16,435 research outputs found
Distributed Trap Levels and Hot-Electron Trapping in Power GaN HEMTs Characterization and Modeling
No full textGallium Nitride (GaN)-based high electron mobility transistors (HEMTs) are rapidly emerging as front-runners in high-power mm-wave circuit applications. Possible targets that would benefit of the advantages of GaN–based devices include efficient power supplies, DC/DC converters and AC/DC adapters, as well as the field of radars and telecommunications.
Despite the recent commercial success of GaN-based devices, internal physical mechanisms are often not completely understood and still constitute a challenge to the development of a mature GaN-based technology. Besides the difficulties of growing a high–quality GaN material, point defects at interfaces play a major role in terms of reliability.
In the present thesis, several aspect of the device instability have been investigated from both and experimental and theoretical point of view. Throughout this thesis, our goal is to build a quantitative and qualitative understanding of the main factors undermining the device stability under real application conditions.
By comparing Hard and Soft switching turn-on commutations, we demonstrated how turn-on stress plays a major role in the on-resistance degradation, while off-state bias does not have a relevant influence on device properties. Furthermore, by repeating the experiment on several devices with different L_GD, we were able to demonstrate the important role of electric field in determining the R_ON increase and to rule out a significant contribution of self-heating.
Then, in order to observe the full trapping and de-trapping kinetics of hot-electrons we focused on semi-ON stress analysis by means of a custom setup able to perform Drain Current Transient (DCT) analysis. Firstly, by focusing on the trapping phase, a physical understanding of the hot electron phenomena in GaN-based HEMTs is developed with a cross-comparison between theoretical analysis and experimental data. Linear dependency on the applied electric field and logarithmic dependency on the current density in determining the severity of current collapse are found. Results provide important information for the modeling of hot-electron trapping kinetics in GaN-based power transistors. The first 10 us of operation are critical in determining the current collapse during stress.
Secondly, by focusing on the recovery phase, we propose a general methodology for mapping the properties (activation energy, cross sections) of a distribution of surface/interface states in GaN-based electronic devices. To prove the validity and usefulness of the model, the extracted map distributions are used as input for TCAD simulations. The results obtained by TCAD closely match the experimental transient curves, thus confirming the effectiveness of the developed technique.
The theoretical knowledge built along this thesis allowed us to propose a new approach for compact modeling of the stretched exponential trapping/de-trapping kinetics of p-GaN HEMTs is proposed. Novel insight on the GaN HEMT dynamic performance degradation is given highlighting how the criticality of a trap is dependent on its location in the capture and emission time map. The duty cycle plays a key role in determining the performance degradation trajectory, while the frequency is related to the amplitude of the capture and emission process per cycle.Gallium Nitride (GaN)-based high electron mobility transistors (HEMTs) are rapidly emerging as front-runners in high-power mm-wave circuit applications. Possible targets that would benefit of the advantages of GaN–based devices include efficient power supplies, DC/DC converters and AC/DC adapters, as well as the field of radars and telecommunications.
Despite the recent commercial success of GaN-based devices, internal physical mechanisms are often not completely understood and still constitute a challenge to the development of a mature GaN-based technology. Besides the difficulties of growing a high–quality GaN material, point defects at interfaces play a major role in terms of reliability.
In the present thesis, several aspect of the device instability have been investigated from both and experimental and theoretical point of view. Throughout this thesis, our goal is to build a quantitative and qualitative understanding of the main factors undermining the device stability under real application conditions.
By comparing Hard and Soft switching turn-on commutations, we demonstrated how turn-on stress plays a major role in the on-resistance degradation, while off-state bias does not have a relevant influence on device properties. Furthermore, by repeating the experiment on several devices with different L_GD, we were able to demonstrate the important role of electric field in determining the R_ON increase and to rule out a significant contribution of self-heating.
Then, in order to observe the full trapping and de-trapping kinetics of hot-electrons we focused on semi-ON stress analysis by means of a custom setup able to perform Drain Current Transient (DCT) analysis. Firstly, by focusing on the trapping phase, a physical understanding of the hot electron phenomena in GaN-based HEMTs is developed with a cross-comparison between theoretical analysis and experimental data. Linear dependency on the applied electric field and logarithmic dependency on the current density in determining the severity of current collapse are found. Results provide important information for the modeling of hot-electron trapping kinetics in GaN-based power transistors. The first 10 us of operation are critical in determining the current collapse during stress.
