FABRICATION AND INTEGRATION OF ONE- AND TWO-DIMENSIONAL MATERIALS FOR ADVANCED NANOSCALE DEVICES

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.