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Fabrication of Multilayer Thin Film Piezoelectric Transducers

IP.com Disclosure Number: IPCOM000077569D
Original Publication Date: 1972-Aug-01
Included in the Prior Art Database: 2005-Feb-25
Document File: 3 page(s) / 30K

Publishing Venue

IBM

Related People

Rideout, VL: AUTHOR

Abstract

Acoustic bulk-wave multilayer transducers offer several advantages over conventional single-layer transducers for high-frequency opera;ion (e.g., above 10GHz). Although there is presently considerable scientific interest in multilayer acoustic devices, progress has been hampered by the lack of a suitable fabrication technique and identification of the appropriate materials. Advantages of multilayer acoustic transducers over single-layer transducers include: 1) more efficient electrical impedance matching between the transducer and the electrical driving circuit; 2) higher power handling capability; and 3) trade-off of bandwidth for insertion.

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Fabrication of Multilayer Thin Film Piezoelectric Transducers

Acoustic bulk-wave multilayer transducers offer several advantages over conventional single-layer transducers for high-frequency opera;ion (e.g., above 10GHz). Although there is presently considerable scientific interest in multilayer acoustic devices, progress has been hampered by the lack of a suitable fabrication technique and identification of the appropriate materials. Advantages of multilayer acoustic transducers over single-layer transducers include: 1) more efficient electrical impedance matching between the transducer and the electrical driving circuit; 2) higher power handling capability; and 3) trade-off of bandwidth for insertion.

The term "multilayer transducer structure" means a structure in which either the sign of the driving field or the piezoelectric polarity of the layer is inverted periodically every half-wavelength, or in which the piezoelectrically active layers alternate with inactive ones with a periodic thickness of one wavelength. For multilayer acoustic filters or dispersive delay lines, the layer spacings are not necessarily periodic. The active layers of the device may be electrically connected in series, parallel, or grouped in series-parallel combinations and may be interspersed with electrically conductive or nonconductive layers. The bulk- wave device of primary interest is the series connected, periodic multilayer transducer which consists of a stack of alternating piezoelectrically active and inactive layers shown in the figure. At the top and bottom of the stack are electrically conductive layers (i.e., electrodes).

de Klerk et al (IEEE Trans. on Sonics and Ultrasonics, SU-13,99, 1966) fabricated thin-film multilayer transducers, by vapor deposition of piezoelectrically active CdS and inactive SiO layers onto Al(2)O(3) rods. The maximum number of deposited layers was three. Since the lattice constants and crystal structures of CdS and SiO are incompatible, the layers were textured rather than single crystalline, and large stresses may build up between the layers, especially if a large number of layers are deposited.

Ge, AlAs, ZnTe, and GaAs have compatible lattice constants and lattice structures. Of these, Ge is not piezoelectric and can serve as an inactive layer. The most favorable situation for a multilayer transducer occurs when the acoustic impedances of the active and inactive layers, and the transmission medium...