Device Simulation of Hydrogen-Terminated Diamond Mosfet and Extraction of Small-Signal Parameters

Diamond has exceptional properties suitable for electronic and photonic devices. In particular, hydrogen-terminated diamond (HTD) FET devices have been studied recently for potential radio-frequency (RF) applications by exploiting its high conductivity at diamond surface, high thermal conductivity and simple fabrication process [1-3]. However, the device simulation of such FET device is rarely reported because the surface conductive mechanism is not fully understood. 

In this work, a new device structure including a surface adsorbate layer (ADL) is presented and a possible explanation of the formation of surface conductive layer is provided. Based on our theory, the 2D device simulation is achieved using Sentaurus Technology Computer-Aided Design software; both the capacitance-voltage (C-V) and DC current-voltage (I-V) properties of the HTD MOSFET can be understood well. It is found that the current mainly flow at diamond surface when the drain-source voltage (V_DS) is small but meander into the bulk when |V_DS| becomes larger. The working mode of the device can change from enhancement to depletion as the gate length (L_g) shrinks, and the threshold voltage becomes very sensitive to L_g when L_g≤0.2μm. The off-state leakage current increases drastically when L_g is approaching 50nm, causing the on/off current ratio dropping from 10⁶ to 10³.

In addition, the radio-frequency (RF) small-signal equivalent circuit of the device is generated and the frequency responses of the circuit components are studied. For devices with small gate length (<0.2μm), the non-quasi-static (NQS) effect happens at the frequency over 10GHz, making the HTD device suitable for applications in microwave range. The simulated transition frequency f_T is around 170GHz when L_g=50nm, but it is greatly affected by the source/drain series resistance. Finally, a strategy is presented to extract the values of circuit components from simulated two-port parameters, which works well up to 2GHz. 

[1] M. Schwitters, M. P. Dixon, A. Tajani, D. J. Twitchen, J. I. S. E. Coe, H. El-Haji et al., Diamond-MESFETs-synthesis and  integration, IEEE European Radar Conference, (2005) pp.1-4.

[2] M. Kasu, K. Ueda, H. Ye, Y. Yamauchi, S. Sasaki, T. Makimoto, High RF output power for H-terminated diamond FETs, Diamond and Related Materials, 15(2006) pp.783-786.

[3] J. L. Liu, C. M. Li, R. H. Zhu, J. C. Guo, L. X. Chen, J. J. Wei et al., RF characteristic of MESFET on H-terminated DC arc jet CVD diamond film, Applied Surface Science, 284 (2013) pp.798-803.