Off-state Resistance Research Articles

Large and robust resistive switching in co-sputtered Pt-(NiO-Al2O3)-Pt devices

We have systematically investigated the resistive switching and electroresistance behavior in Pt-[NiO-Al2O3]-Pt (PNAP) capacitor-like structures. The PNAP devices show a large ON-OFF ratio (∼107), which is strongly dependent on the rate of the voltage sweep. Interestingly, the devices exhibit a robust electroresistance behavior in the high resistance OFF state and show an intriguing change of sign of rectification with increasing end voltage. Our direct measurement of the surface temperature of the sample during resistive switching indicates that RESET process is assisted by Joule heating effects. The results are explained on the basis of plausible interplay between Schottky barrier modification due to the trapped charge carriers at the metal–oxide interface and percolation effects of conducting nanofilaments.

Design and Test of Superconducting Persistent Current Switch for Experimental Nb3Sn Superconducting Magnet

A superconducting persistent current switch with an off-state resistance of 10 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\Omega$</tex-math></inline-formula> for an experimental Nb <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> Sn superconducting coil has been designed, fabricated, and tested. The superconducting switch is thermal controlled, consisting of the bobbin of brass, the noninductive superconducting winding, the heater, and the support bar. A temperature sensor is fixed in the bobbin to monitor the temperature of the superconducting switch. The superconducting switch operates at 4.2-K temperature connected in parallel with the power supply and the experimental Nb <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> Sn superconducting coils. One GM cryocooler is employed to cool down the whole system. Based on the finite-element method, the numerical simulations of the switching performance of temperature distribution during heating and cooling cycles are performed. The results of the closed-loop operation show that the switch can successfully operate in the conduction-cooled magnet. The maximum closed-loop current is 170 A.

A Study of Gamma-Ray Exposure of Cu–SiO$_2$ Programmable Metallization Cells

The Cu-SiO 2 based programmable metallization cell (PMC) is a promising alternative to the Ag-chalcogenide glass PMC because of its low power consumption and CMOS-compatibility. Understanding its total ionizing dose (TID) response helps in assessing the reliability of this technology in ionizing radiation environments and benefits its expansion in the space electronics market. In this paper, the impacts of TID on the switching characteristics of Cu-SiO 2 PMC are investigated for the first time. The devices were step irradiated with 60 Co gamma-rays to a maximum dose of 7.1 Mrad ( SiO 2 ). The results show that gamma-ray irradiation has a negligible impact on the virgin-state and on-state resistance of Cu-SiO 2 PMCs. The off-state resistance slightly decreases after the first 1.5 Mrad( SiO 2 ) of exposure, but this reduction saturates after higher levels of TID. Other switching characteristics such as the set voltage, multilevel switching capability and endurance were also studied, all of which did not show observable changes after gamma-ray radiation. The immunity to ionizing radiation is attributed to the suppression of the photo-doping process.

A Physical Model for the Statistics of the Set Switching Time of Resistive RAM Measured With the Width-Adjusting Pulse Operation Method

The correlation between the set time ( $t_{\mathrm {\mathrm {set}}}$ ) and the initial off-state resistance ( $R_{\mathrm{\scriptscriptstyle OFF}}$ ) statistics for a Ti/ZrO2/Pt bipolar resistive random access memory device was investigated. The width-adjusting pulse operation method, which can significantly improve the switching uniformity, was used to accurately measure $t_{\mathrm {\mathrm {set}}}$ , and the gathered statistical data were analyzed using Weibull distributions. Both the Weibull slope ( $\beta _{t}$ ) and the scale factor ( $t_{\mathrm {\mathrm {set63\%}}}$ ) of $t_{\mathrm {\mathrm {set}}}$ distributions were found to increase logarithmically with $R_{\mathrm{\scriptscriptstyle OFF}}$ . The observed $t_{\mathrm {\mathrm {set}}}-R_{\mathrm{\scriptscriptstyle OFF}}$ interdependence provides a guideline in improving the switching uniformity and optimizing the tradeoff between set speed and disturb immunity. An analytical cell-based model was developed to explain the $R_{\mathrm{\scriptscriptstyle OFF}}$ -dependent $t_{\mathrm{\scriptscriptstyle SET}}$ statistics, which can be implemented in statistical compact models and circuit simulators for improving RRAM cell design and memory performances.

