200nm gate-length power InAlAs/InGaAs MHEMTs with T-shaped gate are characterized for DC, RF, and power performance. The MHEMTs show excellent DC output characteristics with an extrinsic transconductance of 510mS/ mm and a threshold voltage of - 1.8V. The fT and fmax obtained for the 0.2μm × 100μm MHEMTs are 138 and 78GHz, respectively. Power characteristics are obtained under different frequencies. When input power （Pin） is - 0. 88dBm （or 2. 11dBm）,the MHEMTs exhibit high power characteristics at 8GHz. Output power （Pout） ,associated gain, power added efficiency （PAE） and density of Pout are 4. 05（13.79）dBm,14. 9（11.68）dB,67. 74（75.1）% ,254（239）mW/mm respectively. These promising results are on the path to the application of millimeter wave devices and integrated circuits with improved manufacturability over InP HEMT.
200nm gate-length GaAs-based InAlAs/InGaAs MHEMTs are fabricated by MBE epitaxial material and EBL （electron beam lithography） technology. Ti/Pt/Au is evaporated to form gate metals. A T-shaped gate is produced using a novel PMMA/PMGI/PMMA trilayer resist structure to decrease parasitic capacitance and parasitic resistance of the gate. Excellent DC and RF performances are obtained and the transconductance （gm） ,maximum saturation drain current density （Joss）, threshold voltage （ VT）, current cut-off frequency （fT） , and maximum oscillation frequency （fmax） of InAlAs/ InGaAs MHEMTs are 510mS/mm,605mA/mm, -1.8V, 110GHz, and 72GHz, respectively.
