Diagnostic tools for accurate reliability investigations of GaN devices

Intensive development of GaN-based HEMT devices has been largely pushed by their intrinsic capabilities for operation at high temperature under high voltage conditions, making the difference with the competitive technologies. However, a poor electrical reliability under high-electric-field operation is still hampering large-scale penetration of these technologies into the RF power market. From the early 2000, an increased number of works have addressed reliability issues. The first ones have been conducted on the basis of roadmaps issued from reliability investigations previously carried out on III-V and silicon based devices. These investigations have enlightened that several parameters such as surface passivation, processing techniques alternatives and piezoelectric effects severely impact device reliability. In order to get a deeper understanding of the correlation between physical and electrical events, we simultaneously report low frequency noise (LFN) measurements data (including separation of the different noise sources involved), and electrical measurements data (lag effects on drain and gate terminals, I-DLTS measurements, ...) conducted on the same devices. The later investigations are appropriate in order to identify defects that are able to produce noise. Noise measurements versus temperature on virgin and stressed devices are reported for different GaN processes developed by a French industrial foundry. Lorentzian noise shapes are identified and activation energies are extracted from Arrhenius plots. Additionally, I-DLTS measurements are performed. Electric lag measurements on the gate and drain terminals are finally used in order to relate stress impact to the electrical integrity of the devices. The identification of failure mechanisms needs accurate statements, and the effectiveness of such a melting of different kind of experiments is demonstrated.