Complementary Switching Research Articles

A HfO2‐Based Complementary Switching Crossbar Adder

Rapid growth of future information technology depends on energy‐efficient computation and ultra‐high density data storage. Non‐volatile redox‐based resistive switching memory (ReRAM) devices offer logic‐in‐memory capabilities and can redefine the von Neumann computer architecture. Especially complementary resistive switches (CRSs) enable the integration of highly dense passive nano‐crossbar arrays in 4F2 structure (F is the minimum feature size) without the need of selector devices. To reduce fabrication complexity further, single ReRAM device in complementary switching (CS) mode is a viable option. Here, the implementation of in‐memory‐adders using Pt|HfO2|Hf|Pt‐based CS devices, which are integrated into 1 × n passive crossbar arrays, is reported. First, the feasibility of all CRS‐logic functions with these CS devices is shown, which offer high‐endurance (109 cycles) under pulse conditions. Afterward, two multi‐bit crossbar adders, the Toggle‐Cell Adder and the Pre‐Calculation Adder, are experimentally demonstrated under pulse conditions realizing addition and subtraction operations. These results prove the functional efficiency of the crossbar adder approach, paving the path for highly advanced ReRAM‐based computing‐in‐memory architectures.

넓은 범위 입력전압에 소프트 스위칭이 가능한 양방향 인터리브드 DC-DC 컨버터

This study deals with a bidirectional interleaved soft switching DC-DC converter for a wide range of input voltages. The proposed converter operates in complementary switching with the purpose of inductor size reduction and zero-voltage switching (ZVS) operation. The current ripple related to complementary switching is minimized by three-phase interleaved operation. The main characteristics of the proposed topology are its soft-switching method of operation and its simple structure. The soft-switching operation and the system efficiency of the proposed converter are verified by experimental results.

Role of metal-oxide interfaces in the multiple resistance switching regimes of Pt/HfO2/TiN devices

The multiple resistive switching of Pt/HfO2/TiN devices is demonstrated as a result of a competition between the switching at opposite metal/oxide interfaces. Three switching operation modes are demonstrated: clockwise (CW) switching (set for negative voltage and reset for positive voltage at Pt electrode), as already reported in literature for similar material stacks; counterclockwise (CCW) switching and complementary switching (CS) that consist in a set and a reset for increasing voltage of the same polarity. The multiple switching operation modes are enabled by a deep-reset operation that brings the cell resistance close to the initial one. As a consequence, the set transition after a deep-reset occurs at the same voltage and currents as those of the forming and leads to a low resistance state whose resistance can be further decreased in a CCW switching or increased back with a CW switching. With a suitable choice of the stop voltage, a CS in obtained, as well. The coexistence of all three CW, CCW, and CS operations demonstrates that both metal-oxide interfaces are active in the formation and the dissolution of conductive filaments responsible for the switching. All these observations are discussed in terms of a competition between ion migration processes occurring at the opposite metal-oxide interfaces.

(Invited) Simulation and Modeling of the Switching Dynamics in Resistive Switching Devices

