HPSD and Hitachi Commercializes TED-MOS

Contributing to creating a decarbonized society by improving the efficiency and energy saving performance of devices responsible for power generation, transmission, transformation and electrification.

Tokyo, January 26, 2021 --- Hitachi Power Semiconductor Device, Ltd. ( HPSD ) today announced that it will begin sample shipments of Trench Etched DMOS-FET (hereinafter referred to as TED-MOS ), a fin-shaped trench (1) MOSFET (2) from March 2021. This is a new power device product (3) that uses silicon carbide (SiC), next-generation material that enables improved electrical efficiency to deliver power saving in various equipment and facilities that form key social infrastructure such as power systems, railway systems, electric vehicles and data centers.

TED-MOS is the commercialized version of the high durability-structured SiC power device developed by Hitachi, Ltd. (TSE: 6501, Hitachi ) in August 2018 (4). One of core issues with conventional SiC power devices is that electrical fields concentrate around the base corners of the trench on the semiconductor chip surface, making it difficult to realize strong durability. TED-MOS overcomes this by forming fins in the trenches and employing a proprietary Hitachi structure that provides an electric current path on the side walls of the fins. In commercializing this product, HPSD and Hitachi employed a new development technique that enables short-circuit tolerance (5) and resistance to be optimized independently. This achieves a reduced cell pitch and optimized current path design with the lowest resistance to deliver the industry's highest level of durability and low power consumption characteristics, whilst also providing a greater design freedom to enable the development of product designs tailored to a variety of uses. Through the provision of TED-MOS, HPSD will help reduce power consumption and carbon dioxide emissions for various social infrastructure facilities, contributing to the expansion of a decarbonized society.

With global energy demand expected to increase, power semiconductor devices are being utilized for a wide range of social infrastructure, and products demand ever higher efficiency and improved energy saving performance to enable the creation of a decarbonized society. Given these conditions, improving the performance of SiC power devices will offer benefits in industrial fields, including offshore wind power (listed as a key field in the Ministry of Economy, Trade and Industry's Green Growth Strategy Towards 2050 Carbon Neutrality ), next-generation solar, logistics and public transport such as rail, automotive, as well as storage batteries, telecommunications and marine vessels. These improvements will lead to energy savings in inverter and converter systems handling power generation, transmission, transformation and electrification by making them more efficient, smaller, lighter and by simplifying cooling mechanisms through high heat resistance.

To help create a decarbonized society, Hitachi and HPSD have developed and provided a range of power electronics products for rail and electric vehicles. In 2018, Hitachi announced the development of TED-MOS (now commercialized) as a SiC power device that further enhances the performance of the existing SiC DMOS-FET (6) product in terms of high current capacity, low power consumption and so on.

TED-MOS products seek to balance durability with power consumption, which has been an issue for SiC power device solutions. This is achieved by setting up a field relaxation layer to significantly reduce electric field intensity and a current spreading layer to lower resistance around the center of the device, and by adopting a device structure that uses the walls of the fin-shaped trenches made from a low-resistance crystal surface as the electric current path. In addition, by applying a new development technique allowing short-circuit tolerance and resistance to be optimized independently, enabling a reduced cell pitch and optimized current path design with the lowest resistance. Compared with initial the prototype developed in 2018, short-circuit tolerance has been improved 20% whilst resistance has been lowered 40% while maintaining the 1.2kV withstand voltage required for commercialization.

Moving forward, in addition to the product lines for transportation equipment developed and provided to date, Hitachi and HPSD will work to develop and provide products aimed at innovation in social infrastructure to contribute to creating a decarbonized society.

The development technique for TED-MOS, balancing durability with low power consumption

SiC power devices have a performance advantage over their conventional silicon (Si) counterparts due to their high-speed switch on and switch off performance as they conduct electricity more easily. While this makes them well suited for reducing the power consumption of power converters, unlike Silicon, the ease of electricity transmission (resistance) varies depending on the crystal plane. For this reason, whilst trench SiC MOSFET [(2) in Figure 1] devices that conduct current on a lower-resistance crystal plane than conventional DMOS-FET [(1) in Figure 1)] devices, have been commercialized, these structures are prone to the electric field concentration at the bottom corners of the trenches, making it difficult to achieve a balance between low resistance and reliable durability. Additionally, as durability and resistance are determined based on a single trench structure, designing devices to suit a wide range of fields may pose a challenge.

To address this and achieve both durability and low power consumption, with TED-MOS a field relaxation layer was placed on the center of the device to mitigate how voltage is applied and significantly reduce the intensity of the electric field. A current spreading layer was positioned to low

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