Partha Sarathi Padhi

Recently, Al₂O₃/TiO₂ nanolaminates (ATA NLs) have emerged as promising materials because of their excellent optical, mechanical, and dielectric properties. However, as individual sublayer thicknesses (t_s) decrease into the subnanometer range, the impact of interfacial structure evolution on performance degradation remains poorly understood. Here, we have fabricated a series of amorphous subnanometric ATA NLs, with t_s values ranging from ∼1 to 0.17 nm, using atomic layer deposition (ALD) and systematically investigated how interfacial evolution affects their structural, electronic, and dielectric properties, particularly their Maxwell–Wagner (M–W) relaxation behavior. The XRR and TEM measurements of NLs confirm the formation of artificial periodic structures with discrete sublayers as thin as ∼0.67 nm. The NL with a t_s of 0.67 nm exhibited enhanced M–W interfacial polarization-assisted high k (∼230) and low loss (∼0.07) values, whereas the submonolayer systems suffered from degraded dielectric performance. A comprehensive suite of characterization techniques revealed a critical transition in interface morphology, sublayer density, interface chemistry, and functionality in dielectric behavior near the monolayer thickness regime (t_s ≈ 0.35 nm), marking a transition from continuous-to-discontinuous layer growth with an increased level of intermixing. Electronic structure analyses revealed an associated redistribution of Ti³⁺ and oxygen vacancy-induced in-gap states and strong interfacial interdiffusion-driven Al–Ti–O compound formation in the submonolayer regime. These chemical changes from the hybridized electronic environments detrimentally affect dielectric properties due to compromised interfacial confinement. These findings establish a t_s of ≈0.35 nm as the practical lower bound for maintaining atomically discrete oxide layers, underscoring the pivotal role of nanoscale interface engineering and defect control in optimizing dielectric behavior in ultrathin oxide heterostructure-based devices.

Yttrium doped hafnia (Y-doped HfO2) thin film based devices have recently shown their potential for advanced nanoelectronics applications. Here, we report the fabrication of device-grade Hf(1−x)YxO2 (x = 0, 0.10, and 0.20) thin films on both Si(100) and platinized silicon substrates using an optimized Nd:YAG pulsed laser deposition system, wherein detailed structural and compositional characterizations were carried out to establish a structural-dielectric property correlation. The capacitance-frequency (C–F), capacitance-voltage (C–V), and current-voltage (I–V) measurements of these as-grown films were carried out in Pt top-bottom electrode-based metal-insulator-metal capacitor configuration. The increase in high frequency (1 MHz) dielectric constant values from ∼24 to 38, with an increase in Y doping from x = 0 to 0.20, is assigned to the phase transition from pure monoclinic to pure cubic configuration, as confirmed from grazing incidence x-ray diffraction and high resolution transmission electron microscopy measurements. However, the increment in low-frequency dielectric loss (at 100 Hz) and leakage current density values (at 1 V applied bias) from ∼0.6 to 35 and from ∼2.5 × 10−5 to 5.3 × 10−3 A/cm2, respectively, with increasing Y doping is attributed to the enhancement in yttrium-induced oxygen vacancy concentration in the hafnia matrix, as confirmed by x-ray photoelectron spectroscopy measurements. These tailorable device parameters make Y-doped hafnia a promising candidate for next-generation nanoelectronics applications.

Enhanced interface confined carrier relaxation and transport in an Al ₂ O ₃ /TiO ₂ nanolaminate, from a suitable combination of sublayer and cap layer thicknesses, is promising for high density energy storage applications.

Maxwell–Wagner relaxation dominated Al2O3/TiO2 nanolaminates (ATA NLs) have recently demonstrated their potential for high-density energy storage applications. In this report, we have unraveled the defect-mediated transport mechanisms prevailing in Al2O3/TiO2 sub-nanometric laminates. Temperature-dependent ac conductivity measurements revealed the signature of small polaron hopping in TiO2 active layers and trap-assisted tunneling transport through Al2O3 barrier layers, which was corroborated by resonant photoelectron spectroscopy and temperature-dependent current–voltage measurement. The polaronic defect states, found ∼1 eV below the Fermi level, served as the hopping centers and leakage paths for current. The signature of quantum tunneling transport and the negative differential conductance observed toward higher electric field was attributed to the splitting of delocalized minibands. These transport properties of Al2O3/TiO2 nanolaminates will help in tailoring these materials for next-generation storage capacitors.

Considering the potential applications of Al2O3/TiO2 nanolaminates (ATA NLs) in storage capacitors, device-grade ATA NLs are fabricated using an ALD system, wherein the effect of precursor purging time on interfacial, and dielectric properties is thoroughly investigated. With an increase in half-cycle purging time from 2 to 4 s, the observed improvement in interface quality and sublayer density of these NLs is ascribed to the efficient removal of reaction by-products and impurities. Moreover, with an increase in purge time from 2 to 4 s, the increase in dielectric constant and concurrent decrease in dielectric loss from ∼132 to 154 and from ∼0.29 to 0.2, respectively, are primarily assigned to the improvement in sublayer conductivity contrast assisted Maxwell–Wagner interfacial polarization across Al2O3/TiO2 interfaces. The NL based devices fabricated at 4 s purging time, exhibited a capacitance density of ∼18.94 fF/μm2, low equivalent oxide thickness of ∼1.82 nm, and reduced leakage current density of ∼3.04 × 10−5 A/cm2 at 2 V applied bias, which demonstrates its suitability as high-k materials for energy storage applications. Furthermore, this study not only gives an insight of the purging time induced growth chemistry of ATA NLs but also explores the possibility of improving its dielectric performance essential for multifaceted applications.