Towards a low-resistive base contact for the InP-HBT transistor

Join CEA LETI for an exciting technological journey! Immerse yourself in the world of III V
based transistors integrated on compatible CMOS circuits for 6 G future communications
This thesis offers the chance to work on a ambitious project, with potential to continue into
a thesis If you're curious, innovative, and eager for a challenge, this opportunity is perfect
for you!

As the consumption of digital content continues to grow, we can foresee that 6 G
communication systems will have to find more capacity to support the increase in traffic
New Sub THz frequencies based systems are a huge opportunity to increase data rate but
are very challenging to build and maturate the power amplifier required to transmit a
signal will have to offer sufficient power and energy efficiency which is not obtained with
actual silicon technology InP based HBTs (Heterojunction Bipolar Transistors) developed
on large Silicon substrates have the potential to meet the requirements and be integrated
as close as possible to the CMOS circuits to enable minimal system/interconnect losses
Sb based semiconductors for GaAsSb HBT are emerging as highly promising materials,
especially for its electrical properties to integrate the Base layer of the Transistor It is
therefore necessary to produce high performance electrical contacts on this type of
semiconductor while remaining compatible with the manufacturing processes of the Si Fab
technology platforms
Throughout
this thesis, you will gain a broad spectrum of knowledge, beneficiate from the
rich technical environment of the 300 200 mm clean room and the nano characterization
platform You will collaborate with multidisciplinary teams to develop a deep understanding
of the ohmic contacts and analyse existing measurements Several apsects of the metal
(Ni or Ti p GaAs 1 x Sb x contact will be investigated
•Identify wet and plasma solutions allowing the GaAsSb native oxide removing without
damaging the surface with XPS and AFM
•Characterize GaAs 1 x Sb x epitaxy doping level (Hall effect, SIMS, TEM)
•Understand the phase sequence during annealing between the semiconductor and the
metal with XRD and Tof SIMS Manage this intermetallic alloys formation to not
deteriorate the contact interface (TEM image associated)
•Evaluate electrical contact properties using TLM structures Measurement of the
specific contact resistivity, sheet resistance of the semiconductor ant transfer length
associated The student will be a motive force to perform electrical tests on an automatic prober

architecture for embedded system of Automated and Reliable Mapping of indoor installations

The research focuses on the 3D localization of data from measurements inside buildings, where satellite location systems, such as GPS, are not operational. Different solutions exist in the literature, they rely in particular on the use of SLAM (Simultaneous Localization And Mapping) algorithms, but the 3D reconstruction is generally carried out a posteriori. In order to be able to propose this type of approach for embedded systems, a first thesis was carried out and led to a choice of algorithms to embed and a draft of the electronic architecture. A first proof of concept was also realized. Continuing this work, the thesis will have to propose a method allowing the localization device to be easily embedded on a wide range of nuclear measuring equipment (diameter, contamination meter, portable spectrometry, etc.). The work is not limited to a simple integration phase; it requires an architectural exploration, which will be based on adequacy between algorithm and architecture. These approaches will make it possible to respect different criteria, such as weight and small size so as not to compromise ergonomics for the operators carrying out the maps and quality of the reconstruction to ensure the reliability of the input data for the Digital Twin models.

Bayesian Neural Networks with Ferroelectric Memory Field-Effect Transistors (FeMFETs)

Artificial Intelligence (AI) increasingly powers safety-critical systems that demand robust, energy-efficient computation, often in environments marked by data scarcity and uncertainty. However, conventional AI approaches struggle to quantify confidence in their predictions, making them prone to unreliable or unsafe decisions.

This thesis contributes to the emerging field of Bayesian electronics, which exploits the intrinsic randomness of novel nanodevices to perform on-device Bayesian computation. By directly encoding probability distributions at the hardware level, these devices naturally enable uncertainty estimation while reducing computational overhead compared to traditional deterministic architectures.

Previous studies have demonstrated the promise of memristors for Bayesian inference. However, their limited endurance and high programming energy pose significant obstacles for on-chip learning applications.

