Improved Reliability for Back-End-of-Line Compatible Ferroelectric Capacitor With 3 Bits/Cell Storage Capability by Interface Engineering and Post Deposition Annealing

AlON/HfZrOx (HZO)/HfO2 stack with post-deposition annealing (PDA) process at 400 °C is proposed to implement BEOL compatible ferroelectric (FE) capacitors. While interface engineering by AlON and HfO2 enhances $\text{P}_{\text {r}}$ to enable more bits storage, PDA reduces oxygen vacancies in the HZO by eliminating the reaction between HZO and top electrode. The FE capacitors display wake-up free behavior and the first reported 3 bits/cell operation with 8 stable states up to $^{^{^{}}}~10^{{8}}$ cycles (±4 V/ $1~\mu \text{s}$ ), non-overlapped cycle-to-cycle and device-to-device variation ( $\sigma < 0.4~\mu \text{C}$ /cm2), outperforming other FE capacitors and demonstrating high potential for high-density embedded ferroelectric random-access memory (FeRAM).