Optimization study on the epitaxial structures of over-100-GHz metamorphic HEMTs for the millimeter-wave applications

摘要

Metamorphic HEMTs (MHEMTs) have emerged as excellent challenges for the design and fabrication of high-speed HEMTs for millimeter-wave applications. Some of improvements result from improved mobility and larger conduction band discontinuity in the channel, leading to more efficient modulation doping, better confinement, and better device performance. We have studied MHEMFs using In{sub}xGa{sub}(1-x)As/In{sub}0.52Al{sub}0.48As(x > 0.4) modulation-doped heterostructures on the GaAs wafer. For the device performance optimization, we first calibrated the device performance of 0.1- μm MHEMT fabricated in our research center using 2D device simulator. With these calibrated parameter set, the device performance has been investigated with varying the indium mole fraction from 0.4 to 0.65 in the channel layer. The device performances on the DC and RF characteristics exhibits better with increasing the indium mole fraction. The device with 0.65 mole fraction has shown the best RF characteristic. In this article, we show these results in detail, and optimized epitaxial structure for over-100-GHz millimeter-wave frequencies. Our newly designed device with x=0.65 mole fraction for better breakdown characteristic show 341.41 M/mm of maximum saturation current, 386.09mS/mm of transconductance, 123.11 GHz of cut-off frequency, and 231.74 GHz of the maximum frequency of oscillation in our device simulation.