A comprehensive variability study of doped HfO2 FeFET for memory applications

Abstract

We present the results of an extensive analysis of 3 different elements (Si, Gd and Y) used as dopants for HfO2 in ferroelectric FET (FeFET). Firstly, the ferroelectric response of doped HfO2 has been characterized on simple Metal / Ferroelectric / Insulator / Semiconductor (MFIS) capacitors, and the mean domain size of crystallized HfO2 for the 3 dopants has been measured by Piezo Force Microscopy (PFM). Secondly endurance and retention have been tested on FeFETs; the effect of variations in the gate stack to enhance the memory window (MW) has been also evaluated. Thirdly, a thorough study of variability in the pristine state and as function of bipolar cycling have been carried out on the 3 types of FeFETs. A link is drawn between domain size and variability; a certain degree of non-uniformity is shown to be intrinsic to ferroelectric HfO2.