In-situ Monitoring of RF Power Amplifier Circuits Aging for Eco-design and Extended Lifetime
The semiconductor industry, and more specifically the radio-frequency (RF) circuit sector, is facing critical challenges related to eco-design and eco-innovation. These challenges include the need to extend the lifetime of circuits while meeting the growing demands of emerging markets such as 5G and the future 6G. Among these circuits, power amplifiers (PA) play a central role, being both critical components in terms of energy efficiency and key targets for improving robustness against aging and enabling potential reuse.
In this context, in-situ aging monitoring of PAs appears to be a promising approach for developing innovative and sustainable solutions. This research topic is therefore fully aligned with eco-design strategies, leveraging advanced technological platforms such as current and future CMOS SOI technologies, while integrating industrial constraints through existing strategic collaborations with major partners of CEA Leti.
This thesis aims to design an innovative in-situ monitoring solution to evaluate and compensate for the aging of power amplifiers, thereby extending their lifetime through reuse and self-correction strategies. To achieve this, it will rely on methodologies and circuits specifically adapted to practical use cases. The ambition is thus to develop a new generation of robust and durable circuits, integrating intelligent aging management mechanisms. By adopting an eco-design approach, this work aims to address environmental challenges while enhancing the industrial competitiveness of CMOS SOI technologies.
Development of a transportable and high sensibility gamma/neutron spectro-imager to reconstruct and identify radioactive hotspots during decomissioning and dismantling operations
Radioactive hotspots reconstruction is a significant challenge when characterising radioelements in environments that have been impacted by radiological or nuclear activity. A thesis proposal aims to address this issue by developing a compact, highly sensitive multimodal instrument for assessing and characterising gamma-ray and neutron contributions. This system will help to meet the encountered challenges, during decommissioning and dismantling (D&D) operations, in nuclear industry sites. To do this, it will incorporate spectro-imaging specifications to ensure the identification and location of present radioelements. The state of art has already demonstrated the advantages and benefits of combining ionising radiations spectrometry and imaging. However, the suggested solutions show difficulties in deploying measurement systems (size, weight), as well as a sensitivity incompatible with the ground constraints. Results obtained in the frame of thesis works, carried out at SIMRI (Service Instrumentation et Métrologie des Rayonnements Ionisants), have led to the development of a gamma and neutron spectro-imager prototype.
Reliability of RF GaN transistors for 5G millimeter Wave applications
Gallium Nitride components are very good candidates for power amplification at Millimeter Wave frequencies such as 5G (~30GHz), due to their power density and energy efficiency. However, these technologies are commonly integrated on Silicon Carbide substrates, which are thermally efficient but expensive and have small diameters. CEA-LETI's GaN/Si technology provides world-class performance in Ka band, with power densities competing with GaN/SiC technologies. These devices, fabricated on 200mm Si substrates, are compatible with Silicon clean rooms and promise greater available volumes and lower costs. Furthermore, the Silicon-like back-end levels offer possibilities for dense heterogeneous integration with digital circuits, paving the way towards heterogeneous RF Integrated Circuits (RFICs).
However, few studies exist nowadays on the degradation mechanisms tied to these specific components with CMOS-compatible process: advanced barriers, in-situ MIS gates, ohmic contacts, etc... It is mandatory to know and master these effects to qualify the technology as well as better understand the device weaknesses and limitations.
The goal of this PhD is to evaluate the parasitic memory effects as well as the transistor aging under operational conditions using DC and RF measurements, linked to the device physics. The transistors will be subjected to various electrical stress conditions to model their DC & RF degradation: trapping effects measurements (BTI, DCTS), influence of the process and gate technology (Schottky vs MIS), the electrical confinement inside the structure (GaN:C, AlGaN back-barrier, etc…). Time Dependent Dielectric Breakdown (TDDB) measurements will be made on MIS gates from DC to RF domain, to study the time to breakdown increase with input signal frequency, in a similar manner than gate dielectrics in CMOS devices. Finally, electrical stresses in DC and RF conditions (RF CW stresses) will be performed to evaluate and model the transistor degradation under operational conditions.
