Scanning-electron-microscope observations of propagating acoustic waves in surface acoustic wave devices

Eberharter, G.; Feuerbaum, H.P.

doi:10.1063/1.92044

Cited by 41 publications

(20 citation statements)

References 3 publications

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“…Despite the ability to quantitatively measure the out-of-plane vibration amplitude, optical interferometric methods are unable to measure in-plane vibration components. One competing approach is the observation of the electric field associated with SAW propagation in piezoelectric substrates [4], [5], [6], [7]: in scanning electron microscopy (SEM) observations, electrons illuminate the surface under investigation and secondary electrons generated closest to the surface are collected to create an image representative of surface characteristics. Electric fields on the surface under investigation modulate the secondary electron path and hence the image observed: SAW propagating is observed using SEM.…”

Section: Context and Motivationmentioning

confidence: 99%

Mapping acoustic field distributions of VHF to SHF SAW transducers using a Scanning Electron Microscope

Godet

Friedt

Dembélé

et al. 2016

2016 European Frequency and Time Forum (EFTF)

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Mapping the energy distribution of Surface Acoustic Wave (SAW) devices operating in the Very High Frequency (VHF) and Super-High Frequency (SHF) range provides a quantitative indicator of energy confinement, a core parameter when addressing low loss filters or high quality factor resonators. We here demonstrate the use of Scanning Electron Microscopy (SEM) for mapping Rayleigh wave acoustic field and shear transverse wave (STW) propagating on quartz. Furthermore, the availability of Focused Ion Beam (FIB) for milling the piezoelectric substrate allows for creating obstacles on the acoustic path and hence tune the acoustic wave propagation direction by reflecting the waves along directions which might otherwise exhibit poor electromechanical coupling. I. CONTEXT AND MOTIVATIONAcoustic field distribution in surface acoustic wave (SAW) devices relates to acoustic energy confinement and hence acoustic losses (in filters and delay lines) or quality factor (in resonators). Classical mapping techniques are based on optical interferometry [1], [2], [3], in which crystalline lattice motion associated with SAW propagation is detected in an interferometer setup with the SAW surface acting as one of the arm end. Despite the ability to quantitatively measure the out-of-plane vibration amplitude, optical interferometric methods are unable to measure in-plane vibration components. One competing approach is the observation of the electric field associated with SAW propagation in piezoelectric substrates [4], [5], [6], [7]: in scanning electron microscopy (SEM) observations, electrons illuminate the surface under investigation and secondary electrons generated closest to the surface are collected to create an image representative of surface characteristics. Electric fields on the surface under investigation modulate the secondary electron path and hence the image observed: SAW propagating is observed using SEM.In this presentation, we use a SEM for the observation of Rayleigh SAW on lithium niobate and shear transverse waves (STW) propagating on quartz. In all cases, we focus on delay line geometries: despite not exhibiting a standing wave pattern as observed on resonators, the propagating wave is readily observed in both configurations. The reason for selecting these two experimental setups as appropriate to emphasize some advantages of the SEM approach over the optical characterization methods are in the former case the wavelength of the device -operating at 2.45 GHz with an acoustic velocity of 3992 m/s [8] -exhibits a wavelength of 1.6 µm or only 2 to 5 optical wavelengths, and in the latter case the shear polarization of the wave which does not exhibit out-of-plane displacement component. In all cases, we have also observed that SEM imaging speed -a few seconds at most -is greatly improved over the raster scanning technique of the optical interferometer which always last a few minutes to hours : a 1024×768 pixel SEM image requires an acquisition time of 122 ms, allowing much faster sampling rates than scanning probe techniqu...

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Section: Context and Motivationmentioning

confidence: 99%

Mapping acoustic field distributions of VHF to SHF SAW transducers using a Scanning Electron Microscope

Godet

Friedt

Dembélé

et al. 2016

2016 European Frequency and Time Forum (EFTF)

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“…Unless faster SAW modes [1], [2] or materials [3] are found to be applicable on an industrial scale, submicron characterization tools have to be employed. The most common methods are based on optical probes [4], [5], which have the inherent disadvantage of the diffraction limited lateral resolution, electron probes [6], and more recently X-ray diffraction [7].…”

Section: Introductionmentioning

confidence: 99%

AFM observation of surface acoustic waves emitted from single symmetric SAW transducers

Hesjedal

Behme

2001

IEEE Trans. Ultrason., Ferroelect., Freq. Contr.

