However, the relatively large dielectric insertion loss, soft mode effect, and limited figure of merit at high-frequency microwave regions still restrict practical see more applications in tunable microwave elements. Therefore, optimizing the microwave dielectric properties by lowering the dielectric loss tangent and enhancing dielectric tunability has become an important issue for device CDK inhibitor applications [13–19]. Multifunctional tunable ferroelectric BaTiO3/SrTiO3 (BTO/STO) heterostructures with artificial multilayer and/or superlattice structures have achieved a great enhancement on physical properties compared to the single-crystal epitaxial films of BTO, STO,

and BST [20–27]. Especially, the interface and nanosize effects have been found to significantly enhance the dielectric properties from the BTO/STO multilayer system at low frequency

range [28–33]. However, there are quite a few reports on high-frequency microwave properties in the gigahertz range. Recently, we have systematically studied [(BaTiO3)0.4/(SrTiO3)0.6] N multilayered thin films and found that the high-frequency microwave dielectric properties and related physical properties can be significantly improved by optimizing the growth conditions. The optimized dielectric performance was achieved with the best value for the loss tangent (0.02) at approximately 18 GHz with each BTO layer thickness near 7.0 nm [34]. However, the high dielectric constant of Entospletinib order near 1,600 achieved from the [(BaTiO3)0.4/(BaTiO3)0.6] N multilayer is too high to meet the device Baricitinib requirements for impedance matching which is normally less than 500 [35]. To reduce the dielectric constant for meeting the impedance matching requirement, we have redesigned and further investigated a new combination of BTO/STO multilayer systems of the optimized [(BaTiO3)0.5/(BaTiO3)0.5]16 based on our above optimized multilayered structure. Here, we report our recent achievements on the microstructural studies and high-frequency microwave (5 to 18 GHz) dielectric measurements of [(BaTiO3)0.5/(SrTiO3)0.5]16

on (001) MgO substrates. Methods A KrF excimer pulsed laser deposition system with a wavelength of 248 nm was employed to fabricate the ferroelectric BTO/STO multilayered thin films on (001) MgO substrates. Single-phase pure BTO and STO targets were employed for the fabrication. The single-crystal MgO substrates were selected for the epitaxial growth of the superlattices because of their low frequency-dependent dielectric constant (approximately 9.7) and low loss tangent values (approximately 3.3 × 10−7). The optimal growth conditions were found at a temperature higher than 840°C with an oxygen pressure of 250 mTorr under a laser energy density of about 2 J/cm2 with a repetition rate of 4 Hz.