V. Jousseaume

Experimental and theoretical study of electrode effects in HfO 2 based RRAM

In this work, the impact of Ti electrodes on the electrical behaviour of HfO2-based RRAM devices is conclusively clarified. To this aim, devices with Pt, TiN and Ti electrodes have been fabricated (see Fig. 1). We first provide several experiments to clearly demonstrate that switching is driven by creation-disruption of a conductive filament. Thus, the role of TiN/Ti electrodes is explained and modeled based on the presence of HfOx interfacial layer underneath the electrode. In addition, Ti is found responsible to activate bipolar switching. Moreover, it strongly reduces forming and switching voltages with respect to Pt-Pt devices. Finally, it positively impacts on retention. To support and interpret our results we provide physico-chemical measurements, electrical characterization, ab-initio calculations and modeling.

Electrical properties of polyaniline–polystyrene blends above the percolation threshold

Blends of conductive polymers with classical ones can exhibit good mechanical properties and good electrical conductivity and deserve great attention for application in electronic industrial technology. Conductive polyaniline solutions have been chemically prepared using bis(2-ethyl hexyl)hydrogen phosphate (DiOHP) as the dopant chemical species. The codissolution method leads to conductive polyaniline–polystyrene (PANI–PSt) composites with good mechanical properties. The dependence of electrical conductivity on the volume fraction of PANI in the blend is found to be characteristic of a percolation system. Electrical conductivity and thermoelectric power measurements are interpreted on the basis of hopping mechanisms between polaronic clusters.

Electrical and optical properties of WO3 thin films

Abstract Tungsten trioxide (WO3) thin films were prepared by spray pyrolysis. The optical and electrical properties of intensively colored films were studied. It was found that the near-infrared reflectivity increases in the colored state. This behavior is typical of degenerate semiconducting materials. However, the variations of the electrical conductivity with the temperature for these films, indicates semiconducting behavior, while the carrier concentration (n), measured by the Hall effect, is typical of degenerate material. The optical properties can be easily explained by the Drude theory, which is related to the bulk properties of the samples. It is shown that the value of n is also related to the bulk properties of the films, while the conductivity is controlled by the grain boundary effect. The results are interpreted in terms of a modified version of Setos model, taking into account thermionic emission and tunneling of carriers through the potential barriers at the grain boundaries.

Aging of electrical conductivity in conducting polymer films based on polyaniline

The aim of this work is to present an electrical study of the aging of conducting polyaniline–polystyrene (PANl–PSt) blends. Results concerning time dependence of the electrical conductivity of some samples artificially aged at different temperatures are presented. It is shown that the electrical conductivity decreases with time with a rate depending principally on the nature of the dopant. When aged at the same temperature, similar degradation kinetics are observed as well for doped polyaniline as for PANl–PSt blend. A study of the electrical conductivity variations versus temperature is presented for samples which have been aged at the same temperature but for different durations. Experimental results are discussed in the frame of the heterogeneous picture already proposed for nonaged samples.

X‐ray photoelectron spectroscopy of conducting polyaniline and polyaniline–polystyrene blends

Conductive polyaniline solutions were chemically prepared using bis (2-ethylhexyl) hydrogen phosphate (DiOHP) as the dopant chemical species. The codissolution method leads to conductive polyaniline–polystyrene (PANI–PSt) composites with good mechanical properties. The electronic structure of both conducting PANI films and PANI–PSt blends was investigated by X-ray photoelectron spectroscopy, which allowed one to quantify the proportion of benzenoid amine, quinoid imine, and protonated units. Blending polyaniline with PSt does not involve important modifications in the polymer electronic structure.

Investigation of the impact of the oxide thickness and RESET conditions on disturb in HfO 2 -RRAM integrated in a 65nm CMOS technology

In this work, a comprehensive investigation of disturb in HfO2-Resistive Random Access Memories (RRAM) integrated in an advanced 65nm technology is presented. The effects of the oxide thickness and RESET conditions on disturb immunity of the High-Resistance-State (HRS) are explored. Constant Voltage Stress is applied on a large amount of samples at various temperatures. Data are collected and analyzed on a statistical basis. The SET dependence to the RESET conditions is investigated and correlated to the length of the induced depleted gap along the conductive filament. The conduction mechanism of the HRS is correlated to the failure/SET process of the RRAM device through a voltage acceleration model. It is shown that thicker dielectric oxide and stronger RESET conditions give rise to longer failure times.

Sb-doped GeS 2 as performance and reliability booster in Conductive Bridge RAM

In this work, for the first time at our knowledge, the improvement of chalcogenide-based CBRAM performance and reliability by Sb doping of the GeS2 electrolyte is presented. An original analysis, based on in-depth physico-chemical characterization, device electrical measurements, empirical model and first principle calculations, is shown. We argue that optimized ~10% Sb doping in the GeS2 electrolyte allows to achieve SET speed of 30ns at 2.2V (i.e. 0.66pJ SET programming power), while assuring 10 years data retention at 125°C, >105 cycling and high robustness to Sn-Pb soldering profile. Finally, the improved thermal stability of the filament in the GeS2-Sb matrix is clearly elucidated by means of molecular dynamics calculations.

Temperature impact (up to 200 °C) on performance and reliability of HfO 2 -based RRAMs

This paper provides an overview of the temperature impact (up to 200 °C) on the electrical behavior of oxide-based RRAM, during forming, low-field resistance reading, SET/RESET, disturb, data retention and endurance. HfO2-RRAM devices (in a 1T1R configuration) integrated in an advanced 65 nm technology are studied for this aim. We show that forming operation is strongly activated in temperature (i.e. -0.5 V per hundred Celsius degree), being much less for SET and RESET voltages (i.e. <; -0.05 V per hundred Celsius degree); disturb of HRS at fixed voltage showed to be independent of temperature; endurance up to 3.106 cycles, with optimized set of stress parameters showed no significant variation; data retention at 150 °C up to 68 days showed stable programming window, after different initial programming algorithms.

Stability of electrical properties in polyaniline-polystyrene blends

The thermal stability of free standing polystyrene-polyaniline-DiOHP blend electrical properties is described. Electrical conductivity measurements have been performed at different temperatures for a long degradation time. A good stability with time and temperature is observed. The electrical conductivity variations versus temperature are explained on the assumption of a main contribution of hopping mechanisms between conducting clusters.

On the impact of Ag doping on performance and reliability of GeS 2 -based Conductive Bridge Memories

In this work, we study the impact of Ag doping on GeS2-based CBRAM devices employing Ag as active electrode. Several devices with Ag doping varying between 10% and 24% are extensively analyzed. First, we assess switching voltages and time-to-set as a function of Ag concentration in the electrolyte layer. Subsequently, we evaluate data retention at different temperatures. The results show that a Ag doping increase in the GeS2 yields a strong improvement on data retention performance, increasing the 10-years data-ret temperature from 68°C for the 10% Ag doping to 100°C for the 24%, without any significant increase of the set voltage (50mV higher).