We report a numerical simulation study of gate capacitance components in a tunneling field-effect transistor (TFET), showing key differences in the partitioning of gate capacitance between the source and drain as compared with a MOSFET. A compact model for TFET capacitance components, including parasitic and inversion capacitances, was built and calibrated with computer-aided design data. This model should be useful for further investigation of performance of circuits containing TFETs. The dependence of gate-drain capacitance C gd on drain design and gate length was further investigated for reduction of switching delay in TFETs.Index Terms-Modeling, parasitic capacitance, tunneling fieldeffect transistor (TFET).

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In this work, we demonstrate by simulation and experiment that the performance of a p+ Si0.5Ge0.5 source tunnel field-effect transistor (TFET) can be improved by inserting an undoped Ge layer between source and channel. The Ge layer suppresses diffusion of boron into the Si channel and it also forms a Si0.5Ge0.5/Ge/Si hole quantum well, leading to an abrupt boron profile and a high hole concentration at the source edge. At the Ge/Si heterojunction, the presence of compressive strain in the Ge layer increases the valence band offset, while the tensile strain in the Si channel increases the conduction band offset, which effectively reduces the tunnel barrier and enhances the tunnel probability. Compared with a control device without the Ge layer, TFETs with a Si0.5Ge0.5/Ge source show a higher on-state current I ON and improved threshold voltage V TH and subthreshold characteristics.

Ku-band oscillators have been experimentally found to have a high dc-to-radio-frequency (RF) efficiency. Using a packaged pseudomorphic high electron-mobility transistor (pHEMT) device, a maximum efficiency of 60% was measured at 14.5 and 15 GHz with output powers of 16 and 23 mW, respectively. Oscillator circuits also revealed efficiencies of 48% at 16 GHz and 41% at 17.1 GHz with RF output power levels of 11 and 13 mW, respectively.

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