Copper-Airbridged Low-Noise GaAs PHEMT With$hboxTi/hboxWN_x/hboxTi$Diffusion Barrier for High-Frequency Applications

C.-S Lee,Huang-Choung Chang,L.-H Chu,S.-H Chen,S.-W Chang,C.-T Lee,Y.-C Lien,Y.-C Hsieh,E.Y Chang

doi:10.1109/ted.2006.876578

Abstract

A GaAs pseudomorphic HEMT (PHEMT) with Cu-metallized interconnects was successfully developed. Sputtered WN x was used as the diffusion barrier and Ti was used as the adhesion layer to improve the adhesion between WN x /Cu interface in the thin-metal structure. After copper metallization, the PHEMTs were passivated with silicon nitride to avoid copper oxidation. The Cu-airbridged PHEMT showed the saturation I DS was 250 mA/mm and the g m was 456 mS/mm. The Ti adhesion layer plays a significant role on the g m and V p uniformity of the Cu-metallized PHEMTs. The GaAs PHEMTs with Ti/WN x /Ti/Cu multilayer have better noise figure and associated gain than those of the devices without the Ti adhesion layer. The fabricated Cu-metallized GaAs PHEMT with Ti/WN x /Ti/Cu multilayer has a noise figure of 0.76 dB and an associated gain of 8.8 dB at 16 GHz. The cutoff frequency (f T ) is 70 GHz when biased at V DS =1.5V. These results show that the Ti/WN x /Ti multilayer can serve as a good diffusion barrier for Cu metallization process of airbridge interconnects on GaAs lownoise PHEMTs

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