The development of a reverse-blocking IGBT for use in matrix converters

Power Electronics / Power Management

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10 August 2005 Power Electronics / Power Management

Information from Mitsubishi Electric

Currently, the method most often used to control the frequency of three-phase AC power in equipment for power applications uses inverters. The matrix converter method is currently the focus of attention as an alternative that will eventually replace this inverter method.

Because the switches from which matrix converters are built require reverse-blocking IGBTs which, as their name suggests, can block current in the reverse direction, power devices used for matrix converters have, in the past, been made from IGBTs in series with diodes.

Mitsubishi Electric has developed a reverse-blocking IGBT as a power device for use in matrix converters. As shown in the Figure, the reverse-blocking IGBT surrounds the IGBT cell region by a deep diffusion-isolation P-layer that extends all the way to the back surface, so that the interface between the N-layer and the P-type collector layer on the back surface is not exposed on the dicing surface. As a result, this structure can block a reverse current because the depletion layer extends from the diffusion-isolation P-layer and the P-layer on the back surface to the N-layer when a voltage is applied in the reverse direction.

The current/voltage waveform when a reverse bias is applied to the prototype reverse-blocking IGBT developed in the project is also shown. The horizontal axis shows the collector-emitter voltage (VCES) when the gate is shorted to the emitter, and the vertical axis shows the collector cut-off current (ICES). At 25°C, the reverse-blocking IGBT could block voltages of over 1300 V in the forward direction and over 1500 V in the reverse direction. Even at 125°C, the prototype had a blocking capability of 1200 V, although there was some increase in the leakage current.

The resulting reverse-blocking IGBT has succeeded in matching the performance of third-generation planar IGBTs in terms of the trade-offs between saturation voltage and switching loss, the key characteristics of an IGBT, while still maintaining the withstand voltage in both forward and reverse directions. These characteristics are obtained through the use of fourth-generation planar MOS structure, along with a shallow P collector on the backside using Mitsubishi's proprietary thin-wafer technology. This reverse-blocking IGBT produces the effect of using a diode, and actual use has confirmed the absence of problems with the equivalent diode properties.

The performance achieved by this development gives substantial advantages over that of the conventional structure in which IGBTs are connected in series with diodes. It thus has an important role to play in developing the matrix converters of the future.

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The development of a reverse-blocking IGBT for use in matrix converters

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