Ferroelectric HfO2 - Material Fundamentals and Possible Applications
We first discuss dopant effects on the ferroelectricity of HfO2. We prepared many kinds of doped HfO2 with both cations (Y, Sc, Al, Si, Ge, Zr, and Nb) and anion (N). We have noticed about not only dopant-dependent but also dopant-independent contributions to ferroelectric properties. The former one obviously comes from dopant atomic nature such as ionic charge or size, while the latter one is the point we are interested in. A small amount of N doping enables to achieve the ferroelectric HfO2, while Zr slowly and Ge moderately help the ferroelectric phase formation of HfO2. More interestingly, the dopant sensitivity curve seems to be similar in shape irrespective of dopant species. This fact suggests that HfO2 ferroelectricity is achieved by HfO2 intrinsic properties.
Concerning possible applications, many ferroelectric devices have already been proposed. In case of ferroelectric HfO2, it is interesting to note that we will be able to enjoy nanometer- thick ferroelectric films in addition to conventional ferroelectric applications. We are interested in ferroelectric tunnel junctions (FTJs), and low voltage ferroelectric FETs (Fe-FETs) including negative capacitance FETs (NC-FETs). Some of them will be discussed in the presentation.