| 1. |
- Andersson, Christer, 1982, et al.
(författare)
-
Epitaxial and Layout Optimization of SiC Microwave Power Varactors
- 2011
-
Ingår i: Asia-Pacific Microwave Conference Proceedings, APMC (APMC 2011 ;Melbourne, VIC; 5 - 8 December 2011). - 9780858259744 ; , s. 1642-1645
-
Konferensbidrag (refereegranskat)abstract
- SiC Schottky diode varactors have been designed for use in tunable microwave power circuits. Epitaxial growth results show excellent material uniformity with low access layer sheet resistances. Two types of device layouts have been evaluated. Island type layouts reduce the parasitic series resistance by 50-60% compared to typical finger layouts. The Q-factors of downscaled island devices are approaching the intrinsic material performance, but are limited by an increasing parasitic parallel capacitance.
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| 2. |
- Billström, Niklas, et al.
(författare)
-
High performance GaN front-end MMICs
- 2011
-
Ingår i: 14th European Microwave Week 2011: "Wave to the Future", EuMW 2011 - 6th European Microwave Integrated Circuit Conference, EuMIC 2011, Manchester, 10 October through 11 October 2011. - 9782874870231 ; , s. 348-351
-
Konferensbidrag (refereegranskat)
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| 3. |
- Chehrenegar, Pirooz, 1964, et al.
(författare)
-
Design and characterization of a highly linear 3 GHz GaN HEMT amplifier
- 2011
-
Ingår i: 2011 Workshop on Integrated Nonlinear Microwave and Millimetre-Wave Circuits, INMMiC 2011. Vienna, 18-19 April 2011. - 9781457706493
-
Konferensbidrag (refereegranskat)abstract
- In this paper a highly linear amplifier using an in-house gallium nitride (GaN) high electron mobility transistor (HEMT) technology is presented. A 3 dB bandwidth of 2.7-3.6 GHz with a maximum gain of 18 dB was measured. The output third-order intercept point (OIP3) was measured to 39 dBm with a maximum power consumption of 2.1 W. With a reduction of power consumption to 1 W the noise figure was improved by 0.6 dB while the OIP3 was degraded 3 dB.
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| 4. |
- Fagerlind, Martin, 1980, et al.
(författare)
-
Investigation of the interface between silicon nitride passivations and AlGaN/AlN/GaN heterostructures by C(V) characterization of metal-insulator-semiconductor-heterostructure capacitors
- 2010
-
Ingår i: Journal of Applied Physics. - : AIP Publishing. - 0021-8979 .- 1089-7550. ; 108:1
-
Tidskriftsartikel (refereegranskat)abstract
- Capacitance-voltage [C(V)] measurements of metal-insulator-semiconductor-heterostructure capacitors are used to investigate the interface between silicon nitride passivation and AlGaN/AlN/GaN heterostructure material. AlGaN/AlN/GaN samples having different silicon nitride passivating layers, deposited using three different deposition techniques, are evaluated. Different interface state distributions result in large differences in the C(V) characteristics. A method to extract fixed charge as well as traps from the C(V) characteristics is presented. Rough estimates of the emission time constants of the traps can be extracted by careful analysis of the C(V) characteristics. The fixed charge is positive for all samples, with a density varying between 1.3 x 10(12) and 7.1 x 10(12) cm(-2). For the traps, the peak density of interface states is varying between 16 x 10(12) and 31 x 10(12) cm(-2) eV(-1) for the three samples. It is concluded that, of the deposition methods investigated in this report, the low pressure chemical vapor deposited silicon nitride passivation shows the most promising results with regards to low densities of interface states. (C) 2010 American Institute of Physics. [doi:10.1063/1.3428442]
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| 5. |
- Hjelmgren, Hans, 1960, et al.
(författare)
-
Transient Simulation of Microwave SiC MESFETs With Improved Trap Models
- 2010
-
Ingår i: IEEE Transactions on Electron Devices. - 1557-9646 .- 0018-9383. ; 57:3, s. 729-732
-
Tidskriftsartikel (refereegranskat)abstract
- Measured and simulated transient characteristics ofa SiC metal–semiconductor field-effect transistor are compared. Self-heating, gate tunneling, substrate, and surface traps are taken into account in the simulations. By explicitly filling surface traps at the vicinity of the gate during pinchoff, close correspondence between simulated and measured gate lags is achieved.
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| 6. |
- Thorsell, Mattias, 1982, et al.
(författare)
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An X-Band AlGaN/GaN MMIC Receiver Front-End
- 2010
-
Ingår i: IEEE Microwave and Wireless Components Letters. - 1558-1764 .- 1531-1309. ; 20:1, s. 55-57
-
Tidskriftsartikel (refereegranskat)abstract
- This letter presents an integrated AlGaN/GaN X-band receiver front-end. This is to the authors knowledge the first published results of an integrated AlGaN/GaN MMIC receiver front-end. The receiver uses an integrated SPDT switch to reduce size, weight and cost compared to circulator based transceiver front-ends. The integrated front-end has more than 13 dB of gain and a noise figure of 3.5 dB at 11 GHz.
