9 research outputs found
Nouvelles Architectures Hybrides (Logique / Mémoires Non-Volatiles et technologies associées.)
Les nouvelles approches de technologies mémoires permettront une intégration dite back-end, où les cellules élémentaires de stockage seront fabriquées lors des dernières étapes de réalisation à grande échelle du circuit. Ces approches innovantes sont souvent basées sur l'utilisation de matériaux actifs présentant deux états de résistance distincts. Le passage d'un état à l'autre est contrôlé en courant ou en tension donnant lieu à une caractéristique I-V hystérétique. Nos mémoires résistives sont composées d'argent en métal électrochimiquement actif et de sulfure amorphe agissant comme électrolyte. Leur fonctionnement repose sur la formation réversible et la dissolution d'un filament conducteur. Le potentiel d'application de ces nouveaux dispositifs n'est pas limité aux mémoires ultra-haute densité mais aussi aux circuits embarqués. En empilant ces mémoires dans la troisième dimension au niveau des interconnections des circuits logiques CMOS, de nouvelles architectures hybrides et innovantes deviennent possibles. Il serait alors envisageable d'exploiter un fonctionnement à basse énergie, à haute vitesse d'écriture/lecture et de haute performance telles que l'endurance et la rétention. Dans cette thèse, en se concentrant sur les aspects de la technologie de mémoire en vue de développer de nouvelles architectures, l'introduction d'une fonctionnalité non-volatile au niveau logique est démontrée par trois circuits hybrides: commutateurs de routage non volatiles dans un Field Programmable Gate Arrays, un 6T-SRAM non volatile, et les neurones stochastiques pour un réseau neuronal. Pour améliorer les solutions existantes, les limitations de la performances des dispositifs mémoires sont identifiés et résolus avec des nouveaux empilements ou en fournissant des défauts de circuits tolérants.Novel approaches in the field of memory technology should enable backend integration, where individual storage nodes will be fabricated during the last fabrication steps of the VLSI circuit. In this case, memory operation is often based upon the use of active materials with resistive switching properties. A topology of resistive memory consists of silver as electrochemically active metal and amorphous sulfide acting as electrolyte and relies on the reversible formation and dissolution of a conductive filament. The application potential of these new memories is not limited to stand-alone (ultra-high density), but is also suitable for embedded applications. By stacking these memories in the third dimension at the interconnection level of CMOS logic, new ultra-scalable hybrid architectures becomes possible which exploit low energy operation, fast write/read access and high performance with respect to endurance and retention. In this thesis, focusing on memory technology aspects in view of developing new architectures, the introduction of non-volatile functionality at the logic level is demonstrated through three hybrid (CMOS logic ReRAM devices) circuits: nonvolatile routing switches in a Field Programmable Gate Array, nonvolatile 6T-SRAMs, and stochastic neurons of an hardware neural network. To be competitive or even improve existing solutions, limitations on the memory devices performances are identified and solved by stack engineering of CBRAM devices or providing faults tolerant circuits.SAVOIE-SCD - Bib.électronique (730659901) / SudocGRENOBLE1/INP-Bib.électronique (384210012) / SudocGRENOBLE2/3-Bib.électronique (384219901) / SudocSudocFranceF
Rapid Recovery of Program Execution Under Power Failures for Embedded Systems with NVM
After power is switched on, recovering the interrupted program from the
initial state can cause negative impact. Some programs are even unrecoverable.
To rapid recovery of program execution under power failures, the execution
states of checkpoints are backed up by NVM under power failures for embedded
systems with NVM. However, frequent checkpoints will shorten the lifetime of
the NVM and incur significant write overhead. In this paper, the technique of
checkpoint setting triggered by function calls is proposed to reduce the write
on NVM. The evaluation results show an average of 99.8% and 80.5$% reduction on
NVM backup size for stack backup, compared to the log-based method and
step-based method. In order to better achieve this, we also propose
pseudo-function calls to increase backup points to reduce recovery costs, and
exponential incremental call-based backup methods to reduce backup costs in the
loop. To further avoid the content on NVM is cluttered and out of NVM, a method
to clean the contents on the NVM that are useless for restoration is proposed.
