Structural and electrical characterization of polycrystalline NbO2 thin film vertical devices grown on TiN-coated SiO2/Si substrates

Abstract

We report on the electrical properties of polycrystalline NbO2 thin film vertical devices grown on TiN coated SiO2/Si substrates using pulsed laser deposition. First, we analyzed the thickness and contact size dependences of threshold switching of NbO2 films grown in 10 mTorr Ar/O2 mixed growth pressure, where 25.1%/74.9% of NbO2/Nb2O5 surface composition content was estimated by ex-situ x-ray photoelectron spectroscopy. The leakage current properties in the insulating state were dominated by trap-charge assisted Poole-Frankel conduction mechanism. The threshold switching and self-sustained current oscillatory behavior of films with different NbO2/Nb2O5 composition ratios was measured and analyzed. The second film was grown in lower (1 mTorr) growth pressure which resulted in a higher (34.2%/65.8%) NbO2/Nb2O5 film surface composition. The film grown in higher growth pressure demonstrated lower offstate leakage current, faster switching and self-sustained oscillations with higher frequency than the film grown in lower growth pressure.

Negative Differential Resistance Characteristics in Forming‐Free NbOx with Crystalline NbO2 Phase

“…Therefore, the deposited NbO x films typically consisted of the NbO, NbO 2 , and Nb 2 O 5 phases, despite the bulk composition of Nb:O ≈ 1:2. [ 26–29 ] In addition, the amorphous NbO x devices require an electroforming process. It is still controversial whether the electroforming process could create a crystalline NbO 2 phase region [ 30–32 ] or filaments of high‐current‐density oxygen vacancies.…”

Raman evidence for absence of phase transitions in negative differential resistance thin film devices of niobium dioxide

“…This often implies a thin layer film of NbO x (typically few tens of nm), probed vertically across its thickness, with the device area limited laterally by the size of one of the contacts which can also be typically a few tens of nm. This means a very small NbO 2 volume in the device [11,12]. Wang et al [13] fabricated Nb/NbO 2 /TiN sandwich vertical devices and studied the response of NbO 2 to an applied electric field.…”

“…We also investigate the occurrence of the clear hysterisis in our measurements in which the current is swept and the corresponding voltage measured. Some earlier works also find hysterisis in the I-V characteristics [9,12] while it has not been ( ) hysteresis is assumed to be the time required to attain thermal equilibrium in the effective sample volume after Joule heating, a hypothesis which is reinforced by diminishing hysteresis if the whole sample is progressively heated from outside. In the following we discuss such averaged, symmetrised I-V curves in the current-control regime for the different samples.…”

Engineering the Threshold Switching Response of Nb2O5-Based Memristors by Ti Doping

“…While memristive switching has been observed in a range of materials and device structures, two terminal metal–oxide–metal (MOM) devices based on niobium oxides have attracted particular attention because of their simple structure, reliability, and diverse switching characteristics. − The latter include non-volatile resistive switching, volatile threshold switching, and a combination of resistive and threshold switching, with the specific response depending on the film stoichiometry, crystallinity, electrode metals, device geometry, and operating conditions (e.g., maximum currents, bias polarity, etc.,). ,,− For example, devices based on NbO 2 and non-stoichiometric NbO x typically exhibit volatile threshold switching, − while those based on Nb 2 O 5 exhibit unipolar (or non-polar) switching when inert (e.g., Au and Pt) top and bottom electrodes are used , and threshold switching when one of the inert electrodes is replaced by a reactive metal. , The dependence on electrode metal highlights the fact that switching is sensitive to interface reactions and field-induced oxygen exchange between the electrode and oxide. ,, Understanding such dependencies is critical for engineering devices with well-defined switching characteristics and remains an active area of research.…”