AVS 71 Session EM-ThM: Advances in Material Deposition Techniques

Perovskite oxides ABO₃ thin film have desirable properties for advanced materials applications including energy storage and conversion, catalysis, environmental remediation, and electronics, etc. There have been various deposition methods of perovskite oxide thin films, such as molecular beam epitaxy, pulsed-laser deposition, sputtering, chemical vapor deposition, and atomic layer deposition (ALD) for electronic device fabrication and semiconductor manufacturing. Among them, ALD is the preferred method to deposit these oxide thin films for nanoscale thickness control and conformal coating. ALD processes have been demonstrated for many perovskite oxides, such as SrTiO₃, BaTiO₃, BiFeO₃, SrRuO₃, LaCoO₃, LaAlO₃, SrHfO₃. In almost all cases, the desirable properties of the perovskite oxides are not realized for an amorphous structure and crystallization is required. In this presentation, we will review up-to-date literature work on organometallic precursors and their ALD processes for perovskite oxides. We will categorize perovskite oxides by their applications including ferroelectric, ferromagnetic, multiferroic, high-k gate oxide for CMOS, high-k dielectrics and high work function metals for DRAM, and optoelectronic for photonics. We will highlight achievements and challenges for each category from precursor syntheses, ALD processes, and applications perspectives.

Driven by the escalating demand for advanced data storage from AI, IoT, and AR/VR technologies, Phase-Change Memory (PCM) is emerging as a leading candidate for Storage-Class Memory (SCM). Traditional von Neumann architectures face data handling challenges due to the speed gap between DRAM and NAND flash, making SCM development crucial. PCM is highly attractive for SCM due to its efficiency, nonvolatility, high speed, scalability, and endurance.

In this study, we developed a high-performance PCM with a Ta-doped Sb₂Te₃ (TST)/TiTe₂ (TT) superlattice-like (SLL) structure. TST was synthesized by doping Sb₂Te₃, known for its high-speed operation, with Ta via co-sputtering. Ta, a transition metal with low electronegativity and high thermal stability, was chosen to enhance speed and reduce power consumption. The optimal Ta concentration (Ta_0.41Sb₂Te₃) was determined from prior research to maximize performance, significantly reducing resistance drift and increasing the 10-year data retention temperature, thereby improving durability and thermal stability.

The TST/TT SLL structure was developed by introducing TT as a thermal confinement layer. TT possesses both electrical conductivity and low thermal conductivity. Both TST and TT are expected to grow in the c-plane direction with insignificant lattice mismatch, facilitating SLL fabrication. Crucially, SLL structures were fabricated using only sputtering deposition, an industry-friendly technique, unlike traditional methods such as atomic layer deposition. The optimized SLL structure exhibited well-aligned c-plane growth and distinct van der Waals gaps, confirmed by XRD and TEM analyses.

The fabricated PCM device, based on the TST/TT SLL structure on a W-plug electrode substrate, demonstrated significant performance improvements. It achieved fast switching at 15 ns, a notable improvement over conventional devices, and a high ON/OFF resistance ratio exceeding 100. Compared to TST-based PCM, the SLL structure-based PCM operated at a lower voltage for the same pulse width, indicating reduced operating power. This enhancement is attributed to the thermal confinement effect of the TT layer, which efficiently concentrates Joule heating, enabling phase transition at lower voltages.

In conclusion, this study successfully developed an industry-friendly sputtering deposition process for fabricating TST/TT SLL structures, resulting in high-performance PCM devices with enhanced speed and low-power operation. The optimized SLL structure, with its thermal confinement effect, presents a promising pathway for advancing PCM technology and developing scalable, high-speed, and low-power SCM solutions.

MXenes, a rapidly expanding family of two-dimensional transition metal carbides and/or nitrides, have sparked intense scientific interest due to their unique combination of metallic conductivity, tunable surface chemistry, and hydrophilic behavior (surface area=15.247 m² g⁻¹). These properties not only make them ideal candidates for standalone electrode materials but also allow seamless integration with other functional compounds to form high-performance composites. In this study, a hybrid material was designed by coupling Ti₃C₂ MXene with Erbium oxide (Er₂O₃), a rare-earth metal oxide known for its redox-active behavior, to engineer a next-generation electrode for energy storage devices. The layered Ti₃C₂ sheets were synthesized via selective chemical etching, followed by hydrothermal composite formation with Er₂O₃. The structural, morphological, and chemical characteristics of the resulting materials were thoroughly analyzed using XRD, FESEM, FTIR, and Raman spectroscopy. The hybrid system demonstrated a striking enhancement in electrochemical performance due to the synergistic interplay between the high conductivity of MXene and the faradaic contribution from Er₂O₃. The pure MXene electrode delivered a specific capacitance of 476.19 F g⁻¹, while the optimized MXene/Er₂O₃ composite achieved a high capacitance. In addition, there was an improvement in cycling stability (85.99%) of the composite when compared to MXene (77.4%) for 2000 cycles. This remarkable improvement underscores the potential of rare-earth metal oxide/MXene hybrids in advancing the design of efficient, high-capacity energy storage systems. The work opens new avenues for tailoring MXene-based architectures toward scalable, high-performance energy storage and conversion technologies.

Rising carbon dioxide emissions have driven research into sustainable methods for converting carbon rich waste gases from industry into value-added materials. One such method is the CO_x Thermal Oxidation Process (CO-OP), in which CO or CO₂ reacts with magnesium silicide (Mg₂Si) to produce crystalline silicon encapsulated in both graphitic and amorphous carbon. The resulting composite shows potential as a lithium-ion battery anode, while the process itself offers a method for CO₂ removal. However, industrial gas streams are rarely pure and the influence of feed composition on CO-OP remains unexplored. While CO-OP with CO₂ has been studied, implementation in industrial processes would be impractical if it required purified CO₂. This study investigates how feed compositions common in methane steam reforming (CO₂, CO, CO+H₂, and CO₂+H₂) affect the morphology of the produced composite and how these morphology changes influence battery performance. Preliminary results indicate that CO increases the carbon content of the composite as compared to CO₂ and creates a core/shell structure, increasing mechanical stability. Morphology, surface area, and carbon distribution vary significantly with gas composition which in turn affects the battery performance significantly. X-ray diffraction confirms high purity across all samples after leaching. These insights guide future improvement of CO-OP for integration with industrial emission streams, creating a new method of carbon capture and improving battery technology.