Based on aforementioned problems and techniques, the recovery technology is
proposed, and the case is used to analyze how to recover rapidly under
different power failures.Comment: This paper has been accepted for publication to Microprocessors and
Microsystems in March 15, 202
A Reliability Prediction Method for Phase-Change Devices Using Optimized Pulse Conditions
Owing to the outstanding device characteristics of Phase-Change Random Access Memory (PCRAM) such as high scalability, high speed, good cycling endurance, and compatibility with conventional complementary metal-oxide-semiconductor (CMOS) processes, PCRAM has reached the point of volume production. However, due to the temperature dependent nature of the phase-change memory device material and the high electrical and thermal stresses applied during the programming operation, the standard methods of high-temperature (Temperature \u3e 125 °C) accelerated retention testing may not be able to accurately predict bit sensing failures or determine slight pulse condition changes needed if the device were to be programmed at an elevated temperature several times, in an environment where the ambient temperature is between 25 and 125 °C. In this work a new reliability prediction method, different than standard PCRAM reliability methods is presented. This new method will model and predict a single combination of temperature and pulse conditions for temperatures between 25 and 125 °C, giving the lowest Bit Error Rate (BER). The prediction model was created by monitoring the cell resistance distributions collected from sections of the PCRAM 1Gigabit (Gb) array after applying a given RESET or SET programming pulse shape at a given temperature, in the range of 25 to 125 °C. This model can be used to determine the optimal pulse conditions for a given ambient temperature and predict the BER and/or data retention loss over large arrays of devices on the Micron/Numonyx 45nm PCRAM part
Ferroelectric : CNTs structures fabrication for advanced functional nano devices
Doutoramento em Ciência e Engenharia de MateriaisThis work is about the combination of functional ferroelectric oxides with Multiwall
Carbon Nanotubes for microelectronic applications, as for example potential 3
Dimensional (3D) Non Volatile Ferroelectric Random Access Memories (NVFeRAM).
Miniaturized electronics are ubiquitous now.
The drive to downsize electronics has been spurred by needs of more performance
into smaller packages at lower costs. But the trend of electronics miniaturization
challenges board assembly materials, processes, and reliability. Semiconductor
device and integrated circuit technology, coupled with its associated electronic
packaging, forms the backbone of high-performance miniaturized electronic
systems. However, as size decreases and functionalization increases in the modern
electronics further size reduction is getting difficult; below a size limit the signal
reliability and device performance deteriorate. Hence miniaturization of siliconbased
electronics has limitations.
On this background the Road Map for Semiconductor Industry (ITRS) suggests
since 2011 alternative technologies, designated as More than Moore; being one of
them based on carbon (carbon nanotubes (CNTs) and graphene) [1].
CNTs with their unique performance and three dimensionality at the nano-scale
have been regarded as promising elements for miniaturized electronics [2]. CNTs
are tubular in geometry and possess a unique set of properties, including ballistic
electron transportation and a huge current caring capacity, which make them of
great interest for future microelectronics [2]. Indeed CNTs might have a key role in
the miniaturization of Non Volatile Ferroelectric Random Access Memories (NVFeRAM).
Moving from a traditional two dimensional (2D) design (as is the case of
thin films) to a 3D structure (based on a tridimensional arrangement of
unidimensional structures) will result in the high reliability and sensing of the signals
due to the large contribution from the bottom electrode. One way to achieve this 3D
design is by using CNTs.
Ferroelectrics (FE) are spontaneously polarized and can have high dielectric
constants and interesting pyroelectric, piezoelectric, and electrooptic properties,
being a key application of FE electronic memories.
However, combining CNTs with FE functional oxides is challenging. It starts with
materials compatibility, since crystallization temperature of FE and oxidation
temperature of CNTs may overlap. In this case low temperature processing of FE
is fundamental.
Within this context in this work a systematic study on the fabrication of CNTs - FE
structures using low cost low temperature methods was carried out. The FE under
study are comprised of lead zirconate titanate (Pb1-xZrxTiO3, PZT), barium titanate
(BaTiO3, BT) and bismuth ferrite (BiFeO3, BFO). The various aspects related to the
fabrication, such as effect on thermal stability of MWCNTs, FE phase formation in
presence of MWCNTs and interfaces between the CNTs/FE are addressed in this
work.
The ferroelectric response locally measured by Piezoresponse Force Microscopy
(PFM) clearly evidenced that even at low processing temperatures FE on CNTs
retain its ferroelectric nature.
The work started by verifying the thermal decomposition behavior under different
conditions of the multiwall CNTs (MWCNTs) used in this work. It was verified that
purified MWCNTs are stable up to 420 ºC in air, as no weight loss occurs under non
isothermal conditions, but morphology changes were observed for isothermal
conditions at 400 ºC by Raman spectroscopy and Transmission Electron Microscopy
(TEM). In oxygen-rich atmosphere MWCNTs started to oxidized at 200 ºC. However
in argon-rich one and under a high heating rate MWCNTs remain stable up to 1300
ºC with a minimum sublimation. The activation energy for the decomposition of
MWCNTs in air was calculated to lie between 80 and 108 kJ/mol.
