| 1. |
- Azam, Sher, 1971-, et al.
(author)
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A New Load Pull TCAD Simulation Technique for Class D, E & FSwitching Characteristics of Transistors
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Other publication (other academic/artistic)abstract
- We have further developed a computational load pull simulation technique inTCAD. It can be used to study the Class-D, E & F switching response of the transistors. Westudied our enhanced version of previously fabricated and tested SiC transistor. Thesimulated Gain (dB), Power density (W/mm), switching loss (W/mm) and power addedefficiency (PAE %) at 500 MHz were studied using this technique. A PAE of 84 % at500MHz with 26 dB Power gain and power density of 2.75 W/mm is achieved. Thistechnique allows the prediction of switching response of the device before undertaking anexpensive and time-consuming device fabrication. The beauty of this technique is that, weneed no matching and other lumped element networks to study the large signal switchingbehavior of RF and microwave transistors.
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| 2. |
- Azam, Sher, 1971-, et al.
(author)
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Broadband Power Amplifier performance of SiC MESFET and CostEffective SiGaN HEMT
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Other publication (other academic/artistic)abstract
- This paper describes the broadband power amplifier performance of two differentwide band gap technology transistors at 0.7 to 1.8 GHz using cost effective NitronexGaN HEMT on Silicon (Si) and Cree Silicon Carbide MESFET. The measured resultsfor GaN amplifier are; maximum output power at Vd = 28 V is 42.5 dBm (~18 W), amaximum PAE of 39 % and a maximum gain of 19.5 dB is obtained. The measuredmaximum 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 at700 MHz for SiC MESFET amplifier the Pmax was 42.2 dBm (~16.6 W) with a PAE of34.4 %.
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| 3. |
- Azam, Sher, et al.
(author)
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Comparison of Two GaN Transistor Technologies in Broadband Power Amplifiers
- 2010
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In: MICROWAVE JOURNAL. - : Horizon House Publications, Inc.. - 0192-6225. ; 53:4, s. 184-192
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Journal article (peer-reviewed)abstract
- This article compares the performance of two different GaN transistor technologies, GaN HEMT on silicon substrate (PA1) and GaN on SiC (PA2), utilized in two broadband power amplifiers operating at 0.7 to 1.8 GHz. The study explores the broadband power amplifier potential of both GaN HEMT technologies for phased-array radar (PAR) and electronic warfare (EW) systems. The measured maximum output power for PA1 is 42.5 dBm (18 W) with a maximum PAE of 66 percent and a gain of 19.5 dB. The measured maximum output power for PA2 is 40 dBm with a PAE of 37 percent and a power gain slightly above 10 dB. The high power gain, ME, wider bandwidth and unconditional stability was obtained without feedback for the amplifier based on GaN HEMT technology, fabricated on Si substrate.
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| 4. |
- Azam, Sher, 1971-, et al.
(author)
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Comparison of Two GaN TransistorsTechnology in Broadband Power Amplifiers
-
Other publication (other academic/artistic)abstract
- This paper compares the performance of two different GaN technology transistors(GaN HEMT on Silicon substrate (PA1) and GaN on SiC PA2) utilized in two broadbandpower amplifiers at 0.7-1.8 GHz. The study explores the broadband power amplifierpotential of both GaN HEMT technologies for Phased Array Radar (PAR) and electronicswarfare (EW) systems. The measured maximum output power for PA1 is 42.5 dBm(~18 W) with a maximum PAE of 39 % and a gain of 19.5 dB. While the measuredmaximum output power for PA2 is 40 dBm with PAE of 35 % and a power gain slightlyabove 10 dB. We obtained high power, gain, wider band width and unconditionalstability without feedback for amplifier based on GaN HEMT technology fabricated on Sisubstrate.
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| 5. |
- Azam, Sher, et al.
(author)
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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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In: IEEE European Microwave Week, October 10-15, Amsterdam, The Netherlands. ; , s. 444-447
-
Conference paper (peer-reviewed)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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| 6. |
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| 7. |
- Azam, Sher, 1971-, et al.
