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Direct current (dc) bias-induced acoustic resonance phenomena is observed in micromachined tunable thin-film capacitors based on paraelectric [Ba.sub.0.3][Sr.sub.0.7]Ti[O.sub.3] thin films. The frequency of the first-order resonance has shifted down with increasing bias, whereas the antiresonance frequency might shift up or down with increasing bias.

Micromachining technology was used for the fabrication of a [Ba.sub.x][Sr.sub.1-x]Ti[O.sub.3] (BST)-based thin film resonator. Direct current (DC) bias-dependent acoustic resonance phenomena were observed in the resonators.

The epitaxial SrTi[O.sub.3] thin films were deposited on (001) LaAl[O.sub.3 single crystals by pulsed laser deposition to study the postannealing effect at 1100 degree Celsius in [O.sub.2] atmosphere for 4 h. The structural and dielectric characterizations indicate that the enhancement of permittivity is mainly due to the relaxation of the misfit strain between the film and substrate.

The effect of dilution of tunable ferroelectric with linear materials are theoretically addressed. The main impact of the dilution on the main dielectric parameters of the material is shown to be very sensitive to the composite type.

Structural and dielectric properties of strain-controlled epitaxial SrTiO3 (STO) films by two-step growth technique are investigated using in situ and ex situ observations. In the two-step grown film, the first layer accumulates defects, which leads to two effects of strain relaxation and lower loss of the film.

The reliability of tunable ferroelectric thin film capacitors is analyzed. The effect of illumination of the ferroelectric film by ultraviolet light on the tunable performance of the capacitors is examined.

A theory of digital phase shifters based on transition from a superconducting (S) state into a normal (N) state in high-T, superconductor (HTS) films is developed. It is shown that the insertion-loss level in the phase shifters is determined by the commutation quality of the HTS film and does not depend on the S-N switching element shape and size. The procedure for designing the S-N phase shifter with minimum insertion loss is equivalent to designing a matching circuit for the termination Z = [-square root of [R.sub.S][R.sub.N]] ([R.sub.S] and [R.sub.N] are the resistances of the switching element in the S- and N-states, respectively). Different versions of S-N phase shifters are suggested and discussed. High-quality S-N phase shifters can be successfully designed in a 1-10-GHz frequency range and find application on the receiving end of microwave systems. Index Terms - Microwave phase shifters, microwave switch, superconductor.