Output Conductance of Line-TFETs for Different Device Parameters and its Effect on Basic Analog Circuits

Abstract

This work addresses the impact of different device parameters on the analog characteristics of Line-Tunneling Field Effect Transistors (Line-TFETs). Source-to-drain separation, pocket thickness, pocket doping, gate-source alignment and the gate length are varied in order to evaluate their impact on the conduction mechanisms and on the overall transfer characteristics of the device. The variation of the main parameters responsible for device variability (pocket thickness and doping and gate-source alignment) is performed in order to analyze their impact on current mirrors, revealing that gate-source overlap improves the analog characteristics of the Line-TFET and that pocket doping should be limited to values smaller than 1018cm-3. Even though the drain current and the transconductance (gm) of this device are proportional to the gate area, simulations compared to experimental data show that the output conductance (gd) of Line-TFETs is practically independent of the gate length. The conduction mechanisms were analyzed through numerical simulations, revealing that this unique characteristic is due to source-to-drain tunneling, which defines the average value of gd on the saturation-like region and does not depend upon the gate length. The impact of this characteristic on analog circuit design is illustrated considering the example of a common-source stage and comparing its design when using MOSFET devices. This example reveals that the designer may choose whether to increase gm or gd in order to increase the circuit gain when using Line-TFETs, fundamentally differing from the MOSFET design.