Resistive switching devices based on the valence change mechanism (VCM) or electrochemical mechanism (ECM) have attracted great attention due to their potential use in future non-volatile memories. Both types of cells exhibit a bipolar operation principle: The cells can be set from a high resistive state (HRS) to a low resistive state (LRS) with one voltage polarity and reset back to the HRS by applying the opposite voltage polarity. ECM cells consist of an ion-conducting layer sandwiched between a Ag/Cu active electrode and an inert counter electrode. The switching mechanism is based on the growth and dissolution of Ag/Cu filament within the ion-conducting host matrix involving the physical and electrochemical processes illustrated in Fig. 1.[1] The VCM stack typically consists of a mixed ionic-electronic conducting layer, e.g. a metal oxide, a high work function metal electrode and an oxidizable counter electrode. The switching process involves the movement of oxygen vacancies within the MIEC and subsequent local redox reactions in the cation sublattice.[2] Fig.1: Illustration of the electrochemical processes occurring during SET switching in an ECM cell: charge-transfer reactions, nucleation, ion migration, filamentary growth. From [1] – Reproduced by permission of the PCCP Owner Societies In order to fulfill the requirements of a nonvolatile memory a resistive switching device has to be switchable with a voltage amplitude of a few volts in the ns-regime and to offer a read-disturb immunity of up to ten years. This is equivalent to the driving physical processes exhibiting a nonlinearity of more than 15 orders of magnitude.[3]To understand the underlying electrochemical and physical processes is hence of fundamental importance. In the present paper, simulation models for ECM and VCM cells will be presented with special emphasis on the underlying physical and electrochemical processes. Based on simulation results the SET and RESET switching kinetics will be discussed in detail. ECM compact models,[1] continuum models[4] and kinetic Monte Carlo (kMC) models[5, 6] will be presented. All ECM models include the electrochemical and physical processes illustrated in Fig. 1: nucleation, electron-transfer reactions at the boundaries, ion migration and filamentary growth. The models are capable of capturing the observed experimental phenomena: nonlinear switching kinetics, multilevel switching, current-voltage characteristics and switching variability.[5]The multilevel switching is attributed to different tunneling gaps between the growing filament and the counter electrode at low current compliance and a filament widening if a galvanic contact is achieved. By comparison of the simulation results with experimental data the processes limiting the switching speed are discussed. Furthermore, the influence of mechanical stress on the filamentary growth will be addressed using kMC simulations. The developed VCM simulation model is based on the solution of the drift-diffusion equation for oxygen vacancies and electrons coupled to Poisson’s equation and the heat transfer equation. Electron transport across the metal/oxide interface via thermionic emission and tunneling is also included within the model. Using this simulation model the nature of the gradual RESET and abrupt SET transition will be discussed. The gradual RESET can be explained as a result of a drift-diffusion balance. Moreover, the simulation results reveal that the switching kinetics in VCM devices are dominated by temperature-accelerated ion movement. Furthermore, the transition between bipolar and complementary switching can be explained by the variation of the metal/oxide interface properties.[7] This work was supported in part by the Deutsche Forschungsgemeinschaft (SFB 917). [1] S. Menzel, S. Tappertzhofen, R. Waser, I. Valov, PCCP 2013, 15, 6945. [2] R. Waser, R. Dittmann, G. Staikov, K. Szot, Adv. Mater. 2009, 21, 2632. [3] S. Menzel, M. Salinga, U. Böttger, M. Wimmer, Adv. Func. Mater. 2015 (submitted) [4] S. Menzel, N. Adler, J. van den Hurk, S. Tappertzhofen, I. Valov, R. Waser, 2013 5th IEEE International Memory Workshop (IMW) 2013, 92. [5] S. Menzel, B. Wolf, S. Tappertzhofen, I. Valov, U. Böttger, R. Waser, 2014 6th IEEE International Memory Workshop (IMW), 2014 [6] S. Menzel, U. Böttger, R. Waser, J. Appl. Phys. 2012, 111, 014501/1. [7] A. Schönhals, D. J. Wouters, A. Marchewka, T. Breuer, K. Skaja, V. Rana, S. Menzel, R. Waser, 2015 7th IEEE International Memory Workshop (IMW), 2015 (accepted) Figure 1

Realization of Boolean Logic Functionality Using Redox‐Based Memristive Devices

Emerging resistively switching devices are thought to enable ultradense passive nanocrossbar arrays for use as random access memories (ReRAM) by the end of the decade, both for embedded and mass storage applications. Moreover, ReRAMs offer inherent logic‐in‐memory (LIM) capabilities due to the nonvolatility of the devices and therefore great potential to reduce the communication between memory and calculation unit by alleviating the so‐called von Neumann bottleneck. A single bipolar resistive switching device is capable of performing 14 of 16 two input logic functions in the logic concept presented by Linn et al. (“CRS‐logic”). In this paper, five types of selectorless devices are considered to validate this CRS‐logic concept is experimentally by means of the IMP and AND logic operations. As reference device a TaO x ‐based ReRAM cell is considered, which is compared to three more advanced device configurations consisting either of a threshold supported resistive switch (TS‐ReRAM), a complementary switching device (CS), or a complementary resistive switch (CRS). It is shown that all of these devices offer the desired LIM behavior. Moreover, the feasibility of XOR and XNOR operations using a modified logic concept is applied for both CS and CRS devices and the pros and cons are discussed.

