Simulation and Experimental Demonstration of the Importance of IR-Drops During Laser Fault-Injection

International audienceLaser fault injections induce transient faults into ICs by locally generating transient currents that temporarily flip the outputs of the illuminated gates. Laser fault injection can be anticipated or studied by using simulation tools at different abstraction levels: physical, electrical or logical. At the electrical level, the classical laser-fault injection model is based on the addition of current sources to the various sensitive nodes of CMOS transistors. However, this model does not take into account the large transient current components also induced between the VDD and GND of ICs designed with advanced CMOS technologies. These short-circuit currents provoke a significant IR-drop that contribute to the fault injection process. This paper describes our research on the assessment of this contribution. It shows through simulation and experiments that during laser fault injection campaigns, laser-induced IR-drop is always present when considering circuits designed with deep submicron technologies. It introduces an enhanced electrical fault model taking the laser-induced IR-drop into account. It also proposes a methodology that allows the use of the model to simulate laser-induced faults at the electrical level in large-scale circuits. On the basis of further simulations and experimental results, we found that, depending on the laser pulse characteristics, the number of injected faults may be underestimated by a factor of up to 2.4 if the laser-induced IR-drop is ignored. This could lead to incorrect estimations of the fault injection threshold, which is especially relevant to the design of countermeasure techniques for secure integrated systems

Ultrafast Laser Pulse Interaction with Dielectric Materials: Numerical and Experimental Investigations on Ablation and Micromachining

Ultrafast lasers have great capability and flexibility in micromachining of various materials. Due to the involved complicated multi-physical processes, mechanisms during laser-material interaction have not been fully understood. To improve and explore ultrafast laser processing and treatment of dielectric materials, numerical and experimental investigations have been devoted to better understanding the underlying fundamental physics during laser-material interaction and material micromachining. A combined continuum-atomistic model has been developed to investigate thermal and non-thermal (photomechanical) responses of materials to ultrafast laser pulse irradiation. Coexistence of phase explosion and spallation can be observed for a considerably wide range of laser fluences. Phase explosion becomes the primary ablation mechanism with the increase of laser fluence, and spallation can be restrained due to the weakened tensile stress by the generation of recoil pressure from ejection of hot material plume. For dielectric materials, due to the much lower temperature gradient by non-linear absorption, the generated thermal-elastic stress is much weaker than that in non-transparent materials, making spallation less important. Plasma dynamics is studied with respect to ejection directions and velocities based on fluorescence and shadowgraph measurements. The most probable direction (angle) is found insensitive to laser fluence/energy. The plasma expansion velocity is closely related to electron thermal velocity, indicating the significance of thermal ablation in dielectric material decomposition by laser irradiation. A numerical study of ultrafast laser-induced ablation of dielectric materials is presented based on a one-dimensional plasma-temperature model. Plasma dynamics including photoionization, impact ionization and relaxation are considered through a single rate equation. Material decomposition is captured by a temperature-based ablation criterion. Dynamic description of ablation process has been achieved through an improved two-temperature model. Laser-induced ablation threshold, transient optical properties and ablation depth have been investigated with respect to incident fluences and pulse durations. Good agreements are shown between numerical predictions and experimental observations. Fast increase of ablation depth, followed by saturation, can be observed with the increase of laser fluence. Reduction of ablation depth at fluences over 20 J/cm2 is resulted from plasma defocusing effect by air ionization. Thermal accumulation effect can be negligible with repetition rate lower than 1 kHz for fused silica and helps to enhance the ablation depth at 10 kHz (100 pulses) to almost double of that with single pulse. The ablation efficiency decreases with fluence after reaching the peak value at the fluence twice of the ablation threshold. The divergence of tightly focused Gaussian beam in transparent materials has been revealed to significantly affect the ablation process, particularly at high laser fluence. A comprehensive study of ultrafast laser direct drilling in fused silica is performed with a wide range of drilling speeds (20-500 μm/s) and pulse energy (60-480 μJ). Taper-free and uniform channels are drilled with the maximum length over 2000 μm, aspect ratio as high as ~40:1 and excellent sidewall quality (roughness ~0.65 μm) at 270 μJ. The impacts of pulse energy and drilling speeds on channel aspect ratio and quality are studied. Optimal drilling speeds are determined at different pulse energy. The dominating mechanisms of channel early-termination are beam shielding by material modification at excessive laser irradiation for low speed drilling and insufficient laser energy deposition for high speed drilling, respectively. An analytical model is developed to validate these mechanisms. The feasibility of direct drilling high-aspect-ratio and high-quality channels by ultrafast laser in transparent materials is demonstrated

