A Complementary Resistive Switch-based Crossbar Array Adder

Redox-based resistive switching devices (ReRAM) are an emerging class of non-volatile storage elements suited for nanoscale memory applications. In terms of logic operations, ReRAM devices were suggested to be used as programmable interconnects, large-scale look-up tables or for sequential logic operations. However, without additional selector devices these approaches are not suited for use in large scale nanocrossbar memory arrays, which is the preferred architecture for ReRAM devices due to the minimum area consumption. To overcome this issue for the sequential logic approach, we recently introduced a novel concept, which is suited for passive crossbar arrays using complementary resistive switches (CRSs). CRS cells offer two high resistive storage states, and thus, parasitic sneak currents are efficiently avoided. However, until now the CRS-based logic-in-memory approach was only shown to be able to perform basic Boolean logic operations using a single CRS cell. In this paper, we introduce two multi-bit adder schemes using the CRS-based logic-in-memory approach. We proof the concepts by means of SPICE simulations using a dynamical memristive device model of a ReRAM cell. Finally, we show the advantages of our novel adder concept in terms of step count and number of devices in comparison to a recently published adder approach, which applies the conventional ReRAM-based sequential logic concept introduced by Borghetti et al.Comment: 12 pages, accepted for IEEE Journal on Emerging and Selected Topics in Circuits and Systems (JETCAS), issue on Computing in Emerging Technologie

Resistive communications based on neuristors

Memristors are passive elements that allow us to store information using a single element per bit. However, this is not the only utility of the memristor. Considering the physical chemical structure of the element used, the memristor can function at the same time as memory and as a communication unit. This paper presents a new approach to the use of the memristor and develops the concept of resistive communication

Advancements Towards Single Site Information Storage and Processing Using HfO2 Resistive Random Access Memory (ReRAM)

Resistive Random Access Memory (ReRAM) has attracted much attention among researchers due to its fast switching speeds, lower switching voltages, and feasible integration into industry compatible CMOS processing. These characteristics make ReRAM a viable candidate for next-generation Non- Volatile Memory. Transition-Metal-Oxides have been proven to be excellent materials for ReRAM applications. This work investigates the effect of various, post-deposition anneals (PDA) on the switching parameters of Ni/Cu/HfO2/TiN Resistive Memory Devices (RMD). Results are presented in the form of a Small Business Innovation Research (SBIR) grant proposal. The use of the SBIR format emphasizes understanding of the experimental design, commercial viability, and broader impacts of ReRAM technology

Processos de condução eletrónica em células de memória ReRAM do tipo VCM com óxidos metálicos

