Abstract
In the present study, we quantitatively evaluated dielectric breakdown in silicon-based micro- and nanofluidic devices under practical electrophoretic conditions by changing the thickness of the insulating layer. At higher buffer concentration, a silicon nanofluidic device with a 100 nm or 250 nm silicon dioxide layer tolerated dielectric breakdown up to ca. 10 V/cm, thereby allowing successful electrophoretic migration of a single DNA molecule through a nanochannel. The observed DNA migration behavior suggested that parameters, such as thickness of the insulating layer, tolerance of dielectric breakdown, and bonding status of silicon and glass substrate, should be optimized to achieve successful electrophoretic transport of a DNA molecule through a nanopore for nanopore-based DNA sequencing applications.
Highlights
Micro- and nanofabrication of silicon semiconductors is well established and is generally easier than fabrication of glass or quartz
For quantitative evaluation of the effectiveness of the silicon dioxide layer as an insulation layer, the applied voltage was raised by 1 V every 2 s from 0 to 15 V in a stepwise manner (Figure 2)
One possible reason is that the surface of the silicon device used in the previous study was prepared using a 207 nm layer of dry thermal oxide, which produces an Si–SiO2 interface with excellent electrical properties, whereas the silicon dioxide layer on the surface of our device was deposited via electron cyclotron resonance (ECR) plasma chemical vapor deposition (CVD)
Summary
Micro- and nanofabrication of silicon semiconductors is well established and is generally easier than fabrication of glass or quartz. To eliminate the intrinsic properties of Si as a semiconductor, Si near the surface is often converted to SiO2 through methods such as dry and wet thermal oxidation [2], low-pressure chemical vapor deposition (CVD) [3], and plasma-enhanced CVD [4], prior to bonding with a cover substrate. The SiO2 layer grows up to about 2.5 μm thick, when the temperature is raised to 800 ◦C and the silicon wafer is exposed to pure steam Both of the methods are a “non-linear” growth process, because it becomes more difficult for oxygen to penetrate the previously formed SiO2 layer. The use of polymer substrates is another alternative for insulating microfluidic devices, and is suitable for electrophoretic experiments because they enable high voltage operation and are fabricated [10]
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