Laboratoire des Technologies de la Microélectronique

We report on a numerical study of electronic transport in chemically doped 2D graphene materials. By using ab initio calculations, a self-consistent scattering potential is derived for boron and nitrogen substitutions, and a fully quantum-mechanical Kubo-Greenwood approach is used to evaluate the resulting charge mobilities and conductivities of systems with impurity concentration ranging within [0.5, 4.0]%. Even for a doping concentration as large as 4.0%, the conduction is marginally affected by quantum interference effects, preserving therefore remarkable transport properties, even down to the zero temperature limit. As a result of the chemical doping, electron-hole mobilities and conductivities are shown to become asymmetric with respect to the Dirac point.

Abstract Chalcogenide phase-change materials (PCMs), such as Ge-Sb-Te alloys, have shown outstanding properties, which has led to their successful use for a long time in optical memories (DVDs) and, recently, in non-volatile resistive memories. The latter, known as PCM memories or phase-change random access memories (PCRAMs), are the most promising candidates among emerging non-volatile memory (NVM) technologies to replace the current FLASH memories at CMOS technology nodes under 28 nm. Chalcogenide PCMs exhibit fast and reversible phase transformations between crystalline and amorphous states with very different transport and optical properties leading to a unique set of features for PCRAMs, such as fast programming, good cyclability, high scalability, multi-level storage capability, and good data retention. Nevertheless, PCM memory technology has to overcome several challenges to definitively invade the NVM market. In this review paper, we examine the main technological challenges that PCM memory technology must face and we illustrate how new memory architecture, innovative deposition methods, and PCM composition optimization can contribute to further improvements of this technology. In particular, we examine how to lower the programming currents and increase data retention. Scaling down PCM memories for large-scale integration means the incorporation of the PCM into more and more confined structures and raises materials science issues in order to understand interface and size effects on crystallization. Other materials science issues are related to the stability and ageing of the amorphous state of PCMs. The stability of the amorphous phase, which determines data retention in memory devices, can be increased by doping the PCM. Ageing of the amorphous phase leads to a large increase of the resistivity with time (resistance drift), which has up to now hindered the development of ultra-high multi-level storage devices. A review of the current understanding of all these issues is provided from a materials science point of view.

A method for integrating separately developed information resources that overcomes incompatibilities in syntax and semantics and permits the resources to be accessed and modified coherently is described. The method provides logical connectivity among the information resources via a semantic service layer that automates the maintenance of data integrity and provides an approximation of global data integration across systems. This layer is a fundamental part of the Carnot architecture, which provides tools for interoperability across global enterprises.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

We report on a numerical study of quantum transport in disordered two dimensional graphene and graphene nanoribbons. By using the Kubo and the Landauer approaches, transport length scales in the diffusive (mean free path and charge mobilities) and localized regimes (localization lengths) are computed, assuming a short range disorder (Anderson-type). The electronic systems are found to undergo a conventional Anderson localization in the zero-temperature limit, in agreement with localization scaling theory. Localization lengths in weakly disordered ribbons are found to strongly fluctuate depending on their edge symmetry, but always remain several orders of magnitude smaller than those computed for 2D graphene for the same disorder strength. This pinpoints the role of transport dimensionality and edge effects.

A new concept to take advantage of the parasitic resistance that appears on port X of the second-generation current conveyors is introduced. This parasitic resistance, which is controllable in current, leads to the definition of the second generation current controlled conveyors (CCCII). A current controlled bandpass filter, operating in the current mode, is also described. It uses only two CCCII+s and two capacitors. Its central frequency can be adjusted by acting on the bias current of the conveyors. SPICE simulation results, in agreement with theory, are given for central frequencies around 30 MHz.

Wearable sensors are receiving a great deal of attention as they offer the potential to become a key technological tool for healthcare. In order for this potential to come to fruition, new electroactive materials endowing high performance need to be integrated with textiles. Here we present a simple and reliable technique that allows the patterning of conducting polymers on textiles. Electrodes fabricated using this technique showed a low impedance contact with human skin, were able to record high quality electrocardiograms at rest, and determine heart rate even when the wearer was in motion. This work paves the way towards imperceptible electrophysiology sensors for human health monitoring.

