SwePub - search: WFRF:(Thorsell Mattias 1982)

Enumeration	Reference	Cover	Find
1.	Andersson, Christer, 1982, et al. (author) Nonlinear Characterization of Varactors for Tunable Networks by Active Source-Pull and Load-Pull 2011 In: IEEE Transactions on Microwave Theory and Techniques. - 0018-9480 .- 1557-9670. ; 59:7, s. 1753-1760 Journal article (peer-reviewed)abstract Varactors are key components in the realization of tunable networks, for instance, in high-efficiency power-amplifier architectures. This paper presents a method to measure the varactor quality factor (Q-factor) in the presence of nonlinear distortion. The importance of correctly choosing the loading condition at the second harmonic is illustrated by multiharmonic active source- and load-pull measurements. Furthermore, the method also allows for accurate extraction of the bias-dependent series resistance without the need of area consuming resonant structures. The proposed method is applied to characterize a silicon-carbide (SiC) Schottky diode varactor at 3 GHz. The measured results reemphasize that varactors are not linear tunable, but inherently nonlinear components that require proper consideration of the higher order harmonics.
2.	Angelov, Iltcho, 1943, et al. (author) On the large-signal modeling of High Power AlGaN/GaN HEMTs 2012 In: IEEE MTT-S International Microwave Symposium Digest. - 0149-645X. - 9781467310871 Conference paper (peer-reviewed)abstract In this paper are given some recent results on modeling of High Power GaN HEMT devices. The GaN HEMT is very promising for high power application, but we push device to the limits, so many issues are becoming critical. For example, access resistances Rs, Rd in high power GAN HEMT are bias and temperature dependent-their extraction from cold FET measurements can lead to over optimistic prediction for output power. Thermal management, self-heating modeling are another very important issue-they influence reliability, power and PAE. Models without dynamic self-heating are not practical for GaN. The models without breakdown can easily predict world records for PAE, output power/mm etc. Some examples are given using vectorial Large Signal Measurements (LSNA/NVNA) to provide useful, global info about device behavior, influence of traps, knee voltage walkout etc.
3.	Frank, Markus, 1970, et al. (author) Differential Impedance Measurement Method of RFID Transponder Chips at UHF 2013 In: Proceedings of the 43rd European Microwave Conference. - 9782874870316 ; 2013, s. 68-71 Conference paper (peer-reviewed)abstract A novel on-wafer measurement method of RFID transponder chips is presented. A comparison is made between single ended one-port, single ended two-port and differential two-port excitation. The two-port method is a flexible way of measuring chips consisting of both several individuals as well as chip types with different geometries with one and the same probe type. The theory of un-terminating and de-embedding is described and verified by measurements. A qualitative analysis is defined, which explains certain phenomena seen in communication tests performed on RFID protocol level. This is further supported by measurement results from the presented method.
4.	Prasad, Ankur, 1987, et al. (author) Symmetrical Large-Signal Modeling of Microwave Switch FETs 2014 In: IEEE Transactions on Microwave Theory and Techniques. - : Institute of Electrical and Electronics Engineers (IEEE). - 0018-9480 .- 1557-9670. ; 62:8, s. 1590-1598 Journal article (peer-reviewed)abstract This paper presents a new symmetrical field-effect transistor (FET) model suitable for microwave switches. The model takes advantage of the inherent symmetry of typical switch devices, justifying a new small-signal model where all intrinsic model parameters can be mirrored between the positive and negative drain-source bias regions. This small-signal model is utilized in a new and simplified approach to large-signal modeling of these type of devices. It is shown that the proposed large-signal model only needs a single charge expression to model all intrinsic capacitances. For validation of the proposed model, small-signal measurements from 100 MHz to 50 GHz and large-signal measurements at 600 MHz and 16 GHz, are carried out on a GaAs pHEMT. Good agreement between the model and the measurements is observed under both small-and large-signal conditions with particularly accurate prediction of higher harmonic content. The reduced measurement requirements and complexity of the symmetrical model demonstrates its advantages. Further, supporting operation in the negative drain-source voltage region, the model is robust and applicable to a variety of circuits, e. g., switches, resistive mixers, oscillators, etc.
5.	Prasad, Ankur, 1987, et al. (author) Symmetrical modeling of GaN HEMTS 2014 In: Technical Digest - IEEE Compound Semiconductor Integrated Circuit Symposium, CSIC. - 1550-8781. - 9781479936229 Conference paper (peer-reviewed)abstract This paper presents a symmetrical small signal model for GaN HEMTs valid for both positive and negative Vds. The model takes advantage of the intrinsic symmetry of the devices typically used for switches. The parameters of the model are extracted using a new symmetrical optimization based extraction method, optimizing simultaneously for both positive and negative drain-source bias points. This ensures a symmetrical small signal model with lower modeling error. The small signal model can be further used to simplify the development of a large-signal model. The small signal model is validated with measured S- parameters of a commercial GaN HEMT.
6.	Sudow, Mattias, 1980, et al. (author) A Single-Ended Resistive $X$-Band AlGaN/GaN HEMT MMIC Mixer 2008 In: IEEE Transactions on Microwave Theory and Techniques. - 0018-9480 .- 1557-9670. ; 56:10, s. 2201-2206 Journal article (peer-reviewed)abstract A broadband highly linear X-band mixer in AlGaN/GaN monolithic microwave integrated circuit technology has been designed, processed, and characterized. The design is based on a 4 times 100 mum AlGaN/GaN HEMT in a single-ended circuit topology. The mixer has an IF bandwidth of 2 GHz with a conversion loss (CL) of
7.	Sudow, Mattias, 1980, et al. (author) An AlGaN/GaN HEMT-Based Microstrip MMIC Process for Advanced Transceiver Design 2008 In: IEEE Transactions on Microwave Theory and Techniques. - 0018-9480 .- 1557-9670. ; 56:8, s. 1827-1833 Journal article (peer-reviewed)abstract A MMIC process in AlGaN/GaN technology for advanced transceiver design has been developed. The process is based on microstrip technology with a complete model library of passive elements and AlGaN/GaN HEMTs. The transistor technology in this process is suitable for both power and low noise design, demonstrated with a power density of 5 W/mm, and an ${rm NF}_{min}$ of 1.4 dB at $X$ -band. Process stability of subcircuits, complementary to power amplifiers and LNAs, in a transceiver system have been investigated. The results indicate that an all AlGaN/GaN MMIC transceiver is realizable using this technology.
