Ferroelectric Field Effect Transistor With Annealing-Free Ultralow Process Temperature (250 °C) of Hf x Zr 1- x O 2 for BEOL Application

A low process temperature and a large memory window (MW) in ferroelectric field-effect transistors (FeFETs) based on Hf ${}_{x}$ Zr ${}_{{1}-{x}}$ O₂ (HZO) ferroelectric (FE) layers and oxide semiconductors are strongly required for back-end-of-line (BEOL) applications. However, conventional low-temperature fabrication approaches typically involve high costs and complex processing steps, which significantly hinder their practicality for large-scale manufacturing. This work demonstrates an annealing-free HZO FE thin-film capacitor and an oxide-semiconductor-based FeFET fabricated at an ultralow process temperature of $250~^{\circ }$ C. A remanent polarization ( $2{P} _{r}$ ) of $17.4~\mu $ C/cm² is achieved in the annealing-free HZO film, benefiting from: 1) the introduction of ZrO₂ seed layers on both sides of the HZO film; 2) careful optimization of the ZrO₂ and HZO layer thicknesses; and 3) slow atomic layer deposition (ALD)-driven crystallization at $250~^{\circ }$ C. Furthermore, by employing a metal-FE-metal-insulator-semiconductor (MFMIS) device structure and engineering the interfacial properties, an annealing-free FeFET exhibiting a MW of approximately 1.9V and an endurance exceeding $10^{{7}}$ cycles is achieved. Overall, this work establishes a new paradigm that integrates ALD-driven crystallization with device structure optimization, enabling low-cost, high-reliability, and BEOL-compatible FE memory technologies.