High-Performance Ferroelectric Thin Film Transistors with Large Memory Window Using Epitaxial Yttrium-Doped Hafnium Zirconium Gate Oxide

Preventing ferroelectric materials from losing their ferroelectricity over a low thickness of several nanometers is crucial in developing multifunctional nanoelectronics. Epitaxially grown 5 at. % yttrium-doped Hf_0.5Zr_0.5O₂ (YHZO) thin films exhibit an atomically smooth surface, an ability to maintain ferroelectricity even at a thickness of 10 nm, and excellent insulating properties, making them suitable for use as gate oxides in ferroelectric thin film transistors (FeTFTs). Through the epitaxial growth of a YHZO/La_0.67Sr_0.33MnO₃ (LSMO)/SrTiO₃ (STO) heterostructure, YHZO effectively retains its ferroelectricity and orthorhombic single phase, leading to enhancing electron mobility (∼19.74 cm² V^-1 s^-1) and memory window (3.7 V) in the amorphous InGaZnO₄ (a-IGZO)/YHZO/LSMO/STO FeTFTs. These FeTFTs demonstrate a consistent memory function with remarkable endurance (∼10⁶ cycles) and retention (∼10⁴ s). Furthermore, they sustain a constant memory window even under ±6 V bias stress for 10⁴ s and exhibit excellent stability even under ±6 V/1 ms pulse cycling for 10⁷ cycles. For comparison, a transistor with the same structure was fabricated using epitaxial nonferroelectric LaAlO₃ (LAO) and epitaxial undoped Hf_0.5Zr_0.5O₂ (HZO) as alternatives to YHZO. This study presents a novel approach to exploit the potential of YHZO in FeTFTs, contributing to the development of next-generation logic-in-memory.