Recent discoveries of ferroelectricity and field-induced ferroelectricity in HfO2 and ZrO2 have led to increased interest in devices based on both materials, enabling a growing number of applications, including high aspect ratio ferroelectric capacitors and field effect transistors. One-transistor/one-capacitor memory arrays of Kbit to Gbit size are reported. From detailed reliability characterization, a complete picture of ferroelectric oxide/metal interface dynamics can be presented, explaining key reliability issues like field cycle endurance and retention.