AVS 72 Session EM-ThP: Electronic Materials and Photonics Poster Session

NbMoTaW refractory high-entropy alloy thin films were deposited using two separate sputtering paths: a single pre-alloyed equimolar composite target and individual Nb, Mo, Ta, and W elemental targets. While previous studies examined NbMoTaW films deposited from composite targets, the influence of deposition path on the microstructure and mechanical behavior remains insufficiently understood. In order to produce the same or similar equimolar compositions of the NbMoTaW films sputtered from the composite target, the sputtering power has to be tuned for each individual target. The sputtering pressure was varied between 0.2 and 1.25 Pa. Both deposition paths produced near-equiatomic NbMoTaW films with stable BCC structure. FESEM, XRD and nanoindentation results showed similar pressure-dependent trends in grain size, crystallite size, dislocation density, lattice constant, microstrain, and hardness. The results indicate that sputtering pressure and film thickness dominate the microstructural and mechanical behavior, while deposition path mainly suggests processing flexibility.

Overall, this study shows that comparable NbMoTaW films can be produced by either path when composition is controlled. Composite-target sputtering offers simplicity and reproducibility, whereas individual-target co-sputtering provides compositional flexibility and cost-effective alloy design capability.

A RF-sputtered HfO₂ thin film deposited on N₂+O₂ plasma-passivated non-epitaxial 4H-SiC substrate was investigated aiming to understand the dielectric breakdown behavior of MOS capacitors and its correlation with interface quality and defect-assisted transport mechanisms. The use of substrates without epilayers enables the evaluation of electrical limitations associated with bulk and interface defects, which are often less evident in optimized epitaxial structures.

Raman and FTIR analyses confirmed the formation of predominantly monoclinic HfO₂ and revealed the presence of an ultrathin interfacial oxide layer induced by plasma passivation (Fig. 1). Raman spectra showed characteristic monoclinic HfO₂ modes at ~526, 582, and 640 cm⁻¹, while FTIR measurements identified Hf–O vibrational bands together with Si–O–Si stretching modes associated with interfacial SiO₂ formation. These results indicate the formation of a chemically stable dielectric film and suggest that plasma treatment modifies the HfO₂/SiC interface.

Current–voltage measurements revealed high leakage current and a progressive current increase before dielectric failure (Fig. 2). The pre-breakdown region exhibited behavior consistent with trap-assisted conduction and trap-controlled space-charge-limited transport, suggesting the participation of defects located within the dielectric and at the HfO₂/SiC interface. Dielectric breakdown occurred at ~17 V (electric field of ~3 MV/cm). Although this value is lower than those typically reported for optimized epitaxial HfO₂/SiC systems, the devices maintained stable electrical behavior prior to catastrophic failure, without abrupt fluctuations associated with premature localized conduction paths.

Post-breakdown SEM and FIB analyses revealed highly localized dielectric failure confined to the probe contact region (Fig. 3). The damaged region exhibited severe morphological deformation, with local fusion of Al, HfO₂, and SiC caused by intense current flow during breakdown. In contrast, adjacent regions remained structurally preserved, maintaining a distinguishable dielectric layer and interface with the SiC substrate. These observations indicate that breakdown was dominated by localized electrical overstress rather than dielectric delamination or structural inhomogeneity.

Ferroelectric tunnel junctions (FTJs) based on hafnium zirconium oxide (HZO) stacks show a promising platform for next-generation in-memory computing. The asymmetric Ta/HZO/TaN electrode stack is particularly attractive because the two metals exhibit different oxygen affinities. However, Ta readily scavenges oxygen and forms sub–stoichiometric TaOx under electrical stress, whereas TaN remains chemically stable and functions as an diffusion barrier. This provides an accessible asymmetric interface for investigating cycling-induced evolution. Ultrathin HZO films < 10nm, demonstrate remanent polarization (Pr) values of 8–30 µC/cm² and facilitate tunneling-based ON/OFF resistance modulation, with ON/OFF ratios ranging from 5 to 30. However, the device-level mechanisms responsible for the non-monotonic tunnel electroresistance (TER) trajectory- including initial wake-up enhancement, subsequent fatigue, and memory-window collapse- continue to be significant challenges for existing predictive models.

In this work, Ta/HZO(6nm)/TaN FTJ devices were fabricated and subjected to comprehensive materials and device characterization, and all parameters were calibrated to experimentally extracted structural, interfacial, and polarization data to conduct the empirical and theoretical interpretation and modeling. The calibrated material and device model implemented in Sentaurus TCAD simulation reproduces the characteristic wake–up behavior emerging within 10²- 10⁴cycles, as well as the progressive fatigue that drives memory–window collapse under extended cycling, which agrees with experimental measurements. The resulting predictive model delineates degradation trajectories that align with endurance regimes from our experimental data from HZO-based devices.

