Harmonic surface acoustic waves on gallium nitride thin films

ABSTRACTGallium nitride (GaN) is a robust piezoelectric semiconductor with excellent thermal and chemical stability, making it an attractive material for surface acoustic wave (SAW) sensors operating in high temperature and harsh environments. The sensitivity of SAW devices is proportional to the square of the operating frequency. Therefore, high operating frequencies into the GHz regime are desirable for SAW sensors. For GaN, this requires sub-micron interdigital transducers (IDTs) when devices are designed to operate at the fundamental Rayleigh mode frequency. The necessity for sub-micron IDTs can increase fabrication costs and complexity. By designing SAW devices to operate at harmonic frequencies, GHz operation can be realized with relatively large IDTs, resulting in simpler and more cost effective solutions for GaN based SAW sensors. Devices have previously been designed to operate at the 5th and higher harmonics on lithium niobate, but there are no reports of using this technique on GaN in the literature. In this study, GaN thin films have been grown via metal organic vapor phase epitaxy on sapphire substrates. SAW devices designed to operate at the fundamental frequency and higher harmonics have been fabricated and measured. Operating frequencies greater than 2 GHz have been achieved using IDTs with 5 μm fingers. In addition, reduction of electromagnetic feedthrough around the 5th and 7th harmonic is demonstrated through varying ground electrode geometries.

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Double flow reversal in thin liquid films driven by megahertz-order surface vibration

Proceedings of The Royal Society A Mathematical Physical and Engineering Sciences ◽

10.1098/rspa.2013.0765 ◽

2014 ◽

Vol 470 (2169) ◽

pp. 20130765 ◽

Cited By ~ 26

Author(s):

Amgad R. Rezk ◽

Ofer Manor ◽

Leslie Y. Yeo ◽

James R. Friend

Keyword(s):

Thin Films ◽

Acoustic Waves ◽

Surface Acoustic Waves ◽

Intermolecular Forces ◽

Liquid Films ◽

Thin Liquid Films ◽

Propagation Direction ◽

Flow Reversal ◽

Order Surface ◽

Over Time

Arising from an interplay between capillary, acoustic and intermolecular forces, surface acoustic waves (SAWs) are observed to drive a unique and curious double flow reversal in the spreading of thin films. With a thickness at or less than the submicrometre viscous penetration depth, the film is seen to advance along the SAW propagation direction, and self-similarly over time t 1/4 in the inertial limit. At intermediate film thicknesses, beyond one-fourth the sound wavelength λ ℓ in the liquid, the spreading direction reverses, and the film propagates against the direction of the SAW propagation. The film reverses yet again, once its depth is further increased beyond one SAW wavelength. An unstable thickness region, between λ ℓ /8 and λ ℓ /4, exists from which regions of the film either rapidly grow in thickness to exceed λ ℓ /4 and move against the SAW propagation, consistent with the intermediate thickness films, whereas other regions decrease in thickness below λ ℓ /8 to conserve mass and move along the SAW propagation direction, consistent with the thin submicrometre films.

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Changes in catalytic activities of Cu thin films by surface acoustic waves propagated on ferroelectric LiNbO3

Journal of the Chemical Society Chemical Communications ◽

10.1039/c39900000296 ◽

1990 ◽

pp. 296 ◽

Cited By ~ 5

Author(s):

Yasunobu Inoue ◽

Masahiko Matsukawa

Keyword(s):

Thin Films ◽

Acoustic Waves ◽

Surface Acoustic Waves ◽

Catalytic Activities

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Notice of Removal: Comparison between Ir, Ir0.85Rh0.15 and Ir0.7 Rh0.3 thin films as electrodes for surface acoustic waves applications above 800 °C in air atmosphere

2017 IEEE International Ultrasonics Symposium (IUS) ◽

10.1109/ultsym.2017.8091906 ◽

2017 ◽

Author(s):

Amine Taguett ◽

Thierry Aubert ◽

Omar Elmazria ◽

Florian Bartoli ◽

Marc Lomello ◽

...

