As shown in Fig. 3-15 (a), the vertical design of the IGBT has been evolving.
Starting from the PT structure, thin PT (generally called “Field Stop”) structure is becoming mainstream as thin wafers are now used. (Gate structure is the same as MOSFET.)
VCE(sat) characteristic of PT type has a current value (called “Q point”) that crosses at high temperature and at room temperature.
Since the high-temperature VCE(sat) is always high in the NPT type (like MOSFET), it is easier to balance the collector current even when operating in parallel.
Note: VCE(sat)characteristic - voltage drop when collector current flows in forward direction.