| 1. |
|
|
| 2. |
|
|
| 3. |
- Sudow, Mattias, 1980, et al.
(författare)
-
A Single-Ended Resistive $X$-Band AlGaN/GaN HEMT MMIC Mixer
- 2008
-
Ingår i: IEEE Transactions on Microwave Theory and Techniques. - 0018-9480 .- 1557-9670. ; 56:10, s. 2201-2206
-
Tidskriftsartikel (refereegranskat)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
|
|
| 4. |
- Sudow, Mattias, 1980, et al.
(författare)
-
An AlGaN/GaN HEMT-Based Microstrip MMIC Process for Advanced Transceiver Design
- 2008
-
Ingår i: IEEE Transactions on Microwave Theory and Techniques. - 0018-9480 .- 1557-9670. ; 56:8, s. 1827-1833
-
Tidskriftsartikel (refereegranskat)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.
|
|
| 5. |
- Suijker, Erwin M., et al.
(författare)
-
GaN MMIC power amplifiers for S-band and X- band
- 2008
-
Ingår i: 38th European Microwave Conference, EuMC 2008; Amsterdam; Netherlands; 27 October 2008 through 31 October 2008. - 9782874870064 ; , s. 297-300
-
Konferensbidrag (refereegranskat)abstract
- The development of two GaN MMIC power amplifiers is reported. The amplifiers are processed in the AlGaN/GaN technology of Chalmers University of Technology using 0.25 ?m HEMTs. The S-band amplifier operates at frequencies from 3 to 4 GHz and has a maximum output power of 5.6 W with an associated efficiency of 28 %. The X-band amplifier has a maximum output power of 4.8 W.
|
|
| 6. |
- Thorsell, Mattias, 1982, et al.
(författare)
-
Characterization of the temperature dependent access resistances in AlGaN/GaN HEMTs
- 2008
-
Ingår i: Workshop on Integrated Nonlinear Microwave and Millimetre-Wave Circuits, 2008. INMMIC 2008.. - 9781424426454 ; , s. 17-20
-
Konferensbidrag (refereegranskat)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.
|
|
| 7. |
- Thorsell, Mattias, 1982, et al.
(författare)
-
Thermal characterization of the intrinsic noise parameters for AlGaN/GaN HEMTs
- 2008
-
Ingår i: International Microwave Symposium Digest, 2008, Atlanta. - 0149-645X. - 9781424417810 ; , s. 463-466
-
Konferensbidrag (refereegranskat)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.
|
|
| 8. |
- Thorsell, Mattias, 1982, et al.
(författare)
-
Thermal Study of the High-Frequency Noise in GaN HEMTs
- 2009
-
Ingår i: IEEE Transactions on Microwave Theory and Techniques. - 0018-9480 .- 1557-9670. ; 57:1, s. 19-26
-
Tidskriftsartikel (refereegranskat)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.
|
|
| 9. |
- Dammann, M., et al.
(författare)
-
Reliability and degradation mechanism of AlGaN/GaN HEMTs for next generation mobile communication systems
- 2009
-
Ingår i: Microelectronics and Reliability. - : Elsevier BV. - 0026-2714. ; 49:5, s. 474-477
-
Tidskriftsartikel (refereegranskat)abstract
- Excellent reliability performance of AlGaN/GaN HEMTs on SiC substrates for next generation mobile communication systems has been demonstrated using DC and RF stress tests on 8 x 60 mu m wide and 0.5 mu m long AlGaN/GaN HEMTs at a drain voltage of V-d = 50 V. Drain current recovery measurements after stress indicate that the degradation is partly caused by slow traps generated in the SiN passivation or in the HEMT epitaxial layers. The traps in the SiN passivation layer were characterized using high and low frequency capacitance-voltage (CV) measurements of MIS test structures on thick lightly doped GaN layers. (C) 2009 Elsevier Ltd. All rights reserved.
|
|
| 10. |
- Fagerlind, Martin, 1980, et al.