Vertical GaN power devices development using localized epitaxy
This PhD offers a unique opportunity to enhance your skills in GaN power devices and develop cutting-edge architectures. You’ll work alongside a multidisciplinary team specializing in materials engineering, characterization, device simulation, and electrical measurements. If you’re eager to innovate, expand your knowledge, and tackle state-of-the-art challenges, this position is a valuable asset to your career!
Vertical GaN power components hold great promise for power applications beyond the kV range. Localized epitaxy of GaN enables the creation of thick structures on Si substrates at a competitive cost, with demonstrated success for diodes and pseudo-vertical transistors. However, this approach’s significant surface area limits the energy density of the devices. This PhD aims to develop denser, fully vertical components using layer transfer methods. You’ll study their electrical characteristics to monitor the impact of technological variations on their performance.
Throughout this PhD, you’ll gain comprehensive knowledge in microelectronics processes, electrical characterization, and TCAD (Technology Computer-Aided Design) simulation. You’ll collaborate with a multidisciplinary team including our partner CNRS-LTM and deepen your understanding of GaN power devices, all while being part of a lab dedicated to the development of wide-bandgap power devices. You will have the opportunity to write publications and patents.
Development of Single-Ion Eutectogel Electrolytes through Polymerization of Deep Eutectic Solvents (DES)
The proposed PhD thesis focuses on the development of innovative polymer electrolytes for next-generation batteries, aimed at improving the safety and performance of energy storage systems.
Polymer electrolytes represent a promising solution to replace traditional liquid electrolytes. However, their development is limited by challenges related to ionic conductivity and low ion transport numbers. The addition of Deep Eutectic Solvents (DES) into the polymer matrix enhances ionic conductivity. Furthermore, the "single-ion" approach, based on grafting the counter-ion onto the polymer chain, leads to unipolar conduction.
CEA has recently developed "single-ion eutectogel" electrolytes, obtained by polymerizing a DES composed of a single-ion monomer and a hydrogen bond donor (HBD). These electrolytes exhibit very promising performance, achieving unipolar ionic conductivities greater than 0.1 mS/cm at room temperature. However, it is essential to further explore the relationships between formulation, structure, and properties, as well as the conduction mechanisms within these materials, in order to continue their development.
The thesis will be structured in three main phases:
Study of the reference system: Establish a research methodology to link polymerizable formulations, polymer structure, and their electrochemical properties. This will include the study of the starting DES and the electrolyte resulting from its polymerization. The study of conduction mechanisms within these electrolytes will be a central focus of this phase.
Optimization of properties: Based on the results from the previous phase, optimize the properties of the electrolytes through formulation work to select the most promising electrolyte for the next phase.
Integration into a complete system: Explore the integration of the electrolyte into a battery cell, using the in situ polymerization process to synthesize the electrolyte directly within the cell.
Physicochemical techniques (NMR, DSC, TGA, FTIR, RAMAN, SEC, SAXS, ...) and electrochemical techniques (EIS, CV, GCPL, ...) will be used throughout the project.
The PhD will be carried out in collaboration with CEA and LEPMI, providing access to state-of-the-art infrastructures and recognized expertise in formulation, polymer chemistry, and polymer electrolyte electrochemistry.
Simulation and characterization of integrated structures during and after the millisecond laser annealing step
Laser annealing processes are now used in a large range of applications in most advanced microelectronics technologies. Whether in the context of advanced planar CMOS components or 3D integration technologies, the specific characteristics of laser annealing enables to reach very high temperatures in very short times, at die scale, and to work in conditions out of thermodynamic equilibrium. This has many advantages in terms of physical effects (activation of high dopants with low diffusions, transformation of silicides, etc.), but also thermal budget (high temperatures which remain on the surface of the material). However, this kind of ultrashort optical annealing can generate pattern effect temperature variations on the chip surface between two zones with different radiative andor thermal properties. These temperature differences may alter the electrical performances of the devices and thus have to be evaluated and overcome. A part of this work will consist, by the help of bibliography study, in finding integrative solutions (design, absorbent layer,…), in order to encounter this issue. Besides, at LETI, a wide knowledge of Nanosecond Laser Annealing (NLA) is in place for many years, and process teams are in the acquisition phase of a millisecond laser equipment (DSA). This work will represent, thanks to the numerical simulation, one of the essential building blocks for the development of the millisecond laser annealing at LETI which is mandatory for advanced technologies roadmap.
