Journal Article

Enhanced ferroelectricity in ultrathin films grown directly on silicon

Kwon, Daewoong, Ramesh, Ramamoorthy, dos Reis, Roberto, Yadav, Ajay K., Cheema, Suraj S., Mehta, Apurva, Hsu, Shang-Lin, Thakare, Vishal, Zhang, Xiang, Shafer, Padraic, Proksch, Roger, Wagner, Ryan, Arenholz, Elke, Xiao, Jun, Serrao, Claudy R., Wang, Li-Chen, Tan, Ava J., Hu, Chenming, Salahuddin, Sayeef, Shanker, Nirmaan, Karbasian, Golnaz, Karapetrova, Evguenia, McCarter, Margaret R., Datar, Adhiraj, Ciston, Jim, Zhang, Haigang, Chopdekar, Rajesh V, Hsu, Cheng-Hsiang

2020

Overview

Ultrathin ferroelectric materials could potentially enable low-power logic and nonvolatile memories 1 , 2 . As ferroelectric materials are made thinner, however, the ferroelectricity is usually suppressed. Size effects in ferroelectrics have been thoroughly investigated in perovskite oxides—the archetypal ferroelectric system 3 . Perovskites, however, have so far proved unsuitable for thickness scaling and integration with modern semiconductor processes 4 . Here we report ferroelectricity in ultrathin doped hafnium oxide (HfO 2 ), a fluorite-structure oxide grown by atomic layer deposition on silicon. We demonstrate the persistence of inversion symmetry breaking and spontaneous, switchable polarization down to a thickness of one nanometre. Our results indicate not only the absence of a ferroelectric critical thickness but also enhanced polar distortions as film thickness is reduced, unlike in perovskite ferroelectrics. This approach to enhancing ferroelectricity in ultrathin layers could provide a route towards polarization-driven memories and ferroelectric-based advanced transistors. This work shifts the search for the fundamental limits of ferroelectricity to simpler transition-metal oxide systems—that is, from perovskite-derived complex oxides to fluorite-structure binary oxides—in which ‘reverse’ size effects counterintuitively stabilize polar symmetry in the ultrathin regime. Enhanced switchable ferroelectric polarization is achieved in doped hafnium oxide films grown directly onto silicon using low-temperature atomic layer deposition, even at thicknesses of just one nanometre.

• Publisher: Nature Publishing Group UK,Nature Publishing Group
• Subject: 142/126 / 142/136 / 639/301/1005/1007 / 639/301/119/544 / 639/301/119/996 / Asymmetry / Atomic layer epitaxy / Broken symmetry / Control / Dielectric films / Electric properties / Electronic devices / Ferroelectric crystals / Ferroelectric materials / Ferroelectricity / Ferroelectrics / Ferroelectrics and multiferroics / Film thickness / Fluorite / Growth / Hafnium / Hafnium oxide / Humanities and Social Sciences / INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY / Microscopy / multidisciplinary / Oxides / Perovskites / Polarization / Science / Science (multidisciplinary) / Shift work / Silicon / Size effects / Spectrum analysis / Surfaces, interfaces and thin films / Symmetry / Thin films / Transistors / Transition metal oxides