Electrical Transport In Micro And Nanoscale Devices Of Amorphous Phase Change Materials

Nanoscale Electronic Devices and Their Applications helps readers acquire a thorough understanding of the fundamentals of solids at the nanoscale level in addition to their applications including operation and properties of recent nanoscale devices. This book includes seven chapters that give an overview of electrons in solids, carbon nanotube devices and their applications, doping techniques, construction and operational details of channel-engineered MOSFETs, and spintronic devices and their applications. Structural and operational features of phase-change memory (PCM), memristor, and resistive random-access memory (ReRAM) are also discussed. In addition, some applications of these phase-change devices to logic designs have been presented. Aimed at senior undergraduate students in electrical engineering, micro-electronics engineering, physics, and device physics, this book: Covers a wide area of nanoscale devices while explaining the fundamental physics in these devices Reviews information on CNT two- and three-probe devices, spintronic devices, CNT interconnects, CNT memories, and NDR in CNT FETs Discusses spin-controlled devices and their applications, multi-material devices, and gates in addition to phase-change devices Includes rigorous mathematical derivations of the semiconductor physics Illustrates major concepts thorough discussions and various diagrams

Recent progress in materials science and the trends of nanoscale electronics have brought greater attention to the transport of heat and electricity in confined geometries. Research on developing metrology and understanding the electro-thermal phenomena can make a significant improvement in novel electronic devices such as phase change memory. Phase change memory is a particularly promising candidate for next-generation data storage because of its exceptional scalability and cycle endurance. The phase change memory devices store information through thermally-induced phase transitions of Ge2Sb2Te5 and related compounds. Because the temperature governs the phase change processes, thermal conduction in Ge2Sb2Te5 films strongly influences the device figures of merit including the programming time and the required energy. The present doctoral research develops innovative metrologies to characterize the thermal properties of Ge2Sb2Te5 films that are relevant for device operations and quantifies the importance of electro-thermal phenomena in phase change memory. Large temperature transients and rapid cycling of phase change memory pose unique challenges for thermal characterization of phase change materials. Here we develop experimental structures based on a micro-thermal stage that reproduces the heating time scales and the temperature excursions of phase change memory devices in the characterization samples. The measurement results show the thermal conductivity of Ge2Sb2Te5 films from room temperature to above 400 °C in amorphous, face-centered cubic, and hexagonal close-packed phases. Another key benefit of the micro-thermal stage is that a single structure enables simultaneous characterization of thermal and electrical properties using four-probe electrical-resistance thermometry with a programmable Ge2Sb2Te5 bridge. This work reports the in-plane electrical resistance and the out-of-plane thermal conductivity during repetitive cycling. We identify electron contribution to the thermal transport in Ge2Sb2Te5 films using the electrical properties and the Wiedmann Franz Law. The electrons are responsible for up to 70 % of the thermal transport in the hexagonal closed-packed phase, but phonons dominate the thermal transport in the amorphous and the face-centered cubic phases, which are consistent with the Einstein model for highly disordered materials. Phase change memory devices experience both large current densities and temperature excursions exceeding 600 °C, and these extreme conditions increase the relevance of thermoelectric transport and provide an ideal opportunity for studying their impact. This work develops a novel silicon-on-insulator experimental structure to measure the phase and temperature-dependent thermoelectric properties of Ge2Sb2Te5 films including the first data for films of thickness down to 25 nm. The Ge2Sb2Te5 films annealed at different temperatures contain varying fractions of the amorphous and crystalline phases, which strongly influence the thermoelectric properties. The data are consistent with modeling based on effective medium theory and suggest that careful consideration of phase purity is needed to account for thermoelectric transport. The simulations considering the thermoelectric heating show a Ge2Sb2Te5 peak temperature increase up to 44 % and a decrease in the programming power up to 30 %. The simulation results and the analysis discussed here provide physical insights into thermal phenomena and cell optimization opportunities.

"Phase Change Materials: Science and Applications" provides a unique introduction of this rapidly developing field. Clearly written and well-structured, this volume describes the material science of these fascinating materials from a theoretical and experimental perspective. Readers will find an in-depth description of their existing and potential applications in optical and solid state storage devices as well as reconfigurable logic applications. Researchers, graduate students and scientists with an interest in this field will find "Phase Change Materials" to be a valuable reference.

Nanoscale memories are used everywhere. From your iPhone to a supercomputer, every electronic device contains at least one such type. With coverage of current and prototypical technologies, Nanoscale Semiconductor Memories: Technology and Applications presents the latest research in the field of nanoscale memories technology in one place. It also covers a myriad of applications that nanoscale memories technology has enabled. The book begins with coverage of SRAM, addressing the design challenges as the technology scales, then provides design strategies to mitigate radiation induced upsets in SRAM. It discusses the current state-of-the-art DRAM technology and the need to develop high performance sense amplifier circuitry. The text then covers the novel concept of capacitorless 1T DRAM, termed as Advanced-RAM or A-RAM, and presents a discussion on quantum dot (QD) based flash memory. Building on this foundation, the coverage turns to STT-RAM, emphasizing scalable embedded STT-RAM, and the physics and engineering of magnetic domain wall "racetrack" memory. The book also discusses state-of-the-art modeling applied to phase change memory devices and includes an extensive review of RRAM, highlighting the physics of operation and analyzing different materials systems currently under investigation. The hunt is still on for universal memory that fits all the requirements of an "ideal memory" capable of high-density storage, low-power operation, unparalleled speed, high endurance, and low cost. Taking an interdisciplinary approach, this book bridges technological and application issues to provide the groundwork for developing custom designed memory systems.