研究目的
To propose a new approach with S-parameters measurement performed during RF stresses without removing the devices under test (in a thermally controlled oven) for GaN reliability analysis.
研究成果
The paper presents a stress analysis on GaN device(s) using a fully embedded RF-thermal stress workbench featuring S-parameters intermediate measurement facilities. The proposed automated stress workbench can be easily embedded with different new equipment such as large-signal VNA, or also (LF/HF) noise figure analyzers to provide the users with more pertinent data collected during the stress session.
研究不足
The study focuses on ambient stresses at 1 dB, 3 dB and 5 dB output compression points, using a 4.2 GHz continuous wave signal carrier, without considering changes in the temperature.
1：Experimental Design and Method Selection:
The bench allows to track the conventional DC and RF markers (drain-source currents IDS, output powers POUT) and temperature inside the Espec SU-241 thermal chamber. A set of SPDT and SP4T switches enable S-parameters measurement capabilities (Agilent N5230C VNA) outside the main stress measurement chain.
2：Sample Selection and Data Sources:
Devices under test are developed using GaN on SiC substrate process with 24% Al content. HEMT devices feature 2x75 μm2 gate width and
3：25 μm gate length (Ft = 40 GHz and Fmax = 100 GHz). List of Experimental Equipment and Materials:
Espec SU-241 thermal chamber, Agilent N5230C VNA, HP 83650B power source, HP 8487A power sensor, Agilent E4418B power meter.
4：Experimental Procedures and Operational Workflow:
POUT and IDS are saved each 10 minutes. S-parameters acquisition is performed at T0, after 10 minutes of stress and then each 6 hours of stress period.
5：Data Analysis Methods:
The correlation between static current drops and RF power variation is analyzed, and S-parameters are used to bring additional data concerning the gain S21 related to the carriers in the 2DEG, the reflection coefficient S11 revealing a possible change in CGS command capacitance, and eventually S12 isolation.
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