| 1. |
- 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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| 2. |
- Abadei, Saeed, 1961, et al.
(författare)
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Low-frequency and microwave performances of laser-ablated epitaxialNa 0.5 K 0.5 NbO 3 films on high-resistivitySiO 2 /Si substrates
- 2002
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Ingår i: Journal of Applied Physics. - : AIP Publishing. - 0021-8979 .- 1089-7550. ; 91, s. 2267-
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Tidskriftsartikel (refereegranskat)abstract
- The dielectric properties of laser-ablated 0.5-μm-thick c-axis epitaxialNa 0.5 K 0.5 NbO 3 (NKN) films on high-resistivity (>7.7 kΩ cm) siliconSiO 2 /Si substrates are studied experimentally in the temperature interval of 30–320 K and at frequencies of 1.0 MHz–40 GHz. The films are grown by laser ablation from a stoichiometric target. For the measurements, planar 0.5-μm-thick gold electrodes (interdigital and straight slot) are photolithography defined on the top surface of NKN films. The slot width between the electrodes is 2.0 or 4.0 μm. At low frequencies(f 1. At microwave frequencies(f>10 GHz), the voltage dependence of the capacitance is given by the NKN film. More than a 13% capacitance change at 40 V dc bias and a Q factor of more than 15 are observed at 40 GHz, which make the structure useful for applications in electrically tunable millimeter-wave devices
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| 3. |
- Abadei, Saeed, 1961, et al.
(författare)
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Low frequency characterisation of laser ablation deposited thin Na0.5K0.5NbO3 (NKN) films for microwave application
- 2001
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Ingår i: Integrated Ferroelectrics. - : Informa UK Limited. - 1058-4587 .- 1607-8489. ; 263:1, s. 173-179
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Tidskriftsartikel (refereegranskat)abstract
- Experimental results on three types of Na0.5K0.5NbO3 (NKN) film capacitor structures are presented. The epitaxial NKN thin films have been deposited on (100) Si (high resistivity), SiO2/Si (low resistivity) and Pt/Si (low resistivity) substrates using laser ablation deposition. Both straight slot and interdigital electrode have been deposited on top of the NKN films. The leakage current and low frequency dielectric properties (I-V, C-V, tanδ-V) of the structures have been measured at 1 MHz as a function of electric field at room temperature. In all three types of capacitor structures the leakage currents in a-b plane are very small, while along c-axis there are extremely large leakage currents. On low resistivity silicon substrates the tunability of the dielectric permittivity is about 12% and loss tangent is low also. On high resistivity (ρ>10 kOhm cm) silicon substrate the tunability at 1 MHz is extremely high, about 10 times, and the losses are also high. On the other hand at microwave frequencies the losses are small (tanδ
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| 4. |
- Ahmed, Taimur, 1983, et al.
(författare)
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Growth temperature dependent dielectric properties of BiFeO3 thin films deposited on silica glass substrates
- 2012
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Ingår i: Thin Solid Films. - : Elsevier BV. - 0040-6090. ; 520:13, s. 4470-4474
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Tidskriftsartikel (refereegranskat)abstract
- We have studied the dependence of dielectric properties on the deposition temperature of BiFeO3 thin films grown by the pulsed laser deposition technique. Thin films have been grown onto amorphous silica glass substrates with pre-patterned Au in-plane capacitor structures. It is shown that on the amorphous glass substrate, BiFeO3 films with a near-bulk permittivity of 26 and coercive field of 80 kV/cm may be grown at a deposition temperature of about 600 degrees C and 1 Pa oxygen pressure. Low permittivity and higher coercive field of the films grown at the temperatures below and above 600 degrees C are associated with an increased amount of secondary phases. It is also shown that the deposition of BiFeO3 at low temperature (i.e. 500 degrees C) and post deposition ex-situ annealing at elevated temperature (700 degrees C) increases the permittivity of a film. The applied bias and time dependence of capacitance of the films deposited at 700 degrees C and ex-situ annealed films are explained by the de-pinning of the ferroelectric domain-walls.
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| 5. |
- Alam Mallick, Shoaib, et al.
(författare)
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Dielectric properties of Mn doped Bismuth Barium Titanate based ceramic thin films prepared by PLD technique
- 2017
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Ingår i: Ceramics International. - : Elsevier BV. - 0272-8842. ; 43:12, s. 8778-8783
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Tidskriftsartikel (refereegranskat)abstract
- In this article, the effect of Mn doping on the permittivity and dielectric loss in 0.67BiFeO(3)-0.33BaTiO(3) (BF-BT) based film bulk acoustic resonator test structures has been investigated. BF-BT thin films were deposited on the fused silica substrates with Pt/TiO2/Ti as bottom electrode. During the study of the BF-BT based parallel-plate structures, it has been revealed that BF-BT is in the ferroelectric state at room temperature. Higher permittivity (epsilon) is observed at a growth temperature of 600 degrees C and lower dielectric loss is achieved at 0.3 wt% Mn doping contents. These results show that the proposed BF-BT based FBAR test structure has a great potential for applications in tunable thin Film Bulk Acoustic Resonator (FBAR) devices. Comparison of the measured and simulation results has been made by utilizing the Mason equivalent circuit.
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| 6. |
- ANDERSSON, MICHAEL, 1988, et al.