New applications, such as neuromorphic computing, and the limitations of current semiconductor technologies demand a revolution in electronic devices. As one of the key enablers of a new electronics paradigm, redox-based resistive switching random access memory (ReRAM) has been the focus of much research and development. Among the ReRAM research community, Ta2O5 has emerged as one of the most popular materials, for enabling high endurance and high switching speed. Ta2O5-based ReRAM rely on the nonvolatile change of the resistance via the modulation of the oxygen content in conductive filaments, as it is described in the valence change mechanism. However, the filaments’ structure and exact composition are currently under intense debate, which hinders the development of better device design rules. The two current models in the literature consider filaments composed of oxygen vacancies and those containing metallic Ta. This work attempts to solve this dispute by reporting a detailed study of the electrical transport through the conductive filaments inside Ta2O5-based ReRAM. In parallel, the electrical transport and structure of substoichiometric TaOx thin films, grown to try and match the material of the filaments, was studied in detail. A strong correlation between the transport mechanisms in the conductive filaments inside the Ta2O5 ReRAM and in the TaOx thin films with x 1 was found. This clearly links the physical properties of the materials composing the filaments and the substoichiometric TaOx thin films. Structural analysis performed on the TaOx films reveals the presence of Ta clusters inside the films. Moreover, the electrical transport of metallic Ta films shows the same transport mechanism as TaOx with x 1, for most of the measured temperature range, from 2 K to 300 K. Beyond the transport mechanisms, both cases share a carrier concentration on the order of 1022 cm−3 and a positive magnetoresistance associated with weak antilocalization at T < 30 K. Therefore, it is concluded that the transport in the TaOx films with x 1 is dominated by a percolation chain of Ta clusters embedded in an insulating Ta2O5 matrix. These clusters exhibit disordered metal-like behaviour, where quantum corrections to the Boltzmann transport dominate the conduction. In conclusion, the electrical transport in the conductive filaments inside Ta2O5-based ReRAM devices is determined by percolation through Ta clusters, which is in line with independent observations of metallic Ta in the filaments. This work strongly supports the metallic Ta filament model.Novas aplicações, tais como computação neuromórfica, e as limitações da tecnologia de semicondutores atual exigem uma revolução nos dispositivos eletrónicos. Sendo uma peça chave para um novo paradigma da eletrónica, a memória ReRAM (redox-based resistive switching random access memory) tem sido alvo de muita investigação e desenvolvimento. O Ta2O5 é um dos materiais mais populares para usar em dispositivos ReRAM, permitindo alta durabilidade e velocidades de comutação elevadas. As ReRAM com Ta2O5 baseiam-se na mudança não volátil da resistência elétrica através da modulação da quantidade de oxigénio em filamentos condutores, como é descrito no mecanismo de alteração de valência (valence change mechanism). No entanto, a estrutura dos filamentos e a sua composição química exata, são ainda alvo de intenso debate, limitando o desenvolvimento de melhores receitas de fabricação de dispositivos. Os dois modelos atuais na literatura consideram filamentos compostos por lacunas de oxigénio e filamentos com Ta metálico. Este trabalho procura resolver esta disputa ao reportar um estudo detalhado do transporte elétrico através de filamentos condutores em dispositivos ReRAM de Ta2O5. Paralelamente, foi estudado em detalhe o transporte elétrico e a estrutura de filmes finos de TaOx subestequiométrico, depositados de forma a emular o material dos filamentos. Foi encontrada uma forte correlação entre os mecanismos de transporte nos filamentos condutores dentro dos dispositivos ReRAM de Ta2O5 e nos filmes finos de TaOx com x 1. Isto estabelece uma ligação clara entre as propriedades físicas dos materiais que compõem tanto os filamentos como os filmes finos de TaOx. A análise estrutural efetuada nos filmes de TaOx revela a presença de aglomerados de Ta. Por outro lado, o transporte elétrico em filmes finos de Ta é dominado pelos mesmos mecanismos de condução observados nos filmes de TaOx com x 1, para a maior parte da gama de temperatura de 2 K a 300 K. Ambos os casos partilham ainda uma concentração de portadores da ordem de 1022 cm−3 e uma magnetoresistência positiva associada a anti-localização fraca para T < 30 K. Portanto, é concluído que o transporte em filmes de TaOx com x 1 é dominado por uma cadeia de percolação de aglomerados de Ta embutidos numa matriz isoladora de Ta2O5. Estes aglomerados exibem um comportamento típico de metais desordenados, para os quais a condução é dominada por correções quânticas ao transporte de Boltzmann. Em conclusão, o transporte elétrico em filamentos condutores dentro de dispositivos ReRAM baseados em Ta2O5 é dominado pela percolação de aglomerados de Ta, o que corrobora observações independentes de Ta metálico nos filamentos. Assim, este trabalho suporta o modelo baseado no filamento metálico de Ta.Programa Doutoral em Engenharia Físic

Neuro-memristive Circuits for Edge Computing: A review

The volume, veracity, variability, and velocity of data produced from the ever-increasing network of sensors connected to Internet pose challenges for power management, scalability, and sustainability of cloud computing infrastructure. Increasing the data processing capability of edge computing devices at lower power requirements can reduce several overheads for cloud computing solutions. This paper provides the review of neuromorphic CMOS-memristive architectures that can be integrated into edge computing devices. We discuss why the neuromorphic architectures are useful for edge devices and show the advantages, drawbacks and open problems in the field of neuro-memristive circuits for edge computing

