Powering Reliability - Ensuring Automotive Quality beyond AEC Q100/101

Transportation represents today about a quarter of the worldwide CO₂ emissions. Rising fuel prices and increased emission regulations are stimulating advanced technologies like Piezo direct injection and the development of alternate propulsion systems. The worldwide demand for hybrid-electric vehicles (HEVs) is forecasted to advance at a rapid pace. They could reach more than five million units in 2013 representing about 6% of the world's light vehicle demand. In the last 13 years the electronic content of a car increased by 255%. The electrification of the power train is one of the most challenging objectives in the development of next generation cars and will fuel an even accelerated this growth of power electronics.

In industrial motor drives, IGBTs are switches of choice for drive inverters and with hybridization coming, IGBTs will soon conquer the automotive power train market as well. The IGBT is a MOS-gate controlled power switch. Cell structure and manufacturing processes are very similar to a MOSFET. A MOS-gated Channel is connecting two n(+)-type regions, which are embedded in adjacent p-wells in a n-type epi layer, which was grown on a P-type wafer. This is the structure of a classical punch-through (PT) IGBT as invented about 25 years ago by Frank Wheatley. Fig.1 shows the basic structure and the equivalent circuit of an IGBT. Starting with n-type float zone material and adding an p(+) implant after top side processing and wafer thinning results in a so called non-punch-thru (NPT) IGBT.

Figure 1: IGBT Cross-Section Equivalent Circuit

For both, PT and NPT IGBTs, this additional P+ layer is the major, but significant difference to a MOSFET structure, since it allows hole injection into the high resistance n-epi-layer leading to high conductivity in that area, very similar to the characteristic of a bipolar transistor. As a result, the IGBT combines the high impedance gate and the high switching speed of a MOSFET with the low conduction loss of a bipolar junction transistor (BJT). Combining a small die area and gate charge with low on-state losses, IGBTs soon began dominating the power supply and drive market. However, due to the high current density, special care is needed to set gate drive parameters accordingly especially for turn off under high current conditions. This happens also in self clamped applications like in automotive ignition.