Buffer-Free Production of Single-Crystalline Complex-Oxide Membranes and Their Applications

There have been serious efforts to develop a universal method for producing freestanding epitaxial membranes, which would allow for the creation of artificial heterostructures with interfacing structurally and chemically incompatible materials. In particular, a combination and match of complex-oxide membranes that exhibit unique electronic, photonic, and magnetic properties is expected to enable a wide range of innovative applications. Recent developments in graphene-based remote epitaxy and mechanical lift-off techniques have allowed for the generation of a variety of freestanding complex-oxide membranes, including perovskite SrTiO₃, spinel CoFe₂O₄, and garnet Y₃Fe₅O₁₂. However, it is particularly difficult to form an atomically clean graphene surface on growth substrates of complex-oxides in a scalable and controlled manner, which significantly limits the manufacturing of large-area oxide membranes of high quality. In addition, typical 2D materials, including graphene, are easily damaged during plasma processing in an oxygen environment, which is commonly required for complex-oxide film growth.<br/><br/>Here, alternative lift-off methods are introduced to expand the material spectrum of complex-oxide thin films that can be released from substrates and integrated onto platforms of interest. Firstly, chemical lift-off is used to obtain a single-crystalline BaTiO₃ (BTO) membrane by dissolving the water-soluble interlayer of Sr₃Al₂O₆, which is otherwise hard to be produced by remote epitaxy due to requirement of high growth temperature. It is then transferred onto a complementary metal–oxide–semiconductor (CMOS) platform. This provides an efficient route to fabricate capacitive memory devices with superior device performance, such as a noticeably large memory window and low energy consumption due to outstanding properties of single-crystalline BTO. Also, such BTO-based memory components integrated onto a silicon wafer ensure their great CMOS compatibility. Next, buffer-free mechanical lift-off is demonstrated to exfoliate a Pb(Mg_1/3Nb_2/3)O₃-PbTiO₃ membrane with atomic precision and to develop pyroelectric devices with ultra-broad band response and significantly improved detectivity compared to the clamped counterparts.