Demonstration of GaN HEMT with Cu-based Ti/TiN/Cu Ohmic metal and TiN/Cu gate metal: comparison with Au-based device

Abstract In this study, GaN high electron mobility transistor (HEMT) on silicon substrate was utilized Cu-based metal for the ohmic contacts (Source and Drain terminals) and the Schottky contact (Gate terminal) as part of the metallization process. Furthermore, the same epi-wafer was used in this study to fabricate Au-based HEMTs, which served as control samples. Transmission electron microscopy (TEM) analysis comparing Ti/TiN/Cu ohmic contacts of Cu-based HEMT to Control sample. The Au-based Ohmic contact forms rough surfaces, discrete TiN islands, and defects in the AlGaN layer, potentially degrading device reliability. The Cu-based Ohmic contact features a smooth surface, minimal defects in the AlGaN layer, a stable Ti/TiN interface, and effective prevention of Cu diffusion, enhancing device reliability and scalability. The specific contact resistance ( ρ c ) of the Cu-based and Au-based ohmic contact metals produced in this study were 6.68 × 10 −6 Ω-cm 2 (2.04 Ω mm −1 ) and 9.64 × 10 −6 Ω-cm 2 (2.06 Ω mm −1 ), respectively. In addition, compared with the Cu-based and Au-based HEMT components in this study, the Cu-based HEMT, which used TiN/Cu Gate metal, exhibited excellent electrical characteristics (I DS : 1023 mA mm −1 , G m : 570 mS mm −1 ). Through reliability testing, it was confirmed that the Cu-based Gate metal does not cause Vth shift or affect I DS . The f T and f max of the Cu-based HEMT were 33.0 GHz and 99.6 GHz, respectively, which were 12.6 GHz (61.8%) and 26.1 GHz (35.5%) higher than the f T and f max of the control sample (Au-based HEMT). This increase demonstrated that the Cu-based HEMT achieved higher switching speeds, enhancing its suitability for high-frequency applications. The Cu-based HEMT components achieved the same characteristics as Au-based HEMT components under frequency measurements. In future development of low-cost systems, copper-based HEMT components will play an important economic role.