Mechanism of polarization “Wake-Up” in ferroelectric Hafnia-Zirconia thin films

Abstract

As an emerging non-volatile memory technology, HfO2-based ferroelectrics exhibit excellent compatibility with silicon CMOS process flows; however, during repeated programming and erase of the polarization state of HfO2-based ferroelectric capacitors, the magnitude of the measured polarization increases, a phenomenon known as “wake-up”. Here-in, we study the cause of wake-up effect in Hf0.5Zr0.5O2 (HZO) capacitors using non-destructive methods that probe statistically significant sample volumes. Synchrotron X-ray diffraction reveals a concerted shift in HZO Bragg peak position as a function of polarization switching cycle number in films prepared under conditions such that they exhibit extremely large (∼3000%) wake-up. Piezoresponse force microscopy measurements are utilized to visualize domain switching with wake-up. The combination of these observations clearly demonstrates that wake-up is caused by a field driven phase transformation of the tetragonal phase to the metastable ferroelectric orthorhombic phase during polarization switching of HZO capacitors.