Les dispositifs spintroniques exploitent le degré de liberté du spin électronique pour traiter l'information. Dans cette thèse, nous étudions les propriétés de transport quantique dépendant du spin pour optimiser les performances des composants associés. Par l’approche ab initio, nous calculons la magnétorésistance à effet tunnel (tunneling magnetoresistance, TMR), l’effet Hall de spin (spin Hall effect, SHE) et l’efficacité de l’injection de spin (spin injection efficiency, SIE). Nous montrons ainsi que les métaux lourds (heavy metals, HM) influencent la TMR dans des jonctions tunnel magnétiques (magnetic tunnel junctions, MTJs) à base de MgO. L’utilisation de W, Mo, ou Ir peut améliorer la TMR. De plus, le dopage par substitution aide à optimiser le SHE dans les HMs, ce qui renforce les angles de Hall de spin (SHA) pour rendre plus efficace le renversement d’aimantation par couple spin-orbite (spin-orbit torque, SOT) dans les MTJ. Afin de contourner les problèmes induits par le désaccord de maille entre couches ferromagnétiques et MgO, nous avons conçu une MTJ basée sur l'hétérojonction VSe₂/MoS₂ de van der Waals (vdW) et calculons la TMR à température ambiante. L’apparition d’effets de résonance tunnel permet d’utiliser la tension appliquée pour moduler la TMR dans cette structure. Nous proposons également d’y favoriser le SOT en utilisant des matériaux 2D avec un fort SHE. MoTe₂ et WTe₂ apparaissent comme de bons candidats. Ces dichalcogénures de métaux de transition (transition metal dichalcogenides, TMDC) présentent un fort SHE ainsi que de grands SHA grâce à leur faible conductivité électrique. Enfin, motivés par la demande d'un dispositif commutable bidimensionnel à grande longueur de diffusion spin, nous étudions un système d'injection de spin dans le silicène et obtenons des SIE élevés sous tension appliquée. L’ensemble de ces travaux apportent un éclairage pour la recherche de nouveaux dispositifs spintroniques. / Spintronics devices manipulate the electron spin degree of freedom to process information. In this thesis, we investigate spin-dependent quantum transport properties to optimize the performances of spintronics devices. Through ab initio approach, we research the tunneling magnetoresistance (TMR), spin Hall effect (SHE), as well as spin injection efficiency (SIE). It has been demonstrated that heavy metals (HMs) are able to modulate TMR effects in MgO-based magnetic tunnel junctions (MTJs), and tungsten, molybdenum, and iridium are promising to enhance TMR. Moreover, substitutional atom doping can effectively optimize SHE of HMs, which would strengthen spin Hall angles (SHAs) to achieve efficient spin-orbit torque (SOT) switching of MTJs. To eliminate the mismatch between ferromagnetic and barrier layers in MgO-based MTJs, we design the MTJ with bond-free van der Waals (vdW) heterojunction VSe₂/MoS₂ and report the room-temperature TMR. The occurrence of quantum-well resonances enables voltage control to be an effective method to modulate TMR ratios in vdW MTJ. We put forward the idea of SOT vdW MTJ, which employs SOT to switch vdW MTJ and requires vdW materials with strong SHE. Research on MoTe₂ and WTe₂ verifies the possibility of realizing this idea. Both of them are layered transition metal dichalcogenides (TMDC) and exhibit strong SHEs, as well as large SHAs thanks to their low electrical conductivity. Lastly, motivated by the demand of a two-dimensional (2D) switchable device with long spin diffusion length, we construct the spin injection system with silicene monolayer, and reveal high SIEs under electric fields. Works in this thesis would advance the research of spintronics devices.

<div> <div> <p>Phase transition materials (PTM) have garnered immense interest in concurrent post-CMOS electronics, due to their unique properties such as - electrically driven abrupt resistance switching, hysteresis, and high selectivity. The phase transitions can be attributed to diverse material-specific phenomena, including- correlated electrons, filamentary ion diffusion, and dimerization. In this research, we explore the application space for these materials through extensive device-circuit co-design and propose new ideas harnessing their unique electrical properties. The abrupt transitions and high selectivity of PTMs enable steep (< 60 mV/decade) switching characteristics in Hyper-FET, a promising post-CMOS transistor. We explore device-circuit co-design methodology for Hyper-FET and identify the criterion for material down-selection. We evaluate the achievable voltage swing, energy-delay trade-off, and noise response for this novel device. In addition to the application in low power logic device, PTMs can actively facilitate non-volatile memory design. We propose a PTM augmented Spin Transfer Torque (STT) MRAM that utilizes selective phase transitions to boost the sense margin and stability of stored data, simultaneously. We show that such selective transitions can also be used to improve other MRAM designs with separate read/write paths, avoiding the possibility of read-write conflicts. Further, we analyze the application of PTMs as selectors in cross-point memories. We establish a general simulation framework for cross-point memory array with PTM based <i>selector</i>. We explore the biasing constraints, develop detailed design methodology, and deduce figures of merit for PTM selectors. We also develop a computationally efficient compact model to estimate the leakage through the sneak paths in a cross-point array. Subsequently, we present a new sense amplifier design utilizing PTM, which offers built-in tunable reference with low power and area demand. Finally, we show that the hysteretic characteristics of unipolar PTMs can be utilized to achieve highly efficient rectification. We validate the idea by demonstrating significant design improvements in a <i>Cockcroft-Walton Multiplier, </i>implemented with TS based rectifiers. We emphasize the need to explore other PTMs with high endurance, thermal stability, and faster switching to enable many more innovative applications in the future.</p></div></div>