Littelfuse, Inc.
IGBT with waved floating P-Well electron injection

Abstract:

An IGBT includes a floating P well and a floating N+ well that extends down into the floating P well. A bottom surface of the floating P well has a waved contour with thinner portions and thicker portions. When the device is on, electrons flow laterally from an N+ emitter and through a channel region. Some electrons pass downward, but others pass laterally through the floating N+ well to one of the thinner portions of the floating P type well. The electrons then pass down from the thinner portions into the N- drift layer. Other electrons pass farther through the floating N+ well to subsequent, thinner electron injector portions of the floating P type well and then into the N- drift layer. The extra electron injection afforded by the waved floating well structure reduces V.sub.CE(SAT). The waved contour is made without adding any masking step to the IGBT manufacturing process.