A Gold Free Aluminum Metalized GaAs PHEMT With Copper Based Air Bridges and Backside

This paper presents the results of electrical performance studies of the newly developed GaAs pHEMT transistors with Al-based metallization of the ohmic and barrier contacts, and fully copper metallization of interconnects, air bridges, and backside. The transistors exhibited a source-drain saturation current of I_dss=280 mA/mm and a maximum transconductance of g_m=450 mS/mm at U_ds=1.5 V. The current cut off frequency for transistors with 600 μm total gate width was 80 GHz at U_ds=1.5 V and U_gs=-0.35 V, and the power gain limiting frequency was 100 GHz. Output power at 1 dB gain compression with matched input and output load an impedance was P_1db=26 dBm or 670 mW/mm at an efficiency level of about 28% and the transistor gain G=11 dB. Measurements were performed at U_ds=8 V, I_ds=1/3 of I_dss at 12 GHz. The obtained results demonstrate the promise of Al and Cu metallization in the low cost manufacture of microwave transistors and monolithic integrated circuits based on them.