Implementation and Design of a Novel Student Developed Modular HTOL/HTRB System Using Thermoelectric Control

Abstract

Addressing reliability issues is critical to the successful design and implementation of new semiconductor material systems proposed for next generation power electronic devices. For military systems, reliability is central to successful device designs, often outweighing other design factors. Several reliability testing schemes are central to validating power semiconductor device reliability. Of these, high temperature operating life (HTOL) and high temperature reverse bias (HTRB) testing are often used as go/no-go metrics for the success or failure of a fabricated lot of devices. To educate students in the importance of these testing regimens for devices, several undergraduate and graduate students have developed a custom, modular thermoelectrically cooled and controlled HTOL/HTRB system which allows for joint long term HTOL/HTRB testing at both institutions. Under constraints for cost, the system was designed to utilize a novel thermoelectric cooling scheme to provide a temperature range of 55 °C from 5 °C to 62 °C with less than 0.5 °C variation under 15 W heat load from devices-under-test (DUTs). A hermetic DUT environment was designed using nitrogen purging and active humidity sensing to control relative humidity (RH) within the environment to beneath 5% RH. Undergraduate students gained experience designing for manufacturability and machining with CAD tools not typically explored in typical electrical engineering design projects. An automated switch-matrix was designed and implemented to automate testing and allow for programming of complex stress-measure-stress reliability testing profiles. Control and automation was enabled using common MBED processors used throughout an undergraduate electrical engineering curriculum. To accomplish a unified design which could be installed at multiple locations, students investigated and implemented a server rack mounted design which uses commonly available banana and BNC connections for "plug-and-play" of the system. A control program was developed using a LabVIEW program which managed the system wide control and programming of different reliability testing regimens, such as stress-measure-stress, stepped-stress, and constant current, voltage, or power testing. Results for the fabricated system performance are shown demonstrating the successful achievement of the design metrics. To demonstrate the use of the system, results from recent undergraduate student led HTOL testing on novel GaN Schottky diode parts are presented. Current and future senior capstone and masters-level research projects using the novel system are reviewed.