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Resistive switching in binary metal oxides consists of conductivity changes originating from the electrical creation/dissolution of conductive filaments (CFs) at nanoscale. The investigation of CF local properties can only be achieved through physical and electrical studies at the scale of 10 nm or less, that is, the characteristic size of CFs. This work reports on the direct manipulation of individual CFs formed through insulating NiO films by conductive atomic force microscopy (CAFM) and the comparison between forming/reset processes induced by CAFM and those observed in large-area devices with the same NiO film. The switching variability due to local defects, such as grain boundaries and dislocations, is directly evidenced by CAFM during electroforming process. Our results also indicate that the forming voltage under CAFM can be significantly smaller than the one observed in large-area devices, thus providing evidence for the electric-field enhancement underneath the CAFM tip. Filament deactivation, or reset, at extremely low currents close to 100 nA is demonstrated and described in terms of electrode-limited CF. These results suggest that device engineering and CF size limitation may allow for a significant reduction of forming voltage and reset current in resistive switching random-access memory switching. [ABSTRACT FROM AUTHOR]

Resistive switching memory (RRAM) based on the redox-induced conductivity change in some metal oxides attracts considerable interest as a new technology for next-generation nonvolatile electronic storage. Although resistance-switching phenomena in several transition metal oxides have been known from decades, the details of the switching mechanisms and the nature of the different resistive states are still largely debated. For nonvolatile memory applications, the scaling potential of RRAMs is the most relevant issue, and understanding the scaling capability of RRAM devices requires a sound interpretation of resistance-switching operation and reliability aspects. This work addresses the scaling dependence of RRAM switching parameters. The dependence on the electrode area and on the size of the conductive filament (CF) responsible for low-resistance memory state is investigated. The RRAM conduction modes depending on CF size are discussed based on temperature dependent resistance analysis. Reset characteristics in different resistance states are explained by a Joule heating model for CF oxidation. [ABSTRACT FROM AUTHOR]

The morphological and electrical evolution of HfO2 and ZrO2 thin films is investigated on the nanoscale using conducting atomic-force microscopy in ultrahigh vacuum. Films of different thicknesses have been grown by atomic layer deposition. With increasing film thickness the film structure changes from amorphous to polycrystalline. By conducting atomic-force microscopy using local current–voltage curve statistics and two-dimensional current imaging it is found that the formation of crystallites has different effects on the electrical properties of the two dielectrics. In the case of HfO2, the crystalline fraction causes weak spots in the oxide, whereas for the ZrO2 films the crystallites exhibit lower leakage currents compared to the amorphous matrix and leakage is mainly determined by thickness fluctuations. [ABSTRACT FROM AUTHOR]

Presents information on a study which characterized the intrinsically gettered Czochralski silicon using electron beam induced current technique. Experimental details; Results and discussion; Conclusions.

The resistance switching dynamics of TiN/HfO2/Pt devices is analyzed in this paper. When biased with a voltage ramp of appropriate polarity, the devices experience SET transitions from high to low resistance states in an abrupt manner, which allows identifying a threshold voltage. However, we find that the stimulation with trains of identical pulses at voltages near the threshold results in a gradual SET transition, whereby the resistive state visits a continuum of intermediate levels as it approaches some low resistance state limit. On the contrary, RESET transitions from low to high resistance states proceed in a gradual way under voltage ramp stimulation, while gradual resistance changes driven by trains of identical spikes cover only a limited resistance window. The results are discussed in terms of the relations among the thermo-electrochemical effects of Joule heating, ion mobility, and resistance change, which provide positive and negative closed loop processes in SET and RESET, respectively. Furthermore, the effect of the competition between opposite tendencies of filament dissolution and formation at opposite metal/HfO2 interfaces is discussed as an additional ingredient affecting the switching dynamics. [ABSTRACT FROM AUTHOR]

