Interface States in Gate Stack of Carbon Nanotube Array Transistors

A deep understanding of the interface states in metal–oxide–semiconductor (MOS) structures is the premise of improving the gate stack quality, which sets the foundation for building field-effect transistors (FETs) with high performance and high reliability. Although MOSFETs built on aligned semiconducting carbon nanotube (A-CNT) arrays have been considered ideal energy-efficient successors to commercial silicon (Si) transistors, research on the interface states of A-CNT MOS devices, let alone their optimization, is lacking. Here, we fabricate MOS capacitors based on an A-CNT array with a well-designed layout and accurately measure the capacitance–voltage and conductance–voltage (C–V and G–V) data. Then, the gate electrostatics and the physical origins of interface states are systematically analyzed and revealed. In particular, targeted improvement of gate dielectric growth in the A-CNT MOS device contributes to suppressing the interface state density (D_it) to 6.1 × 10¹¹ cm^–2 eV^–1, which is a record for CNT- or low-dimensional semiconductors-based MOSFETs, boosting a record transconductance (g_m) of 2.42 mS/μm and an on–off ratio of 10⁵. Further decreasing D_it below 1 × 10¹¹ cm^–2 eV^–1 is necessary for A-CNT MOSFETs to achieve the expected high energy efficiency.