Hf_1-xZr_xO₂-Based Ferroelectric Heterostructures for Non-Volatile Memories and Artificial Synaptic Devices

The rapid development of information technology requires memory devices with fast speed, low power consumption, high density, <i>etc</i>. HfO₂-based ferroelectric thin films are promising for the advanced information memory devices, especially due to the good silicon compatibility and intrinsic advantages of ferroeelctricity. Recently, we used atomic layer deposition to construct high-quality Hf_1-<i>x</i>Zr<i>_x</i>O₂ (HZO) ferroelectric thin film heterostructures and investigated corresponding prototype memory devices, including ferroelectric capacitors for FeRAM and ferroelectric tunnel junctions for neural network computing. The ferroelectric endurance properties of TiN/HZO/TiN capacitor were studied, and it was found that the ferroelectric fatigue severity increases first and then decreases with increasing pulse voltage or width. Accordingly, a recovery method by introducing wake-up effect was utilized to realize a weaker fatigue, a sufficient switched polarization (7–12 μC/cm²) by 100 ns voltage pulses, and especially an enhanced endurance of &gt;1.01×10¹² (&gt;5.0×10¹³ in expectation). On the basis of growing high-quality HZO heterostructure, ferroelectric tunnel junctions (FTJs) based on a SiO₂/HZOcomposite barrier and both conducting electrodes were designed and fabricated on Si substrates. The FTJ achieves the fastest write speed of 500 ps under 5 V or 10 ns speed at a low voltage of 1.5 V, low write current density ~1.3×10⁴ A/cm², and 8 discrete states. Interestingly, in the FTJ-based memristive synapse, gradually tunable nonvolatile conductance states (128 states) with high linearity were obtained, and by inputting the corresponding experimental results into an online neural network simulation, a high accuracy in recognizing fashion product images was achieved. These results indicate that silicon-compatible HfO₂-based ferroelectric heterostructures are important candidates for high-performance nonvolatile memory and artificial synaptic devices.