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The resistive switching characteristics of forming free TiO2–x/TiO2–yubscript> memory devices containing Pt nanocrystals (NCs) beneath the top electrode were systematically investigated through experiments and numerical simulation insights. By embedding Pt nanocrystals, we have the possibility to narrow down the possible locations where the switching effect will evolve and thus significantly improve the inherent variability of the devices. Besides, the deployment of bilayer structures can tune the resistance levels, since the presence of the layer with low oxygen content (TiO2–y) acts practically as series resistance, limiting the operating currents and at the same time forcing the switching effect to evolve in the layer with the higher oxygen content (TiO2–z). A numerical model is implemented, in order to shed light into the origin of the SET/RESET transitions and illustrate the direct impact of NCs on the conducting filament (CF) shape and distribution of oxygen vacancies. It is demonstrated that a higher density of oxygen vacancies is created in the vicinity of NCs, which can directly impact the operating current values and the uniformity of the switching characteristics. The presence of NCs also facilitates the reduction of the operating voltages (∼3 V), and, as a result, it significantly improves power consumption, without sacrificing the switching ratio (∼103), temporal/spatial variability (σ/μ < 0.2), and pulse endurance (108 cycles) characteristics of our memory cells. Evidence about the impact of the NCs position within the material configuration are also presented. The direct impact of Pt NCs on the depression and potentiation characteristics of the synaptic weight denotes similarly the huge applicability of our approach to tune a wide range of resistive switching properties. [ABSTRACT FROM AUTHOR] more...

Isotopically pure material was used in diffusivity measurements of silicon in silicon dioxide layers.

A new study uses the wafer bonding technique to investigate the interaction between silicon interstitials and dislocation loops during thermal oxidation.

The interstitial injection during nitrous oxidation of silicon at low temperatures was monitored using dislocation loops and boron-doped delta layers.

Although multilevel capability is probably the most important property of resistive random access memory (RRAM) technology, it is vulnerable to reliability issues due to the stochastic nature of conducting filament (CF) creation. As a result, the various resistance states cannot be clearly distinguished, which leads to memory capacity failure. In this work, due to the gradual resistance switching pattern of TiO2-x-based RRAM devices, we demonstrate at least six resistance states with distinct memory margin and promising temporal variability. It is shown that the formation of small CFs with high density of oxygen vacancies enhances the uniformity of the switching characteristics in spite of the random nature of the switching effect. Insight into the origin of the gradual resistance modulation mechanisms is gained by the application of a trapassisted-tunneling model together with numerical simulations of the filament formation physical processes. [ABSTRACT FROM AUTHOR] more...

A model for the time dependence of the surface recombination velocity of silicon interstitials at nonoxidizing or inert Si/SiO2 interfaces was developed. The model considers the experimentally observed diffusion of silicon interstitials through a thermal oxide. It was observed that the model can accurately simulate one-dimensional and two-dimensional experiments. The segregation coefficient of silicon interstitials at the silicon-oxide interface can be obtained from experimental data. more...

The operating principle of resistive random access memories (RRAMs) relies on the distribution of ionic species and their influence on the electron transport. Taking into account that formation and annihilation of conducting filaments (CFs) is the driving mechanism for the switching effect, it is very important to control the regions where these filaments will evolve. Thus, homolayers of titanium oxide with different oxygen contents were fabricated in order to tune the local electrical and thermal properties of the CFs and narrow down the potential percolation paths. We show that the oxygen content in the top layer of the TiO2-x/TiO2-y bilayer memristors can directly influence the morphology of the layers which affect the diffusion barrier and consequently the diffusivity and drift velocity of oxygen vacancies, yielding in important enhancement of switching characteristics, in terms of spatial uniformity (σ/μ<0.2), enlarged switching ratio (~104), and synaptic learning. In order to address the experimental data, a physical model was applied, divulging the crucial role of temperature, electric potential and oxygen vacancy density on the switching effect and offering physical insights to the SET/RESET transitions and the analog switching. The forming free nature of all the devices in conjunction with the self-rectifying behavior, should also be regarded as important assets towards RRAM device optimization. [ABSTRACT FROM AUTHOR] more...

Research was conducted to collate growthand shrinkage of oxidation stacking faults (OSF) in silicon implanted with oxygen (SIMOX) and bulk silicon. SIMOX exhibited lengthier faults which may be attributed to silicon interstitial supersaturation. Results revealed that OSF shrinkage in N2 was the same for SIMOX and bulk silicon samples. Data also provided clearer insights on the basic properties of siicon self-interstitials. more...

