Diamond Schottky diodes interactions in power electronics application
Résumé
Since several years, the power electronics community shows a growing interest for wide band gap semiconductors to design power converters with higher performances. Considering the wide band gap materials physical properties (Silicon Carbide, Gallium Nitride and diamond), diamond seems to be the best candidate for power electronics applications, especially at high temperatures. Recent progresses have been done on diamond power devices leading to devices with promising electrical performances [1], [2]. Regarding to the actual electrical performances of all diamond semiconductors, Schottky diodes are the closest diamond device for integration in industrial power converters, this study is focused on diamond Schottky diodes integration.
Today, most of diamond Schottky devices are composed of several small area Schottky contacts (separated cathodes) with a common ohmic contact (common anode) [3]. However, to design usual power converter based on diamond devices, diamond Schottky diodes have to be associated at the device level to increase the effective device current. In this work, it is shown that due to the device structure, a common impedance is shared between the diodes. A diode current is spread in the p+ layer between the Schottky contact and the Ohmic contact, then two diodes share a current path involving the common impedance. A special care is then needed in the way to separately use some diodes of such a diamond device depending to the required application.
To highlight this phenomenon, a 3D device model is done to quantify this current spreading and impedance sharing. Moreover, different issues of this phenomenon for device integration are presented as examples. First, two kinds of diodes association in a power converter are presented, illustrating the impact of such impedance on the diodes operation. Each converter is designed for a 200 V DC bus voltage, the current per diode can be set up to 300 mA (750 A/cm²). A converter using diode parallelization and a multiphase converter are then compared in this way. Second, a small diode of the device is used as a thermosensitive parameter to have online temperature information when others diodes of the device are used for power conversion, it is shown that this diode temperature sensor is affected by the others diodes due to this shared impedance. Finally, a novel diode device architecture (simulations and experiments) is presented in the way to decouple the current path of diodes by using electrical isolation. This kind of architecture can be used for each application requiring one or some diodes isolated from the other ones. This method can also be used for transistors device designs.