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| 7. |
- Andersson, Christer, 1982, et al.
(författare)
-
A packaged 86 W GaN transmitter with SiC varactor-based dynamic load modulation
- 2013
-
Ingår i: 43rd European Microwave Conference, EuMC 2013 - Held as Part of the 16th European Microwave Week, EuMW 2013, Nuremberg, Germany, 7-10 October 2013. - 9782874870316 ; , s. 283-286
-
Konferensbidrag (refereegranskat)abstract
- Output power scaling based on class-J dynamic load modulation (DLM) theory is used to design an unprecedentedly high power microwave transmitter with varactor-based DLM functionality. Matching networks are realized on high dielectric constant substrates in order to reduce the form factor. The fully matched DLM PA incorporates a 24-mm GaN HEMT powerbar and a stack of four SiC varactors, all fit into a CuW package (40 mm × 20 mm). Peak output power is reconfigurable by changing the drain voltage, while retaining the DLMeffect. Under pulsed conditions at 40 V the PA delivers a peak power of 86 W at 2.14 GHz. Efficiency enhancement by DLM is 10-15 percentage-units at 6 dB output power back-off (OPBO). Employing digital predistortion (DPD) with a vector switched generalized memory polynomial (VS-GMP) the ACLR is -46 dBc at an average output power of 17 W and a drain efficiency of 34%. These results prove the potential for high output power levels in varactor-based DLM transmitters.
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| 8. |
- Andersson, Christer, 1982, et al.
(författare)
-
A SiC Varactor With Large Effective Tuning Range for Microwave Power Applications
- 2011
-
Ingår i: IEEE Electron Device Letters. - : Institute of Electrical and Electronics Engineers (IEEE). - 0741-3106 .- 1558-0563. ; 32:6, s. 788-790
-
Tidskriftsartikel (refereegranskat)abstract
- SiC Schottky diode varactors have been fabricated for use in microwave power applications, specifically the dynamic load modulation of power amplifiers. A custom doping profile has been employed to spread the C(V) over a large bias voltage range, thereby increasing the effective tuning range under large voltage swing conditions. The small-signal tuning range is approximately six, and punch through is reached at a bias voltage of -60 V, while the breakdown voltage is on the order of -160 V. An interdigitated layout is utilized together with a self-aligned Schottky anode etch process to improve the Q-factor at 2 GHz, which is 20 at zero bias and approximately 160 at punch through.
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| 9. |
- Andersson, Christer, 1982, et al.
(författare)
-
Decade bandwidth high efficiency GaN HEMT power amplifier designed with resistive harmonic loading
- 2012
-
Ingår i: IEEE MTT-S International Microwave Symposium Digest. - 0149-645X. - 9781467310871
-
Konferensbidrag (refereegranskat)abstract
- The use of resistive loading at higher harmonics in wideband power amplifier design is proposed. Although the theoretical efficiency of such operation is lower than other classes the significantly simplified load network design potentially allows for multi-octave realizations. A decade bandwidth (0.4-4.1 GHz) GaN HEMT power amplifier was thereby designed, delivering more than 40 dBm output power with 10-15 dB gain and 40-62% drain efficiency. Linearized modulated signal amplification was then successfully demonstrated at multiple frequencies (0.9 to 3.5 GHz), using various downlink signals (LTE, WCDMA, WiMAX), with resulting ACLR lower than 46 dBc.
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| 10. |
- Andersson, Christer, 1982, et al.
(författare)
-
Nonlinear Characterization of Varactors for Tunable Networks by Active Source-Pull and Load-Pull
- 2011
-
Ingår i: IEEE Transactions on Microwave Theory and Techniques. - 0018-9480 .- 1557-9670. ; 59:7, s. 1753-1760
-
Tidskriftsartikel (refereegranskat)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.
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| 11. |
- Andersson, Christer, 1982, et al.
(författare)
-
Theory and Design of Class-J Power Amplifiers With Dynamic Load Modulation
- 2012
-
Ingår i: IEEE Transactions on Microwave Theory and Techniques. - 0018-9480 .- 1557-9670. ; 60:12, s. 3778-3786
-
Tidskriftsartikel (refereegranskat)abstract
- A theory for class-J microwave amplifier operation as a function of drive level and fundamental load impedance is derived. Calculations show that, under appropriate operating conditions, it is sufficient to modulate the transistor load reactance to enable high-efficiency operation (>70%) over a large output power dynamic range (>10 dB) with high transistor power utilization. Such dynamic load modulation (DLM) networks are an ideal application of continuously tunable varactor technologies. Multiharmonic load–pull measurements are performed on a GaN HEMT and experimentally verify the theory of operation. A demonstrator amplifier using an SiC varactor technology is then designed and characterized by static measurements. The amplifier has a peak power of 38 dBm at 2.08 GHz and maintains efficiencies above 45% over 8 dB of power dynamic range. An analysis of the load network losses is performed to show the potential of the class-J DLM transmitter concept.