(author)
-
High Power, High Efficiency SiC Power Amplifier for Phased ArrayRadar and VHF Applications
-
Other publication (other academic/artistic)abstract
- Wide band gap semiconductor (SiC & GaN) based power amplifiers offer severalsystem critical advantages such as less current leakage, better stability at high temperatureand easier impedance matching. This paper describes the design and fabrication of a singlestageclass-AB power amplifier for 30 to 100 MHz using SiC Schottky gate MetalSemiconductor Field Effect Transistor (MESFET). The maximum output power achieved is46.2 dBm (~42 W) at 50 V DC supply voltage at the drain. The maximum power gain is 21dB and a maximum PAE of 62 %. The amplifier performance was also checked at a higherdrain bias of 60 V at 50 MHz. At this bias voltage the maximum output power was 46.7dBm (~47 W) with a power gain of 21 dB and a maximum PAE of 42.7 %. An averageOIP3 of 54 dBm have been achieved for this amplifier.
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| 8. |
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| 9. |
- Azam, Sher, 1971-, et al.
(author)
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High Power, Single Stage SiGaN HEMT Class EPower Amplifier at GHz Frequencies
-
Other publication (other academic/artistic)abstract
- A high power single stage class E power amplifier is implemented with lumped elements at 0.89-1.02GHz using Silicon GaN High Electron Mobility Transistor as an active device. The maximum drain efficiency (DE) and power added efficiency (PAE) of 67 and 65 % respectively is obtained with a maximum output power of 42.2 dBm (~ 17 W) and amaximum power gain of 15 dB. We obtained good results at all measured frequencies.
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| 10. |
- Azam, Sher, 1971-
(author)
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Microwave Power Devices and Amplifiers for Radars and Communication Systems
- 2009
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Doctoral thesis (other academic/artistic)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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| 11. |
- Azam, Sher, 1971-, et al.
(author)
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Performance of SiC Microwave Transistors in Power Amplifiers
- 2008
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In: Proc. of MRS Symposium on wide bandgap semiconductor electronics 8. - 9781605110394 ; , s. 203-208
-
Conference paper (peer-reviewed)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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| 12. |
- Azam, Sher, et al.
(author)
-
Pulse Input Class-C Power Amplifier Response of SiC MESFET using Physical Transistor Structure in TCAD
- 2008
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In: Solid-State Electronics. - : Elsevier BV. - 0038-1101 .- 1879-2405. ; 52:5, s. 740-744
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Journal article (peer-reviewed)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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| 13. |
- Azam, Sher, et al.
(author)
-
Single-stage, High Efficiency, 26-Watt power Amplifier using SiC LE-MESFET
- 2006
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In: Microwave Conference, 2006. APMC 2006. Asia-Pacific December 12-15. ; , s. 441-444
-
Conference paper (peer-reviewed)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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| 14. |
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| 15. |
- Azam, Sher, 1971-
(author)
-
Wide Bandgap Semiconductor (SiC & GaN) Power Amplifiers in Different Classes
- 2008
-
Licentiate thesis (other academic/artistic)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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| 16. |
- Kashif, Ahsan-Ullah, et al.
(author)
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A TCAD approach for non-linear evaluation of microwave power transistor and its experimental verification by LDMOS
- 2010
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In: Journal of Computational Electronics. - : SpringerLink. - 1569-8025 .- 1572-8137. ; 9:2, s. 79-86
-
Journal article (peer-reviewed)abstract
- A simulation technique is developed in TCAD to study the non-linear behavior of RF power transistor. The technique is based on semiconductor transport equations to swot up the overall non-linearity’s occurring in RF power transistor. Computational load-pull simulation technique (CLP) developed in our group, is further extended to study the non-linear effects inside the transistor structure by conventional two-tone RF signals, and initial simulations were done in time domain. The technique is helpful to detect, understand the phenomena and its mechanism which can be resolved and improve the transistor performance. By this technique, the third order intermodulation distortion (IMD3) was observed at different power levels. The technique was successfully implemented on a laterally-diffused field effect transistor (LDMOS). The value of IMD3 obtained is −22 dBc at 1-dB compression point (P 1 dB) while at 10 dB back off the value increases to −36 dBc. Simulation results were experimentally verified by fabricating a power amplifier with the similar LDMOS transistor.
