Piezoelectric thin films are essential building blocks for next-generation microelectromechanical systems (MEMS). However, their functional performance has historically been limited by substrate mechanical constraints—a phenomenon known as the “clamping effect.” This phenomenon typically suppresses ferroelectric- and ferroelastic-domain mobilities. This review summarizes a paradigm shift in thin-film design: it redefines substrate clamping as a vital “restoring force” that ensures reversible domain switching rather than viewing it as purely degradative. By implementing a “hybrid strain engineering” approach that precisely tunes epitaxial and thermal strains in lead zirconate titanate thin films, our group demonstrates the feasibility of maximizing extrinsic contributions from non-180° (ferroelastic) domain-wall motion. Employing in situ synchrotron X-ray diffraction (XRD) at SPring-8, our group provides direct evidence of ultrafast, reversible 90°-domain switching at megahertz frequencies. This design guideline enables the giant piezoelectric responses in MEMS cantilevers, outperforming conventional clamped films and providing a scalable path for Beyond 5G/6G communication technologies and high-efficiency actuators.

The remarkable diversity of the physical properties of glass is primarily attributed to its ability to incorporate various chemical species. Glass is a solidified liquid, i.e., a monolithic material with a “randomly” connected network; therefore, its properties can be tailored through compositional design. Titanium dioxide (TiO₂), which is classified as an intermediate oxide, affects the structural, thermal, optical, and mechanical properties of glass. Moreover, the valence of titanium influences the optical properties of glass and its thermal stability against the precipitation of crystallites. This study investigates the substitution effect of TiO₂ on aluminoborate glasses with high hardness and Young’s modulus. The glasses are prepared using a conventional melt-quenching method. Ti-free glasses possess high transparency in the visible region, and the coefficient of thermal expansion correlates with those of the substituted metal oxides. Both the thermal stability against crystallization and the mechanical properties change with composition. Although structural data for B₂O₃ and Al₂O₃ in all glasses are not available, the elastic properties may mainly depend on the dissociation energies of the metal oxides.