This work presents a major advancement in mmWave Bulk Acoustic Wave (BAW) resonator technology by achieving a record-high Quality factor $(Q)$ of 184 at 51 GHz using a 35% Scandium alloyed Aluminum Nitride Overmoded Bulk Acoustic Resonator (ScAlN OBAR). Achieving high $Q$ at such elevated frequencies is extremely challenging due to intrinsic material losses and energy leakage. To address this major bottleneck for radio frequency (RF) front-end filter applications, we isolate and mitigate key loss contributors through a systematic design and fabrication of four OBAR variants. The final design not only demonstrates superior $Q$ performance but also maintains fabrication simplicity, standing out against competing technologies which require significantly more complex architectures to achieve comparable $Q$.

Scandium containing aluminum nitride (ScAlN) combines strong piezoelectricity and second-order nonlinearities with compatibility to CMOS backend processes, making it a promising material for integrated photonics. In this work, we demonstrate electro-optic modulation in high-concentration Sc\textsubscript{0.30}Al\textsubscript{0.70}N using Mach–Zehnder interferometer and ring resonator modulators fabricated on a CMOS-compatible platform. Devices were characterized under AC and DC excitation with lock-in detection, and simulation-calibrated measurements yielded an $r_{13}$ value of approximately 0.19 pm/V. While this coefficient is lower than values reported for ScAlN with similar Sc content, it was consistent across device geometries and reflects films grown under conditions optimized for piezoelectric rather than electro-optic performance. These results establish a clear baseline for the Pockels effect in highly Sc concentrated ScAlN and highlight the need for growth strategies specifically tailored to electro-optic applications in scalable photonic–electronic integration.

This work demonstrates an Overmoded Bulk Acoustic Resonator (OBAR) design that incorporates 35% Scandium doped Aluminum Nitride (Sc0.35Al0.65N) as the piezoelectric layer. The ScAlN OBAR presented here is a Bulk Acoustic Wave (BAW) resonator that excites a second overtone within a stack formed by a ScAlN layer and a set of alternating metallic layers. The metal electrodes act simultaneously as the acoustic cavity and as acoustic Bragg mirrors. Individual resonators are connected to each other by thick floating electrodes and top interconnects to form the devices demonstrated herein. The fabricated ScAlN OBAR with best performance exhibits a series resonant frequency of 51.3 GHz, electromechanical coupling ( $k_{t}^{2}$ ) of 6.1% and a Quality factor (Q) at series resonance of 108. The measurements of various ScAlN OBAR devices with different geometries show that Q is increasing as the perimeter and area of the individual resonator increases and $k_{t}^{2}$ is increasing as the number of resonators in series increases. Material losses and surface roughness with associated acoustic energy leakage are discussed as possible sources of damping in these mmWave resonators. The investigations trace a path for further technological improvement and show that the ScAlN OBAR is a promising device for mmWave acoustics and filtering applications. [2025-0071]

Scandium doped Aluminum Nitride (ScAlN) has become a piezoelectric material of interest for Bulk Acoustic Wave (BAW) resonators as it offers an intrinsically high electromechanical coupling (k(t)(2)). However, little is known about ScAlN at mm-wave frequencies. In this work, we demonstrate an innovative Overmoded Bulk Acoustic Resonator (OBAR) design that incorporates 35% Scandium doped Aluminum Nitride (Sc0.35Al0.65N) piezoelectric layer. The ScAlN OBAR presented herein is a BAW device that is excited in the 2(nd) overtone by means of the ScAlN layer and a stack of metal electrodes that act simultaneously as acoustic cavity and as acoustic Bragg mirrors. The fabricated device demonstrates k(t)(2) of 6.1% and Quality factor (Q) of 114 at 52 GHz - a substantial improvement in the k(t)(2). Q figure of merit of ScAlN acoustic resonators at mm-wave frequencies.

