We propose a theoretical study for charging the floating gate composed of Si nanocrystals (NCs), in a non-volatile flash memory. Only a few electrons tunnel from the channel of a metal-oxide-semiconductor transistor into the two-dimensional array of nanocrystals.

Our model is based on the geometrical and physical properties of the device, in order to take the dispersion of the relevant parameters into account: NC radii, inter-NC distances, tunnel oxide and gate oxide thicknesses. The energy subbands of the channel are explicitly included, together with the doping density.

This three-dimensional model of electron tunneling into a NC is numerically solved through a two-dimensional finite element approach, which allows extensive numerical experimentations.

The tunneling times to charge a single NC or the whole NC floating gate are evaluated in a finer detail, and the influence of the dispersion of the relevant parameters is discussed.

Such a study may help the experimentalists to build efficient quantum flash memories.

The paper reports on the amorphization kinetics of chalcogenides ternary alloy induced by Ar or Sb ion irradiation. The reflectivity data, obtained “in situ” during irradiation, allow a description of the amorphization process in terms of a threshold fluence. The results demonstrate that amorphization is caused by the elastic collisions of the projectiles with target nuclei. The influence of the ion mass and energy, of the target temperature in the amorphization is also reported.

The resistance random access memory is attracting much attention as a high-density and high-speed non-volatile memory, having large resistance switching ration and good affinity with the conventional CMOS technologies. We demonstrate the resistance switching in the NiO thin film without using Pt electrode.

The optical properties of Tb-doped SiO2 films have been studied from multi-wavelength spectroscopic ellipsometry (SE) measurements performed over the 250–1100 nm wavelength range. The SE modeling carried out with care to adhere as much to the ellipsometric fitting qualities. The refractive index dispersions, the layer thickness, and the lateral thickness variation of the films are given and discussed regarding the optical constitution of these films and the ellipsometric validity of these parameters

A simple technique for the formation of Ge nanocrystals embedded in amorphous Lu2O3 high-k dielectric was demonstrated by pulsed laser ablation followed by rapid thermal annealing in N2 ambient. The structure and composition of the Ge nanocrystals in the oxide matrix have been studied by transmission electron microscopy (TEM) and x-ray photoelectron spectroscopy (XPS) analysis. A significant change in the structure and chemical composition of the film was obtained upon annealing. Cross-sectional and plan-view TEM images confirmed the formation of small Ge nanocrystals in amorphous Lu2O3 matrix with a mean size of about 6nm in diameter and a high areal density of 7 × 1011cm−2. The nanocrystals are well-isolated by the amorphous Lu2O3 in between, with almost spherical shape which are favorable for non-volatile memory (NVM) application due to an effective charge confinement. XPS measurements on the as-deposited sample indicate the existence of Ge in its oxidized state, consisting of GeO2 and Ge suboxides. A spontaneous reduction of GeO2 and GeOx was obtained after the annealing treatment, which provides Ge nuclei for nanocrystal formation. It is found that a low annealing temperature of 400oC is sufficient to dissociate the GeO2 and GeOx leading to the formation of Ge nanocrystals. The application of the nanocrystals in NVM devices was demonstrated by C-V characterization of the memory capacitor devices fabricated with Al2O3 control oxide layer. C-V results show a significant effect of the structure and composition of the film on the electrical performance of the device. The annealed device exhibits good memory behavior with a large memory window of 1.2V achieved with a low operation voltage.

The property of PCMO RRAM memory devices have been studied in terms of electrical pulse width, Pulse polarity, voltage ramping, film thickness, resistivity distribution, and temperature dependent of resistance. The PCMO material is deposited using MOD, PVD, or PLD process. The experimental results clearly indicated the resistance increase is due to localization of valence electrons. The narrow pulse induced resistance increase near the cathode indicated the localization of valence electrons is the effect of high density of excessive non-equilibrium electrons through the well known Jahn-Teller effect. High density of non-equilibrium electrons may also be induced by any other means such as displacement current, space charge limited current, SCLC, and radiation. High field intensity collapses the localized valence electrons and returns the device to the low resistance state. This is the intrinsic property of transition metal oxides. We expect all doped and un-doped transition metal oxides to exhibit resistance switching property.

Silicon-based nonvolatile memory modules are widely used in microcontrollers, where they are embedded into a monolithic system on a chip (SoC) which also includes high speed logic transistors, cache SRAM, and peripheral circuits for communicating with the external world. The physical principle most widely exploited for nonvolatile code and data storage is charge storage in floating gates. Recently, charge storage in nitride traps and nanocrystals also has been explored.

