DENSO contributes to a decarbonised society

A power semiconductor is like the muscles in the human body. It moves components, such as inverters and motors (limbs), based on commands from an ECU (brain). Typical power semiconductors used in in-vehicle products are made from silicon (Si). In comparison, SiC offers superior performance in high-temperature, high-frequency, and high-voltage environments, and helps significantly reduce the power loss, size, and weight of inverters. Thus, SiC devices have attracted attention because they accelerate the electrification of vehicles. For example, a booster power module, which incorporates DENSO's SiC power semiconductor, is about 30% smaller in volume with 70% less power loss than a conventional product with a Si power semiconductor. As a result, products have been made smaller and vehicle fuel efficiency improved. DENSO calls these SiC technologies "REVOSIC," conveying the idea of making "changes" in society through innovative technologies. The company has been developing a comprehensive range of technologies from wafers to power modules, and will continue R&D on REVOSIC SiC technologies and spreading their use in electric vehicles to help realise a decarbonised society.

Introduction of developers

Tomoo Morino, R&D department, power module engineer.

“I was in charge of determining the specifications of the SiC power semiconductor with the power module design department and designing the device structure based on the specifications. SiC has a low resistance compared to Si and so electric current can flow more easily. Due to this property, a prototype SiC device was damaged by a sudden surge of a large electric current. We collaborated with other departments to discuss how to prevent damage to devices in the market while taking full advantage of the low-loss performance of SiC, and the issue was solved with an idea which our department could not come up with alone: high-speed cut-off of the electric current using a special driver IC.” Stated Tomoo

“For now, few products are equipped with SiC, but as electric vehicles spread, we will increase the number of products with SiC and thus reduce CO2 emissions.” Tomoo continued

Tomohiro Mimura, R&D department, Power Module Engineer.

“I was in charge of the process design for manufacturing SiC power semiconductor devices. The hardness of SiC is second only to diamond, so it is more difficult to process than Si. I struggled to design a mass production process that can stably deal with microstructures of less than one micrometre. DENSO has been researching SiC for many years, and so there are many predecessors and senior employees. To solve this problem with SiC, I frequently talked with senior employees to learn from their experience and know-how, and also took full advantage of existing technologies. This made it possible to commercialise the product. “ commented Tomohiro

“I hope to further improve the performance and quality of the device and reduce its cost so that SiC can be used in many more products.” Added Tomohiro

Satoru Sugita / Design Department, power module engineer.

“I was in charge of the mounting design. I was responsible for determining the requirements to ensure reliability (e.g., materials, dimensions, processing conditions) required for installing SiC power semiconductors in power cards. In the design process, mounting defects occurred due to the high Young's modulus* (about triple that of Si), which is one of the characteristics of SiC materials. Such defects did not occur when Si was used. To cope with this unprecedented phenomenon, it was necessary to think laterally, beyond conventional ideas. To accurately understand the problem, I brought in an internal specialised department and external manufacturers of analysis instruments to gather different viewpoints and conducted genchi-genbutsu on-site verifications. This helped solve the problem and reflect the findings in the design requirements.” Satoru said

“I hope to contribute to the use of electric vehicles and help create a decarbonised society by encouraging many customers to install SiC power semiconductor in various products.” Continued Satoru