Combined 'moth-eye' structured and graded index-layer anti-reflecting coating for high index glasses.

We present a hybrid antireflective coating (ARC) providing a complete continuous graded refractive index (GRIN) transition from a high-index substrate down to ambient air. The ARC comprises a first GRIN layer of dense silicon-oxy-nitride with a varying, height adjusted material composition. Secondly, a layer of quasi-periodic nanopillars imitating AR-"moth-eye structure" is added to the dense GRIN layer. Demonstrated on a high index glass with a refractive index of ne=1.73 the hybrid GRIN-ARC is applicable to a broad material selection and allows to eliminate any step-like transition up to a refractive index of the substrate of ∼2.0. The ARC offers antireflective properties for large incidence angles and over an extremely broad spectrum ranging from 400 nm up to 2.5 µm. Compared to the sole substrate, the hybrid GRIN-ARC results in an increase of transmittance of more than 10% in the maximum, and more than 6% in the peripheral regions of the spectrum.

High Rate Deposition of Piezoelectric AlScN Films by Reactive Magnetron Sputtering from AlSc Alloy Targets on Large Area.

This paper reports on the deposition and characterization of piezoelectric AlXSc1-XN (further: AlScN) films on Si substrates using AlSc alloy targets with 30 at.% Sc. Films were deposited on a Ø200 mm area with deposition rates of 200 nm/min using a reactive magnetron sputtering process with a unipolar-bipolar hybrid pulse mode of FEP. The homogeneity of film composition, structural properties and piezoelectric properties were investigated depending on process parameters, especially the pulse mode of powering in unipolar-bipolar hybrid pulse mode operation. Characterization methods include energy-dispersive spectrometry of X-ray (EDS), X-ray diffraction (XRD), piezoresponse force microscopy (PFM) and double-beam laser interferometry (DBLI). The film composition was Al0.695Sc0.295N. The films showed good homogeneity of film structure with full width at half maximum (FWHM) of AlScN(002) rocking curves at 2.2 ± 0.1° over the whole coating area when deposited with higher share of unipolar pulse mode during film growth. For a higher share of bipolar pulse mode, the films showed a much larger c-lattice parameter in the center of the coating area, indicating high in-plane compressive stress in the films. Rocking curve FWHM also showed similar values of 1.5° at the center to 3° at outer edge. The piezoelectric characterization method revealed homogenous d33,f of 11-12 pm/V for films deposited at a high share of unipolar pulse mode and distribution of 7-10 pm/V for a lower share of unipolar pulse mode. The films exhibited ferroelectric switching behavior with coercive fields of around 3-3.5 MV/cm and polarization of 80-120 µC/cm².

Sputter deposition of stress-controlled piezoelectric AlN and AlScN films for ultrasonic and energy harvesting applications.

This paper reports on the deposition and characterization of piezoelectric AlN and AlXSc1-XN layers. Characterization methods include XRD, SEM, active thermo probe, pulse echo, and piezometer measurements. A special focus is on the characterization of AlN regarding the mechanical stress in the films. The stress in the films changed between -2.2 GPa (compressive) and 0.2 GPa (tensile) and showed a significant dependence on film thickness. The cause of this behavior is presumed to be the different mean grain sizes at different film thicknesses, with bigger mean grain sizes at higher thicknesses. Other influences on film stress such as the sputter pressure or the pulse mode are presented. The deposition of gradient layers using those influences allowed the adjustment of film stress while retaining the piezoelectric properties.

Sputter deposition of silicon oxynitride gradient and multilayer coatings.

The optical properties of silicon oxynitride films deposited by reactive dc magnetron sputtered films have been investigated. In particular the absorption characteristics of silicon nitride thin films in the visible spectrum and their optical bandgap were analyzed with regard to their composition and deposition properties. It can be shown that there is a significant difference between the absorption in the visible spectrum and the optical bandgap for these layers. The influence of unipolar and bipolar pulse modes on the optical layer properties is presented. The extinction coefficient for silicon nitride single layers could be reduced to a value of 2 x 10(-4) at 500 nm without external heating. There is also the dependence of the absorption of silicon oxynitride layers on the discharge voltage. We present the resulting spectra of rugate and edge filters that consist of these layers and offer lower absorption than single layers.