On the Origin of Steep $I$ – $V$ Nonlinearity in Mixed-Ionic-Electronic-Conduction-Based Access Devices
TL;DR: In this article, numerical modeling is used to explain the origin of the large ON/OFF ratios, ultralow leakage, and high ON-current densities exhibited by back-end-of-the-line-friendly access devices based on copper-containing mixed-ionic-electronic-conduction (MIEC) materials.
Abstract: Numerical modeling is used to explain the origin of the large ON/OFF ratios, ultralow leakage, and high ON-current densities exhibited by back-end-of-the-line-friendly access devices based on copper-containing mixed-ionic-electronic-conduction (MIEC) materials. Hall effect measurements confirm that the electronic current is hole dominated; a commercial semiconductor modeling tool is adapted to model MIEC. Motion of large populations of copper ions and vacancies leads to exponential increases in hole current, with a turn-ON voltage that depends on material bandgap. Device simulations match experimental observations as a function of temperature, electrode aspect ratio, thickness, and device diameter.
Citations
More filters
TL;DR: A high performance bilayer self-selective device using HfO2 as the memory switching layer and a mixed ionic and electron conductor as the selective layer is developed and shows attractive potential for low power and high density 3D data storage applications.
Abstract: Vertical crossbar arrays provide a cost-effective approach for high density three-dimensional (3D) integration of resistive random access memory. However, an individual selector device is not allowed to be integrated with the memory cell separately. The development of V-RRAM has impeded the lack of satisfactory self-selective cells. In this study, we have developed a high performance bilayer self-selective device using HfO2 as the memory switching layer and a mixed ionic and electron conductor as the selective layer. The device exhibits high non-linearity (>103) and ultra-low half-select leakage (<0.1 pA). A four layer vertical crossbar array was successfully demonstrated based on the developed self-selective device. High uniformity, ultra-low leakage, sub-nA operation, self-compliance, and excellent read/write disturbance immunity were achieved. The robust array level performance shows attractive potential for low power and high density 3D data storage applications.
83 citations
TL;DR: In this paper, the authors address low-frequency fluctuations focusing on $1/f$ and random telegraph noise contributions in intrinsic, i.e., typical, cells, and the analytical models are presented to predict the resistance broadening for different RRAM states.
Abstract: Resistive-switching memory (RRAM) is attracting a widespread interest for its outstanding properties, such as low power, high speed, and good endurance. A crucial concern for RRAM is the current fluctuation, which induces significant broadening of resistance levels in single-bit and multilevel applications. This paper addresses low-frequency fluctuations focusing on $1/f$ and random telegraph noise contributions in intrinsic, i.e., typical, cells. The current fluctuations are studied in both the time and frequency domains, and the analytical models are presented to predict the resistance broadening for different RRAM states. Finally, the resistance dependence of noise and broadening is studied with the support of a 3-D finite-element model.
37 citations
TL;DR: In this paper, the authors review recent progress in modeling resistive switching devices at multiple scales; they briefly describe simulation tools appropriate at each scale and the key insight that has been derived from them.
Abstract: Resistance switching devices based on electrochemical processes have attractive significant attention in the field of nanoelectronics due to the possibility of switching in nanosecond timescales, miniaturization to tens of nanometer and multi-bit storage. Their deceptively simple structures (metal-insulator-metal stack) hide a set of complex, coupled, processes that govern their operation, from electrochemical reactions at interfaces, diffusion and aggregation of ionic species, to electron and hole trapping and Joule heating. A combination of experiments and modeling efforts are contributing to a fundamental understanding of these devices, and progress towards a predictive understanding of their operation is opening the possibility for the rational optimization. In this paper we review recent progress in modeling resistive switching devices at multiple scales; we briefly describe simulation tools appropriate at each scale and the key insight that has been derived from them. Starting with ab initio electronic structure simulations that provide an understanding of the mechanisms of operation of valence change devices pointing to the importance of the aggregation of oxygen vacancies in resistance switching and how dopants affect performance. At slightly larger scales we describe reactive molecular dynamics simulations of the operation of electrochemical metallization cells. Here the dynamical simulations provide an atomic picture of the mechanisms behind the electrochemical formation and stabilization of conductive metallic filaments that provide a low-resistance path for electronic conduction. Kinetic Monte Carlo simulations are one step higher in the multiscale ladder and enable larger scale simulations and longer times, enabling, for example, the study of variability in switching speed and resistance. Finally, we discuss physics-based simulations that accurately capture subtleties of device behavior and that can be incorporated in circuit simulations.
