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We explore overcoming the non-oxidizing environment requirement issues in silicon oxide (SiOx) based memristors and investigate potential next steps for use of SiOx as a memristor material. A SiOx/HfOx stacked material was engineered, developed and tested to verify operation of the SiOx-based memristors, and the stacked material exhibits interfacial proton accumulation leading to ultra-low-voltage operation (

Selectorless graphite-based resistive random-access memory (RRAM) has been demonstrated by utilizing the intrinsic nonlinear resistive switching (RS) characteristics, without an additional selector or transistor for low-power RRAM array application. The low effective dielectric constant value (k) layer of graphite or graphite oxide is utilized, which is beneficial in suppressing sneak-path currents in the crossbar RRAM array. The tail-bits with low nonlinearity can be manipulated by the positive voltage pulse, which in turn can alleviate variability and reliability issues. Our results provide additional insights for built-in nonlinearity in 1R-only selectorless RRAMs, which are applicable to the low-power memory array, ultrahigh density storage, and in-memory neuromorphic computational configurations.

In this work, one diode-one resistor (1D-1R) SiO x -based resistive switching (RS) elements were fabricated using PN Si diode as a selector to eliminate sneak-path issues. Our work and results include: 1) demonstrating sub-μs pulsed programming; 2) rectification ratio > 106 (meeting ITRS roadmap criteria) for integrated 1D-1R cross-bar arrays; 3) multi-bit operation; 4) 106 endurance cycles; and 5) robust read/write disturbance immunity for unselected cells in 16×16 1D-1R arrays.

The effects of incorporating a thin silicon layer into a SiO2-based resistive-switching random access memory are presented. An improved performance, including a lower electroforming voltage and a more stable device current in the high-resistance programmed state, has been achieved by physical vapor deposition of a thin silicon layer onto the sidewall region of the device. Tristate pulse endurance performance over 106 cycles has been demonstrated. The programmed data show immunity to read disturb testing at 1 V and can be sustained up to 150°C thermal exposure. It is concluded that the improved performance is due to formation of a more robust and more uniform conducting filament. As a result of this advantage, stable tristate programming can be realized in the SiO2-based resistive memory device.

ArF excimer laser‐enhanced photochemical vapor deposition of Si from Si2H6 in an UHV deposition chamber has been used to achieve Si epitaxy at temperatures as low as 250 °C. The system design criteria are discussed. Modified Schimmel etching/Nomarski microscopy, transmission electron microscopy, and reflection high energy electron diffraction have been used to study the microstructure of Si films as a function of laser power, substrate temperature and disilane partial pressure. The growth rates were observed to be linearly dependent on laser intensity and Si2H6 partial pressure. The morphology of the films is excellent and defects such as dislocation loops and stacking faults are not seen.

An ArF excimer laser has been used with the beam parallel to the Si(100) substrate in order to deposit homoepitaxial silicon films at temperatures from 250 to 350 °C with growth rates from 1 to 10 A min −1 . The growth involves photolytic decomposition of Si 2 H 6 and the generation and adsorption of growth precursors on the hydrogenated silicon surface. The deposition yield of solid silicon from photo-excited Si 2 H 6 is estimated to be 0.20 ± 0.04. Growth rates vary linearly with laser intensity and Si 2 H 6 partial pressure over the ranges 1–15 mJ cm − pulse −1 and 5–40 m Torr respectively. Epitaxy is maintained for temperatures above the threshold for thermal dissociation of surface (SiH 2 ) n chains at about 250 °C, and for temperatures below the onset of Si 2 H 6 pyrolysis and rapid thermal desorption of surface H 2 at about 350 °C. Epitaxy is achieved for laser intensities and Si 2 H 6 partial pressures that result in low initial photofragment concentrations (below 10 13 cm −3 ), and for total pressure and flow conditions such that there is little secondary photolysis of the initial photofragments. Very low defect density films in terms of stacking faults and dislocation loops (less than 10 5 cm −2 ), and excellent crystallinity, have been grown, as confirmed by Schimmel defect etching in conjunction with Nomarski microscopy, transmission electron microscopy, electron diffraction and in situ reflection high energy electron diffraction.

