Device Simulation of Hydrogen-Terminated Diamond Mosfet and Extraction of Small-Signal Parameters
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 (VDS) is small but meander into the bulk when |VDS| becomes larger. The working mode of the device can change from enhancement to depletion as the gate length (Lg) shrinks, and the threshold voltage becomes very sensitive to Lg when Lg≤0.2μm. The off-state leakage current increases drastically when Lg 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 fT is around 170GHz when Lg=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.
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