Automotive requirements are becoming ever more severe in terms of device operation under high stress and in harsh working conditions. In this context, passivation layers play a fundamental role in determining electrical performance and reliability. This study focuses on the primary and secondary passivation layers applied to the state-of-the-art power devices and their influence on reliability. Power diodes assembled in standard module packages are used as test vehicles, and high-voltage temperature humidity bias tests are performed to stress the structures. A complete failure mode analysis highlights the phenomena behind the degradation of the passivation layers. Different passivation schemes are evaluated through the application of specific inorganic and organic combinations of layers. Finally, a summary of the typical degradation mechanisms and interactions is presented.
The high voltage temperature humidity bias test (HV-THB) has become increasingly popular for evaluating the performances of power semiconductor devices. Given the new challenges of the power semiconductor industry, several applications and devices need to be designed to withstand harsh environments during working operations, with a remarkable focus on high-humidity conditions. The HV-THB test allows one to activate and study different failure mechanisms which were not highlighted by the standard low voltage THB test, enabling new designs in several energy conversion fields, such as energy harvesting, industry and automotive applications. After a brief introduction of current test standards, this work goes through the current methodologies and state-of-the-art of the HV-THB test. The following sections are then dedicated to the knowledge about the failure mechanisms and the models for accelerated testing. Eventually, there is a section devoted to the main passivation materials in order to understand their effects on the HV-THB capabilities of the devices.
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