Relaxation analysis to understand positive bias induced trapping in ferroelectric FETs with Si and Gd dopants

In this work, the relaxation analysis is performed to understand the VTH instability in FeFETs with two different dopants, i.e., Si and Gd. The FeFETs with different dopants show the different delay-after-write characteristics, i.e., Gd:HfO2 FeFETs show a better delay-after-write stability compared to the case of Si:HfO2 FeFETs. With the relaxation analysis, Si:HfO2 FeFETs exhibit an obvious VTH recovery during the relaxation phases. Furthermore, the power law fitting is used to analyze the VTH shift under the positive program bias, indicating that a wide and easily accessible defects can exist in the IL and/or Si:HfO2 since the smaller overdrive voltage dependence exponent (γ) is obtained in Si:HfO2. Last, the smaller VTH shift/recovery in Gd:HfO2 FeFETs can be attributed to a relatively tighter defect distribution, indicating that the dopants in the ferroelectric layer and the defects in IL and/or ferroelectric dielectric have to be carefully optimized to achieve the better VTH stability.