Nano-scale devices and high power transistors\ud
present extreme impedances, which are far removed from the\ud
50-Ω reference impedance of conventional test equipment,\ud
resulting in a reduction in the measurement sensitivity as\ud
compared with impedances close to the reference impedance. This\ud
letter describes a novel method based on active interferometry\ud
to increase the measurement sensitivity of a VNA for measuring\ud
such extreme impedances, using only a single coupler. The\ud
theory of the method is explained with supporting simulation.\ud
An interferometry-based method is demonstrated for the\ud
first time with on-wafer measurements, resulting in an\ud
improved measurement sensitivity for extreme impedance device\ud
characterization of up to 9%
For reliability predictions, gallium nitride transistors require accurate estimations of the peak operating temperatures within the device. This paper presents a new application of thermoreflectance-based temperature measurements performed on a gallium nitride high electron mobility transistor. The submicron spatial and nanosecond temporal resolutions of the measurement system enables for the first time, the dynamic temperature measurement of a transistor operating up to 5 MHz. The GaN transistor is first biased in class-A and excited with a 1 MHz AC signal to demonstrate the dynamic temperature measurement. The transistor is then incorporated in a 20-40 V DC/DC boost converter to measure the dynamic temperature distributions across the semiconductor die operating under real loading conditions at 1 and 5 MHz switching frequencies. This technique captures the temperature variations that occur during the switching of the transistor and the recorded peak temperatures are 7.4 C higher compared with conventional measurement and simulation approaches. Index Terms-Thermoreflectance measurement, boost converter, gallium nitride, power transistor.
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