We introduced the Two–regime saturating–exponential/power–law non–monotonic model with cycle–dependent Pr, which captures the experimentally observed wake–up and fatigue behavior in HZO FTJs. In the wake–up regime, oxygen vacancies redistribute from interfaces into the HZO bulk, progressively depinning ferroelectric domains and increasing switchable polarization. With continued cycling, a fatigue regime emerges in which irreversible trap generation at the reactive Ta/HZO interface due to cumulative TaOx formation, which creates an asymmetric depolarizing field. This field destabilizes polarization and precipitates memory–window collapse. Interface trap densities are modeled independently to capture the disparate electrochemical behaviors of Ta and TaN. Cumulatively, our study quantitatively separates polarization– and trap–driven TER contributions and pinpoints the crossover cycle where the dominant mechanism shifts.

Metal–ferroelectric–metal (MFM) tunnel junctions based on HfZrO(HZO) have emerged as leading candidates for next–generation non–volatile memory and neuromorphic computing, yet the coupled dependence of tunneling electroresistance (TER), current density, and polarization retention on electrode work–function asymmetry remains poorly constrained by existing design frameworks. To address this gap, we present a comprehensive TCAD investigation that establishes stability–aware design rules for HZO ferroelectric tunnel junctions (FTJs) by treating electrode work functions as continuous, tunable variables and validating the model against experimental Ta/HZO/TaN and Ti/HZO/TiN devices.

After fabricating and calibrating devices, we conducted a systematic non–symmetric sweep of top and bottom electrodes’ workfunction from 3.8-5.2 eV for varying HZO thickness (5-10 nm) through modeling and Sentaurus TCAD simulation in this study. Furthermore, we mapped target MFM electrodes based on workfuction and interface layers between electrodes and HZO. Each parameter point employed two solve sequences: a WRITE → READ (+/- 0.2V) sequence to extract on- (Jon) and off-current (Joff) and TER, and a 1 µs zero–bias hold to quantify polarization decay and compute the depolarization field (Edep). The model was calibrated against measured Ta/HZO/TaN and Ti/HZO/TiN stacks, reproducing Ta/HZO/TaN metrics (TER ~ <10 at 0.2-0.3 V and Jon < 1 x 10^-3 A/cm², coercive voltage (Vc) < 1.0 V). For metrics for Ti/HZO/TiN devices, we used metrics (TER ~ 16 and on-current (Jon) ~ 1.2 x 10^-2 A/cm², coercive voltage (Vc) < 0.9 V), validating the chosen band–offset and ferroelectric parameters.

Our result indicates that ferroelectric polarization is required to meet dual stability constraints for stable polarization only when the net internal field (built–in field from electrode work–function asymmetry and the depolarization field from incomplete screening) remains below the coercive field. Since these contributions can add or subtract depending on polarization direction, both programmed and erased states are required to hold simultaneously to ensure reliable retention Ebi +Edep < Ec for programmed state and Ebi +Edep > -Ecfor erased state). Based on Pareto analysis, a narrow window where high TER and high on-current coexist can be achieved when built-in fields remain below the coercive threshold. Finally, we mapped optimal target work-function offsets with and without interlayers, offering a CMOS-compatible route to high-performance, retention-robust FTJs suitable for memory and neuromorphic applications.

Nickel oxide (NiO) is a transparent conductive oxide (TCO) widely used in electrochromic devices, photodetectors, gas sensors, dye-sensitized solar cells, and perovskite solar cells as a hole transport layer. NiO possesses a wide bandgap of 3.6–4.0 eV and functions as a p-type semiconductor, where Ni3+ species contribute to hole transport. In addition, NiO exhibits excellent chemical and thermal stability along with antiferromagnetic, electronic, and optoelectronic properties. However, using NiO as an inorganic hole transport layer (HTL) causes some challenges, such as an energy level mismatch between NiO and perovskite layers, which results in increased charge transfer barriers. Furthermore, defects at the NiO perovskite interface act as recombination centers for electron–hole pairs, reducing carrier lifetime. One successful approach found to be is surface modification of NiO with organic ligands.

In this work, gas-phase surface modification of NiO thin films using hexafluoroacetylacetone (hfacH) and acetylacetone (acacH) was investigated under vacuum conditions. The objective of this study is to understand the chemical reactivity of fluorinated and non-fluorinated β-diketones on the NiO surface and correlate these interactions with changes in the electronic and optical properties of the films. Surface treatment with acetylacetone resulted in enhanced electrical conductivity over the investigated temperature range, while hexafluoroacetylacetone treatment improved the optical transparency. Both ligands also increased the work function of NiO, indicating their potential for tuning and improving energy level alignment in optoelectronic applications.

