The role of nitrogen doping on the stability and memory window of resistive state switching in N-doped Ta₂O₅ deposited by atomic layer deposition is elucidated. Nitrogen incorporation increases the stability of resistive memory states which is attributed to neutralization of electronic defect levels associated with oxygen vacancies. The density functional simulations with the screened exchange hybrid functional approximation show that the incorporation of nitrogen dopant atoms in the oxide network removes the O vacancy midgap defect states, thus nullifying excess defects and eliminating alternative conductive paths. By effectively reducing the density of vacancy-induced defect states through N doping, 3-bit multilevel cell switching is demonstrated, consisting of eight distinctive resistive memory states achieved by either controlling the set current compliance or the maximum voltage during reset. Nitrogen doping has a threefold effect: widening the switching memory window to accommodate the more intermediate states, improving the stability of states, and providing a gradual reset for multi-level cell switching during reset. The N-doped Ta₂O₅ devices have relatively small set and reset voltages (< 1 V) with reduced variability due to doping.

Resistive random access memory (RRAM) devices with Ni/AlO_x/Pt-structure were manufactured by deposition of a solution-based aluminum oxide (AlO_x) dielectric layer which was subsequently annealed at temperatures from 200 °C to 300 °C, in increments of 25 °C. The devices displayed typical bipolar resistive switching characteristics. Investigations were carried out on the effect of different annealing temperatures for associated RRAM devices to show that performance was correlated with changes of hydroxyl group concentration in the AlO_x thin films. The annealing temperature of 250 °C was found to be optimal for the dielectric layer, exhibiting superior performance of the RRAM devices with the lowest operation voltage (10⁴), the narrowest resistance distribution, the longest retention time (>10⁴ s) and the most endurance cycles (>150).

The holy grail of achieving efficient operation of infrared (IR) rectennas continues to be the realization of a high performance rectifier. In this paper, we have fabricated metal–insulator–metal (MIM) diodes based on TiO2, ZnO, and NiO thin films using shadow mask evaporation, photolithography, and sputtering. The electron affinities of oxides have been measured by a combination of variable angle spectroscopic ellipsometry and x-ray photoelectron spectroscopy, as well as deduction from the extraction of metal/oxide barrier heights of Fowler–Nordheim tunneling plots. Our results confirm a low value for the electron affinity of NiOx of ∼2.1–2.5 eV, which correlates with the high zero-bias dynamic resistance (RD0) of ∼500 kΩ of an associated MIM diode. These values render NiOx to be unsuitable for use in a rectenna device. Better performance has been observed from diodes based on TiO2 and ZnOx films. The best rectification performance was achieved for a Au/2.6 nm ZnOx/Cr diode, scaled down to 1 μm2 device area, showing a zero-bias dynamic resistance of RD0 = 71 kΩ, zero-bias responsivity β0 = 0.28 A/W, and a coupling efficiency of ηc = 2.4 × 10−5% for rectification at 28.3 THz. The main significance of this study is that it employs a methodology whereby key parameters of the MIM stack are derived from physical measurements, which are then used to assist in the fitting of electrical current–voltage data to produce a reliable appraisal of diode performance in an IR rectenna.

The effect of fluorine doping on the switching stability of Ta₂O₅ resistive random access memory devices is investigated. It shows that the dopant serves to increase the memory window and improve the stability of the resistive states due to the neutralization of oxygen vacancies. The ability to alter the current in the low resistance state with set current compliance coupled with large memory window makes multilevel cell switching more favorable. The devices have set and reset voltages of <1 V with improved stability due to the fluorine doping. Density functional modeling shows that the incorporation of fluorine dopant atoms at the two-fold O vacancy site in the oxide network removes the defect state in the mid bandgap, lowering the overall density of defects capable of forming conductive filaments. This reduces the probability of forming alternative conducting paths and hence improves the current stability in the low resistance states. The doped devices exhibit more stable resistive states in both dc and pulsed set and reset cycles. The retention failure time is estimated to be a minimum of 2 years for F-doped devices measured by temperature accelerated and stress voltage accelerated retention failure methods.

Despite the tremendous efforts in the past decade devoted to the development of filamentary resistive-switching devices (RRAM), there is still a lack of in-depth understanding of its over-reset phenomenon. At higher reset stop voltages that exceed a certain threshold, the resistance at high resistance state reduces, leading to an irrecoverable window reduction. The over-reset phenomenon limits the maximum resistance window that can be achieved by using a higher V _reset , which also degrades its potential in applications such as multi-level memory and neuromorphic synapses. In this letter, the over-reset is investigated by cyclic reset operations with incremental stop voltages, and is explained by defect generation in the filament constriction region of Ta ₂ O ₅ RRAM devices. This is supported by the statistical spatial defects profile obtained from the random telegraph noise based defect probing technique. The impact of forming compliance current on the over-reset is also evaluated.

We present physical and electrical characterization of niobium-doped zinc oxide (NbZnO) for thin film transistor (TFT) applications. The NbZnO films were deposited using atomic layer deposition. X-ray diffraction measurements indicate that the crystallinity of the NbZnO films reduces with an increase in the Nb content and lower deposition temperature. It was confirmed using X-ray photoelectron spectroscopy that Nb⁵⁺ is present within the NbZnO matrix. Furthermore, photoluminescence indicates that the band gap of the ZnO increases with a higher Nb content, which is explained by the Burstein-Moss effect. For TFT applications, a growth temperature of 175 °C for 3.8% NbZnO provided the best TFT characteristics with a saturation mobility of 7.9 cm²/Vs, the current On/Off ratio of 1 × 10⁸, and the subthreshold swing of 0.34 V/decade. The transport is seen to follow a multiple-trap and release mechanism at lower gate voltages and percolation thereafter.