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

Unpredictable bits generation based on RRAM parallel configuration

In this letter a cell with the parallel combination of two TiN/Ti/HfO2/W resistive random access memory (RRAM) devices is studied for the generation of unpredictable bits. Measurements confirm that a simultaneous parallel SET operation in which one of the two RRAMs switches to the low resistance state (LRS) is an unpredictable process showing random properties for different sets of cells. Furthermore, given a device pair, the same device switches during subsequent write operations. The proposed cell is also analyzed under different current compliances and pulse widths with the same persistent behavior being observed. The features of the proposed cell, which provide data obfuscation without compromising reliability, pave the way for its application in Physical Unclonable Functions (PUFs) for hardware security purposes.Peer ReviewedPostprint (author's final draft

True random number generator based on RRAM-bias current starved ring oscillator

This work presents a RRAM-bias current starved ring oscillator (CSRO) as TRNG, where the cycle-to-cycle variability of a RRAM device is exploited as source of randomness. A simple voltage divider composed of this RRAM and a resistor is considered to bias the gate terminal of the extra transistor of every current starved (CS) inverter of the RO. In this way, the delay of the inverters is modified, deriving an unpredictable oscillation frequency every time the RRAM switches to the HRS. The oscillation frequency is finally leveraged to extract the sequence of random bits. The design is simple and add low area overhead. Experimental measurements are performed to analyze the cycle-to-cycle variability in the HRS. The very same measurements are subsequently used to validate the TRNG by means of electrical simulations. The obtained results passed all the NIST tests without the need for post-processing.This work was supported by the Spanish MCIN/AEI/10.13039/501100011033 under Project PID2019-103869RB-C33. The work of M. B. González was supported by the Ramón y Cajal under Grant RYC2020-030150-I.Peer ReviewedPostprint (published version

Fragmentació del DNA espermàtic

La fragmentació del DNA és la conseqüència final de l'apoptosi. En el testicle és ben sabut que el camí utilitzat per controlar el nombre adequat de cèl·lules germinals mitjançant cèl·lules de Sertoli depèn de la via Fas. Tot i això, hi ha espermatozoides que han estat assenyalats per prendre la via de l'apoptosi, que s'escapen d'aquest procés. Altres fonts possibles de dany al DNA espermàtic poden ser l'estrès oxidatiu, provocat per radicals lliures d'oxigen (sovint produïts per leucòcits presents en l'ejaculació, però també per part d'altres espermatozoides), i també processos naturals, com ara la recombinació i l'empaquetament de la cromatina, que impliquen la formació de fragments en les cadenes de DNA. La relació entre la fragmentació del DNA espermàtic i l'esterilitat masculina sembla clara, però, en qualsevol cas, encara hi ha controvèrsia sobre l'efecte d'aquesta fragmentació quan se segueixen processos de reproducció assistida, ja que hi ha passos naturals que són esquivats i també hi ha un efecte oocitari molt important.DNA fragmentation is the last phenomenon occurred during apoptosis. It is known that Fas-mediated apoptosis is the way used in testes to control the number of germ cells that are excessive with the supportive capacity of the Sertoli cells. Even dough, spermatozoa that have been earmarked to undergo apoptosis escape this process. Other potential source of sperm DNA damage is oxidative stress due to reactive oxygen species (produced by leukocytes present in ejaculate, but also by other spermatozoa) and deficiencies in natural processes such as recombination and chromatin packaging that involves the induction of DNA strand breaks. It seems clear that DNA damage on sperm is related to male fertility but it is still controversial if this DNA fragmentation has an effect when Assisted Reproduction Techniques are performed, due to natural steps are bypassed and there is also an oocyte effect that can not be forgotten

True random number generator based on the variability of the high resistance state of RRAMs

Hardware-based security primitives like True Random Number Generators (TRNG) have become a crucial part in protecting data over communication channels. With the growth of internet and cloud storage, TRNGs are required in numerous cryptographic operations. On the other hand, the inherently dense structure and low power characteristics of emerging nanoelectronic technologies such as resistive-switching memories (RRAM) make them suitable elements in designing hardware security modules integrated in CMOS ICs. In this paper, a memristor based TRNG is presented by leveraging the high stochasticity of RRAM resistance value in OFF (High Resistive) state. In the proposal, one or two devices can be used depending on whether the objective is focused on saving area or obtaining a higher random bit frequency generation. The generated bits, based on a combination of experimental measurements and SPICE simulations, passed all 15 National Institute of Standards and Technology (NIST) tests and achieved a throughput of tens of MHz.Postprint (published version

Differential microRNA expression profile between stimulated PBMCs from HIV-1 infected elite controllers and viremic progressors

