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1.	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.
2.	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.
3.	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.
4.	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.
5.	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].
6.	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.
7.	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.
8.	Bonmann, Marlene, 1988, et al. (författare) Graphene field-effect transistors with high extrinsic fT and fmax 2019 Ingår i: IEEE Electron Device Letters. - 0741-3106 .- 1558-0563. ; 40:1, s. 131-134 Tidskriftsartikel (refereegranskat)abstract In this work, we report on the performance of graphene field-effect transistors (GFETs) in which the extrinsic transit frequency (fT) and maximum frequency of oscillation (fmax) showed improved scaling behavior with respect to the gate length (Lg). This improvement was achieved by the use of high-quality graphene in combination with successful optimization of the GFET technology, where extreme low source/drain contact resistances were obtained together with reduced parasitic pad capacitances. GFETs with gate lengths ranging from 0.5 μm to 2 μm have been characterized, and extrinsic fT and fmax frequencies of up to 34 GHz and 37 GHz, respectively, were obtained for GFETs with the shortest gate lengths. Simulations based on a small-signal equivalent circuit model are in good agreement with the measured data. Extrapolation predicts extrinsic fT and fmax values of approximately 100 GHz at Lg=50 nm. Further optimization of the GFET technology enables fmax values above 100 GHz, which is suitable for many millimeter wave applications.
9.	Bonmann, Marlene, 1988, et al. (författare) Studies of hysteresis in capacitance and current characteristics of flexible graphene field-effect transistors 2017 Ingår i: Graphene Week 2017, Athens, Greece, 25-29 September, 2017. Konferensbidrag (refereegranskat)abstract Owing to the unique combination of mechanical and electrical properties of graphene, e.i., flexibility andhigh carrier velocity, it is a promising material for emerging applications in flexible high frequencyelectronics. One of the challenges in the development of reliable high performance devices is associatedwith impurities, which are normally present at the graphene/dielectric interfaces. Impurities reduce thecarrier mobility via scattering (Ref. 1) and introduce interface states. Interface states can trap and detrapcharge carriers which typically leads to hysteresis. Fig.1 and Fig.2 show hysteresis in the gatecapacitance and drain current versus gate voltage dependences measured in this work in the graphenefield-effect transistors (GFETs) on flexible PET substrates. It is important to clarify the nature and thedistribution of traps to be able to improve the GFET design, materials and fabrication process in thedevelopment of hysteresis-free flexible GFETs. In this work, we continue developing the model (Ref. 2),which describes the influence of interface states on gate capacitance-voltage and drain resistancevoltagecharacteristics and allows for reasonable good fitting of the forward sweep (Fig.1 and Fig.2,solid lines). Here, we include also the backward sweep, which, as it can be seen, requires moreadvanced modelling, taking into account trapping/ de-trapping dynamics and the analysis of interfacestate distribution. This work helps to clarify the origin of hysteresis in greater depth and allows forcombination with other models, e.g., include hysteresis effects in the model of the responsivity of flexibleGFET THz power detectors [3].
10.	Feijoo, Pedro C., et al. (författare) Does carrier velocity saturation help to enhance fmax in graphene field-effect transistors? 2020 Ingår i: Nanoscale Advances. - : Royal Society of Chemistry (RSC). - 2516-0230. ; 2:9, s. 4179-4186 Tidskriftsartikel (refereegranskat)abstract It has been argued that current saturation in graphene field-effect transistors (GFETs) is needed to get optimal maximum oscillation frequency (f(max)). This paper investigates whether velocity saturation can help to get better current saturation and if that correlates with enhancedf(max). We have fabricated 500 nm GFETs with high extrinsicf(max)(37 GHz), and later simulated with a drift-diffusion model augmented with the relevant factors that influence carrier velocity, namely: short-channel electrostatics, saturation velocity effect, graphene/dielectric interface traps, and self-heating effects. Crucially, the model provides microscopic details of channel parameters such as carrier concentration, drift and saturation velocities, allowing us to correlate the observed macroscopic behavior with the local magnitudes. When biasing the GFET so all carriers in the channel are of the same sign resulting in highly concentrated unipolar channel, we find that the larger the drain bias is, both closer the carrier velocity to its saturation value and the higher thef(max)are. However, the highestf(max)can be achieved at biases where there exists a depletion of carriers near source or drain. In such a situation, the highestf(max)is not found in the velocity saturation regime, but where carrier velocity is far below its saturated value and the contribution of the diffusion mechanism to the current is comparable to the drift mechanism. The position and magnitude of the highestf(max)depend on the carrier concentration and total velocity, which are interdependent and are also affected by the self-heating. Importantly, this effect was found to severely limit radio-frequency performance, reducing the highestf(max)from similar to 60 to similar to 40 GHz.