Secondly, by focusing on the recovery phase, we propose a general methodology for mapping the properties (activation energy, cross sections) of a distribution of surface/interface states in GaN-based electronic devices. To prove the validity and usefulness of the model, the extracted map distributions are used as input for TCAD simulations. The results obtained by TCAD closely match the experimental transient curves, thus confirming the effectiveness of the developed technique.
The theoretical knowledge built along this thesis allowed us to propose a new approach for compact modeling of the stretched exponential trapping/de-trapping kinetics of p-GaN HEMTs is proposed. Novel insight on the GaN HEMT dynamic performance degradation is given highlighting how the criticality of a trap is dependent on its location in the capture and emission time map. The duty cycle plays a key role in determining the performance degradation trajectory, while the frequency is related to the amplitude of the capture and emission process per cycle
Recent Results From the EU POF-PLUS Project: Multi-Gigabit Transmission Over 1 mm Core Diameter Plastic Optical Fibers
No full textRecent activity to achieve multi-gigabit transmission over 1 mm core diameter graded-index and step-index plastic optical fibers for distances up to 50 meters is reported in this paper. By employing a simple intensity-modulated direct-detection system with pulse amplitude or digital multi-tone modulation techniques, low-cost transceivers and easy to install large-core POFs, it is demonstrated that multi-gigabit transmission up to 10 Gbit/s over 1-mm core diameter POF infrastructure is feasible. The results presented in this paper were obtained in the EU FP7 POF-PLUS project, which focused on applications in different scenarios, such as in next-generation in-building residential networks and in datacom applications
Employing M1 direct calibration/de-embedding approaches for large signal model validation at mm-wave frequencies
No full textIn this contribution, we employ direct calibration/de-embedding approaches to validate the large signal device model of state-of-the-art HBTs and CMOS technologies operating in the mm-wave frequency band WR6. The capability of placing the first tier calibration reference plane in close proximity to the DUT allows the large signal metric to be directly compared with foundry models.Green Open Access added to TU Delft Institutional Repository 'You share, we take care!' - Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.Electronic
Dynamic Estimation of Vital Signs with mm-wave FMCW Radar
No full textIn this paper, we propose a method for continuous monitoring of vital signs-in particular, respiration frequency-with a commercial mm-wave radar. The nearly constant frequency (NCF) model is adopted to represent chest displacement due to respiration and simulate radar response. Based on this model, an extended Kalman filter (EKF) based estimator is developed to track the breathing frequency of a person. The impact of dynamic model parameters is investigated in numerical simulation. The possibility to track breathing frequency with the proposed method is demonstrated by experimental data processing. Green Open Access added to TU Delft Institutional Repository ‘You share, we take care!’ – Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.Microwave Sensing, Signals & System
A 23-to-29GHz Receiver with mm-Wave N-Input-N-Output Spatial Notch Filtering and Autonomous Notch-Steering Achieving 20-to-40dB mm-Wave Spatial Rejection and -14dBm In-Notch IP1 dB
No full textDigital beamforming receivers (RXs) support MIMO operation and offer great flexibility and accuracy in multi-beam formation and calibration. However, compared with analog phased-array and hybrid systems, due to the absence of any rejection for spatial in-band blockers, the RX/ADC dynamic range and linearity should be high enough to prevent array saturation. Therefore, the use of self-steering spatial notch filters (SNFs) is necessary to aid the digital beamformers and reduce RX/ADC power consumption while strong blockers exist. To address that, the sub-6GHz RXs in [1], [2] synthesize a baseband spatial notch impedance and translate it to RF by passive mixers. However, this technique cannot be directly applied at mm-wave frequencies as the impedance translational performance of the passive mixers degrades significantly. Hence, the mm-wave beamformer in [3] realizes a cascadable SNF at an intermediate frequency (IF). However, the front-end mm-wave components like mixers and phase shifters have to tolerate strong blockers, thus degrading RX linearity. Besides, it uses multiple IF buffers and VGAs for signal scaling and combining, which could be power-hungry if a similar method is adopted to realize a mm-wave SNF. To improve on those limitations, we propose a scalable SNF structure, which (1) suppresses the strongest in-band blocker at mm-wave frequencies, (2) supports N-input-N-output MIMOs, and (3) requires no active blocks except the phase shifters. A two-step autonomous notch-steering technique is also developed to adjust the SNF notch direction power-efficiently and accurately.Green Open Access added to TU Delft Institutional Repository 'You share, we take care!' - Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.Electronic
Experiencing the armed struggle : the Soweto generation and after
