Ultrathin Ferroelectric complex oxides
In recent years, there has been a renewed interest in ferroelectrics in low power integrated electronics such as memory. The discovery of ferroelectric hafnia has led to further scaling of layers to sub 10 nm thicknesses. However, the multiphasic nature of hafnia yields poor endurance and across-wafer repeatability. Complex oxides such as perovskites offer a an extremely flexible structure class of materials that offer a wide variety of ferroelectrics with tunable dielectric properties. However, dead-layer effects, negative conduction band offsets with Si, and complex stoichiometries, make the integration and scaling of these materials challenging on devices in large wafer production. Ferroelectricity has been observed in ultrathin films in epitaxy but polycrystalline films, which are preferred in production, have yet to be demonstrated. The development of complex oxide-based materials will be undertaken targeting ferroelectricity in ultrathin layers for devices. Pulsed laser deposition (PLD) will be used on 200mm wafer scale to deposit and optimise complex oxide, perovskite-based materials. Interfacial and strain engineering will be used to minimise dead-layers, and other phenomena that could negatively effect ferroelectricity in these layers. Understanding the growth, structural mechanisms, the role of strain and interfacial chemistries on the ferroelectric response will be key to building a knowledge library and proof-of-concept for the operation of ultrathin ferroelectric complex oxides.