Evidence for mobility enhancement in double-gate silicon-on-insulator metal-oxide-semiconductor field-effect transistors

Abstract

The methodology of mobility extraction from the Y-function or from the transconductance peak is revisited in the context of silicon-on-insulator (SOI) metal-oxide-semiconductor field-effect transistors (MOSFETs). Based on a simple two-channel model, we discuss the biasing conditions that enable the Y-function to be applied to both single-gate (SG) and double-gate (DG) modes. Systematic mobility measurements in thick and ultrathin SOI transistors are presented for the front channel, back channel, and in quasi-double-gate mode. In SG-mode, the mobility is overestimated as soon as the opposite channel is activated. In partially depleted or relatively thick, fully depleted MOSFETs, the two channels are separated; hence, the total apparent mobility in DG mode is the sum of the front and back channel mobilities. By contrast, the two-channel model fails in ultrathin transistors, where the two channels become strongly coupled and volume inversion occurs. Volume inversion is reflected in a remarkable increase of the apparent mobility in DG mode.