Roberto L. de Orio

• Dr.techn.
• TU Wien

In advancing the study of magnetization dynamics in STT-MRAM devices, we employ the spin drift–diffusion model to address the back-hopping effect. This issue manifests as unwanted switching either in the composite free layer or in the reference layer in synthetic antiferromagnets—a challenge that becomes more pronounced with device miniaturization....

We employ a fully three-dimensional model coupling magnetization, charge, spin, and temperature dynamics to study temperature effects in spin-orbit torque (SOT) magnetoresistive random access memory (MRAM). SOTs are included by considering spin currents generated through the spin Hall effect. We scale the magnetization parameters with the temperatu...

Because of their nonvolatile nature and simple structure, the interest in MRAM devices has been steadily growing in recent years. Reliable simulation tools, capable of handling complex geometries composed of multiple materials, provide valuable help in improving the design of MRAM cells. In this work, we describe a solver based on the finite elemen...

The realization of high interconnect densities for three-dimensional integration demands development of new wafer-to-wafer bonding approaches. Recently introduced Cu-to-Cu wafer-to-wafer hybrid bonding schemes overcome scaling limitations, but like other Cu-based interconnect structures, they are prone to electromigration. Migration and growth of v...

We present a generalization of the coupled spin-charge drift-diffusion formalism capable of accurately describing the spin and charge transport properties through magnetic tunnel junctions. Correction terms enable reproducing oscillations of the spin current in ferromagnets typical for quasi-ballistic transport. Our approach proves necessary to acc...

The development of reliable simulation tools provides a valuable help in the design of modern MRAMdevices. Thanks to its versatility in the choice of meshes and discretization, the finite element method is a useful framework for the numerical solution of the magnetization dynamics. We review a finite element implementation of both the Landau-Lifshi...

Designing advanced single-digit shape-anisotropy MRAM cells requires an accurate evaluation of spin currents and torques in magnetic tunnel junctions (MTJs) with elongated free and reference layers. For this purpose, we extended the analysis approach successfully used in nanoscale metallic spin valves to MTJs by introducing proper boundary conditio...

Interconnect segments of gold metallization used for GaAs devices are susceptible to significant electromigration degradation and have a microstructure with thousands of grains. In this work, a complete physics-based analysis of electromigration in gold is presented. A novel approach for the numerically efficient simulation of an interconnect conta...

A reinforcement learning strategy is applied to find a reliable switching scheme for deterministic switching of a perpendicularly magnetized spin-orbit torque magnetoresistive memory cell. Current pulses sent along orthogonal metal wires allow the field-free reversal of the magnetization. The current pulses are optimized such that reliable switchin...

Designing advanced single-digit shape-anisotropy MRAM cells requires an accurate evaluation of spin currents and torques in magnetic tunnel junctions (MTJs) with elongated free and reference layers. For this purpose, we extended the analysis approach successfully used in nanoscale metallic spin valves to MTJs by introducing proper boundary conditio...

The writing process in spin transfer torque magnetoresistive random access memories (STT–MRAM) is facilitated by elevated temperatures. In this work we investigate the temperature distribution and development in the free layer (FL) of an STT-MRAM during switching. With our fully three-dimensional (3D) finite element method simulation approach, we n...

Finding and optimizing robust schemes for field-free switching remains a challenging problem in spin-orbit torque magnetoresistive random access memories. In this work reinforcement learning is employed for the optimization of switching schemes for such memory cells. A cell is switched purely electrically by applying pulses to two orthogonal metal...

We demonstrate by means of numerical simulations the switching of a perpendicularly magnetized free layer by spin-orbit torques based on a two-pulse switching scheme with improved writing power efficiency. In this scheme, the first pulse selects the cell, while the second pulse completes the switching deterministically. It is shown that the magnitu...

A drift-diffusion approach to coupled spin and charge transport has been commonly applied to determine the spin-transfer torque acting on the magnetization in metallic valves. This approach, however, is not suitable to describe the predominant tunnel transport in magnetic tunnel junctions. In this work we present a coupled Finite Element solution t...

Spin-orbit torque memory is a suitable candidate for next generation nonvolatile magnetoresistive random access memory. It combines high-speed operation with excellent endurance, being particularly promising for application in caches. In this work, a two-current pulse magnetic field-free spin-orbit torque switching scheme is combined with reinforce...