The most demanding use profiles with respect to temperatures, data retention times, and low failure rates are encountered in automotive engine control applications, where junction temperatures up to 150°C are common, for 1000's of hours. Starting with the 130nm technology node, embedded Flash technology has been integrated with copper interconnects, and at the 90nm node, low dielectric constant interlevel dielectrics are also employed to increase circuit performance. To achieve automotive reliability, the materials surrounding the silicon floating gate, nanocrystal, or nitride charge storage area must be evaluated for parasitic charge storage, write/erase stress-induced leakage current, and other parameters important for reliability. Any movement of parasitic charge, potentially over a long period of time, can reduce the sensing window of the Flash EEPROM bitcell.

Hybrid virus/inorganic nanoscrystals are considered as important building blocks towards new types of functionality for electronic devices. We use tobacco mosaic viruses to assemble platinum nanoparticles and conjugate with quantum dots. By forming a thin hybrid nanocomposite layer in the crossbar junction, we show electronic memory effect based on electrical bistable states with a large on/off ratio, and long retention time. Such hybrid bio-inorganic nanostructures for the first time are promising for future bio-inspired nanoelectronics.

Phase-change memory is promising because it has a simple structure and has scalability that originates from its unique operating mechanism. However, the programming current should be reduced in accordance with the scaling of cell size [1,2]. We previously reported PCM (Phase Change Memory) cells that operate under 1.5-V/100-μA writing pulses [3, 4]. This PCM had a cell structure composed of 180-nm-W (tungsten) bottom contact to an O-GST (Oxygen-doped GeSbTe) film. Its low-power characteristic is suitable for 0.13-μm generation embedded applications. In the present study, we introduced a new W/O-GST/TaO/W cell structure and found further decrease of programming current the improved stability in the fabrication process. We analyzed the mechanism by which oxygen in GST and the additional TaO layer reduce the power consumption during SET/RESET operations.

N-doped ZnO thin films were deposited by pulsed laser deposition on SiO2/Si substrates. X-ray diffraction analysis revealed that the films had the wurtzite structure, and were highly oriented along the c-axis direction. Au and Al electrical contacts were deposited by sputtering on the top surface of the samples, forming a two-terminal structure in each case. The current-voltage characteristics of the two terminal structure, and the temperature dependence of the resistance switching effect, were studied in the 125-300 K temperature range. The results of these measurements are presented and discussed in terms of the different Schottky barrier heights, as well as in terms of interfacial defect-induced gap states.

In this paper, characterizations of sputtered undoped and nitrogen-doped Sb2Te3 (ST and STN) films by X-ray diffraction (XRD) and resistance measurements are described and their application of lateral phase-change memory (PCM) is presented. Nitrogen concentration of the films was controlled by changing the flow rate ratio of N2/Ar during sputtering. Resitivity of STN films drops by 3-4 orders of magnitude due to crystallization. Resistivity increase of the STN film (N2/Ar=0.15) at above 270°C results from phase precipitation of SbN. Experimental results reveal that the temperature of crystallization to face-centered cubic (fcc) significantly increases from below 100°C to 160–220°C with increasing the ratio of N2/Ar (in the range of 0–0.15) and crystal structure further transforms from fcc to hexagonal. At high flow rate ratio of N2/Ar (>0.15), hexagonal Te phase firstly appears at 160°C and then orthorhombic SbN appears at 290°C.

This work focuses on electrical characterisation of NiFe/SiO2/Si diodes that can be used as spin injection into silicon for future spintronic devices. Capacitance-voltage characteristics show a large increase of the Si/SiO2 interfacial state density compared to 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 can be accounted for by using trap assisted electron transport mechanism. These traps may be attributed to ferromagnet atoms in the oxide bulk.

Phase Change Random Access Memory [PRAM] is one of the candidates for next generation memory due to its non-volatility, high speed, high density and compatibility with Si-based semiconductor process. Ge2Sb2Te5 [GST] thin film, an active layer in this device, is utilized because it has the well-known property of rapid crystallization without phase separation in erasable compact discs industry.

In order to integrate PRAM to beyond 512Mbit, a high writing current and degradation of cell transition at small cell size become a problem. To resolve these problem, Confined Cell structure PRAM was suggested. However, it was difficult to fill GST layer in a small hole with a conventional sputtering tool because a big overhang occurred.

In this work, we prepared GST films on the small hole patterned wafer by a new concept sputtering tool which designed developed a new concept sputtering tool. The structure of GST film was observed with cross section SEM and the film composition was measured with XRF.

It was observed an overhang was suppressed and a GST film was filled in a small hole with a new concept tool. In addition, the uniformity of the GST film composition was good at less than 1% in 200mm φ substrate.