Development and Characterization of a High-Speed Material-Testing Machine, and Experimental Analysis of Frictional Flash Heating and Dynamic Weakening in Rock

Experimental investigation of dependence of sliding-friction on velocity is necessary to understand the physics of earthquakes. Velocity-dependent friction is ideally studied in experiments by imposing step-wise changes in sliding-rate. In this dissertation, a novel High-Speed Biaxial (HSB) testing machine capable of imposing steps from quasi-static (1 mm.s¯¹) to seismic (1 m.s¯¹) sliding-rates has been developed and characterized. The HSB can achieve steps to seismic sliding-rates in only a few milliseconds under loads as high as 0.5 MN. Herein, the dynamics of the hydro-pneumatic loading-system of the HSB is studied, and by developing an analytical model, feasibility of achieving the desired velocity-steps under different load-path scenarios is assessed. Moreover, the HSB prototype is instrumented and tested to validate the model analysis. Based on the experimental results, a model of vibrations is developed for the continuous loading-system. The model is used to identify and treat vibration sources in the HSB prototype, and a modified design is proposed to reduce vibrations in the ultimate testing machine. After development and verification of the HSB prototype, a series of sliding friction experiments were conducted to study dependence of friction on sliding-rate, slip history and normal-stress. At seismic sliding-rates, frictional heating can lead to dramatic frictional-weakening in rock. Here, I report on high-speed friction experiments for which flash-heated contacts are thermally imaged on rock samples. The thermographic images provide the first documentation of the geometry and spatial distributions of load-bearing contacts formed in rock during frictional sliding at seismic rates. The thermographs display a highly heterogeneous distribution of temperature and stress at millimetric scale. The maximum temperature observed in our experiments (500 °C) is remarkably higher than average surface temperature calculated by other studies (100 °C), which reflects the localization of stress to small portions of the contact surface. The observations indicate that, opposed to the original micro-scale flash-weakening model, flash-heating occurs in multiple length- and time-scales. Accordingly, a multi-scale flash-weakening model is proposed and developed, which can simulate the transient friction more accurately. The new findings can play a key role in understanding nucleation and propagation of earthquake ruptures in natural faults

Innovation: Key to the future

The NASA Marshall Space Flight Center Annual Report is presented. A description of research and development projects is included. Topics covered include: space science; space systems; transportation systems; astronomy and astrophysics; earth sciences; solar terrestrial physics; microgravity science; diagnostic and inspection system; information, electronic, and optical systems; materials and manufacturing; propulsion; and structures and dynamics

Center for Advanced Space Propulsion Second Annual Technical Symposium Proceedings

The proceedings for the Center for Advanced Space Propulsion Second Annual Technical Symposium are divided as follows: Chemical Propulsion, CFD; Space Propulsion; Electric Propulsion; Artificial Intelligence; Low-G Fluid Management; and Rocket Engine Materials

Approximate Computing Strategies for Low-Overhead Fault Tolerance in Safety-Critical Applications