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| 12. |
- Angelov, Iltcho, 1943, et al.
(författare)
-
On the large-signal modeling of High Power AlGaN/GaN HEMTs
- 2012
-
Ingår i: IEEE MTT-S International Microwave Symposium Digest. - 0149-645X. - 9781467310871
-
Konferensbidrag (refereegranskat)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.
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| 13. |
- Ejebjörk, Niclas, 1984, et al.
(författare)
-
Optimization of SiC MESFET for high power and high frequency applications
- 2011
-
Ingår i: Materials Science Forum. - : Trans Tech Publications Inc.. - 1662-9752 .- 0255-5476. ; 679-680, s. 629-632, s. 629-632
-
Konferensbidrag (refereegranskat)abstract
- SiC MESFETs were scaled both laterally and vertically to optimize high frequency and high power performance. Two types of epi-stacks of SiC MESFETs were fabricated and measured. The first type has a doping of 3×10^17 cm-3 in the channel and the second type has higher doping (5×10^17 cm-3) in the channel. The higher doping allows the channel to be thinner for the same current density and therefore a reduction of the aspect ratio is possible. This could impede short channel effects. For the material with higher channel doping the maximum transconductance is 58 mS/mm. The maximum current gain frequency, fT, and maximum frequency of oscillation, fmax, is 9.8 GHz and 23.9 GHz, and 12.4 GHz and 28.2 GHz for the MESFET with lower doped channel and higher doping, respectively.
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| 14. |
- Fagerlind, Martin, 1980, et al.
(författare)
-
Illumination effects on electrical characteristics of GaN/AlGaN/GaN heterostructures and heterostructure field effect transistors and their elimination by proper surface passivation
- 2012
-
Ingår i: Journal of Applied Physics. - : AIP Publishing. - 0021-8979 .- 1089-7550. ; 112:1, s. Art. no. 014511-
-
Tidskriftsartikel (refereegranskat)abstract
- The effect of ambient illumination is investigated for differently processed GaN/AlGaN/GaN heterostructure materials. For samples of the same material with different passivation, the difference in sheet resistance of illuminated and non-illuminated material can be as large as 130% (for annealed heterostructure without passivation) and as small as 3% (for heterostructure passivated with low pressure chemical vapor deposition (LPCVD) silicon nitride). The time constant for the decay of the persistent photoconductance (PPC) is also very different for the differently processed samples. The majority of the effect on the conductance is from photons with energies between 3.1 and 3.7 eV. The investigation indicates that delayed recombination of electrons emitted from surface states and from deep level states in the AlGaN layer dominates the PPC. A theory is formulated by which the difference in illumination sensitivity for the differently passivated materials can be explained by different distributions of electrons between the channel two dimensional electron gas and an accumulation layer formed in the cap layer. For practical heterostructure field effect transistor (HFET) measurements, the illumination sensitivity is generally lower than that of the Hall measurements. Furthermore, HFETs fabricated with the LPCVD silicon nitride passivation are practically illumination invariant.
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| 15. |
- Fagerlind, Martin, 1980, et al.
(författare)
-
IMPROVING GAN/ALGAN/GAN HFET TRANSCONDUCTANCE AND GATE LEAKAGE BY REDUCING THE ELECTRON SHEET DENSITY THROUGH HIGH TEMPERATURE ANNEALING
- 2010
-
Ingår i: The 34th Workshop on Compound Semiconductor Devices and Integrated Circuits.
-
Konferensbidrag (refereegranskat)abstract
- An LPCVD silicon nitride is used to passivate GaN/AlGaN/GaN heterostructures. The nitride is deposited before the high temperature annealing step that is used to form ohmic contacts. The contact annealing will reduce the electron sheet density of a non-passivated heterostructure, but is seen to have almost no effect on the LPCVD passivated heterostructure. From a first examination the reduction of ns is a negative effect. However, in this report it is shown that introducing an extra annealing step before the LPCVD deposition can be used to improve device characteristics. A pre-LPCVD annealing at 800°C reduces ns by 15%, resulting in: almost no change in sheet resistance, around 40% larger transconductance and a substantially lower gate current.
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| 16. |
- Fagerlind, Martin, 1980, et al.
(författare)
-
Influence of Large-Aspect-Ratio Surface Roughness on Electrical Characteristics of AlGaN/AlN/GaN HFETs
- 2012
-
Ingår i: IEEE Transactions on Device and Materials Reliability. - : Institute of Electrical and Electronics Engineers (IEEE). - 1530-4388 .- 1558-2574. ; 12:3, s. 538-546
-
Tidskriftsartikel (refereegranskat)abstract
- The effect of large-aspect-ratio surface roughness of AlGaN/GaN wafers is investigated. The roughness has a surface morphology consisting of hexagonal peaks with maximum peak-to-valley height of more than 100 nm and lateral peak-to-peak distance between 25 and 100 mu m. Two epitaxial wafers grown at the same time on SiC substrates having different surface orientation and with a resulting difference in AlGaN surface roughness are investigated. Almost no difference is seen in the electrical characteristics of the materials, and the electrical uniformity of the rough material is comparable to that of the smoother material. The reliability of heterostructure field-effect transistors from both materials have been tested by stressing devices for up to 100 h without any significant degradation. No critical effect, from the surface roughness, on device fabrication is experienced, with the exception that the roughness will directly interfere with step-height measurements.
