Channel and contact length scaling of two-dimensional transistors using composite metal electrodes

Abstract

Two-dimensional semiconductors are a potential channel material for transistors with highly scaled contacted poly pitch (CPP). Total scaling of CPP requires the simultaneous reduction of channel length and contact length. However, the physical width limit of contact metals makes it difficult to form effective small-size contacts. In addition, decreasing the contact length below the transfer length induces a current crowding phenomenon, resulting in an exponential increase in contact resistance and poor device performance. Here we show that composite metal contact electrodes of gold/titanium/nickel can offer shape-preserving effects that allow the extreme scaling of contact length in two-dimensional transistors while maintaining a low contact resistance. We use the approach to create molybdenum disulfide transistors with a CPP of around 60 nm—contact length and channel length scaled to around 30 nm and transfer length scaled to under 30 nm—that exhibit on/off ratios over 10⁸, on-state currents of around 300 μA μm⁻¹ and off-state currents down to around 1 pA μm⁻¹. We also fabricate arrays of all-out scaled two-dimensional transistors that exhibit low variability in key performance metrics and demonstrate their integration into advanced logic circuits.