Reset Switching Research Articles

A 100-nW 9.1-ENOB 20-kS/s SAR ADC for Portable Pulse Oximeter

This brief presents an energy-efficient 10-bit accuracy with 20-kS/s successive approximation register analog-to-digital converter for portable pulse oximeter. A data-dependent capacitor reset (DDCR) switching scheme for the capacitive digital-to-analog converter (CDAC) to reduce the average switching energy and the number of unit capacitors is proposed and implemented. Compared with the conventional capacitor switching scheme for CDACs, the proposed DDCR switching scheme reduces the average switching energy and the total number of unit capacitors by 97% and 75%, respectively. We achieved a signal-to-noise-and-distortion ratio of 56.5 dB and a spurious-free dynamic range of 64.7 dBc at the Nyquist input frequency. The measured peak differential and integral nonlinearities are 0.44 and 0.58 least significant bit, respectively. The figure of merit is 9.1 fJ/conversion-step. The prototype, fabricated in the 0.11- $\mu\mbox{m}$ CMOS process, occupies 0.033 mm2.

Improving resistance uniformity and endurance of resistive switching memory by accurately controlling the stress time of pulse program operation

In this letter, the impact of stress time of pulse program operation on the resistance uniformity and endurance of resistive random access memory (RRAM) is investigated. A width-adjusting pulse operation (WAPO) method which can accurately setup and measure switching time is proposed for improving the uniformity and endurance of RRAM. Different from the traditional single pulse operation (TSPO) method in which only one wide pulse is applied in each switching cycle, WAPO method utilizes a series of pulses with the width increased gradually until a set or reset switching process is completely finished and no excessive stress is produced. Our program/erase (P/E) method can exactly control the switching time and the final resistance and can significantly improve the uniformity, stability, and endurance of RRAM device. Improving resistance uniformity by WAPO compared with TSPO method is explained through the interdependence between resistance state and switching time. The endurance improvement by WAPO operation stems from the effective avoidance of the overstress-induced progressive-breakdown and even hard-breakdown to the conductive soft-breakdown path.

Simulation, Design, Fabrication, and Testing of a MEMS Resettable Circuit Breaker

We describe a novel concept for a microelectromechanical systems (MEMS) resettable circuit breaker. The concept involves fabricating the circuit breaker and the reset switch using a single microcantilever. The MEMS resettable circuit breaker consists of a microcantilever that is pulled toward the bottom electrode by electrostatic actuation. The MEMS cantilever also has a thermal heater, and when a current passes through the heater, it overcomes the electrostatic actuation force thereby disconnecting the circuit. A detailed finite element analysis using thermal-electric-structural multiphysics phenomena was studied. Electrostatic-structural coupled-field analysis shows the circuit breaker switch has a pull-in voltage of about 31 V for a singlecrystal Si cantilever with a thickness of 2 μm, a length of 1000 μm, and a width of 500 μm. Thermal-electric coupledfield analysis shows the switch maximum temperature is 80.5 °C at a 50-mA current flow. Thermal-electric-structural sequential analysis shows the cantilever tip has a maximum upward displacement of 0.3 μm, which is just enough to open the switch. The impact of the initial film stress in the SiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> insulation layer was also simulated, and the results show that the film stress has a significant impact on the initial cantilever position after release. Fabrication of the chips was done using two wafers, a silicon-on-insulator (SOI) wafer, and a double-side polished silicon wafer. The SOI wafer device silicon layer was selected as cantilever material. Platinum was selected as heater material and chrome-gold was selected for bonding, trace, and electrostatic electrodes. Electrical testing results confirmed the proposed and simulated operation principle of the MEMS resettable circuit breaker. The results showed that the switch achieved good contact at an electrostatic switch-ON voltage of about 55 V. The measured circuit breaker current threshold is in the range of 45-55 mA.

