Impact of laser attacks on the switching behavior of RRAM devices

The ubiquitous use of critical and private data in electronic format requires reliable and secure embedded systems for IoT devices. In this context, RRAMs (Resistive Random Access Memories) arises as a promising alternative to replace current memory technologies. However, their suitability for this kind of application, where the integrity of the data is crucial, is still under study. Among the different typology of attacks to recover information of secret data, laser attack is one of the most common due to its simplicity. Some preliminary works have already addressed the influence of laser tests on RRAM devices. Nevertheless, the results are not conclusive since different responses have been reported depending on the circuit under testing and the features of the test. In this paper, we have conducted laser tests on individual RRAM devices. For the set of experiments conducted, the devices did not show faulty behaviors. These results contribute to the characterization of RRAMs and, together with the rest of related works, are expected to pave the way for the development of suitable countermeasures against external attacks.Postprint (published version

Fabrication, Characterization and Integration of Resistive Random Access Memories

The functionalities and performances of today's computing systems are increasingly dependent on the memory block. This phenomenon, also referred as the Von Neumann bottleneck, is the main motivation for the research on memory technologies. Despite CMOS technology has been improved in the last 50 years by continually increasing the device density, today's mainstream memories, such as SRAM, DRAM and Flash, are facing fundamental limitations to continue this trend. These memory technologies, based on charge storage mechanisms, are suffering from the easy loss of the stored state for devices scaled below 10 nm. This results in a degradation of the performance, reliability and noise margin. The main motivation for the development of emerging non volatile memories is the study of a different mechanism to store the digital state in order to overcome this challenge. Among these emerging technologies, one of the strongest candidate is Resistive Random Access Memory (ReRAM), which relies on the formation or rupture of a conductive filament inside a dielectric layer. This thesis focuses on the fabrication, characterization and integration of ReRAM devices. The main subject is the qualitative and quantitative description of the main factors that influence the resistive memory electrical behavior. Such factors can be related either to the memory fabrication or to the test environment. The first category includes variations in the fabrication process steps, in the device geometry or composition. We discuss the effect of each variation, and we use the obtained database to gather insights on the ReRAM working mechanism and the adopted methodology by using statistical methods. The second category describes how differences in the electrical stimuli sent to the device change the memory performances. We show how these factors can influence the memory resistance states, and we propose an empirical model to describe such changes. We also discuss how it is possible to control the resistance states by modulating the number of input pulses applied to the device. In the second part of this work, we present the integration of the fabricated devices in a CMOS technology environment. We discuss a Verilog-A model used to simulate the device characteristics, and we show two solutions to limit the sneak-path currents for ReRAM crossbars: a dedicated read circuit and the development of selector devices. We describe the selector fabrication, as well as the electrical characterization and the combination with our ReRAMs in a 1S1R configuration. Finally, we show two methods to integrate ReRAM devices in the BEoL of CMOS chips

Low Power Memory/Memristor Devices and Systems

This reprint focusses on achieving low-power computation using memristive devices. The topic was designed as a convenient reference point: it contains a mix of techniques starting from the fundamental manufacturing of memristive devices all the way to applications such as physically unclonable functions, and also covers perspectives on, e.g., in-memory computing, which is inextricably linked with emerging memory devices such as memristors. Finally, the reprint contains a few articles representing how other communities (from typical CMOS design to photonics) are fighting on their own fronts in the quest towards low-power computation, as a comparison with the memristor literature. We hope that readers will enjoy discovering the articles within

Thermal Laser Attack and High Temperature Heating on HfO2-based OxRAM Cells

International audienceThe last 10 years have seen the rise of new NVM technologies as alternative solutions to Flash technology, which is facing downsizing issues. Apart from offering higher performance than the state of the art of Flash, one of their key features is lower power consumption, which makes them even more suitable for the IoT era. But one of the other main concerns regarding IoT is data security, which is yet to be evaluated for emerging NVM. Our previous work aimed at putting under test the integrity of HfO 2 based resistive RAM (OxRAM cells). Bit-set occurrences were found after thermal laser attacks. This present work investigates the difference in behaviour when a selector is added to the resistive element, thanks to attack on different stacks. The results obtained give interesting tracks for the design of secure OxRAM-based ICs. It also studies the kinetic role of temperature through heating experiments