| 1. |
- Asghar, M., et al.
(författare)
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Properties of dominant electron trap center in n-type SiC epilayers by means of deep level transient spectroscopy
- 2007
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Ingår i: Journal of Applied Physics. - : AIP Publishing. - 0021-8979 .- 1089-7550. ; 101:7
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Tidskriftsartikel (refereegranskat)abstract
- Characterization of dominant electron trap in as-grown SiC epilayers has been carried out using deep level transient spectroscopy. Two electron traps E1 and Z1 at Ec-0.21 and Ec-0.61 are observed, respectively, Z1 being the dominant level. Line shape fitting, capture cross section, and insensitivity with doping concentration have revealed interesting features of Z1 center. Spatial distribution discloses that the level is generated in the vicinity of epilayers/substrate interface and the rest of the overgrown layers is defect-free. Owing to the Si-rich growth conditions, the depth profile of Z1 relates it to carbon vacancy. The alpha particle irradiation transforms Z1 level into Z 1/Z2 center involving silicon and carbon vacancies. Isochronal annealing study further strengthens the proposed origin of the debated level. © 2007 American Institute of Physics.
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| 2. |
- Azam, Sher, et al.
(författare)
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Designing, Fabrication and Characterization of Power Amplifiers Based on 10-Watt SiC MESFET & GaN HEMT at Microwave Frequencies
- 2008
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Ingår i: IEEE European Microwave Week, October 10-15, Amsterdam, The Netherlands. ; , s. 444-447
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Konferensbidrag (refereegranskat)abstract
- This paper describes the design, fabrication and measurement of two single-stage class-AB power amplifiers covering the frequency band from 0.7-1.8 GHz using a SiC MESFET and a GaN HEMT. The measured maximum output power for the SiC amplifier at Vd = 48 V was 41.3 dBm (~13.7 W), with a PAE of 32% and a power gain above 10 dB. At a drain bias of Vd= 66 V at 700 MHz the Pmax was 42.2 dBm (~16.6 W) with a PAE of 34.4%. The measured results for GaN amplifier are; maximum output power at Vd = 48 V is 40 dBm (~10 W), with a PAE of 34% and a power gain above 10 dB. The results for SiC amplifier are better than for GaN amplifier for the same 10-W transistor.
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| 3. |
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| 4. |
- Azam, Sher, 1971-
(författare)
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Microwave Power Devices and Amplifiers for Radars and Communication Systems
- 2009
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- SiC MESFETs and GaN HEMTs posses an enormous potential in power amplifiers at microwave frequencies due to their wide bandgap features of high electric field strength, high electron saturation velocity and high operating temperature. The high power density combined with the comparably high impedance attainable by these devices also offers new possibilities for wideband power microwave systems. Similarly Si-LDMOS being low cost and lonely silicon based RF power transistor has great contributions especially in the communication sector.The focus of this thesis work is both device study and their application in different classes of power amplifiers. In the first part of our research work, we studied the performance of transistors in device simulation using physical transistor structure in Technology Computer Aided Design (TCAD). A comparison between the physical simulations and measured device characteristics has been carried out. We optimized GaN HEMT, Si-LDMOS and enhanced version of our previously fabricated and tested SiC MESFET transistor for enhanced RF and DC characteristics. For large signal AC performance we further extended the computational load pull (CLP) simulation technique to study the switching response of the power transistors. The beauty of our techniques is that, we need no lumped or distributive matching networks to study active device behavior in almost all major classes of power amplifiers. Using these techniques, we studied class A, AB, pulse input class-C and class-F switching response of SiC MESFET. We obtained maximum PAE of 78.3 % with power density of 2.5 W/mm for class C and 84 % for class F power amplifier at 500 MHz. The Si-LDMOS has a vital role and is a strong competitor to wideband gap semiconductor technology in communication sector. We also studied Si-LDMOS (transistor structure provided by Infineon