Microlens Arrays Enable Parallel Nanofabrication
Scientists at Riken research institute in Wako and at Osaka University in Suita, both in Japan, have demonstrated a laser-based nanofabrication technique that promises a hundredfold or more boost in productivity over general laser scanning systems. The parallel approach could be used to create three-dimensional components for micro- or nanoelectromechanical systems or for nanophotonic optoelectronic devices.
In the parallel laser nanofabrication setup, an array of microlenses splits a laser beam into multiple write beams that produce identical structures in a photopolymerizable resin by two-photon absorption. The approach has been used to fabricate 2-D letters and 3-D microsprings.
According to colleagues Satoshi Kawata and Hong-Bo Sun, current laser scanning nanofabrication technology offers significant benefits, including the ability to construct 3-D structures with high accuracy, but it suffers from low throughput because a single beam traces out each structure. They thus have been investigating means of parallel processing akin to that used to manufacture semiconductor chips, wherein many integrated circuits are manufactured at once, which drives down cost.
Building on earlier work involving two-photon polymerization of a resin, they transformed a single laser beam into hundreds of write beams using a 10 × 10-mm array of 200-µm microlenses with a 250-µm center-to-center separation. A Coherent Inc. Ti:sapphire laser and a Quantronix Corp. regenerative amplifier created 138-fs pulses of 799-nm radiation that passed through the array and that were focused onto a photopolymerizable resin. To maximize uniformity, the researchers employed only the center of the original beam and ensured that the resulting microbeams were perpendicular to the resin.
When two near-IR photons were absorbed at the same time, the resin polymerized. This two-photon process took place in only a small area, where the resin hardened and remained behind when washed in ethanol. The scientists moved the focal points by translating the microarray in the X-Y direction while moving the resin-bearing substrate up and down.
They used the setup to create a variety of structures, including arrays of 2-µm-wide letter N's and 5-µm-diameter microsprings. The parallel beam approach produced 227 nearly identical N's in five minutes, the same time it would have taken a single beam to make one letter.
The group is working to improve the technique's spatial resolution and is trying to fabricate functional devices. Even without these advancements, the method has drawn commercial interest, and the team already has collaborated with some corporations.
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