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Publications (7)1.44 Total impact

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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: Thin film voltage tunable ferroelectric capacitors on various substrates are promising for use in high power microwave and other RF systems. Benefits of ferroelectric capacitors include miniaturization and integration with other passive devices.Commercialization of ferroelectric components requires compliance with certain industry standards for reliability. For ferroelectric capacitors the requirement to pass the THB test requires a silicon nitride layer in the back end of the process (after interconnect metalization). However the nitride layer deposition process results in a drastic increase in the leakage of the BST capacitors. This effect is attributed to the exposure of the ferroelectric material to atomic hydrogen which is a by-product of the PECVD deposition process.This paper presents results of different passivation materials for ferroelectric capacitors and for a barrier layer which preserves the performance of ferroelectric capacitors during a PECVD nitride deposition. This allows qualification of ferroelectric capacitors to industry reliability standards.
    Integrated Ferroelectrics 01/2008; 104(1):80-89. · 0.38 Impact Factor
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    ABSTRACT: Power handling capability of tunable microwave devices employing ferroelectric Ba<sub>x</sub>Sr<sub>1-x</sub>TiO<sub>3</sub> film-based varactors: was experimentally measured and analyzed. A microstrip resonator, excited by either harmonic or two-tone microwave signals of elevated power, was selected as an example of tunable test fixture. The nonlinear distortion of the resonant curve under microwave pulsed power and generation of the third-order intermodulation distortion products in microwave resonator, using ferroelectric varactors were measured. Formulas to estimate power handling capability connected with the microwave electric field dielectric nonlinearity and the ferroelectric film overheating are derived for the tunable microwave devices based on ferroelectric films
    Microwave Symposium Digest, 2006. IEEE MTT-S International; 07/2006
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    ABSTRACT: The power handling capability of tunable microwave devices employing planar and parallel-plate Ba<sub>x</sub>Sri<sub>1- x</sub>TiO<sub>3</sub> film-based capacitors was experimentally measured and analyzed. A microstrip resonator, excited by either harmonic or two-tone microwave signals of elevated power, was selected as an example of tunable test fixture.
    Microwave Conference, 2005 European; 11/2005
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    Japanese Journal of Applied Physics 01/2004; 43(9 B):6740-6745. · 1.07 Impact Factor
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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; 01/2002