Polymer templates realized through a combination of block
copolymer
lithography (BCL) and nanoimprint lithography (NIL) are used to direct
atomic layer deposition (ALD) to obtain high-quality ZnO nanopatterns.
These patterns present a uniform array of ZnO nanostructures with
sub-100 nm feature and spatial resolutions, exhibiting narrow distributions
in size and separation, and enhanced mechanical stability. The process
benefits from the high lateral resolutions determined by the copolymer
pattern, controlled growth rates, material quality and enhanced mechanical
stability from ALD and repeatability and throughput from NIL. The
protocol is generic and readily extendible to a range of other materials
that can be grown through ALD. By virtue of their high feature density
and material quality, the electrical characteristics of the arrays
incorporated within MOS capacitors display high hole-storage density
of 7.39 × 1018 cm–3, excellent retention
of ∼97% (for 1000 s of discharging), despite low tunneling
oxide thickness of 3 nm. These attributes favor potential application
of these ZnO arrays as charge-storage centers in nonvolatile flash
memory devices.
Fabrication methodologies with high precision and tenability for nanostructures of metal and metal oxides are widely explored for engineering devices such as solar cells, sensors, nonvolatile memories (NVM) etc. In this direction, metal and metal oxide nanopatterned arrays are the state-of-the-art platforms upon which the device structures are built where the tunable orderly arrangement of the nanostructures enhances the device performance. We describe here a coalition of fabrication protocols that employ block copolymer self-assembly and nanoimprint lithography (NIL) to obtain metal oxide nanopatterns with sub-100 nm spatial resolution. The protocols are easily scalable down to sub-50 nm and below.Nanopatterned arrays of ZnO created by using NIL assisted templates through area selective atomic layer deposition (ALD) and radio frequency (RF) sputtering find application in NVM and photovoltaics. We have employed NIL that produced nanoporous polymer templates using Si molds derived from block copolymer lithography (BCL) for pattern transfer into ZnO. The resulting ZnO nanoarrays were highly dense (8.6 x 10 9 nanofeatures per cm 2 ) exhibiting periodic feature to feature spacing and width that replicated the geometric attributes of the template. Such nanopatterns find application in NVM, where a change in the density and periodicity of the arrays influences the charge storage characteristics. The above assembly and patterning protocols were employed to fabricate metal-oxide-semiconductor (MOS) capacitor devices for investigating application in NVM. Patterned ZnO nanoarrays were used as charge storage centres for the MOS capacitor devices. Preliminary results upon investigating the flash memory performance showed good flat-band voltage hysteresis window at a relatively low operating voltage due to high charge trap density.
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