Residual stress in piezoelectric poly(vinylidene-fluoride-co-trifluoroethylene) thin films deposited on silicon substrates

The residual stress and its evolution with time in poly(vinylidene-fluoride-co-trifluoroethylene) (P(VDF-TrFE) (72/28)) piezoelectric polymer thin films deposited on silicon wafers were investigated using the wafer curvature method. Double-side polished silicon wafers with minimized initial wafer warpage were used to replace single-side polished silicon wafers to obtain significantly improved reliability for the measurement of the low residual stress in the P(VDF-TrFE) polymer thin films. Our measurement results showed that all the P(VDF-TrFE) films possessed a tensile residual stress, and the residual stress slowly decreased with time. Our analysis further indicates that the tensile stress could arise from the thermal mismatch between the P(VDF-TrFE) film and the silicon substrate. Besides possible viscoelastic creep mechanism in thermoplastic P(VDF-TrFE) films, microcracks with widths in the range of tens of nanometers appeared to release the tensile residual stress.

[1]  G. Reiter,et al.  Residual stresses in thin polymer films cause rupture and dominate early stages of dewetting , 2005, Nature materials.

[2]  Skandar Basrour,et al.  X-ray characterization of residual stresses in electroplated nickel used in LIGA technique , 2000 .

[3]  K. Kimura,et al.  Polarization Behavior in Vinylidene Fluoride-Trifluoroethylene Copolymer Thin Films , 1986 .

[4]  Claude A. Klein,et al.  How accurate are Stoney’s equation and recent modifications , 2000 .

[5]  G. Stoney.  The Tension of Metallic Films Deposited by Electrolysis , 1909 .

[6]  K. T. Ramesh,et al.  The mechanical properties of lead-titanate/polymer 0–3 composites , 1999 .

[7]  Tong-Yi Zhang,et al.  Microbridge testing of silicon nitride thin films deposited on silicon wafers , 2000 .

[8]  Qiming Zhang,et al.  Thickness dependence of ferroelectric polarization switching in poly(vinylidene fluoride–trifluoroethylene) spin cast films , 2001 .

[9]  Timothy P. Weihs,et al.  Measuring stiffnesses and residual stresses of silicon nitride thin films , 1990 .

[10]  J. McDonald,et al.  Stress in thermally annealed parylene films , 1992 .

[11]  C. Goldsmith,et al.  Measurement of stresses generated in cured polyimide films , 1983 .

[12]  V. T. Srikar,et al.  Micro-Raman measurement of bending stresses in micromachined silicon flexures , 2003 .

[13]  Effect of secondary crystallization on residual stresses in moulded polymers , 1990 .

[14]  Wataru Sakai,et al.  Crystalline structures and ferroelectric properties of ultrathin films of vinylidene fluoride and trifluoroethylene copolymer , 2005 .

[15]  Jean-Yves Robic,et al.  Residual stresses in evaporated silicon dioxide thin films: Correlation with deposition parameters and aging behavior , 1995 .

[16]  Gerhard Elsner,et al.  Residual stress and thermal expansion of spun‐on polyimide films , 1987 .

[17]  S. Croll,et al.  The origin of residual internal stress in solvent‐cast thermoplastic coatings , 1979 .

[18]  Seung Tae Choi,et al.  Study on residual stress in viscoelastic thin film using curvature measurement method , 2001 .

[19]  K. Yao,et al.  Residual stress analysis in ferroelectric Pb(Zr0.52Ti0.48)O3 thin films fabricated by a sol-gel process , 2003 .

[20]  Kui Yao,et al.  Comparative investigation of the structure and properties of ferroelectric poly(vinylidene fluoride) and poly(vinylidene fluoride–trifluoroethylene) thin films crystallized on substrates , 2010 .