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| 17. |
- Fagerlind, Martin, 1980, et al.
(författare)
-
Optimization of recessed ohmic contacts for AlGaN/AlN/GaN heterostructures using C(V) characterization of MSHM structures
- 2011
-
Ingår i: Physica Status Solidi (C) Current Topics in Solid State Physics. - 1610-1642 .- 1862-6351. ; 8:7-8, s. 2204-2206
-
Tidskriftsartikel (refereegranskat)abstract
- Recess etching is used to reduce the resistance of ohmiccontacts to an AlGaN/AlN/GaN heterostructure. Theminimization of the resistance relies on exact etching ofthe barrier. For this purpose C(V) measurements of theetched contacts, before annealing, are used to characterizethe effect of the recess etch. Using the C(V) measurementsa Cl2/Ar based ICP/RIE etch recipe with a stabilizedetch rate of approximately 3 Å/s is developed. By utilizing the recess etch the contact resistivity is reducedfrom the non etched 0.9 Ω•mm to 0.3 Ω•mm when approximately2 nm remains of the barriers, while maintaininga low sheet resistance. The C(V) measurementsmake it possible to monitor sheet carrier density vs. etchdepth. Furthermore, the C(V) measurement gives large-areaaverage values that is not easily obtained with AFMmeasurements.
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| 18. |
- Felbinger, Jonathan, 1984, et al.
(författare)
-
Fabrication and Characterization of Thin-Barrier Al05Ga05N/AlN/GaN HEMTs
- 2011
-
Ingår i: IEEE Electron Device Letters. - 0741-3106 .- 1558-0563. ; 32:7, s. 889-891
-
Tidskriftsartikel (refereegranskat)abstract
- The growth, fabrication, and performance of AlGaN/AlN/GaN high-electron-mobility transistors (HEMTs) with a total barrier thickness of 7 nm are reported. An optimized surface passivation and an Ohmic recess etch yield HEMTs exhibiting 0.72 S/mm peak extrinsic DC transconductance at a current density of 0.47 A/mm. Devices with a gate length of 90 nm achieve 78 GHz unity-current-gain frequency and up to 166 GHz maximum frequency of oscillation. The minimum noise figure at 10 GHz is 0.52 dB with an associated gain of 9.5 dB.
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| 19. |
- Gustafsson, David, 1983, et al.
(författare)
-
A Wideband and Compact GaN MMIC Doherty Amplifier for Microwave Link Applications
- 2013
-
Ingår i: IEEE Transactions on Microwave Theory and Techniques. - 0018-9480 .- 1557-9670. ; 61:2, s. 922-930
-
Tidskriftsartikel (refereegranskat)abstract
- This paper addresses the limitations and difficulties, in terms of DC-current density restrictions, and process limitations, associated with implementing impedance inverters with high characteristic impedance for monolithic microwave integrated circuit (MMIC) Doherty power amplifiers (DPAs). It is theoretically shown that impedance inverters with high characteristic impedance can be realized by utilizing the output capacitance of the active devices, together with a compact Tee-network of transmission lines with feasible linewidths. The utility of the impedance inverter is proven by design and fabrication of a GaN MMIC-DPA for microwave link applications. Continuous wave (CW) measurements demonstrate a maximum output power of 35 +/- 0.5 dBm over a frequency range of 6.6-8.5 GHz. The power added efficiency (PAE) in 9 dB output power back-off (OPBO) is better than 30% in a frequency range of 6.7-7.8 GHz. Moreover, linearized modulated measurements, employing a 10 MHz 256-QAM signal with 7.8 dB peak to average power ratio (PAPR), demonstrate higher than 35% average PAE, with 27.5 +/- 0.2 dBm average output power, and an adjacent channel power ratio (ACPR) less than -45 dBc, across a 6.8-8.5 GHz frequency range. The fabricated chip-size measures 2.1 mm x 1.5 mm.
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| 20. |
- Habibpour, Omid, 1979, et al.
(författare)
-
High gain graphene field effect transistors for wideband amplifiers
- 2014
-
Ingår i: 44th European Microwave Conference, EuMC 2014 - Held as Part of the 17th European Microwave Week, EuMW 2014; Fiera di RomaRome; Italy; 6 October 2014 through 9 October 2014. - 9782874870354 ; , s. 371-373
-
Konferensbidrag (refereegranskat)abstract
- We demonstrate graphene field of transistors (G-FETs) providing power gain of > 7 dB in a 50 O system. The G-FETs have S21 > 0 dB up to 7 GHz. The result indicates the feasibility for G-FET based wideband amplifiers.
