GaN-Transistor

The Fraunhofer ISIT is focusing on vertical GaN power devices, especially on advanced transistor and diode concepts with blocking voltages of some 100 V and switching speeds down to the ns range. The application specific chip designs and processes are facilitated by professional simulation software. The dedicated wafer equipment at ISIT allows the processing of bulk-GaN material with limited wafer diameter as well as 8” GaN-on-Si EPI wafers and the subsequent electrical characterization. As the GaN process line is integrated in a professional MEMS clean room, novel fabrication approaches and unconventional materials can be utilized to explore innovative device and integration concepts.

For decades, these power devices have used silicon (Si) as the semiconductor material. A few years ago, our group started investigating the use of gallium nitride (GaN) for the fabrication of semiconductor devices. The reasons for using this wide bandgap material are the superior properties of GaN, such as higher switching speed and improved RDS(on)/VBR(DSS) ratio, compared to silicon.

The state of the art of GaN devices are lateral HEMTs (High Electron Mobility Transistor) using the 2D electron gas effect (see Figure 1a). This limits the current path to the very surface of the device and hence hinders the full potential of GaN.

The primary goal is to unlock the full potential of GaN-based diodes and transistors through vertical device structures (see Figure 1b). To meet the requirement for mass-market viability, the novel devices are designed for the voltage range up to 600 V and fabricated on a 200 mm process platform established at ISIT.

The wafer material consists of 3 layers: a buffer layer deposited on a Si carrier wafer (with (111) surface), followed by a functional GaN-based layer system. The 200 mm substrates with epitaxial layers are purchased from external suppliers and processed in the ISIT clean room.

A technology platform for power devices based on the III-V semiconductor material gallium nitride (GaN) is being established at Fraunhofer ISIT. The development and processing of new power devices based on GaN epitaxy on 200 mm (111) silicon wafers will take place in Fraunhofer ISIT's clean room, which is originally equipped and used for Si-based microelectromechanical systems (MEMS) such as sensors, scanning micromirrors and piezoelectric systems. New equipment and processes are being added to the existing technology park for the development of vertical GaN devices. The additional equipment was procured as part of the "Research Factory Microelectronics Germany" project funded by the German Federal Ministry of Education and Research. They expand ISIT's capabilities in dry and wet etching, cleaning, annealing and rapid thermal processing as well as in electrical characterization of the manufactured components.

Most of the equipment is already installed and in use. The new facilities primarily serve to avoid contamination of GaN by Si and complement key processes for GaN-based devices leading to innovative research and development projects. With this perspective, Fraunhofer ISIT also expands the device measurement capabilities for static and dynamic wafer and device testing for the new III-V semiconductors.

GaN processing technology and device platform

• Application-specific development of diodes and transistors
• Adaptation and optimization of devices according to customer requirements
• Proof of concept fabrication on 200 mm process line
• Process and device simulation, testing and device reliability

Integrated micro-inductors with magnetic core by Powder MEMS technology

• Customized integrated inductors on PCB and silicon
• Integrated solutions with power devices
• Simulation-based design and combined cooling system