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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On-wafer microwave characterization and uncertainty evaluation of two-port coplanar waveguide (CPW) high impedance nanodevices devices are proposed. The test vehicles are built up with resistive metallic nano-films integrated in tapered CPW structures. Microwave conductance in the range 100-500µS associated to parallel capacitances in the order of hundreds aF are exemplary shown up to 20GHz. In addition, the uncertainty related to the post-calibration residual errors terms together with a sensitivity study to the technological process variability using FEM-based EM modelling are considered.

Abstract-This paper describes the design, fabrication, and testing of an on-wafer substrate that has been developed specifically for measuring extreme impedance devices using an on-wafer probe station. Such devices include carbon nano-tubes (CNTs) and structures based on graphene which possess impedances in the kΩ range and are generally realised on the nano-scale rather than the micro-scale that is used for conventional onwafer measurement. These impedances are far removed from the conventional 50-Ω reference impedance of the test equipment. The on-wafer substrate includes methods for transforming from the micro-scale towards the nano-scale and reference standards to enable calibrations for extreme impedance devices. The paper includes typical results obtained from the designed wafer.