The dielectric resonator

The effects of ultraviolet (UV) irradiation on the relaxation processes in Ba0.3Sr0.7TiO3 thin film capacitors were experimentally investigated in a range of wavelengths λ=(310–400) 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 τ(λ)minima and I(λ)maxima towards the shorter wavelengths. Phenomena observed are analyzed using Bouguer’s law.

Effect of ultraviolet radiation on slow-relaxation processes in ferroelectric capacitance structures

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.

Evaluation of the space charge trap energy levels in the ferroelectric films

The impact of oxygen annealing on the switching time of ferroelectric thin film capacitor structures Pt/Ba0.3Sr0.7TiO3/Pt was investigated. The response of their capacitance on pulsed control voltages before and after annealing was experimentally measured. It was demonstrated that the annealing results in suppression of the capacitance slow relaxation processes and increase of the threshold control voltages. These structures can therefore be attractive for fabrication of fast acting microwave devices.

Suppression of slow capacitance relaxation phenomenon in Pt/Ba0.3Sr0.7TiO3/Pt thin film ferroelectric structures by annealing in oxygen atmosphere

A ferroelectric (FE) varactor with a film structure BaxSr1– x TiO3 (BSTO)/SiC on a diamond substrate, designed for the use under elevated microwave (MW) power, was produced by an ion-plasma deposition technique. Comparative testing of the BSTO varactors produced on Al2O3 and diamond/SiC substrates was performed at the frequency of 3 GHz and different levels of MW power (up to $P\sim 10$ var). A significant difference in thermal response under MW power of the varactors on Al2O3 and diamond was demonstrated: the overheating of FE film was observed as $\Delta T\sim (20-30)$ K on Al2O3 and $\Delta T\sim 2$ K on diamond at maximum MW power.

Ferroelectric Varactor on Diamond for Elevated Power Microwave Applications

Design of tunable Gunn diode-based active antenna module including a new type of planar dielectric resonator (PDR) tuned by a ferroelectric (FE) varactor is presented. The module is designed in such a way that the PDR acts both as a stabilizing resonator and as a radiator. Microwave properties of FE elements used for voltage-controlled oscillator (VCO) tuning are considered. The module operates at a frequency around of 17 GHz and demonstrates the radiated power of 8.8plusmn0.1 dBm over the 130-MHz tuning range and a phase-noise level of -80 dBc/Hz at 100-kHz offset. 65deg width of the radiation pattern in both the E-and H-planes corresponding to a gain of 5.1 dBi was measured. The VCO module has been tested in the regime of the frequency modulation. The output signal spectra measured and simulated for modulating bipolar voltage pulses of repetition frequency f=2 MHz are presented.

A.Y. Shimko

Papers

Active integrated antenna based on planar dielectric resonator with tuning ferroelectric varactor