No full textIncludes bibliographical references (p. 354-369).This study explores the experiences of the rank-and-file soldiers of Umkhonto we Sizwe and the Azanian People's Liberation Anny. Extensive interviews by the author and other researchers reveal the voices of the soldiers themselves. The African National Congress and Pan African Congress archives at the University of the Western Cape and the University of Fort Hare supplement and verify these oral testimonies, as do some published sources. Most previously published materials about the armed struggle against apartheid have already focused on diplomacy, strategy and tactics, operations, leadership, and human rights abuses to the neglect of the soldiers' actual experiences. This study complements these with significant new oral history materials from the Soweto generation of soldiers and their successors. When dealing with MK, many authors have documented issues of the camp structure in Angola, and operations inside South Africa, so much of this detail is only addressed briefly, leaving space to explore the soldiers' experiences. In the case of APLA, very little has been written on its history, and more detail is provided on these subjects. This study therefore deals with the soldiers' politicisation and motivation for joining the armed struggle, their experiences in leaving South Africa and training in exile, the crises in exile which limited their effectiveness for a time, their return to fight in South Africa, and their difficulties in the "new" South Africa. These materials reveal that vast problems remain facing these veterans of the struggle against apartheid, and that they have the potential, if properly supported and employed, to contribute substantially to the development of present day South Africa. Conversely, if their neglect continues, they also have the potential to bring vast harm to the country. Further use of the investigative tools of oral history, especially if extended to the former soldiers' vernacular languages, is necessary to augment the history of South Africa, and these soldiers' contributions
Grouped People Counting Using mm-wave FMCW MIMO Radar
No full textThe problem of radar-based counting of multiple individuals moving as a single group is addressed using an mm-wave multiple-input-multiple-output (MIMO) frequency-modulated continuous wave (FMCW) radar. This problem is challenging because the different individuals are closer to each other than the range/azimuth resolution, and their bulk Doppler signatures are difficult to distinguish, as they tend to move together. A processing pipeline is proposed, based on the combination of a multiple target tracking algorithm with a classifier to track each group and count the number of people within. Specific salient features are defined for the classifier and extracted from range-azimuth maps and cadence velocity diagrams (CVDs). The proposed pipeline has been experimentally validated in several outdoor scenarios with grouped people. The results show that the combination of tracking algorithm and classifier in the proposed pipeline outperforms alternative methods from the literature as well as a commercial toolbox for people counting.Green Open Access added to TU Delft Institutional Repository ‘You share, we take care!’ – Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.Microwave Sensing, Signals & System
MM Recital
No full textMM RecitalEmbargo status: Restricted until 06/2172. To request the author grant access, click on the PDF link to the left
Social Signals and Multimedia: Past, Present, Future
No full textThe rising popularity of Artificial Intelligence (AI) has brought considerable public interest as well faster and more direct transfer of research ideas into practice. One of the aspects of AI that still trails behind considerably is the role of machines in interpreting, enhancing, modeling, generating, and influencing social behavior. Such behavior is captured as social signals, usually by sensors recording multiple modalities, making it classic multimedia data. Such behavior can also be generated by an AI system when interacting with humans. Using AI techniques in combination with multimedia data can be used to pursue multiple goals, two of which are high-lighted here. First, supporting people during social interactions and helping them to fulfil their social needs either actively or passively.Second, improving our understanding of how people collaborate, build relationships, and process self identity. Despite the rise of fields such as Social Signal Processing, a similar panel organised at ACM Multimedia 2014, and an area on social and emotional signal sat the ACM MM since 2014, we argue that we have yet to truly fulfil the potential of the combining social signals and multimedia. This panel asks where we have come far enough and what remaining challenges there are in light of recent global events.Green Open Access added to TU Delft Institutional Repository ‘You share, we take care!’ – Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.Pattern Recognition and Bioinformatic
Wideband Sub-mm Wave Superconducting Integrated Filter-bank Spectrometer
No full textThe design of an octave bandwidth sub-mm wave superconducting on-chip filter-bank spectrometer for Astronomy is presented. An array of THz band-pass filters subdivides the bandwidth 220-440 GHz into channels with a spectral resolution of 400 and an average maximum coupling strength f/ Delta {f} of 40%. The filter-bank performance is assessed by means of a transmission line formalism that approximates its behavior. The chip is under fabrication and its measurements will follow.Green Open Access added to TU Delft Institutional Repository ‘You share, we take care!’ – Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.Tera-Hertz Sensin
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