Regrowth-Free GaN RF HEMTs Achieving <i>f</i> _max of 403 GHz via Periodic Contact Structures

A regrowth-free sub-THz HEMT is demonstrated using a periodic contact scheme that transforms conventional linear contacts into a configuration with far better overall contact resistance (<italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">R</i><sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">C</sub>). This method yielded a consistent low <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">R</i><sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">C</sub> down to 0.15 Ωmm. Furthermore, this technique is based on a Au-free low-temperature annealing metalization (Ti/Al), which results in extremely smooth edges, allowing for sub 500 nm channel scaling. These features enabled – for the first time – the demonstration of regrowth-free GaN RF HEMT with <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">f</i><sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">t</sub>/<italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">f</i><sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">max</sub> of 176/403 GHz. These results are comparable to the best GaN HEMTs with similar geometry, highlighting the enormous potential of periodic contact structures for high performance RF and sub-THz devices.