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ECSEL Research for GaN technologies, devices, packages and applications to address the challenges of the future GaN roadmap

Alternative title: Forskning på GaN teknologi, transistorer, pakking og applikasjon for å adressere framtidens GaN retning.

Awarded: NOK 5.0 mill.

For the UltimateGaN project, Eltek will develop new cost-effective converters with high efficiency and very high reliability. The GaN transistors that the Ultimate Gan project is developing will be used to achieve this goal. IP65 rectifier for outdoor 5G telecom application. This rectifier is extremely important for Telekom for the next 5-10 years due to the 5G development which will require very many smaller base stations that will be distributed over larger areas due to coverage. There is a focus on the thermal design that allows the system to use convection cooling without external cooling. The GaN transistor fits very well with this very demanding application because the losses are small and the GaN transistor housing is very suitable for cooling in a closed IP65 box. The prototype types tested show very good utility between diet and efficiency, which is just under 98% peak. Reliability seems from tests to be very good. GaN transistors are the reason for low losses, ie high efficiency and very good thermal performance with 2kW output power with low AC voltage in with + 55degC environment and with solar power on top of this. This is what it looks like now, this is a product for the future and 5G development. All products will be extremely validated to find weaknesses on GaN transistors and product. This validation will first be performed internally with up to several hundred units for each product tested to the outer limits to detect possible design and GaN transistors. This will show that European industry can make very good semiconductor components such as the GaN transistor and power electronics that will be world leaders in terms of cost, efficiency and reliability. Since the efficiency of the products is very high, this has a very positive impact on reduced power consumption and a better environment. P65 2kW / 48V rectifiers are now the demonstrator for the UltimateGan project. This is a product for 5G application World Wide with extreme performance. 100 pcs of IP65 2kW / 48V rectifier is manufactured and used for DVT (Design Verification Test). The thermal design is extremely demanding even for high reliability and here the GaN transistor plays a key role. The unit has been tested for + 55degC ambient temperature and lowest input voltage 185Vac with very good result. Here we have at least 25degC temperature margin on the semiconductor chips which indicates high reliability. The mounting method of the GaN transistor has been researched with many different solutions and the chosen method is confirmed with testing high / low temperature, input voltage and load to be very reliable. This is patented. The Gan transistor has also proven to be very robust in terms of surge voltages and testing has shown 6kV differential voltage passes without problem. This is significantly higher than what the standard for surge requires which is 2kV. This is one of the reasons for high field reliability. Peak efficiency is 97.75% with relatively low cost. EMC radiated and wired class B confirmed fulfilled with test of a rectifier and a system of 4 rectifiers with controler and DC distribution. All validation tests according to IPC9592 rev B, HTOB, PTC and UTC have been performed with approved result as well as corrosion test. Safety has also been passed and approved. The next step is production of 240x IP652kW / 48Vdc rectifiers for PVT (Production Verification Test). After this, mass production for field application starts and here Eltek will monitor reliability in the field.During this work, Eltek discovered after about 100x produced rectifiers of PVT batch that the failure rate increased dramatically in the Burn-In phase of production which can happen when a product goes into mass production. This resulted in a large failure analysis of all possible root causes of all operating cases. This delayed the product launch by more than 6 months, but all possible failure mode were analysed, tested and verified with corrective actions. The problem was in the synchronous rectifier part of the 48V output, which has received many updates of HW and SW art. The good news was that the GaN transistors in the rectifier worked as expected. The launch of the IP65 rectifier for 5G WW takes place in January 2023.

The direct outcome of the project is a rectifier 2kW/48vdc for outdoor use for 5G application which will be lounched i January 2023. This product has due to the use of GaN transitor state of the art performance WW regarding density, relibility and cost.

The new concept of following a vertical approach to address research through the entire supply chain of technology, packaging, reliability and application will enable a significant improvement of efficiency that goes beyond the limits of silicon based semiconductors in combination with packages that fully utilize the shrink-path of power GaN devices and which are not ready as of today. The global state-of-the-art first generation GaN devices are mainly based on US and Asian suppliers. Only a cooperative project like UltimateGaN with European market leaders and world-class researchers can take on the challenges and bring Europe at the forefront in terms of GaN enabled opportunities. Eltek's tasks in the project: We will use GaN technologies for power converters in telecom applications with output power of 1kW and 3kW. The focus will be to use GaN transistor in the LLC DC/DC stage and in the output synchronous rectifier in the 1kW and 3kW telecom rectifiers. In particular, the GaN transistors in the LLC DC/DC stage will be investigated during the start-up sequence and short circuit sequence for failure mode situations.These tests involve the implementation and functional tests of GaN transistors with new drivers, printed circuit board (PCB) layouts, some planar magnetics and parasitic effects. • Drivers for 1kW/48Vdc design with cost reduction and switching frequency in the range of 500kHz to 1MHz. • Driver for the 3kW/48Vdc designwith efficiency above 98%. The goal is to achieve 98.5% efficiency, with field proven very high reliability. • Test and validate a volume production of converters. • Field trials of the power supply solution in real applications. A number of power conversion units will be installed in the field exposed to various environmental factors such as humidity and temperature for testing for longer term field reliability. • Failure Root Cause Analyses and corrective action for various parts of the GaN technology value chain.

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