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ABSTRACT: Ferroelectric materials such as (Ba<sub>x</sub> Sr<sub>1-x</sub>) TiO<sub>3</sub> (BST) exhibit a non-zero piezoelectric coefficient under a DC field. The piezoelectric coefficient increases from 0 as the applied DC bias increases from 0V. This gives rise to electrostrictive resonance behaviour in capacitors fabricated with these materials. This paper presents the results of high frequency measurements and simulations of induced piezoelectricity for multilayer BST thin film structures under a 10V DC bias. The Mason model and transmission line theory is used as the basis of the simulation and our work extends it to include the effects of other layers in the passivated capacitor device. High-frequency capacitors with 100 nm thick (Ba<sub>0.5</sub>Sr<sub>0.5</sub>) TiO<sub>3</sub> and Pt electrodes were fabricated on polycrystalline Al<sub>2</sub>O<sub>3</sub> ceramic and Si substrates with an amorphous oxide buffer layer. Correlation between measurements and simulations allowed us to evaluate the piezoelectric coefficient, its switchability and tunability as well as the contribution of the multilayer film structure to the electrostrictive resonance behaviour. The model fits very well with the measurements and can be used to adjust the resonance peaks to the desired frequencies.
Microwave Conference, 2008. EuMC 2008. 38th European; 12/2008
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ABSTRACT: Ba0.7Sr0.3TiO3 (BST) single and quadruple layer capacitors with Pt electrodes were fabricated together on polycrystalline alumina substrates with a SiO2-based multicomponent amorphous buffer layer (SiO2/Al2O3). This paper presents the results of the characterization of these capacitors, to demonstrate their suitability for application as decoupling (high value) capacitors and as components in tunable RF applications (e.g., phase shifters and filters). BST films of different compositions, (Ba0.7Sr0.3)TiO3 and (Ba0.5Sr0.5)TiO3, were grown by metal-organic decomposition (MOD) and RF magnetron reactive sputtering. The capacitance density of 90–140 nm thick BST films was in the range of 20 to 70 fF/μm 2. Parallel plate capacitors with areas from 16 μm2 to 2.25 mm2 were fabricated using photolithography and ion milling techniques. For large capacitors (0.125 to 2.25 mm2), capacitance and tanδ were measured at low frequencies (1 KHz - 1 MHz) using an LCR meter. Smaller capacitors (16 μm2 to 3600 μm2) were additionally characterized in the frequency range of 50 MHz - 20 GHz. In such case, capacitance, tanδ and equivalent series resistance (ESR) were extracted from two port scattering parameters obtained using a vector network analyzer (VNA). The relationship between dielectric loss, tunability and calculated figure of merit vs. BST composition and deposition temperature was outlined. In addition, loss and ESR at high frequencies was investigated. The typical achieved leakage current density of sputtered BST films for 2.25 mm2 capacitors fabricated on SiO2/Al2O3 was 7.3×10-9 A/cm2 at 300 kV/cm (65 fF/μm2), about 2 times lower than for (Ba0.7Sr0.3)TiO3 films deposited by MOD (1.4×10-8 A/cm2 at 300 kV/cm, 34.5 fF/μm2). Furthermore, the tunability of (Ba0.7Sr0.3)TiO3 deposited by both methods on SiO2/Al2O3 was ∼60% at 350 kV/cm.
MRS Proceedings. 12/2002; 784.
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Materials Research Society Symposium - Proceedings;
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Materials Research Society Symposium - Proceedings;