Complementary and bipolar regimes of resistive switching in TiN/HfO2/TiN stacks grown by atomic‐layer deposition

Atomic‐layer deposition (ALD) technique in combination with in vacuo X‐ray photoelectron spectroscopy (XPS) analysis has been successfully employed to obtain fully ALD‐grown planar TiN/HfO2/TiN metal–insulator–metal structures for resistive random access memory (ReRAM) memory elements. In vacuo XPS analysis of ALD‐grown TiN/HfO2/TiN stacks reveals the presence of the ultrathin oxidized layers consisting of TiON (∼0.5 nm) and TiO2 (∼0.6 nm) at the bottom TiN/HfO2 interface (i); the nonoxidized TiN at the top HfO2/TiN interface (ii); the oxygen deficiency in the HfO2 layer does not exceed the XPS detection limit (iii). Electroformed ALD TiN/HfO2/TiN stacks reveal both conventional bipolar and complementary types of resistive switching. In the complementary resistive switching regime, each programming sequence is terminated by a reset operation, leaving the TiN/HfO2/TiN stack in a high‐resistance state. The observed feature can avoid detrimental leaky paths during successive reading operation, which is useful in the passive ReRAM arrays without a selector element. The bipolar regime of resistive switching is found to reveal the gradual character of the SET and RESET switching processes. Long‐term potentiation and depression tests performed on ALD‐grown TiN/HfO2/TiN stacks indicate that they can be used as electronic synapse devices for the implementation of emerging neuromorphic computation systems.

Electronic resistance switching in the Al/TiO(x)/Al structure for forming-free and area-scalable memory.

Electronic bipolar resistance switching (eBRS) in an Al/TiOx/Al structure, where the TiOx layer was reactively sputter-deposited, was examined in conjunction with a structural analysis using transmission electron microscopy. A thin (3-5 nm) insulating Al(Ti)Ox layer was formed at the bottom Al electrode interface, which provided the necessary asymmetric potential barrier for the eBRS to emerge, whereas the top Al electrode interface appeared to have provided the fluent carrier (electron) injection. The set and reset switching were related to the trapping and detrapping of the carriers at the trap centers, the characteristic energy of which was ∼0.86 eV, across the entire electrode area. The general features of this material system as the feasible RS memory were insufficient: endurance cycle, <∼8000, and retention time at 85 °C, 10(6) s. However, the detailed analysis of the switching behavior based on the space-charge limited current conduction mechanism, and its variation with the switching cycles, provided useful information on the general features of the eBRS, which could also be applicable to other binary (or even ternary) metal-oxide RS systems based on the electronic switching mechanism.

Role of Anode on Resistance Switching Phenomenon of Metal Oxide Resistive Random Access Memory

ABSTRACTAlthough the presence of oxygen reservoir is assumed in many theoretical models which explain resistive switching of ReRAM with an electrode/metal oxide (MO)/electrode structure, the location of oxygen reservoir is not clear. We have previously reported a method for preparing an extremely small ReRAM cell which has removable bottom electrode (BE), by using AFM cantilever. In this study, we used this cell structure to specify the location of oxygen reservoir. Since an anode is assumed to work as an oxygen reservoir in most models, we investigated the effect of changing anodes for the same filament on the presence or absence of the occurrence of reset switching. It was revealed that reset occurred independently of catalytic ability and Gibbs free energy (ΔG) of anode material. However, reset was caused by repairing oxygen vacancies of which filament consists when metals with high ΔG is used as an anode, whereas by oxidizing an anode when metals with low ΔG is used as an anode. This result suggests that the MO film works as an oxygen reservoir for anode with high ΔG, whereas an anode works as an oxygen reservoir for anode with low ΔG.

Statistical characteristics of reset switching in Cu/HfO2/Pt resistive switching memory.

