A Study of Linearity of C-H Diamond FETs for S-Band Power Application

In this article, we report a study on the dc and RF linearity performances of a hydrogen-terminated (C-H) diamond field-effect transistor. An atomic-layer-deposited Al
₂
O
₃
(ALD-Al
₂
O
₃
) based C-H diamond (100) MOSFET was fabricated and then characterized by dc- I-V, C-V, small-signal, large-signal, pulsed I-V, and two-tone inter-modulation characteristics. The typical transfer results suggest that the presented device achieves a maximum transconductance (g
_m-max
) × gate-voltage swing (GVS) product of 673.2 V·mS/mm, which is a record value among single-crystal diamond FETs to the best of our knowledge. The improved g
_m
-linearity in this work can be attributed to the enhanced mobility performance, and the extracted effective mobility ( μ
_eff
) varies from 105 to 200 cm
²
/ V·s. Furthermore, theoretical calculations reveal that the obtained high-performance μ
_eff
is mainly due to the low-density surface charged impurities ( ≈ 3.7×10
¹²
cm
^-2
) and the alleviated surface roughness scattering. Small-signal RF measurement shows that the drain current swing (DCS) of f
_T
is as high as -434 mA/mm. Unexpectedly, the RF output power performance at 2.6 GHz suffers from the severe drain current compression under the RF input drive. The subsequent pulsed I- V results reveal that the cause could be ascribed to the drain-lag trapping effect. Even so, the device still shows attractive IM3-to-Carrier ratio (-C/IM3) values in the linear region, which indicates that the diamond MOSFET is a prospective candidate for the RF linearity application.