Si overlayer in silicon separated by oxygen oxidation results in oxidation stacking faults (OSF) due to Si interstitials generation. Low OSF densities result due to migration of Si interstitials to the bulk silicon. This movement can be suppressed when a high density of microdefects are produced in the Si layer. The size distribution of OSF shows that the nucleation regime is neithertotally homogenous nor totally heterogenous. more...

In this work, we present the results obtained using a CO2 laser source at 10.6 µm wavelength for the study of the non-melt annealing of phosphorus doped germanium in the millisecond regime. Main objective of this paper is the demonstration of electrically active n+-p junctions in germanium by implanting phosphorus in p-type substrate while trying to maintain minimal dopant diffusion, which is a critical issue for scaling germanium devices. In addition to the phosphorus diffusion studies, we also explore the presence of nitrogen introduced in the substrate together with phosphorus and we conclude that it can further reduce dopant movement at the expense of lower activation level. The observation is confirmed by both electrical and SIMS measurements. Moreover, density functional theory calculations show that nitrogen-phosphorus co-doping of germanium creates stable N-P complexes that, indeed, are consistent with the deactivation and diffusion suppression of phosphorus. [ABSTRACT FROM AUTHOR] more...

In this work, a picosecond diode pumped solid state laser and a nanosecond Nd:YAG laser have been used for the annealing and the partial nano-crystallization of an amorphous silicon layer. These experiments were conducted as an alternative/complementary to plasma-enhanced chemical vapor deposition method for fabrication of micromorph tandem solar cell. The laser experimental work was combined with simulations of the annealing process, in terms of temperature distribution evolution, in order to predetermine the optimum annealing conditions. The annealed material was studied, as a function of several annealing parameters (wavelength, pulse duration, fluence), as far as it concerns its structural properties, by X-ray diffraction, SEM, and micro-Raman techniques. [ABSTRACT FROM AUTHOR] more...

In this work, we demonstrate that TiO2-x based Resistive Random Access Memory devices can function without an initial electroforming process and a wide range of switching ratios could be achieved by controlling the oxygen content, the compliance current, the sweep bias amplitude, and the width of the voltage pulse applied on the memory cell. The influence of deposition ambient and more particularly of oxygen flux during thin film sputtering at room temperature to the resistive properties of titanium oxide will be discussed in detail. By controlling the density of oxygen vacancies into the dielectric matrix, we can also improve the repeatability and the operation of the device, in terms of distribution of the SET/RESET voltages. We propose that ultra high density of vacancies deteriorate the switching phenomenon, whereas high vacancy density results in better switching behavior. Moreover, we conclude that the oxygen vacancies density and distribution have a direct impact on the conducting filament diameter, in terms of sensitivity of the conducting paths (high OFF/ON ratio). By increasing the oxygen content, we reduce the size of vacancy based filaments, resulting in a more stable operation of our device. In addition, manipulation of population of oxygen ions into the Ti top electrode enables the creation of multilevel switching states. Switching speed, endurance, and retention performance reveals the excellent functionality of our device as a non-volatile memory element and conduction mechanism analysis demonstrates the manifestation of Poole-Frenkel emission in conjunction with trap-assisted tunneling, which is also deployed in order to interpret the gradual increase of current during SET process. [ABSTRACT FROM AUTHOR] more...

We report arsenic and phosphorus diffusion experiments and activation related phenomena in codoped germanium substrates utilizing conventional thermal annealing. Chemical profiles were obtained by secondary ion mass spectroscopy, sheet resistance was estimated by the Van der Pauw method. Our study covers the temperature range from 600 to 750 °C. We accurately described the dopant profiles with a quadratic dependence of the dopants diffusion coefficient on the free electron concentration. In our simulations we considered the dopant pile-up near the surface and dopant loss owing to outdiffusion during the annealing. Although the double donor codoping technique exhibited no advantage over monodoping with P concerning the level of activation and junction depth, it was interesting to observe the different diffusion behavior of the two dopants. Whereas the diffusion of As indicates a retardation under codoping the diffusion of P remains either unaffected or is slightly enhanced by codoping. The activation level of the codoped samples remains lower compared to the respective monodoped samples, except for the highest annealing temperature. [ABSTRACT FROM AUTHOR] more...

