Nonvolatile optical phase shift in ferroelectric hafnium zirconium oxide.

A nonvolatile optical phase shifter is a critical component for enabling the fabrication of programmable photonic integrated circuits on a Si photonics platform, facilitating communication, computing, and sensing. Although ferroelectric materials such as BaTiO 3 offer nonvolatile optical phase shift capabilities, their compatibility with complementary metal-oxide-semiconductor fabs is limited. Hf 0.5 Zr 0.5 O 2 is an emerging ferroelectric material, which exhibits complementary metal-oxide-semiconductor compatibility. Although extensively studied for ferroelectric transistors and memories, its application to photonics remains relatively unexplored. Here, we show the optical phase shift induced by ferroelectric Hf 0.5 Zr 0.5 O 2 . We observed a negative change in refractive index at a 1.55 μm wavelength in a pristine device regardless of the direction of the applied electric field. The nonvolatile phase shift was only observed once in a pristine device. This non-reversible phase shift can be attributed to the spontaneous polarization within the Hf 0.5 Zr 0.5 O 2 film along the external electric field.