8.	Sudow, Mattias, 1980, et al. (author) SiC varactors for dynamic load modulation of high power amplifiers 2008 In: IEEE Electron Device Letters. - 0741-3106 .- 1558-0563. ; 29:7, s. 728-730 Journal article (peer-reviewed)abstract SiC Schottky diode varactors with a high breakdown voltage, a high tuning ratio, and a low series resistance have been designed and fabricated. These characteristics are particularly necessary for the dynamic load modulation of high power amplifiers (PAs), which is an attractive alternative to other efficiency enhancement techniques. For a SiC Schottky diode varactor with a 50-µm radius fabricated by using a graded doping profile, a breakdown voltage of 40 V, a tuning range of 5.6, and a series resistance of 0.9 O were achieved. The results show the great potential of this type of varactors for the use in the dynamic load modulation of high power amplifiers. © 2008 IEEE.
9.	Thorsell, Mattias, 1982, et al. (author) Characterization of the temperature dependent access resistances in AlGaN/GaN HEMTs 2008 In: Workshop on Integrated Nonlinear Microwave and Millimetre-Wave Circuits, 2008. INMMIC 2008.. - 9781424426454 ; , s. 17-20 Conference paper (peer-reviewed)abstract The temperature dependence of the access resistances for AlGaN/GaN HEMTs is investigated. The self-heating is measured using infrared microscopy and the access resistances are extracted at different ambient temperatures. Their influence on the intrinsic small signal parameters is studied versus bias and ambient temperature.
10.	Thorsell, Mattias, 1982, et al. (author) Thermal characterization of the intrinsic noise parameters for AlGaN/GaN HEMTs 2008 In: International Microwave Symposium Digest, 2008, Atlanta. - 0149-645X. - 9781424417810 ; , s. 463-466 Conference paper (peer-reviewed)abstract The noise parameters of AlGaN/GaN-HEMTs are measured between 298 K and 423 K. The temperature dependent access resistances are de-embedded and the intrinsic noise parameters are studied as a function of temperature. It is shown that the parasitic access resistances are limiting the highfrequency noise performance of the AlGaN/GaN-HEMT.The intrinsic noise sources are extracted and a noise model is derived and verified for a MMIC amplifier.
11.	Thorsell, Mattias, 1982, et al. (author) Thermal Study of the High-Frequency Noise in GaN HEMTs 2009 In: IEEE Transactions on Microwave Theory and Techniques. - 0018-9480 .- 1557-9670. ; 57:1, s. 19-26 Journal article (peer-reviewed)abstract The high-frequency noise performance of the GaN HEMT is studied for temperatures between 297–398 K. The access resistances ${ R}_{ S}$ and ${ R}_{ D}$ have a limiting effect on the noise performance, and in this paper, their temperature dependence is studied in detail for a ${hbox{2}}times {hbox{100}} mu{hbox{m}}$ GaN HEMT. ${ R}_{ S}$ and ${ R}_{ D}$ show an increase of 0.71 and 0.86 %/K, respectively. The self-heating effect due to dissipated power is also studied to allow accurate intrinsic small-signal and noise parameter extraction. The thermal resistance is measured by infrared microscopy. Based on these results, a temperature dependent noise model including self-heating and temperature-dependent access resistances is derived and verified with measurements.
12.	ÖZEN, MUSTAFA, 1984, et al. (author) High efficiency RF pulse width modulation with tunable load network class-E PA 2011 In: 2011 IEEE 12th Annual Wireless and Microwave Technology Conference, WAMICON 2011. - 9781612840819 Conference paper (peer-reviewed)abstract In this paper, a 10 W peak power 2 GHz highly efficient RF pulse width modulation (RF-PWM) based transmitter is presented. RF-PWM signals are generated with a dedicated 65 nm CMOS modulator and subsequently amplified with a GaN Class-E power amplifier (PA). The modulator use extended drain MOS (EDMOS) high voltage transistors to provide the required voltage swing to drive the GaN used as a switch. The imaginary load impedance of the Class-E is electronically tunable and is implemented with in-house high breakdown voltage SiC varactors. The tunable imaginary load impedance enables optimization of the Class-E versus the duty cycle (pulse width). The peak efficiency is therefore preserved over a wide range of output power levels. The measured drain efficiency of the Class-E output stage is above 70% over a 6.5 dB output power dynamic range. The overall transmitter efficiency is above 60% for the same dynamic range.
13.	Andersson, Kristoffer, 1976, et al. (author) Large-signal waveform acquisition of pulsed signals 2011 In: European Microwave Week 2011: "Wave to the Future", EuMW 2011, Conference Proceedings - 41st European Microwave Conference, EuMC 2011. - 9782874870224 ; , s. 9010-913 Conference paper (peer-reviewed)abstract Techniques for measuring large-signal waveforms of pulsed signals are fairly well described in the literature. However, most techniques are developed for very specific setups and typically require modification of the hardware. In this paper we describe an approach were no modification is necessary to the existing (Large-Signal Network Analyzer) LSNA hardware and software. Furthermore our method is very well suited for integration with other pulsed stimuli e.g. pulsed IV.
14.	Angelov, Iltcho, 1943, et al. (author) Hybrid measurement-based extraction of consistent large-signal models for microwave FETs 2013 In: 43rd European Microwave Conference, EuMC 2013 - Held as Part of the 16th European Microwave Week, EuMW 2013; Nuremberg; Germany; 7 October 2013 through 10 October 2013. - 9782874870316 ; , s. 267-270 Conference paper (peer-reviewed)abstract This paper discusses a procedure to extract large-signal models for microwave transistors. By using experimental data, which not necessarily reflect the actual operating conditions, accurate large-signal models, suitable for CAD tools and working at high frequencies, can be obtained by combining direct extraction of basic parameters and numerical optimization. The idea consists of linking the model parameters directly to experimental data. In this way the extraction procedure is sped up. Examples of large-signal models for GaAs and GaN transistors are reported.
