Insulated-gate bipolar transistor

The Insulated Gate Bipolar Transistor (IGBT) emerged from B. Jayant Baliga's work at General Electric in 1979 as a hybrid power semiconductor that combined the easy control of a MOSFET with the high current capacity of a bipolar transistor. Baliga conceived the idea and filed for a patent on August 28, 1979, and demonstrated practical devices in 1982. The IGBT became the enabling technology for modern power electronics—from electric vehicles to renewable energy inverters to high-speed trains.

The adjacent possible for the IGBT opened through a fundamental limitation of existing power transistors. Bipolar transistors could handle high currents but required significant base drive current to control. MOSFETs could be controlled with minimal current (voltage-driven gates) but couldn't handle the high currents needed for power applications. Thyristors—the dominant power switches of the 1970s—had limited controllability. Baliga asked: could you combine the gate drive simplicity of a MOSFET with the current-carrying capability of a bipolar transistor?

The solution was elegant: use a MOSFET structure to inject minority carriers into a p-n-p bipolar transistor. The gate voltage controlled the MOSFET, which in turn modulated the bipolar transistor's current. A GE Process Ticket dated November 1978 shows Baliga's device development beginning, with reduction to practice completed by July 1979. His paper in Electronics Letters on September 27, 1979 described 'Enhancement and Depletion Mode Vertical Channel MOS Gated Thyristors'—documenting the IGBT mode of operation.

Convergent emergence characterized IGBT development. Hans W. Becke and Carl F. Wheatley at RCA were designing a similar device, filing a patent in March 1980. The parallel development reflected how the need for controllable high-power switches created pressure for innovation at multiple companies simultaneously. The resulting priority dispute between Baliga and the RCA team continues to generate debate.

General Electric commercialized Baliga's IGBT in 1982 after he demonstrated practical discrete devices at the IEEE International Electron Devices Meeting. The cascade from the IGBT was transformative. Electric locomotives and high-speed trains adopted IGBT-based drive systems. Variable-frequency drives for industrial motors became practical. Solar inverters and wind turbine power converters used IGBTs to convert DC to grid-compatible AC. Electric vehicles—from the Toyota Prius to Teslas—depended on IGBT inverters to drive their motors.

Baliga was inducted into the National Inventors Hall of Fame and won the Millennium Technology Prize in September 2024—Finland's €1 million award recognizing the IGBT's role in enabling efficient power conversion. The device conceived in 1979 at GE's Schenectady labs had become essential infrastructure for the electrification of transportation and the renewable energy transition.