Multiple Polarization States in Hf ZrO Thin Films by Ferroelectric and Antiferroelectric Coupling.

HfO-based multi-bit ferroelectric memory combines non-volatility, speed, and energy efficiency, rendering it a promising technology for massive data storage and processing. However, some challenges remain, notably polarization variation, high operation voltage, and poor endurance performance. Here we show Hf ZrO (x = 0.65 to 0.75) thin films grown through sequential atomic layer deposition (ALD) of HfO and ZrO exhibiting three-step domain switching characteristic in the form of triple-peak coercive electric field (E) distribution. This long-sought behavior shows nearly no changes even at up to 125 °C and after 1 × 10 electric field cycling. By combining the electrical characterizations and integrated differential phase-contrast scanning transmission electron microscopy (iDPC-STEM), we reveal that the triple-peak E distribution is driven by the coupling of ferroelectric switching and reversible antiferroelectric-ferroelectric transition. We further demonstrate the 3-bit per cell operation of the Hf ZrO capacitors with excellent device-to-device variation and long data retention, by the full switching of individual peaks in the triple-peak E. The work represents a significant step in implementing reliable non-volatile multi-state ferroelectric devices.