Retention Characteristics of Hf0.5Zr0.5O2-based Ferroelectric Tunnel Junctions

We report on the retention properties of double-layer hafnium zirconium oxide ( Hf0.5Zr0.5O2; HZO) based ferroelectric tunnel junctions ( FTJ). Utilizing HZO as the ferroelectric layer and aluminum oxide ( Al2O3) as the tunneling barrier a scalable FTJ memory operation with good endurance and an on/off ratio of about 10 was achieved. Due to inherent depolarization fields from the double layer structure, the device suffers from strong retention loss over time. An extrapolation to 10 years at room temperature shows vanishing differences between the on and off state currents. We propose a way to avert this retention loss by using a constant bias that can be built-in by a work function difference from the metal electrode. This leads to more stable on-current retention and only small off-current increase, giving rise to an improved retention behavior of the FTJ.