The minimal structural unit that defines living organisms is a single cell. By proliferating and mechanically interacting with each other, cells can build complex organization such as tissues that ultimately organize into even more complex multicellular living organisms, such as mammals, composed of billions of single cells interacting with each other. As opposed to passive materials, living cells actively respond to the mechanical perturbations occurring in their environment. Tissue cell adhesion to its surrounding extracellular matrix or to neighbors is an example of a biological process that adapts to physical cues. The adhesion of tissue cells to their surrounding medium induces the generation of intracellular contraction forces whose amplitude adapts to the mechanical properties of the environment. In turn, solicitation of adhering cells with physical forces, such as blood flow shearing the layer of endothelial cells in the lumen of arteries, reinforces cell adhesion and impacts cell contractility. In biological terms, the sensing of physical signals is transduced into biochemical signaling events that guide cellular responses such as cell differentiation, cell growth and cell death. Regarding the biological and developmental consequences of cell adaptation to mechanical perturbations, understanding mechanotransduction in tissue cell adhesion appears as an important step in numerous fields of biology, such as cancer, regenerative medicine or tissue bioengineering for instance. Physicists were first tempted to view cell adhesion as the wetting transition of a soft bag having a complex, adhesive interaction with the surface. But surprising responses of tissue cell adhesion to mechanical cues challenged this view. This, however, did not exclude that cell adhesion could be understood in physical terms. It meant that new models and descriptions had to be created specifically for these biological issues, and could not straightforwardly be adapted from dead matter. In this review, we present physical concepts of tissue cell adhesion and the unexpected cellular responses to mechanical cues such as external forces and stiffness sensing. We show how biophysical approaches, both experimentally and theoretically, have contributed to our understanding of the regulation of cellular functions through physical force sensing mechanisms. Finally, we discuss the different physical models that could explain how tissue cell adhesion and force sensing can be coupled to internal mechanosensitive processes within the cell body.

-based photonic integrated circuits for energy-efficient nonlinear photonics and quantum optics.

Metal organic chemical vapor deposition of GaAs on standard nominal 300 mm Si(001) wafers was studied. Antiphase boundary (APB) free epitaxial GaAs films as thin as 150 nm were obtained. The APB-free films exhibit an improvement of the room temperature photoluminescence signal with an increase of the intensity of almost a factor 2.5. Hall effect measurements show an electron mobility enhancement from 200 to 2000 cm2/V s. The GaAs layers directly grown on industrial platform with no APBs are perfect candidates for being integrated as active layers for nanoelectronic as well as optoelectronic devices in a CMOS environment.

The statistics of electrical breakdown field (Ebd) of HfO2 and SiO2 thin films has been evaluated over multiple length scales using macroscopic testing of standardized metal-oxide-semiconductor (TiN∕SiO2∕Si) and metal-insulator-metal (TiN∕HfO2∕TiN) capacitors (10−2mm2–10μm2 area) on a full 200mm wafer along with conductive-atomic-force microscopy. It is shown that Ebd follows the same Weibull distribution when the data are scaled using the testing area. This overall scaling suggests that the defect density is ∼1015cm−2 and Ebd is ∼40MV∕cm for nanometer-length scales; as such, breakdown in these materials is most likely initiated by bond breaking rather than punctual defects.

In this paper we clarify for the first time the correlation between endurance, window margin and retention of Resistive RAM. To this aim, various classes of RRAM (OXRAM and CBRAM) are investigated, showing high window margin up to 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">10</sup> cycles or high 300°C retention. From first principle calculations, we analyze the conducting filament composition for the various RRAM technologies, and extract the key filament features. We then propose an analytical model to calculate the dependence between endurance, window margin and retention, linking material parameters to memory characteristics.

and single facet output power exceeding 130 mW at room temperature.

