| 1. |
- Ahmed, Taimur, 1983, et al.
(författare)
-
Growth temperature dependent dielectric properties of BiFeO3 thin films deposited on silica glass substrates
- 2012
-
Ingår i: Thin Solid Films. - : Elsevier BV. - 0040-6090. ; 520:13, s. 4470-4474
-
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.
|
|
| 2. |
- Alam Mallick, Shoaib, et al.
(författare)
-
Dielectric properties of Mn doped Bismuth Barium Titanate based ceramic thin films prepared by PLD technique
- 2017
-
Ingår i: Ceramics International. - : Elsevier BV. - 0272-8842. ; 43:12, s. 8778-8783
-
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.
|
|
| 3. |
- Alleaume, Pierre Franck, et al.
(författare)
-
A highly integrated heterogeneous micro- and mm-wave platform
- 2010
-
Ingår i: IEEE MTT-S International Microwave Symposium Digest. - 0149-645X. - 9781424477326 ; , s. 461-464
-
Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- A highly integrated platform for micro- and mmwave frequency applications is introduced. The platform utilizes heterogeneous process modules with integrated passive and tunable devices together with silicon and GaAs MMIC technology to achieve outstanding flexibility. The different process modules are accounted for and their feasibility is proven through a number of application demonstrators from 23GHz telecom backhauling and 77GHz automotive radar indicating excellent performance. © 2010 IEEE.
|
|
| 4. |
- ANDERSSON, MICHAEL, 1988, et al.
(författare)
-
Comparison of carrier scattering mechanisms in chemical vapor deposited graphene on fused silica and strontium titanite substrates
- 2014
-
Ingår i: Graphene Week 2014.
-
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.
|
|
| 5. |
- ANDERSSON, MICHAEL, 1988, et al.
(författare)
-
Extraction of carrier transport properties in graphene from microwave measurements
- 2014
-
Ingår i: European Microwave Conference (EuMC), 2014 44th. ; , s. 359 - 362
-
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.
|
|
| 6. |
- ANDERSSON, MICHAEL, 1988, et al.
(författare)
-
Feasibility of Ambient RF Energy Harvesting for Self-Sustainable M2M Communications Using Transparent and Flexible Graphene Antennas
- 2016
-
Ingår i: IEEE Access. - 2169-3536 .- 2169-3536. ; 4, s. 5850-5857
-
Tidskriftsartikel (refereegranskat)abstract
- Lifetime is a critical parameter in ubiquitous, battery-operated sensors for machine-to-machine (M2M) communication systems, an emerging part of the future Internet of Things. In this practical article, the performance of radio frequency (RF) to DC energy converters using transparent and flexible rectennas based on graphene in an ambient RF energyharvesting scenario is evaluated. Full-wave EM simulations of a dipole antenna assuming the reported state-of-the-art sheet resistance for few-layer, transparent graphene yields an estimated ohmic efficiency of 5 %. In the power budget calculation, the low efficiency of transparent graphene antennas is an issue because of the relatively low amount of available ambient RF energy in the frequency bands of interest, which together sets an upper limit on the harvested energy available for the RF-powered device. Using a commercial diode rectifier and an off-the-shelf wireless system for sensor communication, the graphene-based solution provides only a limited battery lifetime extension. However, for ultra-low-power technologies currently at the research stage, more advantageous ambient energy levels, or other use cases with infrequent data transmission, graphene-based solutions may be more feasible.
|
|
| 7. |
- ANDERSSON, MICHAEL, 1988, et al.
(författare)
-
Microwave characterization of Ti/Au-graphene contacts
- 2013
-
Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 103:17, s. 173111-
-
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.
|
|
| 8. |
- ANDERSSON, MICHAEL, 1988, et al.
(författare)
-
Towards Graphene Electrodes for High Performance Acoustic Resonators
- 2013
-
Ingår i: WOCSDICE. ; , s. 99-100
-
Konferensbidrag (refereegranskat)abstract
- The tunable FBAR is a promising building block for versatile microwave systems. Utilizing graphene electrodes promises higher tunability and frequency. Increased parasitic resistance may hamper the Q-factor of the resonator. This paper reports the initiated study of graphene and contacts at DC and microwave frequencies for optimization of these parameters leading to graphene FBARs.
|
|
| 9. |
- Asad, Muhammad, 1986, et al.
(författare)
-
Correlation between material quality and high frequency performance of graphene field-effect transistors
- 2019
-
Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Correlations between material quality, equivalent circuit and high frequency parameters of the graphene field-effect transistors, such as mobility, contact resistivity, carrier velocity, drain conductivity, transit frequency and maximum frequency of oscillation, have been established via applying drain resistance, velocity and saturation velocity models. The correlations allow for understanding dominant limitations of the high frequency performance of transistors, which clarifies the ways of their further development. In particular, the relatively high drain conductivity is currently main limiting factor, which, however, can be counterbalanced by increasing the carrier velocity via operating transistors at higher fields, in the velocity saturation mode.
|
|
| 10. |
- Asad, Muhammad, 1986, et al.
(författare)
-
Enhanced high-frequency performance of top-gated graphene FETs due to substrate-induced improvements in charge carrier saturation velocity
- 2021
-
Ingår i: IEEE Transactions on Electron Devices. - 1557-9646 .- 0018-9383. ; 68:2, s. 899-902
-
Tidskriftsartikel (refereegranskat)abstract
- High-frequency performance of top-gated graphene field-effect transistors (GFETs) depends to a large extent on the saturation velocity of the charge car-riers, a velocity limited by inelastic scattering by surface optical phonons from the dielectrics surrounding the chan-nel. In this work, we show that by simply changing the graphene channel surrounding dielectric with a material having higher optical phonon energy, one could improve the transit frequency and maximum frequency of oscillation of GFETs. We fabricated GFETs on conventional SiO2/Si substrates by adding a thin Al2O3 interfacial buffer layer on top of SiO2/Si substrates, a material with about 30% higher optical phonon energy than that of SiO2, and compared performance with that of GFETs fabricated without adding the interfacial layer. From S-parameter measurements, a transit frequency and a maximum frequency of oscillation of 43 GHz and 46 GHz, respectively, were obtained for GFETs on Al2O3 with 0.5 µm gate length. These values are approximately 30% higher than those for state-of-the-art GFETs of the same gate length on SiO2. For relating the improvement of GFET high-frequency performance to improvements in the charge carrier saturation velocity, we used standard methods to extract the charge carrier veloc-ity from the channel transit time. A comparison between two sets of GFETs with and without the interfacial Al2O3 layer showed that the charge carrier saturation velocity had increased to 2·10^7 cm/s from 1.5·10^7 cm/s.
|
|