Growth and Oxidation of Graphene and Two-Dimensional Materials for Flexible Electronic Applications

The non-volatile storage of information is becoming increasingly important in our data-driven society. Limitations in conventional devices are driving the research and development of incorporating new materials into conventional device architectures to improve performance, as well as developing an array of emerging memory technologies based on entirely new physical processes. The discovery of graphene allowed for developing new approaches to these problems, both itself and as part of the larger, and ever-expanding family of 2D materials. In this thesis the growth and oxidation of these materials is investigated for implementing into such devices, exploiting some of the unique properties of 2D materials including atomic thinness, mechanical flexibility and tune-ability through chemical modification - to meet some challenges facing the community. This begins with the growth of graphene by chemical vapour deposition for a high quality flexible electrode material, followed by oxidation of graphene for use in resistive memory devices. The theme of oxidation is then extended to another 2D material, HfS2, which is selectively oxidised for use as high-k dielectric in Van der Waals heterostructures for FETs and resistive memory devices. Lastly, a technique for fabrication of graphene-based devices directly on the copper growth substrate is demonstrated for use in flexible devices for sensing touch and humidity

Resistive switching devices with improved control of oxygen vacancies dynamics

L'abstract è presente nell'allegato / the abstract is in the attachmen

Gestión de jerarquías de memoria híbridas a nivel de sistema

Tesis inédita de la Universidad Complutense de Madrid, Facultad de Informática, Departamento de Arquitectura de Computadoras y Automática y de Ku Leuven, Arenberg Doctoral School, Faculty of Engineering Science, leída el 11/05/2017.In electronics and computer science, the term ‘memory’ generally refers to devices that are used to store information that we use in various appliances ranging from our PCs to all hand-held devices, smart appliances etc. Primary/main memory is used for storage systems that function at a high speed (i.e. RAM). The primary memory is often associated with addressable semiconductor memory, i.e. integrated circuits consisting of silicon-based transistors, used for example as primary memory but also other purposes in computers and other digital electronic devices. The secondary/auxiliary memory, in comparison provides program and data storage that is slower to access but offers larger capacity. Examples include external hard drives, portable flash drives, CDs, and DVDs. These devices and media must be either plugged in or inserted into a computer in order to be accessed by the system. Since secondary storage technology is not always connected to the computer, it is commonly used for backing up data. The term storage is often used to describe secondary memory. Secondary memory stores a large amount of data at lesser cost per byte than primary memory; this makes secondary storage about two orders of magnitude less expensive than primary storage. There are two main types of semiconductor memory: volatile and nonvolatile. Examples of non-volatile memory are ‘Flash’ memory (sometimes used as secondary, sometimes primary computer memory) and ROM/PROM/EPROM/EEPROM memory (used for firmware such as boot programs). Examples of volatile memory are primary memory (typically dynamic RAM, DRAM), and fast CPU cache memory (typically static RAM, SRAM, which is fast but energy-consuming and offer lower memory capacity per are a unit than DRAM). Non-volatile memory technologies in Si-based electronics date back to the 1990s. Flash memory is widely used in consumer electronic products such as cellphones and music players and NAND Flash-based solid-state disks (SSDs) are increasingly displacing hard disk drives as the primary storage device in laptops, desktops, and even data centers. The integration limit of Flash memories is approaching, and many new types of memory to replace conventional Flash memories have been proposed. The rapid increase of leakage currents in Silicon CMOS transistors with scaling poses a big challenge for the integration of SRAM memories. There is also the case of susceptibility to read/write failure with low power schemes. As a result of this, over the past decade, there has been an extensive pooling of time, resources and effort towards developing emerging memory technologies like Resistive RAM (ReRAM/RRAM), STT-MRAM, Domain