X-ray photoelectron spectroscopy (XPS) and time-of-flight secondary ion mass spectrometry (ToF-SIMS) were employed to investigate surface and interface chemical reactivity of NiO following ligand exposure. Ultraviolet photoelectron spectroscopy (UPS), conductivity measurements, and optical transmittance characterization were used to evaluate modifications in the electronic structure and optical behavior of the films before and after surface modification. These findings demonstrate that β-diketone surface functionalization provides an effective route for tuning the optoelectronic properties of NiO for next-generation optoelectronic and photovoltaic applications.

Amorphous carbon thin films exhibit a wide range of properties, such as chemical inertness, high hardness, and tunable optical properties. They are utilized in many different devices such as micro-supercapacitors, batteries, solar cells, sensors, semiconductor devices, and nanomembranes. A key challenge in the successful development of these applications lies in the precision tuning of synthesis and modification parameters to achieve desired material properties.

In this study, hydrogenated amorphous carbon (a-C:H) thin films were prepared by plasma-enhanced chemical vapor deposition (PECVD) of a cyclohexane precursor and subjected to ultraviolet-C (UVC) irradiation with a wavelength of 255nm to tune the film’s properties. The intensity of the irradiation light varied from 2.2 to 16.5 mW/cm². This wide range of irradiance of UVC light effectively altered the physical, chemical, and optical properties of a-C:H thin films.

The surface of a-C:H transformed from hydrophobic to hydrophilic under UVC irradiation. The surface became more hydrophilic with increased UV light intensity, reaching a minimum contact angle of 75.09° at the high intensity irradiation of 16.5 mW/cm². Atomic force microscopy (AFM) data showed a change in surface roughness under UVC irradiation. The surface roughness was reduced with increased UV intensity. The surface became the smoothest with a roughness of 0.202 nm when exposed to UVC irradiation at 16.5 mW/cm².

Fourier-transform infrared (FTIR) spectra exhibited a prominent absorption band between 3000–2800 cm^-1, corresponding to variousν CH_x stretching modes. Deconvolution of this band reveals three primary components: sp³ CH₃ asymmetric stretching (ν_as sp³ CH₃), sp³ CH₂ asymmetric stretching (ν_as sp³ CH₂), and sp³ CH₂ symmetric stretching (νs sp3 CH2). Additionally, low-intensity features observed at 1750–1500 cm⁻¹ are associated with C=C and C=O bonding. Following UVC irradiation, the FTIR spectral features shifted significantly. As the UV intensity increased, there was a decrease in the ν CH_x stretching modes and the appearance of C=O groups due to dehydrogenation and surface oxidation. Optical data indicated that UVC irradiation increased transparency and decreased density of the a-C:H films. The refractive index and extinction coefficient both decreased with an increase in UVC irradiance, reaching a minimum of 1.535 and 0.003, respectively, at 16.5 mW/cm². In contrast, the optical band gap broadened under UVC irradiance, reaching a maximum of 5.23 eV at the highest intensity of 16.5 mW/cm². The findings suggest that UVC post-treatment is a versatile tool for tuning the density, wettability, and optical constants of a-C:H films.

Wurtzite aluminum–scandium nitride (Al_1-xSc_xN) thin films are emerging materials for next–generation electronic and sensing technologies, yet achieving precise composition control and uniform deposition on complex three–dimensional structures remains a significant challenge. In this work, we report the ultrahigh–purity plasma–enhanced atomic layer deposition (PEALD) of Al_1-xSc_xN using a supercycle approach that alternates AlN and ScN constituent processes. The process employs trimethylaluminum (TMA), bis(ethylcyclopentadienyl)scandium chloride [ClSc(EtCp)₂], and N₂–H₂ plasma as co–reactants at substrate temperatures between 215 and 300 °C.

A 60.3 nm–thick Al_0.83Sc_0.17N film deposited at 300 °C on a {111}-oriented Pt bottom electrode on Si (100) exhibits clear ferroelectric switching behavior. The film shows switched polarization values (2P_r) of 163 µC cm^-2 and 139 µC cm^-2 under negative and positive pulsing, coercive fields as low as of ±3.3 MV cm⁻¹, and a dielectric constant of 12.8–13.8 at 100 kHz under ±10 V.

Structural characterization reveals that films grown on {111} Pt are fully c–axis (0001) oriented, demonstrating high crystalline quality even along the sidewalls of three–dimensional features. When deposited on single–crystal GaN, Al_0.83Sc_0.17N exhibits strong in–plane and out–of–plane ordering consistent with epitaxial growth. Deposition over narrow trench structures further confirms uniform, conformal coating. Collectively, these results show that PEALD enables high–quality Al_1-xSc_xN films suitable for advanced three–dimensional electronic and sensing applications.