A major challenge of resistive switching memory (resistive random access memory (RRAM)) for future application is how to reduce the fluctuation of the resistive switching parameters. In this letter, with a statistical methodology, we have systematically analyzed the reset statistics of the conductive bridge random access memory (CBRAM) with a Cu/HfO2/Pt structure which displays bipolar switching property. The experimental observations show that the distributions of the reset voltage (Vreset) and reset current (Ireset) are greatly influenced by the initial on-state resistance (Ron) which is closely related to the size of the conductive filament (CF) before the reset process. The reset voltage increases and the current decreases with the on-state resistance, respectively, according to the scatter plots of the experimental data. Using resistance screening method, the statistical data of the reset voltage and current are decomposed into several ranges and the distributions of them in each range are analyzed by the Weibull model. Both the Weibull slopes of the reset voltage and current are demonstrated to be independent of the on-state resistance which indicates that no CF dissolution occurs before the reset point. The scale factor of the reset voltage increases with on-state resistance while that of the reset current decreases with it. These behaviors are fully in consistency with the thermal dissolution model, which gives an insight on the physical mechanism of the reset switching. Our work has provided an inspiration on effectively reducing the variation of the switching parameters of RRAM devices.

Interpretation of set and reset switching in nickel oxide thin films

Many attempts have been tried to improve switching characteristics of resistive switching materials such as NiOx because it gives scattered switching current and voltage values [J. F. Gibbons and W. E. Beadle, Solid-State Electron. 7, 785–790 (1964); S. Seo et al., Appl. Phys. Lett. 85, 5655–5657 (2004); H. D. Lee et al., Phys. Rev. B 81, 193202 (2010); S. I. Kim et al., Appl. Phys. Lett. 104, 023513 (2014); M.-J. Lee et al., Nano Lett. 9, 1476–1481 (2009)]. The nature of scattering should be understood based on switching mechanism and the source of scattering in order to improve switching properties. Here, the long tail in scatter data—the data points which are observed only one or two times during switching—was investigated. Techniques such as multiple input pulses are proposed in order to avoid switching missing and size scaling of switching devices are suggested in order to improve data scattering. In addition, discovery of double switching curves in unipolar switching is presented.

Reversible conductance switching characteristics in a polymer-In2O3 nanocrystals junction

A transparent polymer-based resistive switching device containing In2O3 nanocrystals (NCs) is fabricated, and its nonvolatile memory characteristics are evaluated. Very clear reversible counter-clockwise bipolar-type resistive switching phenomena are observed. Stable retention is demonstrated. An Analysis of the temperature dependence of the bistable resistance states reveals additional features, not reported in previous studies, that the observed resistance switching is due to oxygen ions drift-induced redox reactions at the polymer/In2O3 NCs interface. The RESET and SET switching times (τRESET and τSET), which are defined as pulse widths extrapolated by the steepest slopes in the transition region, are τRESET ∼ 550 nsec and τSET ∼ 900 nsec. The authors propose that microscopic potential modification occurring near the polymer/In2O3 NCs boundaries plays a key role in determining resistive switching properties.

Control and Analysis of Magnetic Switch Reset Current in Pulsed Power Systems

This letter presents the operation characteristics of the magnetic switch attributed to the input voltage and pulse frequency in the pulsed power system. The reset current control method is proposed for improving efficiency of the magnetic switch because this method will optimally controls the hysteresis loop of the magnetic switch. Also, this method controls the saturation of the magnetic core by adjusting the amount of reset current flowing in the magnetic switch when the input voltage and pulse frequency at the pulsed power system are changed. Experimental results are presented to demonstrate the effectiveness of the proposed reset current control method of the magnetic switch.

The Influence of Water Absorbed in Grain Boundary of a Polycrystalline NiO Layer on the Memory Characteristics of Pt/NiO/Pt Resistive Random Access Memory (ReRAM)

ABSTRACTWe focused on the presence of water absorbed in the grain boundary of a polycrystalline transition metal oxide (TMO) film in an EL/poly-TMO/EL structure. The effect of supplying water to resistive random access memories (ReRAMs) of Pt/NiO/Pt structure on switching voltages and data retention characteristics was investigated. As a result, switching voltages were decreased by supplying water and reset switching was confirmed to be strongly induced by supplying water even at room temperature without applying voltage. These results suggest that water enhances resistive switching effect by providing reducing species and oxidizing species respectively such as H+ and OH-.