Exploiting Intrinsic Variability of Filamentary Resistive Memory for Extreme Learning Machine Architectures

In this paper, we show for the first time how unavoidable device variability of emerging nonvolatile resistive memory devices can be exploited to design efficient low-power, low-footprint extreme learning machine (ELM) architectures. In particular, we utilize the uncontrollable off-state resistance (Roff/HRS) spreads, of nanoscale filamentary-resistive memory devices, to realize random input weights and random hidden neuron biases; a characteristic requirement of ELM. We propose a novel RRAM-ELM architecture. To validate our approach, experimental data from different filamentary-resistive switching devices (CBRAM, OXRAM) are used for full-network simulations. Learning capability of our RRAM-ELM architecture is illustrated with the help of two real-world applications: 1) diabetes diagnosis test (classification) and 2) SinC curve fitting (regression).

Tunable High-Q TSV Inductor Packaging with MEMS

In this paper, we present a Through-Silicon-Via (TSV)-based 3D tunable inductor implementation for RF applications. The proposed inductor structure uses MEMS (Micro Electro-Mechanical Systems) switches to vary inductance by activating and deactivating the switches. MEMS-based switches are used to offer high isolation in the off state. The tunable inductor is tested within an LNA circuit for variation in off-state leakage resistance. Detailed 3D full wave simulation results are presented for different cellular frequency bands.

Memory switching characteristics in amorphous ZnIn2Se4 thin films

ZnIn2Se4 thin films were deposited by flash evaporation of bulk material onto glass and pyrographite substrates under vacuum. The surface aspects of films have been studied by scanning electron microscopy. The dynamic and static current (I) versus voltage (V) characteristics of brass/pyrographite/ZnIn2Se4 thin film/platinum sandwiched devices for different film thicknesses (350–650 nm) and temperatures (313–353 K) were measured. The OFF state I–V characteristics of fabricated thin film devices indicated that the conduction mechanism is of the Poole–Frenkel type. In addition, a threshold memory switching mechanism from a high resistance OFF state to a low resistance ON state was observed in these thin film structures. The I–V characteristics of the memory device were studied at different annealed and ambient temperatures. The threshold voltage was found to increase linearly with film thickness and decrease exponentially with ambient temperature. The results obtained were discussed, and a thermal model for initiating the switching process in this device system could be indicated.

Static impedance behavior of programmable metallization cells

Programmable metallization cell (PMC) devices work by growing and dissolving a conducting metallic bridge across a chalcogenide glass (ChG) solid electrolyte, which changes the resistance of the cell. PMC operation relies on the incorporation of metal ions in the ChG films via photo-doping to lower the off-state resistance and stabilize resistive switching, and subsequent transport of these ions by electric fields induced from an externally applied bias. In this paper, the static on- and off-state resistance of a PMC device composed of a layered (Ag-rich/Ag-poor) Ge30Se70 ChG film with active Ag and inert Ni electrodes is characterized and modeled using three dimensional simulation code. Calibrating the model to experimental data enables the extraction of device parameters such as material bandgaps, workfunctions, density of states, carrier mobilities, dielectric constants, and affinities.

Directly correlating the strain-induced electronic property change to the chirality of individual single-walled and few-walled carbon nanotubes.

