N-polar GaN MIS-HEMTs on sapphire with a proposed figure of merit fmax·VDS, Q of 9.5THz.V

GaN-based HEMTs have demonstrated outstanding performance in solid-state power amplifiers [1]. Products of f
T
/f
max
and three-terminal breakdown voltage are commonly cited to characterize the high frequency performance of power devices [2]. However, such metrics mix the results of small-signal measurements and DC breakdown measurements taken separately and therefore don't consider side effects of high voltage operation on RF performance, such as dispersion, self-heating, and material degradation. To solve this problem, a new figure of merit defined as a product of f
max
and its associated quiescent drain bias (V
ds, q
) is proposed. Exploiting the advantages of the N-polar orientation [3] and the high film quality of MOCVD SiN
x
passivation layer, a 9.5 THz-V f
max
·V
DS, Q
is achieved in this work and exceeds those of the previously reported planar MIS-HEMTs passivated by PECVD SiN
x
[4, 5].