Ferroelectric Nonvolatile Memory Field-Effect Transistors Based on a Novel Buffer Layer Structure

Abstract

We have proposed and developed a ferroelectric nonvolatile field-effect transistor that incorporates a thin MgO buffer layer between a ferroelectric film and an oxidized Si substrate. The use of an MgO/SiO2 buffer for a ferroelectric gate is based on the following findings. First, a thin MgO buffer serves well as a template layer allowing the growth of highly oriented ferroelectric films on amorphous substrates. Second, MgO works well as a diffusion barrier between a ferroelectric film and a substrate, protecting the silicon FET channel region from interdiffusion or reaction that may occur during device processing. Third, thermal oxidation of Si is known to be one of the best ways of passivating silicon surfaces, thus to reduce high quality FET channels. The fabricated devices show excellent performance in ferroelectric polarization switching, memory retention, and fatigue resistance. The devices also demonstrate scalability in device dimension and operating voltage, i.e., they are suitable for low voltage operation (3-5 V or below) showing a sufficient memory window (1-2 V).