Superior QLC Retention (10 Years, 85°C) and Record Memory Window (12.2 V) by Gate Stack Engineering in Ferroelectric FET: from “MIFIS” to ”MIKFIS”
Song‐Hyeon Kuk, Bong Ho Kim, Youngkeun Park, Kyul Ko, Hyeon-Seong Hwang, Dahye Lee, Byung Jin Cho, Jae-Hoon Han, Sanghyeon Kim
Abstract
As stacking hundreds of layers, 3D NAND faces new challenges and needs for further scaling. Ferroelectric field-effect-transistor (FEFET) is a potential solution, with advancements in gate stack engineering, specifically the metal-insulator-ferroelectric-insulator-semiconductor (MIFIS) stack, achieving a memory window (MW) over 10 V. However, the gate stack with a feasible MW is still thicker <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$( > 18\ \text{nm})$</tex> than that of charge-trap-flash (CTF) NAND, degrading bit density. Additional MW expansion methods using bandgap engineering (BE) with an oxide-nitride-oxide (ONO) layer were also proposed, but further increased the gate stack thickness. Moreover, the previous approaches have critical drawbacks such as monoclinic-(m-) phases in thick <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\text{FE}-\text{HfO}_{2}$</tex> films, unstable retention, degraded write voltage and speed, and higher equivalent oxide thickness (EOT). To address the issues, we propose a novel gate stack, metal-insulator-high k-ferroelectric-insulator-semiconductor (MIKFIS). The main idea is that the <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\text{FE}-\text{HfO}_{2}$</tex> thickness can be scaled down by partially replacing it with paraelectric (PE) <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\text{HfO}_{2}$</tex>, without increasing the gate stack thickness. In addition, fabricated MIKFIS FEFETs show a record MW of 12.2 V with the Si channel, highly reliable 10-year retention with quad-level-cell (QLC) operations at <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$24^{\mathrm{o}}\mathrm{C}$</tex> and <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$85^{\mathrm{o}}\mathrm{C}$</tex> for the first time. The origin of the stable retention is revealed by accurately measuring absolute polarization (P) directly from the FEFETs. The superiority of the MIKFIS FEFET indicates that a MIKFIS stack is a strong candidate for the gate stack in 3D FE NAND.