Novel metallisation and packaging schemes for WBG devices operating at very high temperatures (>500°C) and in harsh environments

Research Project, 2011 – 2014

Wide band gap (WBG) materials and devices have been the subject of several successful Swedish research projects and programs. High competence levels have been acquired as a consequence, and a number of small enterprises (SME) have been established. Several funding organizations, including VR, SSF, VINNOVA and STEM, have provided support for this research. The focus has mainly been on process technology and materials science related to the WBG materials silicon carbide (SiC) and gallium nitride (GaN). These materials give a far better performance than silicon devices under similar operating conditions. Thus, a Swedish platform has already been established when it comes to the design of active components tailored to specific performance requirements. It is now high time to investigate how specific process steps and material combinations can be developed and optimized so as to widen the field of WBG applications towards reliable operation in harsh environments, i.e. conditions where no other semiconductor material can be used. Success in this respect means that a number of solutions to problems that are currently pressing upon society and environment can finally be realized. ?Harsh environments? refer to extreme environmental conditions such as: high ambient temperature, severe temperature cycling, high power dissipation, mechanical shock or vibration, high pressure, corrosion, electromagnetic radiation. Despite the promises inherent in the WBG materials, the maximum operating conditions for present WBG devices are primarily limited by the metallurgical stability of the on-chip metallization and dielectrics, as well as the availability of reliable packaging solutions. Although urgently needed, there are a number of applications where current WBG technology cannot provide satisfactory solutions: power converters for aircraft, actuators for high voltage systems, power-modules for hybrid electrical vehicles, devices for space exploration and devices for deep oil/gas extraction, to mention a few. There is also a growing need to immerse more parts of the electronic systems directly in the harsh environment in order to reduce weight, simplify the interconnections and improve overall reliability. Adequate know-how regarding high-temperature metallization and packaging of WBG-devices for use in harsh environments is still limited. At the meantime, many new high-volume non-military applications in the energy and automotive sectors have emerged, applications that require reliable and high-temperature stable circuits at reasonable costs. However, without a well characterized and fully functional metallization and packaging concept suitable for harsh conditions, the inherent potential of the WBG devices can not be fully utilized. It is here that the long proven competence in thin-film technology and metallurgy available at UU directly complements the on-going WBG-activities at Chalmers and KTH. In the suggested project, solutions to the above-mentioned problems that will allow for operation of WBG devices at least up to 500 C and under harsh conditions will be investigated. A holistic approach will be adopted, addressing the full chain of ideas, from proof-of-concept, design and prototyping to production and application, and targeting the following aspects: - Formation of high-temperature stable ohmic and Schottky contacts to WBG materials, - Thermodynamically stable diffusion barrier layers inserted between the contacts in WBG-devices and the interconnect metal layers, - An optimized interplay between the interconnect metallization, diffusion barriers and the dielectric insulator layers, - A stable high-temperature die-attach solution for module assembly with special attention to the inherent electrical and mechanical properties of the joining materials, - A wire-bonding process that can withstand high-temperature cycling as well as mechanical vibration and shock, - A generic back-end process line within the MyFab organization for metallization of WBG devices for high-temperature and harsh-condition operation. Our ultimate objective is to stimulate innovation at universities and SMEs working with WBG devices and to provide a basis for the establishment of new industries. We believe that this will facilitate the design and manufacture of novel generations of value-added high-temperature WBG devices suitable for harsh applications in a wide range of fields, including sensors, automotive electronics and high-power electronic modules.

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