T. Kaydanova

Direct inkjet printing of composite thin barium strontium titanate films

Composite Ba 0 . 6 Sr 0 . 4 TiO 3 /MgO thin films with 60% tuning and tan δ of 0.007 at 2 GHz were deposited using metal organic decomposition inks by spin coating on single crystal MgO substrates. The films with approximately 1 mol% MgO in Ba 0 . 6 Sr 0 . 4 TiO 3 had a better tuning/loss ratio than either the 0 or the 10 mol% MgO substituted films. Crystalline Ba 0 . 5 Sr 0 . 5 TiO 3 films were produced on both MgO and alumina substrates by inkjet printing of metalorganic precursors with subsequent thermal decomposition followed by annealing at 900 °C. Barium strontium titanate lines as narrow as 100 μm were printed on the alumina substrates. The inkjet-printed films were predominantly (100) oriented on MgO and (110) oriented on alumina. The crystalline quality of the inkjet-printed films was improved by annealing at 1100 °C for 3 h in oxygen. Both the printed and the spin-coated films had smooth surfaces (300 A root-mean-square roughness) as required for subsequent deposition of high-resolution metal electrodes. An inkjet-printed Ba 0 . 5 Sr 0 . 5 TiO 3 film (3500 A) on MgO annealed at 1100 °C had 20% tunability of the dielectric constant (∈) at 9. 1 V/μm direct current bias and tan 8 < 0.002 at 1 MHz.

Millimeter-Wave Loaded Line Ferroelectric Phase Shifters

Ferroelectric loaded line phase shifters operating at millimeter waves for phased array antenna applications are presented. Phase shifters were manufactured on using Ba0.3Sr0.7TiO3 thin films. The magnetron sputtering process was used to fabricate these Ba0.3Sr0.7TiO3 ferroelectric films with a thickness ∼1 μm. The phase shifter operating at V-band (60 GHz) demonstrated continuous phase shift up to 220 deg and figure of merit (FOM) 22 deg/dB. The phase shifter operating at Ka-band (30 GHz) showed phase shift up to 360 deg and FOM 40 deg/dB.

Crossover between extrinsic and intrinsic dielectric loss mechanisms in SrTiO3 thin films at microwave frequencies

The do bias field. dependence of the dielectric loss in SrTi03 thin films deposited onto MgO substrate is investigated. The experimental data obtained at different frequencies of the ac field (8 and 16 GHz) from differently processed films (as deposited and oxygen annealed) strongly suggest the occurrence of a crossover in the dominant loss mechanism. The crossover is driven by the do bias field: at weak fields the loss is governed by an extrinsic mechanism(s) whereas, at higher fields, the contribution of an intrinsic mechanism (dc field-induced quasi-Debye loss) becomes predominant

Shift of phase transition temperature in strontium titanate thin films

The results of structural and electrical characterizations of SrTiO3 thin films deposited onto MgO and LaAlO3 substrates by pulsed laser deposition technique are presented. The influence of substrate and annealing procedure on the crystalline structure and dielectric properties of these ferroelectric thin films are investigated. The obtained experimental data are analyzed in terms of the Landau theory taking into account the room-temperature lattice mismatch of the ferroelectric and substrates as well as the difference in their thermal expansion. It is shown that the behavior of the SrTiO3 thin films could not be attributed to the effect of the film/substrate mechanical coupling. As a possible nature of the observed behavior one can consider the non-stoichiometry of the film composition caused by the chemical contact of the film with the substrate and by the annealing.

Nonlinear Properties of Thin Ferroelectric Film-Based Capacitors at Elevated Microwave Power

A key interest in high power high frequency microwave devices is their performance at high power levels. The authors discuss two mechanisms determining the capacitance variations of a thin ferroelectric film-based nonlinear capacitor under elevated microwave power levels analytically and experimentally studied over wide frequency range. The mechanisms are the dielectric nonlinearity under the microwave electric field and ferroelectric film heating due to microwave energy dissipation. It is shown that for thin ferroelectric film parallel plate capacitive structures up to millimeter-wave frequency range, the electric field effect is the dominant mechanism in the capacitance variations, and for limitations on power handling.

Conservation of Permittivity and Tunability of Ferroelectrics Over Temperature

The existence of an intersection point of electric field strength dependencies of permittivity of ferroelectrics at different temperatures is theoretically described by Ginzburg-Devonshire (GD) theory and experimentally confirmed by studying (Ba0.3Sr0.7)TiO3 (BSTO) and SrTiO3 (STO) thin film varactors. GD analysis enables one to propose a way to improve the thermal stability of ferroelectric microwave devices. In particular, parameters of a L-band digital (0°/180°) phase-shifter fabricated from thick BSTO film varactors were stabilized in the temperature range T = (210–310) K by application of variable to DC control voltages.

Electric field stabilization for temperature driven variation of permittivity in ferroelectric devices

The Ginzburg–Devonshire phenomenological approach is used to define the correlation between temperature and electric field magnitudes required to keep permanent values of permittivity of ferroelectrics in rather broad range of operating temperatures. The existence of a crossover of the electric field dependencies for e at different temperatures is demonstrated theoretically. It makes it possible to establish the upper limit of electrical field strength necessary to provide the thermal stability of ferroelectric devices. Theoretical results have been confirmed experimentally with (Ba,Sr)TiO3 thin film measurements.

Structural Investigation of Thin SrTiO3 Films Grown on MgO and LaAlO3 Substrates

Structural investigations of SrTiO3 thin films deposited by pulsed laser ablation onto MgO and LaAlO3 substrates are presented. The residual strain along the c-axis (the growth direction) was evaluated with conventional X-ray diffraction. Evaluation of the in-plane strain was accomplished with grazing-incidence X-ray diffraction. The unit cell of the STO film on LAO substrate had an orthorhombic structure with a coexistence of compressive strain along a-axis and tensile strain along b-axis. The film on an MgO substrate was tetragonal, stretched along the c-axis and compressed in-plane. The elemental composition of the samples was investigated using an INCA system for X-ray elemental analysis attached to a Hitachi S-4300 SEM. A comparison of the residual strain and stoichiometric ratio between as-deposited films and films annealed for four hours at 1100°C in flowing oxygen is presented.

The generalized analysis of ferroelectric-based nonlinear transmission lines

The general analysis of a ferroelectric-based nonlinear transmission line (NLTL) is presented. Analysis allows the estimation of the efficiency of NLTL meant for increasing the wave steepness under propagating along NLTL. Figure of merit defined as the relative change of the reciprocal steepness of the wave front at NLTL input and output is suggested to characterize the NLTL efficiency. Formulas allowing the calculation of figure of merit for ferroelectric-based distributed NLTLs and lumped element networks are derived with the use of a phenomenological description of capacitance-volt age dependencies of ferroelectric (FE) capacitive elements of NLTLs

Procedures of Measurements of Ferroelectric Films Parameters in Frequency Range (20–60) GHz

Two measuring procedures for characterization of ferroelectric films in K-U-band frequency ranges are presented: electrodeless measurements of ferroelectric film parameters based on quasi-optical resonator and method based on measurements of self-resonance of ferroelectric varactor.