Although Sc doped AlN (ScAlN) has been used extensively in micro-electro-mechanical systems (MEMS) devices and more recently in optical devices, there have not been thorough studies of its intrinsic optical losses. Here we explore the optical losses of the Sc0.30Al0.70N waveguide system by observing racetrack resonator waveguide quality factors. Using a partial physical etch, we fabricate waveguides and extract propagation losses as low as 1.6 ± 0.3 dB/cm at wavelengths around 1550 nm, mostly dominated by intrinsic material absorption from the Sc0.30Al0.70N thin film layer. The highest quality factor of the resonators was greater than 87,000. The propagation loss value is lower than any value previously published and shows that this material can be broadly used in optical modulators without significant loss.

Surface acoustic wave spectroscopy has been established as non‐destructive and fast method for characterization of mechanical properties of surfaces and bulk materials in both research and industry. The present work shows that by application of a novel and robust aluminum nitride (AlN) coated piezoelectric contact sensor the advantages of the method can be extended from room temperature to at least 600°C. An overview of sensor concepts and applications of the method is discussed first, followed by theoretical and practical considerations for design and coating of a novel temperature stable contact sensor. After fabrication of such a sensor using magnetron sputtering, it was tested in a modified surface acoustic wave spectroscopy setup with an incorporated heating table concerning signal amplitude and frequency range. The AlN coated sensor was found to perform well up to 600°C, with temperature limited by the specification of the heating table. At room temperature, performance was acceptable when compared with a conventional contact sensor using a PVDF piezoelectric foil. Application of the high temperature capabilities of the setup was demonstrated by measuring temperature stability of hydrogen‐free amorphous carbon coatings (a‐C and ta‐C) depending on their sp 3 carbon ratio. In another example, high precision temperature dependent measurement of Young's modulus for ultrasonic fatigue test specimen was taken, achieving an accuracy better than 1%. Use of the developed sensor opens up new possibilities in material science for in situ study of temperature depending mechanical properties for coatings and surfaces.

This paper discusses the development of a reactive sputtering process for the deposition of epitaxially grown AlN films on Si(111) using a technology suitable for 8 '' substrates. X-ray diffraction (XRD) and rocking curves (RC) are used to determine the crystalline orientation. The influence of substrate temperature, target-substrate distance and target voltage on the full width at half maximum (FWHM) of the RC is investigated. The film deposition was performed on Si(111) wafers and on AlN-on-Si(111) templates prepared by metal organic chemical vapor deposition (MOCVD). Based on the sixfold symmetry identifiable in the pole figure of the AlN(302) plane reflections, oriented in-plane film growth on Si(111) was verified for the process. Best oriented films sputtered directly on Si(111) achieved for 500 nm AlN films featured a RC-FWHM of 0.93. of AlN(100) and 0.77. of AlN(002). Root mean square roughness (RMS) of the samples varied between 2.3 nm and 2.8 nm. The deposition rate was between 70 nm/min and 100 nm/min. Films deposited onto the MOCVD templates grew maintaining the crystalline quality of the MOCVD substrate, verified by the FWHM of the RC of in-plane and out-of-plane reflections.

Inline magnetron sputtering allows deposition of precise optical filters on large substrates. Examples of filters deposited on flat and curved glass substrates will be presented.

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.

Reactive magnetron sputter deposition is shown to be a suitable method for depositing Fluorine doped silica films for temperature compensated SAW devices.

This paper reports on how both the growth conditions and thickness of aluminum thin films impact the surface morphology and subsequent anodization behavior when sputtered onto Si and glass substrates up to a 1-mu m thickness, respectively. Specifically, the effects of oxygen incorporation during sputtering and variations between continuous vs. stepwise deposition are thoroughly investigated here. Previous studies demonstrated the tremendous impact of oxygen concentration while sputtering, which, in turn, allows minimizing the grain sizes for 200-nm-thick sputtered AlOx-films. The then anodized aluminum oxide (AAO) thin films can then be used, for instance to grow quasi defect-free, large-area gold nanorod arrays for plasmonic applications. The challenge when preparing thicker films as emphasized here, is to avoid gradients of oxygen concentration and grain size for any film thickness. We have developed reproducible protocols how to minimize such gradients: the deposition process is purposely interrupted after every 100/200/300-nm AlOx deposition step for approximately 5 min. to allow thermal relaxation under pure nitrogen atmosphere. The subsequent anodization and pore filling with gold then revealed highly improved properties for AAO-films up to the 1-mu m thickness, exhibiting a homogenous nanorod distribution with a very low number of defects.

