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Precise surface reflectance control at specific deep‐ultraviolet (DUV) wavelengths across wide angles is crucial for semiconductor inspection and lithography tools. The inherent challenges in designing DUV antireflective multilayers stem from limited transparent materials and the resultant fabrication complexity owing to numerous interfaces. Here, wide‐angle antireflective multilayers finely tuned to 248 nm designed using an active learning scheme is presented. The active learning scheme employing factorization machines (FM) identifies the optimal configurations for binary‐material‐based multilayers (AlF3/LaF3, AlF3/MgF2, and AlF3/Al2O3) with varying index contrasts, achieving minimal figure‐of‐merit (i.e., average angular reflectance) values at predetermined total thicknesses. High‐index‐contrast AlF3/Al2O3 multilayers are fabricated via atomic layer deposition, thus enabling the conformal coating of high‐numerical‐aperture (NA) lenses with atomic precision. An optimized AlF3/Al2O3 tri‐layer with a total thickness of 180 nm results in an average (0°–45°) reflectance of 0.4% on a CaF2 planar substrate and 0.6% on a CaF2 convex lens (NA = 0.47), similar to the performance of an ideal single‐layer coating requiring a practically unavailable refractive index. Phasor analysis, which considers only first‐order reflections between adjacent layers, supports the benefits of high‐index‐contrast binary materials and the use of the FM‐based active learning scheme in antireflective multilayer design. [ABSTRACT FROM AUTHOR]

To date, various optimization algorithms have been used to design non-intuitive photonic structures with unconventional optical performance. Good training datasets facilitate the optimization process, particularly when an objective function has a non-convex shape containing multiple local optima in a continuous parametric space. Herein, we developed a discrete-to-continuous optimization algorithm and confirmed its validity by designing and fabricating deep-ultraviolet antireflective MgF2/LaF3 multilayers. For discrete optimization, a multilayer was encoded into a binary vector with multiple bits; a 10 nm thick MgF2 or LaF3 layer was assigned a binary digit of 0 or 1, respectively. Using the binary-based training datasets, a factorization machine formulated a surrogate function, which discovered the ground binary vector representing a near-optimal figure of merit. Then, the figure of merit was refined through continuous optimization (e.g., using an interior-point method) of the ground binary vector. MgF2/LaF3 multilayers with a variety of bit levels were created to attain a minimum average angular (0°–45°) reflectance at 193 nm. A MgF2/LaF3 multilayer optimized at ten bits (i.e., a total thickness of approximately 100 nm) yielded an average reflectance of 0.2%, which agreed well with the experimental results. Moreover, an integrated ray-wave optics simulation predicted that a single CaF2 plano-convex lens coated with the optimized multilayer could exhibit a transmittance of 99.7%. The developed optimization approach will be widely applicable to any photonic structures that can represent a binary vector with multiple bits, such as microwave metasurfaces, in addition to being useful for producing ideal optical multilayers. [ABSTRACT FROM AUTHOR]

We investigated the effect of ZnO layer thickness on the optical and electrical properties of ZnO/Ag/ZnO multilayer films deposited on glass substrates. The transmission window became wider and shifted toward the lower energy side with increasing ZnO thickness. The ZnO/Ag/ZnO (40 nm/18.8 nm/40 nm) multilayer sample showed transmittance of ~96% at 550nm. As the ZnO thickness was increased from 8 nm to 80 nm, the carrier concentration gradually decreased from 1.74 × 10 cm to 4.33 × 10 cm, while the charge mobility varied from 23.8 cm/V-s to 24.8 cm/V-s. With increasing ZnO thickness, the samples exhibited similar sheet resistances of 3.6 Ω/sq to 3.9 Ω/sq, but the resistivity increased by a factor of 4.58. The samples showed smooth surfaces with root-mean-square roughness in the range of 0.47 nm to 0.94 nm. Haacke's figure of merit (FOM) was calculated for all the samples; the ZnO (40 nm)/Ag (18.8 nm)/ZnO (40 nm) multilayer produced the highest FOM of 148.9 × 10 Ω. [ABSTRACT FROM AUTHOR]

We report on the development of high-performance transparent conducting GaSnO (GTO)/Ag/GTO multilayer electrodes for display applications. The optical and electrical characteristics of the GTO/Ag/GTO multilayers were investigated as functions of GTO layer (d GTO) and Ag layer (d Ag) thicknesses. With increasing d GTO from 10 to 50 nm, the sheet resistance slightly increased from 3.83 to 4.81 Ω/sq, the carrier concentration decreased from 4.76 × 1022 to 1.12 × 1022 cm−3, and the mobility (μ) slightly changed from 10.7 to 10.3 cm2/V. The 40 nm-thick GTO-based multilayer exhibited the mean transmittance (T av) of 91.6% and had the Haacke's figure of merit (FOM) of 87.84 × 10−3 Ω−1. The μ value increased from 7.97 to 11.67 cm2/V and sheet resistance varied from 7.81 to 3.47 Ω/sq as increasing d Ag from 9 to 15 nm. The T av of the GTO (40 nm)/Ag/GTO (40 nm) samples decreased from 94.5% to 84.9% with increasing d Ag. The optical bandgaps of the GTO and GTO/Ag/GTO (40 nm/12 nm/40 nm) films were estimated to be 4.06 and 3.94 eV, respectively. Finite-difference time-domain calculations were conducted to explain the d Ag and d GTO dependent transmittance of the GTO/Ag/GTO samples. With the phasor analyses, the d GTO dependence of the transmittance of GTO/Ag (12 nm)/GTO multilayers is described and discussed. Furthermore, the optical and electrical features of the optimal GTO/Ag/GTO (40 nm/12 nm/40 nm) electrode are compared with those of sputter-deposited 92 nm-thick indium tin oxide (ITO) films. [ABSTRACT FROM AUTHOR]

