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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Loss Reduction in Coupled Resonance Surface Acoustic Wave Filters Operating at GHz Frequencies

Johanna Meltaus

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 AS1 at Helsinki University of Technology (Espoo, Finland) on the 8th of December, 2006, at 12 noon.

Overview in PDF format (ISBN 951-22-8517-7)   [1143 KB]
Errata (in PDF format)
Dissertation is also available in print (ISBN 951-22-8516-9)

Abstract

This thesis discusses loss mechanisms in periodic and quasi-periodic leaky surface acoustic wave (LSAW) coupled resonator filters (CRFs) operating at GHz frequencies and methods to suppress those mechanisms. The work focuses on resistive losses in the interdigital transducer (IDT) electrodes, acoustic loss resulting from conversion of SAW to bulk acoustic waves (BAW) at discontinuities of periodicity, and filter topologies striving for minimizing these mechanisms. Furthermore, losses resulting from acoustic radiation from connecting electrodes (busbars) of IDTs on LSAW substrates are studied.

Novel topologies for low-loss filters at 1-2 GHz frequencies presented in this work comprise (i) two different CRF tracks operating electrically in parallel, (ii) a 5-IDT longitudinal CRF with distributed gaps, and (iii) a double-resonance filter structure proposed here for the first time. In all of the devices, 42°-LiTaO3 is used as the piezoelectric substrate. The operation of the proposed devices is analyzed and their attainable performance is demonstrated with experimental results. Extremely low-loss filter performance with insertion loss on the order of 1 dB is obtained in 2 GHz range with all proposed topologies.

In addition, principles and methods for design and simulation of CRFs is discussed in this thesis, and stochastic (global) optimization algorithms specifically suited for multi-element CRFs are proposed. Furthermore, non-synchronous resonator elements for use with CRFs on leaky substrates are considered, and the effect of contact pad topology on filter performance is discussed based on experimental results.

This thesis consists of an overview and of the following 6 publications:

  1. J. Meltaus, V. P. Plessky, S. Härmä, and M. M. Salomaa, SAW Filter Based on Parallel-Connected CRFs with Offset Frequencies, IEEE Transactions on Ultrasonics, Ferroelectrics, and Frequency Control, accepted for publication. © 2006 IEEE. By permission.
  2. J. Meltaus, V. P. Plessky, S. Härmä, and M. M. Salomaa, Low-Loss, Multimode 5-IDT SAW Filter, IEEE Transactions on Ultrasonics, Ferroelectrics, and Frequency Control 52 (6), pp. 1013-1019 (2005). © 2005 IEEE. By permission.
  3. J. Meltaus, P. Hämäläinen, and V. P. Plessky, Design of Coupled SAW Filters Using Genetic and Evolution Algorithms, Helsinki University of Technology Publications in Engineering Physics, Report TKK-F-A847 (2006). IEEE Transactions on Evolutionary Computation, submitted for publication. © 2006 by authors and © 2006 IEEE. By permission.
  4. J. Meltaus, S. S. Hong, O. Holmgren, K. Kokkonen, and V. P. Plessky, Double-Resonance SAW Filters, IEEE Transactions on Ultrasonics, Ferroelectrics, and Frequency Control, accepted for publication. © 2006 IEEE. By permission.
  5. J. Meltaus, S. S. Hong, and V. P. Plessky, Acoustic Radiation Losses in Busbars, Helsinki University of Technology Publications in Engineering Physics, Report TKK-F-A848 (2006). IEEE Transactions on Ultrasonics, Ferroelectrics, and Frequency Control, submitted for publication. © 2006 by authors and © 2006 IEEE. By permission.
  6. J. Meltaus, S. S. Hong, and V. P. Plessky, Non-Synchronous Resonators on Leaky Substrates, Proceedings of the 2005 IEEE International Ultrasonics Symposium, pp. 2153-2156 (2005). © 2005 IEEE. By permission.

Keywords: surface acoustic waves, bandpass filters, leaky waves, losses

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© 2006 Helsinki University of Technology

Last update 2011-05-26