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  • 1. Berge, John
    et al.
    Gevorgian, Spartak
    Tunable bulk acoustic wave resonators based on Ba0.25Sr0.75TiO3 thin films and a HfO2/SiO2 Bragg reflector2011In: IEEE Transactions on Ultrasonics, Ferroelectrics and Frequency Control, ISSN 0885-3010, E-ISSN 1525-8955, Vol. 58, no 12, p. 2768-2771Article in journal (Refereed)
    Abstract [en]

    A switchable and tunable bulk acoustic wave resonator based on a paraelectric phase Ba0.25Sr0.75TiO3 thin film and an all-dielectric HfO2/SiO2 Bragg reflector is presented. The achieved tuning range (3.8%) and effective electromechanical coupling coefficient (7.1%) are the highest reported for solidly mounted tunable bulk acoustic wave resonators. The non-conductive Bragg reflector stack provides excellent integration possibilities.

  • 2. Berge, John
    et al.
    Norling, Martin
    Vorobiev, Andrei
    Gevorgian, Spartak
    Field and temperature dependent parameters of the dc field induced resonances in BaxSr1-xTiO3-based tunable thin film bulk acoustic resonators2008In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 103, no 6Article in journal (Refereed)
  • 3. Berge, John
    et al.
    Norling, Martin
    Vorobiev, Andrei
    Gevorgian, Spartak
    The effect of Bragg reflectors on the electromechanical performance of parallel-plate ferroelectric capacitors2010In: IOP Conference Series: Materials Science and Engineering - Fundamentals and Technology of Multifunctional Oxide Thin Films, 2010Conference paper (Refereed)
    Abstract [en]

    Parallel-plate capacitors based on ferroelectric thin films are considered as high density capacitors and varactors. Due to the small thickness of the ferroelectric films, typically less than 1.0 mu m, high electric fields are generated even at relatively low voltages inducing piezoelectric effect associated with electrostriction. This induced piezoelectric effect has negative impact on ferroelectric capacitors since it causes extra loss (electroacoustic transformation of microwave energy). In this work the use of Bragg reflectors between the substrate and ferroelectric film is proposed as a possible way of suppression of the enhanced losses associated with the piezoelectric activity of the ferroelectric film.

  • 4. Berge, John
    et al.
    Vorobiev, Andrei
    Gevorgian, Spartak
    Design considerations for tunable bulk acoustic wave resonators based on paraelectric phase BaxSr1-xTiO3 thin films2010Conference paper (Refereed)
    Abstract [en]

    Paraelectric phase BaxSr1-xTiO3 (BSTO) is due to the pronounced field induced piezoelectric effect a promising candidate to realize hysteresis-free tunable thin film bulk acoustic wave resonators (TFBARs) at GHz frequencies. Compared to the conventional fixed-frequency TFBAR technology, mainly based on piezoelectric AlN films, the design of tunable BSTO based resonators require additional considerations due to the demanding conditions necessary for the growth of the BSTO active layer (high temperature, O2 ambient). In this work a number of problems and possible solutions are presented for the specific case of solidly mounted resonators based on an acoustic Bragg reflector structure. Simulation results for a proposed tunable resonator based on a BSTO film and a SiO2/HfO2 reflector stack co-optimized for both longitudinal and shear waves are presented and compared to simulations and existing experimental data from other structures.

  • 5. Berge, John
    et al.
    Vorobiev, Andrei
    Gevorgian, Spartak
    The effect of growth temperature on the nanostructure and dielectric response of BaTiO3 ferroelectric films2007In: Thin Solid Films, Vol. 515, no 16, p. 6302-6308Article in journal (Refereed)
    Abstract [en]

