Abstract
A CaTiO3-doped (K,Na)NbO3 (KNN-CT) film is a lead-free piezoelectric film that is expected to substitute Pb(Zr,Ti)O3 (PZT) film in piezoelectric micro electro mechanical systems (MEMS). However, the full set of the material constants (elastic constants, piezoelectric constants and dielectric constants) of the KNN-CT film have not been reported yet. In this study, all the material constants of a sputter-deposited blanket KNN-CT film were investigated by the resonance responses of MEMS-based piezoelectric resonators and the phase velocities of leaky Lamb waves on a self-suspended membrane. The phase velocities measured by a line-focus-beam ultrasonic material characterization (LFB-UMC) system at different frequencies were fitted with theoretical ones, which were calculated from the material constants, including fitting parameters. A genetic algorithm was used to find the best-fitting parameters. All the material constants were then calculated. Although some problems arising from the film quality and the nature of deliquescence are observed, all the material constants were obtained exhibiting accuracy within 16 m/s in the phase velocity of leaky Lamb wave.
Highlights
Pb(Zr,Ti)O3 (PZT) films are used for commercialized piezoelectric micro electro mechanical systems (MEMS), such as ink-jet printer heads and vibratory gyroscopes, due to their well-balanced performance
The phase velocity of leaky Lamb wave is measured by the line-focus-beam ultrasonic material characterization (LFB-UMC) system
In the LFB-UMC system, a water coupler exists on one side of the membrane, as shown in Figure 2a, and Campbell’s method is extended to calculate the phase velocities of leaky Lamb wave
Summary
Pb(Zr,Ti)O3 (PZT) films are used for commercialized piezoelectric micro electro mechanical systems (MEMS), such as ink-jet printer heads and vibratory gyroscopes, due to their well-balanced performance. Shibata et al investigated KNN films deposited by RF magnetron sputtering [4,5,6,7,8,9]. The sputtered KNN film on Pt/Ti/SiO2/Si exhibited excellent transverse piezoelectric coefficient e31* from −10.0 to −14.4 C/m2 compared to other lead-free piezoelectric materials [8]. Compared to ScAlN, few material constants of KNN-CT were reported at present. Genetic approaches such as crossover, Micromachines 2018, 9, 558 constants of KNN-CT were reported at present. Genetic approaches such as crossover, mutation and selection were introduced to escape local convergence and reach optimized fitting parameters from relatively far initial values
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