Sputter-deposited SrVO x was employed to create transparent conducting SrVO x /Ag/SrVO x films and their optical-electrical properties were examined as functions of SrVO x and Ag thicknesses. With the increase in the thickness of SrVO x films from 15 to 45 nm in the SrVO x /Ag/SrVO x films, the carrier concentration, sheet resistance, and electron mobility were in the range of 2.0 × 1022 − 1.03 × 1022 cm−3, 3.15−2.76 Ω/sq., and 21.99−19.76 cm2/Vs, respectively. The 25 nm-thick SrVO x -based multilayer gave the highest average transmittance (T av) of 91.5%. The 25 nm-thick SrVO x -based multilayer gave the largest Haacke's figure of merit (FOM) of 144.5 × 10−3 Ω−1. With increasing Ag layer thickness from 9 to 21 nm, the carrier concentration, mobility and sheet resistance of the multilayers were in the range of 1.05 × 1022 − 1.99 × 1022 cm−3, 15.56−22.46 cm2/Vs, and 1.97−6.48 Ω/sq., respectively. The T av of the SrVO x (25 nm)/Ag/SrVO x (25 nm) multilayer gradually decreased from 95.5 to 82.6% with the Ag layer thickness. The rigorous coupled-wave (RCW) simulations were performed to describe the wavelength-dependent transmittance characteristics of the SrVO x (25 nm)/Ag (15 nm)/SrVO x (25 nm) samples. Based on the phasor examination, the effect of the SrVO x film thickness on the transmittance characteristics of the multilayers is described and discussed. [ABSTRACT FROM AUTHOR]

To replace thick ITO single layer electrodes, ZnSnO (ZTO)/Ag/indium tin oxide (ITO) multilayer films were investigated as a function of Ag layer thickness. The ZTO/Ag/ITO films showed maximum transmittance in the range of 79.4–89.2%, depending on the Ag layer thickness. The relationship between transmittance and Ag thickness was simulated using the scattering matrix method to understand the high transmittance. As the Ag thickness increases from 6 to 14 nm, the carrier concentration increases from 4.12 × 10 21 to 1.11 × 10 22 cm −3 and the mobility increases from 8.14 to 17.4 cm 2 /V s. The ZTO (20 nm)/Ag (10 nm)/ITO (30 nm) multilayer films had a sheet resistance of 9 Ω/sq. The ZTO/Ag/ITO multilayer had Haacke’s figure of merit of 28.3 × 10 –3 Ω –1 . The ZTO/Ag/ITO films deposited on PET substrates showed dramatically improved mechanical flexibility when subjected to bending test compared to 60 nm-thick ITO single layer electrodes. [ABSTRACT FROM AUTHOR]

We report on the formation of highly transparent and low conductance TiO 2 /Ag/TiO 2 multilayer films with high figure of merit (FOM). The optical and electrical properties of the multilayer films were investigated as a function of Ag layer thickness. As the Ag thickness increased, the transmission window narrowed and the transmittance was gradually lowered. The TiO 2 /Ag/TiO 2 multilayer films have the highest transmittance of 86.3–97% at 591 nm for different Ag thicknesses. The relationship between transmittance and TiO 2 thickness was simulated using the scattering matrix method to understand the abnormally high transmittance. As the Ag thickness increased from 15 to 25 nm, the carrier concentration of the TiO 2 /Ag/TiO 2 samples gradually increased from 6.18×10 21 to 1.07×10 22 cm −3 and the mobility also increased from 16.7 to 25.2 cm 2 /V-s. Meanwhile, the sheet resistance slightly decreased from 6.17 to 2.27 Ω⧸sq with the Ag thickness. The TiO 2 /Ag/TiO 2 multilayer (with Ag thicknesses of 17–21 nm) had Haacke׳s FOMs of 121×10 −3 –157.2×10 –3 Ω −1 . [ABSTRACT FROM AUTHOR]

We report on the optimization of the optical and electrical properties of IGZO/Ag/IGZO multilayer films as a function of IGZO thickness. The transmission window slightly widened and shifted toward lower energies with increasing IGZO thickness. The IGZO(39 nm)/Ag(19 nm)/IGZO(39 nm) showed transmittance 88.7% at 520 nm. The optical transmittance spectra were examined by finite-difference time-domain (FDTD) simulations. The carrier concentration decreased from 1.73 × 10 22 to 4.99 × 10 21 cm −3 with increasing the IGZO thickness, while the charge mobility insignificantly changed from 19.07 to 19.62 cm 2 /V. The samples had sheet resistances of 4.17–4.39 Ω/sq with increasing IGZO thickness, while the resistivity increased from 1.89 × 10 −5 to 6.43 × 10 −5 Ω cm. The 39 nm-thick IGZO multilayer sample had a smooth surface with a root mean square roughness of 0.63 nm. The IGZO(39 nm)/Ag(19 nm)/IGZO(39 nm) multilayer showed a Haacke's FOM of 49.94 × 10 −3 Ω −1 . [ABSTRACT FROM AUTHOR]