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Semiconductor History | DENSO Hirose — The Prius IGBT Survives the Heat
· 1997-10
Personal memoryBy kevin · · updated · Report an issue
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Semiconductor History | DENSO Hirose — The Prius IGBT Survives the Heat
kevin
Oct, 1997
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In October 1997, Toyota began mass production at Hirose of the planar insulated-gate bipolar transistor used in the first Prius. DENSO now traces its own power-device expertise to that project at the site, then a Toyota factory and today DENSO’s Hirose Plant.
The IGBT sat inside the inverter between the battery and traction motor. It had to switch large currents quickly enough to control the motor, yet lose little enough energy that heat did not erase the hybrid system’s fuel-saving advantage.
Toyota’s development history records how unforgiving that problem was. Bench tests ended in repeated overheating and explosions, while the production device needed both faster switching and enough breakdown endurance to survive beside an engine and through years of vibration, temperature swings, and electrical stress.
The good was the short distance between layers of the system. Toyota had decided in 1984 to learn automotive electronics internally rather than accept critical technology as a supplier’s black box; it signed a broad semiconductor technology agreement with Toshiba in 1987, completed the Hirose semiconductor factory in 1989, and drew training and engineering help from Nippondenso and Toyota Central R&D Labs.
That accumulated knowledge let device, cooling, inverter, motor, vehicle-control, production, and test engineers trade problems across boundaries. The Prius was unveiled on October 14 and went on sale on December 10, turning a difficult power transistor into part of a product that ordinary drivers could buy.
The bad was the cost of owning every hard problem. Internal chip production required a cleanroom, process control, yield learning, specialized packaging, long automotive qualification, and responsibility for failures that could stop the vehicle; better switching also raised the thermal and reliability demands placed on cooling and the module around the die.
The site’s later history shows that “in-house” never means organizationally fixed. Toyota transferred Hirose to DENSO in April 2020 as the two companies consolidated electronic-component operations, and DENSO now lists the plant as a producer of inverters, ECUs, and power semiconductors.
The cover exposes the wire bonds, bus bars, dies, and insulating structure inside a generic IGBT module. It is not a Prius module or a DENSO product, but it shows the packaging problem that had to survive after the silicon worked.
Sources: Toyota Motor Corporation 75-Year History, “In-house production of electronic components and semiconductors at Hirose Plant” and electronics chronology; Toyota, “The Story Behind the Birth of the Prius, Part 2”; DENSO, “Supporting the Electric Vehicle Revolution: Next-Generation SiC Semiconductor Chip Development” and Japan global-network profile.
Photo: “IGBT 2441,” Daniel*D, CC BY-SA 3.0, via Wikimedia Commons.
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