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The introduction of metal nanocrystals (NCs) has been confirmed to improve electrical uniformity of oxide-based resistive random access memory (RRAM) devices significantly; however, the current reports do not systematically elucidate the relationship between the size/distribution of NCs and the electrical uniformity of RRAM devices. In this paper, we focused on the impact of metal NCs size and areal density on the resistive switching (RS) performances of oxide RRAM by atomic layer deposition (ALD) based on the experimental results and theoretical calculation. The dependence of ALD cycles of 50–130 during Pt or CoPtx NCs growth on the RS parameters of Al2O3 or HfO2 memory units has been evaluated systematically. The RRAM embedded Pt or CoPtx NCs shows the trends: with increasing ALD cycles, the forming voltage, set/reset voltage, the resistance in off and on state, and ${R}_{ \mathrm{\scriptscriptstyle OFF}}/{R}_{ \mathrm{\scriptscriptstyle ON}}$ ratio entirely first decrease, then flatten, and increase later with a minimum value at about 100 cycles. Although all metal NCs with various sizes enhance the electric field strength compared to at the planar region, only metal NCs with proper NCs size and areal density (9 nm/6– $10\times 10^{\textsf {11}}$ /cm2 in this paper) can effectively produce stronger localized electric field at the tip of metal NCs, leading to optimal RS behavior. [ABSTRACT FROM AUTHOR]

When developing silicon carbide (SiC) devices, the reliability of the internal body diode is an important issue. Stacking faults (SFs) are expanded from basal plane defects by using a body diode. Although it is well known that ON-voltage degradation occurs due to SFs, their effects on dynamic reliability have not been studied well. Furthermore, including the effects of SFs, there are not many reports about the dynamic reliability of SiC-MOSFETs. In this paper, a double-pulse switching test using 3.3-kV SiC-MOSFETs was carried out to clarify the failure mechanism of the switching operation of SiC-MOSFETs and effects of SFs on the safe operation area (SOA). Before the switching test, current stress was applied to the body diode of the devices under test (DUTs) to expand the SFs. The circuit configuration was half-bridge type, and a double-pulse gate signal was applied to the lower arm DUT. The switching voltage was 1.8 kV, and the switching current increased at about 8-A steps to failure. As a result, reverse recovery SOA (RRSOA) reliability decreased depending on the amount of SFs in the SiC-MOSFET. Because RRSOA failure was caused by avalanche due to the hole concentration during reverse recovery and the SFs raised local current density, reverse bias SOA (RBSOA) hardly decreased even if SFs containing SiC-MOSFETs were used. This is because RBSOA failure was caused by degradation of the gate isolation layer due to overheating and the temperature coefficient of the SFs electric resistance indicated negative. [ABSTRACT FROM AUTHOR]

In this paper, we demonstrate the linear conductance-change characteristics of a conductive-bridging RAM (CBRAM) to be employed as an artificial synapse device in neuromorphic systems. The CBRAM with a bilayer electrolyte structure (${\mathrm {Cu/Cu}}_{{2}-{x}}\text{S}$ / $\mathrm {WO}_{{3}-{x}}$ /W) exhibits analog switching behavior during the depression process due to the well-controlled dissolution of the conductive filament. To analyze the origin of this motion, we investigate the effective voltage applied to $\mathrm {Cu}_{{2}-{x}}\text{S}$ and $\mathrm {WO}_{{3}-{x}}$. Our findings reveal that $\mathrm {Cu}_{{2}-{x}}\text{S}$ , acting as a voltage divider, helps in suppressing the large voltage drop in $\mathrm {WO}_{{3}-{x}}$ , where the formation/dissolution of filament occurs. Furthermore, due to the diode-like characteristics of $\mathrm {Cu}_{{2}-{x}}\text{S}$ and the division of voltage drop between $\mathrm {WO}_{{3}-{x}}$ and $\mathrm {Cu}_{{2}-{x}}\text{S}$ , an optimum programming energy is applied to $\mathrm {WO}_{{3}-{x}}$ during the depression process. This leads to linear conductance-change characteristics under identical pulses. However, abrupt conductance-change characteristics are observed during the potentiation process. Thus, we use only the device characteristics of the depression part for the neuromorphic system. An excellent classification accuracy is achieved due to the linear conductance-change characteristics and optimized pulse conditions. [ABSTRACT FROM AUTHOR]

Resistive random access memory (ReRAM), a new emerging nonvolatile memory technology based on changes in electrical resistivity of a dielectric film, offers promising advantages such as scalability, fast switching, and low operation voltage. However, for ReRAM to become a successful technology, it is necessary to accurately control the stochastic nature of the conductive nanoscale filaments (CNFs) that governs the resistive switching (RS) behavior of the device and limits its long-term stability and reliability. In this paper, we developed a highly scalable nanostructured/textured electrode that is composed of an array of Al nanotips based on an anodic aluminum oxide template. The nanotips improve the RS characteristics by intensifying the electric field at the apex of each nanotip which is demonstrated using numerical simulations. The localized electric field induces the repetitive nucleation/ formation/rupture of the CNFs in a more controlled fashion compared to a flat Al electrode. As a result, the nanotip sample exhibits uniform and reduced forming/reset voltages as low as 4.70 ± 0.98V/1.00 ± 0.19 V, stable endurance, and long-term retention. As a result, we were able to achieve ultralow-power and error-free operation of 100 cells covering a large area, significantly demonstrating improved uniformity and reliability compared to devices made using flat Al electrodes. This universal bottom-up strategy of self-organized nanostructured-electrodes provides a pathway toward large-scale, highly reliable, and RS memory devices. [ABSTRACT FROM AUTHOR]