Mechanism of OFF-state lifetime improvement in complementary atom switch

An improvement mechanism of the OFF-state lifetime in a complementary atom switch (CAS) is investigated by detecting a time-dependent stress voltage transition between two atom switches. The CAS consists of two bipolar-resistive-change elements connected in series with opposite direction, which are applicable for a nonvolatile crossbar switch routing signals. In the OFF-state, one switch is biased to the forward (turn-on) direction and the other to reverse (turn-off) during the crossbar switch operation. It is revealed that the switch elements do not only share the voltage stress with each other, but also mitigate the stress voltage of the forward-biased one by the reverse-biased one. The complementary sharing of the stress voltage in the two atom switches results in enlarging the OFF-state lifetime of the CAS, which is essential for keeping the crossbar switch reliability high.

A Dual-Channel Current Source Driver for Complementary Switches

In this paper, a dual-channel current source driver is presented as an efficient means of driving complementary switches. The driver transfers charge between the gates of the power devices through a single magnetic core with a discontinuous current. This promotes lower conduction loss than continuous current resonant gate drivers (RGDs), and lower component count or conduction loss than existing discontinuous current RGD applied to complementary switches. In addition, controlled switching speed is achieved through nonzero inductor current resulting in lower current stress, and faster switching compared to some pulse RGD circuits. There is good correlation between the analysis and experimental results of a 1.8-MHz prototype.

Role of interfacial layer on complementary resistive switching in the TiN/HfOx/TiN resistive memory device

The role of the bottom interfacial layer (IL) in enabling stable complementary resistive switching (CRS) in the TiN/HfOx/IL/TiN resistive memory device is revealed. Stable CRS is obtained for the TiN/HfOx/IL/TiN device, where a bottom IL comprising Hf and Ti sub-oxides resulted from the oxidation of TiN during the initial stages of atomic-layer deposition of HfOx layer. In the TiN/HfOx/Pt device, where formation of the bottom IL is suppressed by the inert Pt metal, no CRS is observed. Oxygen-ion exchange between IL and the conductive path in HfOx layer is proposed to have caused the complementary bipolar switching behavior observed in the TiN/HfOx/IL/TiN device.

Resistive switching effects in CeO2/La0.7(Sr0.1Ca0.9)0.3MnO3/Pt heterostructures prepared by pulse laser deposition method

Abstract The heterostructural junctions of CeO2/La0.7(Sr0.1Ca0.9)0.3MnO3/Pt (CeO2/LSCMO/Pt) were prepared using pulse laser deposition technique. Their resistive switching (RS) behavior was investigated. As compared to the metal/manganite/Pt junction, the CeO2/LSCMO/Pt device displayed an improved switching characteristic. The RS effects with characteristics of bipolar, threshold, and complementary were realized by adjusting the thicknesses of the CeO2 layer in the CeO2/LSCMO/Pt junctions. Under a higher external bias voltage, the threshold and complementary switching modes of the junctions could turn into bipolar switching mode. The switching behavior shows strong dependence on the O2 partial pressure during the fabrication, indicating that the amount and behavior of the oxygen at the interface play an important role in the determination of the RS behavior. The observed switching behavior is related to the modification of the accumulation/depletion layers as well as the interfacial potential barrier due to the migration of the oxygen vacancies.

