Electromigration (EM) is a complex multiphysics problem including electrical, thermal, and mechanical aspects. Since the first work on EM was published in 1907, extensive studies on EM have been ...conducted theoretically, experimentally, and by means of computer simulation. Today EM is the most significant threat for interconnect reliability in high performance integrated circuits.
Over years, physicists, material scientists, and engineers have dealt with the EM problem developing different strategies to reduce EM risk and methods for prediction of EM life time. During the same time a significant amount of work has been carried out on fundamentally understanding of EM physics, of the influence of material and geometrical properties on EM, and of the interconnect operating conditions on EM. In parallel to the theoretical studies, a large amount of work has been performed in experimental studies, mostly motivated by urgent and specific problem settings which engineers encounter during their daily work. On the basis of accelerated electromigration tests, various time-to-failure estimation methods with Blacks equation and statistics have been developed. The big question is, however, the usefulness of this work, since most contributions about electromigration and the accompanying stress effects are based on a very simplified picture of electromigration.
The intention of this review paper is to present the most important aspects of theoretical and experimental EM investigations together with a brief history of the development of the main concepts and methods. We present an overview of EM models from their origins in classical materials science methods up to the most recent developments for submicron interconnect features, as well as the application of ab initio and first principle methods. The main findings of experimental studies, important for any model development and application, will also be presented.
Full text
Available for:
GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
Electromigration failure is a major reliability concern for integrated circuits. The continuous shrinking of metal line dimensions together with the interconnect structure arranged in many levels of ...wiring with thousands of interlevel connections, such as vias, make the metallization structure more susceptible to failure. Mathematical modeling of electromigration has become an important tool for understanding the electromigration failure mechanisms. Therefore, in this work we review several electromigration models which have been proposed over the years. Starting from the early derivation of Black’s equation, we present the development of the models in a somewhat chronological order, until the recent developments for fully three-dimensional simulation models. We focus on the most well known, continuum physically based models which have been suitable for comprehensive TCAD analysis.
Full text
Available for:
GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
In this paper we analyze the possibility of creating a universal non-volatile memory in a near future. Unlike DRAM and flash memories a new universal memory should not require electric charge ...storing, but alternative principles of information storage. For the successful application a new universal memory must also exhibit low operating voltages, low power consumption, high operation speed, long retention time, high endurance, and a simple structure. Several alternative principles of information storage are reviewed. We discuss different memory technologies based on these principles, highlight the most promising candidates for future universal memory, make an overview of the current state-of-the-art of these technologies, and outline future trends and possible challenges by modeling the switching process.
Full text
Available for:
GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
A model capturing the effect of general strain on the electron effective masses and band-edge energies of the lowest conduction band of silicon is developed. Analytical expressions for the effective ...mass change induced by shear strain and valley shifts/splittings are derived using a degenerate kldrp theory at the zone-boundary X point. Good agreement to numerical band- structure calculations using the nonlocal empirical pseudopotential method with spin-orbit interactions is observed. The model is validated by calculating the bulk electron mobility under general strain with a Monte Carlo technique using the full-band structure and the proposed analytical model for the band structure. Finally, the impact of strain on the inversion-layer mobility of electrons is discussed.
We investigate the robustness of a purely electrical field-free switching of a perpendicularly magnetized free layer based on SOT. The effective magnetic field which leads to deterministic switching ...of a rectangular as well as of a square free layer is created dynamically by a two-current pulse scheme. It is demonstrated that the switching is very robust, being insensitive to fluctuations of the write pulses’ durations and to relatively large variations of the heavy metal wires’ dimensions. Furthermore, it remains reliable for a wide range of synchronization failures between the pulses. The combination of a rectangular free layer shape with a partial overlap with the second current line accelerates the switching of the cell allowing a fast, 0.25 ns, switching.
Full text
Available for:
GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Electron spin attracts much attention as an alternative to the electron charge degree of freedom for low-power reprogrammable logic and non-volatile memory applications. Silicon appears to be the ...perfect material for spin-driven applications. An order of magnitude enhancement of the electron spin lifetime in (0 0 1) silicon thin films by shear strain is shown. It is demonstrated that spin-flip scattering processes between the two 0 0 1 valleys are responsible for spin relaxation in thin (0 0 1) silicon films. The enhancement of the spin lifetime is the result of the suppression of inter-valley scattering caused by the shear strain induced equivalent 0 0 1 valley splitting.
Full text
Available for:
GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
We propose a magnetic field-free spin-orbit torque switching scheme based on two orthogonal current pulses, for which deterministic switching is demonstrated via numerical simulations. The first ...current pulse selects the cell, while the second current pulse ensures deterministic switching of the selected cell. 100% switching probability has been obtained for a wide range of amplitudes and durations of the pulses, thus precise timings are not required. This has also been verified considering a variability of ±5% of the saturation magnetization and anisotropy constant. An important feature of the scheme is that the magnitude of the second current is lower than the critical current for spin-orbit torque switching. The lower second current pulse improves the efficiency of the switching, reducing the corresponding pulse power by 75% and the total writing power by 40%, while maintaining the same switching time. Due to the sub-critical current, the corresponding spin-orbit torque is weak and does not disturb the bits of non-selected cells. Therefore, a single additional wire can be routed through several cells in a row, reducing the number of transistors per cell, and simplifying the cell integration in a memory array.
Since Stratton published his famous paper four decades ago, various transport models have been proposed which account for the average carrier energy or temperature in one way or another. The need for ...such transport models arose because the traditionally used drift-diffusion model cannot capture nonlocal effects which gained increasing importance in modern miniaturized semiconductor devices. In the derivation of these models from Boltzmann's transport equation, several assumptions have to be made in order to obtain a tractable equation set. Although these assumptions may differ significantly, the resulting final models show various similarities, which has frequently led to confusion. We give a detailed review on this subject, highlighting the differences and similarities between the models, and we shed some light on the critical issues associated with higher order transport models.
SIMON is a single electron tunnel device and circuit simulator that is based on a Monte Carlo method. It allows transient and stationary simulation of arbitrary circuits consisting of tunnel ...junctions, capacitors, and voltage sources of three kinds: constant, piecewise linearly time dependent, and voltage controlled. Cotunneling can be simulated either with a plain Monte Carlo method or with a combination of the Monte Carlo and master equation approach. A graphic user interface allows the quick and easy design of circuits with single-electron tunnel devices. Furthermore, as an example of the usage of SIMON, we discuss the essential problem of random background charge and present possible solutions.
PDF
