Microstructure and electrical properties of CeO_2 ultra-thin films for MFIS FeRAM applications

A detailed investigation about the dependence of microstructure and electrical properties on annealing temperature was carried out for cerium oxide(CeO2) ultra-thin films(18 nm to 110 nm) on n-type Si(100) substrates by RF magnetron sputtering. Substrate temperature was kept constant at 400 ℃ for all samples. The as-deposited films were subsequently annealed in air ambient at 700,800 and 900 ℃ for 1 h respectively. The crystallinity and surface morphology of the CeO2 films were analyzed with X-ray diffractometer(XRD),scanning electron microscope(SEM),atomic force microscope(AFM) and Raman scattering measurement. Electrical properties of the Au/CeO2/Si/Au structure were examined by high frequency capacitance-voltage(C-V) characteristics at 1 MHz and leakage current density-electric field(J-E) characteristics. A Raman peak of the CeO2 thin films was seen at 463 cm-1. From C-V data,these films exhibit dielectric constants ranging from 18 to 23,the hysteresis width(-VFB) ranging from 0.015 V to 0.12 V and the density of trapped charges ranging from 1.45×1011 to 3.01×1011 cm-2. A leakage current of 4.75×10-8 -9.0×10-7 A/cm2 at 2 MV/cm was observed. The experimental results show that the CeO2 buffer layers are suitable for non-volatile metal-ferroelectric-insulator-semiconductor(MFIS) structure field-effect-transistors(FETs) memory applications.

Characterization of ultra-thin Y_2O_3 films as insulator of MFISFET structure

The possibility of ultra-thin Y2O3 (yttrium sesquioxide) films as insulator of metal ferroelectric insulator semiconductor (MFIS) structure was investigated. The ultra-thin Y2O3 films with thickness of 10-40 nm were fabricated on p-type Si (100) substrates by molecular beam epitaxy(MBE) in vacuum and subsequently submitted to rapid thermal processing (RTP) in air ambient at 700, 800 and 900 ℃ for 30 min, respectively. The films were characterized by X-ray diffractometry and Raman spectroscopy. High frequency capacitance—voltage (C—V) characteristics and current—voltage (I—V) characteristics of the Y2O3/Si structure were analyzed. A Raman peak of the Y2O3 thin films was observed at 378 cm-1. From the C—V data, these films exhibit dielectric constants ranging from 13 to 17.28, the hysteresis width (△VFB) ranging from 0.07 to 0.22 V and the density of trapped charges ranging from 1.65×1011 to 4.01×1011 cm-2. A leakage current of 4.75×10-8 -9.0×10-6 A/cm2 at 1.5 MV/cm was observed. The results show that the Y2O3 buffer layers are suitable for non-volatile MFIS structure field-effect-transistors (FETs) memory application.