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Title: Advanced trench gated power semiconductor devices
Author: Spulber, Oana
Awarding Body: De Montfort University
Current Institution: De Montfort University
Date of Award: 2003
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The drive towards the rational use of energy demands fast, reliable, efficient and low-cost power switches. Since its development in the mid-eighties, the Insulated Gate Bipolar Transistor (IGBT) has become the most commonly used device in medium power semiconductor market, replacing the bipolar transistor at its lower end, and currently competing with the Integrated-Gate Commu­tated Thyristor (IGCT) to replace the Gate Tum-Off thyristor (GTO) in applications up to 6.SkV. This is due to its attractive features, such as voltage gate control, reduced static and switching losses, wide safe operating area, ruggedness and easy manufacturing process. However, at high voltage ratings, the IGBT performance is limited by its high conduction losses. To overcome this problem several solutions have been proposed, such as a trench geometry for the gate and various anode engineering methods. Although the Trench IGBT shows a significantly lower forward drop than the planar gate version, its switching losses are large due to the high stored charge. Several MOS-gated thyristors have also been proposed, but they could not be developed at an industrial level, primarily due to reduced current control at high anode current densities. The present research analyses a new gate geometry for the IGBT, which combines the advan­tages of both planar and trench gate structures. It is demonstrated that the new device represents a better trade-off between the planar and trench IGBT, both in terms of static and dynamic performance. To improve the switching losses of the new device even further:, yet another novel approach to the gate design is evaluated. An important issue of the Emitter Switched Thyristor (EST) is represented by its reduced forward biased safe operating area (FBSOA). By reducing the doping of the N+ floating emitter, it is demonstrated that the FBSOA of the Trench EST can be improved without degrading its on­state losses. Moreover, it is shown that, by disconnecting the bottom P base from the top P base, and leaving the bottom P region floating, the device can be turned on without a snap-back. Furthermore, the present work demonstrates a new trench gate geometry for the Clustered Insulated Gate Bipolar Transistor (CIGBT). The CIGBT is a novel MOS-gated thyristor which can achieve current saturation even at high gate voltages, thus solving the main problem of the EST and the other thyristor-based structures. The trench gated version of this structure shows on­state losses lower by 25% and tum-off losses lower by 28% than the TIGBT under identical circuit conditions. It also eliminates the reliability problems related to the trench manufacture, promising to become a viable alternative to the current power devices.
Supervisor: Not available Sponsor: Microserv Project (European Union)
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available