nanostructures themselves, it is widely used in the semiconductor industry as a way to electrically connect intermediaries, called ‘bond pads’, which are roughly tens of microns in size, to the outside world. In turn, the nanostructures are connected to the bond pads by standard lithographic techniques. Wirebonders could easily be adapted for nanosoldering, skipping the intermediate lithographic steps, saving time and money. In addition, automated wirebonders already exist, and so it is not difficult to imagine that our technique could be automated for mass production.”
In their research paper the two Berkeley scientists demonstrate that solder contacts are a simple, efficient means of producing functional nanostructure devices based on graphene, nanotubes, or other materials. Not only the contacts are Ohmic, but also the resultant devices are clean and the device characteristics are consistent.
Possible application areas might be specifically the wirebonding industry to produce ‘nano-wirebonders,’ and more generally the semiconductor industry for various fabrication purposes.
The research paper on nanosoldering is here