Structural and Dielectric Properties of Subnanometric Laminates of Binary Oxides

Abstract

Capacitors with a dielectric material consisting of amorphous laminates of Al2O3 and TiO2 with subnanometer individual layer thicknesses can show strongly enhanced capacitance densities compared to the bulk or laminates with nanometer layer thickness. In this study, the structural and dielectric properties of such subnanometer laminates grown on silicon by state-of-the-art atomic layer deposition are investigated with varying electrode materials. The laminates show a dielectric constant reaching 95 combined with a dielectric loss (tan δ) of about 0.2. The differences of the observed dielectric properties in capacitors with varying electrodes indicate that chemical effects at the interface with the TiN electrode play a major role, while the influence of the local roughness of the individual layers is rather limited.

Maxwell–Wagner Relaxation-Driven High Dielectric Constant in Al2O3/TiO2 Nanolaminates Grown by Pulsed Laser Deposition

“…Lower activation energies obtained for set-2 (i.e., for TiO 2 layers) compared to set-1 (i.e., for Al 2 O 3 layers) (Figures a,b) further corroborate the higher conductivity of TiO 2 layers compared to Al 2 O 3 layers, possibly due to a higher concentration of charge carriers at the surface/subsurface region of TiO 2 sublayers. − This observed conductivity contrast between TiO 2 and Al 2 O 3 sublayers promotes charge accumulation across interfaces and further supports M–W interfacial polarization in the subnanometric regime . Because the calculated activation energies of conduction for both the layers lie in a range from ∼0.11 to 0.21 eV, electron hopping via oxygen vacancies (OVs) can be assigned as the conduction mechanism in ATA NLs. , For TiO 2 layer conduction processes, the decrease in the activation energy from 0.16 to 0.11 eV with t s decreasing from ∼1 to 0.8 nm suggests an increased hopping probability of charge carriers in TiO 2 . On the contrary, the activation energy of Al 2 O 3 layer conduction remains almost constant at ∼0.21 eV indicating an equal rate of hopping for all the thicknesses .…”

“…In addition, the high cut-off frequency in these ATA NLs was realized by varying the concentration of charge carriers arising from semiconducting TiO 2 layers . Furthermore, the effect of the bottom electrode and the total NL thickness on the dielectric performance of these ATA NLs has also been studied. , Although the origin of high dielectric constant and high cut-off frequency is proposed to be the M–W type relaxation, a clear understanding of the M–W relaxation mechanism and its dependence on physical and chemical homogeneity of individual subnanometric layers across the interfaces is still missing.…”

Status of Al2O3/TiO2‐Based Antireflection and Surface Passivation for Silicon Solar Cells

“…Low densities of fast interface states near a midgap with a value of 4.85 Â 10 9 eV À1 cm À2 were achieved with a 40 nm nanolaminate comprising 0.8 nm Al 2 O 3 and 0.7 nm TiO 2 using ozone as the coreactant. [67] This sub-nanometer laminate on highly doped Si with more than 10 21 atoms cm À3 without annealing exhibited an oxide charge density of 3.72 Â 10 11 cm À2 , which was attributed to the contribution of the positive interface charges in the dielectric stack/Si system with TiN electrodes deposited by the ALD process at 450 C. [68] Table 1 shows the lifetimes of silicon wafers passivated with Al 2 O 3 /TiO 2 dual layers and nanolaminates according to each layer thickness. Most of the samples were evaluated based on FZ Si and Al 2 O 3 , and the TiO 2 thickness was not specifically indicated in the case of nanolaminates.…”

“…[ 67 ] This sub‐nanometer laminate on highly doped Si with more than 10 21 atoms cm −3 without annealing exhibited an oxide charge density of 3.72 × 10 11 cm −2 , which was attributed to the contribution of the positive interface charges in the dielectric stack/Si system with TiN electrodes deposited by the ALD process at 450 °C. [ 68 ]…”

Structural Evolution that Affects the Room-Temperature Internal Friction of Binary Oxide Nanolaminates: Implications for Ultrastable Optical Cavities

“…These two-dimensional composite thin films are extensively used in semiconductor devices, − electrochemical storage devices, and optical coatings. , Their unique properties arise from modifications to the environment of atoms at the nanometer to subnanometer scale. For example, in nanolaminates of Al 2 O 3 /TiO 2 and Al 2 O 3 /HfO 2 for microelectronics a dielectric constant κ higher than SiO 2 is obtained when the individual layer thickness is reduced to a few nanometers. The large interfacial area between layers also plays a critical role in modifying the structural properties of nanolaminates.…”