V-JFET Transistors for over voltage protection in power device series connected applications

Nowadays, MOSFET and IGBT components are widely used in medium and high power converters. They are subjected to increasing requirements: electrical performances, simple implementation, reliability, integration, smaller volume and price. Moreover, their integration process offers the possibility to reduce and to eliminate the need for pick and place, bonding (wafer-and/or ball-bonding) and other assembly processes necessary in hybrid assemblies, and in the same time to add some useful functionality like sensors for protection and control. This paper presents a possible solution for the monolithic integration of over voltage protection circuits for power MOSFETs or IGBTs. The solution contains a vertical JFET transistor, integrated together, in the same die, with the main switch (MOSFET/IGBT). The specific characteristic of vertical JFET with diffused gates is used to control over voltage and voltage balance among devices associated in series connection. Thanks to voltage threshold control, the voltage protection level can be adjusted under operation. This new feature allows modifying the protection level and smoothness thanks to operating conditions. It allows redistributing voltage balance when one of several units, in the series connection, is out of operation, allowing the operation under failure mode operation. In addition, switching smoothness can also be adjusted thanks to VJFET control sensitivity. The paper presents the power electronic application fields. Then, vertical JFET operation and characteristics will be recalled. It is shown how it can be used for over voltage management. Two solutions are presented. One of them is studied and experimented to highlight the operation principles. Experimental results are provided based on prototypes realized, including a power MOSFET and a V-JFET within the same voltage terminations. Monolithic integration conditions are briefly addressed