Voltage and power-controlled regimes in the progressive unipolar RESET transition of HfO₂-based RRAM.

Resistive switching (RS) based on the formation and rupture of conductive filament (CF) is promising in novel memory and logic device applications. Understanding the physics of RS and the nature of CF is of utmost importance to control the performance, variability and reliability of resistive switching memory (RRAM). Here, the RESET switching of HfO2-based RRAM was statistically investigated in terms of the CF conductance evolution. The RESET usually combines an abrupt conductance drop with a progressive phase ending with the complete CF rupture. RESET1 and RESET2 events, corresponding to the initial and final phase of RESET, are found to be controlled by the voltage and power in the CF, respectively. A Monte Carlo simulator based on the thermal dissolution model of unipolar RESET reproduces all of the experimental observations. The results contribute to an improved physics-based understanding on the switching mechanisms and provide additional support to the thermal dissolution model.

Investigation on the RESET switching mechanism of bipolar Cu/HfO2/Pt RRAM devices with a statistical methodology

The RESET switching of bipolar Cu/HfO2/Pt resistance random access memory (RRAM) is investigated. With a statistical methodology, we systematically analyze the RESET voltage (VRESET) and RESET current (IRESET). VRESET shows a U-shape distribution as a function of RON according to the scatter plot of the raw experimental data. After data correction by a series resistance (RS), VRESET is nearly constant, while IRESET decreases linearly with RCF. These behaviours are consistent with the thermal dissolution model of RESET. Moreover, the IRESET and VRESET distributions are strongly affected by the RON distribution. Using a ‘resistance screening’ method, the IRESET and VRESET distributions are found to be compatible with the Weibull distribution model. The Weibull slopes of the VRESET and IRESET distributions are independent of RCF, indicating that the RESET point corresponds to the initial phase of conductive filament (CF) dissolution, according to our cell-based model for the unipolar RESET of RRAM devices. The scale factor of the VRESET distributions is roughly constant, while that of the IRESET distributions scale with 1/RCF. Accordingly, the RESET switching of the HfO2-based solid electrolyte memory is compatible with the thermal dissolution mechanism, improving our understanding on the physics of resistive switching of RRAM devices.

Threshold Switching and Conductance Quantization in Al/HfO2/Si(p) Structures

Volatile threshold switching and non-volatile memory switching modes of resistive switching are reported in Al/HfO2/Si(p) metal–oxide–semiconductor structures with different values of current compliance limit during electroforming. When the current is limited to below 100 µA, a reproducible threshold switching loop is reported under injection from the p-type silicon substrate. The conduction in the low resistance state is linear above a voltage threshold called holding voltage and the conductance is a non-integer multiple of the quantum of conductance. Depending on the size of the conducting filament created during the electroforming process, one or several quasi-one dimensional quantum subbands are found to contribute to the current. Abrupt transitions between different discrete conductance values are reported during increasing and decreasing voltage sweeps. These results provide strong experimental evidence suggesting that the conduction filament behaves as a quantum wire (QW). No structural instability of the filament has to be invoked to explain either the highly structured conduction properties or the set and reset switching transitions. It is claimed that the whole phenomenology can be understood by electron injection from the valence band into a narrow conducting path which behaves as a QW.

Ionic bipolar resistive switching modes determined by the preceding unipolar resistive switching reset behavior in Pt/TiO2/Pt

Various types of bipolar resistive switching (BRS) at the filament ruptured region by the unipolar resistive switching (URS) reset in the structure Pt/TiO2/Pt were categorized in terms of operation polarity and switching parameters. The differences in BRS behavior, even under identical current–voltage switching, are closely related to the previously performed URS reset parameter, especially the power consumed during the reset process. Various modes of BRS from the URS reset status in the structure Pt/TiO2/Pt are reported, and interpreted in terms of a distinct oxygen vacancy configuration in the ruptured region of a Magnéli filament.

