In-Sensor Computing for MEMS Sensors: Toward an Electromechanical Neural Network
The rise of machine learning models for processing sensor data has led to the development of Edge-AI, which aims to perform these data processing tasks locally, directly at the sensor level. This approach reduces the amount of data transmitted and eases the load on centralized computing centers, providing a solution to decrease the overall energy consumption of systems. In this context, the concept of in-sensor computing has emerged, integrating data acquisition and processing within the sensor itself. By leveraging the physical properties of sensors and alternative computing paradigms, such as reservoir computing and neuromorphic computing, in-sensor computing eliminates the energy-intensive steps of signal conversion and processing.
Applying this concept to MEMS sensors enables the processing of signals such as acceleration, strain, or acoustic signals, with a significant reduction, or even elimination, of traditional electronic components. This has rekindled interest in mechanical computing devices and their integration into MEMS sensors like microphones and accelerometers. Recent research explores innovative MEMS devices integrating recurrent neural networks or reservoir computing, showing promising potential for energy efficiency. However, these advancements are still limited to proof-of-concept demonstrations for simple classification tasks with a very low number of neurons.
Building on our expertise in MEMS-based computing, this doctoral work aims to push these concepts further by developing a MEMS device that integrates a reprogrammable neural network with learning capabilities. The objective is to design an intelligent sensor that combines detection and preprocessing on a single chip, optimized to operate with extremely low energy consumption, in the femtoJoule range per activation. This thesis will focus on the design, fabrication, and validation of this new device, targeting low-frequency signal processing applications in high-temperature environments, paving the way for a new generation of intelligent and autonomous sensors.
Design and reliability of modular architecture for reconfigurable and repairable PV panels
The integration of photovoltaic modules has become a challenge for adaptation to climate change, notably with the installation of specific PV modules in urban spaces, on vehicles or on agricultural farms. These modules are required to operate in more complex situations presenting high temporal variability and changing exposure to the sun. The scientific challenges of the project are to determine the conditions needed for optimizing the performance of PV modules regarding these external disturbances by the study of reconfigurable electrical module architectures. A reliability model will be developed to integrate the impact of the system architecture, in order to guarantee an improved level of reliability. In-depth work will be carried out on the entire PV module, from cell technologies to the final electrical characteristics requested, including electrical switching technologies. In a second phase, we will develop a design methodology in conjunction with a precise state of the art of available power switching technologies. The method will be applied to a use case responding primarily to the problem of shading and/or localised failure of the PV module. Finally, the proposed architectures will be evaluated by life cycle analysis. The designs authorizing maintenance or replacement of certain elements will be detailed and compared to the performance of usual modules.
Identification versus anonymisation from an embedded client operating on a blockchain
The first worldwide deployment of a blockchain dates back to 2010 with Bitcoin, which introduced a completely digital monetary system and a crypto-currency, bitcoin. Within Bitcoin, all transactions are publicly accessible and traceable, which should generate trust between stakeholders. However, the traceability of transactions, and ultimately of the crypto-currency, does not imply the traceability of users authenticated by an account address, or more precisely by a set of account addresses that are independent of each other. In this context, it can be complex to trace the individuals or legal entities owning the crypto-currency.
Crypto-currency is not the only use case supported by blockchain technology. The deployment of Ethereum in 2014, based on the use of smart contracts, opened up many other uses, in particular the protection of identifying data. In this area, the need for traceability versus furtivity can vary greatly from one use case to another. For example, on a blockchain that records the access of a worker owning an employment certificate to an industrial site, no information enabling the worker to be identified or his activity to be traced should appear. On the other hand, in the case of data collected by IoT sensors and processed by remote Edge devices, traceability of data and processing is desirable.
The thesis proposes to study different techniques for tracing digital assets on a blockchain, for stealthing their owners, and offering the possibility of auditing and identification by an authorised body. The aim is to build embedded devices, Edge or personal possibly embedding artificial intelligence, secured by hardware components, integrating different cryptographic solutions and account, data or identity wallet structures to meet the needs of the different use cases envisaged.
Advanced functions for monitoring power transistors (towards greater reliability and increased lifespan of power converters for energy)
In order to increase the power of electronic systems, a common approach is to parallelize components within modules. However, this parallelization is complicated by the dispersion of transistor parameters, both initial and post-aging. Fast switching of Wide Bandgap (WBG) semiconductors components often requires slowdowns to avoid over-oscillation and destruction.
An intelligent driving scheme, including adjusted control, control of internal parameters of circuits and devices, as well as a feedback loop, could improve reliability, service life and reduce the risk of breakage.
The objectives of the thesis will be to develop, study and analyze the performance of control and piloting functions of power components, in silicon carbide (SiC) or gallium nitride (GaN), which could ultimately be implemented in a dedicated integrated circuit (ASIC type).
This thesis subject aims to solve critical problems in the parallelization of power components, thus contributing to eco-innovation by increasing the lifespan of power modules.
The design of integrated circuits requires, at the end of the chain, circuit editing and failure analysis tools. One of these tools is the probing of electrical potential levels using an electron beam available in a SEM (Scanning Electron Microscope) to determine the electrical signal present in an area of the circuit, which may be a metal level or a transistor. This electronic probing technique was widely used in the 90s, and then partially abandoned despite a few recurrent publications on the technique. In recent years, this technique has been revived by using the backside of the component, probing via the silicon substrate and accessing the active areas of the component.
