Enhanced ferroelectricity in ultrathin films grown directly on silicon
Enhanced ferroelectricity in ultrathin films grown directly on silicon
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DOI：
10.1038/s41586-020-2208-x
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发表时间：
2020-04-01
期刊：
影响因子：
64.8
通讯作者：
Salahuddin, Sayeef
中科院分区：
文献类型：
--
作者：
Cheema, Suraj S.;Kwon, Daewoong;Salahuddin, Sayeef
超薄铁电材料有可能实现低功耗钙钛矿铁电四方逻辑和非易失性存储器(1,2)。然而，随着铁电材料变得更薄，铁电性通常受到抑制。铁电体的尺寸效应已在钙钛矿氧化物（典型的铁电系统）中得到了彻底的研究(3)。然而，迄今为止，钙钛矿已被证明不适合厚度缩放以及与现代半导体工艺的集成(4)。在这里，我们报道了超薄掺杂氧化铪（HfO2）的铁电性，这是一种通过原子层沉积在硅上生长的萤石结构氧化物。我们证明了反演对称性破缺和自发的、可切换的偏振的持续性，厚度小至一纳米。我们的结果表明，与钙钛矿铁电体不同，不仅不存在铁电临界厚度，而且随着薄膜厚度的减小，极性扭曲也会增强。这种增强超薄层铁电性的方法可以为极化驱动存储器和基于铁电的先进晶体管提供一条途径。这项工作将对铁电性基本极限的研究转移到更简单的过渡金属氧化物系统，即从钙钛矿衍生的复合氧化物到萤石结构二元氧化物，其中“反向”尺寸效应违反直觉地稳定了超薄区域中的极对称性。直接生长在掺杂氧化铪薄膜中实现了增强的可切换铁电极化 使用低温原子层沉积的硅，即使厚度仅为一纳米。
Ultrathin ferroelectric materials could potentially enable low-power perovskite ferroelectric tetragonality 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 (HfO2), 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.