25 citations
Cites background from "On the Origin of Steep $I$ – $V$ No..."
...Their simple structure, consisting of two metallic electrodes separated by a solid dielectric or electrolyte, seems at odds with the wide range of I-V characteristics that can be achieved by the appropriate choice of materials [4]: from linear to non-linear bipolar and nonpolar resistance switching to threshold switching [5] (an abrupt but reversible change in resistance), see Fig....
[...]
TL;DR: A new method that enables reactive molecular dynamics simulations of electrochemical processes and applies it to study electrochemical metallization cells (ECMs) is described and it is found that nanowires with an electroactive shell, where ions migrate towards a smaller inactive electrode core, result in faster switching than planar devices.
Abstract: We describe a new method that enables reactive molecular dynamics (MD) simulations of electrochemical processes and apply it to study electrochemical metallization cells (ECMs). The model, called EChemDID, extends the charge equilibration method to capture the effect of external electrochemical potential on partial atomic charges and describes its equilibration over connected metallic structures, on-the-fly, during the MD simulation. We use EChemDID to simulate resistance switching in nanoscale ECMs; these devices consist of an electroactive metal separated from an inactive electrode by an insulator and can be reversibly switched to a low-resistance state by the electrochemical formation of a conducting filament between electrodes. Our structures use Cu as the active electrode and SiO2 as the dielectric and have dimensions at the foreseen limit of scalability of the technology, with a dielectric thickness of approximately 1 nm. We explore the effect of device geometry on switching timescales and find that nanowires with an electroactive shell, where ions migrate towards a smaller inactive electrode core, result in faster switching than planar devices. We observe significant device-to-device variability in switching timescales and intermittent switching for these nanoscale devices. To characterize the evolution in the electronic structure of the dielectric as dissolved metallic ions switch the device, we perform density functional theory calculations on structures obtained from an EChemDID MD simulation. These results confirm the appearance of states around the Fermi energy as the metallic filament bridges the electrodes and show that the metallic ions and not defects in the dielectric contribute to the majority of those states.
20 citations
01 Jan 2016
8 citations
References
More filters
966 citations
TL;DR: In this paper, the thermionic emission theory has been used to study the currentvoltage characteristics of a metal-semiconductor-metal (MSM) structure, and the critical voltage at which the minority carrier injection increases rapidly can be varied by varying the semiconductor doping and thickness.
Abstract: The current-voltage characteristics of a metal-semiconductor-metal structure (essentially two metal-semiconductor contacts connected back to back) have been studied based on the thermionic emission theory. When a uniformly doped semiconductor is thin enough that it can be completely depleted before avalanche breakdown occurs, the structure can exhibit many novel transport behaviors. Two outstanding features of the structure are that (1) a wide range of high-level injection of minority carriers can be achieved by varying the barrier heights of the two contacts and (2) the critical voltage at which the minority carrier injection increases rapidly can be varied by varying the semiconductor doping and thickness.
Experimental silicon MSM structures of PtSi-Si-PtSi have been made from n-type silicon with doping of 4×1014 cm−3 and thickness of 12 μm. The critical voltage at room temperature is about 30 V. The current increases over five orders of magnitude with only 10 per cent increase of the voltage. The above results and other measurements over wide temperature range do substantiate the theoretical predictions.
395 citations
TL;DR: A more physical model based on numerical solutions of coupled drift-diffusion equations for electrons and ions with appropriate boundary conditions is provided to obtain physical insight into the transport processes responsible for memristive behavior in semiconductor films.