15.	Angelov, Iltcho, 1943, et al. (author) Nonlinear active device modeling 2019 In: Radio Frequency and Microwave Power Amplifiers: Principles, Device Modeling and Matching Networks. ; , s. 73-165 Book chapter (other academic/artistic)abstract The chapter covers main characteristics of the devices used in power amplifiers (PAs) and provides basic knowledge about the specifications of these devices and the transistor models that are used in PA designs. The Preface covers the basic characteristics of main semiconductor device types used in PA designs. These devices have been in use for many decades, the technology of which is well established and its production is repeatable with high yield. Now, these devices show really impressive results. They work up to the terahertz region and can deliver kilowatts of power at low radio frequencies (RF). Probably one of the most promising devices now is the GaN high-electron-mobility transistor (HEMT), and they yield high-power and high-frequency results in number of applications. There are a plenty number of literature on these devices regarding how to design PA, and using these transistors has put a tremendous success in its field. A very small part of these references is listed here. The models come in small signal (SS), large signal (LS) categories, and for all these devices, extraction procedures, software is available.
16.	Angelov, Iltcho, 1943, et al. (author) On the Compact Equivalent Circuit Modeling 2010 In: APMC 2010 invited workshop. ; APMC 2010 invited workshop:APMC 2010 invited workshop Conference paper (peer-reviewed)
17.	Angelov, Iltcho, 1943, et al. (author) On the Large Signal Evaluation and Modeling of GaN FET 2010 In: IEICE Transactions on Electronics. - 0916-8524. ; E93C:8, s. 1225-1233 Journal article (peer-reviewed)abstract The large signal performance and model for GaN FET devices was evaluated with DC, S-parameters, and large signal measurements. The large signal model was extended with bias and temperature dependence of access resistances, modified capacitance and charge equations, as well as breakdown models. The model was implemented in a commercial CAD tool and exhibits good overall accuracy.
18.	Angelov, Iltcho, 1943, et al. (author) On the Modeling of High Power FET Transistors 2016 In: 2016 11th European Microwave Integrated Circuits Conference (Eumic), London, England, Oct 03-04, 2016. - 9782874870446 ; , s. 245-248 Conference paper (peer-reviewed)abstract The paper address some of the problems faced when modeling high power and high power density GaN and GaAs FETs. When operating a high power levels (>1kW) additional effects are observed in GaN devices that are not seen in low power operation (1W). Similar effects start to act on GaAs devices when operated at high power densities. In order to account for these effects, FET models were extended to include temperature, and bias dependence of the access resistances, as well as inflection points in the transconductance, and capacitances. Thus enabling accurate models of the latest generation of enhancement mode, KV range FETs. The recent extensions are evaluated, implemented, and available in major CAD tools like ADS, Cadence, and Microwave office.
19.	Axelsson, Olle, 1986, et al. (author) Application Relevant Evaluation of Trapping Effects in AlGaN/GaN HEMTs With Fe-Doped Buffer 2016 In: IEEE Transactions on Electron Devices. - 1557-9646 .- 0018-9383. ; 63:1, s. 326-332 Journal article (peer-reviewed)abstract This paper investigates the impact of different iron (Fe) buffer doping profiles on trapping effects in microwave AlGaN/gallium nitride (GaN) high electron mobility transistors (HEMTs). We characterize not only the current collapse due to trapping in the buffer, but also the recovery process, which is important in the analysis of suitable linearization schemes for amplitude modulated signals. It is shown that the simple pulsed dc measurements of current transients can be used to investigate transient effects in the RF power. Specifically, it is revealed that the design of the Fe-doping profile in the buffer greatly influences the recovery time, with the samples with lower Fe concentration showing slower recovery. In contrast, traditional indicators, such as S-parameters and dc as well as pulsed $I$-$V$ characteristics, show very small differences. An analysis of the recovery shows that this effect is due to the presence of two different detrapping processes with the same activation energy (0.6 eV) but different time constants. For highly doped buffers, the faster process dominates, whereas the slower process is enhanced for less doped buffers.
20.	Axelsson, Olle, 1986, et al. (author) Impact of Trapping Effects on the Recovery Time of GaN Based Low Noise 2016 In: IEEE Microwave and Wireless Components Letters. - : Institute of Electrical and Electronics Engineers (IEEE). - 1558-1764 .- 1531-1309. ; 26:1, s. 31-33 Journal article (peer-reviewed)abstract This study investigates recovery time of the gain of AlGaN/GaN HEMT based low noise amplifiers (LNA) after an input overdrive pulse. Three LNAs, fabricated in two commercial MMIC processes and a Chalmers in-house process, are evaluated. The Chalmers process has an unintentionally doped buffer instead of the intentional Fe doping of the buffer which is standard in commercial GaN HEMT technologies. It is shown that the LNAs from the two commercial processes experience a severe drop in gain after input overdrive pulses higher than 28 dBm, recovering over a duration of around 20 ms. In contrast the LNA fabricated in-house at Chalmers experienced no visible effects up to an input power of 33 dBm. These results have impact for radar and electronic warfare receivers, which need to be operational immediately after an overdrive pulse. The long time constants suggest that these effects are due to trapping in the transistors with the Fe doped buffer playing an important role.
21.	Axelsson, Olle, 1986, et al. (author) Noise temperature of an electronic tuner for noise parameter measurement systems 2012 In: 79th ARFTG Microwave Measurement Conference: Non-Linear Measurement Systems, ARFTG 2012. ; , s. Article number 6291197- Conference paper (peer-reviewed)abstract In this paper, the noise temperature of an electronic tuner is determined and its significance for the suitability of such tuners in noise parameter measurement systems discussed. The noise temperature of the tuner was found to be higher than the ambient room temperature in the laboratory and vary significantly between tuner states. For impedance states with small input reflections coefficients, the excess noise temperature is around 25 K. For some of the states with higher reflection coefficients, this figure increases, reaching around 45 K at \|Γ\| = 0.75. Unless accounted for, this leads to errors in noise parameter extraction when using an electronic tuner in noise parameter measurements.