11.	Generalov, Andrey, 1987, et al. (författare) A 400-GHz Graphene FET Detector 2017 Ingår i: IEEE Transactions on Terahertz Science and Technology. - 2156-342X .- 2156-3446. ; 7:5, s. 614-616 Tidskriftsartikel (refereegranskat)abstract This letter presents a graphene field effect transistor (GFET) detector at 400 GHz, with a maximum measured optical responsivity of 74 V/W, and a minimum noise-equivalent power of 130 pW/Hz1/2. This letter shows how the detector performance degrades as a function of the residual carrier concentration in the graphene channel, which is an important material parameter that depends on the quality of the graphene sheet and contaminants introduced during the fabrication process. In this work, the exposure of the graphene channel to liquid processes is minimized resulting in a low residual carrier concentration. This is in part, an important contributing factor to achieve the record high GFET detector performance. Thus, our results show the importance to use graphene with high quality and the importance to minimize contamination during the fabrication process.
12.	Generalov, Andrey, 1987, et al. (författare) A heterodyne graphene FET detector at 400 GHz 2017 Ingår i: International Conference on Infrared, Millimeter, and Terahertz Waves, IRMMW-THz. - 2162-2027 .- 2162-2035. ; , s. Artno:8067234- Konferensbidrag (refereegranskat)abstract We present a THz heterodyne detector based on a single layer graphene field effect transistor (GFET) integrated with a bowtie antenna at 400 GHz. The heterodyne detection is achieved by coupling RF and LO signals quasi-optically to the same GFET. The down converted IF signal is extracted via a coplanar stripline connected to the GFET source and drain terminals. The measured IF bandwidth is 5 GHz.
13.	Generalov, Andrey, 1987, et al. (författare) Optimization of THz graphene FET detector integrated with a bowtie antenna 2016 Ingår i: European Conference on Antennas and Propagation. - 2164-3342. - 9788890701863 Konferensbidrag (refereegranskat)abstract This paper discusses the integration of the split bowtie antenna with a graphene FET THz detector to maximize the detector efficiency at 1 THz. The detector utilizes the principle of distributed resistive self-mixing in GFET, and the split bowtie antenna provides an asymmetric feed to the GFET. The antenna is placed on a substrate lens to improve the directivity and can be used to create an imaging array. The dimensions of the split bowtie antenna are optimized for the best impedance matching with the GFET and to improve the pixel density of the array. The off-axis pixel performance is improved by modifying the edge-pixel antennas. The improvement in directivity of corresponding pixels is up to 1.3 dB.
14.	Li, Junjie, 1995, et al. (författare) High frequency noise characterisation of graphene field-effect transistors at different temperatures 2019 Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract Graphene is a promising material for high frequency electronics applications thanks to its intrinsically high carrier mobility and velocity, and graphene transistors are continuously pushed toward higher operating frequencies [1]. For high frequency low noise amplifiers, it is important to evaluate the noise parameters of the graphene field-effect transistors (GFETs). In this work, we present the noise performance of the GFETs made of chemical vapour deposition (CVD) in the frequency and temperature ranges of 2-18 GHz and -60-25 C. The noise figure with 50 Ohm impedance termination (F50) was measured using the cold-source method and then the minimum noise figure (Fmin) was estimated using the Pospieszalski’s noise model [2, 3]. In Fig. 1 and Fig. 2, the Fmin of a GFET with a gate length of 0.5 μm as a function of the frequency (f) and drain voltage (Vd) at different temperatures are shown. This GFET revealed maximum frequency of oscillation (fmax) of 18 and 21 GHz at 25 and -60 °C, respectively. It can be seen from Fig. 1, that the Fmin at 8 GHz is approx. 2 dB lower than that of the previously published CVD GFETs and comparable with that of the best published SiC GFETs [4, 5]. The Fmin decreases significantly with temperature down to 0.3 dB at 8 GHz, competing with Si CMOS [6]. It can be seen from Fig. 2, that Fmin decreases with the Vd and saturates above approx. 1 V, where GFETs operate in the velocity saturation mode [1]. Analysis of the dependences allows for further development of the GFETs for advanced low noise amplifiers.