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| 21. |
- Hjelmgren, Hans, 1960, et al.
(författare)
-
Extraction of an Electrothermal Mobility Model for AlGaN/GaN Heterostructures
- 2012
-
Ingår i: IEEE Transactions on Electron Devices. - 1557-9646 .- 0018-9383. ; 59:12, s. 3344-3349
-
Tidskriftsartikel (refereegranskat)abstract
- An electron mobility model for AlGaN/GaN heterostructures taking both the lattice temperature and electric field into account is proposed. Numerical device simulation of an ungated Al0.25Ga0.75N/GaN HEMT structure on 4H-SiC substrate is compared to measured electrical characteristics. Mobility model parameters are extracted by comparing iso-thermal numerical simulations with microwave (6 GHz) large signal measurements. The extracted model was used in static simulations, showing good agreement with measurements.
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| 22. |
- Lai, Szhau, 1985, et al.
(författare)
-
Accurate Phase-Noise Prediction for a Balanced Colpitts GaN HEMT MMIC Oscillator
- 2013
-
Ingår i: IEEE Transactions on Microwave Theory and Techniques. - : Institute of Electrical and Electronics Engineers (IEEE). - 0018-9480 .- 1557-9670. ; 61:11, s. 3916-3926
-
Tidskriftsartikel (refereegranskat)abstract
- This paper presents an X-band balanced Colpitts oscillator in GaN HEMT technology and a method to calculate its phase noise accurately. The method employs a low-frequency (LF) noise measurement and the oscillator waveforms from a harmonic-balance simulator. These data are post-calculated by Hajimiri's phase-noise model, in which the LF noise can be activated with a cyclo-stationary effect in the calculation of phase noise. Compared to commercial phase-noise simulation using predefined stationary noise, the calculation gives significantly improved phase-noise prediction in the 30-dB/decade region near carrier. The prediction is within 3-dB accuracy at 10-kHz, 100-kHz, and 1-MHz offset frequencies. In addition to the method used for phase-noise prediction, the potential for wideband tuning of this oscillator topology is analytically investigated. The measured phase noise of the oscillator is -102 dBc/Hz at 100-kHz offset from a 8.6-GHz carrier frequency for drain voltage and current of Vd = 15 V amd Id = 40 mA.
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| 23. |
- Lai, Szhau, 1985, et al.
(författare)
-
Low Phase Noise GaN HEMT Oscillators With Excellent Figures of Merit
- 2014
-
Ingår i: IEEE Microwave and Wireless Components Letters. - 1558-1764 .- 1531-1309. ; 24:6, s. 412-414
-
Tidskriftsartikel (refereegranskat)abstract
- This letter presents guidelines for the design of low phase noise oscillators in GaN high electron mobility transistor (HEMT) technology. The design starts from bias-dependent low-frequency (LF) noise measurements. Oscillator topology and bias point are then chosen for operation in regions where LF noise is low. The best LF noise properties are obtained for low drain voltage and current. Thus, the low phase noise can be achieved at low dc power which also means that power normalized phase noise figure of merit (FOM) will be good.
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| 24. |
- Lundqvist, Björn, et al.
(författare)
-
Thermal conductivity of isotopically enriched silicon carbide
- 2013
-
Ingår i: THERMINIC 2013 - 19th International Workshop on Thermal Investigations of ICs and Systems, Proceedings. - : IEEE. ; , s. 58-61, s. 58-61
-
Konferensbidrag (refereegranskat)abstract
- Since the semiconductor silicon carbide presents attractive opportunities for the fabrication of novel electronic devices, there is significant interest in improving its material quality. Shrinking component sizes and high demands for efficiency and reliability make the capability to release excess heat an important factor for further development. Experience from Si and Diamond tells us that isotopic enrichment is a possible way to increase the thermal conductivity. We have produced samples of 4H-SiC that contain 28Si and 12C to a purity of 99.5%. The thermal conductivity in the c-direction of these samples has been measured by a transient thermoreflectance method. An improvement due to enrichment of at least 18% was found. The result is valid for a temperature of 45K above room temperature. A preliminary study of the temperature dependence of the thermal conductivity demonstrates a strong temperature dependence in agreement with earlier reports for 4H. © 2013 IEEE.
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| 25. |
- Malmros, Anna, 1977, et al.
