Conception and integration of microlasers within a silicon photonics platform
For about ten years, the continuous increase in internet traffic has pushed the electrical interconnections of data centers to their limits in terms of bandwidth, density, and consumption. By replacing these electrical links with optical fibers and integrating all the necessary optical functions on a chip to create transmitters-receivers (transceivers), silicon photonics represents a unique opportunity to address these issues. The integration of a light source within a photonic chip is an essential building block for the development of this technology. While many demonstrations rely on the use of external lasers or bonded laser chips, it is the direct heterogeneous fabrication of a laser within the photonic chip that would allow the desired level of performance while limiting costs.
The objective of this thesis is to provide an innovative solution for the management of very short-distance communications (inter-chip, intra-chip) by realizing, on silicon, III-V membrane microlaserswith buried heterostructures. This type of microlasermeets the numerous challenges of very short-distance links thanks to an efficiency/integrabilitycompromise superior to the state of the art of datacomlasers while being compatible with CMOS fabrication lines.
Based on the work carried out during a previous thesis, the PhD student will be responsible for (i) designing the microlasersusing the available digital simulation tools in the laboratory, then (ii) manufacturing these microlasersby relying on the technological platforms of CEA-LETI, and finally (iii) electro-optically characterizing the components. This thesis work will be carried out in collaboration between CEA-LETI and LTM/CNRS and will constitute a strategic brick necessary for future generations of photonic transceivers.
Device for light extraction through evanescent coupling in Photonic Integrated Circuit
The objective of the PhD is to develop a new class of optical devices used to provide interfaces between Photonics Integrated Circuits (PICs) and free space optics. These devices have been investigated in a seminal work conveyed in a former PhD work. It consists in the use of a nanoimprinted prismatic structure bonded on the surface of a PIC. Through evanescent coupling and reflections in the structure, guided waves can be transferred from the PIC toward an external optical system. With the use of electro-optic materials, this extractor may offer interesting applications as a switchable extractor.
The candidate will delve into the theory of the device to improve its performance. He/she will perform experiments on packaging, holography and PIC characterization. His/her objective will be to manufacture a large panel of sample devices to be tested. One particular concern is to evaluate the behavior of the fabricated devices in a large spectral domain form visible to short Infra-Red wavelengths.
The candidate will use FDTD simulation software to evaluate the propagation characteristics of the wave as it travels from a confined space to a free space. He/she will define optimal prismatic structures to be replicated with nanoimprint. He/she will implement the polymer structure on PIC samples through delicate transfer and bonding protocol in a clean room. He/she will record micro-holographic optical elements with lasers to improve the angular potential of the final device. Large part of the PhD will concern the use of optical set-ups.
Development of a bifunctionnal zwitterionic nano-coating for aptasensors - a new linker for biological probes that hinders non-specific adsorptions
The field of biosensor development frequently encounters the issue of non-specific signals. These signals often limits the performance of biosensors and complicates industrial transfers. The functionalization steps for biosensors design generally include three steps: i) functionalization of the transducer with a linker molecule, ii) immobilization of a biological probe (antibodies, aptamers, oligonucleotides...) using the linker, iii) treatment with an entity to block non-specific interactions. The literature is full of solutions that highlight the blocking of these non-specific interactions with different types of chemical or biological entities: proteins (BSA, casein...), polymers (PEG, PVP) or small molecules (ethanolamine, hexylamine...).
However, an alternative functionalization approach with a linker that offers both the ability to immobilize biological probes while ensuring the blocking of non-specific interactions represents an innovative path for the development of biosensors.
