MOBILITY ENGINEERING Produced by SAE Media Group
MOBILITY ENGINEERING
Magazines
Magazine cover

Current Issue

Archives

Magazine cover

Current Issue

Archives

Magazine cover

Current Issue

Archives

Magazine cover

Current Issue

Archives

Fabrication and Electrical Characterization of Correlated Oxide Field Effect Switching Devices for High Speed Electronics

The response of correlated oxides to strong electric fields and their dynamics is investigated using electrical transport measurements and electronic structure studies.

Metal insulator transitions (MITs) in oxides are an intriguing problem from both a fundamental materials physics and an applied technology perspective. Though the precise roles of electron correlations and lattice distortions on the phase transition remains an active area of research, many recent theoretical studies have suggested intimate interplay among the orbital splitting/polarization, correlation effects, and Peierls dimerization in the 3d1 system. Occupied states have been probed by x ray photoelectron spectroscopy (XPS), and a rough structure of unoccupied 3d-like states have been deduced by O K-edge x-ray absorption measurements. NbO2, a 4d1 system, like VO2 crystallizes in a distorted rutile type structure with Nb dimers and undergoes a temperature induced MIT, albeit at a considerably higher temperature of ~1083 K. It is commonly accepted that because 4d orbital valence states are more dispersed in both space and energy, Mott physics is less important in 4d transition metal oxides than in 3d ones. Along this line of reasoning, it is perhaps surprising that the insulating state of NbO2 persists to higher temperatures than that of VO2.

Optical Conductivity of Materials Under Test

A proposed explanation for this difference is that the Peierls effect in NbO2 is stronger due to larger Nb metal-metal overlap of 4d orbitals, leading to greater orbital splitting between occupied d|| states and the unoccupied eg-states; however, given the many attempts to revise and improve theoretical and computational studies of VO2, the physical and electronic properties of NbO2 also should be examined more thoroughly. Currently, there are few experimental studies that provide insight into the electronic structure of NbO2.

There have been diffraction, calorimetry, electrical, and magnetic studies on bulk NbO2, which have shown that it transforms from a high temperature rutile structure metal to a low temperature Nb dimerized diamagnetic insulator at ~1083 K. Recently epitaxial NbO2 thin films have been grown on (0001) Al2O3, (111) MgO, (111) MgAl2O4, and (111) perovskite oxide substrates. The key to achieving epitaxy of (100) rutile type compounds is exploiting substrate surfaces with eutactic planes.

Epitaxial NbO2 films were grown on (0001) Al2O3 by DC reactive sputtering of a Nb metal target at 650°C, 200W, 10 mTorr, 7.5 sccm O2, and 42.5 sccm Ar. An epitaxial (010) VO2 film was grown on (0001) Al2O3 by RF sputtering a V2O5 ceramic target at 450°C, 150W, 5 mTorr, 1.3 sccm O2, and 48.7 sccm Ar. Deposition conditions were optimized to both achieve stoichiometric phases as well as film smoothness for reliable ellipsometry measurements. X-ray reflectivity was used to measure the film thickness, and x-ray diffraction was used for phase and orientation determination.

Raman spectroscopy was performed in a confocal microscope using a 532 nm laser source; a filter prevents the collection of signals <170 cm-1. Electrical transport measurements were performed in the van der Pauw geometry; contact pads of 5 nm of Ti and then 50 nm of Au were sputtered on the films. Ex situ XPS scans were taken with Al K-alpha radiation and with an electron flood gun that prevents charging, and the samples were grounded to the spectrometer. The energy scale of the XPS data is referenced so that Au4f7/2 peak is at 84.0 eV.

The real optical conductivity of V1, N1, and N2 are shown in Figs. 1(a) (c). Sum rule analysis [Fig. 1(d)] can be performed on optical conductivity spectra to determine the effective number of electrons neff per formula unit of NbO2 accounting for optical excitation from 0 to a cutoff energy of E.

This work was done by Shriram Ramanathan of Harvard University for the Air Force Research Laboratory. AFRL-0285

Topics:
Aerospace Electrical systems Electronic Components Electronic equipment Electronics Electronics & Computers Fabrication Instrumentation Insulation Manufacturing processes Materials properties Measuring Instruments Metals Metrology Optical Components Optics Photonics Research and development Semiconductors & ICs Sensors and actuators Spectroscopy Switches Test & Measurement
This Brief includes a Technical Support Package (TSP).
Document cover
Fabrication and Electrical Characterization of Correlated Oxide Field Effect Switching Devices for High Speed Electronics

(reference AFRL-0285) is currently available for download from the TSP library.

Don't have an account?

More From SAE Media Group

    Magazine cover
    Aerospace & Defense Technology Magazine

    This article first appeared in the April, 2020 issue of Aerospace & Defense Technology Magazine (Vol. 5 No. 2).

    Read more articles from this issue here.

    Read more articles from the archives here.

    Overview

    The document titled "Fabrication and Electrical Characterization of Correlated Oxide Field Effect Switching Devices for High Speed Electronics" is a final report authored by Shriram Ramanathan, covering research conducted from June 1, 2012, to July 31, 2015. The report is sponsored by the Air Force Office of Scientific Research and focuses on the investigation of thin film correlated oxides, which are materials that exhibit unique electronic properties due to strong electron correlations.

    The primary objective of the research was to explore the electrical transport characteristics and electronic structures of various correlated oxide systems, specifically VO2, SmNiO3, and NbO2. These materials are notable for their thermal insulator-metal transitions, which are critical for applications in high-speed electronics. The study emphasizes the microscopic connections between insulator-metal switching, orbital occupancy, and electron-phonon interactions, highlighting how these factors influence the performance of electronic devices.

    The report details the methodologies employed in the fabrication and characterization of field effect switching devices made from these correlated oxides. It discusses the experimental techniques used to measure electrical transport properties, including the response of these materials to strong electric fields. The findings reveal significant insights into the dynamics of correlated oxides, particularly their potential for use in next-generation electronic applications.

    The document also includes various figures and data representations that illustrate the Raman shift and intensity of different materials, providing a visual understanding of the electronic properties being studied. The research contributes to the broader understanding of how correlated oxides can be utilized in the development of advanced electronic devices, potentially leading to improvements in speed and efficiency.

    In summary, this report presents a comprehensive study of correlated oxides, focusing on their fabrication and electrical characterization for high-speed electronics. It underscores the importance of understanding the fundamental properties of these materials to harness their capabilities in future technological applications. The findings are expected to pave the way for innovations in electronic device design, particularly in fields requiring rapid switching and high performance.

    Top Stories

    INSIDERDesign

    Feature Image Venus Aerospace’s Rotating Detonation Rocket Engine Completes First Flight...

    INSIDERDesign

    Feature Image Bombardier is Digitally Upgrading its Aircraft Design, Engineering and...

    INSIDERDefense

    Feature Image How the US Army is Advancing Research in Robotics, AI and Autonomy

    INSIDERManned Systems

    Feature Image New Copper Alloy Could Provide Breakthrough in Durability for Military Systems

    Original EquipmentManned Systems

    Feature Image ACT Expo 2025: Heavy-Duty EVs, H2 Trucks and Tariff Talk Dominate Day One

    Technology ReportPower

    Feature Image ICE and Hybrid-Electric Propulsion Show Staying Power

    Webcasts