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

The purpose of this thesis is to investigate piezoelectric and ferroelectric thin film device technologies for application in microwave oscillators. Thin film varactors based on ferroelectric materials are considered. Experimental development of practical varactors based on paraelectric phase BaxSr1−xTiO3, in terms of layout design and model extraction, is presented in the thesis. Experimental results of voltage-controlled oscillators based on ferroelectric varactors operating at 16 GHz and 19 GHz are also presented. The ferroelectric device technology is furthermore compared to traditional varactor technologies, and discussed from the perspective of oscillator applications. Thin film bulk acoustic resonators based on piezoelectric materials and biased electrostrictive materials are considered. Specifically, fixed-frequency resonators based on AlN and tunable resonators based on paraelectric phase BaxSr1−xTiO3 are investigated in the thesis. An integration concept is developed for AlN resonators, and experimentally demonstrated by 2 GHz oscillators. Additionally, modelling and measurement techniques for resonators based on AlN and BaxSr1−xTiO3 are developed. The investigated technologies are compared to traditional planar resonator technologies.

Piezoelectric and ferroelectric device technologies for microwave oscillators

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

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.

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

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. MW properties of FE elements used for VCO tuning are considered. The module operates at frequency around of 17 GHz and demonstrates the radiated power of 8.8 ± 0.1 dBm over the 130 MHz tuning range and a phase-noise level of −95 dBc/Hz at 100 kHz offset. 65° width of the radiation pattern in both the E and H planes corresponding to a gain of 5.1 dBi was measured. The maximal VCO power limited by the dielectric nonlinearity of a FE film in the microwave electric field and by the FE film overheating is estimated for FE film-based varactors of the planar and parallel structures.

Vco/radiator module tuned by ferroelectric varactor

Design of tunable Gunn diode-based active antenna module including new type of planar dielectric resonator is presented. The module is designed in such a way that a planar dielectric resonator acts both as a stabilizing resonator and as a radiator. A ferroelectric varactor is used for radiation frequency tuning. The module operates at frequency around of 17 GHz and demonstrates the radiated power 8.8 plusmn 0.1 dBm over the tuning range 130 MHz and phase noise level -80 dBc/Hz at 100 kHz offset. 65deg width of radiation pattern in both E and H planes corresponding the gain of 5.1 dBi were measured.

S.V. Krasilnikov

Papers

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

Vco/radiator module tuned by ferroelectric varactor

Tunable Active Antenna Module Based on Planar Dielectric Resonator