Novel Approaches for Thermal and Electrical Characterization of GaN HEMTs

Doktorsavhandling, 2025

The evaluation of microwave components requires detailed knowledge of different performance aspects, and component models must be extracted from highly accurate characteristics. However, heating and trapping effects in active components create multifaceted characteristics with complex behavior. This creates major measurement challenges and can cause established measurement methods to yield inaccurate and inadequate information. This thesis outlines solutions to problems faced in the characterization of GaN-based devices and circuits by introducing new measurement techniques capable of capturing complex characteristics and mitigating distortion due to trapping effects.

A new method to perform the Ids-Vds characterization is shown, which minimizes trap-related memory effects by controlling the ordering of the bias points in the sweep. This allows extracting rudimentary IV properties, and facilitates studying the effects of trapping and heating separately. In addition, a method for electric-based thermal evaluation of GaN semiconductor technologies is outlined, where trap-related distortion in the thermal resistance is suppressed, which facilitates the comparison of thermal properties of different devices. A method to electrically characterize the lateral heat spread is also introduced, by utilizing the HEMT temperature characteristics to design a thermal sensor suitable for integration into GaN MMICs. This enables the use of standard electrical test equipment to measure lateral thermal coupling in packaged circuits. Thermal compensation is explored using a new biasing technique to compensate for thermal performance degradation in an LNA, in which the gate- and drain-voltage dependencies of the RF performance are utilized to maintain a constant gain as the temperature increases. Lastly, GaN HEMT breakdown measurements and characteristics are examined, and a method for RF breakdown characterization is introduced. This allows studying the breakdown at different signal conditions, and comparisons show that the breakdown voltage increases with frequency, which demonstrates the need to evaluate devices under application-relevant conditions. Overall, the proposed methods in this thesis enable more comprehensive and accurate assessments of thermal and electrical device properties, which is crucial in the development of new devices and circuits.