Design and optimization of color routers for image sensors
Color routers represent a promising technology that could revolutionize the field of image sensors. Composed of nanometricstructures called metasurfaces, these devices allow the modification of light propagation to improve the quantum efficiency of pixels. Thanks to recent technical advances, it is now possible to design and manufacture these structures, paving the way for more efficient image sensors.
The thesis topic focuses on the design and optimization of color routers for image sensors. Several research avenues will be explored, such as the implementation of new metasurfacegeometries (`freeform`) or innovative configurations to reduce pixel pitch (0.5µm or 0.6µm). Various optimization methods can be used, such as the adjointmethod, machine learning, or the use of auto-differentiable solvers. The designs must be resilient to the angle of light incidence and expected variations during manufacturing. After this simulation phase, the proposed structures will be manufactured, and the student will have the mission to characterize the chips and analyze the obtained results (quantum efficiency, modulation transfer function...).
This thesis will be co-supervised by STMicroelectronics and CEA LETI in Grenoble. The student will be integrated into the teams of engineer-researchers working on this project. He/she will be led to collaborate with various specialists in various fields such as lithography and optical characterization.
The student's main activities:
- Optical simulation using numerical methods (FDTD, RCWA)
- Development of optimization methodologies for metasurfacedesign (adjointmethod, topological optimization...)
- Electro-optical characterization and analysis of experimental data
Topologic optimization of µLED's optical performance
The performance of micro-LEDs (µLEDs) is crucial for micro-displays, a field of expertise at the LITE laboratory within CEA-LETI. However, simulating these components is complex and computationally expensive due to the incoherent nature of light sources and the involved geometries. This limits the ability to effectively explore multi-parameter design spaces.
This thesis proposes to develop an innovative finite element method to accelerate simulations and enable the use of topological optimization. The goal is to produce non-intuitive designs that maximize performance while respecting industrial constraints.
The work is divided into two phases:
Develop a fast and reliable simulation method by incorporating appropriate physical approximations for incoherent sources and significantly reducing computation times.
Design a robust topological optimization framework that includes fabrication constraints to generate immediately realizable designs.
The expected results include optimized designs for micro-displays with enhanced performance and a methodology that can be applied to other photonic devices.
Study and evaluation of silicon technology capacities for applications in infrared bolometry
Microbolometers currently represent the dominant technology for the realization of uncooled infrared thermal detectors. These detectors are commonly used in the fields of thermography and surveillance. However, the microbolometer market is expected to grow explosively in the coming years, particularly with their integration into automobiles and the proliferation of connected devices. The CEA Leti LI2T, a recognized player in the field of infrared thermal detectors, has been transferring successive microbolometer technologies to the industrial partner Lynred for over 20 years. To remain competitive in this growing market for microbolometers, the laboratory is working on breakthrough microbolometers incorporating CMOS components as the sensitive element. In this context, the laboratory has initiated studies focusing on temperature-dependent silicon technology capabilities, with promising initial results not reported in the literature. The thesis topic fits into this context and aims to demonstrate the interest of these components for microbolometric applications. It will therefore cover the analytical modeling of these components and their associated physical effects, as well as the reading of such a component in a microbolometer imager approach. A reflection on technological integration will also be conducted. The student will benefit from several already realized technological lots to experimentally characterize the physical effects and familiarize themselves with the subject. To understand the encountered phenomena, the student will have access to the laboratory's entire test set-ups (semiconductor parameter tester, noise analyzer, optical bench, etc.) as well as the numerical analysis Tools (Matlab/Python, TCAD simulations, SPICE simulations, Comsol, etc.). By the end of the thesis, the student will be able to address the question of the interest of these components for microbolometric applications.
Physics of perovskite materials for medical radiography: experimental study of photoconduction gain
X-rays is the most widely used medical imaging modality. It is used to establish diagnostics, monitor the evolution of pathologies, and guide surgical procedures.
The objective of this thesis is to study a perovskite type semiconductor material for its use as a direct X-ray sensor. Perovskite-based matrix imagers demonstrate improved spatial resolution and increased signal, and can thus help improve patient treatment. Prototype X-ray imagers manufactured at the CEA already provide radiographic images but their performances are limited by the instability of the sensor material.
You job will be to study the mechanisms responsible for the photoconduction gain and photocurrent drift of thick perovskite layers from both a theoretical and an experimental standpoint. To this end, you will adapt the electro-optical characterization benches of the laboratory, conduct experiments and analyze the data collected. You will also have the opportunity to perform advanced characterizations with specialized laboratories within the framework of national and international collaborations. The results of this thesis will provide a better understanding of the material properties and guide its ellaboration to produce high-performance X-ray imagers.
Development of multiplexed photon sources for quantum technologies
Quantum information technologies offers several promises in domains such as computation or secured communications. There is a wide variety of technologies available, including photonic qubits. The latter are robust against decoherence and are particularly interesting for quantum communications applications, even at room temperature. They also offers an alternative to other qubits technologies for quantum computing. For the large-scale deployment of those applications, it is necessary to have cheap, compact and scalable devices. To reach this goal, silicon photonics platform is attractive. It allows implementing key components such as generation, manipulation and detection of photonic qubits.
Solid-state photon generation may occur with different physical processes. Among those, the non-linear photon pair generation has several benefits, such as working at room temperature, the ability to generate heralded single photon, or entangled photon pairs…
You will work on multiplexed parametric photon pair sources in order to surpass the inherent limits of the physical process for generating photon pairs. This will include the development, the fabrication monitoring, and the characterization in the laboratory. In the goal of a full integration on chip, it is necessary to be able to filter effectively unwanted light, in order to keep only photons of interest.