(författare)
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Comparison of carrier scattering mechanisms in chemical vapor deposited graphene on fused silica and strontium titanite substrates
- 2014
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Ingår i: Graphene Week 2014.
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Konferensbidrag (refereegranskat)abstract
- Graphene is explored for numerous applications for both electronics and photonics. These range from high frequency and low noise field effect transistors to conductive and highly transparent LED electrodes. To exploit the full potential of graphene, the remarkable intrinsic carrier transport properties and tunable, potentially low sheet resistance must be efficiently utilized. However, graphene carrier mobility is currently strongly degraded by extrinsic factors arising mainly from the dielectric environment, i.e. substrate and gate oxide. A proposed route to enhance transport is the use of a high-κ substrate to screen charged impurities at the graphene-substrate interface. In this paper, mobility and carrier concentration in CVD grown graphene films on fused silica (FS, κ=3.9) and strontium titanite (STO, κ=300) substrates are extracted from microwave measurements and compared to Hall data. To model the mobilities scattering by charged impurities (CI), substrate polar phonons (SPP) and resonant centers (RS) are included. Resonant scatterers dominates on strontium titanite and together with charged impurities on fused silica. While resonant scatterers are likely reduced by moving from wet to dry graphene transfer methods, the nominal mobility improvement by screening of charged impurities on high- κ strontium titanite would be masked at room temperature by increased surface phonon scattering.
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| 7. |
- ANDERSSON, MICHAEL, 1988, et al.
(författare)
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Extraction of carrier transport properties in graphene from microwave measurements
- 2014
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Ingår i: European Microwave Conference (EuMC), 2014 44th. ; , s. 359 - 362
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Konferensbidrag (refereegranskat)abstract
- Carrier transport parameters of graphene grown by chemical vapor deposition (CVD) and graphene-metal contacts are extracted from microwave measurements in the frequency range 0.1–20 GHz using Corbino disks. It is shown that the charged impurities are effectively screened by the high permittivity of the SrTiO3 substrate. In the case of fused silica substrate the charged impurities are not completely screened and the mobility is limited either by the charged impurities or/and resonant scatterers depending on their relative concentration.
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| 8. |
- ANDERSSON, MICHAEL, 1988, et al.
(författare)
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Microwave characterization of Ti/Au-graphene contacts
- 2013
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Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 103:17, s. 173111-
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Tidskriftsartikel (refereegranskat)abstract
- In this paper, we report on a microwave characterization of the interface between Ti/Au contacts and chemical vapor deposition graphene using structures of Corbino geometry, with primary focus on extracting and modeling the capacitance associated with the contact region. It is found that with the current contact resistivity, ρc∼10^−6 Ωcm2, the contact capacitance, on the order Cc∼1 μF/cm2, has a negligible effect on microwave transmission through the contact below ∼100 GHz. Finally, a parallel plate capacitance model for the contact is presented.
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| 9. |
- Berg, Håkan, et al.
(författare)
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The effect of longitudinal substrate currents on the losses in silicon substrate coplanar-strip and coplanar waveguides
- 2000
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Ingår i: International Journal of RF and Microwave Computer-Aided Engineering. - 1096-4290 .- 1099-047X. ; 10:5, s. 284-288
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Tidskriftsartikel (refereegranskat)abstract
- The strip currents in silicon substrate CPS and CPW induce longitudinal currents in the substrate (along the strips of the lines) causing extra microwave losses. It is shown that these losses may be minimized without introducing extra masks and process steps if the slot widths in the lines are chosen properly
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| 10. |
- Berge, John, 1979, et al.
(författare)
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Field and temperature dependent parameters of the dc field induced resonances in BaxSr1-xTiO3-based tunable thin film bulk acoustic resonators
- 2008
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Ingår i: Journal of Applied Physics. - : AIP Publishing. - 0021-8979 .- 1089-7550. ; 103:6, s. 064508-
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Tidskriftsartikel (refereegranskat)abstract
- Electrically tunable solidly mounted thin film bulk acoustic resonators based on Ba0.25 Sr0.75 Ti O3 and BaTi O3 films are fabricated and measured in wide dc bias voltage and temperature ranges. At room temperature, the tunability of the series and parallel resonances for the Ba0.25 Sr0.75 Ti O3 resonator are 1.7% and 0.3%, respectively, for 15 V bias voltage applied over the 350 nm thick ferroelectric film (43 Vμm). The electromechanical coupling coefficient increases with dc bias up to 3.7% at 15 V. The measured tunability and coupling coefficient are limited partly by the quality of the used films. Potentially, they may be substantially increased for high quality films allowing application of higher dc fields. The resonator quality factor is approximately 100. The measured resonator response is in good agreement with available models based on the electromechanical equations describing the ferroelectric film under applied dc and ac electric fields. Measurements of the resonance frequencies of the Ba0.25 Sr0.75 Ti O3 resonator as a function of temperature in the range 40-520 K reveal a sharp step at 150 K which is related to a structural phase transition of the ferroelectric material. The series resonance frequency is tuned to lower frequencies with increasing dc bias for all temperatures, while the parallel resonance frequency reveals a change in the sign of the tunability at approximately 150 K, from being tuned to lower frequencies at high temperatures to being tuned to higher frequencies at low temperatures. Measurements of BaTi O3 resonators in the temperature range 300-520 K are presented and compared to the Ba0.25 Sr0.75 Ti O3 results. © 2008 American Institute of Physics.
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