Abstract: The memristor, the fourth passive circuit element, was predicted theoretically nearly 40 years ago, but we just recently demonstrated both an intentional material system and an analytical model that exhibited the properties of such a device. Here we provide a more physical model based on numerical solutions of coupled drift-diffusion equations for electrons and ions with appropriate boundary conditions. We simulate the dynamics of a two-terminal memristive device based on a semiconductor thinfilm with mobile dopants that are partially compensated by a small amount of immobile acceptors. We examine the mobile ion distributions, zero-bias potentials, and current‐voltage characteristics of the model for both steady-state bias conditions and for dynamical switching to obtain physical insight into the transport processes responsible for memristive behavior in semiconductor films.
279 citations
"On the Origin of Steep $I$ – $V$ No..." refers background in this paper
...[10] modeled an 1-D metal–semiconductor– metal (MSM) structure with mobile ions, electrons, and holes, fixed acceptors, and bulk-limited transport, with ohmic contacts for electrons....
[...]
IBM1
TL;DR: In this article, the authors presented a physical contact tunneling model that is critical for studying the increasingly important contact behavior in future scaled CMOS. And they compared the performance of raised S/D and Schottky S/d MOSFETs.
Abstract: We present, for the first time, a physical contact tunneling model that is critical for studying the increasingly important contact behaviour in future scaled CMOS. The tunneling processes are self-consistently treated with all current transport in the semiconductor. With this new model, we compared the performance of raised S/D and Schottky S/D MOSFETs. Both raised S/D and Schottky S/D MOSFETs can be designed to give good short-channel characteristics. Our analyses show that despite the lower sheet resistance of the Schottky S/D MOSFETs, contact resistance could be large due to finite Schottky barrier height. A lower barrier height contact material should be used to minimize the contact resistance.
185 citations
"On the Origin of Steep $I$ – $V$ No..." refers methods in this paper
...The Sentaurus TCAD device simulator self-consistently solves the continuity and Poisson equations and offers a unified contact Schottky model [14] at each ion-blocking metal electrode....
[...]
IBM1
TL;DR: Experimental results show that a novel AD based on Cu-ion motion in novel Cu-containing Mixed Ionic Electronic Conduction (MIEC) materials provide the ultra-high current densities needed for PCM, exhibit high ON/OFF ratios with excellent uniformity, are highly scalable, and are compatible with <400°C Back-End-Of-the-Line (BEOL) fabrication.
Abstract: Phase change memory (PCM) could potentially achieve high density with large, 3Dstacked crosspoint arrays, but not without a BEOL-friendly access device (AD) that can provide high current densities and large ON/OFF ratios. We demonstrate a novel AD based on Cu-ion motion in novel Cu-containing Mixed Ionic Electronic Conduction (MIEC) materials[1, 2]. Experimental results on various device structures show that these ADs provide the ultra-high current densities needed for PCM, exhibit high ON/OFF ratios with excellent uniformity, are highly scalable, and are compatible with <400°C Back-End-Of-the-Line (BEOL) fabrication.
108 citations
"On the Origin of Steep $I$ – $V$ No..." refers background or methods in this paper
...Although dependent on total electrode area [1], [2], [4], the voltage margin of any given MIEC device structure is nearly independent of the size of the gap (thickness) between the two electrodes, dgap (Fig....
[...]
...M IXED-IONIC-ELECTRONIC-CONDUCTION (MIEC)based access devices (ADs) [1]–[5] exhibit ideal characteristics for 3-D stacking of large crosspoint arrays of any resistive nonvolatile memory in the back-end-of-theline (BEOL)....
[...]
...Large AuPd pads were patterned for wire-bonding; samples received the same sub-400 °C anneal as nanoscale via-based MIEC devices [1]....
[...]
...ON-current densities offered by BEOL-friendly ADs based on Cu-containing MIEC materials [1]–[5]....
[...]
...ADs based on Cu-containing MIEC materials exhibit bipolar diodelike characteristics with ultralow leakage and large ON/OFF ratios [1]–[5]....
[...]