Oxide Electrode Interface Research Articles

Set compliance current induced resistive memory characteristics of W/Hf/HfOx/TiN devices

In this paper, the authors have investigated the effect of current compliance during the set process on the resistive memory characteristics and switching mechanism of W/Hf/HfOx/TiN devices. The presence of an Hf thin cap layer enables the stable and uniform bipolar resistive switching behavior. Compliance current can modify the barrier height at the oxide-electrode interface by increasing or reducing the oxygen vacancies and induce different switching mechanisms. Low compliance current (50 μA) based switching confirms the Schottky conduction mechanism due to the interfacial effects, while high compliance current (500 μA) involves the ohmic conduction mechanism, signifying the formation of a conductive filament. No significant dispersion of reset current and reset voltage has been found for each set compliance current varying from 50 to 500 μA, indicating uniform performance of the devices. The devices also exhibited a read endurance up to 2000 cycles.

Raman Microscopy Insights on the Out-of-Plane Electrical Transport of Carbon Nanotube-Doped PEDOT:PSS Electrodes for Solar Cell Applications.

In the present report, we focused on the study of the out-of-plane electrical transport of multiwalled carbon nanotube (MWCNT)-doped poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) composites (PEDOT:PSS-MWCNTs) as electrodes for solar cell applications. The out-of-plane direct current and alternating current electrical transport, rarely studied but not less relevant, was additionally supported with in-plane and out-of-plane confocal Raman microscopy and grazing incidence small-angle X-ray scattering characterizations. The main relevance of our study is the monitoring of the polymer structure all across the polymeric film by using confocal Raman spectroscopy and its correlation with electrical transport. Modifications in the PEDOT benzenoid and quinoid conformations were observed in the vicinities of MWCNTs, and the enrichment of PSS at the indium tin oxide electrode interface was also evidenced. In consequence, the low MWCNT loadings into PEDOT:PSS lead to an increase of the out-of-plane conductivity, but the heavier MWCNT loadings lead to a drastic decrease. The tuning of the doping level of these polymer composites and the understanding of the interface structure are crucial to fabricate electrodes with higher out-of-plane conductivities for organic solar cell applications.

Intrinsic Resistance Switching in Amorphous Silicon Suboxides: The Role of Columnar Microstructure

We studied intrinsic resistance switching behaviour in sputter-deposited amorphous silicon suboxide (a-SiOx) films with varying degrees of roughness at the oxide-electrode interface. By combining electrical probing measurements, atomic force microscopy (AFM), and scanning transmission electron microscopy (STEM), we observe that devices with rougher oxide-electrode interfaces exhibit lower electroforming voltages and more reliable switching behaviour. We show that rougher interfaces are consistent with enhanced columnar microstructure in the oxide layer. Our results suggest that columnar microstructure in the oxide will be a key factor to consider for the optimization of future SiOx-based resistance random access memory.

Thermodynamic stability of sulfide electrolyte/oxide electrode interface in solid-state lithium batteries

Thermodynamic analyses were made on the sulfide electrolyte–oxide electrode interfaces in all solid-state lithium batteries using chemical potential diagrams, constructed under the local thermodynamic equilibrium approximation. The chemical potential diagrams were first made for the Li–S–O system and the Li–Co–O system, to show that the stable region for the Li2S phase and the combined region of LiCoO2/CoO2 phases do not have a common overlap area in the same log a(Li) vs. log p(O2) plot. Three dimensional diagrams of the Li–Co–S–O system and the Li–Co–P–S–O system were constructed by fixing log a(Li) at selected values. Based on the constructed diagrams, the chemical nature of the sulfide electrolyte–oxide electrode interface could be considered from both the high temperature electrochemical and chemical points of view. This aided the interpretation of recently reported microscopic analyses on the interfaces. The causes of the “high resistive layer” and cobalt diffusion can be reasonably interpreted as chemical processes, caused by the high Li potential during charging. The results present in this paper are also compared to recent results from theoretical calculations on the energetics of interface structure. The possible applications of the here presented chemical diagrams are discussed in terms of the stoichiometric numbers and energies of the local interface atomic arrangement.