We fabricate carbon nanotube (CNT)-field effect transistors (FETs) with a changeable channel length and investigate the electron transport properties of single-walled, double-walled and triple-walled CNTs under uniaxial strain. In particular, we characterize the atomic structure of the same CNTs in the devices by transmission electron microscopy and correlate the strain-induced electronic property change to the chirality of the CNTs. Both the off-state resistance and on-state resistance are observed to change with the axial strain following an exponential function. The strain-induced band gap change obtained from the maximum resistance change in the transfer curve of the ambipolar FETs is quantitatively compared with the previous theoretical prediction and our DFTB calculation from the chirality of the CNTs. Although following the same trend, the experimentally obtained strain-induced band gap change is obviously larger (57%-170% larger) than the theoretical results for all the six CNTs, indicating that more work is needed to fully understand the strain-induced electronic property change of CNTs.

The Susceptibility of &lt;formula formulatype="inline"&gt; &lt;tex Notation="TeX"&gt;${\hbox {TaO}}_{\rm x}$&lt;/tex&gt;&lt;/formula&gt;-Based Memristors to High Dose Rate Ionizing Radiation and Total Ionizing Dose

This paper investigates the effects of high dose rate ionizing radiation and total ionizing dose (TID) on tantalum oxide (TaOx) memristors. Transient data were obtained during the pulsed exposures for dose rates ranging from approximately 5.0 ×107 rad(Si)/s to 4.7 ×108 rad(Si)/s and for pulse widths ranging from 50 ns to 50 μs. The cumulative dose in these tests did not appear to impact the observed dose rate response. Static dose rate upset tests were also performed at a dose rate of ~3.0 ×108 rad(Si)/s. This is the first dose rate study on any type of memristive memory technology. In addition to assessing the tolerance of TaOx memristors to high dose rate ionizing radiation, we also evaluated their susceptibility to TID. The data indicate that it is possible for the devices to switch from a high resistance off-state to a low resistance on-state in both dose rate and TID environments. The observed radiation-induced switching is dependent on the irradiation conditions and bias configuration. Furthermore, the dose rate or ionizing dose level at which a device switches resistance states varies from device to device; the enhanced susceptibility observed in some devices is still under investigation. As a result, numerical simulations aremore » used to qualitatively capture the observed transient radiation response and provide insight into the physics of the induced current/voltages.« less

A Combined &lt;italic&gt;Ab Initio&lt;/italic&gt; and Experimental Study on the Nature of Conductive Filaments in &lt;inline-formula&gt; &lt;tex-math notation="TeX"&gt;${\rm Pt}/{\rm Hf}{\rm O}_{2}/{\rm Pt}$ &lt;/tex-math&gt;&lt;/inline-formula&gt; Resistive Random Access Memory

Through ab initio calculations, we propose that the conductive filaments in Pt/HfO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> /Pt resistive random access memories are due to HfO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</sub> suboxides, possibly tetragonal, where x ≤ 1.5. The electroforming process is initiated by a continuous supply of oxygen Frenkel defect pairs through an electrochemical process. The accumulation of oxygen vacancies leads to metallic suboxide phases, which remain conductive even as ultranarrow 1-nm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> filaments embedded in an insulating HfO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> matrix. Our experiments further show that the filaments remain as major leakage paths even in the OFF-state. Moreover, thermal heating may increase the OFF-state resistance, implying that there are oxygen interstitials left in the oxide layer, which may recombine with the oxygen vacancies in the filaments at high temperature.

A Four-Terminal, Inline, Chalcogenide Phase-Change RF Switch Using an Independent Resistive Heater for Thermal Actuation

An inline chalcogenide phase-change radio-frequency (RF) switch using germanium telluride and driven by an integrated, electrically isolated thin-film heater for thermal actuation has been fabricated. A voltage pulse applied to the heater terminals was used to transition the phase-change material between the crystalline and amorphous states. An ON-state resistance of 4.5 Ω (0.08 Ω-mm) with an OFF-state capacitance and resistance of 35 fF and 0.5 MΩ, respectively, were measured resulting in an RF switch cutoff frequency (F <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">co</sub> ) of 1.0 THz and an OFF/ON resistance ratio of 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">5</sup> . The output third-order intercept point measured , with zero power consumption during steady-state operation, making it a nonvolatile RF switch. To the best of our knowledge, this is the first reported implementation of an RF phase change switch in a four-terminal, inline configuration.