The multiple resistive switching of Pt/HfO2/TiN devices is demonstrated as a result of a competition between the switching at opposite metal/oxide interfaces. Three switching operation modes are demonstrated: clockwise (CW) switching (set for negative voltage and reset for positive voltage at Pt electrode), as already reported in literature for similar material stacks; counterclockwise (CCW) switching and complementary switching (CS) that consist in a set and a reset for increasing voltage of the same polarity. The multiple switching operation modes are enabled by a deep-reset operation that brings the cell resistance close to the initial one. As a consequence, the set transition after a deep-reset occurs at the same voltage and currents as those of the forming and leads to a low resistance state whose resistance can be further decreased in a CCW switching or increased back with a CW switching. With a suitable choice of the stop voltage, a CS in obtained, as well. The coexistence of all three CW, CCW, and CS operations demonstrates that both metal-oxide interfaces are active in the formation and the dissolution of conductive filaments responsible for the switching. All these observations are discussed in terms of a competition between ion migration processes occurring at the opposite metal-oxide interfaces. [ABSTRACT FROM AUTHOR]

Arrays of vertical nanowires structured in Au/NiO/Au segments with 50 nm diameter are characterized by conductive atomic force microscopy to investigate unipolar resistive switching in NiO at the nanoscale. The switching cycles are characterized by extremely low power consumption down to 1.3 nW, which constitutes a significant improvement in nanowire-based resistive switching memory devices. The trend of the reset current as a function of the set resistance, typical of unipolar memories, is extended to a much wider current range than what is reported in literature, confirming the role of Joule heating in the reset process for very low reset currents. [ABSTRACT FROM AUTHOR]

In the view of improving standard TANOS stacks, a possible route is the replacement of Al2O3 blocking oxide with materials with higher dielectric constant κ, as this would increase the electric field across the tunnel oxide. A possible solution is to integrate rare earth scandates. Among the scandates, DyScO3 appears as an attractive material due to the reported high-κ value. Films with 10-30 nm nominal thickness were grown by atomic layer deposition (ALD) on Si substrates for process optimization and structural characterization. Sc(thd)3 and Dy(thd)3 were used as Sc and Dy precursors and O3 as oxidizing agent. First, Sc2O3 and Dy2O3 growth process was optimized by changing growth temperature (Tg) and ALD cycle. The best conditions for the deposition of the ternary DyScO films were found to be Tg=350 °C and Dy:Sc=1:1 pulsing ratio. Optimized films were also grown on Si-rich SiN for integration as blocking oxide. After deposition, films were subjected to rapid thermal annealing up to 1030 °C to check their thermal stability. Film thickness was checked by x-ray reflectivity, together with roughness and electron density. Film crystallinity was investigated by grazing incidence x-ray diffraction. Film uniformity and thermal stability were explored by time-of-flight secondary ion mass spectrometry (ToF-SIMS) depth profiles. Dielectric constant κ was extracted from capacitance-voltage (C-V) electrical measurements. As deposited amorphous DyScO films on silicon remain amorphous after annealing up to 900 °C. Film electron density reduces while thickness increases with annealing, surface roughness remaining at ∼1.5 nm. The measured Sc:Dy atomic ratio by total x-ray fluorescence analyses is 1.33 in the as deposited film. ToF-SIMS depth profiles showed that film uniformity and composition is not preserved at 900 °C, in films deposited on Si, as major Si diffusion affects the ternary oxide. Only at 600 °C the diffusion phenomena and film composition are preserved. The extracted DyScO dielectric constant is κ∼20 in films annealed at 600 °C on Si. When deposited on Si-rich SiN, DyScO uniformity remains well preserved up to 900 °C, with an improvement of the thermal stability with respect to deposition on Si. Si diffusion is evident at 1030 °C only. The κ-value extracted from C-V resulted to be κ∼20. [ABSTRACT FROM AUTHOR]

