Polarization and Resistive Switching in Epitaxial 2 nm Hf0.5Zr0.5O₂ Tunnel Junctions

In the quest for reliable and power-efficient memristive devices, ferroelectric tunnel junctions are being investigated as potential candidates. Complementary metal oxide semiconductor-compatible ferroelectric hafnium oxides are at the forefront. However, in epitaxial tunnel devices with thicknesses around ≈4–6 nm, the relatively high tunnel energy barrier produces a large resistance that challenges their implementation. Here, we show that ferroelectric and electroresistive switching can be observed in ultrathin 2 nm epitaxial Hf0.5Zr0.5O2 (HZO) tunnel junctions in large area capacitors (≈300 μm2). We observe that the resistance area product is reduced to about 160 and 65 Ω·cm2 for OFF and ON resistance states, respectively. These values are 2 orders of magnitude smaller than those obtained in equivalent 5 nm HZO tunnel devices while preserving a similar OFF/ON resistance ratio (210%). The devices show memristive and spike-timing-dependent plasticity behavior and good retention. Electroresistance and ferroelectric loops closely coincide, signaling ferroelectric switching as a driving mechanism for resistance change.