For the first time, we report a 3D stacked sub-15 nm diameter NanoWire FinFET-like CMOS technology (3D-NWFET) with a new optional independent gate nanowire structure named PhiFET. Extremely high driving currents for 3D-NWFET (6.5 mA/mum for NMOS and 3.3 mA/mum for PMOS) are demonstrated thanks to the 3D configuration using a high-k/metal gate stack. Co-processed reference FinFETs with fin widths down to 6 nm are achieved with record aspect ratios of 23. We show experimentally that the 3D-NWFET, compared to a co-processed FinFET, relaxes by a factor of 2.5 the channel width requirement for a targeted DIBL and improves transport properties. PhiFET exhibits significant performance boosts compared to Independent-Gate FinFET (IG-FinFET): a 2-decade smaller I <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">OFF</sub> current and a lower subthreshold slope (82 mV/dec. instead of 95 mV/dec.). This highlights the better scalability of 3D-NWFET and PhiFET compared to FinFET and IG-FinFET, respectively.

Security is gaining increasing relevance in the development of embedded devices. Towards a secure system at each level of design, this paper addresses security aspects related to Network-on-Chip (NoC) architectures, foreseen as the communication infrastructure of next-generation embedded devices. In the context of NoC-based multiprocessor systems, we focus on the topic, not yet thoroughly faced, of data protection. In this paper, we present a secure NoC architecture composed of a set of Data Protection Units (DPUs) implemented within the Network Interfaces (NIs)\footnote{Part of this work is under patent pending}. The run-time configuration of the programmable part of the DPUs is managed by a central unit, the Network Security Manager (NSM). The DPU, similar to a firewall, can check and limit the access rights (none, read, write, or both) of processors accessing data and instructions in a shared memory - in particular distinguishing between the operating roles (supervisor/user and secure/unsecure) of the processing elements. We explore different alternative implementations for the DPU and demonstrate how this unit does not affect the network latency if the memory request has the appropriate rights. We also focus on the dynamic updating of the DPUs to support their utilization in dynamic environments, and on the utilization of authentication techniques to increase the level of security.

International audience

International audience

We report on a theoretical study of surface roughness effects on charge transport in silicon nanowires with three different crystalline orientations, [100], [110] and [111]. Using an atomistic tight-binding model, key transport features such as mean-free paths, charge mobilities, and conductance scaling are investigated with the complementary Kubo-Greenwood and Landauer-Büttiker approaches. The anisotropy of the band structure of bulk silicon results in a strong orientation dependence of the transport properties of the nanowires. The best orientations for electron and hole transport are found to be the [110] and [111] directions, respectively.

This paper presents a chipless radio frequency identification (RFID) sensor tag having both identification and sensing capabilities. It is based on one resonant scatterer operating as a signal processing antenna in the 3-7.5 GHz band. The scatterer is used to monitor a physical parameter variation, as well as to identify the remote sensor. To make a resonator sensitive to the humidity, silicon nanowires are deposited on the tag surface using a simple process. The tag needs only one conductive layer so that it can be directly printed on the product to sense and to identify. Measurements done using a bistatic radar configuration in the frequency domain validate this concept. To demonstrate the reliability of such an application, two chipless RFID sensors placed in various environments are simultaneously detected using an anticollision technique based on spectral separation.

We present a detailed study of the growth of Ge nanocrystals (NCs) on SiO2 by chemical vapor deposition. A two-step process was developed. First, Si nuclei are deposited on SiO2 using SiH4 as a gaseous precursor. Then, Ge NCs grow selectively on the Si nuclei previously formed. The density of the Ge NCs is adjustable in between 109 and 1012 cm−2. Their mean size varies between 5 and 50 nm. We have shown, combining grazing incidence x-ray diffraction and x-ray photoelectron spectroscopy, that pure Ge NCs are grown in a polycrystalline phase on a SiO2 surface.

Addition of yttrium in HfO2 thin films prepared on silicon by metal organic chemical vapor deposition is investigated in a wide compositional range (2.0–99.5at.%). The cubic structure of HfO2 is stabilized for 6.5at.%. The permittivity is maximum for yttrium content of 6.5–10at.%; in this range, the effective permittivity, which results from the contribution of both the cubic phase and silicate phase, is of 22. These films exhibit low leakage current density (5×10−7A∕cm2 at −1V for a 6.4nm film). The cubic phase is stable upon postdeposition high temperature annealing at 900°C under NH3.