The thesis is aimed at the study through experiments, simulations, and design, the possibilities for the implementation, optimization and application of the Ferroelectric Spin-Orbit (FESO) device, a novel spintronic technology based on the coupling between ferroelectricity and spin-orbit coupling, leading to innovative non-volatile ultra-low power computing solutions. This work is divided into five chapters. The first chapter introduces the main spin related transport phenomena, together with a mathematical formulation enabling a numerical resolution, through Finite Element Method (FEM) simulations, of the spin drift-diffusion equations in an arbitrary spintronic device. The general aspects of the MESO (Magnetoelectric Spin-Orbit) and the FESO device are also presented. The second chapter deals with the modeling and the design of technological applications based on the FESO device, particularly memory architectures and logic gates. For memories, the design for both Random Access Memories and Content Addressable Memories is developed and tested by simulations tools, an evaluation of its physical integration is also proposed. For logic gates, the FESO device is shown to successfully implement a non-volatile inverter and a majority gate with ultra-low power consumption. Beyond merging of storage and computation unit, circumventing the von Neumann bottleneck, the non-volatility also opens the door to power gating, to ultimately reduce the static leakage, a crucial problem of advanced technological nodes. The third chapter investigates the optimization of the readout structure of FESO and MESO devices through FEM simulations, based on the spin Hall effect. The most relevant figures of merit are identified in the spin charge interconversion signal, ΔRscc and in the normalized form, ΔRscc/Rtot. The first figure of merit is related to the output signal, the second to the interconversion efficiency, those figure of merit being ultimately related to the error rate and voltage operation, respectively. The optimization is carried out by studying, with a particular focus, the spin injection efficiency and the geometrical scaling. The performances achieved validate the assumptions made in the previous chapter and guarantee the operation. The fourth chapter extends the FEM model formulation to incorporate 2D spin-charge interconversion due to Rashba-Edelstein effect. After discussing the generalized boundary conditions in relation to the symmetry of the interfaces, the relative equations are included. The model is tested and validated on two case studies and then applied to the FESO geometry, in order to extend the modeling and the optimization to a wider class of materials. This is, to our knowledge, the first implementation of the modeling of this 3D to 2D spin to charge interconversion in realistic 3D systems. The results are in agreement with the expected gain in output signal and readout efficiency expected for Rashba systems respect to system with only spin Hall effects. The fifth chapter gathers some of the experimental activity of this thesis, on the fabrication and characterization of FESO devices made with oxide-based two-dimensional electron gases (2DEGs). A top-down fabrication method is shown, that allows for a successful formation of a 2DEG at the SrTiO3/Ta interface, whose properties can be electrically controlled in a non-volatile way. The measurement of the interconversion yields a spin signal of 250 mΩ, one of the largest observed so far. The following of the chapter analyses the results, with a particular focus on the different contributions of the measured signal. This work demonstrates the potential of FESO devices for next-generation non-volatile, low-power computing and paves the way to its experimental realization and optimization through oxide-based 2DEGs.


Plus d'information :https://www.spintec.fr/phd-defense-ferroelectric-spin-orbit-device-modeling-design-optimization-and-fabrication-with-oxide-based-2degs/
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Pour suivre la soutenance ​​​en visioconférence : https://univ-grenoble-alpes-fr.zoom.us/j/3241920232

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