Dysprosium scandate DyScOx with a κ value of ∼20 has been investigated as blocking dielectric in charge trapping memory capacitors. DyScOx films with 28 and 18 nm thicknesses are deposited by atomic layer deposition on two different kinds of silicon nitride used as charge trapping layer, while SiO2 is used as tunnel oxide and TaN is used as metal gate. Memory capacitors with Al2O3 as blocking layer with similar equivalent oxide thickness (EOT) to DyScOx are also characterized as benchmarks. DyScOx thermal stability on both Si3N4 and Si-rich SiN at annealing temperatures up to 900 °C demonstrates the complementary metal-oxide semiconductor process compatibility of the oxide. Especially when deposited on Si-rich SiN, comparable program and slightly better retention performance with Al2O3 are observed for DyScOx, whereas erase still needs to be improved. Some variations in the electrical performance are found between the DyScOx-based stacks with different charge trapping layer and have been discussed. Scaling the total stack EOT by reducing DyScOx thickness from 28 to 18 nm allows a large program/erase window, but with the penalty of an increased charge loss during retention. Our results suggest that the key factors in further improvement of DyScOx as blocking dielectric are the dielectric quality and leakage current. [ABSTRACT FROM AUTHOR]

Tuning the desorption temperature of an As cap layer allows to achieve In0.53Ga0.47As(001) surfaces with (2 × 4) and (4 × 2) reconstructions which exhibit different chemical reactivity upon exposure in atmospheric pressure. Trimethyl-Al based atomic layer deposition of Al2O3 films on the two exposed surfaces causes a non-equivalent interface composition. This behavior is associated with a worse electrical quality of the interface with the exposed (4 × 2) In0.53Ga0.47As reconstruction. [ABSTRACT FROM AUTHOR]

Er-doped HfO2 (Er∼15%) films are grown by atomic layer deposition on Si(100). The characteristics of the doped oxide are compared with those of HfO2. In Er-doped HfO2, the stabilization of the cubic structure, together with the effect of the high polarizability of Er3+, allow to obtain a dielectric constant of ∼33 after annealing at 900 °C. The insertion of Er within the metallic sublattice of HfO2 reduces the net density of fixed charges, due to the creation of oxygen vacancies. For similar equivalent oxide thickness, lower leakage currents are measured for Er-doped HfO2 than for HfO2. [ABSTRACT FROM AUTHOR]

A detailed analysis of the band alignment between molecular beam deposited amorphous HfO2 and GaAs is reported. The conduction band offset, measured by internal photoemission (IPE), is 1.9±0.2 eV. The valence band offset (VBO) is probed by x-ray photoelectron spectroscopy (XPS). The accurate determination of the VBO requires a careful evaluation of differential charging phenomena and consequently a proper correction of the energy scale. The measured VBO value is 2.1±0.1 eV. Since the HfO2 gap is 5.6 eV, as detected by photoconductivity analysis, the results obtained by IPE and XPS are in excellent agreement. [ABSTRACT FROM AUTHOR]

The interface between (100)Si and HfO2 grown by atomic layer deposition is strongly influenced by the choice of the oxygen precursor. In particular, the use of oxidants with different oxidizing power such as H2O and O3 produces interfaces differing both in terms of density of electronic traps and defect microstructure. While H2O produces a Si/SiO2-like interface, characterized by the presence of the Pb0 center, the high reactivity of O3 induces a modification in the defect wavefunction, as revealed by electrically detected magnetic resonance. Post growth annealing in N2 at T>=600 °C allows the recovery of a Si/SiO2-like interface. [ABSTRACT FROM AUTHOR]

La2O3 films are obtained by annealing in vacuum La(OH)3 layers produced upon air exposure of La2O3 layers grown using atomic layer deposition. Sample thickness determines whether hexagonal or cubic La2O3 form. The observed infrared active phonon mode with minimum frequency for hexagonal La2O3 films is located at 198 cm-1, in good agreement with the first principles calculations, and at a lower frequency than the corresponding mode for cubic La2O3 is at 235 cm-1. Accordingly, electrical measurements reveal a dielectric constant around 27 for hexagonal La2O3 films, significantly higher than the one around 17 derived for cubic La2O3 layers. [ABSTRACT FROM AUTHOR]