Evidence of electrochemical resistive switching in the hydrated alumina layers of Cu/CuTCNQ/(native AlOx)/Al junctions

We have investigated bipolar resistive switching of Cu/CuTCNQ/Al cross-junctions in both vacuum and different gas environments. While the generally observed S-shaped I-V hysteresis was reproduced in ambient air, it was reversibly suppressed in well-degassed samples in vacuum and in dry N2. The OFF-switching currents in ambient air peaked when approximately +2.6 V was applied to the Al electrode at low voltage sweep rates. OFF-switching at constant bias was accelerated in humid and oxygen-rich atmospheres. For unbiased samples stored in air, ON-state (RON) and OFF-state (ROFF) resistances increased with time, and RON surpassed the initial ROFF after approximately one week. Retention times were enhanced for samples stored in vacuum and those with a larger cross-junction area. We suggest that resistive switching occurs in a hydrated native alumina layer at the CuTCNQ/Al interface that grows in thickness during exposure to ambient humidity: ON-switching by electrochemical metallization of free Al and/or Cu ions and OFF-switching by anodic oxidation of the Al electrode and previously grown metal filaments.

High performance floating‐gate technology compatible antifuse

An antifuse structure that is fully compatible with the standard floating-gate technology is presented. The antifuse consists of an oxide-nitride-oxide dielectric layer, sandwiched between polysilicon and N-well layers. The characteristics of the antifuse are investigated. The off-state resistance of the antifuse is larger than 10 GΩ. The programmed antifuses show linear ohmic characteristics and have a tight resistance distribution centred around 350 Ω. The time dependent dielectric breakdown measurements show that the extrapolated lifetime of the unprogrammed antifuse at 5.5 V is as long as 40 years, and the resistance change of post-program antifuses under the continuous reading mode test is lower than 5%.

Superconducting Joint and Persistent Current Switch for a 7-T Animal MRI Magnet

The fabrication and test of the multifilament NbTi superconducting joints and NbTi/CuNi persistent current switch for a 7-T animal magnetic resonance imaging magnet are presented. The joints were fabricated by the solder matrix replacement method in the open air environment, and the samples were tested by a measuring facility that was developed based on the current-decay method and can supply a background magnetic field up to 0.6 T. The measured results indicate that the NbTi/Cu sample joints can carry a current up to 1000 A with a resistance lower than 3 ×10-14 Ω, while the NbTi/CuNi sample joint can carry a current up to 630 A with a resistance lower than 4 ×10-14 Ω under a magnetic field of 0.6 T. The thermally triggered switch was designed based on a two-dimensional axisymmetric finite-element analysis thermal model that is built with the commercial code ANSYS. It has an off-state resistance of 5 Ω and an equal switch-off to recovery time of about 2.5 s at a heating current of 120 mA.

Organic low voltage rewritable memory device based on PEDOT:PSS/f-MWCNTs thin film

We report on devices constructed using a small quantity (⩽0.01wt.%) of functionalized multiwalled carbon nanotubes (f-MWCNTs) embedded in a conducting polymer (poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate), PEDOT:PSS) matrix and aluminum top electrodes, prepared on indium-tin-oxide (ITO) substrates. Our ITO/(PEDOT:PSS+f-MWCNTs)/Al devices show current bistability. The low resistance ON-state, as well as the high resistance OFF state, retain the information for hours and are stable after hundreds of write–read–erase–read (WRER) cycles, being potentially interesting for erasable and rewritable volatile memory device applications. Moreover, the operation voltages used for performing these WRER cycles are very low. The threshold voltage for OFF to ON switching can be adjusted changing the f-MWCNTs concentration. Our results suggest that the nanotubes are necessary for the production of an inhomogeneous electric field playing a role in the electroforming (dielectric breakdown) of the aluminum oxide layer at the Al2O3/(PEDOT:PSS) interface.