Get PDF Email Share Share with Facebook Tweet This Post on reddit Share with LinkedIn Add to CiteULike Add to Mendeley Add to BibSonomy Get Citation Copy Citation Text D. Gloess, U. Hartung, A. Drescher, P. Frach, and H. Bartzsch, "Freeform and Laser Optical Coatings by Inline Magnetron Sputtering," in Optical Interference Coatings Conference (OIC) 2019, OSA Technical Digest (Optica Publishing Group, 2019), paper WB.2. Export Citation BibTex Endnote (RIS) HTML Plain Text Citation alert Save article

Sc x Al 1-x N is a promising material to expand the application range of nitride materials, since scandium increases the piezoelectric constants while retaining the crystalline wurtzite structure. In this work, stationary reactive pulse magnetron sputtering is used for the deposition of functional layers with a scandium content x = 0...0.44. Layer morphology, piezoelectric properties and breakdown voltage are studied XRD measurements reveal that high scandium content yields to a weak wurzite formation. The lattice constant dependent on the parameter x is calculated on the base of XRD data and the curve characteristic agrees with the density functional theory. The highest piezoelectric coefficient d 33 was observed at a scandium content of 36.6 %, it amounts to 27.5 pC/N. Parallel capacitor structures are generated by means of chlorine-basedICP etching and lift-off structuring of the top electrodes. Technological details of the structuring process are presented. The etch rate depends strongly on the scandium content. The permittivity was determined on the base of these test structures. It increases significantly with increasing scandium content. High capacitance values up to 7.4 nF were measured The adequate breakdown voltage of 51 V for scandium concentrations of x = 0.22 or higher suggest a use of such layers for integrated thin film capacitors in addition to well-tried piezoelectric applications.

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 n(e) =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 similar to 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 mu m. 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. (C) 2019 Optical Society of America under the terms of the OSA Open Access Publishing Agreement

A time-sequential working, spatially-multiplexed autostereoscopic 3D display design consisting of a fast switchable RGB-color filter array and a fast color display is presented. The newly-introduced 3D display design is usable as a multi-user display, as well as a single-user system. The wavelength-selective filter barrier emits the light from a larger aperture than common autostereoscopic barrier displays with similar barrier pitch and ascent. Measurements on a demonstrator with commercial display components, simulations and computational evaluations have been carried out to describe the proposed wavelength-selective display design in static states and to show the weak spots of display filters in commercial displays. An optical modelling of wavelength-selective barriers has been used for instance to calculate the light ray distribution properties of that arrangement. In the time-sequential implementation, it is important to avoid that quick eye or eyelid movement leads to visible color artifacts. Therefore, color filter cells, switching faster than conventional LC display cells, must distribute directed light from different primaries at the same time, to create a 3D presentation. For that, electric tunable liquid crystal Fabry–Pérot color filters are presented. They switch on-off the colors red, green and blue in the millisecond regime. Their active areas consist of a sub-micrometer-thick nematic layer sandwiched between dielectric mirrors and indium tin oxide (ITO)-electrodes. These cells shall switch narrowband light of red, green or blue. A barrier filter array for a high resolution, glasses-free 3D display has to be equipped with several thousand switchable filter elements having different color apertures.

AlxSc1-xN films were deposited by reactive pulse magnetron co-sputtering from aluminum and scandium targets without additional substrate heating at deposition rates between 100 and 150 nm/min. With increasing incorporation of scandium into the hexagonal wurtzite structure, the piezoelectric properties are drastically improved. The piezoelectric charge coefficient d(33) is increased from 8.4 pC/N for AlN up to 23.6 pC/N for AlxSc1-xN with 33% scandium. Between 35 and 43% scandium content a relative broad maximum with high piezoelectric coefficients between 26.9 and 273 pC/N was detected. A further increase of scandium concentration above 50% results in the formation of the cubic and centrosymmetric rock salt structure and therefore the complete loss of piezoelectric properties.By FE-SEM, XRD and TEM investigations it was shown that up to up to 43% scandium concentration the wurtzite structure becomes more and more disordered and the c/a ratio is decreased from 1.6 to 1.27. Nevertheless, no aluminum or scandium segregation could be detected by high resolution TEM investigations. The Young's modulus of the wurtzite phase is reduced with increasing scandium concentration from 340 GPa to 185 GPa. The drastic improvement of the piezoelectric properties can be explained by weakening of the chemical bonding and by high distortion of the wurtzite structure. (C) 2016 Elsevier B.V. All rights reserved.

