Ferroelectric properties of thin HfO₂ films

Abstract

When the ferroelectricity of HfO₂ thin film was announced in 2011, it did not particularly attract a great amount of attention, nonetheless, in recent years, there has been a lot of interest, not only in its application, but also from a materials science point of view. Conventionally, most ferroelectric materials have had a perovskite structure, such as is represented by PZT, with a thickness of several hundred nanometers. In contrast, the discussion of the thickness of ferroelectric thin film has changed rapidly and is now down to a few nanometers with the emergence of HfO₂. It even has approximately the same degree of residual polarization. Moreover, HfO₂ material has a high affinity with semiconductor processes, which have been used for the state-of-the-art CMOS gate stack, so that it can be used in semiconductor devices with confidence. The characteristics of ferroelectric HfO₂ are that its ferroelectricity is generated mainly through doping. This article will discuss the results by focusing on this doping effect. Furthermore, this material has the potential to be used in different areas from those of conventional applications, and therefore we will discuss it specifically from the point of view of novel electronic devices.