This work studies the reliability of embedded systems with approximate computing on software and hardware designs. It presents approximate computing methods and proposes approximate fault tolerance techniques applied to programmable hardware and embedded software to provide reliability at low computational costs. The objective of this thesis is the development of fault tolerance techniques based on approximate computing and proving that approximate computing can be applied to most safety-critical systems. It starts with an experimental analysis of the reliability of embedded systems used at safety-critical projects. Results show that the reliability of single-core systems, and types of errors they are sensitive to, differ from multicore processing systems. The usage of an operating system and two different parallel programming APIs are also evaluated. Fault injection experiment results show that embedded Linux has a critical impact on the system’s reliability and the types of errors to which it is most sensitive. Traditional fault tolerance techniques and parallel variants of them are evaluated for their fault-masking capability on multicore systems. The work shows that parallel fault tolerance can indeed not only improve execution time but also fault-masking. Lastly, an approximate parallel fault tolerance technique is proposed, where the system abandons faulty execution tasks. This first approximate computing approach to fault tolerance in parallel processing systems was able to improve the reliability and the fault-masking capability of the techniques, significantly reducing errors that would cause system crashes. Inspired by the conflict between the improvements provided by approximate computing and the safety-critical systems requirements, this work presents an analysis of the applicability of approximate computing techniques on critical systems. The proposed techniques are tested under simulation, emulation, and laser fault injection experiments. Results show that approximate computing algorithms do have a particular behavior, different from traditional algorithms. The approximation techniques presented and proposed in this work are also used to develop fault tolerance techniques. Results show that those new approximate fault tolerance techniques are less costly than traditional ones and able to achieve almost the same level of error masking.Este trabalho estuda a confiabilidade de sistemas embarcados com computação aproximada em software e projetos de hardware. Ele apresenta métodos de computação aproximada e técnicas aproximadas para tolerância a falhas em hardware programável e software embarcado que provêem alta confiabilidade a baixos custos computacionais. O objetivo desta tese é o desenvolvimento de técnicas de tolerância a falhas baseadas em computação aproximada e provar que este paradigma pode ser usado em sistemas críticos. O texto começa com uma análise da confiabilidade de sistemas embarcados usados em sistemas de tolerância crítica. Os resultados mostram que a resiliência de sistemas singlecore, e os tipos de erros aos quais eles são mais sensíveis, é diferente dos multi-core. O uso de sistemas operacionais também é analisado, assim como duas APIs de programação paralela. Experimentos de injeção de falhas mostram que o uso de Linux embarcado tem um forte impacto na confiabilidade do sistema. Técnicas tradicionais de tolerância a falhas e variações paralelas das mesmas são avaliadas. O trabalho mostra que técnicas de tolerância a falhas paralelas podem de fato melhorar não apenas o tempo de execução da aplicação, mas também seu mascaramento de erros. Por fim, uma técnica de tolerância a falhas paralela aproximada é proposta, onde o sistema abandona instâncias de execuções que apresentam falhas. Esta primeira experiência com computação aproximada foi capaz de melhorar a confiabilidade das técnicas previamente apresentadas, reduzindo significativamente a ocorrência de erros que provocam um crash total do sistema. Inspirado pelo conflito entre as melhorias trazidas pela computação aproximada e os requisitos dos sistemas críticos, este trabalho apresenta uma análise da aplicabilidade de computação aproximada nestes sistemas. As técnicas propostas são testadas sob experimentos de injeção de falhas por simulação, emulação e laser. Os resultados destes experimentos mostram que algoritmos aproximados possuem um comportamento particular que lhes é inerente, diferente dos tradicionais. As técnicas de aproximação apresentadas e propostas no trabalho são também utilizadas para o desenvolvimento de técnicas de tolerância a falhas aproximadas. Estas novas técnicas possuem um custo menor que as tradicionais e são capazes de atingir o mesmo nível de mascaramento de erros

Report of the panel on volcanology, section 4

Two primary goals are identified as focal to NASA's research efforts in volcanology during the 1990s: to understand the eruption of lavas, gases, and aerosols from volcanoes, the dispersal of these materials on the Earth's surface and through the atmosphere, and the effects of these eruptions on the climate and environment; and to understand the physical processes that lead to the initiation of volcanic activity, that influence the styles of volcanic eruptions, and that dictate the morphology and evolution of volcanic landforms. Strategy and data requirements as well as research efforts are discussed

Improved micro-contact resistance model that considers material deformation, electron transport and thin film characteristics

This paper reports on an improved analytic model forpredicting micro-contact resistance needed for designing microelectro-mechanical systems (MEMS) switches. The originalmodel had two primary considerations: 1) contact materialdeformation (i.e. elastic, plastic, or elastic-plastic) and 2) effectivecontact area radius. The model also assumed that individual aspotswere close together and that their interactions weredependent on each other which led to using the single effective aspotcontact area model. This single effective area model wasused to determine specific electron transport regions (i.e. ballistic,quasi-ballistic, or diffusive) by comparing the effective radius andthe mean free path of an electron. Using this model required thatmicro-switch contact materials be deposited, during devicefabrication, with processes ensuring low surface roughness values(i.e. sputtered films). Sputtered thin film electric contacts,however, do not behave like bulk materials and the effects of thinfilm contacts and spreading resistance must be considered. Theimproved micro-contact resistance model accounts for the twoprimary considerations above, as well as, using thin film,sputtered, electric contact