Variability of short channel junctionless field-effect transistors caused by fluctuation of dopant concentration

Short channel junctionless field-effect transistors (JL-FET) were fabricated on a silicon-on-insulator substrate. The channel dimensions were scaled to 20 nm in length and 4 nm in thickness, using anisotropic wet etching of SOI layer. Highly doped channels were formed by diffusion of dopants from the source and drain region at a high temperature annealing. N-type and p-type JL-FETs show drain current modulation of more than 6 orders by 1 V gate bias swing. In the measurement of many JL-FETs on the wafer, variation of threshold voltages as large as 400 mV was observed. A major cause of the variation is considered to be the fluctuation of dopant concentrations in the channel. A stronger channel potential confinement is the key to settle the variation.