As scaling of the feature size -the main driving force behind an outstanding increase of the performance of modern electronic circuits -displays signs of saturation, the main focus of engineering research in microelectronics shifts towards finding new paradigms. Any future solution must be scalable and energy efficient while delivering high perform...

Mitigation of the degradation for down-scaled interconnects requires an in-depth understanding of the failure mechanisms of electromigration and, therefore, the development of adequate simulation models based on this understanding. We present a novel concept for modeling of nano-interconnect structures, the effective domain method, which describes...

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 ob...

In this work, a method to determine critical circuit blocks for electromigration in an integrated circuit based on a temperature analysis of the metallization layers is developed. Considering a given maximum resistance increase due to the electromigration, a maximum temperature of operation of the interconnects is obtained. By comparing this maximu...

In spin-transfer torque magnetoresistive random access memory, the magnetization dynamics of a free layer is usually assumed to be determined by the torque created via a position-independent current density. In circuits, however, it is the voltage, not the current density, which stays fixed during switching. Therefore, the approximate evaluation of...

This paper demonstrates a finite element model to investigate the temperature change of the interconnects of an integrated circuit due to the power dissipation of the transistors in the substrate. The temperature of the local interconnect is more significantly affected, exhibiting an increase of 49 K and 34 K, for the Metal 1 and Metal 2, respectiv...

Simulation of switching in spin-transfer torque magnetoresistive random access memory is usually performed by assuming that the torque is created by a position- and time-independent current density. However, in real circuits the voltage is fixed, not the current density. The assumption of a fixed current density, especially in modern devices with a...

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...

A magnetic field-free switching of a symmetric square free layer with perpendicular magnetization by spin–orbit torque is demonstrated based on micromagnetic modeling and numerical simulations. The field-free switching is accomplished by using a two-pulse switching scheme. An appropriate design of the cell structure yields a deterministic and fast...

A method to calculate the temperature distribution on the BEOL structure and its impact on the EM in a design environment has been developed and implemented. The study for a 45 nm technology indicated a large temperature variation from the local to the global interconnects, which should be considered for the EM induced resistance increase of the li...

Seguindo a contínua miniaturização dos transistores em circuitos integrados, visando sempre o aumento da velocidade de operação, as interconexões metálicas dos CIs também sofrem uma redução contínua em suas dimensões, chegando a ser da ordem de algumas dezenas de nm.Como consequência desta redução, aumentam-se os tempos de propagação dos sinais pel...

This paper reports on the performance of a sub-THz liquid sensor tool coupled to a microfluidic platform. Non-invasive, non-destructive and on-line measurements are demonstrated for the determination of ethanol concentration and for controlling via micromixer device. We have developed a label-free chemical sensing methodology coupling a sub-teraher...

Electromigration damage in interconnects is a well-known bottleneck of integrated circuits, as it is responsible for the performance degradation. High values of temperature and current density accelerate the damage, causing an increase in the lines resistance and circuit lifetime reduction. In this work, a method is proposed to evaluate the electro...

Modeling and simulation of the temporal evolution of electromigration voids are critical to evaluate the reliability of interconnects of modern integrated circuits. In this work, the diffuse interface model is applied to investigate two different mechanisms of the void evolution due to electromigration. Two-dimensional numerical simulations have be...

Electromigration damage in interconnects is a well-known bottleneck of integrated circuits, as it is responsible for performance degradation, affecting parameters like delay, power and frequency. To guarantee a better performance for longer time, the chip designer needs to identify critical wires in the circuit layout and to alter it using techniqu...

The extrapolation of EM lifetimes obtained from high temperature tests to lower temperatures is investigated. It is shown that the usual extrapolation method leads to large errors for the predicted lifetimes at temperatures closer to the real operating conditions. A different approach for estimating the extrapolation parameters is discussed, where...

We demonstrate a coupled equipment- and feature-scale process simulation and its application to plasma-enhanced chemical vapor deposition (PECVD) as part of a sequence for the fabrication of a through-silicon via (TSV) interconnect. The TSV structure is characterized electrically and mechanically by means of finite element simulation. This chain al...

The effects of the presence of scallops along the sidewalls of filled (copper) and open (tungsten) TSVs are studied. The Bosch process is used in order to generate highly vertical deep trenches; however, the process results in scallops along the etched sidewalls. A model for the Bosch process is implemented in an in-house level set simulator in ord...

