Fabrication of ZnO/HfO<inf>2</inf>/ZnO nanowire capacitors by MOCVD

Abstract

Nonvolatile ferroelectric random access memory (FeRAM) is a promising candidate for internet of things (IOT) because of extremely low power consumption. However, its high integration has not been achieved yet owing to a difficulty in downscaling of the memory cell including one transistor and one capacitor. One of the solutions to realize the very small capacitors is the employment of multi-shell nanowires (NWs) including ferroelectrics. We have already established fabrication process of ferroelectric NWs/nanotubes by metal organic chemical vapor deposition (MOCVD) using conductive ZnO NWs as a template. Hence, we have proposed the introduction of ZnO/HfO 2 /ZnO NW capacitors into FeRAM memory cells using HfO 2 as a ferroelectric. In this study, we focus on the crystallization of HfO 2 layers on ZnO NW. ZnO NWs used as a template for NW capacitors were grown on Pt-covered SiO 2 /Si substrate by MOCVD using Zn(C 2 H 5 ) 2 and O 2 as a precursor and oxidizing gas, respectively. HfO 2 was also deposited on ZnO NWs templates at 200 C using Hf(O-t-C 4 H 9 ) 4 and O 2 as a precursor by MOCVD. Subsequently, crystallization of HfO 2 layer was induced by rapid thermal annealing (RTA) at 600∼1200 C for 5min in N 2 before top electrode deposition. The diameter and aspect ratio of ZnO NW used as template were 200nm and 55, respectively. HfO 2 thin film with a thickness of 20nm was uniformly deposited on ZnO NWs by MOCVD. Ferroelectric orthorhombic phase was obtained by RTA below 900 C while paraelectric monoclinic phase was appeared by RTA at 1000 and 1200 C.