Research Papers

Fabrication of Centimeter Long, Ultra-Low Aspect Ratio Nanochannel Networks in Borosilicate Glass Substrates

[+] Author and Article Information
Marie Pinti

e-mail: pinti.3@osu.edu

Tanuja Kambham

e-mail: kambham.1@osu.edu

Bowen Wang

e-mail: wang.3161@osu.edu

Shaurya Prakash

e-mail: prakash.31@osu.edu
Mechanical and Aerospace
Engineering Department,
The Ohio State University,
Columbus, OH 43210

1Corresponding author.

Manuscript received July 25, 2013; final manuscript received August 15, 2013; published online October 3, 2013. Assoc. Editor: Abraham Wang.

J. Nanotechnol. Eng. Med 4(2), 020905 (Oct 03, 2013) (7 pages) Paper No: NANO-13-1042; doi: 10.1115/1.4025366 History: Received July 25, 2013; Revised August 15, 2013

Nanofluidic devices have a broad range of applications resulting from the dominance of surface-fluid interactions. Examples include molecular gating, sample preconcentration, and sample injection. Manipulation of small fluid samples is ideal for micro total analysis systems or lab on chip devices which perform multiple unit operations on a single chip. In this paper, fabrication procedures for two different ultra-low aspect ratio (ULAR) channel network designs are presented. The ULAR provides increased throughput compared to higher aspect ratio features with the same critical dimensions. Channel network designs allow for integration between microscale and nanoscale fluidic networks. A modified calcium assisted glass–glass bonding procedure was developed to fabricate chemically uniform, all glass nanochannels. A polydimethylsiloxane (PDMS)-glass adhesive bonding procedure was also developed as adhesive bonding allows for more robust fabrication with lower sensitivity to surface defects. The fabrication schemes presented allow for a broad array of available parameters for facile selection of device fabrication techniques depending on desired applications for lab on chip devices.

Copyright © 2013 by ASME
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Fig. 2

(a) A microscope image showing channel deformation in a 77 nm deep, 50 μm nominal width channel. (b) A microscope image showing channel deformation in a 77 nm deep, 100 μm nominal width channel fabricated without a metal mask. (c) A microscope image showing a visually uniform channel width for a 77 nm deep channel fabricated with a metal mask as marked by the white arrows.

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Fig. 1

A schematic representation of the two fluidic network designs. Design 1 had two micron depth channels connected by a bank of nanometer depth channels. The depth of each feature was controlled by the etching time. The microchannels were 3 cm long and 131 μm ± 1 μm wide with a typical depth of 8.0 μm ± 0.1 μm. The nanochannel array consisted of 3–6 nanochannels that were 0.5 cm long and 33 μm ± 1 μm wide. The depth of the nanochannels ranged from 16.0 nm ± 0.1 nm to 227 nm ± 5 nm. Design 2 had nanoscale depth features only. The upper branch was 1 cm long and 106 μm wide. At the Y-junction the channel split into two 56 μm wide branches. Depths of the “Y” nanochannel network ranged from 77 nm ± 6 nm to 446 nm ± 5 nm.

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Fig. 3

(a) A flow chart of channel network fabrication for Design 1. Briefly, a metal etch mask was applied to a piranha cleaned borosilicate substrate. UV lithography was used to pattern microchannel features. UV lithography with a modified spin process was used to create nanochannel pattern. (b) A schematic representation of the defect formed at the micronanochannel interface using standard UV lithography without a modified spin process. The photoresist did not fully fill the microchannel, leading to delamination at the micronanochannel interface. The nanochannels were fluidically connected by a ridge of the same depth as the nanochannels.

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Fig. 4

SEM images of the micro-nanochannel interface of the hybrid channel network (Design 1). Figure 4(a) shows the nanoscale defect caused by photoresist delamination resulting in fluidically connected nanochannels. The ridge connecting the channels was the same depth as the channel itself [21]. Figure 4(b) shows a device fabricated using the modified spin procedure, resulting in elimination of the defect.

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Fig. 6

A plot of measured current as a function of applied voltage for a 22 nm PDMS-glass device. A linear trend was observed suggesting that the in the voltage range tested the nanochannel permits ions to move across and is evidence for electrokinetic transport through nanochannels.

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Fig. 7

A cross section image of a 56 μm wide and 77 nm deep nanofluidic channel bonded using calcium assisted bonding. The channel height varies at different points in the channel from 62 to 77 nm, presumably due to cutting the nanochannels for imaging [28].

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Fig. 8

Microscope images of nanochannels of various depths filling with isopropyl alcohol in a capillary fill. Lines denoting the channel walls have been added to the image of the 77 nm deep channel for visual clarity.

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Fig. 5

An SEM image of a 227 nm deep 33 μm wide nanochannel bonded using a 2 μm thick PDMS adhesive layer [19]. The inset shows a zoomed in image of the channel cross section.



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