An Aqueous Route to Oxygen-Deficient Wake-Up-Free La-Doped HfO₂ Ferroelectrics for Negative Capacitance Field Effect Transistors

Abstract

The crucial role of nanocrystalline morphology in stabilizing the ferroelectric orthorhombic (o)-phase in dopedhafnia films is achieved via chemical solution deposition (CSD) by intentionally retaining carbonaceous impurities to inhibit grain growth. However, in the present study, large-grained (>100 nm) La-doped HfO 2 (HLO) films are grown directly on silicon by adopting engineered water-diluted precursors with a minimum carbonaceous load and excellent shelf life. The ophase stabilization is accomplished through a well-distributed La dopant, which generates uniformly populated oxygen vacancies, eliminating the need for oxygen-scavenging electrodes. These oxygen-deficient HLOs show a maximum remnant polarization of 37.6 μC/cm 2 (2P r ) without wake-up and withstand large fields (>6.2 MV/cm). Furthermore, CSD-HLO in series with Al 2 O 3 improves switching of MOSFETs (with an amorphous oxide channel) based on the negative capacitance effect. Thus, uniformly distributed oxygen vacancies serve as a standalone factor in stabilizing the o-phase, enabling efficient wake-up-free ferroelectricity without the need for nanostructuring, capping stresses, or oxygen-reactive electrodes.

Advancements in Metal Oxide Thin Film Quality in Solution-Processed High-κ Dielectrics for High-Performance Transistors

“…Nevertheless, in the recent past, solution-phase deposition, simply termed as “solution processing”, has gained significant research interest due to its ease of fabrication under atmospheric pressure. − The challenging aspect of solution processing is the delivery of high-quality electronic-grade dielectric film. Spin coating of solution-phase precursors under thermal treatment yields porous mass due to evaporation of impurity ligands associated with the precursor, which are generally metal salts containing the required cation (e.g., for Al 2 O 3 , Al 3+ cations are sourced from Al(NO 3 ) 3 ). , The traditional approach to increase the densification in spin-coated thin films is a multilayered coating approach; however, it has challenges such as increased processing steps, time-consuming, and dissolution of the previously coated layer while depositing the subsequent layer. , To avoid this, many modifications in the solution processing are addressed in the literature, and one such method is spraying deposition. , The atomized droplets of liquid-phase precursors undergo thermal decomposition when coming in contact with the substrate and maintained at an elevated temperature. The large surface of atomized droplets facilitates the easy removal of impurity gases and promotes densification.…”

Structure and stability of La- and hole-doped hafnia with/without epitaxial strain

“…In fact, doping elements with lower valence states than Hf (charge uncompensated defect), such as La and so on, also has a similar effect [44]. On the other hand, the introduction of La perhaps leads to the appearance of oxygen vacancies (charge compensated defect) and makes leakage current decrease [46,47], which makes the reason for stabilizing the ferroelectric o phase by doping La ambiguous.…”