EPE Association: EPE 2003 - Topic 01g: New Devices

EPE 2003 - Topic 01g: New Devices
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   Transient behaviour of high voltage bipolar SiC-diodes
By W. Bartsch; H. Mitlehner; R. Schoerner; K. Dohnke; B. Thomas; R. Stein; D. Stephani [View]
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Abstract: This work presents a comparison of the switching behaviour of paralleled bipolar SiC diodes with emitters fabricated by epitaxy as well as by Aluminium implantation. The turn-off behaviour of these devices will be discussed with respect to different DC link voltages at several junction temperatures, rates of current decay and snappy behaviour.

   Serial connection of SiC VJFETs - features of a fast high voltage switch
By R. Elpelt; P. Friedrichs; R. Schörner; K.-O. Dohnke; H. Mitlehner; D. Stephani [View]
[Download]

Abstract: We present a high voltage stacked switch (up to 8 kV / 10A), based on the serial connection of vertical Silicon Carbide (SiC) junction field eect transistors (VJFETs) together with a standard power MOSFET in a cascode-like circuit. After introduction and discussion of the basic principles a careful analysis of the static characteristics as well as the dynamical switching behavior is conducted by means of experimental measurements together with two-dimensional device simulation. The presented stacked switch can, in principle, be extended to any desired blocking voltage. The current capability depends largely on the cooling eorts and the active SiC area used in each stage of the stack. The dynamic performance of the switch also yields a very fast switching ability. Thus unipolar SiC switches become feasible, exhibiting good on-state performance with blocking voltages exceeding 4 kV and switching frequencies well above 10 kHz.

   State of the art and technological challenges of SiC power MOSFETs designed for high blocking voltages
By D. Peters; H. Mitlehner; R. Elpelt; R. Schörner; D. Stephani [View]
[Download]

Abstract: Normally-off n-type inversion channel mode SiC-MOSFETs blocking voltages between 1200 V and 3000 V are presented and discussed. The on-resistance of a 3kV blocking device with 1.45 mm2 active area amounts to 3 W at room temperature, corresponding to a specific on-resistance of 45 mWcm2. This value is taken at 20V gate source voltage corresponding to an electrical field strength in the gate oxide of 2.6 MV/cm. The 4H SiC MOSFET utilizes a 76 nm thick thermal grown gate oxide and a polycrystalline silicon gate electrode. This oxide thickness provides a significantly improved reliability as demonstrated in first reliability tests of 1200V. The temperature coefficient of the onresistance is positive and allows easy paralleling of these devices. At a drain current of 1 A in on-state the drain source voltage rises from 3.8 V at 25°C to 5.2 V at a junction temperature of 150°C. The inversion channel mobility could be improved to 10 cm2 /Vs at room temperature. For this case the channel resistance still dominates the overall on-resistance but decreases with temperature. At 150 °C the channel contributes 20% to the on-resistance. In contrast to high voltage silicon MOSFETs the reverse diode of the SiC MOSFET exhibits excellent switching behavior and might be used as the free wheeling diode.

   Analysis of effects of the coaxial transformer design on distribution of winding currents and flux density
By B. Grzesik; M. Stêpieñ [View]
[Download]

Abstract: The novel construction of the modular concentric transformer for power electronics is described and analyzed in the paper. Proposed design of the transformer is dedicated for high frequency (the best results are in the range of 500 kHz to 3 MHz). The transformer has two windings made of concentrically arranged, thin-walled pipes, formed as a multi-turn spiral and put into magnetic core. The primary (inner) turns are connected in series and secondary (outer) ones are connected in parallel. The transformer described in the paper has turn-to-turn ratio 2:1, but in general the turn ratio can be different. The transformer is of high efficiency (above 98%) and very high ratio of windings coupling (about 0.998). High power density (above 100 kW/kg) for output power about 5 kW is its additional advantage. The paper is focused on influence of the shape and arrangement of the windings and magnetic core on the transformer properties. The results of analysis (efficiency, output power and power density) determine optimal design of transformer with respect of relevant transformer parameters. The analysis is based on FEM and is carried out using ANSYS software. The selected results of FEM analysis (in particular parameters of the equivalent circuit of the transformer) are compared with the results of the laboratory measurements.

   STIL implementation in fly-back and PFC converters
By B. Peron [View]
[Download]

Abstract: For a long time, power supply designers of the off-line converters have thought about new concepts such as the synchronous rectification, resonant topologies and other solutions to improve the capability of power converters. All these solutions come, after the AC rectification stage, and most often, no new concepts and no new components have been developed for the front-end stage. The major problems, in this part of the converter, are the low frequency harmonic currents and the inrush current due to the charging of the bulk capacitor. The Power Factor Corrector (PFC) introduced few years ago, allows the first problem to be improved while resistive impedance (stand-alone resistor, NTC) shorted by a power switch (SCR, a TRIAC or a relay) allows the peak current at the start-up to be reduced. However, all these common solutions used to limit the inrush current do not satisfy all the expectations of power supply. In addition to the limitation of the inrush current magnitude, the perfect solution should include: - No degradation of power efficiency in the steady state, - No degradation of the power density of the converter, - Compatibility with the EMC test corresponding to lightning induced surges (contribute to MTBF) [1], - Fast response to AC line brownouts [2]. Based on the ASD™ technology [3], STMicroelectronics now proposes a new component used in a Half Controlled Rectifiers Bridge (HCRB) configuration. The new device, called the STIL, has been designed to satisfy the criteria listed above. This paper describes how to get the most of the STIL devices when it is used in PFC and fly-back converters and, it highlights all the benefits of this solution in the off-line converter design.

