| 1. |
- Alderman, Byron, et al.
(författare)
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A New Pillar Geometry for Heterostructure Barrier Varactor Diodes
- 2001
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Ingår i: 12th International Symposium on Space Terahertz Technology. ; , s. 330-339
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Konferensbidrag (refereegranskat)abstract
- We report on a novel diode geometry, with reduced thermal resistance, for Heterostructure Barrier Varactor, HBV, diodes. The pillar geometry presented here involves the complete removal of the substrate, electrical contacted is made by the forward and reverse side processing of metallic pillars. We propose that there is a limit to the maximum number of barriers that can be used to increase the power capability of a HBV. An analytical model has been developed to study these effects. In considering the case of a perfect thermal heat sink the limit is found to be fourteen, in applying this model to the new pillar structure this is reduced to six.
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| 2. |
- Anderberg, Martin, 1992, et al.
(författare)
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A 183-GHz Schottky diode receiver with 4 dB noise figure
- 2019
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Ingår i: IEEE MTT-S International Microwave Symposium Digest. - : IEEE. - 0149-645X. ; 2019-June, s. 172-175
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Konferensbidrag (refereegranskat)abstract
- Atmospheric science based on space-borne millimeter wave measurements require reliable and state-of-the art receivers. In particular, the water vapor line at 183.3 GHz motivates the development of sensitive mixers at this frequency. Traditional assembly techniques employed in the production of Schottky diode receivers involve flip-chip mounting and soldering of discrete dies, which prohibit the implementation of reliable and repeatable production processes. In this work, we present a subharmonic 183 GHz mixer implementing a repeatable assembly method using beamlead Schottky diodes. The mixer was integrated with a InP HEMT MMIC low noise intermediate frequency amplifier resulting in a record-low receiver noise temperature of 450 K at 1 mW of local oscillator power measured at room-temperature. The measured Allan time was 10 s and the third order local oscillator spurious power was less than -60 dBm. The proposed assembly method is of particular importance for space-borne missions but also applicable to a wide range of terahertz applications.
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| 3. |
- 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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| 4. |
- 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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| 5. |
- ANDERSSON, MICHAEL, 1988, et al.
(författare)
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Noise Figure Characterization of a Subharmonic Graphene FET Mixer
- 2012
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Ingår i: IEEE MTT-S International Microwave Symposium Digest. - 0149-645X. - 9781467310871
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Konferensbidrag (refereegranskat)abstract
- We report on the first room temperature noise figure measurement of a graphene FET subharmonic resistive mixer in the interval fRF = 2-5 GHz. Due to an 8 nm thin Al2O3 gate dielectric it can operate with a conversion loss in the range 20-22 dB at only 0 dBm of local oscillator power. The measurement yields a noise figure close to the conversion loss, thus determining the noise to be thermal in origin, which is promising for cryogenic applications. The general route to lower noise figure is an improvement of the conversion loss.
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| 6. |
- ANDERSSON, MICHAEL, 1988, et al.
(författare)
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Towards Graphene Electrodes for High Performance Acoustic Resonators
- 2013
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Ingår i: WOCSDICE. ; , s. 99-100
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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.
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| 7. |
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| 8. |
- Asad, Muhammad, 1986, et al.
(författare)
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Correlation between material quality and high frequency performance of graphene field-effect transistors
- 2019
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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.
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| 9. |
- Asad, Muhammad, 1986, et al.
(författare)
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Graphene field-effect transistors for high frequency applications
- 2018
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Ingår i: ; November 2018
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Konferensbidrag (refereegranskat)abstract
- Realization of competitive high frequency graphene field-effect transistors (GFETs) is hindered, in particular, by extrinsic scattering of charge carriers and relatively high contact resistance of the graphene-metal contacts, which are both defined by the quality of the corresponding graphene top interfaces [1]. In this work, we report on improved performance of GFETs fabricated using high quality chemical vapour deposition (CVD) graphene and modified technology steps. The modified processing flow starts with formation of the gate dielectric, which allows for preserving the high velocity of charge carriers, and, simultaneously, providing very low contact resistance. The transfer line method (TLM) analysis and fitting the GFET transfer characteristics (Fig. 1) both reveal very low specific width contact resistivity of the top contacts, down to 95 Ω⋅μm. Fitting shows also that the field-effect mobility in the GFETs can be up to 5000 cm2/(V⋅s). The measured (extrinsic) transit frequency (fT) and the maximum frequency of oscillation (fmax) are up to 35 GHz and 40 GHz, respectively, for GFETs with gate length Lg=0.5 μm (Fig. 2), which are highest among those reported so far for the GFETs with similar gate length and comparable with those of Si MOSFETs [2,3]. The dependencies of the fT and fmax on the gate length indicate that these GFETs are very promising for the scaling down and in particular for the development of power amplifiers operating in the mm-wave frequency range.
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| 10. |
- Auriacombe, Olivier, 1989, et al.
(författare)
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325 GHz and 650 GHz Dual-polarisation receivers Concept
- 2022
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Ingår i: 32nd International Symposium of Space Terahertz Technology, ISSTT 2022.
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Konferensbidrag (refereegranskat)abstract
- The integrated dual-polarisation receivers utilize a dual probe concept, efficiently integrating the antenna and MMIC package environment which allows for polarisation discrimination without the use of bulky and lossy external orthomode transducers. This concept increases the sensitivity of the instrument and reduces its size, enabling the development of future earth observation arrays. Omnisys Instruments AB (Sweden) and Chalmers University of Technology (Sweden) are working to demonstrate state-of-the-art dual polarisation capability with two integrated receiver modules at 325 GHz and 650 GHz.
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