These results are relevant for the fabrication of MWCNTs – FE structures. Indeed
we demonstrate that PZT can be deposited by sol gel at low temperatures on
MWCNTs. And particularly interesting we prove that MWCNTs decrease the
temperature and time for formation of PZT by ~100 ºC commensurate with a
decrease in activation energy from 68±15 kJ/mol to 27±2 kJ/mol. As a consequence,
monophasic PZT was obtained at 575 ºC for MWCNTs - PZT whereas for pure PZT
traces of pyrochlore were still present at 650 ºC, where PZT phase formed due to
homogeneous nucleation. The piezoelectric nature of MWCNTs - PZT synthesised
at 500 ºC for 1 h was proved by PFM.
In the continuation of this work we developed a low cost methodology of coating
MWCNTs using a hybrid sol-gel / hydrothermal method. In this case the FE used as
a proof of concept was BT. BT is a well-known lead free perovskite used in many
microelectronic applications. However, synthesis by solid state reaction is typically
performed around 1100 to 1300 ºC what jeopardizes the combination with MWCNTs.
We also illustrate the ineffectiveness of conventional hydrothermal synthesis in this
process due the formation of carbonates, namely BaCO3. The grown MWCNTs - BT
structures are ferroelectric and exhibit an electromechanical response (15 pm/V).
These results have broad implications since this strategy can also be extended to
other compounds of materials with high crystallization temperatures. In addition the
coverage of MWCNTs with FE can be optimized, in this case with non covalent
functionalization of the tubes, namely with sodium dodecyl sulfate (SDS).
MWCNTs were used as templates to grow, in this case single phase multiferroic
BFO nanorods. This work shows that the use of nitric solvent results in severe
damages of the MWCNTs layers that results in the early oxidation of the tubes during
the annealing treatment. It was also observed that the use of nitric solvent results in
the partial filling of MWCNTs with BFO due to the low surface tension (<119 mN/m)
of the nitric solution. The opening of the caps and filling of the tubes occurs
simultaneously during the refluxing step. Furthermore we verified that MWCNTs
have a critical role in the fabrication of monophasic BFO; i.e. the oxidation of CNTs
during the annealing process causes an oxygen deficient atmosphere that restrains
the formation of Bi2O3 and monophasic BFO can be obtained. The morphology of
the obtained BFO nano structures indicates that MWCNTs act as template to grow
1D structure of BFO. Magnetic measurements on these BFO nanostructures
revealed a week ferromagnetic hysteresis loop with a coercive field of 956 Oe at 5
K. We also exploited the possible use of vertically-aligned multiwall carbon nanotubes
(VA-MWCNTs) as bottom electrodes for microelectronics, for example for memory
applications. As a proof of concept BiFeO3 (BFO) films were in-situ deposited on
the surface of VA-MWCNTs by RF (Radio Frequency) magnetron sputtering. For in
situ deposition temperature of 400 ºC and deposition time up to 2 h, BFO films cover
the VA-MWCNTs and no damage occurs either in the film or MWCNTs. In spite of
the macroscopic lossy polarization behaviour, the ferroelectric nature, domain
structure and switching of these conformal BFO films was verified by PFM. A week
ferromagnetic ordering loop was proved for BFO films on VA-MWCNTs having a
coercive field of 700 Oe.
Our systematic work is a significant step forward in the development of 3D memory
cells; it clearly demonstrates that CNTs can be combined with FE oxides and can
be used, for example, as the next 3D generation of FERAMs, not excluding however
other different applications in microelectronics.Este trabalho é sobre a combinação de óxidos ferroelétricos funcionais com
nanotubos de carbono (CNTs) para aplicações na microeletrónica, como por
exemplo em potenciais memórias ferroelétricas não voláteis (Non Volatile
Ferroelectric Random Access Memories (NV-FeRAM)) de estrutura tridimensional
(3D).
A eletrónica miniaturizada é nos dias de hoje omnipresente.
A necessidade de reduzir o tamanho dos componentes eletrónicos tem sido
estimulada por necessidades de maior desempenho em dispositivos de menores
dimensões e a custos cada vez mais baixos. Mas esta tendência de miniaturização
da eletrónica desafia consideravelmente os processos de fabrico, os materiais a
serem utilizados nas montagens das placas e a fiabilidade, entre outros aspetos.