Technologies at Kista, Stockholm) for improved DC and RF performance. The interface charges between the oxide and RESURF region are used not only to improve DC drain current and RF power, gain & efficiency but also enhance its operating frequency up to 4 GHz.In the second part of our research work, six single stage (using single transistor) power amplifiers have been designed, fabricated and characterized in three phases for applications in communications, Phased Array Radars and EW systems. In the first phase, two class AB power amplifiers are designed and fabricated. The first PA (26 W) is designed and fabricated at 200-500 MHz using SiC MESFET. Typical results for this PA at 60 V drain bias at 500 MHz are, 24.9 dB of power gain, 44.15 dBm output power (26 W) and 66 % PAE. The second PA is designed at 30-100 MHz using SiC MESFET. At 60 V drain bias Pmax is 46.7 dBm (~47 W) with a power gain of 21 dB.In the second phase, for performance comparison, three broadband class AB power amplifiers are designed and fabricated at 0.7-1.8 GHz using SiC MESFET and two different GaN HEMT technologies (GaN HEMT on SiC and GaN HEMT on Silicon substrate). The measured maximum output power for the SiC MESFET amplifier at a drain bias of Vd= 66 V at 700 MHz the Pmax was 42.2 dBm (~16.6 W) with a PAE of 34.4 %. The results for GaN HEMT on SiC amplifier are; maximum output power at Vd = 48 V is 40 dBm (~10 W), with a PAE of 34 % and a power gain above 10 dB. The maximum output power for GaN HEMT on Si amplifier is 42.5 dBm (~18 W) with a maximum PAE of 39 % and a gain of 19.5 dB.In the third phase, a high power single stage class E power amplifier is implemented with lumped elements at 0.89-1.02 GHz using Silicon GaN HEMT as an active device. The maximum drain efficiency (DE) and PAE of 67 and 65 % respectively is obtained with a maximum output power of 42.2 dBm (~ 17 W) and a maximum power gain of 15 dB.
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| 5. |
- Azam, Sher, 1971-, et al.
(författare)
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Performance of SiC Microwave Transistors in Power Amplifiers
- 2008
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Ingår i: Proc. of MRS Symposium on wide bandgap semiconductor electronics 8. - 9781605110394 ; , s. 203-208
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Konferensbidrag (refereegranskat)abstract
- The performance of SiC microwave power transistors is studied in fabricated class-AB power amplifiers and class-C switching power amplifier using physical structure of an enhanced version of previously fabricated and tested SiC MESFET. The results for pulse input in class-C at 1 GHz are; efficiency of 71.4 %, power density of 1.0 W/mm. The switching loss was 0.424 W/mm. The results for two class-AB power amplifiers are; the 30-100 MHz amplifier showed 45.6 dBm (∼ 36 W) output powers at P1dB, at 50 MHz. The power added efficiency (PAE) is 48 % together with 21 dB of power gain. The maximum output power at P1dB at 60 V drain bias and Vg= -8.5 V was 46.7 dBm (∼47 W). The typical results obtained in 200-500 MHz amplifier are; at 60 V drain bias the P1dB is 43.85 dBm (24 W) except at 300 MHz where only 41.8 dBm was obtained. The maximum out put power was 44.15 dBm (26 W) at 500 MHz corresponding to a power density of 5.2 W/mm. The PAE @ P1dB [%] at 500 MHz is 66 %.
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| 6. |
- Azam, Sher, et al.
(författare)
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Pulse Input Class-C Power Amplifier Response of SiC MESFET using Physical Transistor Structure in TCAD
- 2008
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Ingår i: Solid-State Electronics. - : Elsevier BV. - 0038-1101 .- 1879-2405. ; 52:5, s. 740-744
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Tidskriftsartikel (refereegranskat)abstract
- The switching behavior of a previously fabricated and tested SiC transistor is studied in Class-C amplifier in TCAD simulation. The transistor is simulated for pulse input signals in Class-C power amplifier. The simulated gain (dB), power density (W/mm) and power added efficiency (PAE%) at 500 MHz, 1, 2 and 3 GHz was studied using computational TCAD load pull simulation technique. A Maximum PAE of 77.8% at 500 MHz with 45.4 dB power gain and power density of 2.43 W/mm is achieved. This technique allows the prediction of switching response of the device for switching amplifier Classes (Class-C–F) before undertaking an expensive and time consuming device fabrication. The beauty of this technique is that, we need no matching and other lumped element networks for studying the large signal behavior of RF and microwave transistors.