22.	Axelsson, Olle, 1986, et al. (author) The Effect of Forward Gate Bias Stress on the Noise Performance of Mesa Isolated GaN HEMTs 2015 In: IEEE Transactions on Device and Materials Reliability. - : Institute of Electrical and Electronics Engineers (IEEE). - 1530-4388 .- 1558-2574. ; 15:1, s. 40-46 Journal article (peer-reviewed)abstract This study investigates degradation of gallium nitride (GaN) high-electron mobility transistor (HEMT) noise performance after both dc and RF stress with forward gate current. The results are used to facilitate optimization of the robustness of GaN low-noise amplifiers (LNAs). It is shown that forward biasing the gate of a GaN HEMT results in permanent degradation of noise performance and gate current leakage, without affecting S-parameters and drain current characteristics. The limit of safe operation of the 2 x 50 mu m devices in this study is found to be between 10 and 20 mW dissipated in the gate diode for both dc and RF stress. We propose that degradation could be caused by excessive leakage through the mesa sidewalls at the edges of each gate finger. Circuit simulations may be used together with device robustness rating to optimize LNAs for maximum input power tolerance. Using a resistance in the gate biasing network of 10 k Omega, it is estimated that an LNA utilizing a 2 x 50 mu m device could withstand input power levels up to 33 dBm without degradation in noise performance.
23.	Bergsten, Johan, 1988, et al. (author) Electron Trapping in Extended Defects in Microwave AlGaN/GaN HEMTs with Carbon-Doped Buffers 2018 In: IEEE Transactions on Electron Devices. - : IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC. - 1557-9646 .- 0018-9383. ; 65:6, s. 2446-2453 Journal article (peer-reviewed)abstract This paper investigates AlGaN/GaN high-electron mobility transistors (HEMTs) fabricated on epistructures with carbon (C)-doped buffers. Metalorganic chemical vapor deposition is used to grow two C-doped structures with different doping profiles, using growth parameters to change the C incorporation. The C concentration is low enough to result in n-type GaN. Reference devices are also fabricated on a structure using iron (Fe) as dopant, to exclude any process related variations and provide a relevant benchmark. All devices exhibit similar dc performance. However, pulsed I - V$ measurements show extensive dispersion in the C-doped devices, with values of dynamic R-mathrm-scriptscriptstyle ON 3 -4 times larger than in the dc case. Due to the extensive trapping, the devices with C-doped buffers can only supply about half the output power of the Fe-doped sample, 2.5 W/mm compared to 4.8 W/mm at 10 GHz. In drain current transient measurements, the trap filling time is varied, finding large prevalence of trapping at dislocations for the C-doped samples. Clusters of C around the dislocations are suggested to be the main cause for the increased dispersion.
24.	Bergsten, Johan, 1988, et al. (author) Performance Enhancement of Microwave GaN HEMTs Without an AlN-Exclusion Layer Using an Optimized AlGaN/GaN Interface Growth Process 2016 In: IEEE Transactions on Electron Devices. - : Institute of Electrical and Electronics Engineers (IEEE). - 1557-9646 .- 0018-9383. ; 63:1, s. 333-338 Journal article (peer-reviewed)abstract The impact of the sharpness of the AlGaN/GaN interface in high-electron mobility transistors (HEMTs) is investigated. Two structures, one with an optimized AlGaN/GaN interface and another with an unoptimized, were grown using hot-wall metal-organic chemical vapor deposition. The structure with optimized sharpness of the interface shows electron mobility of 1760 cm(2)/V . s as compared with 1660 cm(2)/V . s for the nonoptimized interface. Gated Hall measurements indicate that the sharper interface maintains higher mobility when the electrons are close to the interface compared with the nonoptimized structure, indicating less scattering due to alloy disorder and interface roughness. HEMTs were processed and evaluated. The higher mobility manifests as lower parasitic resistance yielding a better dc and high-frequency performance. A small-signal equivalent model is extracted. The results indicate a lower electron penetration into the buffer in the optimized sample. Pulsed-IV measurements imply that the sharper interface provides less dispersive effects at large drain biases. We speculate that the mobility enhancement seen AlGaN/AlN/GaN structures compared with the AlGaN/GaN case is not only related to the larger conduction band offset but also due to a more welldefined interface minimizing scattering due to alloy disorder and interface roughness.
25.	Bremer, Johan, 1991, et al. (author) Analysis of Lateral Thermal Coupling for GaN MMIC Technologies 2018 In: IEEE Transactions on Microwave Theory and Techniques. - 0018-9480 .- 1557-9670. ; 66:10, s. 4430-4438 Journal article (peer-reviewed)abstract This paper presents a study of the lateral heat propagation in an aluminum gallium nitride/gallium nitride (AlGaN/GaN) heterostructure grown on a silicon carbide substrate. The study is enabled by the design of a temperature sensor that utilizes the temperature-dependent I-V characteristic of a semiconductor resistor, making it suitable for integration in GaN monolithic microwave integrated circuit technologies. Using the sensor, we are able to characterize the thermal transient response and extract lateral thermal time constants from the measurements. Time constants in the range from 25 mu s to 1.2 ms are identified. Furthermore, the heat propagation properties are characterized for heat source-to-sensor distances of 86-484 mu m, resulting in delay times from 3.5 to 111 mu s. It is shown that both the time constants and propagation delay increase with temperature. An empirical model of the sensor current versus temperature and voltage is proposed and used to predict the junction temperature of the sensor. The study provides knowledge for heat management design and proposes an integrated temperature measurement solution for future highly integrated GaN applications.
26.	Bremer, Johan, 1991, et al. (author) Compensation of Performance Degradation Due to Thermal Effects in GaN LNA Using Dynamic Bias 2018 In: 2018 48th European Microwave Conference, EuMC 2018. - 9781538652855 ; , s. 1213-1216 Conference paper (peer-reviewed)abstract This paper investigates the possibilities of using a dynamic bias control scheme for a low noise amplifier to compensate for performance degradation due to thermal effects. The study was performed by characterization of bias voltage and temperature dependence between -25°C to 75°C of a GaN MMIC LNA. The performance, in terms of gain, linearity and noise, degraded, at elevated chip temperatures. Nonlinear behavioral models were developed and used to predict performance for different bias and temperature conditions. Bias conditions to achieve constant gain and noise figure versus temperature are determined. Enhanced RF performance, with improved gain and linearity is demonstrated and is shown to require increased power and involves a trade-off between improving noise figure and gain.
