Associate Professor, Department of Innovative and Engineered Materials, Interdisciplinary Graduate School of Science and Engineering, Tokyo Institute of Technology
Development of novel “size-effect free” high permittivity thin film
Dielectric materials with a high dielectric constant are important for the development of high density capacitors for the development of highly integrated devices. However, the dielectric constant of these materials, especially having perovskite type of structure, is widely known to decrease as the film thickness decreases, which is widely known as “size effect in dielectric thin film”. Because of this, it has been difficult to prepare high density capacitors.
In this study, I focused on c-axis-oriented thin films of bismuth layer-structured dielectrics (BLD) having a natural superlattice structure made of the alternating stacks of the bismuth oxide layers and pseudoperovskite layers along c-axis orientation (Fig. 1). We found that c-axis-oriented BLD films had dielectric constants above 200 and were “size effect free” (Fig. 2). In addition, they had good insulating characteristics and had stable dielectric constants independent of the applied voltage and the strain from the substrate. These unique characteristics are considered to occur because of the stacked structure.
I am now trying to develop novel characteristics by exploiting the advanced stack structure.
