Miaojia Yuan

Post-Moore nanoscale devices are driving the next wave of semiconductor advancement through three-dimensional architectures and material innovation. However, the shrinking source/drain contact area has made metal–semiconductor contact resistivity (ρc) a critical performance bottleneck. Conventional heavy doping techniques can no longer meet the stringent ρc requirement (<10−9 Ω cm2) for advanced technology nodes. Various strategies have been adopted to reduce it such as inserted silicide. However, ρc is typically limited to the range of 10−4–10−6 Ω cm2. Up until now, the mechanism behind these strategies is highly controversial. In this review, we comprehensively explain the underlying physical mechanisms governing ρc from the perspectives of Schottky barrier height and Fermi level pinning. Then, an analysis of state-of-the-art approaches for ρc reduction is reviewed, involving interface modification and oxide interlayer integration toward conventional semiconductor and advanced two-dimensional-based semiconductor. Finally, we discuss remaining challenges and proposing synergistic strategies on future research directions for achieving low contact resistivity in post-Moore nanoscale devices.

Metal-semiconductor contact resistance poses a critical challenge due to the reduced contact area in next-generation semiconductor devices, which can be tuned by the Schottky barrier heights (SBHs). However, the strong surface Fermi-level pinning (FLP) introduces the uncontrolled SBHs for conventional doping strategies. In this study, we propose the interfacial-layer control of Fermi-level depinning and dipole engineering and demonstrate the critical effect of TiO2 as the interfacial layer for reducing SBHs in the NiSi/Si system. Our theoretical results reveal that a 0.7 nm TiO2 interlayer is required to achieve the low SBH of 0.12 eV compared with the intrinsic system of 0.65 eV. FLP mitigation through metal-induced gap state reduction remains foundational for SBH control, and the dipole charge effect provides an additional degree for interfacial energy band tailoring. Even though the SBHs exhibit the higher values depending on the different oxygen vacancy sites and concentration, it is still lower than that of pristine systems, demonstrating its feasibility in reducing SBHs. These findings provide solid foundation for minimizing contact resistance in state-of-the-art semiconductor technologies.

Complementary field-effect transistor technology enhances integration density and reduces power consumption by vertically stacking n-MOS and p-MOS transistors. However, the three-dimensional (3D) architecture poses challenges in threshold voltage control when depositing metal with distinct work function (WF) for the gates. Using first-principles calculations, we explore wide-range WF modulation (3.20–5.25 eV) of defective TiN widely used in industry for 3D integration, enabling its application for both n- and p-MOS gates. Compared with bulk defects, WF is strongly affected by the surface defect types and their concentrations. Surface N adsorption can increase TiN WF from 4.73 to 5.25 eV when the concentration is within 12.5%–62.5%. In contrast, surface Ti vacancies can reduce the WF to 3.20 eV at a concentration of 62.5%. In addition, the stress effect indicates that WF increases under compressive stress and conversely for tensile stress. The above phenomenon can be attributed to the charge transfer and charge redistribution by different defects. This WF modulation technique in this work has the potential to meet the requirements of next-generation 3D architecture.

Two-dimensional ferromagnetic materials hold great promise to develop energy-efficient magnetoelectric memory devices and next-generation spintronics. However, one of the crucial challenges for these materials is the realization of tunable magnetocrystalline anisotropy (MCA) to balance thermal stability and energy efficiency. Here, we systematically study the adsorption effects of 3d transition metals (3d-TMs) on the electronic structure and magnetic property of the Fe3GeTe2 (FGT) monolayer. The adsorption systems exhibit different ground state configurations depending on the adatoms, while the controlled perpendicular magnetic anisotropy has also been achieved. Notably, the Mn/FGT system can maintain the out-of-plane magnetic orientation with a changing amplitude of MCA energy up to 3.057 erg/cm2 as the external strain varies from −4% to 1%. In contrast, the Fe/FGT structure undergoes spin reorientation from in-plane to out-of-plan magnetization with a distinct modification behavior of MCA. We elucidate that the underlying atomistic mechanism mainly arises from the alteration of Fe-derived 3d-orbital states in response to the strain effect, leading to competitive changes in the different coupling states. These findings can not only provide useful guidance to optimize two-dimensional magnets for fundamental research but also reveal the promising potential of TMs/FGT materials for the development of ultra-low energy spintronic devices.