High Frequency Switching Power Converters based on AlN-based Power Transistors

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GaN-based lateral power electronic transistors show excellent switching speed and low switching losses in power converters up to 600V. However, limitations on material and device level still prevent the transistors to perform close to the material limit in terms of blocking voltage and current density. With increasing switching speed, parasitic inductances generate increasing oscillations and related losses. Monolithic integration could be an efficient solution, but the integration of power switches so far comes with new conduction losses if operated at higher voltages. Main technological obstacles fortranslating the GaN device advantages into system benefits are 1) dispersion effects in very fast and high-voltage switching due to semiconductor material design and quality, 2) limitation of the usable blocking voltage due to side-effects of the GaN-on-Si concept, 3) backgating effects due the GaN-on-Si hetero epitaxy preventing efficient operation of monolithically integrated HV power switches, and 4) a high-loss intrinsic reverse conduction path in GaN HFETs. The project explores technological paths on the levels of epitaxy, device design, integration and system. Overcoming current performance restrictions and speed limitations by combining RF and power electronics device technologies and design methods is a key activity of the proposed project. For both, switched RF- and power electronic applications, we want to demonstrate the advantages of novel integration schemes on GaN-AlN based semiconductor implementations that are not suffering from the deficiencies of the GaN-on-Si hetero-epitaxial stack and of electrically conductive substrates. We want to explore the synergetic cooperation between monolithic and special hybrid integration schemes placed close to the power switches. We further want to monolithically implement various sensing functionalities like drain-bias and current sensors into the power transistors and use this information for a safer and more efficient operation of power switching converters and amplifiers. For this purpose, we select the GaN-AlN system on semi-isolating SiC, since this forms an ideal combination i terms of achievable specific power density.We want to demonstrate new circuit and power converter concepts where these capabilities will provide the maximum technological benefit in terms of efficiency and highest frequency power switching. Monolithically integrated drivers, bi-directional switches, half-bridges and sensors will be demonstrated for a new design and control concept of an isolated 400V DC-DC converter in the kW range. It will be further demonstrated that current obstacles for GaN core chips for VHF DC converter and buck converter module as envelope modulator up to GHz switching range can be solved, i.e. dispersion effects leading to high dynamic Ron, and the lack of different transistor variations on one chip preventing highly efficient integrated drivers and switch-mode optimized devices.