(författare)
-
Combined TiN- and TaN temperature compensated thin film resistors
- 2012
-
Ingår i: Thin Solid Films. - : Elsevier BV. - 0040-6090. ; 520:6, s. 2162-2165
-
Tidskriftsartikel (refereegranskat)abstract
- The opposite signs of the temperature coefficient of resistance (TCR) of two thin film materials, titanium nitride (TiN) and tantalum nitride (TaN), were used to form temperature compensated thin film resistors (TFRs). The principle of designing temperature compensated TFRs by connecting TFRs of each compound in series or in parallel was demonstrated. TiN, TaN, and combined TiN and TaN TFRs for monolithic microwave integrated circuits (MMICs) were fabricated by reactive sputtering. DC characterization was performed over the temperature range of 30-200 degrees C. The TiN TFRs exhibited an increase in resistivity with temperature with TCRs of 540 and 750 ppm/degrees C. The TaN TFR on the other hand exhibited a negative TCR of -470 ppm/degrees C. The shunted TFRs were fabricated by serial deposition of TiN and TaN to form a bilayer component. The TCRs of the series- and shunt configurations were experimentally reduced to -60 and 100 ppm/degrees C, respectively. The concept of temperature compensation was used to build a Wheatstone bridge with an application in on-chip temperature sensing.
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| 26. |
- Malmros, Anna, 1977, et al.
(författare)
-
Electrical properties, microstructure, and thermal stability of Ta-based ohmic contacts annealed at low temperature for GaN HEMTs
- 2011
-
Ingår i: Semiconductor Science and Technology. - : IOP Publishing. - 1361-6641 .- 0268-1242. ; 26:7
-
Tidskriftsartikel (refereegranskat)abstract
- Ta-based ohmic contacts to gallium nitride high electron mobility transistor (GaN HEMT) epitaxial structures were investigated. Two metallization schemes were considered: Ta/Al/Ni(Ta)/Au and Ta/Al/Ta. The latter was superior in terms of lower contact resistance (R-c) and wider process window. The metallizations were applied to two different heterostructures (GaN/Al0.14Ga0.86N/GaN and Al0.25Ga0.75N/GaN). The lowest measured R-c was 0.06 and 0.28 Omega mm, respectively. The main advantage of the Ta-based ohmic contacts over conventional Ti-based contacts was the low anneal temperature. The optimum temperature of annealing was found to be 550-575 degrees C. From optical and scanning electron microscopy, it was clear that excellent surface morphology and edge acuity were obtained at these low temperatures. This facilitates lateral scaling of the GaN HEMT. TEM images were taken of the contact cross sections onto which EDX measurements were performed. The aim was to investigate the microstructure and the contact mechanism. Storage tests at 300 degrees C for more than 400 h in air ambient showed no deterioration of R-c.
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| 27. |
- Malmros, Anna, 1977, et al.
(författare)
-
Evaluation of an InAlN/AlN/GaN HEMT with Ta-based ohmic contacts and PECVD SiN passivation
- 2014
-
Ingår i: Physica Status Solidi (C) Current Topics in Solid State Physics. - : Wiley. - 1610-1642 .- 1862-6351. ; 11:3-4, s. 924-927
-
Tidskriftsartikel (refereegranskat)abstract
- An InAlN/AlN/GaN HEMT with Au-free Ta-based ohmic contacts and a high-quality PECVD SiN passivation is reported. The ohmic contacts were annealed at 550 degrees C, resulting in a contact resistance of 0.64 Omm. The gate length was 50 nm. The device performance and the process were evaluated by performing DC-, pulsed IV-, RF-, and load-pull measurements. It was observed that current slump was effectively mitigated by the passivation layer. The DC channel current density increased by 71 % to 1170 mA/mm at the knee of the IV curve, and the transconductance increased from 382 to 477 mS/mm after passivation. At the same time the gate leakage increased, and the extrinsic f(max) decreased from 207 to 140 GHz. Output powers of 4.1 and 3.5 W/mm were measured after passivation at 31 and 40 GHz, respectively.
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| 28. |
- Malmros, Anna, 1977, et al.
(författare)
-
TiN thin film resistors for monolithic microwave integrated circuits
- 2010
-
Ingår i: Journal of Vacuum Science and Technology B: Nanotechnology and Microelectronics. - : American Vacuum Society. - 2166-2746 .- 2166-2754. ; 28:5, s. 912-915
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Tidskriftsartikel (refereegranskat)abstract
- Titanium nitride (TiN) thin film resistors (TFRs) have been fabricated by reactive sputter deposition. The TFRs were characterized in terms of composition, thickness, and resistance. Furthermore, a first assessment of the resistor reliability was made by measurements of the resistivity (rho) versus temperature, electrical stress, long-term stability, and thermal infrared measurements. TiN layers with thicknesses up to 3560 angstrom, corresponding to a sheet resistance (R-s) of 10 Omega/square, were successfully deposited without any signs of stress in the films. The critical dissipated power (P-c) showed a correlation with the resistor footprint-area indicating that Joule-heating was the main cause of failure. This was partly substantiated by the thermal infrared measurements.
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| 29. |
- Pomeroy, J, et al.
