FABRICATION AND INTEGRATION OF ONE- AND TWO-DIMENSIONAL MATERIALS FOR ADVANCED NANOSCALE DEVICES
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Date
2020-04
Authors
Kemelbay, Aidar
Journal Title
Journal ISSN
Volume Title
Publisher
Nazarbayev University School of Engineering and Digital Sciences
Abstract
As the miniaturization of electronic circuits reach physical limits, new materials
and physical phenomenon need to be exploited to further increase device density
and efficiency. A number of approaches have been proposed. One of the common
approaches in the scientific community is the search to understand and practically
fabricate novel materials and devices at the nanoscale. In this work, we present
several nanofabrication processes and unique synthetic methods that we have
developed to achieve novel 1D and 2D semiconducting, dielectric, and ferroelectric
materials, relevant for the integration in advanced nanoscale devices.
In particular, single-walled carbon nanotubes (CNTs) were synthesized and
integrated into bottom- and top-gate field effect transistors. We demonstrated
a novel CNT surface pretreatment method that enables uniform and conformal
ALD coating of suspended nanotubes with various dielectric materials. Obtained
all-oxide TiO2-Al2O3 compound high-k dielectric showed an improved dielectric
permittivity.
Another class of semiconductor that we investigated, was transition metal
dichalcogenide (TMD) layered thin film materials. We developed a novel synthetic
method that we termed “lateral conversion,” which was used to grow WS2, WSe2,
MoS2 and MoSe2 van der Waals materials. In this method, a metal-oxide layer
is converted into TMD material using a chalcogenation reaction that propagates
laterally between two inert silica layers. The method results in a multilayer structure
with TMD material covered by a capping layer that protects it from the environment,
contamination, and oxidation. It was shown that the technique provides control
over the TMD position, shape, and thickness with sub-micron precision, at wafer
scale.
A third class of materials that was studied in this work are hafnia-based
ferroelectric thin films. The ability to integrate ferroelectric thin films into electronic devices with atomic layer deposition (ALD) has been a long-standing
dream. With the discovery of ferroelectric properties in ALD hafnium oxide, the
realization of some advanced architecture devices became one step closer. Here,
ALD was used to synthesize Hf0.5Zr0.5O2, with precisely tuned stoichiometry.
Next, the crystallization of initially amorphous Hf0.5Zr0.5O2 was performed using
widely researched rapid thermal annealing (RTA), as well as by using intense
pulsed ion beams (IPIBs), which was done for the first time for such application.
RTA-produced ferroelectric thin films, showed successful orthorhombic phase
stabilization and annealing-temperature-dependent remnant polarization, whereas
early IPIBs experiments demonstrated the ability to crystallize HfO2, ZrO2 and
Hf0.5Zr0.5O2 thin films, inducing different crystallographic phases.
Description
Keywords
single-walled carbon nanotubes, carbon nanotubes, CNTs, transition metal dichalcogenide, TMD, CNT surface, hafnia-based ferroelectric thin films, atomic layer deposition, ALD, intense pulsed ion beams, IPIBs, Research Subject Categories::TECHNOLOGY