Electrical properties of metal-ferroelectric-insulator-semiconductor structures based on ferroelectric polyvinylidene fluoride copolymer film gate for nonvolatile random access memory application

Abstract

Metal-ferroelectric–insulator-semiconductor device structures with ferroelectric vinylidene fluoride-trifluoroethylene copolymer and ${\mathrm{SiO}}_2$ buffer layer integrated gate stack over $n\text{-}\mathrm{Si}$ are formed, and their potential for fabricating polymeric nonvolatile random access memory devices is demonstrated. Capacitance-voltage $\left(C–V\right)$ studies show that switchable polarization in poled polyvinylidene fluoride PVDF copolymer film changes the $\mathrm{Si}$ -surface potential and causes modulation of the $\mathrm{Si}$ -surface conductance. The $\left(C–V\right)$ hysteresis and bidirectional flatband voltage shift at $-10$ to $+6\mathrm{V}$ , depending on the polarization field direction and remnant polarization at the ferroelectric PVDF copolymer gate, presents a memory window. The space charge at $n\text{-}\mathrm{Si}$ and switchable polarization both reduce the field across the ferroelectric PVDF. The observed asymmetry of the negative flatband-voltage shifts in the negatively poled ferroelectric polymer state is the result of the depletion layer formation, which reduces the field across the polymeric gate. Internal field due to negative and positive bound charges within PVDF copolymer and ${\mathrm{SiO}}_2$ , respectively, influences polarization switching by pinning of dipoles. Higher negative gate bias is needed to overcome the pinning effect and to switch the polarization field. @2004 American institute of Physics.