The doctoral dissertations of the former Helsinki University of Technology (TKK) and Aalto University Schools of Technology (CHEM, ELEC, ENG, SCI) published in electronic format are available in the electronic publications archive of Aalto University - Aaltodoc.
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Optimization of Reflector and Transducer Properties for Surface Acoustic Wave Devices on 128° LiNbO3

Saku Lehtonen

Dissertation for the degree of Doctor of Science in Technology to be presented with due permission of the Department of Engineering Physics and Mathematics for public examination and debate in Auditorium F1 at Helsinki University of Technology (Espoo, Finland) on the 19th of November, 2004, at 12 o'clock noon.

Overview in PDF format (ISBN 951-22-7361-6)   [1881 KB]
Dissertation is also available in print (ISBN 951-22-7360-8)

Abstract

Aluminium grating structures used for reflecting surface acoustic waves (SAW) on 128° LiNbO3 are studied in this dissertation. The properties of gratings are obtained from simulated and measured frequency responses of tailored test structures. In the simulations, Green's functions are used to characterize the piezoelectric substrate, the finite element method (FEM) is applied for calculating the fields in the metallic electrodes, and the boundary element method (BEM) is employed at the interface. The majority of the simulated responses are obtained with a rigorous two-dimensional tool for finite structures.

The reflection and transmission coefficients of the grating are extracted applying time gating to the test structure responses. Both their amplitudes and phases are evaluated. The former is used for obtaining the reflectivity of the reflectors. Furthermore, energy comparisons serve to address the attenuation inside the gratings, and, for short reflectors, provide the means to estimate the performance of the gratings. A number of analysis methods are used for the extraction of parameters. The quantitative results, presented in the framework of the coupling-of-modes terminology, are given as a function of the electrode geometry.

The observed great difference in the reflectivity of narrow short-circuited electrodes and that of wide floating electrodes is exploited in novel unidirectional structures introduced. The great advantage of the unidirectional schemes proposed is the large critical dimension of the structures, allowing the use of standard optical lithography up to the frequencies 2.5-3 GHz. In particular, low-loss and wideband unidirectional transducers are demonstrated for 2.45 GHz.

This thesis consists of an overview and of the following 7 publications:

  1. Lehtonen S., Plessky V. P., Koskela J. and Salomaa M. M., 2003. Second-harmonic reflectors on 128° LiNbO3. IEEE Transactions on Ultrasonics, Ferroelectrics, and Frequency Control 50, number 8, pages 972-978. © 2003 IEEE. By permission.
  2. Lehtonen S., Plessky V. P. and Salomaa M. M., 2004. Short reflectors operating at the fundamental and second harmonics on 128° LiNbO3. IEEE Transactions on Ultrasonics, Ferroelectrics, and Frequency Control 51, number 3, pages 343-351. © 2004 IEEE. By permission.
  3. Lehtonen S., Plessky V. P., Béreux N. and Salomaa M. M., 2004. Minimum-loss short reflectors on 128° LiNbO3. IEEE Transactions on Ultrasonics, Ferroelectrics, and Frequency Control 51, number 10, pages 1203-1205. © 2004 IEEE. By permission.
  4. Lehtonen S., Plessky V. P., Béreux N. and Salomaa M. M., Phases of the SAW reflection and transmission coefficients for short reflectors on 128° LiNbO3. IEEE Transactions on Ultrasonics, Ferroelectrics, and Frequency Control, accepted for publication. © 2004 by authors and © 2004 IEEE. By permission.
  5. Lehtonen S., Plessky V. P., Hartmann C. S. and Salomaa M. M., Extraction of the SAW attenuation parameter in periodic reflecting gratings. IEEE Transactions on Ultrasonics, Ferroelectrics, and Frequency Control, accepted for publication. © 2004 by authors and © 2004 IEEE. By permission.
  6. Lehtonen S., Plessky V. P., Hartmann C. S. and Salomaa M. M., 2003. Unidirectional SAW transducer for gigahertz frequencies. IEEE Transactions on Ultrasonics, Ferroelectrics, and Frequency Control 50, number 11, pages 1404-1406. © 2003 IEEE. By permission.
  7. Lehtonen S., Plessky V. P., Hartmann C. S. and Salomaa M. M., SPUDT filters for the 2.45 GHz ISM band. IEEE Transactions on Ultrasonics, Ferroelectrics, and Frequency Control, accepted for publication. © 2004 by authors and © 2004 IEEE. By permission.

Errata of publication 1

Keywords: SAW, grating, 128° lithium niobate, reflectivity, attenuation

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© 2004 Helsinki University of Technology

Last update 2011-05-26