Wall Memory and Phase Change Memory(PRAM). Emerging non-volatile memory technologies promise new memories to store more data at less cost than the expensive-to build silicon chips used by popular consumer gadgets including digital cameras, cell phones and portable music players. These new memory technologies combine the speed of static random-access memory (SRAM), the density of dynamic random-access memory (DRAM), and the non-volatility of Flash memory and so become very attractive as another possibility for future memory hierarchies. The research and information on these Non-Volatile Memory (NVM) technologies has matured over the last decade. These NVMs are now being explored thoroughly nowadays as viable replacements for conventional SRAM based memories even for the higher levels of the memory hierarchy. Many other new classes of emerging memory technologies such as transparent and plastic, three-dimensional(3-D), and quantum dot memory technologies have also gained tremendous popularity in recent years...En el campo de la informática, el término ‘memoria’ se refiere generalmente a dispositivos que son usados para almacenar información que posteriormente será usada en diversos dispositivos, desde computadoras personales (PC), móviles, dispositivos inteligentes, etc. La memoria principal del sistema se utiliza para almacenar los datos e instrucciones de los procesos que se encuentre en ejecución, por lo que se requiere que funcionen a alta velocidad (por ejemplo, DRAM). La memoria principal está implementada habitualmente mediante memorias semiconductoras direccionables, siendo DRAM y SRAM los principales exponentes. Por otro lado, la memoria auxiliar o secundaria proporciona almacenaje(para ficheros, por ejemplo); es más lenta pero ofrece una mayor capacidad. Ejemplos típicos de memoria secundaria son discos duros, memorias flash portables, CDs y DVDs. Debido a que estos dispositivos no necesitan estar conectados a la computadora de forma permanente, son muy utilizados para almacenar copias de seguridad. La memoria secundaria almacena una gran cantidad de datos aun coste menor por bit que la memoria principal, siendo habitualmente dos órdenes de magnitud más barata que la memoria primaria. Existen dos tipos de memorias de tipo semiconductor: volátiles y no volátiles. Ejemplos de memorias no volátiles son las memorias Flash (algunas veces usadas como memoria secundaria y otras veces como memoria principal) y memorias ROM/PROM/EPROM/EEPROM (usadas para firmware como programas de arranque). Ejemplos de memoria volátil son las memorias DRAM (RAM dinámica), actualmente la opción predominante a la hora de implementar la memoria principal, y las memorias SRAM (RAM estática) más rápida y costosa, utilizada para los diferentes niveles de cache. Las tecnologías de memorias no volátiles basadas en electrónica de silicio se remontan a la década de1990. Una variante de memoria de almacenaje por carga denominada como memoria Flash es mundialmente usada en productos electrónicos de consumo como telefonía móvil y reproductores de música mientras NAND Flash solid state disks(SSDs) están progresivamente desplazando a los dispositivos de disco duro como principal unidad de almacenamiento en computadoras portátiles, de escritorio e incluso en centros de datos. En la actualidad, hay varios factores que amenazan la actual predominancia de memorias semiconductoras basadas en cargas (capacitivas). Por un lado, se está alcanzando el límite de integración de las memorias Flash, lo que compromete su escalado en el medio plazo. Por otra parte, el fuerte incremento de las corrientes de fuga de los transistores de silicio CMOS actuales, supone un enorme desafío para la integración de memorias SRAM. Asimismo, estas memorias son cada vez más susceptibles a fallos de lectura/escritura en diseños de bajo consumo. Como resultado de estos problemas, que se agravan con cada nueva generación tecnológica, en los últimos años se han intensificado los esfuerzos para desarrollar nuevas tecnologías que reemplacen o al menos complementen a las actuales. Los transistores de efecto campo eléctrico ferroso (FeFET en sus siglas en inglés) se consideran una de las alternativas más prometedores para sustituir tanto a Flash (por su mayor densidad) como a DRAM (por su mayor velocidad), pero aún está en una fase muy inicial de su desarrollo. Hay otras tecnologías algo más maduras, en el ámbito de las memorias RAM resistivas, entre las que cabe destacar ReRAM (o RRAM), STT-RAM, Domain Wall Memory y Phase Change Memory (PRAM)...Depto. de Arquitectura de Computadores y AutomáticaFac. de InformáticaTRUEunpu