Artificial relative permittivity enhancement in BaTiO3 thin films

Barium titanate (BTO) is a well known ferroelectric perovskite for its large permittivity and low dielectric loss, which can vary by applying an electric field, suitable for tunable capacitors [1]. However, these properties... [ view full abstract ]

Barium titanate (BTO) is a well known ferroelectric perovskite for its large permittivity and low dielectric loss, which can vary by applying an electric field, suitable for tunable capacitors [1]. However, these properties are strongly degraded when deposited as thin films. One of the most important effects contributing to such degradation has been attributed to the presence of charged defects at interfaces [2-3], either as intrinsic interfaces (e.g. grain boundaries) or as extrinsic interfaces (e.g. film/electrode contact). Using this background, our aim is to increase artificially the relative permittivity by creating charged defects within the film. Our main case of study is polycrystalline BTO thin films (undoped) and substituted with Nb (0.05%) and La (0.1%) deposited as single doped films (300 nm) and alternating 3 layer heterostructures BTO:La - BTO:Nb - BTO:La (H1). Their chemical, structural, dielectric and electric properties were analyzed by Electron Paramagnetic Resonance, X-Ray Diffraction, ex-situ and in-situ XPS, leakage currents measurements and Impedance spectroscopy versus frequency (from 100 Hz to 1 MHz; Figure 1) and static electric field (Ebias = 100 kV/cm; Figure 2). Undoped, La-doped and Nb-doped BTO films exhibit a permittivity of 400, 500 and 850, correspondingly, at 100 kHz and room temperature. In the same conditions, H1 showed a permittivity of 1050. Using the permittivity values of single doped films and a simple model of 3 capacitors in series, we found that the experimental H1 permittivity is higher than the calculated one, suggesting that inner interfaces (La-Nb) contribute to this enhancement.

[1] J. Ravez et al., J. Mater. Chem, 9, 1609 (1999)

[2] J. F. Scott, Ferroelectric Memories, Advanced Microelectronics, Vol. 3, 266 pages (2000).

[3] J. Junquera and P. Ghosez, Nature. 422, 506. (2003).