| 1. |
- Bertilsson, Kent, et al.
(författare)
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Calculation of lattice heating in SiC RF power devices
- 2004
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Ingår i: Solid-State Electronics. - : Elsevier BV. - 0038-1101 .- 1879-2405. ; 48:12, s. 1721-1725
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Tidskriftsartikel (refereegranskat)abstract
- Silicon carbide MESFET devices are suitable for high-speed and high-power applications. In this paper we are studying thermal effects in 4H-SiC RF power devices. The simulations are based on a combination of 2D device simulations for the electrical transport, and 3D thermal simulations for the lattice heating. We show that the method gives good accuracy, efficiency, flexibility and capacity dealing with tasks, where a 2D coupled electrical-thermal simulation is not sufficient. We also present an improvement of Roschke and Schwierz mobility model, based on Monte Carlo simulations for the temperature dependencies of the mobility parameters beta and v(sat).
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| 2. |
- Bertilsson, Kent, et al.
(författare)
-
Monte Carlo simulation of vertical MESFETs in 2H, 4H and 6H-SiC
- 2001
-
Ingår i: Diamond and related materials. - 0925-9635 .- 1879-0062. ; 10:3-7, s. 1283-1286
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Tidskriftsartikel (refereegranskat)abstract
- The 4H-SiC static induction transistor (SIT) is a very competitive device for high frequency and high power applications (3-6 GHz range). The large breakdown voltage and the high thermal conductivity of 4H-SiC allow transistors with extremely high current density at high voltages. The SIT transistor shows better output power capabilities but the unity current-gain frequency is lower compared to a MESFET device. In this work we show, using a very accurate numerical model, that a compromise between the features given by the SIT structure and the ordinary MESFET structure can be obtained using the vertical MESFET structure. The device dimension has been selected very aggressively to demonstrate the performance of an optimized technology. We also present results from drift-diffusion simulations of devices, using transport parameters obtained from the Monte Carlo simulation. The simulations indicate that 2H-SiC is superior to both 4H and 6H-SiC for vertical devices. For lateral devices, 2H-SiC is slightly faster compared to an identical 4H-SiC device
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| 3. |
- Bertilsson, Kent, et al.
(författare)
-
Optimization of 2H, 4H and 6H-SiC high-speed vertical MESFETs
- 2002
-
Ingår i: Diamond and related materials. - 0925-9635 .- 1879-0062. ; 11:3-6, s. 1254-1257
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Tidskriftsartikel (refereegranskat)abstract
- Silicon carbide vertical MESFET devices are well suited for high speed and high power electronic devices. In this work we have optimized the geometry of vertical MESFETs for microwave applications, using iterative two-dimensional simulations. Relevant parasitics are included in the simulations to investigate the performance of realistic devices. The state of the art device has f(T)=7 GHz and we show that vertical MESFETs fabricated with traditional technology are totally limited by parasitics. Two different approaches to reduce the parasitics in the vertical MESFET are proposed where f(T) increases significantly.
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| 4. |
- Bertilsson, Kent, et al.
(författare)
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Optimization of 2H, 4H and 6H-SiC MESFETs for High Frequency Applications
- 2002
-
Ingår i: Physica Scripta. - 0031-8949 .- 1402-4896. ; 101, s. 75-77
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Tidskriftsartikel (refereegranskat)abstract
- Silicon carbide MESFET devices are well suited for high speed, high power and high temperature electronics due to high saturation velocity, high critical electrical field, good thermal conductivity and large band-gap. Optimization of a high performance device demands a substantial number of numerical simulations, where several different design parameters have to be investigated thoroughly. In this work, we optimize the geometry of lateral MESFETs for maximal unity current-gain frequency (fT) using iterative 2-dimensional simulations. We also present a comparison of performance for individually optimized devices, realized with lithographic resolutions ranging from 0.2 to 2 μm in different SiC polytypes.
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| 5. |
- Bertilsson, Kent, 1973-
(författare)
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Simulation and Optimization of SiC Field Effect Transistors
- 2004
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Silicon Carbide (SiC) is a wide band-gap semiconductor material with excel-lent material properties for high frequency, high power and high temperature elec-tronics. In this work different SiC field-effect transistors have been studied using theoretical methods, with the focus on both the devices and the methods used. The rapid miniaturization of commercial devices demands better physical models than the drift-diffusion and hydrodynamic models most commonly used at present. The Monte Carlo method is the most accurate physical methods available and has been used in this work to study the performance in short-channel SiC field-effect devices. The drawback of the Monte-Carlo method is the computational power required and it is thus not well suited for device design where the layout requires to be optimized for best device performance. One approach to reduce the simulation time in the Monte Carlo method is to use a time-domain drift-diffusion model in contact and bulk regions of the device. In this work, a time-domain drift-diffusion model is implemented and verified against commercial tools and would be suitable for inclusion in the Monte-Carlo device simulator framework. Device optimization is traditionally performed by hand, changing device pa-rameters until sufficient performance is achieved. This is very time consuming work without any guarantee of achieving an optimal layout. In this work a tool is developed, which automatically changes device layout until optimal device per-formance is achieved. Device optimization requires hundreds of device simulations and thus it is essential that computationally efficient methods are used. One impor-tant physical process for RF power devices is self heating. Self heating can be fairly accurately modeled in two dimensions but this will greatly reduce the computa-tional speed. For realistic influence self heating must be studied in three dimensions and a method is developed using a combination of 2D electrical and 3D thermal simulations. The accuracy is much improved by using the proposed method in comparison to a 2D coupled electro/thermal simulation and at the same time offers greater efficiency. Linearity is another very important issue for RF power devices for telecommunication applications. A method to predict the linearity is imple-mented using nonlinear circuit simulation of the active device and neighboring passive elements.
