Helin Zou

Fabrication of two dimensional polyethylene terephthalate nanofluidic chip using hot embossing and thermal bonding technique

We present in this paper a method for obtaining a low cost and high replication precision 2D (two dimensional) nanofluidic chip with a PET (polyethylene terephthalate) sheet, which uses hot embossing and a thermal bonding technique. The hot embossing process parameters were optimized by both experiments and the finite element method to improve the replication precision of the 2D nanochannels. With the optimized process parameters, 174.67u2009±u20094.51u2009nm wide and 179.00u2009±u20094.00u2009nm deep nanochannels were successfully replicated into the PET sheet with high replication precision of 98.4%. O2 plasma treatment was carried out before the bonding process to decrease the dimension loss and improve the bonding strength of the 2D nanofluidic chip. The bonding parameters were optimized by bonding rate of the nanofluidic chip. The experiment results show that the bonding strength of the 2D PET nanofluidic chip is 0.664u2009MPa, and the total dimension loss of 2D nanochannels is 4.34u2009±u20097.03u2009nm and 18.33u2009±u20099.52u2009nm, in width and depth, respectively. The fluorescence images demonstrate that there is no blocking or leakage over the entire micro- and nanochannels. With this fabrication technology, low cost polymer nanochannels can be fabricated, which allows for commercial manufacturing of nano-components.

Silicon microcontact printing engines

A method of self-aligned, microcontact printing that avoids the need for dedicated alignment and stamping equipment is demonstrated. Complete miniature print engines combining elastically supported print heads with alignment structures that mate with corresponding features on etched substrates to allow mechanical registration are constructed from silicon parts. The impression can be transferred manually or using an in-built mechanism such as electrostatic actuation. 10 mm × 10 mm prototypes are fabricated using microelectromechanical systems technology, using a wafer-scale process based on deep reactive ion etching of either bulk silicon or bonded silicon-on-insulator wafers to form all mechanical parts and polydimethylsiloxane spray coating of etched surfaces to form soft stamps. Electromechanical characterization is performed and manual and electrostatic microcontact printing are both demonstrated through 1-hexadecanethiol ink transfer onto gold-coated surfaces over a 5 mm × 5 mm area with a minimum feature size of ≈2 µm.

Low auto-fluorescence fabrication methods for plastic nanoslits.

Plastic nanofluidic devices are becoming increasingly important for biological and chemical applications. However, they suffer from high auto-fluorescence when used for on-chip optical detection. In this study, the auto-fluorescence problem of plastic nanofluidic devices was remedied by newly developed fabrication methods that minimise their auto-fluorescence: one by depositing a gold (Au) layer on them, the other by making them ultra-thin. In the first method, the Au layer [minimum thickness is 40 nm on 150 μm SU-8, 50 nm on 1 mm polyethylene terephthalate (PET), and 40 on 2 nm polymethyl methacrylate (PMMA)] blocks the auto-fluorescence of the polymer; in the second method, auto-fluorescence is minimised by making the chips ultra-thin, selected operating thickness of SU-8 is 20 μm, for PET it is 150 μm, and for PMMA it is 0.8 mm.

A single-sided process for differentially cooled electrothermal micro-actuators

A simple method for increasing the thermal efficiency of shape bimorph electrothermal micro-actuators is proposed, based on a reduction of gas conduction cooling beneath the hot arms by a deep, localized undercut. A single-sided, single-mask SCREAM-type process for fabricating differentially cooled actuators in a bonded silicon-on-insulator material is demonstrated. The process uses deep reactive ion etching and undercut to form suspended parts and isotropic reactive ion etching and lift-off of sacrificial shields to form localized mesas. The advantage of the method is confirmed using folded electrothermal actuators, and an approximate halving of the drive power is demonstrated by variations in the substrate profile in the vicinity of a series of actuators with the same mechanical design.

A novel bonding method for fabrication of PET planar nanofluidic chip with low dimension loss and high bonding strength

Plastic planar nanofluidic chips are becoming increasingly important for biological and chemical applications. However, the majority of the present bonding methods for planar nanofluidic chips suffer from high dimension loss and low bonding strength. In this work, a novel thermal bonding technique based on O2 plasma and ethanol treatment was proposed. With the assistance of O2 plasma and ethanol, the PET (polyethylene terephthalate) planar nanofluidic chip can be bonded at a low bonding temperature of 50 °C. To increase the bonding rate and bonding strength, the O2 plasma parameters and thermal bonding parameters were optimized during the bonding process. The tensile test indicates that the bonding strength of the PET planar nanofluidic chip can reach 0.954 MPa, while the auto-fluorescence test demonstrates that there is no leakage or blockage in any of the bonded micro- or nanochannels.

Self-aligned micro contact printing using MEMS

Aligned, multilevel micro contact printing without dedicated printing equipment is demonstrated. Miniature print engines are constructed from silicon parts using MEMS technology. The method is extended to include electrostatically driven patterning of flexible substrates.