The loss factor (tan δ) of ferroelectric material at microwaves and the tunability (n) defined as a ratio of the dielectric permittivity at zero dc field to the dielectric permittivity at the given field are strongly connected with the softness of so-called ferroelectric soft mode. The loss factor and the tunability are generalized by the commutation quality factor (CQF). The dielectric response of a ferroelectric material allows one to determine the CQF and to compare it to the theoretical CQF obtained for a perfect ferroelectric sample. In order to compare the theoretical prediction and experimental data, the influence of deposition parameters on microwave properties of BaxSr1−xTiO3 (BSTO) films deposited on sapphire and alumina substrate has been investigated in a wide frequency range (1–30 GHz). The highest CQF at room temperature was obtained for the 30% Ba content target and the deposition temperature 905 °C. The best BSTO films exhibited CQF≅1.6×104 with n=2.1 and tan δ=0.012 at 1 GHz and zero bias. This result is among the best reported for sputtered BSTO films both on sapphire and alumina substrates. Nevertheless the obtained CQF is 3–5 times lower than the upper theoretical limit.

Articles you may be interested inModification of energy band alignment and electric properties of Pt/Ba0.6Sr0.4TiO3/Pt thin-film ferroelectric varactors by Ag impurities at interfaces Suppression of slow capacitance relaxation phenomenon in Pt/Ba0.3Sr0.7TiO3/Pt thin film ferroelectric structures by annealing in oxygen atmosphere Appl. Phys. Lett.The effects of ultraviolet ͑UV͒ irradiation on the relaxation processes in Ba 0.3 Sr 0.7 TiO 3 thin film capacitors were experimentally investigated in a range of wavelengths = ͑310-400͒ nm. It was observed that irradiation with a specific wavelength reduces the time of slow capacitance relaxation up to three orders of magnitude in comparison with relaxation time in the "dark" regime. It was also observed that at a certain wavelength of UV irradiation there was a maximum in the leakage current of the capacitors. This wavelength corresponded exactly with a minimum in the relaxation time of the capacitance. It was shown that the decrease in the ferroelectric film thickness resulted in a shift in ͑͒minima and I͑͒maxima towards the shorter wavelengths. Phenomena observed are analyzed using Bouguer's law.

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Intrinsic dead layer effect and the performance of ferroelectric thin film capacitors

A method to evaluate the space charge trap energy levels in ferroelectric (FE) Ba0.3Sr0.7TiO3 film incorporated into a metal/FE/metal parallel plate capacitors structure is presented. It is based on microwave measurements of the capacitance relaxation time after the end of a dc pulse, when the change in measured capacitance is due to internal processes of space charge relaxation [Q(t)] in the FE film. Using the Q(t) dependencies obtained as a function of temperature, the time constants of slow relaxation processes were defined and the trap energy levels were evaluated as Et=0.7, 0.5, and 0.1 eV.

The RF and microwave response of YBa2Cu307-S films on Ba,Srj-,TiOs/MgO substrates was investigated in an external static magnetic field. Films with a varying thickness, orientation and type of structure were studied in order to understand the mechanisms of RF and microwave residual losses. The measurements of surface resistance (R) as a function of the film t h i c h s s and static ( H ) and RF (H-) magnetic field are discussed. Analysis of theoretical and experimental R(H) dependences has shown that residual RF and microwave losses occur in a static magnetic field on Josephson junctions formed at grain boundaries and at microblock boundaries with trapped Abrikosov vortices and on Abrikosov vortices themselves, and are also caused by non-superconductive inclusions.

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