Improvement in nonvolatile memory operations for metal-ferroelectric-insulator-semiconductor capacitors using HfZrO2 and ZrO2 thin films as ferroelectric and insulator layers

Metal-ferroelectric-insulator-semiconductor (MFIS) capacitors were characterized to elucidate the optimum design schemes for the ferroelectric field-effect transistor applications. The Hf1-x Zr (x) O-2 (HZO) thin films (18 nm) were prepared on the SiO2 and ZrO2 insulator layers (ILs) with different film thicknesses. The choice of 10 nm thick ZrO2 IL was found to be an optimum condition to properly balance between the values of electric fields applied to the HZO (E (HZO)) and ZrO2 (E (IL)) layers, leading to effective improvement in capacitance coupling ratio and to suppression of charge injection for the MFIS capacitors. Furthermore, the crystalline natures of the crystallized HZO films were also found to be strategically controlled on the ZrO2 ILs, which can additionally enhance the E (HZO) with reducing the E (IL). As consequences, the MFIS capacitors using 10 nm thick ZrO2 IL exhibited the ferroelectric memory window as large as 2.5 V at an application of +/- 5 V, which corresponds to 2.7 times wider value, compared to that obtained from the device using 2 nm thick SiO2 IL. Long-time memory retention and robust program endurance were also verified for the fabricated MFIS capacitors.

Automated summary

In this study, Metal-ferroelectric-insulator-semiconductor (MFIS) capacitors were characterized to explore the optimal design schemes for ferroelectric field-effect transistor applications. The findings suggest that the choice of specific film thickness and control of crystalline nature can greatly enhance the performance of the MFIS capacitors, leading to improvements in capacitance coupling ratio, charge injection suppression, and memory retention.