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Surface Acoustic Wave Devices: Materials Stability in Harsh Environments

Published online by Cambridge University Press:  07 January 2013

Denny Richter ,
Michal Schulz ,
Sergey Sakharov ,
Zachary J. Davis  and
Holger Fritze
Denny Richter
Affiliation:
Institute for Energy Research and Physical Technologies, Clausthal University of Technology, Goslar, Germany
Michal Schulz
Affiliation:
Institute for Energy Research and Physical Technologies, Clausthal University of Technology, Goslar, Germany
Sergey Sakharov
Affiliation:
FOMOS Materials Co., Moscow, Russian Federation
Zachary J. Davis
Affiliation:
Centre for Microtechnology and Surface Analysis, The Danish Technological Institute, Taastrup, Denmark
Holger Fritze
Affiliation:
Institute for Energy Research and Physical Technologies, Clausthal University of Technology, Goslar, Germany
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Abstract

The availability of high-temperature stable surface acoustic wave (SAW) devices would enable realization of wireless sensors for monitoring high-temperature processes. One of the most promising substrate materials for SAW based high-temperature sensors is langasite (LGS, La3Ga5SiO14). It can be excited piezoelectrically up to its melting point at 1470 °C. However, gallium evaporation and degradation of the electrodes limit the application of LGS in SAW sensors for harsh environments to some extent.

The objectives of this work include the investigation of the gallium loss in the vicinity of the langasite surface in oxidizing, reducing and vacuum conditions at temperatures up to 900 °C. The gallium content in the vicinity of the LGS surface is not decreased after annealing the samples in air, while a significant gallium loss occurs in vacuum and reducing atmospheres (0.5 % H2/Ar). The latter results in a gallium oxide deficient region of 1.5 μm below the surface after annealing for 12 hours at 900 °C. The gallium loss is virtually completely suppressed after protecting the surface with a thin alumina film.

Further, thin-film electrodes based on platinum and platinum/rhodium are tested. While conventional platinum based electrodes are completely destroyed at 900 °C within hours due to agglomeration, alumina protected electrodes can be operated at least for several days at this temperature. After 400 hours at 700 °C, the alumina protected platinum electrodes show insignificant degradation. The influence of alumina passivation layers on the stability of the SAW devices is examined. Different electrode configurations are tested with respect to their long-term frequency stability at 650 °C.

Keywords

thin filmdiffusionsensor
Type
Articles
Information
MRS Online Proceedings Library (OPL) , Volume 1519: Symposium MM – Materials under Extreme Environments , 2013 , mrsf12-1519-mm03-29
Copyright
Copyright © Materials Research Society 2012

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References

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