BACKGROUND: The emerging relationship between microRNAs (miRNA) and viral-control is a topic of interest in the field of HIV. Host-genome might play an important role in the control of viremia. The aim of this study was to assess the specific miRNA profile that could contribute to the control of HIV replication in Elite Controllers. RESULTS: After adequate normalization, expression profile of 286 human miRNAs (hsa-miR) was evaluated in phytohaemagglutinin-stimulated PBMCs from 29 individuals classified in 4 groups: 8 elite controllers (EC; viral load 5000 cp/ml without treatment), 8 patients under antiretroviral treatment (ART; VL<200 cp/ml) and 5 uninfected individuals (HIV-) through TaqMan Array Human microRNA Cards v3.0. A differential expression pattern consisting of 23 miRNAs became significantly different when comparing EC and VP. Profiling analysis segregated the population in two different blocks: while EC and HIV- clustered together in the same block (EC/HIV-_block 1), VP and ART individuals clustered together in a second block (VP/ART_block 2). Two inversely expressed miRNA patterns were determined within those two blocks: a set of 4 miRNAs (hsa-miR-221, -27a, -27b and -29b) was up-expressed in EC/HIV-_block and down-expressed in VP/ART_block while 19 miRNAs were down-expressed in block 1 and up-expressed in block 2. Differential miRNAs were successfully validated through individual RT-qPCR assays. CONCLUSIONS: Profile in EC resembled HIV- and differentially clusters with VP and ART. Therefore, differential clustering does not rely on undetectable viremia

2020 IEEE Latin America Electron Devices Conference (LAEDC)

Producción CientíficaThree topologies of TiN/Ti/HfO 2 /W resistive switching memories (RRAM) are proposed in this work: crossbar, isolated and isolated-crossbar configurations. All configurations use the same sequence of technological processes. The different topologies are obtained by customizing the layouts corresponding to the bottom electrode (W), and the silicon oxide layer that is deposited on the bottom electrode. A comparative study of the resistive switching mechanisms in the three configurations has been carried out. DC current-voltage cycles and small signal conductance memory maps of single RRAM show relevant differences among the three topologies. Complex structures containing various devices (series, anti-series, parallel, antiparallel) have also been fabricated. Switching loops and memory maps obtained for these complex structures demonstrate that they are fully operative, validating the technological route to manufacture complete RRAM memory chips.Ministerio de Economía, Industria y Competitividad - Fondo Europeo de Desarrollo Regional (grants TEC2017-84321- C4-1-R and TEC2017-84321-C4-2-R

Study of TiN/Ti/HfO2/W resistive switching devices: characterization and modeling of the set and reset transitions using an external capacitor discharge

Producción CientíficaIn this work, we have studied the control of set and the reset transitions in TiN/Ti/HfO2/W resistive switching devices using a new approach based on the injection of a limited amount of charge through the use of a capacitor discharge. Instead of applying conventional voltage or current signals, the capacitor discharge through the devices is able to perform both transitions. An accumulative process is observed if we apply consecutive discharges, and, when increasing the capacitor voltage in each discharge, the transitions between both resistance states are completed. In addition, it has been shown that faster transitions require larger capacitor voltages. Further, the electrical results were used to tune the dynamic memdiode model, which was employed to simulate set and reset processes driven by the capacitor discharges. The model successfully reproduced the measured memristor response to the capacitor discharge.Ministerio de Ciencia, Innovación y Universidades y programa FEDER (proyectos TEC2017-84321-C4-1-R, TEC2017-84321-C4-2-R, TEC2017-84321-C4-3-R y TEC2017-84321-C4-4-R

Influences of the temperature on the electrical properties of HfO2-based resistive switching devices

Producción CientíficaIn the attempt to understand the behavior of HfO2-based resistive switching devices at low temperatures, TiN/Ti/HfO2/W metal–insulator–metal devices were fabricated; the atomic layer deposition technique was used to grow the high-k layer. After performing an electroforming process at room temperature, the device was cooled in a cryostat to carry out 100 current–voltage cycles at several temperatures ranging from the “liquid nitrogen temperature” to 350 K. The measurements showed a semiconducting behavior in high and low resistance states. In the low resistance state, a hopping conduction mechanism was obtained. The set and reset voltages increased when temperature decreased because the thermal energies for oxygen vacancies and ions were reduced. However, the temperature did not influence the power absorbed in the reset transition, indicating the local temperature in the filament controls the transition. The set transition turned from gradual to abrupt when decreasing the temperature, due to a positive feedback between the current increase and the Joule heating at low temperatures.Ministerio de Economía, Industria y Competitividad - Fondo Europeo de Desarrollo Regional (Projects TEC2017-84321-C4-2-R and TEC2017-84321-C4-1-R