A Complementary Dual-Contact MEMS Switch Using a “Zipping” Technique

This paper presents a microelectromechanical systems contact switch having both hard and soft contact materials in a single cantilever-type switching device. It operates with a zipping mechanism within which both contact materials (Pt-to-Pt and Au-to-Au) make individual contact sequentially and then detach in a reverse sequence to take advantage of both contact materials: low contact resistance and high reliability in a hot switching condition. In addition, an extended gate electrode and double T-shape cantilever beam structures effectively facilitate the sequential actuation. The fabricated switch successfully demonstrated a “dual-contact concept”-it made two sequential contacts at 31 (Pt-to-Pt) and 56 V (Au-to-Au) and it was then detached at 49 (Au-to-Au) and 23 V (Pt-to-Pt) in a single switching operation. Also, it achieved a low contact resistance of 0.3-0.5 Ω (including beam and some portion of the signal line resistances) at gate voltage from 60 to 70 V owing to the Au-to-Au contact in the device. Simultaneously, negligible contact resistance variation was observed during 2 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">6</sup> cycles at a voltage/current level of 10 V/10 mA under hot switching and unpackaged environments, representing >100-fold longer lifetime than that of a conventional Au-to-Au cantilever switch fabricated on the same wafer.

Throwing the Books at Them: Amazon's Puzzling Long Run Pricing Strategy

Firms competing to get consumers to adopt new platforms have incentives to charge low prices to promote adoption, followed by higher prices later on. This study explores Amazon’s dynamic pricing strategy by comparing its contemporary pricing on e-books, a new product with complementary hardware, a proprietary file format, and switching costs, with its current pricing on physical books, a now-mature product without complementary hardware or switching costs. Using over 150,000 hourly observations on prices and sales ranks for electronic and physical bestseller books in late 2012 and early 2013, in conjunction with actual quantity data, we estimate the price elasticities of demand for books at Amazon. Puzzlingly, e-books appear to be priced below the static profit maximizing levels. More surprisingly, we find that physical book prices also fall substantially short of the static profit maximizing level two decades after Amazon’s launch. These findings raise questions for both policymakers and shareholders.

An Inductive-coupling Link with a Complementary Switching Transmitter and an Integrating Receiver

A transceiver for a high-speed inductivecoupling link is proposed. The bi-phase modulation (BPM) signaling scheme is used due to its good noise immunity. The transmitter utilizes a complementary switching method to remove glitches in transmitted data. To increase the timing margin on the receiver side, an integrating receiver with a pre-charging equalizer is employed. The proposed transceiver was implemented via a 130-nm CMOS process. The measured timing window for a 10<SUP>-12</SUP> bit error rate (BER) at 1.8 Gb/s was 0.33 UI.