(författare)
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Improved GaN-on-SiC transistor thermal resistance by systematic nucleation layer growth optimization
- 2013
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Ingår i: Compound Semiconductor Integrated Circuit Symposium (CSICS), 2013 IEEE. - : IEEE. - 1550-8781. - 9781479905836 ; , s. 1-4
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Konferensbidrag (refereegranskat)abstract
- Impressive power densities have been demonstrated for GaN-on-SiC based high-power high-frequency transistors, although further gains can be achieved by further minimizing the device thermal resistance. A significant 10-30% contribution to the total device thermal resistance originates from the high defect density AlN nucleation layer at the GaN/SiC interface. This thermal resistance contribution was successfully reduced by performing systematic growth optimization, investigating growth parameters including: Substrate pretreatment temperature, growth temperature and deposition time. Interfacial thermal resistance, characterized by time resolved Raman thermography measurements AlGaN/GaN HEMT structures, were minimized by using a substrate pretreatment and growth temperature of 1200 °C. Reducing the AlN thickness from 105 nm (3.3×10-8W/m2K) to 35 nm (3.3×10-8 W/m2K), led to a ~2.5× interfacial thermal resistance reduction and the lowest value reported for a standard AlGaN/GaN HEMT structure.
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| 30. |
- Shiu, J. Y., et al.
(författare)
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Electrical Characterization and Transmission Electron Microscopy Assessment of Isolation of AlGaN/GaN High Electron Mobility Transistors with Oxygen Ion Implantation
- 2010
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Ingår i: Japanese Journal of Applied Physics. - 1347-4065 .- 0021-4922. ; 49:2, s. Art. no. 021001-
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Tidskriftsartikel (refereegranskat)abstract
- A multienergy oxygen ion implantation process was demonstrated to be compatible with the processing of high-power microwave AlGaN/GaN high electron mobility transistors (HEMTs). A high sheet resistivity and thermally stable isolation were demonstrated. The microstructures of implanted and postannealed specimens were investigated by transmission electron microscopy (TEM). The dependences of the sheet resistivity and different postannealing temperatures were correlated with the defect clusters and microstructure of lattice stacking faults. After 300 degrees C annealing, the sheet resistivity was higher than 10(12) Omega/square, which was attributed to the severe defect interaction eliminating the trapping centers and reducing the leakage current. A maximum output power density of 5.3 W/mm at V-gs = -4 V and V-ds = 50 V at 3 GHz was demonstrated on lag-free HEMTs without field plates on sapphire substrate.
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| 31. |
- Silva Barrera, Oliver, 1985, et al.
(författare)
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High linearity MMIC power amplifier design with controlled junction temperature
- 2014
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Ingår i: International Workshop on Integrated Nonlinear Microwave and Millimetre-Wave Circuits, INMMiC 2014. ; , s. Art. no. 6815096-
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Konferensbidrag (refereegranskat)abstract
- A combination of techniques for designing high linearity power amplifiers under controlled junction temperature required for space applications is explained and demonstrated. Junction temperature calculation is taken into account in the transistor selection to ensure high reliability operation and is verified by IR measurement. A non linear model is used to accurately predict harmonics generation and intermodulation products. Optimal bias point and loads are chosen to improve the linearity performance. The design method is demonstrated in a C band high linearity GaAs MMIC power. The techniques described lead to an output 1dB compression point of 26.6dBm, saturated power 28.9dBm and PAE 20.9%, with a gain higher than 30dB. The output third order intercept point (OIP3) reaches levels over 40dBm with power consumption less than 2W. The design keeps the critical junction temperature under 108°C and de-rating drain bias of 4 volts is used.
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| 32. |
- Thorsell, Mattias, 1982, et al.
(författare)
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Characterization of Electro-Thermal Effects in GaN Based HEMTs
- 2010
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Ingår i: 5th Space Agency - MOD Round Table Workshop on GaN Component Technologies.
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- This paper presents a new method for characterizing electro-thermal effects in GaN based HEMTs. The proposed method characterizes the thermal and bias dependence of the current through the 2-DEG individually. The temperature dependence is characterized by TLM measurements versus ambient temperature, showing an increasing sheet resistivity with temperature. The thermal impedance is determined from low frequency impedance measurements, indicating thermal response up to at least 100 MHz. The isothermal bias dependence is measured above the thermal cut-off with a LSNA, showing a nonlinear current versus voltage characteristic.
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| 33. |
- Thorsell, Mattias, 1982, et al.
(författare)
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Electrothermal Access Resistance Model for GaN-Based HEMTs
- 2011
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Ingår i: IEEE Transactions on Electron Devices. - 1557-9646 .- 0018-9383. ; 58:2, s. 466 - 472
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Tidskriftsartikel (refereegranskat)abstract
- The high-power density in GaN-based high-electron-mobility transistors (HEMTs) increases demands on the accurate extraction and modeling of electrothermal effects such as self-heating. This paper presents a new electrothermal model of the access resistances in GaN HEMTs, taking into account both self heating and bias dependence. A coplanar ungated transfer length method (TLM) structure has been used to extract the resistance versus temperature, bias, and RF power. The temperature dependence is extracted from dc measurements at ambient temperatures between 293 and 443 K. Small-signal measurements are used to extract the time constants in the thermal impedance. The bias dependence of the current is characterized by isothermal large-signal RF measurements between 1 and 6 GHz. A new method for extracting the thermal resistance from the large-signal measurements together with temperature-dependent dc measurements is also presented.