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| 17. |
- Kashif, Ahsan-Ullah, et al.
(author)
-
A TCAD Approach to Design a Broadband Power Amplifier
- 2010
-
Other publication (other academic/artistic)abstract
- Technology Computer Aided Design (TCAD) provides an alternate method to study the power amplifier (PA) design prior to fabrication. It is very useful for the extraction of an accurate large signal model. This paper presents a design approach from device to circuit level to study broadband PA performance of RF-LDMOS using computational load-pull (CLP) analysis. To validate the TCAD approach, we have designed a broadband (1.9 - 2.5 GHz) class AB power amplifier. The concept is verified by designing an output broadband matching network at optimum impedance value (Zf) of RF-LDMOS using ADS software. The large signal results verify this concept and RF output power of 30.8 dBm is achieved with comparable gain and efficiency.
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| 18. |
- Kashif, Ahsan-Ullah, 1974-, et al.
(author)
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Flexible power amplifier designing form device to circuit level by computational load-pull simulation technique
- 2008
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In: Microelectonics Technology and Devices - SBMicro 2008, Vol. 14, issue 1. - Pennington, New Jersey : Electrochemical Society. - 9781566776462 ; , s. 233-239
-
Conference paper (peer-reviewed)abstract
- Matchingnetwork is major issue in broadband power amplifiers due tothe fact that the transistor impedances are varying both withfrequency and signal level. Thus it is difficult to matchthese impedances both at the input and output stages. Thetunable matching networks are very demanding and desired for buildingflexible systems, but their accuracy depends on the transistor performanceunder the large signal operation. Computational load pull (CLP) simulationtechnique is a unique way to extract the impedances ofpower transistor at desired frequencies which make the design ofmatching network much easier for multiple bands power amplifiers. AnLDMOS transistor is studied and its optimum impedances are extractedat 1, 2 and 2.5 GHz. Through optimum impedance, thetunable matching networks can be easily design for broadband amplifiers.
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| 19. |
- Kashif, Ahsan-Ullah, et al.
(author)
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Influence of interface state charges on RF performance of LDMOS transistor
- 2008
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In: Solid-State Electronics. - : Elsevier. - 0038-1101 .- 1879-2405. ; 52:7, s. 1099-1105
-
Journal article (peer-reviewed)abstract
- Si-LDMOS transistor is studied by TCAD simulation for improved RF performance. In LDMOS structure, a low-doped reduced surface field (RESURF) region is used to obtain high breakdown voltage, but it reduces the transistor RF performance due to high on-resistance. The interface charges between oxide and the RESURF region are studied and found to have a strong impact on the transistor performance both in DC and RF. The presence of excess interface state charges at the RESURF region results not only higher DC drain current but also improved RF performance in terms of power, gain and efficiency. The most important achievement is the enhancement of operating frequency and RF output power is obtained well above 1 W/mm up to 4 GHz.
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| 20. |
- Kashif, Ahsan-Ullah, et al.
(author)
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Switching Behavior of Microwave Power Transistor Studied in TCAD for Switching Class Power Amplifiers and Experimental Verification by LDMOS based Class-F Power Amplifier
- 2010
-
Other publication (other academic/artistic)abstract
- This paper presents a TCAD study of high speed switching behavior of RF power-transistor in class-F Power Amplifier. We utilized finite harmonics loads for achieving maximum efficiency, without external circuitry. The in house developed computational load–pull (CLP) simulation technique is further extended to investigate the odd harmonic effects of RF transistor in class-F operation. An LD-MOSFET is studied which provided 81.2 % power added efficiency (PAE) at 1 GHz. The concept is experimentally verified by fabricating a class-F PA using same transistor. In the measurement, 76 % PAE is achieved, which is close to the TCAD simulated results. TCAD is an excellent tool to study the behavior of active devices. It has an ability to enhance and optimize the performance of transistor according to system specifications before fabrication.
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