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Bonding of Bulk Piezoelectric Material to Silicon Using a Gold-Tin Eutectic Bond

Published online by Cambridge University Press:  15 March 2011

Kevin T. Turner
Affiliation:
Massachusetts Institute of Technology, Cambridge, MA 02139, USA
Richard Mlcak
Affiliation:
Boston MicroSystems, Inc., Woburn, MA 01801, USA
David C. Roberts
Affiliation:
Massachusetts Institute of Technology, Cambridge, MA 02139, USA
S. Mark Spearing
Affiliation:
Massachusetts Institute of Technology, Cambridge, MA 02139, USA
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Abstract

A class of MEMS devices, which utilizes microfabrication technology and bulk piezoelectric material, is currently being developed to produce high power density transducers. A thin-film gold-tin eutectic solder bond has been developed to bond electrically and mechanically bulk piezoelectric elements to microfabricated silicon structures in these devices. A 4.3 [.proportional]m thick multilayer film structure, consisting of a titanium adhesion layer, a platinum diffusion barrier, a gold-tin (80 wt.% Au - 20 wt.% Sn) alloy layer, and a pure gold capping layer, was sputter deposited on the piezoelectric components to be bonded. Bonding was accomplished by mating the piezoelectric components with silicon components metallized with a titanium-platinum-gold multilayer film and heating to approximately 300°C in a reducing atmosphere. The bonding technology allows thin, electrically conductive bonds to be formed between dissimilar materials with minimal amounts of applied pressure during bonding. Successful bonding has been achieved between single crystal silicon and polycrystalline lead-zirconate-titanate (PZT-5H) as well as between silicon and single crystal lead zinc niobate-lead titanate (PZN-PT). The process was optimized to produce mechanically robust, void-free bonds. The absence of voids was verified through scanning electron microscope examinations of bond cross-sections. Tensile tests conducted on representative structures indicated that the strength of the bond was limited by the strength of the titanium – PZT-5H interface.

Type
Research Article
Copyright
Copyright © Materials Research Society 2002

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