The authors study the Ge diffusion during HfO2 growth by molecular beam epitaxy on differently in situ prepared germanium substrates and at different growth temperatures. While HfO2 layers grown directly on Ge do not show any germanium contamination, oxygen rich interfacial layers such as GeOx or GeOxNy partly dissolve into the HfO2 layer, giving rise to high Ge contamination (from 1% to 10%). The use of nitridated interfacial layers does not prevent Ge diffusion into the HfO2 during the growth process because of the high oxygen content present in the nitridated germanium layer. [ABSTRACT FROM AUTHOR]

In the perspective of exploring alternative gate dielectrics for the future generation of microelectronic devices, we investigated experimentally and theoretically the interface energy barriers induced on (001) silicon by La2Hf2O7, whose growth has been recently attained by molecular-beam epitaxy. Experimental results show that the 5.6±0.1 eV band gap of La2Hf2O7 is aligned to the band gap of silicon with a valence band offset of 2.4±0.1 eV and a conduction band offset of 2.1±0.1 eV. Density functional theory calculations yield valence band offset values ranging between 1.8 and 2.4 eV. [ABSTRACT FROM AUTHOR]

We report on the growth by atomic layer deposition of HfO2 films on HF-last treated Ge(001) substrates using HfCl4 as a Hf source and either O3 or H2O as oxygen sources. The choice of the oxygen precursor strongly influences the structural, chemical, and electrical properties of the HfO2 films: Those grown using H2O exhibit local epitaxial growth, a large amount of contaminants such as chlorine and carbon, and a large frequency dispersion of the capacitance-voltage (C–V) characteristics. Films grown using O3 are good insulators and exhibit well-shaped C–V curves with a minimum frequency dispersion of the accumulation capacitance. Moreover, they are smoother, less crystallized, and with a lower contaminant content than those grown using H2O. However, the use of O3 leads to the formation of a 2 nm thick layer, possibly GeOx, at the HfO2/Ge interface. [ABSTRACT FROM AUTHOR]

Internal photoemission spectroscopy has been used to determine the band alignment in Lu2O3 based metal-oxide-semiconductor structures. The Si/Lu2O3 interface conduction- and valence-band offsets were determined to be 2.1±0.1 and 2.6±0.1 eV, respectively. The energy barrier for electrons at the Al/Lu2O3 interface is 2.4±0.1 eV. The value of the Lu2O3 transport band gap, obtained by photoconductivity measurements, was found to be 5.8±0.1 eV. Optical absorption spectroscopy gave a value of 4.89±0.02 eV for the Lu2O3 optical band gap. [ABSTRACT FROM AUTHOR]

Rare earth oxides could represent a valuable alternative to SiO2 in complementary metal–oxide–semiconductor devices. Lu2O3 is proposed because of its predicted thermodynamical stability on silicon and large conduction band offset. We report on the growth by atomic-layer deposition of lutetium oxide films using the dimeric {[C5H4(SiMe3)]2LuCl}2 complex, which has been synthesized for this purpose, and H2O. The films were found to be stoichiometric, with Lu2O3 composition, and amorphous. Annealing in nitrogen at 950°C leads to crystallization in the cubic bixbyite structure. The dielectric constant of the as-grown Lu2O3 layers is 12±1. [ABSTRACT FROM AUTHOR]