Homoepitaxial Si films were deposited using an ArF excimer laser beam parallel to the substrate to photodissociate Si2H6 at low temperatures (250–350 °C) under laser intensity and Si2H6 partial pressure conditions that result in low initial photofragment concentrations (< 1013 cm−3). Total pressure and flow conditions were chosen such that there is little secondary photolysis of the initial photofragments. The deposition yield of solid Si from photoexcited Si2H6 is estimated to be 0.20±0.04, indicating that in order for film growth to result solely from the primary products in ArF laser (193 nm) photolysis of Si2H6, a sticking coefficient ≥0.6 must be assigned to the dominant growth precursor. Growth rates vary linearly with laser intensity and Si2H6 partial pressure over a range of 1–15 mJ/cm2 pulse and 5–40 mTorr, respectively. Increasing the distance between the laser‐beam axis and the silicon substrate results in a reduction of the growth rate that can be explained by gas‐phase chemical reaction of th...

Low temperature silicon epitaxy has been achieved at substrate temperatures ranging from 250-350 o C using the 193 nm output of an ArF excimer laser to generate reactive growth precursors by photolytic decomposition of Si 2 H 6 . Growth rate dependencies on substrate temperature, Si 2 H 6 partial pressure, and laser photon flux density are presented. Growth rates are observed to vary linearly with laser beam power and Si 2 H 6 partial pressure, indicating that the overall growth rate is limited by the precursor generation rate

Defect characterization of epitaxial silicon films grown on lightly boron-doped Si (100) substrates by low temperature photo-enhanced chemical vapor Deposition (PCVD) using 193 nm ArF excimer laser dissociation of Si 2 H 6 in an ultra-high-vacuum (3×10 -9 Torr) chamber is discussed. The crystallinity was studied by in situ of reflection high energy electron diffraction (RHEED), and selected area electron diffraction in a transmission electron microscope (TEM), and defects such as stacking faults and dislocation loops were investigated by TEM and dilute Schimmel etching/Nomarski microscopy

Silicon homoepitaxial films have been grown by photodissociation of Si2H6 by the 193 nm line of an ArF excimer laser in an ultra-high vacuum system. Silicon epitaxy has been achieved in two ways: one, in which the laser shines into the chamber parallel to the substrate and another, in which the laser is directly incident on the substrate at grazing angles (87° with respect to the substrate normal). Controllable growth rates of 0.5–4A/min have been achieved for crystalline films by the first method using substrate temperatures as low as 250° C, Si2H6 partial pressures of 20 mTorr and photon flux densities of 1016 photons/pulse.cm2. In the second method, where the laser beam is directly incident on the wafer at grazing angles, very high growth rates of up to 80A/min have been achieved at 300° C, 20 mTorr Si2H6 partial pressure and a photon flux density of 2 × 1015 photons/pulse.cm2. A comparison of the microstructure of the films grown by the two methods is presented on the basis ofin situ reflection high energy electron diffraction (RHEED) analysis and selected area transmission electron microscopy (TEM) studies. In both cases, the growth rates are found to be linearly dependent on the photon flux density for the process parameter ranges studied.

Defect characterization of epitaxial silicon films grown on Si(100) lightly boron-doped wafers by low temperature photochemical vapor deposition using ArF excimer laser decomposition of Si 2 H 6 is discussed. The film morphology and crystallinity were investigated by defect etching-Nomarski optical microscopy, reflection high energy electron diffraction and transmission electron microscopy. The growth parameters such as laser power, Si 2 H 6 partial pressure and substrate temperature were varied to study the dependence of crystallinity on these parameters. Single-crystal films with a very low defect density were obtained at 0.08-0.7 W laser power, 5–20 mTorr Si 2 H 6 partial pressure and 250–350°C substrate temperature.