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| 34. |
- Winters, Michael, 1986, et al.
(författare)
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A DC Comparison Study Between H-Intercalated and Native epigraphenes on SiC substrates
- 2013
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Ingår i: Materials Science Forum. - : Trans Tech Publications Inc.. - 1662-9752 .- 0255-5476. ; 740-742, s. 129-132, s. 129-132
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Konferensbidrag (refereegranskat)abstract
- The aim of this study is to compare DC characteristics of 'as-grown' and hydrogen (H)-intercalated epitaxial graphenes on SiC substrates [1,2]. Epitaxial graphene is grown on SiC at 1400-1600C, and H-intercalation is performed via in-situ introduction of Hydrogen during the graphitization process [5]. The fabrication processing steps used to define test structures are identical for the two materials. Results on the DC behavior and uniformity issues with respect to both materials are reported. The as-grown material behaves as a linear resistance, while H-intercalated demonstrates a non-linear characteristic. Hysteresis effects and time dependent behaviors are also observed in both materials. Extensive Hall measurements are performed on both materials with the aim of providing a qualitative understanding of material uniformity in both epigraphenes.
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| 35. |
- Winters, Michael, 1986, et al.
(författare)
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A temperature dependent measurement of the carrier velocity vs. electric field characteristic for as-grown and H-intercalated epitaxial graphene on SiC
- 2013
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Ingår i: Journal of Applied Physics. - : AIP Publishing. - 0021-8979 .- 1089-7550. ; 113:19
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Tidskriftsartikel (refereegranskat)abstract
- A technique for the measurement of the electron velocity versus electric field is demonstrated on as-grown and H-intercalated graphene. Van der Pauw, coplanar microbridge, and coplanar TLM structures are fabricated in order to assess the carrier mobility, carrier concentration, sheet resistance, and contact resistance of both epi-materials. These measurements are then combined with dynamic IV measurements to extract a velocity-field characteristic. The saturated electron velocity measurements indicate a value of 2.33 x 10(7)cm/s for the as-grown material and 1: 36 x 10(7)cm/s for the H-intercalated material at 300 K. Measurements are taken as a function of temperature from 100K to 325K in order to estimate the optical phonon energy E-so of 4H-SiC by assuming an impurity scattering model. The extracted values of E-so are 97 meV for the as-grown sample and 115 meV for the H-intercalated sample. The H-intercalated result correlates to the anticipated value of 116 meV for 4H-SiC, while the as-grown value is significantly below the expected value. Therefore, we hypothesize that the transport properties of epitaxial graphene on SiC are influenced both by intercalation and by remote phonon scattering with the SiC substrate.
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| 36. |
- Winters, Michael, 1986, et al.
(författare)
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Carrier Mobility as a Function of Temperature in as-Grown and H-intercalated Epitaxial Graphenes on 4H-SiC
- 2014
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Ingår i: Materials Science Forum. - : Trans Tech Publications. - 1662-9752 .- 0255-5476. ; 778-780, s. 1146-1149, s. 1146-1149
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Konferensbidrag (refereegranskat)abstract
- The carrier velocity is measured as a function of electric field in as-grown and H-intercalaed epitaxial graphene grown on semi-insulating 4H-SiC in order to estimate the low field carrier mobility as a function of temperature. The mobility is also measured on the same samples as a function of temperature in a liquid Helium (He) cooled cryostat. The two temperature dependent measurements are compared in order to deduce the dominant carrier scattering mechanisms in both materials. In as-grown material, acoustic phonon scattering and impurity scattering both contribute, while impurity scattering dominates in H-intercalated material.
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| 37. |
- Zirath, Herbert, 1955, et al.
(författare)
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An X-band low phase noise AlGaN-GaN-HEMT MMIC push-push oscillator
- 2011
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Ingår i: 33rd IEEE Compound Semiconductor Integrated Circuit Symposium: Integrated Circuits in GaAs, InP, SiGe, GaN and Other Compound Semiconductors, CSICS 2011, Waikoloa, 16-19 October 2011. - 1550-8781. - 9781612847122
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Konferensbidrag (refereegranskat)abstract
- An X-band low phase noise AlGaN-GaN HEMT MMIC push-push oscillator is designed, fabricated, and characterized. The oscillator is based on two common gate Colpitts oscillators. A minimum phase noise of -101 dBc at 100 kHz offset is achieved. The MMIC was fabricate in an 'in-house process' at Chalmers University of Technology.
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| 38. |
- ÖZEN, MUSTAFA, 1984, et al.
(författare)
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High efficiency RF pulse width modulation with tunable load network class-E PA
- 2011
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Ingår i: 2011 IEEE 12th Annual Wireless and Microwave Technology Conference, WAMICON 2011. - 9781612840819
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Konferensbidrag (refereegranskat)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.
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