A novel antifuse structure based on amorphous bismuth zinc niobate thin films

A novel antifuse structure with amorphous bismuth zinc niobate (a-BZN) dielectrics was proposed. The characteristics of the a-BZN antifuse were investigated. Programming direction of up to down was chosen to rupture the a-BZN antifuse. The breakdown voltage of the a-BZN antifuse was obtained at a magnitude of 6.56 V. A large off-state resistance of more than 1 GΩ for the a-BZN antifuse was demonstrated. The surface micrograph of the ruptured a-BZN antifuses was illustrated. Programming characteristics with the programming time of 0.46 ms and on-state properties with the average resistance value of 26.1 Ω of the a-BZN antifuse were exhibited. The difference of characteristics of the a-BZN antifuse from that of a cubic pyrochlore bismuth zinc niobate (cp-BZN) antifuse and gate oxide antifuse was compared and analyzed.

Performance Test of Superconducting Switch for NMR Magnet

A superconducting switch with an off-state resistance of 10 Ω, operating current of about 67 A, for a NMR magnet in persistent current operation to obtain higher field stability is designed and manufactured. The superconducting switch is solenoid type which consists of four parts: bobbin, superconductor, heater and adiabatic part. And NbTi/CuNi superconducting wire with higher resistance is used and wound on the switch bobbin in a bifilar manner for low inductance and minimum field perturbation. Numerical simulations by FEM method for the switching performance of temperature distribution during heating and cooling cycles are performed. Finally the switching performance tests were carried out and the results show that the minimum heating power is about 0.69 W and the off-time is less than 10 s.

Cubic Pyrochlore Bismuth Zinc Niobate Thin Films for Antifuse Applications

Characteristics of a novel antifuse structure with cubic pyrochlore bismuth zinc niobate (BZN) thin film are investigated. A structure of Ti/Pt/BZN/Al for the BZN antifuses was proposed. The influence of various electric field directions, which were used for rupturing and programming the antifuses, on the BZN antifuse was analyzed, and the electric field direction of up to down was opted to program the antifuses. Excellent properties of the BZN antifuses were illustrated, including low leakage current, high off-state resistance, low programming voltage and time, moderate programming current, low on -state resistance, and tight distribution of on-state resistance. The BZN antifuse will be the most promising alternative to the gate oxide antifuses.

Resistive switching properties of plasma enhanced-ALD La2O3 for novel nonvolatile memory application

Plasma enhanced (PE) atomic layer deposition (ALD) of lanthanum oxide films on silicon and platinum substrates were examined using lanthanum-2,2,6,6-tetramethyl-3,5-heptanedione, and O2 plasma as precursors. The effect of pulse time and deposition temperature on the growth rate was investigated. Resistive switching behaviors of La2O3 prepared by PE-ALD were investigated as a promising candidate for next generation nonvolatile memory technology. The crystalline structure of the obtained film was found to be polycrystalline by transmission electron microscope and the chemical composition of the film was estimated to be stoichiometric La2O3 by x ray photoelectron spectroscopy. The low resistance ON state and high resistance OFF state can be reversibly altered under a low voltage about 1.5 and −0.6 V. More than 1000 reproducible switching cycles by dc voltage sweep were observed with a resistance ratio above 100, which was large enough to read out without obvious degradation. Moreover, the estimated working characteristics such as set and reset voltages distribution were sufficiently stable to fulfill requirement for memory application. Considering the excellent memory switching behavior, resistance switch device composed of a promising ALD high-k La2O3 dielectric film is a possible candidate to be integrated into future memory processes.