Fabrication of high-aspect-ratio polymer nanochannels using a novel Si nanoimprint mold and solvent-assisted sealing

Abstract

We present a low cost nanofabrication method to fabricate high-aspect-ratio (HAR) polymer nanochannels using a novel silicon nanoimprint mold fabrication technique and a solvent-assisted sealing method. These nanofluidic channels are being developed for single biomolecule detection. The silicon nanoimprint mold fabrication process is based on the combination of anisotropic etching of silicon by potassium hydroxide (KOH) solution and the local oxidation of silicon (LOCOS) process. The resulting high-aspect-ratio silicon mold has smooth sidewalls owing to the anisotropic KOH etching process along the silicon crystalline geometry as well as the LOCOS process. The nanostructures in the nanoimprint molds that form the nanochannels can be easily controlled by the initial micropattern sizes defined using conventional UV lithography and the oxidation time, making this technique a practical solution for low cost and high-throughput HAR silicon nanoimprint mold fabrication. Nanoimprint molds having aspect ratios of more than 1:5.5 (width: 200 nm, height: 1.1 lm, length: 1 cm) were successfully fabricated. Nanoimprinting technique was used to create poly(methyl methacrylate) (PMMA) nanotrenches out of this nanoimprint mold. A novel solvent-assisted sealing technique was developed in order to seal the HAR PMMA nanotrenches. This technique enables the generation of nanochannels with various nanoscale dimensions without the need for complicated and expensive nanolithography tools.

Monolithic fabrication of nanochannels using core–sheath nanofibers as sacrificial mold

“…Nanochannels with a non-circular crosssection can be fabricated by patterning nanoscale structures as the sacrificial material using standard photolithography, E-beam lithography, or phase shift lithography, and removing the sacrificial material in a subsequent process (Nichols et al 2008;Lin et al 2007;Guder et al 2010). Slight variations include creating the sacrificial material by thermal oxidation and removing it using chemicalmechanical-polishing (CMP) (Lee et al 2003) or reducing the channel dimensions from micrometer regime to nanometer regime by local oxidation (Mao and Han 2009;Cho et al 2008Cho et al , 2010. Although these methods can position nanochannels precisely with well-controlled dimensions, fabrication complexity and requirement of high-cost fabrication equipments hinder the wide applications.…”

Electrokinetic transport through nanochannels

“…Usually, Poisson-Boltzmann equation is used to find the electric potential in the microchannels; Helmholtz-Smoluchowski theorem is commonly utilized to model the electroosmotic flow through the microchannels. With the advancement of nano-fabrication technology [5], more and more attention has been paid to transport phenomena in devices involving nanochannels [6][7][8][9]. By reducing the dimensions of the channels to the submicron and nanoscales, these theories may not be applicable anymore.…”

High process yield rates of thermoplastic nanofluidic devices using a hybrid thermal assembly technique

“…The common modes employed for enclosing thermoplastic nanochannels are thermal or solvent-assisted fusion bonding. 26 Thermal fusion bonding a substrate to a cover plate of the same material has been executed by: (i) Heating the substrate and cover plate to a temperature slightly above their T g while applying a constant pressure allowing the polymer chains to diffuse between the contact surfaces; or (ii) bonding at a temperature lower than the T g of the material by using UV/O 3 or oxygen plasma treatment of the substrate and cover plate prior to chip assembly, thereby reducing the T g of the first few monolayers of material. 15–17, 27, 28 Although both approaches have been reported to produce high tensile strength between the cover plate and substrate, the first approach is typically discouraged for assembly of thermoplastic nanofluidic devices because it results in bulk polymer flow and significant deformation or collapse of the nanochannels (40% and 60% deformation for PMMA and COC, respectively) rendering devices unusable in most cases ( i.e ., low process yield rates).…”

“…Likewise, solvent-assisted bonding suffers from problems associated with dimensional stability because the solvent can soften the plastic material leading to material dissolution. 26 Hence, there remains the need for the development of methods for assembling thermoplastic nanochannels with high bond strengthes while maintaining structural integrity and producing high process yield rates.…”