NIL: AN ULTRA LOW COST, LARGE AREA WAY FOR NANOELECTRONICS FABRICATION

Nanoimprinting lithography (NIL) is a simple pattern transfer process that is emerging as an alternative nanopatterning technology to traditional photolithography. NIL allows the fabrication of two-dimensional or three-dimensional structures with submicrometer resolution and the patterning and modification of functional materials. A key benefit of nanoimprint lithography is its sheer simplicity. There is no need for complex optics or high-energy radiation sources with a nanoimprint tool. There is no need for finely tailored photoresists designed for both resolution and sensitivity at a given wavelength. The simplified requirements of the technology allow low-cost, high-throughput production processes of various nanostructures with operational ease. NIL already has been applied in various fields such as biological nanodevices, nanophotonic devices, organic electronics, and the patterning of magnetic materials.

Recently researchers have taken this process one step further by demonstrating that direct nanoimprinting of metal nanoparticles enables low temperature metal deposition as well as high-resolution patterning. This approach has substantial potential to take advantage of nanoimprinting for the application in ultralow cost, large area printed electronics.

In nanoimprinting, a mold with nanostructures is pressed to deform and shape a thin material film deposited on a substrate. That is why nanoprinting for metal is harder to achieve. Therefore, to achieve successful nanoimprinting, the material needs to have proper flow properties (viscosity and surface tension) adjustable for complete mold pattern replication within reasonable processing temperatures and pressures. Ideal materials usually are thermoplastics, thermoset polymers, or other deformable materials with the desired flow properties.

Metal nanoimprinting is typically an indirect process where a polymer (e.g., PMMA) pattern is first created by nanoimprinting, which is then used as mask for dry etching of a predeposited metal film or as part of the metal lift-off process. It is conventional metal nanoimprinting involves multiple steps and expensive processes, thereby increasing the cost of manufacturing and offsetting the advantages of the nanoimprinting process. Very few direct metal nanoimprinting processes have been demonstrated so far due to the high melting temperature of metals.

The advantage of this process is that it eliminates the need of intermediate polymer nanoimprinting steps for dry etching or vacuum deposition. Also metal nanoparticle solution is also there as a precursor to use the solution processable form of the metal component for the nanoimprinting process, thereby eliminating the need to exceed the bulk metal melting temperature. The nanoimprinted nanoparticles can be transformed into conductive and continuous metal films by low-temperature nanoparticle melting.