AN-7505 Improved IGBTs with Fast Switching Speed And High-Current Capability

Conventional vertical power MOSFETs are limited at hig h voltages (>500V) by the appreciable resistance of their epitaxial drain region. In a new MOS-gate controlled device called an IGBT, this limitation is overcome by modulating the conductivity of th e resistive drain region, thereby reducing the on-resistance of th e device by a factor of at l east 10. However, the device previously described is slow in turnoff, having a fall time in the range 8 to 40μs. The purpose of our present work has been to reduce the fall time significantly and to increase the latching current level of the IGBTs, while retaining its desirable features. By modification of the epitaxial structure and addition of recombination centers, we have achieved fall times as low as 0.1μs and latching currents as high as 50A, while retaining on-resistance values <0.2Ω for a 0.09cm2 chip area. The techniques used for the introduction of recombination centers include electron, gamma-ray, and neutron irradiation, as well as heavy metal doping. For a series of IGBTs (with forward-blocking voltage capabilities of 400-600V), the fall time can be reduced by more than one order of magnitude with a penalty of les s than a 20 % increase in on-resistance.