(författare)
-
A room temperature HEMT process for AlGaN/GaN heterostructure characterization
- 2009
-
Ingår i: Semiconductor Science and Technology. - : IOP Publishing. - 1361-6641 .- 0268-1242. ; 24:4, s. 045014-
-
Tidskriftsartikel (refereegranskat)abstract
- A simple, room temperature, AlGaN/GaN high electron mobility transistor (HEMT) process is presented. The process consists of only two steps which can be performed by hand. The first step is to deposit gallium (Ga) metal for ohmic contacts, which without thermal processing have a specific contact resistivity ρ_c=0.10 Ohm cm2. Silver (Ag)-based conductive paint is then deposited to form a Schottky contact. The simplicity of the process facilitates fast fabrication and characterization of HEMTs, without unwanted effects on the material. The process is useful for initial material characterization and screening. The process is also found to be a useful tool for process monitoring of the conventional HEMT micro-fabrication process by detecting material/process quality problems. In this work the process is used for initial material characterization and screening, where a leaky buffer can easily be detected. The process is also used to identify the ohmic contact annealing as a potentially damaging step in a conventional micro-fabrication process. A decrease in the electron sheet carrier concentration and an increase of leakage currents are measured after annealing.
|
|
| 11. |
- Fagerlind, Martin, 1980
(författare)
-
Characterization and Analysis of Surface Passivations and Gate Insulators for AlGaN/GaN Microwave HFETs
- 2012
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The large bandgap of gallium nitride (GaN) and aluminum gallium nitride (AlGaN) offers an inherently high intrinsic breakdown field. When the materials are joined into the AlGaN/GaN heterostructure a 2-dimensional electron gas (2DEG) with a high electron density as well as high electron mobility is generated. The combination of high electron density with high mobility and high breakdown field results in excellent power handling capability at high frequencies. These inherently virtuous physical properties are utilized by the GaN-based heterostructure field effect transistor (HFET) technology.This thesis deals with developing appropriate fabrication processes for AlGaN/GaN HFETs by basic material characterization methods. The main focus is on the passivation of the heterostructure surface, which is notorious for its effect on device performance. Several examples of the effect of the passivation process on the electrical properties of the heterostructure are presented. For example, it is shown that passivating a heterostructure using a non optimized plasma based deposition method may redistribute more than 90\% of the channel electrons to a barrier accumulation layer. The use of metal-insulator-semiconducting-heterostructure (MISH) capacitor analysis for extracting interface states is described in detail. Based on a comparison of different passivation methods the low pressure chemical vapor deposition (LPCVD) silicon nitride (\SiNx{}) emerges as a suitable candidate for passivation of AlGaN/GaN heterostructures. In this thesis the effects of different LPCVD \SiNx{} deposition parameters are investigated. Furthermore, LPCVD \SiNx{} passivation will produce devices that are less sensitive to illumination. The illumination sensitivity is reduced to less than 3\% compared to 15\% to 130\% for other passivated and non passivated heterostructures. This thesis also reports on the fabrication and DC characterization of insulated gate HFETs. A 5\dunit{}nm thick layer of LPCVD silicon nitride is deposited below the gate which reduces the gate current by one to two orders of magnitude. This type of device is a promising candidate for reliable HFETs with applications in microwave and power electronics
|
|
| 12. |
- 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.
|
|
| 13. |
- 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.
|
|
| 14. |
- Fagerlind, Martin, 1980, et al.
(författare)
-
Influence of gate position on dispersion characteristics of GaN HEMTs
- 2008
-
Ingår i: WOCSDICE 2008, Abstract book. ; , s. 99-100
-
Konferensbidrag (refereegranskat)abstract
- GAN HEMTs with varying design have been fabricated to optimize device performance. The focus of this report is the minimization of drain current dispersion by the variation of the electric field distribution. In this work this is done by varying the placement of the gate and to some extent varying gate length and length of the gate connected field plate. We present pulsed IV characteristics for a number of different device designs.
|
|
| 15. |
- 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.