Micro gap effect on dilute H2S sensing properties of SnO2 thin film microsensors

The micro gap effect has been investigated on dilute H2S sensing using SnO2 thin film microsensors equipped with Au or Pt micro gap electrode. The micro gap electrode was fabricated by means of MEMS techniques (photolithography and FIB) and the gap size was varied in the range of 0.1–1 μm. For the SnO2 sensors equipped with Au micro gap electrode, the sensor response to dilute H2S was slightly increased with decreasing gap size, suggesting the small micro gap effect. The sensor response was divided into that at oxide–electrode interface (Si) and at oxide grain boundary (Sgb). It was found that the small Sgb/Si ratio was responsible for the small micro gap effect and that the high sensor response at grain boundary was characteristic in SnO2–H2S system. On the other hand, the SnO2 sensors with Pt micro gap electrode, the clear and large micro gap effect was obtained on dilute H2S sensing. In the Pt electrode sensor, the large Sgb/Si value induced the large micro gap effect. It was found that the Pt/SnO2 interface showed much higher sensor response than the Au/SnO2 interface. The electrode material strongly affected the sensing properties of semiconductor gas sensor with micro gap electrode.

Nano-gap Effects in Semiconductor Gas Sensors

The effect of gap size on the gas sensitivity of semiconductor gas sensor was evaluated in the NO2 sensing using WO3 nanosensor, the Cl2 sensing using In2O3 nanosensor and the H2S sensing using SnO2 nanosensor. The nano-gap effect was markedly observed in the NO2-WO3 system and the Cl2-In2O3 system (resistance increase), while the H2S-SnO2 system showed the weak nano-gap effect. This difference resulted from the ratio (Si/Sgb) of sensitivity at semiconductor oxide-electrode interface (Si) to at grain boundary (Sgb). The NO2-WO3 and the Cl2-In2O3 systems showed the large Si/Sgb ratio (32-43), while the small ratio (9.7) was obtained in the H2S-SnO2 system at the gas concentration of 0.5-1 ppm. It was found that the clearer nano-gap effect was obtained for the system having the larger Si/Sgb ratio. In the system having large Si/Sgb ratio, the nano-design of electrode structure like nano-gap electrode was important for high sensitivity gas sensors.

Effect of micro-gap electrode on sensing properties to dilute chlorine gas of indium oxide thin film microsensors

Effects of gap size on dilute Cl2 gas sensing properties have been investigated for the In2O3 thin film microsensors equipped with micro-gap electrode. The micro-gap electrodes with various gap sizes (0.1–2μm) were fabricated on SiO2/Si substrate by means of MEMS techniques (photolithography and FIB). Then the In2O3 thin film was deposited on the micro-gap electrode to be micro gas sensor. The resistance of In2O3 microsensor was increased upon exposure to dilute Cl2 gas of ppm-level, while the sensor responded to Cl2 gas less than 0.5ppm with resistance decrease. Interestingly, in both cases the sensitivities were increased with decreasing gap size, although the starting gap size of sensitivity increase were different from each other. The high sensitivity was obtained for In2O3 microsensor with 0.1μm gap. The number of grains was decreased with decreasing gap size, inducing the increasing contribution of interface between electrode and oxide. The sensitivity was increased due to the high sensitivity at interface. The similar effect of number of grains in the micro-gap was examined for the grains with different size packed in the 0.1μm gap electrode. The different grain size was obtained after calcinations at 600–850°C. With decreasing number of grains, the sensitivity to 1ppm Cl2 (resistance increase) was increased, while the sensitivity to 0.5ppm Cl2 (resistance decrease) was decreased. It is assumed that the condition of oxide–electrode interface or In2O3 surface is changed with calcination.

FeRAM capacitor and oxide electrode interface and electrical properties evaluation

FeRAM capacitor and oxide electrode interface and electrical properties evaluation