Low Contact Resistance CMOS-Compatible RF GaN-on-Silicon HEMTs

This work reports on a low contact-resistance Au-free ohmic contacts of an undoped AlGaN/GaN HEMTs on silicon, including hybrid deposited (HD) Si/Ti/Al/Ti/TiN metal stack. Combination of the barrier trench etching and TiN ohmic ledge, an ohmic topology structure with three electron transport path has been achieved. Using the proposed ohmic contact structure, a low contact resistance (2.6 × 10
^-7
Ω.cm
²
, 0.12 Ω.mm) was obtained when annealed at 725°C for 60 s in N2 ambient. Atomic force microscope (AFM) reveals a highly smooth surface morphology with a root mean square (RMS) roughness of 7.79 nm. The fabricated HEMTs revealed a low on-resistance (R
on
) of 1.5 Ω.mm, a high output current of 1.05 A/mm, and a peak transconductance of 362 mS/mm. The current cutoff frequency (f
T
) of 28 GHz and maximum oscillation frequency (f
max
) of 66 GHz were achieved, resulting in a high f
T
× L
g
product of 14 GHz.μ m. These results are believed to promote the development of the GaN-on-Si HEMT compatible with the CMOS process line.