Structural and electrical properties of ferroelectric BiFeO3/HfO2 gate stack for nonvolatile memory applications

Abstract

Difficulties in the fabrication of direct interface of ferroelectric BiFeO3 on the gate of ferroelectric field effect transistor (FeFET) is well known. This paper reports the optimization and fabrication of ferroelectric/dielectric (BiFeO3/HfO2) gate stack for the FeFET applications. RF magnetron sputtering has been used for the deposition of BiFeO3, HfO2 films and their stack. X-Ray diffraction (XRD) analysis of BiFeO3 shows the dominant perovskite phase of (104), (110) orientation at 2θ=32∘ at the annealing temperature of 500∘C. XRD analysis also confirms the amorphous nature of the HfO2 film at annealing temperature of 400∘C, 500∘C and 600∘C. Multiple angle analysis shows the variation ion the refractive index between 2.98–3.0214 for BiFeO3 and 2.74–2.9 for the HfO2 film with the annealing temperature. Metal/Ferroelectric/Silicon (MFS), Metal/Ferroelectric/Metal (MFM), Metal/Insulator/Silicon (MIS), and Metal/Ferroelectric/Insulator/Silicon (MFIS) structures have been fabricated to obtain the electric characteristic of the ferroelectric, dielectric and their stacks. Electrical characteristics of the MFIS structure show the memory improvement from 2.7V for MFS structure to 4.65V for MFIS structure with 8nm of buffer dielectric layer. This structure also shows the breakdown voltage of 40V with data retention capacity greater than 9×109 iteration cycles.

Keywords

• Endurance
• ferroelectric
• high-k dielectric
• memory window
• MFIS