(Invited) Atom Switch Technology for Low-Power Nonvolatile Logic Application

With the increasing functions in digital circuit, flexibility and energy-efficiency play important roles in addressing future mobile/cloud computing systems. Scaling of CMOS devices and interconnects has contributed to high performance and low power operation of ULSI devices. Due to excessive stand-by power accompanying device shrinking, further scaling is experiencing serious roadblocks, and in near future, scaling will face a physical limit of the device dimension. One of the solutions to enhance device performance without scaling is to introduce “More than Moore” devices, which are integrated on CMOS without increasing the chip-size. Especially, resistive switching devices, such as magnetic random-access memory [1], phase-change memory [2], and electrochemical switch [3-5], have attracted much attention because of their potential for use in not only memory but also logic application.Atom switch is an electrochemical resistive-change device categorized in the cation type [4]. The electrochemical phenomenon is nonvolatile and based on electrolysis of the Cu electrode to produce a precipitation of Cu between the electrodes, which realizing a high ON/OFF conductance ratio. Previously, we reported a replacement of the SRAM-based switch with atom switch integrated in Cu-BEOL (Fig.2) [6]. An elimination of the forming process and high ON/OFF-state reliabilities have been realized by introducing a polymer solid-electrolyte (PSE) [7], a complementary atom switch (CAS) [8] and alloy electrodes [9].As compared to a two-terminal device, a three-terminal device is advantageous for the logic application since the separation of the programming line and signal transfer line simplifies circuit design and reduces the layout area. In this paper, a three-terminal resistive-change device featuring the resistive-change junctions coupled with the diode-inserted gate is discussed. References R. Nebashi, et al., “A 90nm 12ns 32Mb 2T1MTJ MRAM”, IEEE Solid-State Circuits Conference - Digest of Technical Papers, 8-12 Feb. 2009 Page(s):462 - 463,463a. D. Ielmini, et al., “Reliability Impact of Chalcogenide-Structure Relaxation in Phase-Change Memory (PCM) Cells—Part I: Experimental Study”,IEEE Trans. Electron Devices, vol. 56, no. 5, pp. 1070-1077, 2009.M. N. Kozicki, et al., “Applications of programmable resistance changes in metal-doped chalcogenides”, Pennington NJ USA: Electrochem. Soc. 298–309 (1999).T. Sakamoto, et al., “Nanometer-scale switches using copper sulfide”, Appl. Phys. Lett.82, 3032, (2003).R. Waser and M. Aono, “Nanoionics-based resistive switching memories”, Nature Material, vol.6, pp. 833-839 (2007).M. Tada, et al., “Nonvolatile Crossbar Switch using TiOx/TaSiOy Solid-electrolyte”, IEEE Transactions on Electron Devices, vol. 57, no.8, pp.1987-1995, (2010).M. Tada, et al.,“Polymer Solid-Electrolyte (PSE) Switch Embedded on CMOS for Nonvolatile Crossbar Switch”, IEEE Transactions on Electron Devices, vol. 58, no. 12, pp.4398-4405, (2011).M. Tada, et al.,“Improved Off-state Reliability of Nonvolatile Resistive Switch with Low Programming Voltage”, IEEE Transactions on Electron Devices, vol. 59, no. 9, pp.2357-2362, (2012).M. Tada, et al.,“Improved On-state Reliability of Atom Switch Using Alloy Electrodes”, IEEE Transactions on Electron Devices, vol. 60, no. 10, pp.3534-3540, (2013).

Nano-Crossbar Memories Comprising Parallel/Serial Complementary Memristive Switches

This work explores anti-serial (anti-parallel) memristive switches—ASMs (APMs)—as potential cross-point elements in nano-crossbar resistive random access memory arrays. The memory operation principles for both device combinations are shown in detail. The effectiveness of these memristive structures to the solution of the parasitic conducting (current sneak paths) problem is presented via an analytical approach which is based on the basic setup of resistive crossbar memories. Simulation results of crossbars of up to 4,096 elements, arranged in quadratic configurations, are conducted. The provided results supplement this comprehensive analysis of APMs and ASMs, outlining their overall performance characteristics and commenting on their applicability to the practical realization of large crossbar memory systems. Finally, a special array topology is applied to an ASM-based crossbar memory. Its performance is compared to the performance of the pure ASM-based memory. The conducted simulations reveal significantly improved read-out voltage margins which further contribute to addressing the parasitic current paths which prevent the reliable operation of memristive crossbar circuit topologies.

Three-Terminal Nonvolatile Resistive-Change Device Integrated in Cu-BEOL

A diode-inserted complementary atom switch with two resistive-change junctions coupled with the diode-inserted gate is proposed. The atom switch serves the nonvolatile resistive-change junction, where the two atom switches are connected in series with opposite direction and transfer or cutoff the signals. The gate is placed between them through the diode, where back-end-of-the-line- Ta <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">5-x</sub> diode is directly stacked on the two of atom switches, achieving high rectifying separation of the gate. The developed device realizes the three-terminal operation and potentially enables to replace the CMOS routing switch composed of SRAM and transmission gate with nonvolatility.

