Ahmad Bsiesy

Control of 10 nm scale cylinder orientation in self-organized sugar-based block copolymer thin films

The present paper describes the orientational control of 10 nm scale cylinders in sugar-based block copolymer thin films by simply varying the composition of the annealing co-solvent. The affinity of the block copolymer to the solvent vapor could be systematically adjusted in this way.

Stress-induced leakage current and trap generation in HfO2 thin films

Stress-induced leakage current (SILC) is studied in 10 nm HfO2 metal-insulator-metal capacitors. Three regimes are observed in the current-time characteristics, namely, (1) an absorption current, (2) a quasi linear increase of current with time (SILC), and (3) thermal breakdown. Magnitude of SILC is strongly correlated to the nature of the cathode (being large for TiN and weak for Pt and Au), showing that SILC is governed by electron injection. Recovery is observed when short-circuiting the samples, pointing out that SILC is a reversible phenomenon. Desorption current and SILC are not correlated, which indicates that different defects control the absorption current and SILC. SILC is ascribed to the generation of oxygen vacancies upon hot electron injection, while recovery is ascribed to the recombination of oxygen ions with vacancies. In the SILC regime, the current varies as Ktn (n = 1.15 at room temperature). Bias and temperature dependence of K and n are studied. The dependence of K on bias can be desc...

On the mechanisms of cation injection in conducting bridge memories: The case of HfO2 in contact with noble metal anodes (Au, Cu, Ag)

Resistance switching is studied in HfO2 as a function of the anode metal (Au, Cu, and Ag) in view of its application to resistive memories (resistive random access memories, RRAM). Current-voltage (I-V) and current-time (I-t) characteristics are presented. For Au anodes, resistance transition is controlled by oxygen vacancies (oxygen-based resistive random access memory, OxRRAM). For Ag anodes, resistance switching is governed by cation injection (Conducting Bridge random access memory, CBRAM). Cu anodes lead to an intermediate case. I-t experiments are shown to be a valuable tool to distinguish between OxRRAM and CBRAM behaviors. A model is proposed to explain the high-to-low resistance transition in CBRAMs. The model is based on the theory of low-temperature oxidation of metals (Cabrera-Mott theory). Upon electron injection, oxygen vacancies and oxygen ions are generated in the oxide. Oxygen ions are drifted to the anode, and an interfacial oxide is formed at the HfO2/anode interface. If oxygen ion mobi...

Electrical study of ferromagnet-oxide-semiconductor diode for a magnetic memory device integrated on silicon

This work focuses on electrical characterization of NiFe∕SiO2∕Si tunnel diodes that can be used for spin injection into silicon in future spintronic devices. Capacitance-voltage characteristics show a large increase of the Si∕SiO2 interfacial state density compared to similar Al∕SiO2∕Si diodes. This result suggests that nickel and/or iron may have diffused across the SiO2 layer. Consistently the current-voltage experimental characteristics have been modeled by using trap assisted electron transport mechanism. These traps may be attributed to ferromagnet atoms in the oxide bulk.

Rutile-structured TiO2 deposited by plasma enhanced atomic layer deposition using tetrakis(dimethylamino)titanium precursor on in-situ oxidized Ru electrode

In this work, tetrakis(dimethylamino)titanium precursor as well as in-situ oxidized ruthenium bottom electrode were used to grow rutile-structured titanium dioxide thin layers by plasma enhanced atomic layer deposition. Metal–insulator–metal capacitors have been elaborated in order to study the electrical properties of the device. It is shown that this process leads to devices exhibiting excellent results in terms of dielectric constant and leakage current.

