| 1. |
- Song, J., et al.
(författare)
-
Essential Genetic Interactors of SIR2 Required for Spatial Sequestration and Asymmetrical Inheritance of Protein Aggregates
- 2014
-
Ingår i: PLoS Genetics. - : Public Library of Science (PLoS). - 1553-7390 .- 1553-7404. ; 10:7
-
Tidskriftsartikel (refereegranskat)abstract
- Sir2 is a central regulator of yeast aging and its deficiency increases daughter cell inheritance of stress-and aging-induced misfolded proteins deposited in aggregates and inclusion bodies. Here, by quantifying traits predicted to affect aggregate inheritance in a passive manner, we found that a passive diffusion model cannot explain Sir2-dependent failures in mother-biased segregation of either the small aggregates formed by the misfolded Huntingtin, Htt103Q, disease protein or heat-induced Hsp104-associated aggregates. Instead, we found that the genetic interaction network of SIR2 comprises specific essential genes required for mother-biased segregation including those encoding components of the actin cytoskeleton, the actin-associated myosin V motor protein Myo2, and the actin organization protein calmodulin, Cmd1. Co-staining with Hsp104-GFP demonstrated that misfolded Htt103Q is sequestered into small aggregates, akin to stress foci formed upon heat stress, that fail to coalesce into inclusion bodies. Importantly, these Htt103Q foci, as well as the ATPase-defective Hsp104(Y662A)-associated structures previously shown to be stable stress foci, co-localized with Cmd1 and Myo2-enriched structures and super-resolution 3-D microscopy demonstrated that they are associated with actin cables. Moreover, we found that Hsp42 is required for formation of heat-induced Hsp104(Y662A) foci but not Htt103Q foci suggesting that the routes employed for foci formation are not identical. In addition to genes involved in actin-dependent processes, SIR2-interactors required for asymmetrical inheritance of Htt103Q and heat-induced aggregates encode essential sec genes involved in ER-to-Golgi trafficking/ER homeostasis.
|
|
| 2. |
- Yang, Songyuan, et al.
(författare)
-
A Terahertz-wave Double-Band Transition from Substrate Integrated Waveguide to Rectangular Waveguide for InP MMIC
- 2018
-
Ingår i: Proceedings of 2018 IEEE International Conference on Integrated Circuits, Technologies and Applications, ICTA 2018. ; , s. 140-141
-
Konferensbidrag (refereegranskat)abstract
- A double-band terahertz slot transition from the substrate integrated waveguide (SIW) to the rectangular waveguide (RWG) is presented. With better than 10 dB return loss (RL) and 1.3 dB insertion loss (IL) demonstrated by full-EM simulation, the frequency bands of a designed sample are from 164.6 GHz to 182.76 GHz and from 238 GHz to 257.9 GHz. The presented transition is suitable for multilayer MMIC process, especially for the substrate with high loss and high dielectric constant.
|
|
| 3. |
- Yang, Xinxin, 1988, et al.
(författare)
-
A linear-array of 300-GHz antenna integrated GFET detectors on a flexible substrate
- 2020
-
Ingår i: IEEE Transactions on Terahertz Science and Technology. - 2156-342X .- 2156-3446. ; 10:5, s. 554-557
-
Tidskriftsartikel (refereegranskat)abstract
- Terahertz imaging has potential in a variety of applications, such as non-invasive inspection, medical examination, and security. Many of these applications call for flexible focalplane arrays with large fields of view. Here, we demonstrate the implementation of a flexible, 300 GHz, 1 6 linear detector array based on graphene field-effect transistors and integrated bowtie antennas. Conservative estimates based on room temperature measurements at 300 GHz show element voltage responsivities in he range from 20 V/W to 70 V/W, and noise equivalent powers in the range from 0.06 nW/Hz0.5 to 0.2 nW/Hz0.5. Measured radiation patterns, showing good agreement with simulations, reveal half-power beamwidths of 45 and 60 for H- and E-planes, respectively. Characterization of the antenna array in a curved configuration shows that the voltage response is reduced up to 3 dB compared to the flat configuration due to a decrease of the antenna directivity. We believe that our preliminary results could serve as an enabling platform for the future development of flexible antenna arrays based on GFETs for curved focal plane imaging, important for wearable sensors and many other applications.
|
|
| 4. |
- 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.
|
|
| 5. |
- Asad, Muhammad, 1986, et al.
(författare)
-
Graphene field-effect transistors for high frequency applications
- 2018
-
Ingår i: ; November 2018
-
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.
|
|
| 6. |
- Asad, Muhammad, 1986, et al.
(författare)
-
The dependence of the high-frequency performance of graphene field-effect transistors on channel transport properties
- 2020
-
Ingår i: IEEE Journal of the Electron Devices Society. - 2168-6734. ; 8, s. 457-464
-
Tidskriftsartikel (refereegranskat)abstract
- This paper addresses the high-frequency performance limitations of graphene field-effect transistors (GFETs) caused by material imperfections. To understand these limitations, we performed a comprehensive study of the relationship between the quality of graphene and surrounding materials and the high-frequency performance of GFETs fabricated on a silicon chip. We measured the transit frequency (fT) and the maximum frequency of oscillation (fmax) for a set of GFETs across the chip, and as a measure of the material quality, we chose low-field carrier mobility. The low-field mobility varied across the chip from 600 cm2/Vs to 2000 cm2/Vs, while the fT and fmax frequencies varied from 20 GHz to 37 GHz. The relationship between these frequencies and the low-field mobility was observed experimentally and explained using a methodology based on a small-signal equivalent circuit model with parameters extracted from the drain resistance model and the charge-carrier velocity saturation model. Sensitivity analysis clarified the effects of equivalent-circuit parameters on the fT and fmax frequencies. To improve the GFET high-frequency performance, the transconductance was the most critical parameter, which could be improved by increasing the charge-carrier saturation velocity by selecting adjacent dielectric materials with optical phonon energies higher than that of SiO2.
|
|
| 7. |
- Bonmann, Marlene, 1988, et al.
