Permittivity Enhancement of $\hbox {Ta}_{2}\hbox {O}_{5}/\hbox {Co/Ta}_{2}\hbox {O}_{5}$ Trilayer Films

Co inserted layer with different thickness on the permittivity of Ta₂O₅(60 nm)/Co(x nm)/Ta₂O₅(60 nm) trilayer films fabricated on the B270 glass substrates by the reactive sputtering technique was studied. The variation of dielectric constant of the samples is dependent on the thickness of the Co inserted layer observed from 1 kHz and 30 MHz. The dielectric constant of the Ta₂O₅(60 nm)/Co(x nm)/Ta₂O₅(60 nm) thin films was varied roughly from 7.9 up to 90.6 with the thickness (x) of the Co interlayer varied from 0 nm to 20 nm. The value of the dielectric constant is roughly near 7.9 for samples with x between 0 and 2 nm. However, it increases abruptly for samples with x larger than 2 nm, this large enhancement behavior of the dielectric constant could be explained due to the growth mechanism of the Cobalt inter-layer from island clusters to continuous Co layer for samples with x between 2 and 3 nm. For the magnetic induced ferroelectric variation, the variation of the dielectric constant increased with thickness of Co for samples with x larger than 3 nm. However this increase behavior is roughly saturated for applied magnetic field roughly above 20 Oe. This magnetic tunability of the dielectric constant is clearly attributed to the Co layer in the films. From the electric consideration, the adding of a Co inter-layer in Ta₂O₅/Co/Ta₂O₅ structures redistributes the interface charges between Co and Ta₂O₅ layers, and that enhances both the intrinsic polarization and its dielectric constant. The magnetoelectric properties in Ta₂O₅/Co/Ta₂O₅ films are manifested and it has potential for a ferroic sensor application.