Large out-of-plane piezoelectricity of VIA group functionalized MXenes thin films for MEMS

The integration of piezoelectric and micro-electro-mechanical system (MEMS) technologies is promoting the rapid development of the MEMS industry. However, due to the lack of excellent in-plane and out-of-plane piezoelectric coefficients, good ambient temperature stability, and high mechanical durability, the reported two-dimensional piezoelectric thin films are facing severe challenges in the development of MEMS. Therefore, based on density functional theory calculations, we simulated the VIA group (the sixth main family in the periodic table of elements) functional MXenes, namely, Sc₂CXY (Sc₂COS, Sc₂COSe, Sc₂CSO, and Sc₂CSeO). The results show that this kind of material has good dynamic, thermal, and mechanical stability. Importantly, the structure exhibits good in-plane and out-of-plane piezoelectric effects due to the inversion asymmetry, bandgap adjustability, flexibility, and different electronegativity. Among them, the piezoelectric strain value of d₃₃ is one to three orders of magnitude higher than that of d₂₂ or d₃₁, which makes these materials can become a strong candidate for advanced equipment such as nano-wearable electronics, robot bionic skin, and piezoelectric products for MEMS.