Bismuth titanate ferroelectric nanofilms formed directly on Si(100) substrates for memory application

Abstract

To realize ultrasmall ferroelectric-gate transistor memory, we have focused on nanometer—thick lanthanum—substituted bismuth titanate (BLT: Bi4−x La x Ti3O12) and developed the processes to form BLT thin films directly on Si(100) substrates using chemical solution deposition method. The BLT film thickness was well controlled by the mixing ratio of the coating materials. The structural and electrical properties of BLT nanofilms have been systematically investigated. The BLT films with preferred a-axis orientation were formed on p-Si(100) and n-Si(100) substrates by crystallization at 550 °C. The BLT films were found to consist of nano-sized crystal grains, and the lattice spacing and grain size depended on the film thickness. Furthermore, the capacitance–voltage characteristics of the Au/BLT/Si structures showed hysteresis due to the ferroelectricity of the BLT, even for the films of less than 10 nm thick. The dielectric constant of the BLT film decreased from ~13 for 35 nm to ~3 for 11 nm.