    BaTiO3 ferroelectric films were grown on Si/SiO2/Ti/Pt/Au/Pt templates at different temperatures in the range 560-680 degrees C by pulsed laser deposition. Cross section scanning electron microscopy images and atomic force microscopy surface morphology analysis reveal films with columnar structure and in-plane grain size distribution, in the range 10-60 nm, depending on growth temperature. Low-field dielectric measurements were performed as functions of temperature in the range 40-500 K and extemal dc field up to 400 kV/cm. The apparent permittivity of ferroelectric films grown at 680 degrees C shows Curie-Weiss behavior above 400 K with Curie temperature and Curie-Weiss constant 240 K and 1 center dot 10(5) K, respectively. The films grown at lower temperatures reveal a decrease of Curie temperature down to - 80 K, reduced values of apparent permittivity and loss tangent, and broadening of maximum of temperature dependence of apparent permittivity. The film grown at 590 degrees C demonstrates state of the art combination of temperature stability (temperature coefficient of apparent permittivity 300 ppm/K in the range 50350 K), high tunability of apparent permittivity (up to 60% at room temperature), and relatively low loss tangent (less than 0.05 in the frequency range up to 10 GHz). The change in apparent permittivity and its temperature dependence, with variation of growth temperature are analyzed using two different composite models. The first model assumes the film to be a composite with vertical inclusions of low permittivity dielectric material associated with grain boundaries. This model may explain the observed decrease of permittivity with decreasing growth temperature, but not the shift of Curie temperature. The second model assumes a layered type of composite with low permittivity material associated with the film/ electrode interfaces, and allows explanation of the Curie temperature shift. (C) 2006 Elsevier B.V. All rights reserved.

  • 6. Berge, John
    et al.
    Vorobiev, Andrei
    Steichen, William
    Gevorgian, Spartak
    Tunable Solidly Mounted Thin Film Bulk Acoustic Resonators Based on BaxSr1-xTiO3 Films2007In: IEEE Microwave and Wireless Components Letters, ISSN 1531-1309, E-ISSN 1558-1764, Vol. 17, no 9, p. 655-657Article in journal (Refereed)
    Abstract [en]

    Electrically tunable solidly mounted thin film bulk acoustic resonators based on BaxSr1-xTiO3 films are reported for the first time. The films are acoustically isolated from the silicon substrate by a Bragg reflector stack. Applying DC bias induces piezoelectric effect and an acoustic resonance at approximately 4 GHz. Under 10 V applied DC bias the resonance frequency of the resonators based on Ba0.25Sr0.75TiO3 films is tuned 1.2% to lower frequencies. The Q-factor of these resonators is approximately 120, and the electromechanical coupling coefficient is 0.5%. The resonant frequency of the BaTiO3 based resonators shifts upwards 1.3% under 10 V DC bias, and the -factor is approximately 30, with an electromechanical coupling coefficient of 6.2%.

  • 7. Gevorgian, Spartak
    et al.
    Vorobiev, Andrei
    Berge, John
    Electromechanical modelling and reduction of the electroacoustic losses in parallel-plate ferroelectric varactors2006In: Proc. European Microwave Conference 2006, 2006Conference paper (Refereed)
  • 8. Norling, Martin
    et al.
    Berge, John
    Gevorgian, Spartak
    Parameter extraction for tunable TFBARs based on BaxSr1-xTiO32009In: IEEE MTT-S International Microwave Symposium Digest 2009, 2009Conference paper (Refereed)
  • 9. Turalchuk, Pavel
    et al.
    Vendik, Irina
    Vendik, Orest
    Berge, John
    Electrically tunable bulk acoustic filters with induced piezoelectric effect in BSTO film2008In: Proc. European Microwave Conference 2008, 2008, p. 1695-1698Conference paper (Refereed)
  • 10. Vendik, Irina
    et al.
    Turalchuk, Pavel
    Vendik, Orest
    Berge, John
    Modeling tunable bulk acoustic resonators based on induced piezoelectric effect in BaTiO[sub 3] and Ba[sub 0.25]Sr[sub 0.75]TiO[sub 3] films2008In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 103, no 1, p. 014107-1Article in journal (Refereed)
  • 11. Vorobiev, Andrei
    et al.
    Berge, John
    Gevorgian, Spartak
    Comparative study of microstructure and microwave dielectric response of BaxSr1-xTiO3 films grown by pulsed laser deposition and magnetron sputtering2008Conference paper (Refereed)
  • 12. Vorobiev, Andrei
    et al.
    Berge, John
    Gevorgian, Spartak
    The effect of interfacial transition layer on performance of thin film ferroelectric capacitors2006Conference paper (Refereed)
  • 13. Vorobiev, Andrei
    et al.
    Berge, John
    Gevorgian, Spartak
    Thin film Ba0.25Sr0.75TiO3 varactors on Au bottom electrode for microwave applications2006In: Proc. European Microwave Conference 2006, 2006Conference paper (Refereed)
  • 14. Vorobiev, Andrei
    et al.
    Berge, John
    Gevorgian, Spartak
    Thin film Ba0.25Sr0.75TiO3 voltage tunable capacitors on fused silica substrates for applications in microwave microelectronics2007In: Thin Solid Films, Vol. 515, no 16, p. 6606-6610Article in journal (Refereed)
    Abstract [en]