15.	Vorobiev, Andrei, 1963, et al. (författare) Graphene Field-Effect Transistors for Millimeter Wave Amplifiers 2019 Ingår i: International Conference on Infrared, Millimeter, and Terahertz Waves, IRMMW-THz. - 2162-2027 .- 2162-2035. ; 2019-September Konferensbidrag (refereegranskat)abstract In this work, we analyze high frequency performance of graphene field-effect transistors (GFETs), applying models of drain resistance, carrier velocity and saturation velocity. This allows us to identify main limitations and propose an approach most promising for further development of the GFETs suitable for advanced mm-wave amplifiers. Analysis indicates, that the saturation velocity of charge carriers in the GFETs can be increased up to 5e7 cm/s via encapsulating graphene by hexagonal boron nitride layers, with corresponding increase of extrinsic maximum frequency of oscillation up to 180 GHz at 200 nm gate length.
16.	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.
17.	Yang, Xinxin, 1988, et al. (författare) A flexible graphene terahertz detector 2017 Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 111:2 Tidskriftsartikel (refereegranskat)abstract We present a flexible terahertz (THz) detector based on a graphene field-effect transistor fabricated on a plastic substrate. At room temperature, this detector reveals voltage responsivity above 2 V/W and estimated noise equivalent power (NEP) below 3 nW/Hz1/2 at 487 GHz. We have investigated the effects of bending strain on DC characteristics, voltage responsivity, and NEP of the detector, and the results reveal its robust performance. Our findings have shown that graphene is a promising material for the development of THz flexible technology.
18.	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.
19.	Yang, Xinxin, 1988, et al. (författare) Characterization of Al2O3 gate dielectric for graphene electronics on flexible substrates 2016 Ingår i: 2016 Global Symposium on Millimeter Waves (GSMM) & ESA Workshop on Millimetre-Wave Technology and Applications. - 9781509013487 ; , s. 153-156 Konferensbidrag (refereegranskat)abstract In this work, we have fabricated parallel-plate capacitor test structures consisting of 35 nm thick Al2O3 dielectric film and graphene as bottom electrode on polyethylene terephthalate (PET) to characterize the electrical properties of the dielectric film for graphene electronics on flexible substrates.It was found out that leakage current density in the Al2O3 film is less than 0.1 mA/cm2 at 5 V, which allows for applying it as a gate dielectric in graphene-based field effect transistors (GFETs) on flexible substrates. Dielectric constant of the Al2O3 film is approx. 7.6, which is close to the bulk value and confirms good quality of the Al2O3 film. Analysis indicates that the measured loss tangent, which is up to 0.2, is governed mainly by the dielectric loss in the Al2O3 and can be associated with defects in Al2O3 and Al2O3/graphene interface. Our results will be used in further development of GFETs on flexible substrates.
20.	Yang, Xinxin, 1988, et al. (författare) Test structures for evaluating Al2O3 dielectrics for graphene field effect transistors on flexible substrates 2018 Ingår i: IEEE International Conference on Microelectronic Test Structures. ; 31, s. 75-78 Konferensbidrag (refereegranskat)abstract We have developed a test structure for evaluating the quality of Al2O3 gate dielectrics grown on graphene for graphene field effect transistors on flexible substrates. The test structure consists of a metal/dielectric/ graphene stack on a PET substrate and requires only one lithography step for the patterning of the topside metal electrodes. Results from measurements of leakage current, capacitance and loss tangent are presented.
21.	Harrysson Rodrigues, Isabel, 1993, et al. (författare) Terahertz biometric sensors for fingerprint scanning 2022 Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract This study is motivated by a combination of the sustainability and vital need for enhancing authentication security of digital devices, both personal and corporate. We present an inhouse built millimeter-wave frequency biometric sensor setup and obtained original data, measured in real-time, of both an artificial stamp and a real human fingerprint. This setup lays the ground for an intended biometric sensor for further use implementing graphene, which is foreseen to be an important two-dimensional material in future electronics and sensing applications.