Al-doped ZrO2 (Al-ZrO2) films deposited by atomic layer deposition onto silicon substrates and the interface with the TaN metal gate are investigated. In particular, structural properties of as-grown and annealed films in the 6-26 nm thickness range, as well as leakage and capacitive behavior of metal-oxide-semiconductor stacks are characterized. As-deposited Al-ZrO2 films in the mentioned thickness range are amorphous and crystallize in the ZrO2 cubic phase after thermal treatment at 900 °C. Correspondingly, the dielectric constant (k) value increases from 20 ± 1 to 27 ± 2. The Al-ZrO2 layers exhibit uniform composition through the film thickness and are thermally stable on Si, whereas chemical reactions take place at the TaN/Al-ZrO2 interface. A transient capacitance technique is adopted for monitoring charge trapping and flat band instability at short and long time scales. The role of traps nearby the TaN/Al-ZrO2 interface is discussed and compared with other metal/high-k oxide films. Further, analytical modeling of the flat band voltage shift with a power-law dependence on time allows extracting features of bulk traps close to the silicon/oxide interface, which exhibit energy levels in the 1.4-1.9 eV range above the valence band of the Al-ZrO2. [ABSTRACT FROM AUTHOR]

We investigate the formation, crystallinity, size, and depth distribution of Sb nanoclusters in thin SiO[sub 2] matrix by grazing incidence x-ray diffraction (GIXRD) and reflectivity (GIXRR). The complementarity of these two techniques reveals the formation of Sb nanocrystals after a rapid thermal treatment at 1000 °C and their depth distribution. The implantation profile is found to have its maximum centered in the middle of the SiO[sub 2] layer. After thermal treatment, the Sb atom redistribution, monitored by the variation in the electron density profile obtained by GIXRR, corresponds to the formation of metallic Sb nanoclusters, as confirmed by transmission electron microscopy (TEM) and GIXRD. The cluster distribution within the SiO[sub 2] layer presents a maximum at the center of the layer and their average diameter is 67±3 Å. The results are in agreement with TEM analyses. © 2003 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Si nanoclusters have been formed by 5 keV Si[sup +] implantation at a fluence of 1 × 10[sup 16] atoms/cm² into a 200 Å thin thermally grown SiO[sub 2] film on Si (100), followed by thermal treatment at 1000 °C with different annealing times. All the annealed samples show a broad photoluminescence spectrum with increasing intensity as function of annealing time. The use of a dual beam time of flight secondary ion mass spectrometry in negative mode with Cs[sup +] ions at low energy for sputtering allows us to observe variations in Si[sup -] signal due to excess of silicon atoms introduced by implantation. With the high sensitivity achieved using this instrumental configuration it is possible to follow Si[sup -, sub n] signals which give information about the chemical enviroment of the Si atoms. The possibility of studying the time evolution of the nucleation and growth of nanoclusters has been investigated. [ABSTRACT FROM AUTHOR]

Arrays of Au/NiOx/Ni/Au nanowires with a diameter of 50 nm were characterized by conductive atomic force microscopy, which was used to probe the electrical behavior of single nanowires still included in the array. A bipolar switching of the single Au/NiOx/Ni/Au nanowires is demonstrated and is attributed to the choice of an asymmetric couple of electrode materials and, possibly, to a non-uniform Ni oxidation profile inside the NiOx segments. An analysis of the conduction mechanism in a single nanowire is presented to further support this conclusion. [ABSTRACT FROM AUTHOR]

This article presents a correction of an earlier published article regarding the properties of lanthanum films.

Rare earth oxides could represent a valuable alternative to SiO2 in complementary metal–oxide–semiconductor devices. Lu2O3 is proposed because of its predicted thermodynamical stability on silicon and large conduction band offset. We report on the growth by atomic-layer deposition of lutetium oxide films using the dimeric {[C5H4(SiMe3)]2LuCl}2 complex, which has been synthesized for this purpose, and H2O. The films were found to be stoichiometric, with Lu2O3 composition, and amorphous. Annealing in nitrogen at 950°C leads to crystallization in the cubic bixbyite structure. The dielectric constant of the as-grown Lu2O3 layers is 12±1. [ABSTRACT FROM AUTHOR]

The composition of GeO(2) films grown on Ge has been studied for different molecular deposition processes and after exposure to ambient air. The stoichiometry, the interaction with moisture, and the interfacial details of the films are shown to be dramatically process dependent.