Preparation, characterization, and electrical properties of epitaxial NbO₂thin film lateral devices

Abstract

Epitaxial NbO 2 (110) films, 20 nm thick, were grown by pulsed laser deposition on Al 2 O 3 (0001) substrates. The Ar/O 2 total pressure during growth was varied to demonstrate the gradual transformation between NbO 2 and Nb 2 O 5 phases, which was verified using x-ray diffraction, x-ray photoelectron spectroscopy, and optical absorption measurements. Electric resistance threshold switching characteristics were studied in a lateral geometry using interdigitated Pt top electrodes in order to preserve the epitaxial crystalline quality of the films.Volatile and reversible transitions between high and low resistance states were observed in epitaxial NbO 2 films, while irreversible transitions were found in case of Nb 2 O 5 phase. Electric field pulsed current measurements confirmed thermally-induced threshold switching.

The role of defects in the electrical properties of NbO2 thin film vertical devices

“…It is also possible to induce MIT in NbO 2 by applying an electric field, where joule heating produced by the applied electric field can easily cause this material to undergo a MIT. 9 Reversible threshold switching in current has been reported mostly using amorphous NbO 2 films, where the current turns off immediately after lowering the input voltage (V in ) below the threshold voltage (V th ). 3,[10][11][12][13] Current-voltage (IV ) characteristics usually exhibit current-controlled (s-type) negative differential resistance (dV /dI < 0) while switching from a low current semiconducting to a high current metallic state.…”

“…10,18,19 Previous reports on NbO 2 thin films have focused on a broad range of film qualities, ranging from amorphous 16,20 to epitaxial. 9,21,22 (100 nm)/Si wafers provided by Micron Technologies with nominal surface roughnesses < 0.5 nm were used as substrates for growth via pulsed laser deposition (PLD). The distance between the 99.99% purity NbO 2 target and substrate was 7.3 cm.…”

“…epitaxial relationship of the film with the substrate. 9 Figure 2 shows XRR data with corresponding AFM surface scans for both films. Fits of the XRR data using the GenX software 24 demonstrated that both of the films had identical film thickness (31 ± 0.8 nm) with identical roughness (0.8 ± 0.1 nm) within the measurement uncertainties.…”

Structural, electrical, and optical properties of polycrystalline NbO2 thin films grown on glass substrates by solid phase crystallization

“…For example, we demonstrated that a 10‐nm‐thick NbO 2 seed layer improved the mobility of rutile SnO 2 thin films , which are promising for use as the transparent conductive electrodes of photovoltaic cells. Extensive studies on the use of NbO 2 thin films in electronic devices and fuel cells have been conducted. However, the performance of devices was mainly investigated in these studies; film growth and the physical properties of polycrystalline NbO 2 were not studied in detail .…”

STEM Video of Electronically-Driven Metal-Insulator Transitions in Nanoscale NbO 2 Devices

“…50 nm of NbO2 was deposited over the electrodes via pulsed laser deposition at 700 o C substrate temperature in 2 mTorr Ar+O2 growth atmosphere with 1% O2 content using an NbO2 ceramic target (AJA International.). Film quality and thickness were assessed with x-ray photoelectron spectroscopy, x-ray diffraction, and x-ray reflectometry, confirming the major NbO2 phase, which forms with an additional top Nb2O5 layer of 2 nm due to air exposure [2]. STEM video was obtained simultaneously from 3 different detectors, collecting electrons at low (bright field or BF), intermediate (dark field or DF), and higher scattering angles (high-angle dark field or HDF).…”