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 Al2O3 (ALD-Al2O3) 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 $(g_{m-\max}) \times$ gate-voltage swing (GVS) product of 673.2 $\text{V}\cdot $ 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 ( $\mu _{{\mathrm {eff}}}$ ) varies from 105 to 200 cm2/ $\text{V}\cdot \text{s}$ . Furthermore, theoretical calculations reveal that the obtained high-performance $\mu _{{\mathrm {eff}}}$ is mainly due to the low-density surface charged impurities ( ${ \approx } 3.7\times 10^{12}$ 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.