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.