Dispositivos semicondutores e tecnologia de circuitos integrados, juntamente com
a embalagem eletrónica associada, constituem a espinha dorsal dos sistemas
eletrónicos miniaturizados de alto desempenho. No entanto, à medida que o
tamanho diminui e a funcionalização aumenta, a redução das dimensões destes
dipositivos é cada vez mais difÃcil; é bem conhecido que abaixo de um tamanho
limite o desempenho do dispositivo deteriora-se. Assim, a miniaturização da
eletrónica à base de silÃcio tem limitações.
É precisamente neste contexto que desde 2011 o Road Map for Semiconductor
Industry (ITRS) sugere tecnologias alternativas às atualmente em uso, designadas
por Mais de Moore (More than Moore); sendo uma delas com base em carbono
(CNTs e grafeno) [1].
Os CNTs com o seu desempenho único e tridimensionalidade à escala
nanométrica, foram considerados como elementos muito promissores para a
eletrónica miniaturizada [2]. Nanotubos de carbono possuem uma geometria
tubular e um conjunto único de propriedades, incluindo o transporte balÃstico de
eletrões e uma capacidade enorme de transportar a corrente elétrica, o que os
tornou de grande interesse para o futuro da microeletrónica [2]. Na verdade, os
CNTs podem ter um papel fundamental na miniaturização das memórias
ferroelétricas não voláteis (NV-FeRAM). A mudança de uma construção
tradicional bidimensional (2D) (ou seja, a duas dimensões, como são os filmes
finos) para uma construção tridimensional 3D, com base num arranjo
tridimensional de estruturas unidimensionais (1D), como são as estruturas
nanotubulares, resultará num desempenho melhorado com deteção de sinal
elétrico optimizada, devido à grande contribuição do elétrodo inferior. Uma
maneira de conseguir esta configuração 3D é usando nanotubos de carbono.
Os materiais ferroelétricos (FE) são polarizados espontaneamente e possuem
constantes dielétricas altas e as suas propriedades piroelétricas, piezoelétricas e
eletroópticas tornam-nos materiais funcionais importantes na eletrónica, sendo
uma das suas aplicações chave em memórias eletrónicas.
No entanto, combinar os nanotubos de carbono com óxidos FE funcionais é um
desafio. Começa logo com a compatibilidade entre os materiais e o seu
processamento, já que as temperaturas de cristalização do FE e as temperaturas
de oxidação dos CNTs se sobrepõem. Neste caso, o processamento a baixa
temperatura dos óxidos FE é absolutamente fundamental.
Dentro deste contexto, neste trabalho foi realizado um estudo sistemático sobre a
fabricação e caracterização estruturas combinadas de CNTs – FE, usando
métodos de baixa temperatura e de baixo custo. Os FE em estudo foram
compostos de titanato zirconato de chumbo (Pb1-xZrxTiO3, PZT), titanato de bário
(BaTiO3, BT) e ferrite de bismuto (BiFeO3, BFO). Os diversos aspetos relacionados
com a sÃntese e fabricação, como efeito sobre a estabilidade térmica dos
nanotubos de carbono multiparede (multiwall CNTs, MWCNTs), formação da fase
FE na presença de MWCNTs e interfaces entre CNTs / FE foram abordados neste
trabalho. A resposta ferroelétrica medida localmente através de microscopia de
ponta de prova piezoelétrica (Piezoresponse Force Microscopy (PFM)), evidenciou
claramente que, mesmo para baixas temperaturas de processamento óxidos FE
sobre CNTs mantém a sua natureza ferroelétrica.
O trabalho começou pela identificação do comportamento de decomposição
térmica em diferentes condições dos nanotubos utilizados neste trabalho.
Verificou-se que os MWCNTs purificados são estáveis até 420 ºC no ar, já que não
ocorre perda de peso sob condições não isotérmicas, mas foram observadas, por
espectroscopia Raman e microscopia eletrónica de transmissão (TEM), alterações
na morfologia dos tubos para condições isotérmicas a 400 ºC. Em atmosfera rica
em oxigénio os MWCNTs começam a oxidar-se a 200 ºC. No entanto, em
atmosfera rica em árgon e sob uma taxa de aquecimento elevada os MWCNTs
permanecem estáveis até 1300 ºC com uma sublimação mÃnima. A energia de
ativação para a decomposição destes MWCNTs em ar foi calculada situar-se entre
80 e 108 kJ / mol.
Estes resultados são relevantes para a fabricação de estruturas MWCNTs - FE.