An edge-free structure and hermetic encapsulation technique are presented that enable SiOx-based resistive random-access memory (RRAM) operation in air. A controlled etch study indicates that the switching filament is close to the SiOx surface in devices with an exposed SiOx edge. Electrical test of encapsulated, edge-free devices in 1 atmosphere air indicates stable switching characteristics, unlike devices with an edge. This work demonstrates that SiOx RRAM is able to operate in air with proper encapsulation and an edge-free structure. The resistive switching failure mechanism when operating in air is explained by the oxidation of hydrogen-complexed defects in the switching filament.

The physical mechanisms of unipolar resistive switching (RS) in SiOx-based resistive memory are investigated using TaN/SiOx/n++Si and TiW/SiOx/TiW device structures. RS is independent of SiOx thickness and device area, confirming that RS occurs in a localized region along a filamentary pathway. Results from experiments varying electrode type, series resistance, and the oxygen content of SiOxNy materials show the potential to optimize switching performance and control device programming window. Device materials with stoichiometry near that of SiO2 are found to have better operating stability as compared to extrinsic, N-doped SiOxNy materials. The results provide further insight into the physical mechanisms of unipolar operation and lead to a localized switching model based on electrochemical transitions involving common SiOx defects. High-temperature data retention measurements for over 104 s in high- and low-resistance states demonstrate the potential for use of intrinsic SiOx RS devices in future nonvolatile memory applications.

The electroforming voltages (Vef) of silicon oxide resistive random access memory devices with oxide sidewall etched to different degrees are compared. The results show that the Vef is significantly reduced when more sidewall area is formed, and Vef of around 17 V is achieved in devices with maximum sidewall area. Plausible electroforming and state switching mechanisms are discussed using a filament-gap model. Endurance measurements up to 107 pulse cycles are compared for different device types. An external series resistance may be helpful for decreasing voltage stress during pulsed cycling to help enable device survival beyond 107 pulse cycles.

The ambient gas effect in SiOx-based resistive switching memory has been studied. After the electroforming process, resistive switching behavior functions in vacuum as well as in nitrogen without dramatic degradation. However, introducing an oxygen-nitrogen ambient suppresses resistive switching behavior at pressures above 1 Torr. Resistive switching is fully reestablished in oxygen-exposed devices after a vacuum recovery step. The failure phenomena can be described by Monte Carlo simulation using bi-modal statistics to enable feature distribution modeling of failure modes. Design criteria and guidelines are identified for packaging of future oxygen-sensor and of nonvolatile memory applications.

The electroforming voltage (Vef) of silicon oxide resistive random access memories treated with post-deposition-anneal (PDA) and/or post-metal-anneal in different gas ambients is compared. Secondary ion mass spectroscopy result shows significant incorporation of H/D atoms in SiOx after anneals in H2/N2 and D2/N2. Vef is significantly reduced after anneal in H2/N2 or D2/N2, but D2/N2 anneal results in even lower Vef, which could be due to more stable Si passivation in the Si-D/O+ pair as compared to the Si-H/O+ pair. On and off state currents are measured at 200 mV gate bias every 60 s for a total time of 6000 s with results showing good data retention for both on and off states. On and off state currents are observed to decrease when using PDA resulting in lower overall power dissipation.

The resistive switching between high impedance (“off” state) and low impedance (“on” state) is demonstrated on e-beam evaporated SiOx/Si resistive random access memory devices in this paper. The set and reset voltages are independent of the device perimeters and oxide thicknesses after electroforming. A circuit model including filament conductance G is proposed to explain the measured “on” state capacitances under frequency ranges from 1 KHz to 1 MHz. The electrochemical redox process is adopted to explain the formation of Si filament during electroforming and switching. “On” and “off” currents were also measured at various operating temperatures. It is found that both set and reset voltages increase as temperature decreases and that no electroforming is exhibited at low temperature T = 77 K.

