July 2022
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40 Reads
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3 Citations
IEEE Electron Device Letters
In this work, we employed our newly developed optical imaging method to probe detailed acoustodynamic physics in gigahertz unreleased ultrasonic transducers based on an AlN-on-silicon system, revealing mode superposition, anisotropic transduction, and dynamic mode evolution. Superpositioned upon the dominant breathing mode along the vertical direction of the AlN layer, multiple resonant lateral modes are identified, and they are shown to evolve into a surface mode beyond the piezoelectric transduction envelope, with strong anisotropic transduction brought by the shear motion of silicon. This acoustodynamic property is important for verifying and further improving design theories of broadband piezoelectric transducers and thin film piezoelectric-on-substrate systems in general.
![Instrument for stroboscopic optical sampling
a Schematic layout of the optical set-up. NPBS non-polarizing beam splitter, PBS polarizing beam splitter, PD photodetector, Ref. M reference mirror, λ/4 FR quarter-wave Fresnel rhomb (45° polarized), Piezo piezoelectric nanopositioner. The laser is collimated and 45° polarized before entering the NPBS. λ/4 FRs are used to manipulate laser polarization due to their wide spectral flatness. b Electrical spectrum of the laser pulse train obtained by directly measuring a split of the ultrafast laser using a fast PD (12.5 GHz bandwidth) and a wide-band spectrum analyzer, showing an RF frequency comb with teeth equally spaced by the laser repetition rate, fp\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${f}_{p}$$\end{document}. c Schematic layout of the electronics for device excitation, lock-in reference generation, and signal detection. d Schematic explanation of stroboscopic optical sampling in the frequency domain where beating the excitation signal, fex\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${f}_{{ex}}$$\end{document}, with the RF comb using the tooth at nfp\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$n{f}_{p}$$\end{document}, results in a low-frequency beat note at fb\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${f}_{b}$$\end{document}.](https://www.researchgate.net/publication/358366599/figure/fig1/AS:1119965155463176@1644031909766/Instrument-for-stroboscopic-optical-sampling-a-Schematic-layout-of-the-optical-set-up_Q320.jpg)
![Noise of stroboscopic optical sampling at super high frequencies
a Comparison between the noise floor of this work, obtained by disconnecting the power supply to the device under test (shown in red), and the noise floor for state-of-the-art CW laser interferometry12,16,20 (shown in blue), for both measurement bandwidth and noise floor. b The root mean square (RMS) vibration amplitude of the third mode (6.552 GHz) and fifth mode (10.752 GHz) of the BAW while the excitation power is gradually reduced, yielding a noise floor around 55 fm for a 1 s averaging time (red dash-dot line). In both panels (a) and (b), error bars represent ±1σ. The relationship between the displacement and the square root of the RF power is linear as expected because the driven motion is governed by the inverse piezoelectric coupling, ε3=d33E3\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${\varepsilon }_{3}={d}_{33}{E}_{3}$$\end{document}. The arrow indicates that changes in vibration amplitude below 10 fm can be observed when the excitation power is varied.](https://www.researchgate.net/publication/358366599/figure/fig4/AS:1119965155471377@1644031909856/Noise-of-stroboscopic-optical-sampling-at-superhigh-frequencies-a-Comparison-between-the_Q320.jpg)