This PhD project aims to explore the design and surface functionalization with a bifunctional nano-coating responding to this approach. Regarding the blocking, zwitterionic polymers will be at the heart of the development. Indeed, numerous studies demonstrate their ability to drastically reduce the interactions of complex biological environments with surfaces that are functionalized with them. Furthermore, it is possible to exploit the chemical functions of certain types of zwitterions to immobilize biological probes on demand. After optimizing their activity in homogeneous phase, aptamers will be immobilized on silicon transducers (QCM-d and photonic chip) via the bifunctional zwitterionic nano-coating. The objective of the thesis is to obtain a proof of concept of a biosensor functionalized with this new linker that ensures the reduction of non-specific signals while ensuring the specific detection of the target considered (Tyrosinamide model) in model and complex environments derived from biomedical sector, such as serum or plasma.
Sharper Structural Insight in Nanoelectronics with Dark-Field X-Ray Microscopy
Dark-field X-ray microscopy (DFXM) is an emerging, non-destructive synchrotron technique capable of imaging strain and crystalline defects with 30–100 nm resolution over large fields of view. Recent upgrades at the ESRF and the ID03 beamline have increased X-ray intensity by two orders of magnitude, enabling investigation of the most challenging nanoscale structures produced in cleanroom environments. This PhD aims to exploit DFXM for the analysis of advanced microelectronic architectures subjected to critical thermo-mechanical stress. DFXM will provide 3D mapping of strain, orientation and buried defects in complex devices without sample destruction. A comparative study will be performed against complementary local X-ray techniques also available at synchrotron facilities such as Laue microdiffraction and scanning X-ray diffraction microscopy. Multi-scale correlations will be established with TEM and Raman spectroscopy. Finite-element simulations will support interpretation by modelling the mechanical behavior under thermal or operational loads. The objective is to define a robust methodology for multiscale strain analysis in microelectronics devices.
This PhD will take place at the CEA–Leti on the Nanocharacterization platform and is embedded in a strong ESRF@ID03 collaboration and supports advances in quantum technologies, photonics and energy-efficient microelectronics. This work will contribute to improved reliability and design optimization of next-generation devices.
Development of ultra-high-resolution magnetic microcalorimeters for isotopic analysis of actinides by X-ray and gamma-ray spectrometry
The PhD project focuses on the development of ultra-high-resolution magnetic microcalorimeters (MMCs) to improve the isotopic analysis of actinides (uranium, plutonium) by X- and gamma-ray spectrometry around 100 keV. This type of analysis, which is essential for the nuclear fuel cycle and non-proliferation efforts, traditionally relies on HPGe detectors, whose limited energy resolution constrains measurement accuracy. To overcome these limitations, the project aims to employ cryogenic MMC detectors operating at temperatures below 100 mK, capable of achieving energy resolutions ten times better than that of HPGe detectors. The MMCs will be microfabricated at CNRS/C2N using superconducting and paramagnetic microstructures, and subsequently tested at LNHB. Once calibrated, they will be used to precisely measure the photon spectra of actinides in order to determine the fundamental atomic and nuclear parameters of the isotopes under study with high accuracy. The resulting data will enhance the nuclear and atomic databases used in deconvolution codes, thereby enabling more reliable and precise isotopic analysis of actinides.
AI model deployment using Hardware-Aware on-chip Fine Tuning
Emerging unconventional hardware technologies are essential for future Edge-AI applications, but they often suffer from variability, mismatches, and technology dispersion. These non-idealities can strongly reduce AI inference accuracy if no fine-tuning or calibration is applied. Traditional supervised fine-tuning is difficult to industrialize because it raises issues related to data confidentiality, service quality, software complexity, and hardware constraints.
This PhD project aims to develop hardware-algorithm co-design methods that avoid the need for fully supervised on-chip retraining. The main goal is to create task-agnostic, inference-level self-calibration strategies able to compensate hardware mismatches at the system level. The work will study existing adaptation methods, including weight-based, feature-based, output-based, and domain adaptation approaches.
The project will define a relevant Edge-AI application, develop a generic fine-tuning method, and validate it through low-level electrical simulations. If possible, the proposed algorithm may also be tested experimentally on a custom ASIC-based hardware setup.