27.	Bremer, Johan, 1991, et al. (author) Electric-Based Thermal Characterization of GaN Technologies Affected by Trapping Effects 2020 In: IEEE Transactions on Electron Devices. - 1557-9646 .- 0018-9383. ; 67:5, s. 1952-1958 Journal article (peer-reviewed)abstract This article presents an electric-based methodology for thermal characterization of semiconductor technologies. It is shown that for technologies such as gallium nitride (GaN) high electron mobility transistors, which exhibit several field induced electron trapping effects, the thermal characterization has to be performed under specific conditions. The electric field is limited to low levels to avoid activation of trap states. At the same time, the dissipated power needs to be high enough to change the operating temperature of the device. The method is demonstrated on a test structure implemented as a GaN resistor with large contact separation. It is used to evaluate the thermal properties of samples with different silicon carbide suppliers and buffer thickness.
28.	Bremer, Johan, 1991, et al. (author) Method for Suppressing Trap-Related Memory Effects in IV Characterizations of GaN HEMTs 2024 In: IEEE International Conference on Microelectronic Test Structures. - 1071-9032 .- 2158-1029. Conference paper (peer-reviewed)abstract A method to suppress trapping-related effects when performing IV characterizations of field effect transistors is presented. Standard IV measurements usually utilize voltage sweeps with fixed start, stop, and step values. At high electric fields in these sweeps, the charging of electron traps with long time constants may occur. The trapped electrons cause different memory effects such as hysteresis and the kink effect. The proposed method suppresses these effects, by reordering the bias points, so to prevent charging due to high preceding electric fields. The method provides more rudimentary IV measurements, useful for e.g. technology evaluation and modeling purposes.
29.	Chen, Ding-Yuan, et al. (author) Impact of the Channel Thickness on Electron Confinement in MOCVD-Grown High Breakdown Buffer-Free AlGaN/GaN Heterostructures 2023 In: Physica Status Solidi (A) Applications and Materials Science. - : Wiley. - 1862-6319 .- 1862-6300. ; 220:16 Journal article (peer-reviewed)abstract The 2D electron gas (2DEG) confinement on high electron mobility transistor (HEMT) heterostructures with a thin undoped GaN channel layer on the top of a grain-boundary-free AlN nucleation layer is studied. This is the first time demonstration of a buffer-free epi-structure grown with metal-organic chemical vapor deposition with thin GaN channel thicknesses, ranging from 250 to 150 nm, without any degradation of the structural quality and 2DEG properties. The HEMTs with a gate length of 70 nm exhibit good DC characteristics with peak transconductances of 500 mS mm(-1) and maximum saturated drain currents above 1 A mm(-1). A thinner GaN channel layer improves 2DEG confinement because of the enhanced effectiveness of the AlN nucleation layer acting as a back-barrier. An excellent drain-induced barrier lowering of only 20 mV V-1 at a V-DS of 25 V and an outstanding critical electric field of 0.95 MV cm(-1) are demonstrated. Good large-signal performance at 28 GHz with output power levels of 2.0 and 3.2 W mm(-1) and associated power-added efficiencies of 56% and 40% are obtained at a V-DS of 15 and 25 V, respectively. These results demonstrate the potential of sub-100 nm gate length HEMTs on a buffer-free GaN-on-SiC heterostructure.
30.	Chen, Ding Yuan, et al. (author) Microwave Performance of 'Buffer-Free' GaN-on-SiC High Electron Mobility Transistors 2020 In: IEEE Electron Device Letters. - 0741-3106 .- 1558-0563. ; 41:6, s. 828-831 Journal article (peer-reviewed)abstract High performance microwave GaN-on-SiC HEMTs are demonstrated on a heterostructure without a conventional thick doped buffer. The HEMT is fabricated on a high-quality 0.25~\boldsymbol {\mu }\text{m} unintentional doped GaN layer grown directly on a transmorphic epitaxially grown AlN nucleation layer. This approach allows the AlN-nucleation layer to act as a back-barrier, limiting short channel effects and removing buffer leakage. The devices with the 'buffer-free' heterostructure show competitive DC and RF characteristics, as benchmarked against the devices made on a commercial Fe-doped epi-wafer. Peak transconductances of 500 mS/mm and a maximum saturated drain current of 1 A/mm are obtained. An extrinsic \text{f}-{\sf T} of 70 GHz and \text{f}-{\sf max} of 130 GHz are achieved for transistors with a gate length of 100 nm. Pulsed-IV measurements reveal a lower current slump and a smaller knee walkout. The dynamic IV performance translates to an output power of 4.1 W/mm, as measured with active load-pull at 3 GHz. These devices suggest that the 'buffer-free' concept may offer an alternative route for high frequency GaN HEMTs with less electron trapping effects.
31.	Chen, J. T., et al. (author) A GaN-SiC hybrid material for high-frequency and power electronics 2018 In: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 113:4 Journal article (peer-reviewed)abstract We demonstrate that 3.5% in-plane lattice mismatch between GaN (0001) epitaxial layers and SiC (0001) substrates can be accommodated without triggering extended defects over large areas using a grain-boundary-free AlN nucleation layer (NL). Defect formation in the initial epitaxial growth phase is thus significantly alleviated, confirmed by various characterization techniques. As a result, a high-quality 0.2-μm thin GaN layer can be grown on the AlN NL and directly serve as a channel layer in power devices, like high electron mobility transistors (HEMTs). The channel electrons exhibit a state-of-the-art mobility of >2000 cm2/V-s, in the AlGaN/GaN heterostructures without a conventional thick C- or Fe-doped buffer layer. The highly scaled transistor processed on the heterostructure with a nearly perfect GaN-SiC interface shows excellent DC and microwave performances. A peak RF power density of 5.8 W/mm was obtained at VDSQ= 40 V and a fundamental frequency of 30 GHz. Moreover, an unpassivated 0.2-μm GaN/AlN/SiC stack shows lateral and vertical breakdowns at 1.5 kV. Perfecting the GaN-SiC interface enables a GaN-SiC hybrid material that combines the high-electron-velocity thin GaN with the high-breakdown bulk SiC, which promises further advances in a wide spectrum of high-frequency and power electronics.
32.	Chen, J. T., et al. (author) Carbon-doped GaN on SiC materials for low-memory-effect devices 2016 In: ECS Transactions. - : The Electrochemical Society. - 1938-5862 .- 1938-6737. - 9781607685395 ; 75:12, s. 61-65, s. 61-65 Conference paper (peer-reviewed)abstract AlGaN/GaN on SiC HEMT structures suitable for high power, high frequency applications are demonstrated. The material manifests record breaking thermal management and electron mobility. Moreover, thanks to the fact that the buffer layer is doped with carbon, the memory effect of processed devices is very low making system design and manufacturing significantly easier and less expensive.