Control of Cu Conductive Filament in Complementary Atom Switch for Cross-Point Selector Device Application

We present a novel approach to realize bidirectional/bipolar current-voltage characteristics for cross-point selector device application. These utilize the instability of Cu ions in filament state for switch elements. The conductive filament instability was controlled by the compliance current with which the filament was formed. For in-situ control of the device, a complementary atom switch concept was implemented. The proposed device presents another attractive selector among the field of bidirectional selectors with the unique attributes such as the extremely low leakage current and the exponentially increased conduction behavior.

A 5 to 45 GHz Distributed Mixer With Cascoded Complementary Switching Pairs

This letter presents a 5 to 45 GHz broadband distributed mixer implemented by using a standard 0.18 μm CMOS process. The proposed mixer uses a cascoded complementary switching pair to improve port-to-port isolation. The proposed mixer also forms a four-stage distributed topology to achieve a broad bandwidth and reduce conversion loss (CL). The distributed mixer achieves a wide operation bandwidth from 5 to 45 GHz; a low CL of 11 to 13.2 dB; good LO-to-RF, LO-to-IF, and RF-to-IF isolations from 33 to 47 dB, 28 to 53 dB, and 32 to 48 dB, respectively, at an LO power level of 8 dBm with a low 1.4 mW dc power consumption.

(Invited) Resistive Switching in Metal Oxides: From Physical Modeling to Device Scaling

Resistive switching memory (RRAM) devices are receiving considerable interest as future-generation high-density storage technology or possible enablers of storage class memory. For these applications, there is a strong push toward scaling, in terms of low current operation, low power consumption and small device area. To assess the scaling potential of RRAM, however, the physical mechanisms for switching and reliability issues, such as noise, must be understood in deep detail. This work reviews the current understanding of RRAM switching in terms of ion diffusion and migration mechanisms. The model is used to inspire new RRAM operation schemes, such as complementary switching (CS) which may allow self-select memory crossbar and novel multilevel storage approaches. The scaling dependence of random telegraph noise (RTN) is finally discussed based on numerical simulations of drift-diffusion transport and Poisson equation within the conductive filament.

Complementary Dual-Contact Switch Using Soft and Hard Contact Materials for Achieving Low Contact Resistance and High Reliability Simultaneously

This paper reports a dual-contact microelectromechanical switch, which consists of two contacts in a single switch: one with a soft contact material and the other with a hard contact material to achieve low contact resistance and high reliability at the same time under hot switching conditions. In a single switching operation, the proposed dual-contact switch makes contact twice in sequence, where the first contact is made with a hard contact material (Pt-to-Pt) that can withstand an abrupt hot switching condition (high electric field or micro-arcing). The second contact is then accomplished with the soft contact material (Au-to-Au) that has low-contact resistance, through which most of the current flows. In contrast, when the switch releases contact, the Au-to-Au contact is initially detached, and this is followed by the release of the Pt-to-Pt contact. In this way, the dual-contact switch showed longer lifetime than that of a single Au-to-Au contact-only switch by up to fortyfold, and even better lifetime than that of a single Pt-to-Pt contact-only switch by more than two times in open laboratory environments (unpackaged). At the same time, contact resistance of the dual-contact switch was under 0.3 Ω at 50 V of the gate voltage, which is more than seven times smaller than that of the single Pt-to-Pt contact-only switch (2.2 Ω), due to the Au-to-Au contact sub-switch (the contact resistance of the single Au-to-Au contact-only switch was 2.2 Ω).

Set Variability and Failure Induced by Complementary Switching in Bipolar RRAM

The resistive switching memory (RRAM) offers fast switching, low-voltage operation, and scalable device area. However, reliability and variability issues must be understood, particularly in the low-current operation regime. This letter addresses set-state variability and presents a new set failure phenomenon in RRAM, leading to a high-resistance tail in the set-state distribution. The set failure is due to complementary switching of the RRAM, causing an increase of resistance soon after the set transition. The dependence of set failure on the programing current is explained by the increasing voltage stress across the RRAM device causing filament disconnection.