Vertical GaN on Silicon: Wide Band Gap Power at Silicon Cost
YESvGaN develops a new class of power transistors based on the wide band gap material gallium nitride (GaN), for efficient and affordable power conversion at voltages up to 1200 V and currents up to 100 A. This is enabled by an innovative membrane transistor approach, which allows fabricating vertical GaN transistors suitable for high voltage and high current operation while at the same time employing inexpensive semiconductor substrates. The target technology can replace current silicon-based insulated gate bipolar transistors (IGBTs) due to its comparable cost level while operating at the high efficiency of silicon carbide (SiC) field effect transistors (FETs), where the high substrate cost of the latter so far prevents IGBT replacement. This allows for a reduction of energy loss in a broad range of price-driven applications, from the electric vehicle powertrain over industrial motor drives to data-centre uninterruptable power supplies.
YESvGaN chose an ambitious set of objectives. Starting with the development of high-quality epitaxial growth of thick GaN layers on low-cost silicon substrates, allowing for high blocking voltages up to 1200 V. YESvGaN also paves the way to vertical GaN epitaxy on 300 mm silicon for maximum cost reduction. Regarding semiconductor process technology, multiple transistor channel concepts for highly efficient vertical GaN transistors with a specific on-state resistance below 4 mΩcm² at 1200 V rating are developed, together with key processes such as deep ion implantation, including the corresponding equipment. To access and electrically contact the backside of the residual micrometre-thin membrane transistor, specific bonding and debonding, substrate removal and backend processes compatible with the potentially fragile membrane transistors will be developed. Furthermore, assembly and interconnection technology for reliable, low-resistance and low-inductance contacting of membrane transistors to the outside circuitry is addressed, to finally apply and characterize membrane vertical GaN power transistors in prototype half-bridge power converter modules. Fabrication is complemented by reliability characterization along each process step to gain in-depth knowledge of the underlying performance-limitations, degradation and failure-mechanisms. The new transistor technology will be evaluated for pertinent applications on physical and simulation level setting up a comprehensive simulation framework and lab-scale demonstrators.
At the end of the project, fully functional membrane vertical GaN transistors suitable for 1200 V and 100 A operation will be available including their technical data sheet as well as lab-scale demonstrators showing the advantages in terms of system efficiency, power density and cost effectiveness for high power converter applications.