Self-calibrated mmW Injection Locked Oscillators
In our research group we have developed and used during the last few year an innovative technique for frequency generation where the injection locked oscillator are the core. However, this circuits that we found in electronics, but also in other disciplines such as mechanics, biology and fundamental physics, hide still some secrets.
In this PhD you will be starting with the existing knowledge about these circuits leveraging in the broad experience of the research team and you will contribute to extend this knowledge to understand the impact of external perturbations and manufacturing tolerances on the operation of such circuit, for next proposing and implementing self-calibration and stabilization techniques.
The. applications of this circuits are broad, but some of the most appealing are found in the field of high-speed mmW wireless and wired links, extremely high resolution radar, vital signs detection for medical applications and quantum experiments (such as resonant paramagnetic spectrometry.
Depending on the advancement of the research the proposed self-calibration technique will be applied in one of the existing developments in our group in one of these fields.
How defects nucleation affects the the fracture on the SmartCut process
The SmartCut™ technology is widely used in microelectronics for the fabrication of innovative substrates, such as SOI (Silicon-on-Insulator).
The physical phenomena underlying SmartCut™ technology remain one of principal interest of our research. Optimizing the fracture stage is a major focus in our laboratory and in our collaboration with Soitec. Salomon's PhD thesis (expected completion December 2026), the development of post-fracture surface analysis protocols highlighted the link between the evolution of cristalline defects that cause fracture (platelets) and post-fracture surface roughness. We were thus able to characterize the early stages of platelet growth and determine their main characteristics (size and density). This had previously only been achieved through complex characterizations based on TEM observations.
Now that we have highlighted the impact of platelets on post-fracture surface roughness, the next step is to investigate and identify ways to control their nucleation using new processes. This will also involve optimizing the post-fracture state of SOI substrates.
CdTe for medical radiography; control of electrical properties
The use of direct-conversion detectors in medical radiography opens up new possibilities. Due to its properties, the semiconductor material CdTe has emerged as the material of choice for manufacturing these new components. The proposed thesis topic aims to develop the knowledge and processes necessary to produce CdTe crystals with properties tailored to specific application requirements. The work will draw on the laboratory’s advanced expertise in mastering CdTe single-crystal growth processes. The key challenges of the project will be as follows:
- Performing annealing under controlled atmospheres (ex-situ, on small samples) to study their impact on the electrical properties of CdTe,
- Conducting advanced characterizations to better understand the doping mechanisms in CdTe,
- Fabricating “simple” devices and testing them under X-ray flux to quantify the performance of the laboratory’s materials.
The proposed thesis topic is central to the development of a CdTe technology for medical radiography applications. Multidisciplinary work (material and process development, material characterization, fabrication and X-ray testing of simplified devices) is proposed to address this topic.
Energy-minimizing associative neural networks using resistive memories
This PhD project aims to develop Hopfield-type associative neural networks that perform inference through energy-minimizing dynamics.
The goal is to exploit these dynamics for image denoising and reconstruction close to the sensor, under strict energy and latency constraints.
The network synapses will be implemented in ReRAM crossbar arrays, enabling analog in-memory matrix-vector operations.
The work will focus on architecture dimensioning while accounting for array size, weight quantization, device variability and endurance limits.
Reference models will be developed in PyTorch to evaluate alternative neural dynamics and hardware mapping strategies.
Patch-wise image denoising will serve as the main use case to quantify trade-offs between reconstruction quality, latency and energy consumption.
Particular attention will be paid to the robustness of the networks against hardware non-idealities such as noise, variability and memory drift.
The project will also investigate local on-chip learning mechanisms, allowing slow adaptation to changes in the sensor, scene or memory devices.
These learning rules must remain compatible with the endurance constraints of resistive memories.
Ultimately, the PhD should provide hardware-sizing guidelines and support the design of an experimental test vehicle.
The broader scientific objective is to demonstrate that dynamic associative inference can become an efficient, robust and low-power building block for edge AI.