Current electromigration models used for simulation and analysis of interconnect reliability lack the appropriate description of metal microstructure and consequently have a very limited predictive capability. Therefore, the main objective of our work was obtaining more sophisticated electromigration tools. The problem is addressed through a combin...

In order to examine the effects of sidewall scallops on through-silicon via (TSV) performance, the etch processes required to generate several TSV geometries are simulated and the resulting structures are imported into a finite element tool for electrical parameter extraction and reliability analysis.The electrical models, which were confirmed usin...

The formation of a TSV for three-dimensional interconnects using SF6/O2 plasma is explored. Adjusting the O2 gas concentration to 45 sccm, while the SF6 concentration is set to 35 sccm, produced the best combination of chemical and physical etching to provide sidewall angles of 88°. Three TSV aspect ratios are etched (5/58, 10/100, and 20/100 μm) a...

Current electromigration models used for simulation and analysis of interconnect reliability lack the appropriate description of metal microstructure and consequently have a very limited predictive capability. Therefore, the main objective of our work was obtaining more sophisticated electromigration models. The problem is addressed through a combi...

Solder bumps are important interconnect components for three-dimensional (3D) integration. Their mechanical and electrical properties influence the overall reliability of 3D ICs. A particular characteristic of solder bumps is that during technology processing and usage their material composition changes. This compositional transformation influences...

A study of electromigration in open through silicon vias (TSVs) is presented. The calculations are based on the drift-diffusion model for electromigration combined with mechanical simulations. The results show that the highest stresses are located at the aluminium/tungsten interfaces, near the region where the electrical current is introduced into...

The electromigration (EM) lifetime standard deviation dependence on temperature for copper damascene interconnects is investigated. An analytical expression for the standard deviation as a function of temperature is obtained based on error propagation analysis applied to a typical EM-induced void growth model. It is shown that good agreement with e...

A study of electromigration in open through silicon vias (TSVs) is presented. First, the possible effects of the aluminium/tungsten interface are studied in a very simplified structure to find the parameters utmost concerning electromigration. The blocking interface without vacancy sink is found to have the highest resulting vacancy concentrations....

Solder bumps are important interconnect components for 3D integration. Their mechanical and electrical properties influence the overall reliability of 3D ICs. A characteristic of solder bumps is that during technology processing and usage their material composition changes. This compositional transformation influences the operation of 3D ICs and, i...

The reliability of interconnects in modern integrated circuits is determined by the magnitude and direction of the effective valence for electromigration (EM). The effective valence depends on local atomistic configurations of fast diffusivity paths such as metal interfaces, dislocations, and the grain boundary; therefore, microstructural variation...

For the realization of modern integrated circuits new interconnect structures like through-silicon-vias and solder bumps, together with complex multilevel 3D interconnect structures are gaining importance. The application of these new structures unavoidably rises different reliability issues like thermal gradients, electromigration, and stressmigra...

Interconnect lifetimes due to electromigration (EM) failures are traditionally described by a modified Black equation [1] equation (1) where tf is the time to failure (TTF), A is a constant, j is the electrical current density, n is a fitting parameter which describes the impact of the current density, Ea is the fitted activation energy representin...

The resistance change due to electromigration induced voiding in modern copper interconnects ended by a Through Silicon Via (TSV) is analyzed. It is shown that two different modes of resistance increase exist during the period of void growth under the TSV. Primarily responsible are imperfections at the TSV bottom introduced during the fabrication p...

Electromigration (EM) is one of the main reliability concerns in copper interconnects. In particular, it is a critical issue for new emerging technologies, such as through silicon via (TSV) technology. In this work the impact of formation and growth of voids under a TSV located at the cathode end of a typical dual-damascene line is analyzed. The re...

Electromigration (EM) is one of the main reliability concerns in copper interconnects. In particular, it is a critical issue for new emerging technologies, such as through silicon via (TSV) technology. In this work the impact of formation and growth of voids under a TSV located at the cathode end of a typical dual-damascene line is analyzed. The re...

Electromigration induced failure development in a copper dual-damascene structure with a through silicon via (TSV) located at the cathode end of the line is studied. The resistance change caused by void growth under the TSV and the interconnect lifetime estimation are modeled based on analytical expressions and also investigated with the help of nu...