Strain Balanced Self‐Supporting Single‐Crystalline LiNbO₃ Thin Films for Flexible Electronics

Abstract

Functional single‐crystalline films with mechanical flexibility have attracted intensive interest due to excellent material quality and the wide applications in flexible electronics. However, the free‐standing single‐crystalline films with the thickness in sub‐micrometer range usually deform due to insufficient mechanical strength or internal stress. This study introduces a strain balanced model (SBM) of a sandwich structure and an ion slicing‐based strain compensation bonding method for fabricating ultrathin but self‐supporting single‐crystalline thin films. Based on the SBM and the strain compensation bonding method, a centimeter‐scale strain balanced LiNbO3 (LN) thin film (SB‐LNTF) consisting of two pieces of 550 nm single‐crystalline LN film and an intermediate layer of benzocyclobutene is successfully fabricated. In additional to flat, bendable, transparent, and lightweight, the fabricated ultrathin (<10 µm) SB‐LNTF also exhibits excellent self‐supporting property. Standard piezoresponse force microscopy amplitude butterfly curve and a 180° phase switching associated with ferroelectric behavior of LN film are observed, which confirm its high crystal quality of the ion sliced LiNbO3 thin film. A flexible acoustic resonator demonstrated on SB‐LNTF shows strong resonances. In principle, the strain compensation bonding method is also applicable to epitaxial lift‐off films.