Characterization of Metal/Ferroelectric/Insulator/Semiconductor Structure with CeO2 Buffer Layer

Abstract

A PbTiO3 ferroelectric film 813 Å thick was grown on a CeO2/Si(100) substrate by the digital chemical vapor deposition method. As the buffer layer between the perovskite PbTiO3 film and Si substrate, a CeO2 intermediate layer was grown on the Si(100) substrate using an ultrahigh vacuum (UHV) system. The density of surface states at the CeO2/Si(100) interface was estimated from the capacitance-vs-voltage (C-V) characteristics of Al/CeO2/Si(100) samples to be 8×1011/cm2 eV, and CeO2 films on Si(100) are therefore expected to be suitable as gate oxides for metal/ferroelectric/semiconductor-field-effect transistors (FETs). Experimental results derived from the C-V characteristics of metal/ferroelectric/insulator/semiconductor (MFIS)-structured samples show that the MFIS structure has ferroelectric switching properties, as demonstrated by the roughly 2.4 V threshold hysteresis in its C-V characteristics (“memory window”). Furthermore, the retention time of the MFIS sample was estimated to be 100,000 s by measuring the time dependence of capacitance at the voltage at the centuer of the memory window. Interfacial lines of the MFIS structure were clear in a transmission electron microscope image, and an amorphous CeOx layer and an amorphous SiO2 layer were seen between the Si substrate and PbTiO3 film. Secondary ion mass spectroscopy revealed that there was little diffusion of Si atoms into the PbTiO3 layer on the CeO2/Si substrate.