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T9.5.1/N9.5.1

Conduction Mechanisms in SrTiO3 Thin Films on Silicon Bogdan Mereu1,2, George Sarau2, and Marin Alexe1 1 2

Max Planck Institute of Microstructure Physics, Halle, Germany National Institute for Material Physics, Bucharest-Magurele, Romania

ABSTRACT New materials with high dielectric constant are currently being explored to replace silicon dioxide as gate dielectric for device scaling below 0.1 µm. With respect to conventional SiO2, these high permittivity dielectrics provide the required equivalent oxide thickness (EOT) without of further reduction of the insulator physical thickness, which is a key issue to limit gate leakage current and to maintain comparable MOSFET operation and reliability. The present paper presents preliminary results on conduction mechanisms in thin epitaxial SrTiO3 films grown by MBE on Si (100). I-V measurements were performed on Al/STO/Si structures at temperatures ranging from 40 K to 290 K. At temperatures lower than 100 K the conduction mechanism of electrons from gate electrode across the oxide barrier neither Schottky emission nor tunneling. For temperatures higher than 100 K Schottky emission occurs and barrier heights were extracted, showing an approximate linearly increase with temperature. In case of Si/STO interface, a Fowler-Nordheim tunneling mechanism was detected at 40 K and at intermediate fields. The extracted barrier heights are: 0.07 eV at Si/STO interface and from 0.26 eV (130 K) to 0.53 eV (290 K) at Al/STO interface. INTRODUCTION Since the 1960’s, silicon dioxide has been used as gate dielectric in CMOS technology. The very high band gap, which assures large band offsets with silicon, the very small density of interface states at silicon-SiO2 interface made it the ideal gate dielectric without alternatives. In recent years, the scaling down of MOSFET devices reveals the physical limit of silicon dioxide. For oxide thicknesses lower than 2 nm direct tunneling currents and reliability problems affect the normal electrical behavior of MOS transistors. These effects cannot be avoid in the present configuration and the solution comes from the replacing of silicon dioxide as gate dielectric with a higher-k dielectric, so that a physically thicker film can still have a thin equivalent electrical thickness. The increase in physical thickness determines the decrease of tunneling currents. The search for new gate dielectrics has encompassed a wide range of materials, like SiN, nitrided SiO2, Ta2O5, TiO2, Al2O3, Y2O3, HfO2, SrTiO3. Strontium titanate has been investigated for a long time due to its very high bulk dielectric constant and a high degree of structural compatibility with Si, making epitaxy possible. Among prospective high-k dielectrics SrTiO3 has a high bulk dielectric constant, as well as a high degree of structural compatibility with Si making epitaxy possible. It has been demonstrated that single-crystal SrTiO3 thin films can be grown on Si substrates by molecular beam epitaxy (MBE) and can provide for MOS devices interface states densities as low a