Wayne Johnson

  • 9.2 Investigation of the Impacts of Interfacial Layers on the Degradation of GaN-on-Si HEMTs under Electrical Step Stress Testing

    Luke Yates, Georgia Institute of Technology
    Chien-Fong Lo, IQE
    Tingyu Bai, University of California, Los Angeles
    Mark Goorsky, University of California, Los Angeles
    Wayne Johnson, IQE
    Samuel Graham, Georgia Institute of Technology
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  • RF Harmonic Distortion of Coplanar Waveguides on GaN-on-Si and GaN-on-SiC Substrates

    Patrick Fay, Notre Dame
    Lina Cao, University of Notre Dame
    Hansheng Ye, University of Notre Dame
    Jingshan Wang, Notre Dame
    Hugues Marchand, IQE
    Wayne Johnson, IQE

    The RF harmonic distortion of coplanar waveguides (CPWs) fabricated on AlGaN/GaN HEMT heterostructures grown on both high-resistivity Si (GaN-on-Si) and semi-insulating SiC (GaN-on-SiC) substrates is reported for the first time. The loss performance and the nonlinear behavior of the CPW lines were experimentally characterized using both small- and large-signal measurements. From 100 MHz to 20 GHz, low loss (less than 0.3 dB/mm at 20 GHz) was achieved; the attenuation of CPW lines on the GaN-on-Si substrate is ~0.05 dB/mm higher than that of the GaN-on-SiC substrate. The harmonic distortion levels of the GaN-on-Si substrate and GaN-on-SiC were also evaluated experimentally; in contrast to the small-signal loss, more significant differences in second- and third-order nonlinearity, and thus intermodulation, are observed between Si and SiC substrates. Large-signal characterization of the GaN-on-Si substrate was carried out over temperature from 25 °C to 175 °C.  Due to increases in substrate conductivity with temperature, the harmonic distortion levels are found to increase significantly at temperatures above 75 °C.

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