| 1. |
- Abadei, S., et al.
(författare)
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Microwave properties of tunable capacitors basee on magnetron sputtered ferroelectric Na0.5K0.5NbO3 film on low and high resistivity silicon substrates
- 2001
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Ingår i: Integrated Ferroelectrics. - : Informa UK Limited. - 1058-4587 .- 1607-8489. ; 39:1-4, s. 359-366
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- In this work, small signal DC voltage dependent dielectric permittivity, loss tangent, and tuneability of magnetron sputtered epitaxial Na0.5K0.5NO3 films are studied experimentally. (100)-oriented Na0.5K0.5NbO3 films are deposited onto SiO2-buffered CMOS grade low resistivity (p = 10-20 cm) and high resistivity (p = 15-45 kcm) silicon substrates. Planar capacitors with 2 or 4 m gaps between electrodes have been fabricated on top of ferroelectric films. These devices have been characterized in the frequency range 1.0 MHz to 50 GHz at temperatures 30 - 300K. Na0.5K0.5NbO3/SiO2/Si structures on high resistivity silicon substrate exhibit C-V performances typical for Metal-Insulator- Semiconductor (MIS) capacitors. At low frequencies, f 1.0 GHz, the large tuneability and large losses are associated with the MIS structure, while at higher microwave frequencies the tuneability is mainly associated with the ferroelectric, film. At 1.0 MHz and room temperature, the tuneability of Na0.5K0.5NbO3/SiO2/Si structures more than 90%, reducing to 10-15 % at 50 GHz. The losses decrease with increasing the DC bias and frequency. A Q-factor more than 15 at 50 GHz is observed. The dielectric permittivity of the Na0.5K0.5NbO3 film is in the range 50-150 at frequencies 0.045-50 GHz. On low resistivity substrate the performance of Na0.5K0.5NbO3 films is completely screened by the high losses in silicon, and the tuneability is negligible. © 2001 Taylor and Francis.
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| 2. |
- Abadei, S., et al.
(författare)
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DC field dependent properties of Na0.5K0.5NbO3/SiO2/Si structures at millimeter-wave frequencies
- 2001
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Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 78:13, s. 1900-1902
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Tidskriftsartikel (refereegranskat)abstract
- Dielectric properties of laser-ablated 0.5-mum-thick c-axis epitaxial Na0.5K0.5NbO3 films on high-resistivity (7.7 Omega cm) silicon SiO2/Si substrate are studied experimentally at frequencies up to 40 GHz. For measurements, planar 0.5-mum-thick gold electrodes (interdigital and straight slot) are photolithography defined on the top surface of Na0.5K0.5NbO3 films. The slot width between the electrodes is 2 or 4 mum. 13% capacitance change at 40 V dc bias and Q factor more than 15 are observed at 40 GHz, which makes the structure useful for applications in electrically tunable millimeter-wave devices.
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| 3. |
- Berge, John, et al.
(författare)
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The effect of growth temperature on the nanostructure and dielectric response of BaTiO3 ferroelectric films
- 2007
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Ingår i: Thin Solid Films. - : Elsevier BV. - 0040-6090. ; 515:16, s. 6302-6308
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 4. |
- Berge, John, et al.
(författare)
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Tunable bulk acoustic wave resonators based on Ba0.25Sr0.75TiO3 thin films and a HfO2/SiO2 Bragg reflector
- 2011
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Ingår i: IEEE Transactions on Ultrasonics, Ferroelectrics and Frequency Control. - 0885-3010 .- 1525-8955. ; 58:12, s. 2768-2771
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 5. |
- Berge, John, et al.
(författare)
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Tunable Solidly Mounted Thin Film Bulk Acoustic Resonators Based on BaxSr1-xTiO3 Films
- 2007
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Ingår i: IEEE Microwave and Wireless Components Letters. - 1531-1309 .- 1558-1764. ; 17:9, s. 655-657
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Tidskriftsartikel (refereegranskat)abstract
- 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%.
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| 6. |
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| 7. |
- Norling, Martin, 1981, et al.
(författare)
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A 2 GHz oscillator using a monolithically integrated AlN TFBAR
- 2008
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Ingår i: IEEE MTT-S International Microwave Symposium Digest. - 0149-645X. - 9781424417803 ; 1:1, s. 843-846
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Konferensbidrag (refereegranskat)abstract
- A 2 GHz oscillator based on a solidly mounted AlN thin-film bulk acoustic resonator (TFBAR) is reported. The oscillator is realised as a silicon-on-silicon multi-chip module (MCM) where all passive elements, including the TFBAR, are monolithically integrated on a high-resistivity silicon (HRS) carrier. SiGe transistors are flip-chip mounted on the MCM carrier. Measurements of the oscillators reveal a best phase-noise of -125 dBc/Hz at 100 kHz offset.
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| 8. |
- Norling, Martin, 1981, et al.
(författare)
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Oscillators Based on Monolithically Integrated AlN TFBARs
- 2008
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Ingår i: IEEE transactions on microwave theory and techniques. - 0018-9480 .- 1557-9670. ; 56:12, s. 3209-3216
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Tidskriftsartikel (refereegranskat)abstract
- Oscillators based on AlN thin-film bulk acoustic resonators are designed, fabricated and measured. The circuits are realised as silicon-on-silicon multichip modules where SiGe transistors are flip-chip mounted on a novel carrier substrate which includes monolithically integrated resonators and passive components. The paper describes the development and processing of the carrier substrate and resonators, as well as the development of the oscillator circuits. The oscillators operate at 2 GHz. Measurements of the oscillators reveal a lowest phase-noise of -125 dBc/Hz at 100 kHz offset.
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| 9. |
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| 10. |
- Vorobiev, Andrei, 1963, et al.
(författare)
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Effect of interface roughness on acoustic loss in tunable thin film bulk acoustic wave resonators
- 2011
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Ingår i: Journal of Applied Physics. - : AIP Publishing. - 0021-8979 .- 1089-7550. ; 110:2
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Tidskriftsartikel (refereegranskat)abstract
- 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]
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