The paper by S. Trolier-McKinty and P. Muralt reviews the application of thin film piezoelectric materials in microelectromechanical systems (MEMS). These materials offer significant advantages, including large motions with low hysteresis, high energy densities, high sensitivity, wide dynamic ranges, and low power requirements. The authors discuss the impact of various factors on the piezoelectric response, such as film orientation, composition, grain size, defect chemistry, and mechanical boundary conditions. Non-ferroelectric materials like ZnO and AlN are highlighted for their high electrical resistivity and compatibility with CMOS processing, making them suitable for resonator applications. Ferroelectric films, particularly lead zirconate titanate (PZT), are noted for their higher piezoelectric response, enabling lower voltage operation and high sensitivity in sensors and actuators. The paper also emphasizes the importance of piezoelectric coefficients and their impact on device performance, with the highest responses observed in \(\{001\}\) oriented rhombohedrally-distorted perovskites. The introduction outlines the advantages of piezoelectric devices in MEMS, including their ability to implement high-frequency resonant structures, low power requirements, large amplitude actuation with low drive voltages, good scaling with size, and ease of electrical signal processing.The paper by S. Trolier-McKinty and P. Muralt reviews the application of thin film piezoelectric materials in microelectromechanical systems (MEMS). These materials offer significant advantages, including large motions with low hysteresis, high energy densities, high sensitivity, wide dynamic ranges, and low power requirements. The authors discuss the impact of various factors on the piezoelectric response, such as film orientation, composition, grain size, defect chemistry, and mechanical boundary conditions. Non-ferroelectric materials like ZnO and AlN are highlighted for their high electrical resistivity and compatibility with CMOS processing, making them suitable for resonator applications. Ferroelectric films, particularly lead zirconate titanate (PZT), are noted for their higher piezoelectric response, enabling lower voltage operation and high sensitivity in sensors and actuators. The paper also emphasizes the importance of piezoelectric coefficients and their impact on device performance, with the highest responses observed in \(\{001\}\) oriented rhombohedrally-distorted perovskites. The introduction outlines the advantages of piezoelectric devices in MEMS, including their ability to implement high-frequency resonant structures, low power requirements, large amplitude actuation with low drive voltages, good scaling with size, and ease of electrical signal processing.