Pulse magnetron sputtering is very well suited for the deposition of optical coatings. Due to energetic activation during film growth, sputtered films are dense, smooth and show an excellent environmental stability. Films of materials like SiO2, Al2O3, Nb2O5 or Ta2O5 can be produced with very little absorption and scattering losses and are well suited for precision optics. FEP's coating plant PreSensLine, a deposition machine dedicated for the development and deposition of precision optical layer systems will be presented. The coating machine (VON ARDENNE) is equipped with dual magnetron systems (type RM by FEP). Concepts regarding machine design, process technology and process control as well as in situ monitoring are presented to realize the high demands on uniformity, accuracy and reproducibility. Results of gradient and multilayer type precision optical coatings are presented. Application examples are edge filters and special antireflective coatings for the backlight of 3D displays with substrate size up to 300 x 400mm. The machine allows deposition of rugate type gradient layers by rotating a rotary table with substrates between two sources of the dual magnetron system. By combination of the precision drive (by LSA) for the substrate movement and a special pulse parameter variation during the deposition process (available with the pulse unit UBS-C2 of FEP), it is possible to adjust the deposition rate as a function of the substrate position exactly. The aim of a current development is a technology for the uniform coating of 3D-substrates and freeform components as well as laterally graded layers.

Aluminum nitride (AlN) is a piezoelectric material often used as thin film in SAW/BAW devices. Furthermore, there is an increasing interest in its use for energy harvesting applications. Despite it has a relatively low piezoelectric coefficient, it is a suitable choice for energy harvesting applications and due to its low dielectric constant and good mechanical properties. In addition, it is a lead-free material. The films were deposited by reactive pulsed magnetron sputtering using the Double Ring Magnetron DRM 400. This sputter source together with suitable powering and process control allows depositing piezoelectric AlN very homogeneously on 8" substrates with deposition rates of up to 200 nm/min. With the developed technology, film thicknesses of several ten microns are technically and economically feasible. Moreover, by adjusting process parameters accordingly, it is possible to tune properties, like film stress, to application specific requirements. Additionally, it is known that the doping of AlN with Scandium results in a significantly increased piezoelectric coefficient. The influence of process parameters and Sc concentration on film properties were determined by piezometer, pulse echo, SEM, XRD, EDS and nanoindentation measurements. Energy harvesting measurements were done using an electromechanical shaker system for the excitation of defined vibrations and a laservibrometer for determination of the displacement of the samples. The generated power was measured as function of electric load at resonance. An rms power of up to 140 mu W using AlN films and of 350 mu W using AlScN films was generated on Si test pieces of 8x80mm(2). Furthermore, energy harvesting measurements using manually bended steel strips of 75x25mm(2) coated with AlScN were carried out as well. When using only a single actuation, energy of up to 8 mu J could be measured. By letting the system vibrate freely, the damped vibration at resonance 50Hz resulted in a measured energy of 420 mu J.

Optical sensing based on plasmonic nanorod arrays witnesses an increased interest for device applications due to a manifold of benefits of these structures, such as broadband optical tunability and low-cost bottom-up fabrication. Key to this success is the assembly of nanorod antenna arrays mediated through high-quality anodized aluminum oxide (AAO) matrices. The present work reports the greatly improved fabrication of thin-film AAO matrices based on aluminum thin-films deposited by magnetron sputtering under controlled argon/oxygen atmosphere, and investigates the influence of oxygen on the aluminum morphology and hence AAO pore formation upon anodization. Such optimized templates then subsequently allow the fast and reproducible fabrication of nanorod arrays with a nearly 100% pore-filling degree, which is favorable in plasmonic applications, with the plasmonic properties greatly benefiting from homogeneous distances between neighboring nanorods. For an optimal oxygen content of 10–22 at.%, we find the long-axis plasmon resonance peak to show the least optical losses, confirming the optimized nanostructure fabrication and performance.