Gen 3 SiC Devices with Increased Performance and Additional Robustness

Robert Bosch GmbH is the largest Tier 1 supplier in the automotive industry. In addition to manufacturing the subsystems that go into vehicles, the company also makes many of the components it uses in those subsystems through its subsidiaries. One of those subsidiaries is Bosch Semiconductor. For over 60 years, Bosch Semiconductor has been developing MEMS, automotive ICs, and power semiconductors, the majority of which are intended for the automotive industry. PCIM provided the platform for the company to show off its latest Gen 3 SiC MOSFETs, and Ralf Bornefeld, Senior Vice President and Executive Advisor Semiconductors at Robert Bosch took some time out at the exhibition to talk to PSD about the details behind the launch.

Initially, he talked about the company’s roadmap. It plans on delivering a new generation of products every two years, and has only missed out on that target once, to move from a 150mm to a 200mm process between Gen 2 and Gen 3, which Bornefeld describes as taking the same effort as the development of a new generation of products. Gen 3 is scheduled to ramp up early in 2027, with Gen 4 and Gen 5 coming online in 2029 and 2031 respectively.

As for the Gen 3 design itself, Bosch has decided to focus exclusively on trench designs. Bornefeld explains, “We started with trench and we never went planar. Trench technology is better than planar for the individual tuning of devices for performance and robustness. At 3000V and over, the advantages of planar become more competitive, but that is a market that we are not competing in at present. Bosch originally developed trench etching technology in silicon in the mid 1990s. The deep reactive iron etching process is even called the Bosch process in the industry, and it allows us to etch very steep walls with a high aspect ratio. We then used that 20 years of experience to adapt the deep reactive iron etching technology to silicon carbide, which is a much harder material. That is important, as the more perfect the trench etching is, the easier it is to achieve perfect trench gate oxide making the product robust and reliable.”

The company believes in an evolutionary development of each generation, meaning that it only adds a single design element to each new generation, building those advances onto each other until it approaches the unipolar limit, which is a material-based limit where it is no longer possible to scale down the on-resistance of the device. Other companies have used superjunction technology for the drift zone, but up to Gen 4, Bosch will not incorporate it, as Bornefeld says the company have enough ideas to approach the unipolar limit without it. He adds that the technology is more complex to manufacture, and it changes the switching behavior of the device, as the charge in the drift zone is arranged differently, which requires a different control algorithm and customer training and education. Instead, he believes the company’s evolutionary approach brings a real benefit to customers, as the generational change is not so critical, with the general behavior of the device remaining the same, lowering the risks for customers migrating to the next generation. However, he does add that after Gen 4, the company may have to look at superjunction technology for further gains, but by then, customers will be more familiar with how to handle superjunction devices.

As for Gen 3, the new design element is a bubble implanted at the bottom of the trench before it is filled with gate oxide and isolation material. The bubble provides an increase in performance without compromising robustness. For example, in an inverter application, the short circuit withstand time would be increased, while a planar device with similar performance would have a reduced time. In practice, this means that Gen 3 devices provide a 20% reduction in specific on-resistance, around 10% higher short-circuit withstand capability, and a 40% thinner die.

Bornefeld ends by saying, “The change gives the market a lot of confidence in the robustness of our devices, because if somebody buys a product from Bosch, they assume the quality is high, the performance is high, and the robustness is high, and the new element helps achieve this. It will also form the basis of the next generation of devices where it will be combined with another new design element that will further improve the device to approach the unipolar limit. The roadmap is a well thought through sequence of improvements that will get the device to the highest levels of performance, and robustness.”

https://www.bosch-semiconductors.com/