These debugging and failure analysis tools are also tools for attacking integrated circuits. This thesis topic falls within the scope of hardware cybersecurity and so-called invasive attacks. The PhD student will implement this electron beam probing technique on commercial SEMs and under conditions of use specific to cybersecurity. Various techniques will be considered to improve the probed signals and their use.
Power and data transmission via an acoustic link for closed metallic environments
This thesis focuses on the transmission of power and data through metal walls using acoustic waves. Ultimately, this technology will be used to power, read and control systems located in areas enclosed in metal, such as pressure vessels, ship hulls and submarines.
Because electromagnetic waves are absorbed by metal, acoustic waves are needed to communicate data or power through metal walls. These are generated by piezoelectric transducers bonded to either side of the wall. The acoustic waves are poorly attenuated by the metal, resulting in numerous reflections and multiple paths.
The aim of the thesis will be to develop a robust demonstrator of this technology, enabling the remote powering and communication of acoustic data through metal walls. This work will be based on advanced modelling of the acoustic channel in order to optimise the performance of the power and data transmission device. It will also involve developing innovative electronic building blocks to determine and maintain an optimum power transmission frequency, impacted by environmental conditions and typically by temperature.
The goal of this thesis will be the development and implementation of a communication system embedded in an FPGA and/or microcontroller in order to send sensor data through a metal wall of variable thickness. The limitations due to the imperfections of the channel and the electronics will lead to the invention of a large number of compensation methods and systems in the digital and/or analogue domain. Work will also have to be carried out on the choice of piezoelectric transducers and the characterisation of the channel, in conjunction with the acoustic wave activities of the laboratory working on the transmission of acoustic power.
Impact of the Pulse Width Modulation strategy on the semiconductor ageing
The Pulse Witdh Modulation strategy (PWM) is a fundamental technique in power electronics. It is used to control the Energy transfer by modifying the pulse width of the control signals in a power converter. In an automotive traction inverter, this PWM strategy applied to a transistor phase leg allows to convert the DC current from the battery to an AC current adapted to the motor windings. The impact of the PWM on the performances and the reliability of the engine have been widely studied in the litterature. However, the impact of the PWM strategy on the reliability and the ageing of the semiconductor devices inside the power modules has not been adressed. This is particularly true for the power modules intagrating wide bandgap semiconductors (eg: SiC) which are widely used for 10 years. The main objective of this thesis is to understand and model the impact of several PWM strategies on the ageing of SiC power semiconductor devices.
The thesis targets to define a link between the stress on the semicondcutor devices and the shift of its key parameters offering the possibility to define a PWM strategy able to maximize the long term performances and the lifetime of the power electronics system. By combining experimental and theroretical approaches, this thesis will contribute to improve the PWM strategies in power electronics systems.
Acoustics and Electromagnetism (AEM): New approaches for the secure characterization of components such as the SoCs
Work carried out within CEA-Leti has shown that physical attacks can be a threat to the security mechanisms of SoCs (System on Chips). Indeed, fault injections by electromagnetic disturbance have already led to an escalation of privileges by authenticating with an illegitimate password, or more recently have made it possible to bypass one of the highest levels of security of a SoC, which is the Secure Boot. However, the technologies integrated into this type of targets are increasingly sophisticated with Package-on-Package (PoP) electronic devices and technological nodes less than or equal to 7 nm, such as the new Samsung S20. Implementing these attacks requires cutting-edge equipment not currently commercially available (very small diameter probe, high transient current pulse generator, magnetometer and current broadband sensors with high spatial resolution, etc.). The thesis defended in 2022 by Clément Gaine [1] within our team made it possible to study several components of the EM injection chain, in particular a main element such as the electromagnetic injection probe.
Other fields are to be explored, in particular the complete injection chain from the pulse generator to the creation of an electromotive force in the target, induced by the EM probe via very high current gradients (di/dt). Mastering the complete chain makes it possible to design the most suitable injection system to characterize a smartphone type target and resolve the obstacles linked to this type of target such as: the complex microarchitecture, the multilayer software stack, the complex packaging with in particular the stacking of several components on the same chip (PoP).
The main objective of this thesis is to study a new EM injection approach and its potential to circumvent certain security mechanisms of a smartphone. This will allow hardware security characterization tools to evolve in order to meet the growing needs for the security characterization of SoCs. In terms of exploitation, the FORENSIC domain is aimed at circumventing and/or supplementing the limits of legal data mining techniques based on “0-day” vulnerabilities by exploiting flaws in hardware implementations that cannot be corrected on the same target model.
To achieve this objective, the PhD student will first be required to characterize, test and validate the new ultra-fast switching attack approach and the magnetometric and amperometric measurement means recently developed in the laboratory. At the same time, the doctoral student will carry out bibliographical and experimental work on the physiological risk potentially linked to exposure to short-term EM pulses. The results will be used to define new protocols allowing operators to carry out their EM injection experiments in a secure environment and to develop standards in this area if necessary. Secondly, the doctoral student will devote part of his work to modeling the transient magnetic flux and the transfer of induced power in high or low impedance targets, with a focus on the impact of the orientation of the field as well as the polarity of the pulse on the fault or glitch model on different types of transistors (NMOS, PMOS, JFET).
[1] https://cea.hal.science/search/index/?q=*&authFullName_s=Cl%C3%A9ment%20Gaine
More here : https://vimeo.com/441318313 (project video)