A. B. Kozyrev

Microwave properties of (Ba,Sr)TiO3 ceramic films and phase-shifters on their base

Abstract The small signal dielectric properties (ϵ, tanδ) of ceramic (Ba,Sr)TiO3 (BSTO) films in the frequency range (1–30) GHz were under investigation. The Q-factor and tunability were measured for planar BSTO ceramic varactors and are presented in comparison with similar parameters for semiconductor varactors. To illustrate the possibility of the use of BSTO ceramic films at 30 GHz, a phase shifter based on grounded coplanar waveguide (CWG) has been designed and experimentally tested. The device demonstrated phase shift up to Δ ϕ = 370° under the bias voltage (0–350) V and insertion loss L = (4–6) dB in all range of bias voltages.

Response time and power handling capability of tunable microwave devices using ferroelectric films

Abstract The microwave (MW) performance of tunable stripline resonators with ferroelectric (SrTiO3 or (Ba, Sr)TiO3) planar capacitors under exposure to high voltage video pulses and MW (10 GHz) signals are studied. The resonator switching times were less than 30 nanoseconds, and these values were limited by the measurement apparatus. The dependence of film capacitance and MW loss in ferroelectric films as a function of MW signal level, and their variation during the pulse, were measured. The large signal MW dielectric constant and loss tangent varied by less than 10% with increasing MW voltage amplitude for MW field strengths up to 1 MV/m in SrTiO3 films, and 0.5 MV/m in (Ba, Sr)TiO3 films.

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.

A finline 60-GHz phase shifter based on a (Ba,Sr)TiO3 ferroelectric thin film

The design and microwave characteristics of a ferroelectric thin film slotline-waveguide phase shifter operating in the millimeter wavelength range (f∼60 GHz) are presented. In this frequency range, the phase shifter possesses a figure of merit F=32 deg/dB and provides for a continuous phase shift in the interval from zero to 255 deg. The ferroelectric films are characterized by a dielectric loss tangent of tan δ=0.04 at a tunability factor of K≈1.7, which are promising parameters for the given frequency range.

Switching time of planar ferroelectric capacitors using strontium titanate and barium strontium titanate films

A microstripe cavity was used to make microwave (f∼10 GHz) measurements of the time of variation of the permittivity of SrTiO3 and (Ba,Sr)TiO3 films exposed to unipolar video-frequency voltage pulses. It was shown that the permittivity of SrTiO3 films varies over times less than 30 ns. For (Ba,Sr)TiO3 films two characteristic times of variation of the permittivity were identified: a fast variation over times less than 30 ns and a slower variation, on the order of 20 μs.

Influence of metal-ferroelectric contacts on the space charge formation in ferroelectric thin film capacitors

We have studied the response speed characteristics of capacitor structures based on thin Ba0.3Sr0.7TiO3 (BSTO) films with metal-ferroelectric contacts of various types formed under different conditions. It is established that threshold voltages exist for the appearance of a residual space charge in some structures. A comparative analysis of the technological features of contact formation and experimental data on the characteristics of samples leads to the conclusion that, by forming Pt-BSTO contacts in an oxygen-containing atmosphere, it is possible to suppress the injection of carriers into the ferroelectric film in the capacitor structure.

Microwave phase shifter employing srtio3 ferroelectric varactors

Abstract Nonlinear microwave properties of thin SrTiO3 ferroelectric films at ambient temperatures were investigated. A tunability factor of 1.7 and loss tangent of about 0.01–0.015 were measured at frequencies of 2–10 GHz for SrTiO3 thin film planar varactors at room temperature. The performance of an X-band microstrip phase shifter employing the SrTiO3 planar varactors at room temperature is reported. Continuous phase shift in the range of (0–55) deg under bias voltage of 0–400 V at operating frequency band (8.6–9.0) GHz was observed. A figure of merit for the phase shifter is 110 deg/dB and the phase error is smaller than 5 deg. To our knowledge, it is the first demonstration of the microwave application of SrTiO3 varactors operating as nonlinear elements at room temperature and a record result for figure of merit for ferroelectric phase shifters.

Microwave properties of ferroelectric (Ba,Sr)TiO3 varactors at high microwave power

Abstract The microwave (-10 GHz) performance of a tunable resonator employing ferroelectric (Ba,Sr)TiO3 film planar varactors under exposure to high levels of microwave power was studied. The nonlinear characteristics of the ferroelectric films affected by the large signal microwave electrical field were evaluated. The limitations of high power performance for the films and tunable microwave devices based on the films were established.

Microwave properties of YBa2Cu3O7-x/SrTiO3 planar capacitors

Abstract The microwave properties of SrTiO3 (STO)/CeO2 varactors deposited on (1102) oriented Al2O3 substrates, using either YBCO or Ag/YBCO electrodes, was investigated. Measurements were conducted using a microstrip resonator at a frequency of 3 GHz, over temperatures ranging from 78–300 K, and bias voltages up to 260 V across a 20 μm capacitance gap. The temperature and bias voltage dependencies of capacitance and loss of the varactors were analyzed. Below the superconducting transition temperature, the microwave frequency dielectric properties of the STO film (tunability and tanδ) were dominant in establishing the varactor properties for both the YBCO and Ag/YBCO electrode structures. At T = 78 K, the capacitance ratio (= C (0 V)/C (260 V)) was 1.6 for both electrode structures. Tanδ was also identical for both structures, with tanδ = 0.04 – 0.05 under zero bias, and reduction of tanδ by a factor of 1.3 under high dc bias conditions observed.

Thermostabilization of the properties of multilayer ferroelectric variconds for microwave applications

The thermal and microwave properties of ferroelectric metal/dielectric/metal structures have been studied. The possibility of obtaining the temperature coefficient of capacitance on the order of 10−4 K−1 for a ferroelectric varicond based on two thin layers of barium strontium titanate with different compositions is demonstrated for the first time.