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| 6. |
- Bertilsson, Kent, et al.
(författare)
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Simulation of a low atmospheric-noise modified four-quadrant position sensitive detector
- 2001
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Ingår i: Nuclear Instruments and Methods in Physics Research Section A. - 0168-9002 .- 1872-9576. ; 466:1, s. 183-187
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Tidskriftsartikel (refereegranskat)abstract
- A modified four-quadrant position sensitive detector (PSD) is developed. This structure is less sensitive to atmospheric turbulence that is a major drawback with the traditional four-quadrant detector. The inter-electrode resistance is as high as for the four-quadrant detector, which is an advantage compared to the lateral effect PSD. The linearity for the modified four-quadrant detector is good in the whole active range of sensing. The structures are limited to small sensing areas with well focused beams and are suitable for use in detectors up to 1 mm in size.
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| 7. |
- Bertilsson, Kent, et al.
(författare)
-
Simulation of anisotropic Breakdown in 4H-SiC Diodes
- 2000
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Ingår i: IEEE Workshop on Computers in Power Electronics. - : IEEE. ; , s. 118-120
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Konferensbidrag (refereegranskat)abstract
- The breakdown characteristics of two-dimensional 4H-SiC diode structures have been studied using an anisotropic drift-diffusion model. The degree of anisotropy was estimated from recent full band Monte Carlo simulations. Identical diode structures have previously been used in the literature to measure the hole impact ionization coefficients of 4H-SiC. The reported measurements from different research groups show large differences in the impact ionization coefficients. Our numerical simulations show that the differences in these measurements can be explained by the difference in device geometry used by the research teams if one considers an anisotropic impact ionization process. This indicates that it is very important to consider anisotropic impact ionization in design and characterization of 4H-SiC power devices.
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| 8. |
- Bertilsson, Kent, et al.
(författare)
-
The Effect of Different Transport Models in Simulation of High Frequency 4H-SiC and 6H-SiC Vertical MESFETs
- 2001
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Ingår i: Solid-State Electronics. - 0038-1101 .- 1879-2405. ; 45:5, s. 645-653
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Tidskriftsartikel (refereegranskat)abstract
- A full band Monte Carlo (MC) study of the high frequency performance of a 4H-SiC Short channel vertical MESFET is presented. The MC model used is based on data from a full potential band structure calculation using the local density approximation to the density functional theory. The MC results have been compared with simulations using state of the art drift-diffusion and hydrodynamic transport models. Transport parameters such as mobility, saturation velocity and energy relaxation time are extracted from MC simulations
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| 9. |
- Bertilsson, Kent, et al.
(författare)
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The power of using automatic device optimization, based on iterative device simulation, in design of high-performance devices
- 2004
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Ingår i: Solid-State Electronics. - : Elsevier BV. - 0038-1101 .- 1879-2405. ; 48:10-11, s. 1721-1725
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Tidskriftsartikel (refereegranskat)abstract
- An automatic optimization tool for semiconductor devices based on iterative device simulations is developed. The tool is used for optimization of different kinds of semiconductor devices using various performance measures. High performance optimization algorithms, both local and global, are used to achieve an efficient design in shortest possible time. In this paper the effects of different optimization algorithms, performance measures, and number of variables in the optimization are studied. Both the computational efficiency and the devices achieved with different performance measures are studied. We give a demonstration of the usefulness of this method in a comparison between different device topologies, which have been optimized for best performance.
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| 10. |
- Bertilsson, Kent, et al.
(författare)
-
The power of using automatic device optimization, based on iterative device simulations, in design of high-performance devices
- 2003
-
Ingår i: 2003 International Semiconductor Device Research Symposium, ISDRS 2003 - Proceedings. - 0780381394 - 9780780381391 ; , s. 152-153
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Konferensbidrag (refereegranskat)abstract
- Device design is a time consuming work, where the influence of many design parameters has to be investigated carefully. In advanced devices optimal performance is often achieved taking multiple trade-off into consideration, and manual device optimization is often insufficient. In this paper we present the feasibility of using device optimization for design on electronic devices. An optimization tool is developed, which runs device simulations and automatically changes the design parameters, searching for optimal performance according to a specified performance measure. This has been shown to be a very time and cost efficient way for device design, as the search for optimal performance is fuily automatic working in a systematic way 24 hours 7 days a week. From an industrial point of view this is very important as it can reduce the evaluation and optimization cost for new devices considerably. It is impossible to give a fair comparison between different devices unless these are designed to give optimal performance. We give a demonstration of the usefulness of this method in a comparison between different device topologies which individually have been optimized for best performance.
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