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

Abstract

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, 174.67 ± 4.51 nm wide and 179.00 ± 4.00 nm 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 0.664 MPa, and the total dimension loss of 2D nanochannels is 4.34 ± 7.03 nm and 18.33 ± 9.52 nm, 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.

FIG. 1.

SEM pictures of the 2D silicon nano-mold with features having width, height, and length of 175 nm, 180 nm, and 4 mm, respectively.

FIG. 2.

Schematic illustration of the nanofluidic chip fabrication process: (a) the alignment of PET substrate and nano-mold, (b) hot embossing, (c) the department of PET substrate and nano-mold, (d) fabricated 2D PET nanochannels, (e) the alignment of PET substrate and PET cover plate, (f) thermal bonding of PET substrate and PET cover plate, (g) fabricated 2D PET nanofluidic chip.

FIG. 3.

Model used for numerical simulation of the hot embossing process.

FIG. 4.

Definition of replication precision.

FIG. 5.

Simulation results: (a) pressure optimization, (b) temperature optimization, and (c) pressure re-optimization according to the replication precision of 2D PET nanochannels.

FIG. 6.

The damaged 2D silicon nano-mold, most of the nano-protrusions in the nano-mold has been damaged under embossing pressure of 2.5 MPa.

FIG. 7.

Comparison of experiment and simulation results. (a)–(d) Comparison of experiment and simulation for 2D nanochannel profiles at the temperature of 65 °C, 75 °C, 85 °C, and 95 °C, respectively. The SEM images show the experiment results, while the inserted views show the simulation results. (e) Comparison of the replication precision between experiment and simulation results.

FIG. 8.

The influence of O₂ plasma treatment power (a) and time (b) on the contact angles of the PET substrate.

FIG. 9.

Experiment results of the thermal bonding process: (a) bonding pressure optimization, (b) bonding temperature optimization, and (c) bonding pressure re-optimization according the bonding rate of the 2D PET nanofluidic chip.

FIG. 10.

Fluorescence images of the nanochannels filled with a fluorescent dye solution for the nanofluidic chips bonded at different times of (a) 20 min, (b) 30 min, and (c) 40 min.

FIG. 11.

The comparison of Young modulus of native PET substrates and the PET substrate treated by the O₂ plasma with chamber power of 15 W, time of 35 s, and a pressure of 60 Pa.

FIG. 12.

The SEM images show the profile of 2D PET nanochannels. The measured profiles are (a) 174.67 ± 4.51 nm wide and 179.00 ± 4.00 nm deep nanochannels before thermal bonding and (b) 170.33 ± 2.52 nm wide and 172.00 ± 3.00 nm deep nanochannels after thermal bonding with bonding temperature of 69 °C, pressure of 0.2 MPa, and time of 30 min observed by the interchange method.

FIG. 13.

The surface topography of the PET cover plate, the maximum height of the nano-protrusions in the cover plate is 11.33 ± 2.52 nm. The PET cover plate was boned with PET substrate (with nanochannels) under bonding temperature of 69 °C, pressure of 0.2 MPa, and time of 30 min.

FIG. 14.

The microscope images of the PET microchannels: (a) 117.67 ± 2.08 μm wide and 16.47 ± 1.30 μm deep microchannels before thermal bonding and (b) 115.83 ± 0.67 μm wide and 16.00 ± 0.20 μm deep microchannels after thermal bonding with a bonding temperature of 69 °C, pressure of 0.2 MPa and time of 30 min observed by the interchange method.

FIG. 15.

The surface topography of the PET cover substrate, the maximum height of the micro-protrusion in the cover plate is 0.49 ± 0.04 μm.

FIG. 16.

Photograph of the 2D PET nanofluidic chip using the hot embossing technique. The enlarged view shows the fluorescence image of the nanochannels.