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Measuring Residual Stress Effects of Acceptor Doping In Tunable Microwave Dielectric Thin Films

Published online by Cambridge University Press:  01 February 2011

W. D. Nothwang ,
M. W. Cole ,
C. Hubbard  and
E. Ngo
W. D. Nothwang
Affiliation:
U.S. Army Research Laboratory APG, MD 21005
M. W. Cole
Affiliation:
U.S. Army Research Laboratory APG, MD 21005
C. Hubbard
Affiliation:
U.S. Army Research Laboratory APG, MD 21005
E. Ngo
Affiliation:
U.S. Army Research Laboratory APG, MD 21005
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Extract

There has been a recent shift towards a tunable phase shifter for microwave antenna design. Barium strontium titanate [BaxSr(1-x)TiO3] thin films are the principal materials of interest in these applications, primarily because of their low loss, high dielectric constant and large tunability. Both magnesium doped and undoped films were made, and they were deposited on MgO or Pt-Si substrates using metal organic solution deposition and pulsed laser deposition. Residual stress within these materials is known to have a drastic effect on the material, electrical, and dielectric properties. This becomes of particular importance in thin film materials, where the residual stress can be several orders of magnitude higher than in bulk materials. The residual stress in the films was measured in three ways. A Tencor stress analysis system was employed to measure the change in the substrate curvature due to the film stress, and a nano-indentation method was used to calculate the residual stress in a system by measuring the maximum penetration, the force at maximum penetration, and the slope of the initial unloading curve. These methods were validated using XRD lattice calculations. Stresses as high as 2 GPa were observed under certain conditions. The results also show that the surface region of the films is not stress free at these thicknesses (∼200 nm) as was mathematically suggested.

Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 784: Symposium C – Ferroelectric Thin Films XII , 2003 , C8.1
Copyright
Copyright © Materials Research Society 2004

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References

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