|
|
| 16. |
- 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]
|
|
| 17. |
- Fagerlind, Martin, 1980
(författare)
-
Methods for Characterization and Optimization of AlGaN/GaN HEMT Surface Passivation
- 2009
-
Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The Gallium Nitride based high electron mobility transistor is rapidly improving and is emerging as a viable alternative for use in high power applications operating in the microwave frequency domain. The suitability of the AlGaN/GaN material system is due to the possibility to grow epitaxial heterostructures that provide; high electron mobility, high electron saturation velocity, high carrier density and a high dielectric breakdown field.This thesis concerns the optimization of the HEMT fabrication process based on an understanding of the physical mechanisms behind the operation of the device. Optimization of a manufacturing process relies on identification of the process steps that have the largest e®ect on the device operation.A simple and fast process for manufacturing large area HEMT devices has been developed. The process is used to find critical processing steps of the HEMT process. For example, it is shown that the ohmic contact annealing step is responsible for a reduction of charge carrier density. The decrease is material dependent and between 10% and 40% of the electrons are lost after annealing, resulting in an increase of sheet resistance of 5% to 40%. The process is also used to show that the annealing step is also responsible for a more than two orders of magnitude larger buffer leakage. The process can also be used to swiftly characterize a heterostructure material and test its suitability for HEMT fabrication.The importance of the surface passivation for stable device operation is demonstrated and methods to optimize the passivation process is presented.Metal insulator semiconductor capacitor structures are studied to measure the density of states at the passivation-semiconductor interface. The density of interface states is shown be between 4*10^12 cm^-2 and 1.5*10^13 cm-2, dependingon method of passivation deposition. The Low Pressure Chemical Vapor Deposition process has the lowest interface state density.
|
|
| 18. |
- 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.
|
|
| 19. |
|
|
| 20. |
- 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.
|
|
| 21. |
- Moschetti, Giuseppe, 1982, et al.
(författare)
-
DC, RF and noise performance of InAs/AlSb HEMTs with in situ CVD SiNx-film for early-protection against oxidation
- 2013
-
Ingår i: Solid-State Electronics. - : Elsevier BV. - 0038-1101. ; 87, s. 85-89
-
Tidskriftsartikel (refereegranskat)abstract
- A new method for avoiding air exposure of the mesa-floor during processing of shallow-mesa InAs/AlSb HEMTs is reported. The method is based on the in situ chemical vapor deposition (CVD) of a SiNx-film, right after the shallow-mesa dry-etch process. The in situ CVD method allows also growing a dielectric film up to five times thicker than in previous reports of similar early-protection approach. Devices featuring a 25 nm SiNx-film enabled by the in situ CVD method are compared to devices based on a previously developed process, where the mesa floor is protected by a 2 nm SiNx-film deposited by ex situ reactive sputtering (RS). Microscopy observations revealed that the new process is more robust, ensuring a long-term stability against oxidation. DC, RF and noise performance were measured for 110 nm gate-length HEMTs. Devices based on the CVD process demonstrated higher peak transconductance (+13%), elevated I-on/I-off ratio (factor 4.7) and one order of magnitude lower gate current leakage. The cut-off frequency f(T) and the maximum oscillation frequency f(max) at a drain-source voltage of 0.3 V increased up to 175 GHz (+20%) and 130 GHz (+18%), respectively. Moreover, the extracted minimum noise figure for the InAs/AlSb HEMT using the in situ CVD early-protection was 1.4 dB at 6 GHz, instead of 2.3 dB for the RS based devices.
|
|
| 22. |
- Thorsell, Mattias, 1982, et al.
(författare)
-
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.
|
|
| 23. |
- ul Hassan, Jawad, et al.
(författare)
-
On-axis homoepitaxial growth of 4H-SiC PiN structure for high power applications
- 2013
-
Ingår i: Silicon Carbide and Related Materials 2012. - : Trans Tech Publications Inc.. - 9783037856246 ; 740-742, s. 173-176, s. 173-176
-
Konferensbidrag (refereegranskat)abstract
- We demonstrate on-axis homoepitaxial growth of 4H-SiC(0001) PiN structure on 3-inch wafers with 100% 4H polytype in the epilayer excluding the edges. The layers were grown with a thickness of 105 μm and controlled n-type doping of 4 x 1014 cm-3.The epilayers were completely free of basal plane dislocations, in-grown stacking faults and other epitaxial defects, as required for 10 kV high power bipolar devices. Some part of the wafer had a lifetime enhancement procedure to increase lifetime to above 2 μs using carbon implantation. An additional step of epilayer polishing was adapted to reduce surface roughness and implantation damage.
|
|