33.	Desmaris, Vincent, 1977, et al. (author) Characterization of GaN-based Low Noise Amplifiers at Cryogenic Temperatures 2019 In: ISSTT 2019 - 30th International Symposium on Space Terahertz Technology, Proceedings Book. ; , s. 67-68 Conference paper (peer-reviewed)abstract In this paper, we present the first characterization of GaN-based Low-Noise Amplifiers (LNAs) at cryogenic temperatures for prospective use in radio-astronomy receivers. Both commercial and prototype LNAs fabricated in-house demonstrate a nine-fold improvement of their room-temperature noise performance when cooled to about 10 K. Very promising noise temperatures of about 8 K were measured without any specific optimization of the LNA design for cryogenic operation.
34.	Ding Yuan, Chen, 1991, et al. (author) Impact of in situ NH3 pre-treatment of LPCVD SiN passivation on GaN HEMT performance 2022 In: Semiconductor Science and Technology. - : IOP Publishing. - 1361-6641 .- 0268-1242. ; 37:3 Journal article (peer-reviewed)abstract The impact on the performance of GaN high electron mobility transistors (HEMTs) of in situ ammonia (NH3) pre-treatment prior to the deposition of silicon nitride (SiN) passivation with low-pressure chemical vapor deposition (LPCVD ) is investigated. Three different NH3 pre-treatment durations (0, 3, and 10 min) were compared in terms of interface properties and device performance. A reduction of oxygen (O) at the interface between SiN and epi-structure is detected by scanning transmission electron microscopy (STEM )-electron energy loss spectroscopy (EELS) measurements in the sample subjected to 10 min of pre-treatment. The samples subjected to NH3 pre-treatment show a reduced surface-related current dispersion of 9% (compared to 16% for the untreated sample), which is attributed to the reduction of O at the SiN/epi interface. Furthermore, NH3 pre-treatment for 10 min significantly improves the current dispersion uniformity from 14.5% to 1.9%. The reduced trapping effects result in a high output power of 3.4 W mm(-1) at 3 GHz (compared to 2.6 W mm(-1) for the untreated sample). These results demonstrate that the in situ NH3 pre-treatment before LPCVD of SiN passivation is critical and can effectively improves the large-signal microwave performance of GaN HEMTs.
35.	Ding Yuan, Chen, 1991, et al. (author) Thin Al 0.5 Ga 0.5 N/GaN HEMTs on QuanFINE ® Structure 2021 In: CS MANTECH 2021 - 2021 International Conference on Compound Semiconductor Manufacturing Technology, Digest of Papers. ; , s. 153-155 Conference paper (peer-reviewed)abstract The performance of HEMTs fabricated on a thin Al0.5Ga0.5N/GaN heterostructure with a total barrier thickness of 6.5 nm is presented and benchmarked to the epi-structure with a 13 nm thick Al0.3Ga0.7N barrier on an identical QuanFINE® structure. DC transfer characteristics on both samples with a gate length of 100 nm demonstrate a high current above 1 A/mm. A higher extrinsic gm of 550 mS/mm is measured on the sample with a thinner high Al content barrier. Moreover, low trapping effects with a 12-14 % buffer-related dispersion at a VDSQ of 25 V are characterized for both samples, which indicate the advantage of the iron-free QuanFINE® heterostructure.
36.	Divinyi, Andreas, et al. (author) On-Chip Sensors for Temperature Monitoring of Packaged GaN MMICs 2024 In: IEEE Transactions on Components, Packaging and Manufacturing Technology. - 2156-3985 .- 2156-3950. ; 14:5, s. 891-896 Journal article (peer-reviewed)abstract A novel approach to on-chip temperature sensors for non-invasive thermal characterization and monitoring of packaged GaN MMICs is presented. The proposed sensor is fully compatible with commercial GaN foundry processes and enables improved reliability estimation of highly integrated systems. A dedicated test structure is developed to demonstrate the capabilities of the sensor, and an accurate calibration method of its temperature response is proposed. This combination allows for continuous temperature monitoring during operation with electrical acquisition of temperature transients. The method also enables the thermal characterization of the device and package.
37.	Divinyi, Andreas, et al. (author) Transition Time of GaN HEMT Switches and its Dependence on Device Geometry 2023 In: 2023 18th European Microwave Integrated Circuits Conference, EuMIC 2023. ; , s. 46-49 Conference paper (peer-reviewed)abstract This paper presents the impact on the slow transition time of GaN HEMT switch transistor due to size and geometry. Measurements in the time domain are used to characterize the transition time of the switch from off to on. This is done for several switch transistors with variations on total gate width and number of fingers. In order to enable the comparison of transition times a figure of merit is established. This is achieved by using a commonly used model for trapping effects to quantify the amplitude of the slow transient with respect to the gate voltage. The resulting analysis indicates that transition time is sensitive to transistor size and dependent on the geometry of the device as increasing the width of the gate fingers is more advantageous compared to increasing the number of fingers.
38.	Fager, Christian, 1974, et al. (author) Analysis of Thermal Effects in Integrated Radio Transmitters 2018 In: 2018 INTERNATIONAL SYMPOSIUM ON VLSI TECHNOLOGY, SYSTEMS AND APPLICATION (VLSI-TSA). - 1930-8868. - 9781538648254 - 9781538648254 Conference paper (peer-reviewed)abstract The combination of compact size and low efficiency at mm-waves has turned heat dissipation into a fundamental constraint for design of multi-antenna radios. This paper describes methods for analysis of thermal effects at both at the circuit, system and component level. The first part describes how thermal analysis can be combined with advanced RF modeling techniques to predict self-heating and thermal coupling in multi-antenna transmitter systems. Experimental methods are then used to determine thermal coupling effects occurring at chip level. Various experimental and theoretical results, using MIMO amplifiers and GaN HEMTs, are used to demonstrate the methods in realistic application scenarios.