(författare)
-
An Integrated 200-GHz Graphene FET Based Receiver
- 2018
-
Ingår i: International Conference on Infrared, Millimeter, and Terahertz Waves, IRMMW-THz. - 2162-2027 .- 2162-2035. ; 2018-September
-
Konferensbidrag (refereegranskat)abstract
- A receiver composed by a graphene FET 200-GHz mixer and a 1-GHz intermediate frequency amplifier integrated on a silicon substrate was modelled, fabricated and characterized. This is the first demonstration of a millimeter wave integrated receiver based on graphene FETs. The receiver conversion loss is measured to be 25 dB across the 185-205-GHz band with 16 dBm of local oscillator pump power, which is in good agreement with the circuit simulations. The simulations show that the receiver conversion loss can be significantly reduced to 16 dB by reducing the contact resistance and by realizing a higher charge carrier mobility in the mixer transistor.
|
|
| 8. |
- Bonmann, Marlene, 1988, et al.
(författare)
-
Drain current saturation in graphene field-effect transistors at high fields
- 2018
-
Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Development of competitive high frequency graphene field-effect transistors (GFETs) is hindered, first of all, by a zero-bandgap phenomenon in monolayer graphene, which prevents the drain current saturation and limits significantly the GFET power gain. An approach has been proposed to realise the drain current saturation in GFETs without a bandgap formation, but via velocity saturation of the charge carriers at high fields [1]. In this work, we report on the performance of GFETs fabricated using high quality CVD monolayer graphene and modified technology, which reduce the concentration of traps generating the charge carriers at high fields [2]. Fig. 1 shows typical output characteristics of GFETs with gate length of 0.5 μm. The drain current clearly reveals the saturation trends at high fields, which we associate with the saturation of the carrier velocity, see inset to Fig. 2 [2]. Fig. 2 shows typical measured (extrinsic) transit frequency (fT) and the maximum frequency of oscillation (fmax), which are characteristics of the current and power gain, respectively. Since fT and fmax are proportional to the carrier velocity, they reveal similar saturation behaviour. We analyse the saturation effects by applying the Fermi-Dirac carrier statistics. The fT and fmax are up to 34 GHz and 37 GHz, respectively, which are highest among those reported so far for the GFETs with similar gate length and comparable with those reported for Si MOSFETs [3].
|
|
| 9. |
- Bonmann, Marlene, 1988, et al.
(författare)
-
Effects of self-heating on fT and fmax performance of graphene field-effect transistors
- 2020
-
Ingår i: IEEE Transactions on Electron Devices. - 1557-9646 .- 0018-9383. ; 67:3, s. 1277-1284
-
Tidskriftsartikel (refereegranskat)abstract
- It has been shown that there can be a significant temperature increase in graphene field-effect transistors (GFETs) operating under high drain bias, which is required for power gain. However, the possible effects of self-heating on the high-frequency performance of GFETs have been weakly addressed so far. In this article, we report on an experimental and theoretical study of the effects of self-heating on dc and high-frequency performance of GFETs by introducing a method that allows accurate evaluation of the effective channel temperature of GFETs with a submicrometer gate length. In the method, theoretical expressions for the transit frequency (fT) and the maximum frequency of oscillation (fmax) based on the small-signal equivalent circuit parameters are used in combination with the models of the field- and temperature-dependent charge carrier concentration, velocity, and saturation velocity of GFETs. The thermal resistances found by our method are in good agreement with those obtained by the solution of the Laplace equation and by the method of thermo-sensitive electrical parameters. Our experiments and modeling indicate that the self-heating can significantly degrade the fT and fmax of GFETs at power densities above 1 mW/μm², from approximately 25 to 20 GHz. This article provides valuable insights for further development of GFETs, taking into account the self-heating effects on the high-frequency performance.
|
|
| 10. |
- Bonmann, Marlene, 1988, et al.
(författare)
-
Effects of self-heating on high-frequency performance of graphene field-effect transistors
- 2019
-
Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- In this work, we study the effects of self-heating (Joule heating) on the performance of graphene field-effect transistors (GFETs) with high extrinsic transit frequency (ft) and maximum frequency of oscillation (fmax) [1]. It has been shown, that self-heating in the GFETs might be significant and lead to degradation of the output characteristics with potential effects on the ft and fmax [2,3,4]. Due to relatively short gate length of 0.5 μm in the GFETs, used in this work, the local channel temperature cannot be accurately estimated by means of the infrared microscopy. Therefore, we applied the method of thermosensitive electrical parameters [5]. In particular, we analysed the gate and drain currents in response to variations of the external heater temperature and dc power (Fig. 1). The analysis allows for estimation of the thermal resistance, which is, for GFETs on SiO2/Si substrates, approx. 2e4 K/W, and in good agreement with that calculated by the model based on the solution of Laplace’s equation [6]. In turn, the known thermal resistance allows for evaluation of the GFET channel self-heating temperature. Fig. 2 shows the fmax versus dc power (Pdiss) at different external heater temperatures. The self-heating temperature at Pdiss =10 mW is approx. 130 °C. The drop in the fmax at higher Pdiss can be fully explained by self-heating. Apparently, one can expect reduced self-heating effects in the GFETs on higher thermal conductive substrates as hBN or SiC.
|
|