De facto, demonstramos que o PZT pode ser depositado por sol-gel a baixas
temperaturas sobre MWCNTs. E, particularmente interessante foi provar que a
presença de MWCNTs diminui a temperatura e tempo para a formação de PZT,
em cerca de ~ 100 ºC comensuráveis com uma diminuição na energia de ativação
de 68 ± 15 kJ / mol a 27 ± 2 kJ / mol. Como consequência, foi obtido PZT
monofásico a 575 ºC para as estruturas MWCNTs – PZT, enquanto que para PZT
(na ausência de MWCNTs) a presença da fase de pirocloro era ainda notória a 650
ºC e onde a fase de PZT foi formada por nucleação homogénea. A natureza
piezoelétrica das estruturas de MWCNTs - PZT sintetizadas a 500 ºC por 1 h foi
provada por PFM.
Na continuação deste trabalho foi desenvolvida uma metodologia de baixo custo
para revestimento de MWCNTs usando uma combinação entre o processamento
sol – gel e o processamento hidrotermal. Neste caso o FE usado como prova de
conceito foi o BT. BT é uma perovesquita sem chumbo bem conhecida e utilizada
em muitas aplicações microeletrónicas. No entanto, a sÃntese por reação no estado
sólido é normalmente realizada entre 1100 - 1300 ºC o que coloca seriamente em
risco a combinação com MWCNTs. Neste âmbito, também se ilustrou claramente
a ineficácia da sÃntese hidrotérmica convencional, devido à formação de
carbonatos, nomeadamente BaCO3. As estruturas MWCNTs - BT aqui preparadas
são ferroelétricas e exibem resposta electromecânica (15 pm / V). Considera-se
que estes resultados têm impacto elevado, uma vez que esta estratégia também
pode ser estendida a outros compostos de materiais com elevadas temperaturas
de cristalização. Além disso, foi também verificado no decurso deste trabalho que
a cobertura de MWCNTs com FE pode ser optimizada, neste caso com
funcionalização não covalente dos tubos, ou seja, por exemplo com sodium
dodecyl sulfate (SDS)
Conception et réalisation de commutateurs RF à base de matériaux à transition de phase (PTM) et à changement de phase (PCM)
This research work focuses on the design and realization of RF switches based on the integration of new materials such as vanadium dioxide (VO2), Ge2Sb2Te5 (GST) and GeTe chalcogenides alloys. The operating principle of these devices is based on the resistivity change presented by these materials. VO2 exhibits a Metal-Insulator transition (MIT) around 68°C for which the material changes from an insulating state (high resistivity) to a metallic one (low resistivity). The MIT transition can be triggered in different ways (thermally, electrically and optically) with low switching time. GST and GeTe alloys have the particularity to be reversibly switched between a high resistive-amorphous state to low resistive-crystalline state, under a specific heat treatment. Thanks to the non-volatile resistivity change presented by these materials, GST/GeTe-based switches are able to operate in bistable mode. The fabricated devices exhibit good electrical performances (insertion loss and isolation) over a broadband. The aim of our work is to propose an alternative solution to conventional technologies (semiconductors and RF-MEMS), to design RF switches that can be used afterward in the design of reconfigurable devices (filters, antennas).Ces travaux de recherche portent sur la conception et la réalisation de commutateurs RF basées sur l’intégration de matériaux innovants fonctionnels tels que le dioxyde de vanadium (VO2) et les alliages de chalcogénures de types Ge2Sb2Te5 (GST) et GeTe. Le principe de fonctionnement de ces composants repose sur le changement de résistivité que présentent ces matériaux. Le VO2 possède une transition Isolant-Métal (MIT) autour de 68°C à travers laquelle le matériau passe d’un état isolant (forte résistivité) à un état métallique (faible résistivité). La transition MIT présente l’intérêt de pouvoir être initiée sous l’effet de plusieurs types de stimuli externes (thermique, électrique et optique) avec de faibles temps de commutation. Les alliages de types GST et GeTe ont la particularité de commuter réversiblement entre un état amorphe à forte résistivité à un état cristallin à faible résistivité suite à un traitement thermique spécifique. Les commutateurs à base de GST ou de GeTe présentent l'avantage de pouvoir opérer en mode bistable car le changement de résistivité présenté par ces matériaux est de type non volatile. Les composants réalisés ont de bonnes performances électriques (isolation et pertes d’insertion) sur une large bande. Nos travaux de recherche visent à proposer une solution alternative aux solutions classiques (semi-conducteurs et MEMS-RF) pour réaliser des commutateurs RF qui peuvent être par la suite utilisés dans la conception des dispositifs reconfigurables (filtres, Antennes)