N-Polar Deep Recess GaN HEMT With a TiN Schottky Gate Contact Demonstrating 53.4% PAE and 3.7 W/mm Associated Pout at 94 GHz

A stack of TiN/Ru was employed as the Schottky gate metal for a nitrogen-polar deep-recess GaN high electron mobility transistor (HEMT) on a sapphire substrate. TiN/Ru Schottky diodes fabricated on the same HEMT epitaxy demonstrated a 6\times reduction in reverse-bias leakage current compared to Ru-only counterparts. The addition of TiN also resulted in a clear improvement in breakdown voltage for scaled N-polar Schottky gate HEMTs, as measured by the drain-current injection method (DCI). TiN HEMTs exhibited a peak {g}_{\text {m,dc}} of 843 mS/mm. A HEMT with a gate length ( L_{\text {g}} ) of 50 nm demonstrated a peak {g}_{\text {m,RF}} of 1028 mS/mm, peak f_{t} of 193 GHz, and peak f_{\max } of 362 GHz. Load-pull was measured at 94 GHz with a V_{\text {DS}} of 12 V and I_{\text {DS}} of 250 mA/mm. The TiN HEMT demonstrated a power added efficiency (PAE) of 53.4%-a record for N-polar GaN at W-band. The associated output power density was 3.7 W/mm, and the linear power gain (Gp) was an exceptional 10.2 dB.