39.	Ferrand-Drake Del Castillo, Ragnar, 1993, et al. (author) Characterization of Trapping Effects Related to Carbon Doping Level in AlGaN Back-Barriers for AlGaN/GaN HEMTs 2024 In: IEEE Transactions on Electron Devices. - : IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC. - 1557-9646 .- 0018-9383. ; 71:6, s. 3596-3602 Journal article (peer-reviewed)abstract The impact of different carbon concentrations in the Al Ga N graded back-barrier and GaN buffer of high electron mobility transistors (HEMTs) is investigated. Four epi-wafers with different carbon concentrations, ranging from 1 10 to 5 10 cm , were grown by metal organic chemical vapor deposition (MOCVD). HEMTs with 100 and 200 nm gate lengths were fabricated and characterized with dc, Pulsed-IV, drain current transient spectroscopy (DCTS), and large-signal measurements at 30 GHz. It is shown that the back-barrier effectively prevents buffer-related electron trapping. The highest C-doping provides the best 2DEG confinement, while lower carbon doping levels are beneficial for a high output power and efficiency. A C-doping of 1 10 cm offers the highest output power at maximum power added efficiency (PAE) (1.8 W/mm), whereas 3 10 cm doping provides the highest PAE ( 40%). The C-profiles acquired by using secondary ion mass spectroscopy (SIMS), in combination with DCTS, is used to explain the electron trapping effects. Traps associated with the C-doping in the back-barrier are identified and the bias ranges for the trap activation are discussed. The study shows the importance of considering the C-doping level in the back-barrier of microwave GaN HEMTs for power amplification and generation.
40.	Frank, Markus, 1970, et al. (author) Design Equations for Lumped Element Balun With Inherent Complex Impedance Transformation 2017 In: IEEE Transactions on Microwave Theory and Techniques. - 0018-9480 .- 1557-9670. ; 65:12, s. 5162-5170 Journal article (peer-reviewed)abstract This paper demonstrates a novel lumped design approach for complex impedance transformation, based on symmetry relaxation in the out-of-phase-compensated-power-splitter. In the modified topology, a total of four component values are used, of which two values analytically depend upon the other two, keeping the balance parameter maximally flat and independent of the source and load impedance, as well as of the balun internal components. From the condition of zero input reflection loss, the two other component values are also determined analytically, hence specifying all component values uniquely. A Monte Carlo sensitivity analysis predicts an amplitude imbalance, which in practice defines the limit in balance operational bandwidth, of better than +/-1 dB, over a 20% bandwidth at 925 MHz operating frequency. Based on the design equations, demonstrators for four different design cases are fabricated, verifying the simulated performance.
41.	Frank, Markus, 1970, et al. (author) Differential Transmission Line Loop for RFID Reactive Near-Field Coupling 2018 In: IEEE Transactions on Microwave Theory and Techniques. - 0018-9480 .- 1557-9670. ; 66:5, s. 2141-2153 Journal article (peer-reviewed)abstract The differential transmission line loop (DTLL) as an efficient reactive near-field coupling element for programming of radio frequency identification (RFID) inlays is proposed. It is validated, with simulations and measurements, that the differential excitation and the presence of a ground plane are fundamental properties for high performance in coupling while providing high electromagnetic isolation. As a proof of concept, super elliptical loop geometries as coupling elements are investigated for a number of commercially available inlay geometries. From simulations of the DTLL and inlay antenna, coupling efficiencies higher than 80% are predicted. Measurements of the \Delta \Gamma -value indicate a nonlinear input impedance with power, and verify the high values of simulated coupling efficiency. The threshold power levels read from interrogator are below 5 dBm, which are considered as very low in inlay encoding, and hence show that the DTLL is a promising candidate for efficient RFID programming in the reactive near field.
42.	Frank, Markus, 1970, et al. (author) Lumped element balun with inherent complex impedance transformation 2017 In: IEEE MTT-S International Microwave Symposium Digest. - 0149-645X. - 9781509063604 ; , s. 1285-1288 Conference paper (peer-reviewed)abstract A novel lumped design approach for complex impedance transforming baluns is presented in this paper. It is shown that a relaxation of symmetry in the T-networks of the out-of-phase-compensated-power-splitter enables complex impedance transformation. Design equations are analytically derived for a total of 4 component values, of which 2 values depend upon the 2 other, which are free variables. The two free component values are used independently for adjustment of input reflection loss, further keeping the balance parameter maximally flat and independent of the load impedance. For Q-values of source and load, not being excessively high, the balun can be realized with only 8 components. A demonstrator is fabricated, transforming 26.9 + j11.1 Ω to 73.8 + j38.6 Ω. An amplitude balance of ±0.7 dB and phase balance better than ±5° is achieved over a 20 % bandwidth. The return loss is higher than 20 dB.
43.	Frank, Markus, 1970, et al. (author) Shifted Source Impedance and Nonlinearity Impact on RFID Transponder Communication for Drive-Level Offsets 2016 In: IEEE Transactions on Microwave Theory and Techniques. - 0018-9480 .- 1557-9670. ; 64:1, s. 299 - 309 Journal article (peer-reviewed)abstract A measurement and analysis method to quantify the communication quality for ultrahigh-frequency radio frequency identification (RFID) transponder chips under a shifting source environment is presented. A detailed description of theory, setup, and procedure is provided. The differences in on/off impedance (\|ΔΓ\|-value) of the transponder chip are critical for backscatter modulation and, therefore, the overall communication and transponder response. In the present work, a new quantity which includes the difference in on/off impedance, as well as arbitrary source impedance, is defined as an overall figure of merit. A qualitative analysis, considered as novel in the RFID community, shows the impact a source impedance shift has on the communication quality. The bare chip measurement setup enables an ASK modulated wake up signal, realized as a pulse train. The chip response consisting of modulated impedance states are measured in a pulse profile setup. Results show that different degrees of non-linearity in a transponder chip, depending on vendor and type, will have impact on the communication performance.