    Thin film Au/Pt/Ba0.25Sr0.75TiO3/Pt/Au/-Ti capacitor structures were fabricated on fused silica substrates using pulsed laser deposition of ferroelectric films. Low-field dielectric measurements were performed as a function of frequency in the range 1-25 GHz at different external dc fields up to 360 kV/cm. Resonant microwave power absorption observed at frequencies less than 10 GHz under dc field is due to electrostriction and field induced piezoelectric effects. The effects are simulated using an electroacoustic model of the multilayer capacitor structure. A circuit model is applied to investigate the influence of series resistance and inductance of interconnect/lead strips on capacitor performance. Analysis shows that the measured loss tangent of the capacitor is mainly due to series resistance and frequency dispersion of capacitance is caused by series inductance. The de-embedded value of the loss tangent is 0.005 at 10 GHz. The measured loss tangent is less than 0.02 and tunability is up to 40% in the whole frequency range. These parameters indicate high potential of Ba0.25Sr0.75TiO3 Capacitors for applications in voltage controlled devices of microwave microelectronics. (C) 2006 Elsevier B.V. All rights reserved.

  • 15. Vorobiev, Andrei
    et al.
    Berge, John
    Gevorgian, Spartak
    Löffler, Markus
    Olsson, Eva
    Effect of interface roughness on acoustic loss in tunable thin film bulk acoustic wave resonators2011In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 110, no 2Article in journal (Refereed)
    Abstract [en]

    Tunable 5.2 GHz bulk acoustic wave resonators utilizing Ba(x)Sr(1-x)TiO(3) ferroelectric films with similar intrinsic properties but different interface roughness are fabricated and characterized. Increase in roughness from 3.2 nm up to 6.9 nm results in reduction in Q-factor from 350 down to 150 due to extrinsic acoustic losses caused by wave scattering at reflections from rough interfaces and other mechanisms associated with roughness. The increased roughness is a result of distortion of Pt bottom electrode caused by formation of heterogeneous enclosures of TiO(2-x) in the Pt layer. (C) 2011 American Institute of Physics. [doi: 10.1063/1.3610513]

  • 16. Vorobiev, Andrei
    et al.
    Berge, John
    Norling, Martin
    Gevorgian, Spartak
    Silicon substrate integration of BST based tunable TFBARs using all-dielectric SiO2/AlN Bragg reflectors2010In: 10th Topical Meeting on Silicon Monolithic Integrated Circuits in RF Systems (SiRF 2010) - Digest of Papers, 2010, p. 41-44Conference paper (Refereed)
    Abstract [en]

    Integration possibilities of BaxSr1-xTiO3 (BST) based tunable Thin Film Bulk Acoustic Wave Resonators (TFBAR) using all-dielectric SiO2/AlN Bragg reflectors deposited on a high resistivity silicon substrate are considered. SiO2/AlN reflectors withstand the high deposition temperature (>600C) of the BST films opening up possibilities for heterogeneous integration of complex microwave circuits. © 2010 IEEE.

1 - 16 of 16
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  • apa
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
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  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
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  • Other locale
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