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We report the first experimental observation of surface acoustic waves (SAWs) launched from a single symmetric SAW transducer, employing scanning acoustic force microscopy (SAFM). SAFM is a simple technique for the imaging of complex interdigital transducer (IDT) radiation patterns with nanometer lateral resolution. We demonstrate submicron lateral resolution and high sensitivity by investigating a single excitation element on a weakly coupling substrate (GaAs), visualizing the launched wave and second-order effects.

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“…It cannot be considered as a truly non-contact method, as it can significantly influence the sample under study [48], although techniques have been developed to minimize the effect [49]. In fact, many of the available microscopy techniques, such as scanning electron microscopy (SEM) [50], have been adapted to study also surface vibrations. In addition to various scanning probe microscopy techniques, there have been attempts to visualize surface vibrations also with several other more exotic techniques, some of which are not non-destructive or non-contact [51][52][53].…”

Section: Optical Characterization Of Surface Vibrationsmentioning

confidence: 99%

Measurement of evanescent wave properties of a bulk acoustic wave resonator [Letters]

Kokkonen

Meltaus

Pensala

et al. 2012

IEEE Trans. Ultrason., Ferroelect., Freq. Contr.

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Aalto University publication series DOCTORAL DISSERTATIONS 112/2014 © Kimmo Kokkonen AbstractThe research summarized in this dissertation focuses on the development of a heterodyne scanning laser interferometer and of data-analysis techniques for the characterization and analysis of the surface vibration fields in microacoustic devices and test structures.The heterodyne laser interferometer enables a phase-sensitive, absolute-amplitude detection of the out-of-plane component of a surface vibration field, with a minimum detectable amplitude of less than a picometer, while the lateral resolution is better than 1 micrometer. The instrument features a flat frequency response up to 6 GHz.The phase-sensitive absolute-amplitude data enables the visualization of the actual wave behavior in electromechanical components and test structures, but more importantly, it is the basis for further analysis. The research instrument is applied to the study of electroacoustic devices based on surface acoustic wave (SAW) and bulk acoustic wave (BAW) technologies. Two novel SAW devices are studied in detail: a phononic crystal (PnC) structure and a scattering structure resulting in a random wave field. PnCs are acoustic metamaterials that can provide engineered material properties. The laser interferometric measurements were amongst the first to directly characterize the wave interaction with the PnC. SAW slowness curves of an anisotropic substrate material are extracted by measuring and analyzing the scattered random wave field. Data analysis methods are developed further in the context of BAW research by experimentally addressing two important aspects of device design: the correct operation of the acoustic reflector used to confine the energy in the resonator, and investigation of the role of the dispersion and standing wave resonances to the spurious responses often observed in high-Q resonators. Fourier transform techniques are used for selective visualization of wave fields and for the extraction of the dispersion characteristics of the plate-waves. The dispersion data are then further used to analyze the transfer characteristics of an acoustic reflector and to study the properties of lateral eigenresonances and the lateral energy confinement in detail.The research described in this thesis provides a detailed characterization of the operation of SAW and BAW devices and effects within, highlighting and further developing the experimental characterization capabilities and data-analysis methods.Keywords laser interferometry, microacoustics, surface acoustic waves, bulk acoustic waves Tiivistelmä Väitöskirjatyö käsittelee heterodyne-tyyppisen laserinterferometrin sekä interferometrin tuottaman datan analyysitekniikoiden kehittämistä pintavärähtelykenttien karakterisoimiseksi ja analysoimiseksi mikroakustisissa komponenteissa ja testirakenteissa.Työssä rakennettu heterodynelaserinterferometri mahdollistaa pintavärähtelyiden vaiheherkät absoluuttiamplitudimittaukset aina 6 GHz taajuuteen asti. Laitteisto kykenee värähtely-kenttien k...

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Scanning-electron-microscope observations of propagating acoustic waves in surface acoustic wave devices

Cited by 41 publications

References 3 publications

Mapping acoustic field distributions of VHF to SHF SAW transducers using a Scanning Electron Microscope

Mapping acoustic field distributions of VHF to SHF SAW transducers using a Scanning Electron Microscope

AFM observation of surface acoustic waves emitted from single symmetric SAW transducers

Measurement of evanescent wave properties of a bulk acoustic wave resonator [Letters]

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