  Epitaxial ferroelectric Hf0.5Zr0.5O2 films have been successfully integrated
in a capacitor heterostructure on Si(001). The orthorhombic Hf0.5Zr0.5O2 phase,
[111] out-of-plane oriented, is stabilized in the films. The films present high
remnant polarization Pr close to 20 {\mu}C/cm2, rivaling with equivalent
epitaxial films on single crystalline oxide substrates. Retention time is
longer than 10 years for writing field of around 5 MV/cm, and the capacitors
show endurance up to 1E9 cycles for writing voltage of around 4 MV/cm. It is
found that the formation of the orthorhombic ferroelectric phase depends
critically on the bottom electrode, being achieved on La0.67Sr0.33MnO3 but not
on LaNiO3. The demonstration of excellent ferroelectric properties in epitaxial
films of Hf0.5Zr0.5O2 on Si(001) is relevant towards fabrication of devices
that require homogeneity in the nanometer scale, as well as for better
understanding of the intrinsic properties of this promising ferroelectric
oxide.