EPE 2003 - Topic 01g: New Devices
You are here: EPE Documents > 01 - EPE & EPE ECCE Conference Proceedings > EPE 2003 - Conference > EPE 2003 - Topic 01: DEVICES > EPE 2003 - Topic 01g: New Devices
	[return to parent folder]

	Transient behaviour of high voltage bipolar SiC-diodes By W. Bartsch; H. Mitlehner; R. Schoerner; K. Dohnke; B. Thomas; R. Stein; D. Stephani	[View] [Download]
Abstract: This work presents a comparison of the switching behaviour of paralleled bipolar SiC diodes with emitters fabricated by epitaxy as well as by Aluminium implantation. The turn-off behaviour of these devices will be discussed with respect to different DC link voltages at several junction temperatures, rates of current decay and snappy behaviour.

	Serial connection of SiC VJFETs - features of a fast high voltage switch By R. Elpelt; P. Friedrichs; R. Schörner; K.-O. Dohnke; H. Mitlehner; D. Stephani	[View] [Download]
Abstract: We present a high voltage stacked switch (up to 8 kV / 10A), based on the serial connection of vertical Silicon Carbide (SiC) junction field eect transistors (VJFETs) together with a standard power MOSFET in a cascode-like circuit. After introduction and discussion of the basic principles a careful analysis of the static characteristics as well as the dynamical switching behavior is conducted by means of experimental measurements together with two-dimensional device simulation. The presented stacked switch can, in principle, be extended to any desired blocking voltage. The current capability depends largely on the cooling eorts and the active SiC area used in each stage of the stack. The dynamic performance of the switch also yields a very fast switching ability. Thus unipolar SiC switches become feasible, exhibiting good on-state performance with blocking voltages exceeding 4 kV and switching frequencies well above 10 kHz.

	State of the art and technological challenges of SiC power MOSFETs designed for high blocking voltages By D. Peters; H. Mitlehner; R. Elpelt; R. Schörner; D. Stephani	[View] [Download]
Abstract: Normally-off n-type inversion channel mode SiC-MOSFETs blocking voltages between 1200 V and 3000 V are presented and discussed. The on-resistance of a 3kV blocking device with 1.45 mm2 active area amounts to 3 W at room temperature, corresponding to a specific on-resistance of 45 mWcm2. This value is taken at 20V gate source voltage corresponding to an electrical field strength in the gate oxide of 2.6 MV/cm. The 4H SiC MOSFET utilizes a 76 nm thick thermal grown gate oxide and a polycrystalline silicon gate electrode. This oxide thickness provides a significantly improved reliability as demonstrated in first reliability tests of 1200V. The temperature coefficient of the onresistance is positive and allows easy paralleling of these devices. At a drain current of 1 A in on-state the drain source voltage rises from 3.8 V at 25°C to 5.2 V at a junction temperature of 150°C. The inversion channel mobility could be improved to 10 cm2 /Vs at room temperature. For this case the channel resistance still dominates the overall on-resistance but decreases with temperature. At 150 °C the channel contributes 20% to the on-resistance. In contrast to high voltage silicon MOSFETs the reverse diode of the SiC MOSFET exhibits excellent switching behavior and might be used as the free wheeling diode.

	Analysis of effects of the coaxial transformer design on distribution of winding currents and flux density By B. Grzesik; M. Stêpieñ	[View] [Download]
Abstract: The novel construction of the modular concentric transformer for power electronics is described and analyzed in the paper. Proposed design of the transformer is dedicated for high frequency (the best results are in the range of 500 kHz to 3 MHz). The transformer has two windings made of concentrically arranged, thin-walled pipes, formed as a multi-turn spiral and put into magnetic core. The primary (inner) turns are connected in series and secondary (outer) ones are connected in parallel. The transformer described in the paper has turn-to-turn ratio 2:1, but in general the turn ratio can be different. The transformer is of high efficiency (above 98%) and very high ratio of windings coupling (about 0.998). High power density (above 100 kW/kg) for output power about 5 kW is its additional advantage. The paper is focused on influence of the shape and arrangement of the windings and magnetic core on the transformer properties. The results of analysis (efficiency, output power and power density) determine optimal design of transformer with respect of relevant transformer parameters. The analysis is based on FEM and is carried out using ANSYS software. The selected results of FEM analysis (in particular parameters of the equivalent circuit of the transformer) are compared with the results of the laboratory measurements.

	STIL implementation in fly-back and PFC converters By B. Peron	[View] [Download]
Abstract: For a long time, power supply designers of the off-line converters have thought about new concepts such as the synchronous rectification, resonant topologies and other solutions to improve the capability of power converters. All these solutions come, after the AC rectification stage, and most often, no new concepts and no new components have been developed for the front-end stage. The major problems, in this part of the converter, are the low frequency harmonic currents and the inrush current due to the charging of the bulk capacitor. The Power Factor Corrector (PFC) introduced few years ago, allows the first problem to be improved while resistive impedance (stand-alone resistor, NTC) shorted by a power switch (SCR, a TRIAC or a relay) allows the peak current at the start-up to be reduced. However, all these common solutions used to limit the inrush current do not satisfy all the expectations of power supply. In addition to the limitation of the inrush current magnitude, the perfect solution should include: - No degradation of power efficiency in the steady state, - No degradation of the power density of the converter, - Compatibility with the EMC test corresponding to lightning induced surges (contribute to MTBF) [1], - Fast response to AC line brownouts [2]. Based on the ASD™ technology [3], STMicroelectronics now proposes a new component used in a Half Controlled Rectifiers Bridge (HCRB) configuration. The new device, called the STIL, has been designed to satisfy the criteria listed above. This paper describes how to get the most of the STIL devices when it is used in PFC and fly-back converters and, it highlights all the benefits of this solution in the off-line converter design.