44.	Gustafsson, Sebastian, 1990, et al. (author) A Novel Active Load-pull System with Multi-Band Capabilities 2013 In: 81st ARFTG Microwave Measurement Conference. - 9781467349819 Conference paper (peer-reviewed)abstract In this paper a novel active open-loop multi-band load-pull measurement system is presented. The system uses few components where the main parts are an Oscilloscope and an Arbitrary Waveform Generator (AWG). The used AWG is a sophisticated signal generator with two outputs, letting the user take full control over the injected signals in the frequency band 0-4 GHz. This enables new kinds of measurements to be performed, such as multi-band load-pull and in particular inter-modulation product load-pull, which this paper focuses on. The paper describes the measurement setup briefly and the calibration and load-pull algorithms used. As an example to demonstrate the capabilities of the system, a multi-band load-pull is carried out on a GaN HEMT transistor. The frequency bands are 2.14 GHz and 2.65 GHz which create IM3 products at 1.63 GHz and 3.16 GHz. It is shown that the efficiency is affected by the choice of load termination presented at the IM3 frequencies.
45.	Gustafsson, Sebastian, 1990, et al. (author) Accurate Circuit Characterization Methods for mm‐Wave 5G Systems 2016 In: GigaHertz Symposium, March, Linköping. Conference paper (other academic/artistic)
46.	Gustafsson, Sebastian, 1990, et al. (author) An Oscilloscope Correction Method for Vector-Corrected RF Measurements 2015 In: IEEE Transactions on Instrumentation and Measurement. - : Institute of Electrical and Electronics Engineers (IEEE). - 1557-9662 .- 0018-9456. ; 64:9, s. 2541-2547 Journal article (peer-reviewed)abstract The transfer characteristics of the RF front-end circuitry of a real-time oscilloscope (RTO) are not only frequency dependent and nonlinear with signal amplitude but also dependent on the voltage range setting of the oscilloscope. A correction table in the frequency domain is proposed to account for the additional gain and delay introduced when switching between different voltage ranges. The table was extracted from the measured data in which a continuous-wave signal source was connected to the oscilloscope ports, whereas the input power, the frequency, and voltage ranges were varied. The importance of the corrections is demonstrated by its use in an RTO-based two-port vector-corrected measurement system. Measurements from the oscilloscope-based system are compared with a vector network analyzer (VNA), leading to less discrepancy in the measured Sparameters of two amplifiers when using the proposed correction technique.
47.	Gustafsson, Sebastian, 1990, et al. (author) Dispersive Effects in Microwave AlGaN/AlN/GaN HEMTs With Carbon-Doped Buffer 2015 In: IEEE Transactions on Electron Devices. - : Institute of Electrical and Electronics Engineers (IEEE). - 1557-9646 .- 0018-9383. ; 62:7, s. 2162-2169 Journal article (peer-reviewed)abstract Aluminium gallium nitride (AlGaN)/GaN high-electron mobility transistor performance is to a large extent affected by the buffer design, which, in this paper, is varied using different levels of carbon incorporation. Three epitaxial structures have been fabricated: 1) two with uniform carbon doping profile but different carbon concentration and 2) one with a stepped doping profile. The epitaxial structures have been grown on 4H-SiC using hot-wall metal-organic chemical vapor deposition with residual carbon doping. The leakage currents in OFF-state at 10 V drain voltage were in the same order of magnitude (10(-4) A/mm) for the high-doped and stepped-doped buffer. The high-doped material had a current collapse (CC) of 78.8% compared with 16.1% for the stepped-doped material under dynamic I-V conditions. The low-doped material had low CC (5.2%) but poor buffer isolation. Trap characterization revealed that the high-doped material had two trap levels at 0.15 and 0.59 eV, and the low-doped material had one trap level at 0.59 eV.
48.	Gustafsson, Sebastian, 1990, et al. (author) Vector-corrected Nonlinear Multi-port IQ-mixer Characterization using Modulated Signals 2017 In: IEEE MTT-S International Microwave Symposium Digest. - 0149-645X. ; , s. 1433-1436 Conference paper (peer-reviewed)abstract In this paper, large-signal operation of IQ-mixers isstudied using a vector-corrected four-port measurement setup with modulated signals as stimuli. The measurement setup presents unique characterization possibilities since it has two ports at low/baseband frequencies and two ports at RF, making it ideal for characterization of frequency-translating devices such as mixers. A commercial upconverting IQ-mixer is studied, with the I and Q input signals residing at incommensurate frequencygrids, enabling separation of the nonlinear distortion generated in the I and Q branches. Frequency-domain and time-domain measurements reveal imbalances between the I and Q branches in terms of conversion gain and nonlinear distortion. It is also shown for the same mixer that operating the I and Q branches concurrently has limited influence on both conversion gain and nonlinear distortion, compared to non-concurrent operation.
49.	Gustafsson, Sebastian, 1990, et al. (author) Wideband RF characterization setup with high dynamic range low frequency measurement capabilities 2016 In: 2016 87th ARFTG Microwave Measurement Conference. - 9781509013081 Conference paper (peer-reviewed)abstract In this paper, a wideband RF characterization setup with low-frequency (LF) measurement capabilities is presented. Simultaneous LF and RF measurements enable studies of trapping phenomena, thermal effects and other LF-related nonlinear distortion in microwave devices using realistic wideband RF stimuli. The setup is capable of measuring up to 4 GHz through the RF path, and from DC to 125 MHz through the LF path. A study is made on how device linearity is affected by the choice of power supply unit (PSU). LF measurements reveal significant differences in baseband termination in the PSUs, consequently affecting the linearity of the measured RF output spectrum.
50.	Hanning, Lowisa, 1993, et al. (author) Optimizing the Signal-To-Noise and Distortion Ratio of a GaN LNA using Dynamic Bias 2018 In: 2018 91st ARFTG Microwave Measurement Conference: Wideband Modulated Test Signals for Network Analysis of Wireless Infrastructure Building Blocks, ARFTG 2018. - 9781538654491 ; 1 Conference paper (peer-reviewed)abstract This paper shows how the signal-to-noise and distortion ratio (SNDR) for low noise amplifiers (LNA) can be derived from the commonly specified parameters noise figure, gain, third order output intercept point and 1 dB compression point. The parameters dependency of the biasing of the amplifier are also incorporated which enables the possibility to study how SNDR can be optimized for different operating conditions by dynamically change the gate- and drain voltage. An experimental verification shows that improvements in SNDR can be achieved by selecting gate- and drain voltage of the LNA according to the level of the input signal power.

Skapa referenser, mejla, bekava och länka

Permalink

Träfflista för sökning "WFRF:(Thorsell Mattias 1982) "

Refine your search

Year