We present analysis and modeling of a new innovative nanoelectromechanical switch (NEMS) with virtually zero leakage current, 1–3-V operation voltage, 1–10-ns switching time, and small footprint. In addition to acting as a simple switch, the physical structure of NEMS enables positioning of multiple contacts to realize functional logic gates in a single device. The implementation of basic two (or more) input logic gates using a single device improves reliability and reduces charging delay time. The reduction in the number of devices also improves yield and power while simplifying implementation. To evaluate NEMS design, we present an accurate NEMS SPICE circuit simulation model which enables the measurement of NEMS timing and power requirement. Based on the model and the device fabrication data, we show that NEMS ISCAS-85 circuit shows significant improvement over CMOS technology counterpart (using 65- and 45-nm technology). [ABSTRACT FROM AUTHOR]

We demonstrate that a tunnel junction connected in series to the ferroelectric (FE) via a semiconductor (SC) layer can be used to 1 probe the polarization state in an FE thin-film capacitor. A thermodynamic analysis is carried out to demonstrate the carrier depletion and accumulation at the SC/tunnel-junction interface as a function of the polarization direction in the FE layer. Our results indicate that the tunnel junction’s polarization and electroresistance depend on those of the main FE bit for a carefully chosen doping of the SC. This would allow measurement of the tunnel current to probe the polarization state of the FE bit nondestructively with much lower power consumption than the destructive technique where the displacement current at the switching of polarization is read. The proposed approach considers an FE/SC/tunnel-junction stack with top and bottom electrodes and is analogous to the Giant Magnetoresistance (GMR) stacks where the resistance change is indicative of magnetization orientation of the pinned and soft layers, implying the binary bit in the storage medium. [ABSTRACT FROM AUTHOR]

Switching voltage variation of a Cu atom switch (AS) is improved to \(\sigma =9.5\) % by adjusting the buffer oxidation state and electrode surface roughness. The complementary AS (CAS) connects two Cu lines at each edge and is composed of a dual-layered electrolyte of oxidized Ti buffer metal/polymer solid electrolyte. A sufficiently oxidized Ti buffer layer prevents both Cu oxidation and Ti diffusion during the fabrication processes, reducing the OFF-state leakage current and making the ON/OFF current ratio high. A dry cleaning process reduces the Cu electrode surface roughness, tightening the set voltage distribution and enabling the use of a low programming voltage, 1.8 V. A large-scale crossbar switch block consisting of CASs has been operated by the improved switches. [ABSTRACT FROM AUTHOR]

By combining the basic device equations of metal–oxide–semiconductor field-effect transistors with the polarization retention characteristics of ferroelectric thin films, a retention model for ferroelectric-gate field-effect transistor (FeFET) is developed based on the depolarization field of the ferroelectric. This model gives the retention characteristics of FeFET both in short and long time scales. Simulations demonstrate that large polarization will result in large depolarization field, which causes fast polarization loss in turn. The retention characteristics of the off-state is poorer than that of the on-state for p-FeFET, because the depolarization field in accumulation state is much larger than that in strong inversion state. Further analysis indicates that an appropriate holding voltage could be used to restrain the depolarization field in accumulation state to improve the retention characteristics of p-FeFET. [ABSTRACT FROM AUTHOR]

As one of the key aspects in the reliability of redox-based resistive switching memories (ReRAMs), maximizing their endurance is of high relevance for industrial applications. The major limitation regarding endurance is considered the excessive generation of oxygen vacancies during cycling, which eventually leads to irreversible RESET failures. Thus, the endurance could be increased by using combinations of switching oxide and ohmic electrode (OE) metal that provides a high barrier for the generation of oxygen vacancies [defect formation energy (DFE)]. In this work, we present a sophisticated programming algorithm that aims to maximize the endurance within reasonable measurement time. Using this algorithm, we compare ReRAM devices with four different OE metals and confirm the theoretically predicted trend. Thus, our work provides valuable information for device engineering toward higher endurance. [ABSTRACT FROM AUTHOR]

The ab initio perspective based on density functional theory and nonequilibrium Green's function for the modeling of single electron transistors (SETs) based on thiol-ended thiophene and chromium complex of thiol-ended thiophene and their functioning in the Coulomb blockade regime has been discussed. Both thiol-ended thiophene molecule and its chromium complex have been analyzed for the charge stability and conductance dependence on the gate voltage and source-drain bias. The charging energies for the isolated and SET environment for both the islands have been calculated and discussed. Also, the effect of orientation and the dielectric medium has been studied in order to increase the conductance of SET with the combination of a particular orientation and a dielectric medium. The effect of different electrodes on charge stability diagram has also been studied. The analysis shows a remarkably improved conductance for the chromium complex of thiol-ended thiophene molecule in the SET environment than the thiol-ended thiophene molecule in the SET environment resulting in a fast switching metal-organic SET. [ABSTRACT FROM AUTHOR]

Multilevel high-resistance states are achieved in TiN/HfOx/Pt resistive switching random access memory device by controlling the reset stop voltage. Impedance spectroscopy is used to study the multilevel high-resistance states. It is shown that the high-resistance states can be described with an equivalent circuit consisting of the major components Rs , $R$ , and $C$ corresponding to the series resistance of the TiON interfacial layer, the equivalent parallel resistance, and capacitance of the leakage gap between the TiON layer and the residual conductive filament, respectively. These components show a strong dependence on the stop voltage, which can be explained in the framework of oxygen vacancy model and conductive filament concept. On the other hand, $R$ is observed to decrease with dc bias, which can be attributed to the barrier lowering effect of the Coulombic trap well in the Poole–Frenkel emission model. [ABSTRACT FROM AUTHOR]