22.	Hemmeter, Andreas, et al. (författare) Terahertz Rectennas on Flexible Substrates Based on One-Dimensional Metal–Insulator–Graphene Diodes 2021 Ingår i: ACS Applied Electronic Materials. - : American Chemical Society (ACS). - 2637-6113. ; 3:9, s. 3747-3753 Tidskriftsartikel (refereegranskat)abstract Flexible energy harvesting devices fabricated in scalable thin-film processes are crucial for wearable electronics and the Internet of Things. We present a flexible rectenna based on a one-dimensional junction metal–insulator–graphene diode, offering low-noise power detection at terahertz (THz) frequencies. The rectennas are fabricated on a flexible polyimide film in a scalable process by photolithography using graphene grown by chemical vapor deposition. A one-dimensional junction reduces the junction capacitance and enables operation up to 170 GHz. The rectenna shows a maximum responsivity of 80 V/W at 167 GHz in free space measurements and minimum noise equivalent power of 80 pW/√Hz.
23.	Lindström, Michelle, et al. (författare) Lsm7 phase-separated condensates trigger stress granule formation 2022 Ingår i: Nature Communications. - : Springer Science and Business Media LLC. - 2041-1723. ; 13:1 Tidskriftsartikel (refereegranskat)abstract Stress granules are non-membranous organelles connected to stress responses and age-related disease. Here, the authors identify a conserved yeast protein, Lsm7, that facilitates stress granule formation through dynamic liquid-liquid phase separation condensates upon 2-deoxy-D-glucose-induced stress. Stress granules (SGs) are non-membranous organelles facilitating stress responses and linking the pathology of age-related diseases. In a genome-wide imaging-based phenomic screen, we identify Pab1 co-localizing proteins under 2-deoxy-D-glucose (2-DG) induced stress in Saccharomyces cerevisiae. We find that deletion of one of the Pab1 co-localizing proteins, Lsm7, leads to a significant decrease in SG formation. Under 2-DG stress, Lsm7 rapidly forms foci that assist in SG formation. The Lsm7 foci form via liquid-liquid phase separation, and the intrinsically disordered region and the hydrophobic clusters within the Lsm7 sequence are the internal driving forces in promoting Lsm7 phase separation. The dynamic Lsm7 phase-separated condensates appear to work as seeding scaffolds, promoting Pab1 demixing and subsequent SG initiation, seemingly mediated by RNA interactions. The SG initiation mechanism, via Lsm7 phase separation, identified in this work provides valuable clues for understanding the mechanisms underlying SG formation and SG-associated human diseases.
24.	Viti, Leonardo, et al. (författare) High-speed hBN/graphene/hBN room-temperature terahertz nano-receivers 2021 Ingår i: Proceedings of SPIE - The International Society for Optical Engineering. - : SPIE. - 0277-786X .- 1996-756X. ; SPIE 11685 Konferensbidrag (refereegranskat)abstract We report room temperature terahertz detection in hBN/graphene/hBN heterostructures. The obtained record combination of high-speed (response time < 1 ns) and high sensitivity (noise equivalent power ~ 100 pWHz-1/2) is enabled by the photo-thermoelectric effect.
25.	Viti, Leonardo, et al. (författare) High-speed, low-noise thermoelectric graphene detectors at terahertz frequencies 2020 Ingår i: International Conference on Infrared, Millimeter, and Terahertz Waves, IRMMW-THz. - 2162-2027 .- 2162-2035. ; 2020-November, s. 302-302 Konferensbidrag (refereegranskat)abstract We report room temperature terahertz detection in hBN/graphene/hBN heterostructures, integrated in top-gated field effect transistors. The record combination of high-speed (response time < 1 ns) and high sensitivity (noise equivalent power ~ 100 pWHz-1I2) is enabled by the photo-thermoelectric effect and paves the way for the design of ultrafast graphene arrays in the far infrared, opening concrete perspectives for targeting ultrafast applications.
26.	Viti, Leonardo, et al. (författare) Thermoelectric graphene photodetectors with sub-nanosecond response times at terahertz frequencies 2020 Ingår i: Nanophotonics. - : Walter de Gruyter GmbH. - 2192-8614 .- 2192-8606. ; 10:1, s. 89-98 Tidskriftsartikel (refereegranskat)abstract Ultrafast and sensitive (noise equivalent power <1 nW Hz-1/2) light-detection in the terahertz (THz) frequency range (0.1-10 THz) and at room-temperature is key for applications such as time-resolved THz spectroscopy of gases, complex molecules and cold samples, imaging, metrology, ultra-high-speed data communications, coherent control of quantum systems, quantum optics and for capturing snapshots of ultrafast dynamics, in materials and devices, at the nanoscale. Here, we report room-temperature THz nano-receivers exploiting antenna-coupled graphene field effect transistors integrated with lithographically-patterned high-bandwidth (∼100 GHz) chips, operating with a combination of high speed (hundreds ps response time) and high sensitivity (noise equivalent power ≤120 pW Hz-1/2) at 3.4 THz. Remarkably, this is achieved with various antenna and transistor architectures (single-gate, dual-gate), whose operation frequency can be extended over the whole 0.1-10 THz range, thus paving the way for the design of ultrafast graphene arrays in the far infrared, opening concrete perspective for targeting the aforementioned applications.
