Articles you may be interested inDielectric and pyroelectric properties of barium strontium titanate films on orthorhombic substrates with ( 110 ) / / ( 100 ) epitaxy

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Structural distortion of ferroelectric thin films caused by film strain has a strong impact on the microwave dielectric properties. SrTiO 3 thin films epitaxially grown on ͑110͒ DyScO 3 substrates using molecular beam epitaxy are extremely strained (i.e., ϳ1% in-plane tensional strain) from 3.905 Å of bulk SrTiO 3. The room-temperature in-plane dielectric constant and its tuning of the films at 10 GHz are observed to be 6000 and 75% with an electric field of 1 V / m, respectively. The control of strain in SrTiO 3 provides a basis for room-temperature tunable microwave applications by elevating its phase-transition peak to room temperature.

The in-plane dielectric response of [110] oriented Ba0.60Sr0.40TiO3 epitaxial films grown on [100] NdGaO3 is used to determine the field induced polarization at 10GHz. The nonlinear polarization curve is used to determine the linear and nonlinear permittivity terms for the in-plane principal directions, [001] and [1¯10]. Studied films are in the thickness range of 75–1200nm, and clearly show the influences that drive tunability down with increasing residual strain. The variation of the tunability, along the [001] direction, proves to be less sensitive to residual strain then the [1¯10] direction, although [1¯10] is capable of greater tunability at low residual strains.

Epitaxial Ba0.5Sr0.5TiO3 thin films were grown by pulsed-laser deposition on (100) LaAlO3 substrates in two distinct strain states, c∕a>1 and c∕a<1. X-ray diffraction measurements over the temperature range of 20°Cto−120°C showed that the change in the c∕a ratio with decreasing temperature was discontinuous and positive for the film with c∕a>1, and continuous and negative for the film with c∕a<1. These symmetry changes in the c∕a ratio with temperature were correlated with measurements of the in-plane dielectric properties, and showed that the polarization in these two types of structures has characteristically different behavior that is highly directionally-dependent.