Fabrication of Ultrathin Ferroelectric Al<sub>0.7</sub>Sc<sub>0.3</sub>N Films under Complementary‐Metal‐Oxide‐Semiconductor Compatible Conditions by using HfN<sub>0.4</sub> Electrode
Seung Kyu Ryoo, Kyung Do Kim, Wonho Choi, Panithan Sriboriboon, Seungjae Heo, Haengha Seo, Yoon Ho Jang, Jeong Woo Jeon, Min Kyu Yeom, Suk Hyun Lee, Han Sol Park, Yunseok Kim, Cheol Seong Hwang
Abstract
Abstract Aluminum scandium nitride (AlScN) has emerged as a promising candidate for next‐generation ferroelectric memories, offering a much higher remanent charge density than other materials with a stable ferroelectric phase. However, the inherently high coercive field requires a substantial decrease in film thickness to lower the operating voltage. Significant leakage currents present a severe challenge during the thickness scaling, especially when maintaining compatibility with complementary‐metal‐oxide‐semiconductor (CMOS) fabrication standards. This study adopts a HfN 0.4 bottom electrode, which minimizes lattice mismatch with Al 0.7 Sc 0.3 N (ASN), forming a coherent bottom interface that effectively reduces leakage currents even at thickness < 5 nm. CMOS‐compatible HfN 0.4 /ASN/TiN stack, deposited without vacuum break between each layer, demonstrates exceptional scalability, confirming the ferroelectricity of ASN films at thicknesses down to 3 nm. The coercive voltage is decreased to 4.35 V, significantly advancing low‐voltage AlScN devices that align with CMOS standards.