We report on phosphorus diffusion and activation related phenomena in germanium. We have used both conventional thermal processing and laser annealing by pulsed nanosecond Nd:YAG laser. Chemical profiles were obtained by secondary-ion-mass spectroscopy, sheet resistance was estimated by the van der Pauw method, and structural defects were monitored by transmission electron microscopy. Our study covers the temperature range from 440 to 750 °C, and we were able to efficiently simulate the dopant profiles within that temperature range, taking into account a quadratic dependence of the P diffusion coefficient on the free electron concentration. To achieve that we have taken into account dopant activation dependence on temperature as well as dopant pile-up near the surface and dopant loss owing to outdiffusion during the annealing. A combined laser thermal treatment above the melting threshold prior to conventional annealing allowed the elimination of the implantation damage, so we could perceive the influence of defects on both transient dopant diffusion and outdiffusion. [ABSTRACT FROM AUTHOR] more...

In a previous work [Skarlatos et al., J. Appl. Phys. 93, 1832 (2003)] we investigated the influence of implantation energy on oxide growth and defect formation in nitrogen-implanted silicon substrates. It was shown that as the implantation energy decreases from medium to very low values the oxide reduction decreases. This was attributed to nitrogen out-diffusion, which is more effective when nitrogen is placed closer to the silicon surface. On the other hand very low implantation energy avoids the formation of dislocation loops in the silicon substrate, a key point for modern devices performance. In this second part we compare the nitrogen distribution and electrical properties of ultrathin (25–30 Å) oxides grown under the same oxidation conditions on very low (3 keV) and medium (25 keV) energy nitrogen-implantated silicon. Nitrogen distribution measurements show that a lower content of nitrogen remains within the oxides formed using 3 keV energy as compared to the 25 keV case supporting the results of the first part of this work. So at very low implantation energy the same oxide thickness is obtained increasing the implantation dose. On the other hand oxides formed through very low energy implants show superior electrical properties in terms of surface states and leakage currents due to the lower damage induced in the silicon substrate. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR] more...

We demonstrate a nonvolatile electrically erasable programmable read-only memory device using gold nanoparticles as charge storage elements deposited at room temperature by chemical processing. The nanoparticles are deposited over a thermal silicon dioxide layer that insulates them from the device silicon channel. An organic insulator deposited by the Langmuir–Blodget technique at room temperature separates the aluminum gate electrode from the nanoparticles. The device exhibits significant threshold voltage shifts after application of low-voltage pulses (<=±6 V) to the gate and has nonvolatile retention time characteristics. © 2003 American Institute of Physics. [ABSTRACT FROM AUTHOR] more...

It is well known that nitrogen implantation in silicon leads in reduction of the SiO[sub 2] thickness in implanted wafers, which makes this a very promising technique for present and future device processing. In this work we investigate the influence of the implantation energy on oxidation kinetics in nitrogen-implanted silicon. Nitrogen was implanted in silicon wafers at low (3 keV), and medium (25, 80, and 150 keV) energies and oxidations were performed at various temperatures (800-900 °C) and times. The experiment shows that the decrease in the oxide thickness is smaller when nitrogen is implanted closer to the silicon surface. We attribute this to nitrogen out-diffusion during the ramping and the initial oxidation steps, which is more effective when nitrogen is placed closer to the surface. Additional experiments varying the ramping time support this explanation. An additional study of the growth of extended defects under the different implantation conditions has been performed. This study enabled the estimation of an energy-dose "window," in which we can observe very small oxide thickness (25-40 Å) without extended defects formation. [ABSTRACT FROM AUTHOR] more...

Electrical properties of ultra thin gate oxides formed by oxidation of nitrogen implanted silicon and nitrogen distribution were studied. Absence of extended defects in the silicon substrate and lower interfacial damaged have resulted in better nitrogen distribution in the 3 and 25 KeV implanted samples which were identical. more...

The measured Si diffusivity in thermal SiO2 with an experimental method based on isotopic exchange in equilibrium conditions are discussed. The resulting values are compared with literature data and the possible origin of the observed difference is described. more...

Presents a study which assessed arsenic diffusion in silicon-on-insulator formed by deep oxygen implantation. Details on the experiment; Results of the study; Conclusion.

Isotopic exchange is used to measure the silicon self-diffusivity in thermal silicon dioxide. The experiments, using an isotopically enriched [sup 28]Si oxide layer, are specially designed to obtain the actual equilibrium diffusivity in the oxide. A simple Arrhenius law, with an activation energy of 5.34 eV, very nicely describes the measured diffusivities as a function of the temperature. Our values are compared with literature data, and we discuss the possible origin of the observed differences. [ABSTRACT FROM AUTHOR] more...

Proposes a method for the estimation of the fractional interstitialcy component of boron that is based on the interpretation of oxidation-enhanced diffusion data in extrinsic conditions. Important contribution of vacancies to boron diffusion in silicon; Thermodynamic equilibrium between positively ionized and neutral interstitials; Ratio and the difference of the diffusion coefficients in oxidizing and inert ambient. more...