This interdisciplinary research will encompass fields such as numerical simulations, materials science, microelectronic manufacturing processes. You will benefit from the support of laboratories specializing in integration processes, as well as TCAD simulation environments.
Selective epitaxial Regrowth for extended Base contact in High-Performance Antimonide-based HBT Transistors
With the rapid expansion of wireless networks and the imminent arrival of 6G, the need for highly efficient communication systems has never been more critical. In this context, frequencies beyond 140 GHz emerge as a key frontier, where cutting-edge technologies leverage advanced semiconductors like InP, delivering unmatched performance beyond what SiGe solutions can achieve. However, III-V components remain expensive, manufactured on small substrates (100 mm for InP), and incompatible with silicon production lines, which ensure higher industrial yields.
In this context, CEA-LETI, in collaboration with CNRS-LTM, is developing a new HBT transistor technology in which the base layer is made of antimonides, having already demonstrated frequency performance beyond the THz range. To enable integration with Si-CMOS fabrication processes, a novel approach for ohmic contact formation is required. This involves selective epitaxial regrowth of a suitable semiconductor material on the base layer of the HBT-GaAsSb transistor.
The PhD candidate will be responsible for identifying the optimal material that meets the required criteria, based on experiments conducted with the epitaxy team, advanced physical characterizations (ToF-SIMS, HR-TEM, EDX), and band structure modeling of the formed heterojunctions. This research will also be complemented by the fabrication of technological test structures to extract the key electrical parameters necessary for optimizing the DC and RF performance of the HBT transistor.
Photonic Spiking Neural Networks based on Q-switched laser integrated on Silicon
Neuromorphic networks for signal and information processing have acquired recently a renewed interest considering the more and more complex tasks that have to be solved automatically in current applications: speech recognition, dynamic image correlation, rapid decision processing integrating a plurality of information sources, behavior optimization, etc… Several types of neuromorphic networks do exist and, among them, the spiking type (SNN), that is, the one closest in behavior to the natural cortical neurons. SNN are the ones who seem to be able to offer a best energy efficiency and thus offer scalability. Several demonstrations have been made in this domain with electronic circuits and more recently with photonic circuits. For these, the dense integration potential of silicon photonics is a real advantage to create complex and highly connected circuits susceptible to lead to complete demonstrations. The PhD goal is to exploit a photonics spiking neuromorphic network architecture based on pulsed (Q-switched) lasers interconnected by a dense and reconfigurable optical network on chip mimicking the synaptic connections. A complete laser, neuron then circuit model is expected with, in the end, the practical demonstration of an application in mathematical data processing (to be defined).
Towards a Sustainable Blockchain: Reducing Energy Consumption While Ensuring Security and Integrity
Blockchain technology, a key component of distributed ledger systems, enables decentralized digital interactions without the need for a central authority but raises environmental concerns due to its energy consumption, particularly with proof-of-work (PoW) mechanisms like Bitcoin. The literature highlights the sustainability challenges associated with this energy consumption. Several strategies have been proposed to mitigate these impacts, such as optimizing cryptographic puzzles, implementing two-round mining processes, and integrating renewable energy sources. Alternative consensus mechanisms like Proof-of-Stake (PoS) and Proof-of-Authority (PoA) are also explored. This research project aims to evaluate the energy consumption profiles of existing blockchain systems and propose new, more efficient consensus algorithms. It also focuses on integrating renewable energy sources and optimizing smart contracts to reduce their resource consumption. A thorough security analysis will ensure that energy efficiency improvements do not compromise network security and decentralization. Using simulation tools, this research will quantify the improvements brought by new algorithms and strategies, contributing to the sustainability and broader adoption of blockchain technology in an environmentally conscious manner.