Wireless Passive SAW Identification Marks and Sensors

Reindl, L.

doi:10.1007/978-1-4020-2929-5_5

Cited by 16 publications

(2 citation statements)

References 47 publications

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“…The classical approach to this dilemma is stroboscopy, in which the slow detector is only illuminated while the physical phenomenon is in a known, repeatable state, by a short incoming signal. In the case of SEM, the illuminating electron beam is chopped in order to illuminate the SAW device only when the wave packet is in a known position, yielding such famous images as those found in [14].…”

Section: Context and Motivationmentioning

confidence: 98%

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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