Role of the anode material in the unipolar switching of TiN\NiO\Ni cells

In this paper, we investigate the unipolar resistive-switching mechanism in TiN\NiO\Ni cells, whereby the NiO layer is deposited by metal-organic chemical vapor deposition. Irrespective of the cell size down to 80 nm, controlled unipolar switching is observed only on condition the Ni electrode is used as anode. Local elemental analyzes revealed enhanced oxygen concentration at the NiO\Ni interface after reset operation. Based on this result as well as on the quantum-mechanical modeling of the conduction for different resistance states, the reset switching is analyzed in terms of electrochemically assisted oxidation process of the conductive filament close to the Ni anode. Electrical switching results on various stack configurations confirm the major impact of the electrode materials on the reset performances, bringing important insights into the mechanisms involved in the unipolar switching of this system. Literature data are discussed on the basis of this learning, suggesting possible extension of these considerations to other oxide-based switching systems.

Analytical analysis of the generic SET and RESET characteristics of electrochemical metallization memory cells

We report on an analytical model which describes the bipolar resistive switching in electrochemical metallization cells. To simulate the resistive switching, we modeled the growth and dissolution of a metallic filament together with electron tunneling between the growing filament and the counter electrode. The model accounts for the controllability of the low resistive state and the RESET current by tuning the SET current. By analytical analysis the relevant conditions for these generic characteristics are identified. In addition, an explanation for the asymmetry in the SET and RESET switching characteristics is presented. The results of the analytical analysis is generalized to all types of ReRAMs.

Study of polarity effect in SiOx-based resistive switching memory

The SiOx-based resistive switching memory was realized by a simple TaN/SiO2/n++ Si-substrate structure. Post-deposition annealing treatment not only reduced operational variation but also stabilized electrical reliability during repeated switching. The relationship between applied voltage polarity and reset switching parameters is investigated and may indicate that resistive switching occurs at the cathode side. Oxygen-vacancy clustering and asymmetrical thermal-dissipation of the electrodes are discussed as possible causes for the polarity dependence of reset switching parameters. Data retention in high- and low-resistance states was measured for over 104 s, indicating promising potential for future nonvolatile memory applications.

Effect of Heat Diffusion During State Transitions in Resistive Switching Memory Device Based on Nickel-Rich Nickel Oxide Film

The switching behaviors of the resistive switching device based on Ni-rich nickel oxide thin film during the set and reset processes in the pulse voltage experiment have been examined. In the switching from a high-resistance state (HRS) to a low-resistance state (LRS) during the set process, the formation of filament is the dominant process. The switching is easier to occur with a shorter off time between pulses, indicating that heat diffusion plays an important role. On the other hand, in the switching from the LRS to the HRS during the reset process, there is a competition between the formation and deformation of filament, which is much stronger than that in the set process. The heat diffusion during the off time between pulses affects both the formation and deformation of filaments. Thus, there is no definite relationship in statistics between the off time and the occurrence of the reset switching.

Memristive tri-stable resistive switching at ruptured conducting filaments of a Pt/TiO2/Pt cell

A tri-stable memristive switching was demonstrated on a Pt/TiO2/Pt device and its underlying mechanism was suggested through a series of electrical measurements. Tri-stable switching could be initiated from a device in unipolar reset status. The unipolar reset status was obtained by performing an electroforming step on a pristine cell which was then followed by unipolar reset switching. It was postulated that tri-stable switching occurred at the location where the conductive filament (initially formed by the electroforming step) was ruptured by a subsequent unipolar reset process. The mechanism of the tri-stable memristive switching presented in this article was attributed to the migration of oxygen ions through the ruptured filament region and the resulting modulation of the Schottky-like interfaces. The assertion was further supported by a comparison study performed on a Pt/TiO2/TiO2−x/Pt cell.