27.	Viti, Leonardo, et al. (författare) Thermoelectric graphene photodetectors with sub-nanosecond response times at terahertz frequencies 2021 Ingår i: Frontiers in Optics and Photonics. - : De Gruyter. ; , s. 89-98 Bokkapitel (övrigt vetenskapligt/konstnärligt)abstract Ultrafast and sensitive (noise equivalent power <1 nW Hz-1/2) light-detection in the terahertz (THz) frequency range (0.1-10 THz) and at room-temperature is key for applications such as time-resolved THz spectroscopy of gases, complex molecules and cold samples, imaging, metrology, ultra-high-speed data communications, coherent control of quantum systems, quantum optics and for capturing snapshots of ultrafast dynamics, in materials and devices, at the nanoscale. Here, we report room-temperature THz nano-receivers exploiting antenna-coupled graphene field effect transistors integrated with lithographically-patterned high-bandwidth (-100 GHz) chips, operating with a combination of high speed (hundreds ps response time) and high sensitivity (noise equivalent power <120 pW Hz-1/2) at 3.4 THz. Remarkably, this is achieved with various antenna and transistor architectures (single-gate, dual-gate), whose operation frequency can be extended over the whole 0.1-10 THz range, thus paving the way for the design of ultrafast graphene arrays in the far infrared, opening concrete perspective for targeting the aforementioned applications.
28.	Wymeersch, Henk, 1976, et al. (författare) 6G Radio Requirements to Support Integrated Communication, Localization, and Sensing 2022 Ingår i: 2022 Joint European Conference on Networks and Communications and 6G Summit, EuCNC/6G Summit 2022. ; , s. 463-469 Konferensbidrag (refereegranskat)abstract 6G will be characterized by extreme use cases, not only for communication, but also for localization, and sensing. The use cases can be directly mapped to requirements in terms of standard key performance indicators (KPIs), such as data rate, latency, or localization accuracy. The goal of this paper is to go one step further and map these standard KPIs to requirements on signals, on hardware architectures, and on deployments. Based on this, system solutions can be identified that can support several use cases simultaneously. Since there are several ways to meet the KPIs, there is no unique solution and preferable configurations will be discussed.
29.	Xiong, Kunli, 1987, et al. (författare) Plasmonic Metasurfaces with Conjugated Polymers for Flexible Electronic Paper in Color 2016 Ingår i: Advanced Materials. - : Wiley. - 0935-9648 .- 1521-4095. ; 28:45, s. 9956-9960 Tidskriftsartikel (refereegranskat)
30.	Yang, Xinxin, 1988, et al. (författare) Broadband Flexible Graphene RF Power Detectors 2017 Ingår i: Graphene Week 2017, Athens, Greece, 25-29 September, 2017. Konferensbidrag (refereegranskat)abstract With the development of wearable radios, foldable Wi-Fi devices, and conformal wireless sensors,flexible radio frequency (RF) electronics have become a highly active research field [1, 2]. As anessential component for both RF transmitters and receivers, a power detector is required to withstandhigh levels of strain. The flexible RF power detectors based on laminated Si and III-V membranes onpolymer substrates demonstrate poor mechanical reliability, restricting the range of applications [3, 4].In contrast, graphene is an ideal candidate for the use in flexible RF power detectors, because it offersoutstanding electrical and mechanical properties [5]. Furthermore, graphene can be grown over largeareas by chemical vapour deposition and transferable to various flexible substrates [6].In this work, we demonstrate RF power detection up to 67 GHz using coplanar access graphene field -effect transistors (GFETs) on flexible and transparent polyethylene terephthalate substrates. Thefrequency dependence of measured and modelled voltage responsivity at optimum gate bias is shownin Figure 1. At room temperature, this detector reveals voltage responsivity above 10 V/W over thefrequency range from 1 GHz to 67 GHz. The measured voltage responsivity results are well fitted by thenonlinear empirical model [7] with all parameters extracted from S-parameter and DC measurements.In addition, we study the effects of interfacial capacitance, associated with traps, on the hysteresis ofvoltage responsivity. Figure 2 shows the measured voltage responsivity as a function of the gate voltagewith reproducible hysteresis loop at 55 GHz.