This thesis proposes the use of ferroelectric memory field-effect transistors (FeMFETs)—which offer nondestructive readout and high endurance—as a promising alternative for implementing Bayesian neural networks.

Dynamics of a very high temperature heat pump coupled to a thermal storage system. Experimental and numerical study.

In the context of an electricity mix with a high proportion of intermittent renewable energy sources, massive energy storage solutions will be of major interest. For the vast majority of these solutions, electricity is converted into energy that can be stored on a large scale (e.g. pressure energy, chemical or electrochemical energy, etc.), then converted back into electricity. Losses occur during each of these stages (conversion, storage), so the efficiency of the complete system is an important issue and requires a good understanding of each conversion and storage stage.
The innovative system that we want to study is a Carnot battery, i.e. a thermal battery associated with thermodynamic conversion cycles (electrical energy to thermal energy to electrical energy). The anticipated advantages are numerous: the possibility of integrating thermal flows, the absence of geographical constraints, a degree of freedom in the choice of temperatures and storage materials, the use of alternators for inertia, etc. The identified challenges are reactivity and overall efficiency.
The research will focus on the charging cycle (very high temperature heat pump) and its coupling with thermal storage, initially from a static and then a dynamic perspective. Unsteady numerical modelling will be developed and used to design the Carnot battery system. Tests carried out on an experimental installation at the CEA will be used to validate and enhance the modelling results.

Field Effect Transistor with Oxide Semiconductor Channel: Multi-Level Synaptic Functions and Analog Neurons

This thrilling PhD position invites you to dive into the groundbreaking field of 2T0C (Two-Transistor, Zero-Capacitor) BEOL FET (Back-End-of-Line Field-Effect Transistor) based neurons and synapses, a revolutionary approach poised to transform neuromorphic computing. As a PhD student, you will be at the forefront of research that bridges advanced semiconductor technology with brain-inspired architectures, exploring how these innovative neuron circuits can emulate synaptic functions and enhance data processing efficiency.
Throughout this project, you will engage in hands-on design and characterization of cutting-edge 2T0C neuron circuits, utilizing state-of-the-art tools and techniques. You’ll collaborate with a dynamic, multidisciplinary team of engineers and researchers, tackling exciting challenges related to device performance and energy optimization.
Your work will involve extensive characterization of BEOL FET devices and circuits. You will have the opportunity to propose, specify and design new memory read architectures, that enables the exploration of multi-level synaptic behaviors toward the implementation of more energy and area efficient next-generation neuromorphic systems.
Join us for this unique opportunity to push the boundaries of technology and be part of a transformative journey that could redefine the future of computing! Your contributions could pave the way for breakthroughs in brain-inspired systems, making a lasting impact on the field.

3D Hybrid Synapses for Energy-Efficient and Adaptive Edge AI

This PhD thesis is part of the growing field of embedded AI for the Internet of Things (IoT), where constraints in energy, area, and connectivity require rethinking the learning mechanisms of neural networks. The goal is to design neuromorphic architectures based on 3D hybrid synapses combining FeRAM and ReRAM, within an in-memory computing framework. The objective is to enable local adaptation of the model—drawing from machine learning approaches and potentially compatible with plasticity mechanisms such as STDP, VDSP, etc.—while maintaining efficient inference adapted to naturally asynchronous information. The PhD student will develop a heterogeneous memory architecture, design an appropriate local learning protocol, and implement integrated circuit demonstrators. Experimental validation on edge-relevant tasks (e.g., sensory classification) will assess power consumption, network accuracy, and adaptability. Publications and patents are expected outcomes of the thesis.

