Keywords:ferroelectric film, HfO2
About 20 years have passed since the research and development of HfO2 started for high-k gate stacks. At present, ferroelectric HfO2 attarcts much attention rather than just high-k material in dielectric community. Various kinds of metal dopings have strong impact on the stable ferroelectricity in HfO2. What is the dopant specific property, and what is the common feature among various doped HfO2 films. These issues will be discussed for understanding the ferroelectric phase formation mechanism of HfO2.