31.	Yang, Xinxin, 1988 (författare) Characterisation and modelling of graphene FET detectors for flexible terahertz electronics 2020 Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract Low-cost electronics for future high-speed wireless communication and non-invasive inspection at terahertz frequencies require new materials with advanced mechanical and electronic properties. Graphene, with its unique combination of flexibility and high carrier velocity, can provide new opportunities for terahertz electronics. In particular, several types of power sensors based on graphene have been demonstrated and found suitable as fast and sensitive detectors over a wide part of the electromagnetic spectrum. Nevertheless, the underlying physics for signal detection are not well understood due to the lack of accurate characterisation methods, which hampers further improvement and optimisation of graphene-based power sensors. In this thesis, progress on modelling, design, fabrication and characterisation of terahertz graphene field-effect transistor (GFET) detectors is presented. A major part is devoted to the first steps towards flexible terahertz electronics. The characterisation and modelling of terahertz GFET detectors from 1 GHz to 1.1 THz are presented. The bias dependence, the scattering parameters and the detector voltage response were simultaneously accessed. It is shown that the voltage responsivity can be accurately described using a combination of a quasi-static equivalent circuit model, and the second-order series expansion terms of the nonlinear dc I-V characteristic. The video bandwidth, or IF bandwidth, of GFET detectors is estimated from heterodyne measurements. Moreover, the low-frequency noise of GFET detectors between 1 Hz and 1 MHz is investigated. From this, the room-temperature Hooge parameter of fabricated GFETs is extracted to be around 2*10^{-3}. It is found that the thermal noise dominates above 100 Hz, which sets the necessary switching time to reduce the effect of 1/f noise. A state-of-the-art GFET detector at 400 GHz, with a maximum measured optical responsivity of 74 V/W, and a minimum noise-equivalent power of 130 pW/Hz^{0.5} is demonstrated. It is shown that the detector performance is affected by the quality of the graphene film and adjacent layers, hence indicating the need to improve the fabrication process of GFETs. As a proof of concept, a bendable GFET terahertz detector on a plastic substrate is demonstrated. The effects of bending strain on dc I-V characteristics, responsivity and sensitivity are investigated. The detector exhibits a robust performance for tensile strain of more than 1% corresponding to a bending radius of 7 mm. Finally, a linear array of terahertz GFET detectors on a flexible substrate for imaging applications is fabricated and tested. The results show the possibility of realising bendable and curved focal plane arrays. In summary, in this work, the combination of improved device models and more accurate characterisation techniques of terahertz GFET detectors will allow for further optimisation. It is shown that graphene can open up for flexible terahertz electronics for future niche applications, such as wearable smart electronics and curved focal plane imaging.
32.	Yang, Xinxin, 1988, et al. (författare) Describing broadband terahertz response of graphene FET detectors by a classical model 2020 Ingår i: IEEE Transactions on Terahertz Science and Technology. - 2156-342X .- 2156-3446. ; 10:2, s. 158-166 Tidskriftsartikel (refereegranskat)abstract Direct power detectors based on field-effect transistors are becoming widely used for terahertz applications. However, accurate characterization at terahertz frequencies of such detectors is a challenging task. The high-frequency response is dominated by parasitic coupling and loss associated with contacts and overall layout of the component. Moreover, the performance of such detectors is complicated to predict since many different physical models are used to explain the high sensitivity at terahertz frequencies. This makes it hard to draw important conclusions about the underlying device physics for these detectors. For the first time, we demonstrate accurate and comprehensive characterization of graphene field-effect transistors from 1 GHz to 1.1 THz, simultaneously accessing the bias dependence, the scattering parameters, and the detector voltage responsivity. Within a frequency range of more than 1 THz, and over a wide bias range, we have shown that the voltage responsivity can be accurately described using a combination of a small-signal equivalent circuit model, and the second-order series expansion terms of the nonlinear dc $I-V$ characteristic. Without bias, the measured low-frequency responsivity was 0.3 kV/W with the input signal applied to the gate, and 2 kV/W with the input signal applied to the drain. The corresponding cut-off frequencies for the two cases were 140 GHz and 50 GHz, respectively. With a 300-GHz signal applied to the gate, a voltage responsivity of 1.8 kV/W was achieved at a drain-source current of 0.2 mA. The minimum noise equivalent power was below 30 pW/$\sqrt\mathrm{Hz}$ in cold mode. Our results show that detection of terahertz signals in graphene field-effect transistors can be described over a wide frequency range by the nonlinear carrier transport characteristic obtained at static electrical fields. This finding is important for explaining the mechanism of detection and for further development of terahertz detectors.