The materials properties and resistance switching characteristics of hafnium oxide-based binary oxide were investigated for next generation memory device application. A nonstoichometric hafnium oxide (HfOx) film with a mixture structure of monoclinic and tetragonal phase and some metallic Hf-Hf bonds on TiN/Si were prepared by atomic layer chemical vapor deposition (ALCVD). Resistance random access memory devices consisting of Pt/HfOx/TiN/Si with low power operation (< 0.4 mW) and reset current (< 100 mA) were fabricated. The resistance ratio of high resistance state to low resistance state maintains 100∼1000 and after 1000 cycles of repetitively switching. A 1-nm-thick Al2O3 film in the interface between top electrode and HfOx films, the Pt/Al2O3/HfOx/TiN/Si memory devices were found that soft-error of set and reset process often occurred. Interface states in the anode side play an important role in maintaining a stable resistive switching for HfOx-based memory devices.

M/a-Si:H/c-Si based nonvolatile resistive switching devices with active areas down to 50 nm×50 nm have been fabricated and explored. Close to 100% device yield was achieved without necessity of high voltage forming process. Both rectifying switching and non-rectifying switching were demonstrated in a controllable fashion. The potential for this structure as nanoscale nonvolatile memory devices was investigated in terms of scalability, retention time, endurance and switching speed. The device showed switching speed faster than 5 ns, endurance cycles more than 106 and retention time longer than 150 days without any degradation of stored data. The devices exhibit improved resistance switching ratio when scaled down.

In this work we investigate the non-volatile memory behavior of Ni nanoparticles embedded within an insulating matrix. Nickel nanoparticles are deposited at room temperature by a new high-vacuum technique over a 4 nm tunneling thermal SiO2 layer followed by the deposition of HfO2 as a control insulator. Memory windows of ∼1.5V are observed in MOS capacitors at gate pulse voltages of 8V. Charge retention for write and erase state clearly indicate long time charge storage behavior.

Here we report on the synthesis of multiferroic BiFeO3 ceramics by mechanical activation and detailed investigation into its magnetic behavior. The mechanically milled ceramic was calcined at temperatures up to 800°C. X-ray diffraction studies show only the pure BiFeO3 phase forms at 700°C. Vibrating sample magnetometer (VSM) measurements were carried out up to 1.5 Tesla and the results show a weak magnetic ordering in the ceramics. The magnetic measurements were also done on the samples heat treated under various cooling conditions. VSM measurements showed pronounced effect of cooling on the Magnetization vs Field curves. Mössbauer measurements show that short range Fe2O3 ordering is still present in the sample that goes undetected by XRD. This component decreases as the calcination temperature is increased. The nature of magnetic ordering improves upon heating from 600 to 700°C, also suggested by pure BiFeO3 phase formation at 700°C. Magnetization vs Temperature measurements conducted on the sample heat treated at 700°C for 1hr followed by cooling in air show an antiferromagnetic transition at ∼370°C.

We have investigated charge transport properties with current perpendicular to the plane across the interface between a Cr-doped SrZrO3 perovskite oxide film and different top electrode metals. The measured resistance showed a wide variation depending on the top electrode metal, and suggested the interfacial properties with respect to contacting electrode metal kinds are responsible for the change in I-V characteristics (IVCs). The observed I-V curves were modeled with the equation I(V) = aV+bV2, where the variation of a was related to the work function of the metal whereas the variation of b was related to the oxygen affinity of the metal, consistent with space charge limited conduction through a defected interface. Additionally, the resistive switching was attributed to a change in both the a and the b coefficients. We speculate that voltage (or current) induced vacancy motion can account for a change in trap density in the oxide near the metallic electrical contact, and thus trapping or detrapping of charge carriers, showing the conductivity modulation across the junction.

We developed a pulse-type gas-feeding technique in low pressure chemical vapor deposition system in order to grow Si nanoclusters with high density and uniform size. The maximum density and average size of the Si nanoclusters were 7 × 1011/cm2 and 7 nm, respectively. Floating gate memory devices containing the storage node of the Si nanoclusters were fabricated. The memory window was 4.5 V when the writing and erasing voltages were +14 V and −18 V, respectively. The writing and erasing times were measured to be 1 ms and 200 ms, respectively. The retention time of Si nanocluster nonvolatile memory was estimated about 10 years.

Two-terminal electronic devices consisting of stacks of chalcogenide layers containing GeTe, Ge40Se60, SnTe, or SnSe have shown promise for application as electronic phase-change memories (Campbell, K.A. and Anderson, C.M., Microelectronics Journal 38, 52–59 (2007)). Here, we report the synthesis of (Ge40Se60)100−zMz alloys where M = Sn, In, Sb, and Zn, and the corresponding bulk material Raman spectra and differential scanning calorimetry data in order to explore material compositions that might be useful for producing a multi-state phase-change memory device.