Keyword(s):

Thin Films ◽

Acoustic Waves ◽

Surface Acoustic Waves ◽

Air Atmosphere

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Microfluidic pumps employing surface acoustic waves generated in ZnO thin films

Journal of Applied Physics ◽

10.1063/1.3068326 ◽

2009 ◽

Vol 105 (2) ◽

pp. 024508 ◽

Cited By ~ 54

Author(s):

X. Y. Du ◽

Y. Q. Fu ◽

J. K. Luo ◽

A. J. Flewitt ◽

W. I. Milne

Keyword(s):

Thin Films ◽

Acoustic Waves ◽

Surface Acoustic Waves ◽

Zno Thin Films

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Elastic Constants of Diamond-Like Carbon Films by Surface Brillouin Scattering

MRS Proceedings ◽

10.1557/proc-593-311 ◽

1999 ◽

Vol 593 ◽

Cited By ~ 5

Author(s):

A.C. Ferrari ◽

J. Robertson ◽

R. Pastorelli ◽

M.G. Beghi ◽

C.E. Bottani

Keyword(s):

Thin Films ◽

Amorphous Carbon ◽

Elastic Constants ◽

Acoustic Waves ◽

Brillouin Scattering ◽

Surface Acoustic Waves ◽

Carbon Films ◽

Diamond Like Carbon ◽

Amorphous Carbon Films ◽

Tetrahedral Amorphous Carbon

ABSTRACTThe elastic constants of thin Diamond-Like Carbon (DLC) films supply important information, but their measurement is difficult. Standard nanoindentation does not directly measure the elastic constants and has strong limitations particularly in the case of hard thin films on softer substrates, such as tetrahedral amorphous carbon on Si. Surface acoustic waves provide a better mean to investigate elastic properties. Surface Brillouin scattering (SBS) intrinsically probes acoustic waves of the wavelength which is appropriate to test the properties of films in the tens to hundreds of nanometers thickness range. SBS can be used to derive all the isotropic elastic constants of hard-on-soft and soft-on-hard amorphous carbon films of different kinds, with thickness down to less than 10 nm. The results help to resolve the previous uncertainties in mechanical data. The Young's modulus of tetrahedral amorphous carbon (ta-C) turns out to be lower than that of diamond, while the moduli of hydrogenated ta-C (ta-C:H) are considerably lower than those of ta-C because of the weakening effect of C-H bonding.

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LASER-INDUCED SURFACE ACOUSTIC WAVES FOR THIN FILM CHARACTERIZATION

Acta Polytechnica CTU Proceedings ◽

10.14311/app.2020.27.0057 ◽

2020 ◽

Vol 27 ◽

pp. 57-61

Author(s):

Radim Kudělka ◽

Lukáš Václavek ◽

Jan Tomáštík ◽

Sabina Malecová ◽

Radim Čtvrtlík

Keyword(s):

Thin Films ◽

Film Thickness ◽

Young’S Modulus ◽

Acoustic Waves ◽

Young's Modulus ◽

Surface Acoustic Waves ◽

Laser Pulses ◽

Data Application ◽

Thin Film Characterization ◽

Short Laser Pulses

Knowledge of mechanical properties of thin films is essential for most of their applications. However, their determination can be problematic for very thin films. LAW (Laser-induced acoustic waves) is a combined acousto-optic method capable of measuring films with thickness from few nanometers. It utilizes ultrasound surface waves which are excited via short laser pulses and detected by a PVDF foil. Properties such as Young’s modulus, Poisson’s ratio and density of both the film and the substrate as well as film thickness can be explored.Results from the LAW method are successfully compared with nanoindentation for Young’s modulus evaluation and with optical method for film thickness evaluation and also with literature data. Application of LAW for anisotropy mapping of materials with cubic crystallographic lattice is also demonstrated.

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