33.	Yang, Xinxin, 1988 (författare) Graphene FET terahertz detectors on flexible substrates 2017 Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract Terahertz (THz) science and technology have developed rapidly over the past decades, extending the THz application areas from spectroscopy and earth and space sciences to communications, biomedicine and security sensing. Many of these emerging applications require shape-conforming, light-weight and low-cost detectors rather than existing solid-state detection technology. Graphene, which possesses impressive electrical and mechanical properties, is a promising material for enabling flexible devices at THz frequencies.This thesis reports on the modelling, design, fabrication and characterisation of graphene THz detectors on plastic substrates. These detectors are based on field-effect transistors (FETs) fabricated using chemical vapour deposition(CVD)-grown graphene and integrated with split broadband bow-tie antennas. A fabrication process has been developed to achieve high-performance THz detectors on plastic substrates. Since the properties of the dielectric film on graphene are very sensitive to the growth conditions, parallel-plate capacitor test structures on graphene on flexible substrates are fabricated for characterising the electrical properties of the dielectric films.THz power detection in the frequency range from 330 GHz to 500 GHz at room temperature is demonstrated. The devices operate well above the cutoff frequency of the transistors. At room temperature, the voltage responsivity isabove 2 V/W, and the noise-equivalent power (NEP) is below 3 nW/√Hz at 487 GHz.The effects of bending strain on the dc characteristics, voltage responsivity and NEP of these detectors have been investigated. The mechanical studies reveal robust detector performance with tensile strain more than 1% with acorresponding bending radius of 7 mm.This work provides an important route towards high-performance, low-cost THz flexible technology for future niche applications, such as wearable smart electronics, imaging systems, and communications.
34.	Yang, Xinxin, 1988, et al. (författare) Homodyne detection in graphene FET power detectors 2018 Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract We have analysed the specific nonlinearity of GFETs, and demonstrated that the input RF signal should be coupled to both drain and gate to obtain the highest dc current response of GFET power detectors. To enhance the response further, one can use an extrinsic capacitor between gate and drain, and optimise the GFET channel dimensions
35.	Yang, Xinxin, 1988, et al. (författare) Low-frequency Noise Characterization of Graphene FET THz Detectors 2018 Ingår i: International Conference on Infrared, Millimeter, and Terahertz Waves, IRMMW-THz. - 2162-2027 .- 2162-2035. ; 2018-September Konferensbidrag (refereegranskat)abstract Graphene field-effect transistors are promising for direct detection of THz signals at room temperature. The sensitivity of such detectors can be in part limited by the low-frequency noise. Here, we report on the characterization of the low-frequency noise of graphene field-effect transistor THz detectors in the frequency range from 1 Hz to 1 MHz. The room-temperature Hooge parameter is extracted to be around 2×10-3. The voltage responsivity at room-temperature and the corresponding minimum noise equivalent power at 0.3 THz are estimated to be 11 V/W and 0.2 nW/Hz0.5, respectively, at a modulation frequency of 333 Hz, which shows comparable results with other detector technologies.
36.	Yang, Xinxin, 1988, et al. (författare) Wide Bandwidth Terahertz Mixers Based On Graphene FETs 2019 Ingår i: International Conference on Infrared, Millimeter, and Terahertz Waves, IRMMW-THz. - 2162-2027 .- 2162-2035. ; 2019-September Konferensbidrag (refereegranskat)abstract In this work, resistive fundamental terahertz mixers with wide RF and IF bandwidths based on graphene field-effect transistors have been demonstrated. With an RF frequency range from 220 GHz to 487 GHz, the estimated values of the 3-dB IF bandwidth are 32 GHz and 56 GHz for mixers with GFET gate lengths of 1.2 ?m and 0.6 ?m, respectively. This is competitive with the performance of mixers based on traditional semiconductor technologies.

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