Non-thermal Chemical Vapor Deposition (CVD) such as laser-enhanced photo-CVD of Si at low temperatures is important for Si-based heterostructures and doping superlattices. Growth kinetic models must be developed to allow these processes to be fully exploited. Intrinsic Si epitaxial layers were deposited at low substrate temperatures of 250-350ºC using the 193 nm output of an ArF excimer laser to directly dissociate Si2H6. The intrinsic film deposition rate can be described by a kinetic model that considers the gas phase reactions of the primary photolysis products and diffusion ofsilicon-bearing molecules to the growth surface. With the laser beam tangential to the substrate surface, growth rates as a function of beam-to-substrate distance have been characterized and indicate that very little gas phase reaction occurs for the dominant Si growth precursor. In order for intrinsic film deposition to result solely from Si2H6 photolysis products, a sticking coefficient ≥ 0.6 must be assigned to the dominant growth precursor in order to fit the observed yield of Si deposited in the films, indicating that the dominant growth precursor in 193 nm Si2H6 photolysis is perhaps H2SiSiH2.

Low temperature silicon epitaxy has been achieved at substrate temperatures ranging from 250 degree(s)C to 350 degree(s)C using the 193 nm output of ArF excimer laser to generate reactive growth precursors by photolytic decomposition of Si2H6. Growth rate dependencies on substrate temperature, Si2H6 partial pressure, laser photon flux density, and beam-to-substrate distance are presented. A simple expression for the growth rate as a function of process parameters can be obtained by considering the single-photon absorption rate of Si2H6 at the ArF excimer laser wavelength of 193 nm, and the gas kinetic transport of the resulting photofragments to the substrate surface. With the beam tangentially positioned approximately 1 mm from the substrate, a large percentage (7 +/- 1%) of the silicon available from the excited Si2H6 contributes to film formation. As the beam is moved away from the substrate, the chemical reaction rate of the growth precursors becomes significant with respect to the diffusion rate and the growth rate is observed to decrease. By tilting the laser beam to provide a normally incident component striking the substrate surface, the dangling bond density of the surface can be increased by photon assisted H desorption and growth rates are observed to increase. At substrate temperatures less than 400 degree(s)C, the growth rate is weakly dependent on temperatures with an activation energy of approximately equals 0.05 eV, whereas for temperatures above 400 degree(s)C, film deposition becomes dominated by pyrolytic decomposition of Si2H6 with an activation energy of approximately equals 1.2 eV.© (1991) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

The 193 nm output of an ArF excimer laser has been used to selectively photodissociate Si2H6 to deposit homoepitaxial Si films in the temperature range of 250°C to 350°C. Photolytic decomposition of Si2H6 results in the generation and adsorption of growth precursors on a hydrogenated Si surface. A simple growth kinetic model has been developed based on the most likely primary photofragments upon single-photon absorption by Si2H6 at the ArF excimer laser wavelength of 193 nm, and gas kinetic transport of the resulting photofragments to the substrate surface. Growth rates are observed to vary linearly with laser beam power and Si2H6 partial pressure when the laser beam is tangentially positioned less than 0.5 mm from the Si substrate for Si2H6 partial pressures less than 40 mTorr, total chamber pressures of 600 mTorr, and laser beam photon flux densities less than 2×1016 photons/cm2.pulse. Under these conditions, gas-phase diffusion dominates over chemical reaction rates and laser beam absorption is in the optically thin limit. The model then reduces to a simple form that predicts a linear dependence of growth rate on Si2H6 partial pressure and gives an accurate estimate of the expected growth rate. The epitaxial films are specular, and appear to have very low defect density in terms of stacking faults, as determined by modified Schimmel etching and Nomarski microscopy, and dislocation loops as determined by TEM (less than 105 loops/cm2). The crystallinity has been confirmed both by in situ RHEED, where we see a (l×l) streaky pattern, as well as selected electron diffraction, which shows a (100) crystalline orientation.