Superconducting RF Filters for Quantum Applications

Within the Quantum Devices Laboratory, you will work in an environment ranging from fundamental physics to new nano-electronics technologies, with a team that collaborates closely with quantum computing startups and physicists from CEA-IRIG and Institut Néel.
The operating conditions of qubits (cryogenic temperatures <= 1K, GHz frequencies , high signal density) require the development of suitable components and technological bricks. In particular, the passive radiofrequency components developed around the CEA-LETI superconducting interposer technology show extremely interesting electrical properties up to several GHz. These elements, including inductors available over wide value ranges, have already made it possible to establish the first proofs of concept for very compact and low-loss RF filters. The integration of superconducting materials now makes it possible to envisage the creation of new high-performance filters adapted to signal management in cryogenic environments.
You will be required to develop your expertise in the physics of materials and superconducting components. You will study the different superconducting filters that exist in the scientific literature. Using the models developed in the laboratory and the results of the RF measurements in which you will participate, and relying on 3D RF electromagnetic simulation, you will contribute to the design of different RF filters and functions that meet the needs of cryogenic applications.

Electronic effects dans les cascades de collisions dans le GaN

In radiation environments like space and nuclear plants, microelectronic devices are subject to intense flux of particles degrading the devices by damaging the materials they are made of. Particles collide with atoms of the semi-conducting materials, ejecting them for their lattice site. Those displaced atoms also collide and set in motion a new generation of atoms, and so on, leading to a cascade of collisions which creates defects in the material. Moreover, primary or secondary particles (created following interaction with a neutron for example) also specifically interact with electrons of the target material, and lose kinetic energy in doing so by promoting electrons to higher energy bands. This aspect is called electronic stopping. Simulations of collision cascades must therefore describe both nuclei-nuclei collisions and electronic stopping effects.
The preferred method for collision cascades simulations at the atomic scale is Molecular Dynamics (MD). However, electronic effects are not included in this method as electrons are not taken into account explicitly. To circumvent this issue, additional modules have to be employed on top of MD to model electronic effects in a collision cascade. The state-of-the-art regarding electronic stopping simulation of a projectile in a target material is the real time - time dependent density functional theory (RT-TDDFT). The purpose of this thesis is to combine MD and RT-TDDFT to perform collision cascades simulations in GaN and study the influence of electronic effects. In addition to skills common to all thesis, the candidate will develop very specific skills in different atomic scale simulation methods, solid state physics, particle-matter interactions, linux environment and programming.

Innovative cooling solutions for 2.5D and 3D electronic systems

As electronic architectures become increasingly complex and dense, managing thermal dissipation is a critical challenge to ensure system reliability and performance. In constrained environments and demanding applications, localized hotspots require innovative cooling solutions compatible with advanced packaging integrations such as 2.5D and 3D. This PhD project is part of this dynamic and aims to explore wafer-level thermal management approaches, relying in particular on advanced 3D integration processes such as direct bonding.

The PhD candidate will contribute to the design and fabrication of test vehicles incorporating temperature sensors and active thermal structures. The main objective will be to assess the efficiency of novel cooling architectures, with a particular focus on integrating microfluidic channels within the stacks, combined with the use of high thermal conductivity materials. The work will include aspects of thermal (and possibly thermo-mechanical) modeling, cleanroom process development, and experimental characterization.

This research topic, at the crossroads of microelectronics and thermal management, offers a stimulating and interdisciplinary framework, closely aligned with emerging industrial needs in advanced packaging.

Physical modelling of Solid-State Batteries exposed to long cycling and fast-charge protocols

CEA-Leti, a leader in the development and manufacturing of integrated solid-state batteries, is collaborating with InjectPower, a cutting-edge start-up, to develop an innovative power solution for miniaturized implantable medical devices. Thin-film all-solid-state battery technology currently stands out as the leading choice for delivering high energy density and customizable form-factor power sources. However, despite this advantage, capacity retention during cycling remains insufficient, with the goal of 1,000 cycles and less than 10% capacity loss still unmet. Additionally, a comprehensive understanding of the physical mechanisms driving performance degradation in microbatteries is lacking.

During this PhD, you will contribute to the development and refinement of our physical model, focusing on accurately describing microbattery behavior during cycling and fast charging. You will also apply our physically informed Bayesian machine learning model to identify key factors that influence battery performance, including charge-discharge protocols, storage conditions, and device architecture. Model training and validation will be based on data collected from automatic probers on silicon wafers containing thousands of microbatteries.

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