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

To realize ultrasmall ferroelectric-gate transistor memory, we have focused on nanometer-thick lanthanum-substituted bismuth titanate (BLT: Bi4-xLaxTi3O12) 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 degrees 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 similar to 13 for 35 nm to similar to 3 for 11 nm. (C) 2021 The Japan Society of Applied Physics