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| 7. |
- Azam, Sher, et al.
(författare)
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Single-stage, High Efficiency, 26-Watt power Amplifier using SiC LE-MESFET
- 2006
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Ingår i: Microwave Conference, 2006. APMC 2006. Asia-Pacific December 12-15. ; , s. 441-444
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Konferensbidrag (refereegranskat)abstract
- This paper describes a single-stage 26 W negative feedback power amplifier, covering the frequency range 200-500 MHz using a 6 mm gate width SiC lateral epitaxy MESFET. Typical results at 50 V drain bias for the whole band are, around 22 dB power gain, around 43 dBm output power, minimum power added efficiency at P1 dB is 47% at 200 MHz and maximum 60% at 500 MHz and the IMD3 level at 10 dB back-off from P1 dB is below -45 dBc. The results at 60 V drain bias at 500 MHz are, 24.9 dB power gain, 44.15 dBm output power (26 W) and 66% PAE.
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| 8. |
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| 9. |
- Azam, Sher, 1971-
(författare)
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Wide Bandgap Semiconductor (SiC & GaN) Power Amplifiers in Different Classes
- 2008
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- SiC MESFETs and GaN HEMTs have an enormous potential in high-power amplifiers at microwave frequencies due to their wide bandgap features of high electric breakdown field strength, high electron saturation velocity and high operating temperature. The high power density combined with the comparably high impedance attainable by these devices also offers new possibilities for wideband power microwave systems. In this thesis, Class C switching response of SiC MESFET in TCAD and two different generations of broadband power amplifiers have been designed, fabricated and characterized. Input and output matching networks and shunt feedback topology based on microstrip and lumped components have been designed, to increase the bandwidth and to improve the stability. The first amplifier is a single stage 26-watt using a SiC MESFET covering the frequency from 200-500 MHz is designed and fabricated. Typical results at 50 V drain bias for the whole band are, 22 dB power gain, 43 dBm output power, minimum power added efficiency at P 1dB is 47 % at 200 MHz and maximum 60 % at 500 MHz and the IMD3 level at 10 dB back-off from P 1dB is below ‑45 dBc. The results at 60 V drain bias at 500 MHz are, 24.9 dB power gain, 44.15 dBm output power (26 W) and 66 % PAE.In the second phase, two power amplifiers at 0.7-1.8 GHz without feed back for SiC MESFET and with feedback for GaN HEMT are designed and fabricated (both these transistors were of 10 W). The measured maximum output power for the SiC amplifier at Vd = 48 V was 41.3 dBm (~13.7 W), with a PAE of 32 % and a power gain above 10 dB. At a drain bias of Vd= 66 V at 700 MHz the Pmax was 42.2 dBm (~16.6 W) with a PAE of 34.4 %. The measured results for GaN amplifier are; maximum output power at Vd = 48 V is 40 dBm (~10 W), with a PAE of 34 % and a power gain above 10 dB. The SiC amplifier gives better results than for GaN amplifier for the same 10 W transistor.A comparison between the physical simulations and measured device characteristics has also been carried out. A novel and efficient way to extend the physical simulations to large signal high frequency domain was developed in our group, is further extended to study the class-C switching response of the devices. By the extended technique the switching losses, power density and PAE in the dynamics of the SiC MESFET transistor at four different frequencies of 500 MHz, 1, 2 and 3 GHz during large signal operation and the source of switching losses in the device structure was investigated. The results obtained at 500 MHz are, PAE of 78.3%, a power density of 2.5 W/mm with a switching loss of 0.69 W/mm. Typical results at 3 GHz are, PAE of 53.4 %, a power density of 1.7 W/mm with a switching loss of 1.52 W/mm.
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| 10. |
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