Dielectric relaxation in hafnium oxide: A study of transient currents and admittance spectroscopy in HfO2 metal-insulator-metal devices

Dielectric relaxation is studied in 10 nm HfO2 thin films which are deposited by atomic layer deposition on TiN and Pt electrodes. Transient currents are recorded from 10−3 s to 10 s, as a function of bias (0.1 V to 1 V) and temperature (20 °C to 180 °C). A Curie-von Schweidler law is observed, I = Q0/tα. The power law exponent α is constant with bias and strongly depends on the temperature (varying in the 0.65–1.05 range, with a peak at 75 °C). The amplitude Q0 is described by a relation of the form Q0 = C0Vβ, where the factor C0 is weakly activated and the exponent β varies with temperature (in the 0.9–1.5 range as T varies). Transient currents are discussed along with tunneling based models from the literature. To complement transient current experiments, admittance spectroscopy (conductance G and capacitance C) is performed at low frequencies, from 0.01 Hz to 10 kHz. The dispersion law of the conductance is of the form G ∼ ωs. The capacitance is the sum of two terms, a non-dispersive term (C∞) and a l...

Improved patterned media for probe-based heat assisted magnetic recording

In this paper, we describe a new media for heat assisted magnetic recording at ultrahigh density. Thermal simulations were performed to optimize this media. It consists in a patterned porous silicon substrate on which magnetic multilayers are deposited by magnetron sputtering. Magnetic properties of these multilayers are compared to those of layers deposited on regular silicon substrate. Despite the very particular structure of porous silicon surface, no big differences are observed and magnetic properties of the multilayers are conserved. Writing tests will be performed on these media with heating tips.

Understanding the mechanisms of interfacial reactions during TiO2 layer growth on RuO2 by atomic layer deposition with O2 plasma or H2O as oxygen source

In this paper, TiO2 layers grown on RuO2 by atomic layer deposition (ALD) using tetrakis (dimethyla-mino) titanium (TDMAT) and either oxygen plasma or H2O as oxygen source were analyzed using X-ray diffraction (XRD), Raman spectroscopy, and depth-resolved X-ray Photoelectron spectroscopy (XPS). The main objective is to investigate the surface chemical reactions mechanisms and their influence on the TiO2 film properties. The experimental results using XRD show that ALD deposition using H2O leads to anatase TiO2 whereas a rutile TiO2 is obtained when oxygen-plasma is used as oxygen source. Depth-resolved XPS analysis allows to determine the reaction mechanisms at the RuO2 substrate surface after growth of thin TiO2 layers. Indeed, the XPS analysis shows that when H2O assisted ALD process is used, intermediate Ti2O3 layer is obtained and RuO2 is reduced into Ru as evidenced by high resolution transmission electron microscopy. In this case, there is no possibility to re-oxidize the Ru surface into RuO2 due to the weak oxidation character of H2O and an anatase TiO2 layer is therefore grown on Ti2O3. In contrast, when oxygen plasma is used in the ALD process, its strong oxidation character leads to the re-oxidation of the partially reduced RuO2 following the first Ti deposition step. Consequently, the RuO2 surface is regenerated, allowing the growth of rutile TiO2. A surface chemical reaction scheme is proposed that well accounts for the observed experimental results.

Low-frequency dielectric properties of intrinsic and Al-doped rutile TiO2 thin films grown by the atomic layer deposition technique

Dielectric spectroscopy is carried out for intrinsic and aluminum-doped TiO2 rutile films which are deposited on RuO2 by the atomic layer deposition technique. Capacitance and conductance are measured in the 0.1 Hz–100 kHz range, for ac electric fields up to 1 MVrms/cm. Intrinsic films have a much lower dielectric constant than rutile crystals. This is ascribed to the presence of oxygen vacancies which depress polarizability. When Al is substituted for Ti, the dielectric constant further decreases. By considering Al-induced modification of polarizability, a theoretical relationship between the dielectric constant and the Al concentration is proposed. Al doping drastically decreases the loss in the very low frequency part of the spectrum. However, Al doping has almost no effect on the loss at high frequencies. The effect of Al doping on loss is discussed through models of hopping transport implying intrinsic oxygen vacancies and Al related centers. When increasing the ac electric field in the MVrms/cm rang...

Wide Band Frequency Characterization of Al-Doped and Undoped Rutile TiO 2 Thin Films for MIM Capacitors

In this letter, the dielectric properties of rutile TiO2 thin films are studied for metal–insulator–metal capacitor applications. The dielectric constant, the ac conductivity, and the loss tangent are measured in a wide band frequency range, from 1 Hz to 2 GHz. The effect of aluminum doping, as well as the influence of film thickness, on the dielectric properties is presented.