Memory window enhancement in n-type ferroelectric field-effect transistors by engineering ozone exposure in atomic layer deposition of HfZrOx films

Abstract

We demonstrate n-type ferroelectric field-effect transistors (FeFETs) employing atomic-layer-deposited HfZrOx (HZO) films with a large memory window (MW) immediately after the write operation. Charge trapping at the HZO/Si interface in FeFETs is the primary source of memory window reduction. To control the properties of the interfacial layer, we varied the O-3 injection time during atomic layer deposition. The HZO (long O-3 of 7 s)-based FeFET demonstrated a large MW (2.1 V) in the DC transfer curves compared with the HZO (short O-3 of 0.3 s)-based FeFET (0.9 V), although the bulk properties of the HZO films barely changed with the O-3 injection time. In pulsed I-V measurements with an extremely short delay time of 100 ns between pulses, the HZO (long O-3 of 7 s)-based FeFET showed a large MW of 1.0 V. Such improvements in the performance of HZO-based FeFETs indicate that the trap density in the interfacial layer is reduced by the use of a long O-3 injection time. This is supported by the variation in the silicate/SiO2 ratio within the interfacial layer of the HZO films deposited at various O-3 injection times.